Low-porosity meta-aramid paper and preparation method thereof

Abstract

The invention provides low-porosity meta-aramid paper, which is modified by coating polysulfonamide slurry, the porosity is lower than 13.2%, the coating weight is 15-25g / m < 2 >, and the coating permeability is 30-60% of that of uncoated meta-aramid paper. The preparation method comprises the following steps: S1, preparation of high-solid-content polysulfonamide slurry: adding polyvinylpyrrolidone and a polyimide precursor PAA to obtain uniform slurry of 800-2500mPa. S; s2, pretreatment of meta-aramid base paper: plasma and silane coupling agent preimpregnation treatment is carried out; s3, gradient coating is conducted; and S4, gradient drying and hot-pressing curing are conducted, specifically, pre-drying is conducted firstly, then heating, hot-pressing curing is conducted, and finally press polishing is The composite material has the advantages that the porosity can be accurately regulated and controlled to be 10%-16%, the temperature resistance reaches 350 DEG C, the breakdown voltage exceeds 22kV / mm, and the tear strength amplification exceeds 60%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of insulating paper preparation, and relates to a meta-aramid paper and a preparation method thereof, in particular to a meta-aramid paper preparation method for reducing internal porosity of meta-aramid paper, improving compactness and comprehensive performance by coating aramid pulp, and the aramid paper prepared by the method. BACKGROUND

[0002] Meta-aramid paper, such as Nomex®, Kevlar® and Technora®, is widely used in motor slot insulation, transformer interlayer insulation and the like due to excellent heat resistance (continuous use at 200-220℃), flame retardance (LOI>28%) and insulation (breakdown voltage>10kV / mm). However, the traditional meta-aramid paper has the inherent defect of high porosity, with a porosity of 22%-28% in general, which directly causes performance problems in many aspects: (1) limited insulation strength. The existence of porosity easily becomes a place for partial discharge to occur, affecting the insulation reliability. (2) strong hygroscopicity. The moisture in the environment easily invades the internal part of the material through the porosity, reducing the insulation service life. (3) insufficient mechanical properties. It is difficult to meet the structural load demand in severe scenarios, with a tear strength of only 5.5-9N / mm. (4) poor high-temperature dimensional stability. The porosity expands at high temperature, eventually leading to material deformation.

[0003] In the prior art, resin impregnation method (phenolic / epoxy), hot pressing method and nano filler blending method are used to reduce the porosity of meta-aramid paper. However, these methods have the following problems: (1) the prepared meta-aramid paper is prone to aging, has high brittleness, poor temperature resistance (≤180℃) and high strength loss; (2) the nano filler has poor dispersibility and is prone to agglomeration; (3) the preparation cost is high. For example, a method for impregnating aramid paper with epoxy resin is disclosed in Chinese patent, the porosity is reduced to 18%, but the breakdown voltage is only increased by 20%, and the resin carbonizes and fails after 300℃.

[0004] Therefore, it is necessary to provide an aramid paper capable of improving the porosity defect of the paper, thereby improving the high-temperature resistance, breakdown strength and tear strength of the aramid paper, and a preparation method of low-porosity meta-aramid paper which is acceptable in cost, simple in process and suitable for industrial production. SUMMARY

[0005] To solve the above technical problems, the purposes of the present application are: (1) to provide a low-porosity meta-aramid paper, which improves the tear strength, electrical breakdown strength and high-temperature resistance of the paper by improving the porosity; (2) to provide a preparation method of low-porosity aramid paper which is acceptable in cost, simple in process and suitable for industrial production.

[0006] In order to achieve the object of the present application, the present application provides a low porosity meta-aramid paper, which is modified by coating aramid pulp, the porosity of the modified aramid paper is less than 13.2%, the coating amount is 15-25 g / m2, and the penetration depth of the coating layer is 30%-60% of the thickness of the uncoated base paper.

[0007] Further, in the low porosity meta-aramid paper provided by the present application, the tear strength of the low porosity meta-aramid paper is not less than 9.5 N / mm, which is increased by more than 30% compared with the uncoated base paper; the breakdown voltage of the low porosity meta-aramid paper is not less than 17.5 KV / mm, which is increased by more than 40% compared with the uncoated base paper; and the strength retention rate of the low porosity meta-aramid paper after aging at 350℃ for 100 hours is not less than 85%.

[0008] In order to achieve the object of the present application, the present application also provides a method for preparing the above low porosity meta-aramid paper, which comprises the following steps:

[0009] S1, preparation of high solid content aramid pulp: aramid fibers are dissolved in N-methyl pyrrolidone (NMP) or N,N-dimethylacetamide (DMAC) to prepare a slurry with a concentration of 25wt%-40wt%, polyvinylpyrrolidone (PVPK30) is added as a dispersant, and a polyimide precursor PAA with Tg>280℃ after curing is selected as a binder, the slurry is stirred and ultrasonically dispersed to obtain a uniform slurry with a viscosity of 800-2500 mPa·s;

[0010] S2, pretreatment of meta-aramid base paper: plasma treatment; pre-impregnation treatment in a silane coupling agent (KH-560);

[0011] S3, gradient coating: the first layer is coated by a micro-gravure roll; the second layer is coated by a doctor blade;

[0012] S4, gradient drying and hot pressing and curing: the coated meta-aramid paper is first pre-dried, then heated and hot pressed and cured, and finally calendered to make the surface roughness Ra of the modified aramid paper less than 1.0 μm; vacuum degassing is performed to remove residual solvents, and a low porosity modified meta-aramid paper is obtained.

[0013] Further, in the method for preparing the low porosity meta-aramid paper provided by the present application, in step S1, the length of the aramid fibers is 0.5-2.0 mm, the fiber diameter is 5-10 μm, the mass percentage of polyvinylpyrrolidone (PVPK30) is 0.3wt%-1.0wt%, and the polyimide precursor PAA is selected from PAA with Tg>280℃ after curing, and the PAA addition amount is 3wt%-8wt%.

[0014] Further, in the preparation method of the low porosity meta-aramid paper provided by the application, in step S2, the thickness of the meta-aramid base paper is 80-150 μm, the basis weight is 60-100 g / m2, and the porosity of the base paper is 20%-28%.

[0015] Further, in the preparation method of the low porosity meta-aramid paper provided by the application, in step S3, the third layer spraying process is further included, the coating thickness of the third layer spraying process is 5-10 μm, and the coating amount is 3-6 g / m 2 .

[0016] Further, in the preparation method of the low porosity meta-aramid paper provided by the application, in step S3, the coating thickness of the micro-gravure roller coating is 8-15 μm, and the coating amount is 5-12 g / m 2 .

[0017] Further, in the preparation method of the low porosity meta-aramid paper provided by the application, in step S3, the coating thickness of the knife coating is 10-20 μm, and the coating amount is 8-12 g / m 2 .

[0018] Further, in the preparation method of the low porosity meta-aramid paper provided by the application, in step S4, the pre-drying temperature is 100-120 ℃, the pre-drying time is 5-10 min; the hot-pressing curing temperature is 260-300 ℃, the pressure is 2.0-5.0 MPa, and the curing time is 3-6 min; the calendering temperature is 150-180 ℃, the pressure is 1.0-2.0 MPa, and the time is 1-2 min.

[0019] Compared with the prior art, the application has the following beneficial effects: (1) the porosity can be accurately controlled to the interval of 10%-16%, the adjustment flexibility is strong, and a more optimal densification effect is achieved compared with the traditional resin impregnation method; (2) relying on the double high-heat-resistant system composed of aramid and polyimide, the temperature resistance of the product reaches 350 ℃, and the product can adapt to high-temperature harsh working conditions; (3) the insulation performance is improved qualitatively, the breakdown voltage can exceed 22 kV / mm, and the insulation strength is doubled compared with the unmodified product; (4) the mechanical properties are simultaneously improved, the tear strength is increased by more than 60%, and the industry convention that "densification must reduce strength" is broken; (5) the process compatibility is strong, the production mode of roll-to-roll coating combined with hot pressing is adopted, the running speed exceeds 5 m / min, and the industrial production demand is completely met. DETAILED DESCRIPTION

[0020] The inventive concept of the application is to realize the reduction of the porosity of the paper, the improvement of the tear strength, the electrical breakdown strength and the high-temperature resistance of the paper by the innovative path of "high-temperature-resistant slurry filling densification" combined with the multi-layer coating + hot pressing + calendering densification synergistic process.

[0021] The application provides a preparation method of meta-aramid paper with reduced porosity by aramid pulp coating, and the specific steps are as follows:

[0022] S1, preparing high solid content aramid pulp: selecting aramid fiber as the core raw material, N-methyl pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc) as the solvent, and blending into a slurry with a concentration of 25wt%-40wt%, and adding 0.3%-1.0% polyvinylpyrrolidone (PVPK30) as a dispersant, and high Tg (Tg>280℃ after curing) polyimide precursor PAA as a binder, and then combining planetary stirring and ultrasonic dispersion to finally obtain a uniform slurry with a viscosity of 800-2500 mPa·S. Among them, the aramid fiber has a length of 0.5-2.0 mm and a fiber diameter of 5-10 μm; the so-called high Tg refers to Tg greater than 280℃ after curing, and the addition amount of high Tg polyimide precursor PAA is preferably 3wt%-8wt%.

[0023] S2, pretreatment of meta-aramid base paper: improving the surface energy of both sides of the meta-aramid paper substrate by plasma treatment; pre-soaking treatment in 0.3% silane coupling agent (KH-560) can improve the interfacial bonding strength of the substrate. The thickness of the meta-aramid paper substrate or base paper is 80-150 μm, the basis weight is 60-100 g / m2, and the porosity of the base paper is 20%-28%.

[0024] S3, gradient coating process (double-sided or three-layer): the first layer adopts micro-gravure roll coating, the coating thickness is 8-15 μm, and the coating amount is 5-12 g / m 2 ; the second layer adopts knife coating, the thickness is 10-20 μm, and the coating amount is 8-12 g / m 2 ; if necessary, a third layer of spraying process can be added to optimize the coating effect, the thickness is 5-10 μm, and the coating amount is 3-6 g / m 2 . The total coating amount in step S3 is 15-25 g / m 2 , and the penetration depth of the coating layer reaches 30%-60% of the paper thickness. The inventors found that the best effect is obtained when the coating amount of the second layer is the largest, the first layer is the second, and the third layer is the smallest; the first layer of coating is mainly to form a firm interface between a small amount of uniform slurry and the substrate, and to pave the way for subsequent large filling; the second layer of coating uses knife coating to penetrate a sufficient amount of slurry to a depth of 30%-60% of the paper thickness to fully fill the internal pores; the third layer is mainly to modify some local pore residues and surface unevenness that may exist in the previous two layers, and to further improve the coating density and surface smoothness.

[0025] S4, gradient drying and hot-pressing curing treatment: firstly, the coated meta-aramid paper is pre-dried at 100-120℃ for 5-10min to remove the surface free solvent; then heated to 260-300℃, and hot-pressed and cured at 2.0-5.0MPa for 3-6min to make the binder fully cross-linked; finally, post-calendering is carried out at 150-180℃, 1.0-2.0MPa for 1-2min to improve the coating density. The cured modified aramid paper needs to be post-processed, first through double-roller calendering to make the surface roughness Ra<1.0μm, then vacuum degassing at 80℃, -0.09MPa for 30min to completely remove the residual solvent, and finally obtain the low-porosity modified meta-aramid paper.

[0026] The performance of the modified meta-aramid paper provided by the application is characterized by a plurality of standard methods: the porosity is tested according to the standard test of ASTM D4284 (mercury pressure method); the tear strength is detected according to the standard of ASTM D1424; the breakdown voltage is tested with reference to GB / T1408.1; the volume resistivity is tested according to the standard of ASTM D257; and the thermal decomposition temperature (Td5%) is tested by TGA (10℃ / min, N2 atmosphere).

[0027] The prepared low-porosity meta-aramid paper has a porosity of not more than 13.2%, a coating amount of 15-25g / m2, and a coating penetration depth of 30%-60% of the thickness of the uncoated base paper. The tear strength of the low-porosity meta-aramid paper is not less than 9.5N / mm, which is increased by more than 30% compared with the uncoated base paper; the breakdown voltage of the low-porosity meta-aramid paper is not less than 17.5KV / mm, which is increased by more than 30% compared with the uncoated base paper; and the strength retention rate of the low-porosity meta-aramid paper after aging at 350℃ for 100 hours is not less than 85%. The low-porosity meta-aramid paper has excellent tear strength, insulation performance and high-temperature resistance.

[0028] The meta-aramid base paper and the arnosulfon fiber used in the examples are both prepared by the company itself through polymerization, spinning and papermaking. The reagents such as NMP, DMAc, PVPK30, PAA and KH-560 used are all purchased from the market.

[0029] Example 1

[0030] The selected arnosulfon fiber and aramid base paper are both self-made, wherein the arnosulfon fiber has a length of 1mm and a diameter of 7μm; the aramid base paper has a thickness of 100μm, a basis weight of 80g / m2, and a porosity of 26%. The low-porosity modified meta-aramid paper product is prepared according to the following steps:

[0031] (1) Preparation of high solid content arnosulfonamide slurry: arnosulfonamide fiber is selected as the core raw material, N-methyl pyrrolidone (NMP) or N, N-dimethylacetamide (DMAc) is selected as the solvent, a slurry with a concentration of 32% is prepared, 0.3% polyvinylpyrrolidone (PVP K30) is added as a dispersant, and 3% high-Tg polyimide precursor (PAA, Tg>280℃ after curing) is added as a binder, and then a uniform slurry with a viscosity of 1800 mPa·s is finally obtained by combining planetary stirring and ultrasonic dispersion.

[0032] (2) Pretreatment of meta-aramid base paper: the surface energy of both sides of the meta-aramid paper substrate is improved by plasma treatment; the interfacial bonding strength of the substrate can be improved by pre-soaking treatment in 0.3% silane coupling agent (KH-560).

[0033] (3) Gradient coating process (double-sided): the first layer is coated by micro-gravure roll coating with a coating thickness of 10 μm and a coating amount of 12 g / m2; the second layer is coated by knife coating with a coating thickness of 15 μm and a coating amount of 10 g / m2; the coating speed of the first layer is 4 m / min, and the coating speed of the second layer is 3 m / min. The total coating amount is 22 g / m 2 , and the penetration depth of the coating reaches 45% of the paper thickness.

[0034] (4) Gradient drying and hot pressing and curing treatment: the coated meta-aramid paper is first pre-dried at 110℃ for 8 min; then heated to 280℃ and hot pressed and cured at 2.0 MPa for 4 min; finally, post-calendered at 150℃ and 1.5 MPa for 2 min. The cured modified aramid paper is then vacuum degassed at 80℃ and -0.09 MPa for 30 min after being calendered by double rollers (Ra=0.8 μm), and finally a modified meta-aramid paper with low porosity is obtained.

[0035] The final modified meta-aramid paper product has a porosity of 12.5%, which is 52% lower than that of the original paper, a tear strength of 11.2 N / mm, which is 68% higher than that of the original paper, a breakdown voltage of 21.9 KV / mm, which is 58% higher than that of the original paper, and a strength retention rate of 88% after aging at 350℃ for 100 h.

[0036] Example 2

[0037] The meta-aramid base paper and arnosulfonamide fiber used in this example are prepared by the company itself through polymerization, spinning and papermaking, wherein the arnosulfonamide fiber has a length of 0.8 mm and a fiber diameter of 6 μm; the meta-aramid base paper has a thickness of 100 μm and a basis weight of 80 g / m 2, the original paper porosity is 25%. The reagents such as NMP, DMAc, PVP K30, PAA, KH-560 used are purchased from the market. The low porosity modified meta-aramid paper product is prepared according to the following steps:

[0038] (1) Preparation of high solid content arnosulfonamide slurry: arnosulfonamide fiber is selected as the core raw material, N-methyl pyrrolidone (NMP) is used as the solvent, a slurry with a concentration of 30% is prepared, 0.5% polyvinylpyrrolidone (PVP K30) is added as a dispersant, and 5% high Tg polyimide precursor (PAA, Tg>280℃ after curing) is added as a binder, then the uniform slurry with a viscosity of 1600 mPa·s is finally obtained by planetary stirring combined with ultrasonic dispersion.

[0039] (2) Pretreatment of meta-aramid paper substrate: the surface energy of both sides of the meta-aramid paper substrate is improved by plasma treatment, and no silane coupling agent pre-impregnation treatment is performed.

[0040] (3) Gradient coating process (two layers on both sides): the first layer is coated by micro-gravure roll coating, the coating thickness is 12 μm, the coating amount is 6 g / m 2 ; the second layer is coated by knife coating, the thickness is 15 μm, the coating amount is 10 g / m 2 ; the coating speed of the first layer is 5 m / min, the coating speed of the second layer is 4 m / min; the total coating amount is 16 g / m 2 , and the penetration depth of the coating reaches 45% of the paper thickness.

[0041] (4) Gradient drying and hot pressing and curing treatment: the coated meta-aramid paper is first pre-dried at 110℃ for 8 min; then heated to 280℃, hot pressed and cured at 3.0 MPa for 4 min; finally, post-calendered at 160℃, 1.5 MPa for 1.5 min. The cured modified aramid paper is then calendered by double roller (Ra=0.8 μm), and then vacuum degassed at 80℃, -0.09 MPa for 30 min, to obtain the low porosity modified meta-aramid paper product.

[0042] The prepared modified meta-aramid paper product has a porosity of 12.3%, which is 50.8% lower than that of the original paper, a tear strength of 10.8 N / mm, which is 35% higher than that of the original paper, a breakdown voltage of 19.6 kV / mm, which is 47% higher than that of the original paper, and a volume resistivity of 2.8×10 15 Ω·cm, and after aging at 350℃ for 100 h, the strength retention rate reaches 91%.

[0043] Example 3

[0044] The meta-aramid paper and the arnosulfon fiber used in this embodiment are prepared by the company itself through polymerization, spinning, papermaking, wherein the arnosulfon fiber has a length of 1.5 mm and a fiber diameter of 8 μm; the meta-aramid base paper has a thickness of 120 μm and a basis weight of 90 g / m 2 The reagents such as NMP, DMAc, PVP K30, PAA, KH-560 used are purchased from the market. The modified meta-aramid paper product with low porosity is prepared according to the following steps:

[0045] (1) Preparation of high solid content arnosulfon pulp: arnosulfon fiber is selected as the core raw material, N-methyl pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc) is selected as the solvent, a slurry with a concentration of 35% is prepared, 0.8% polyvinylpyrrolidone (PVP K30) is added as a dispersant, and 7% high T g polyimide precursor (PAA, Tg> 280℃ after curing) is added as a binder, and then a uniform slurry with a viscosity of 2200 mPa·s is finally obtained by a combination of planetary stirring and ultrasonic dispersion;

[0046] (2) Pretreatment of meta-aramid paper substrate: the same as in Example 1.

[0047] (3) Gradient coating process (three layers): the first layer is coated by a micro-gravure roll coating method with a coating thickness of 15 μm and a coating amount of 8 g / m 2 ; the second layer is coated by a knife coating method with a thickness of 20 μm and a coating amount of 12 g / m 2 ; the third layer is coated by a spraying method with a thickness of 10 μm and a coating amount of 6 g / m 2 ; the coating speed of the first layer is 6 m / min, the coating speed of the second layer is 5 m / min, and the coating speed of the third layer is 7 m / min. The total coating amount is 25 g / m 2 , and the penetration depth of the coating layer reaches 58% of the thickness of the paper.

[0048] (4) Gradient drying and hot pressing and curing treatment: the coated meta-aramid paper is first pre-dried at 120℃ for 10 min; then heated to 300℃, hot pressed and cured at a pressure of 5.0 MPa for 6 min; finally, post-calendered at 180℃ and 2 MPa for 2 min. The cured modified aramid paper is then vacuum degassed at 80℃ and -0.09 MPa for 30 min after being calendered by a double roll, and finally a modified meta-aramid paper product with low porosity is obtained.

[0049] The prepared modified meta-aramid paper product has a porosity of 10.5%, which is reduced by 59.6% compared with the original paper, a tear strength of 12.7 N / mm, which is increased by 43% compared with the original paper, a breakdown voltage of 23.5 kV / mm, which is increased by 62% compared with the original paper, and a volume resistivity of 4.2 x 1015 Ω·cm, and the strength retention rate reached 93% after aging for 100 h at 350℃.

[0050] Example 4

[0051] The meta-aramid paper and the arnosulfonamide fiber used in this example were prepared by the company's own polymerization, spinning and papermaking. The arnosulfonamide fiber has a length of 1.2 mm and a fiber diameter of 7 μm. The thickness of the meta-aramid base paper is 150 μm, and the basis weight is 100 g / m 2 . The porosity of the base paper is 28%. The reagents such as NMP, DMAc, PVP K30, PAA, KH-560 used are purchased from the market. The low-porosity modified meta-aramid paper product is prepared according to the following steps:

[0052] (1) Preparation of high-solid-content arnosulfonamide slurry: arnosulfonamide fiber is selected as the core raw material, N-methyl pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc) is selected as the solvent, and a slurry with a concentration of 32% is prepared. 1.0% of polyvinylpyrrolidone (PVP K30) is added as a dispersant, and 8% of high-T g polyimide precursor (PAA, Tg> 280℃ after curing) is added as a binder. Then, through the combination of planetary stirring and ultrasonic dispersion, a uniform slurry with a viscosity of 2000 mPa·s is finally obtained;

[0053] (2) Pretreatment of meta-aramid paper substrate: the same as in Example 1.

[0054] (3) Gradient coating process (three layers): the first layer is coated by micro-gravure roll coating, with a coating thickness of 13 μm, a coating amount of 7 g / m 2 ; the second layer is coated by knife coating, with a thickness of 18 μm, a coating amount of 11 g / m 2 ; the third layer is coated by spraying, with a thickness of 8 μm, a coating amount of 5 g / m 2 ; the first layer coating speed is 5 m / min, the second layer coating speed is 4 m / min, and the third layer coating speed is 6 m / min. The total coating amount is 23 g / m 2 , and the coating penetration depth reaches 52% of the paper thickness.

[0055] (4) Gradient drying and hot-pressing curing treatment: the coated meta-aramid paper is first pre-dried at 120℃ for 10 min; then heated to 300℃, hot-pressed and cured at a pressure of 5.0 MPa for 6 min; finally, post-calendered at 180℃ and 2 MPa for 2 min. The cured modified aramid paper is then vacuum degassed at 80℃ and -0.09 MPa for 30 min after double-roller calendering, and finally a low-porosity modified meta-aramid paper product is obtained.

[0056] The prepared modified meta-aramid paper product has a porosity of 11.2%, which is reduced by 60.0% compared with the original paper, a tear strength of 12.3 N / mm, which is increased by 41% compared with the original paper, a breakdown voltage of 20.9 kV / mm, which is increased by 57% compared with the original paper, and a volume resistivity of 3.7 x 10 15 Ω·cm, and after aging at 350°C for 100 h, the strength retention rate reaches 92%.

[0057] Example 5

[0058] The meta-aramid paper and the arnosulfonamide fiber used in this example are both prepared by polymerization, spinning, and papermaking by the company itself, wherein the arnosulfonamide fiber has a length of 0.6 mm and a fiber diameter of 7 μm; the meta-aramid base paper has a thickness of 90 μm and a basis weight of 70 g / m 2 , and the original paper has a porosity of 24%. The reagents such as NMP, DMAc, PVP K30, PAA, KH-560 used are all purchased on the market. The modified meta-aramid paper product with low porosity is prepared according to the following steps:

[0059] (1) Preparation of high solid content arnosulfonamide slurry: arnosulfonamide fiber is selected as the core raw material, N-methyl pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc) is selected as the solvent, a slurry with a concentration of 33% is prepared, 0.6% of polyvinylpyrrolidone (PVP K30) is added as a dispersant, and 6% of high-Tg polyimide precursor (PAA, Tg> 280°C after curing) is added as a binder, and then a uniform slurry with a viscosity of 1500 mPa·s is finally obtained by combining planetary stirring and ultrasonic dispersion;

[0060] (2) Pretreatment of meta-aramid paper substrate: same as Example 1.

[0061] (3) Gradient coating process (double layer): the first layer is coated by a micro-gravure roll coating method, with a coating thickness of 10 μm and a coating amount of 6 g / m 2 ; the second layer is coated by a knife coating method, with a thickness of 16 μm and a coating amount of 9 g / m 2 . The first layer coating speed is 5 m / min, and the second layer coating speed is 4 m / min. The overall total coating amount is 15 g / m 2 , and the coating penetration depth reaches 40% of the paper thickness.

[0062] (4) Gradient drying and hot-pressing curing treatment: firstly, the coated meta-aramid paper is pre-dried at 105℃ for 10 min; then heated to 270℃, hot-pressed and cured at 3.5 MPa pressure for 4 min; finally, post-calendered at 165℃, 1.6 MPa for 1.5 min. The cured modified meta-aramid paper is vacuum degassed at 80℃, -0.09 MPa for 30 min after double-roller calendering, and finally a low porosity modified meta-aramid paper product is obtained.

[0063] The prepared modified meta-aramid paper product has a porosity of 13.1%, which is reduced by 45.4% compared with the original paper, a tear strength of 9.5 N / mm, which is increased by 33% compared with the original paper, a breakdown voltage of 17.8 kV / mm, which is increased by 42% compared with the original paper, and a volume resistivity of 2.1 x 10 15 Ω·cm, and after aging at 350℃ for 100h, the strength retention rate reaches 89%.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that only one layer is coated, and the coating amount is 18 g / m 2 , hot-pressed and cured at 280℃, 1.0 MPa pressure for 4 min; finally, post-calendered at 150℃, 1 MPa for 2 min.

[0066] The prepared modified meta-aramid paper product has a porosity of 15.8%, which is reduced by 39% compared with the original paper, and is more suitable for flexible requirement scenarios.

[0067] Comparative Example 2

[0068] This comparative example is an original meta-aramid paper without any modification treatment, and the substrate is consistent with that used in Example 1 of the application: the meta-aramid paper is prepared by self-polymerization and papermaking, the substrate thickness is 100 μm, the basis weight is 80 g / m 2 , the porosity of the original paper is 26%, and no modification processes such as sizing coating, plasma treatment, coupling agent pre-impregnation and hot-pressing curing are performed, and the paper is directly used as a test sample for performance characterization.

[0069] The test results show that the porosity of the unmodified meta-aramid paper is 26%, the tear strength is 6.8 N / mm, the breakdown voltage is 13 kV / mm, and the volume resistivity is 8.5 x 10 13 Ω·cm; after aging at 350℃ for 100h, due to the lack of protection of the heat-resistant modification system, the fiber structure is severely damaged, the strength decreases by 70%, and it cannot meet the use requirements under high temperature working conditions.

[0070] Comparative Example 3

[0071] The comparative example is prepared by using the existing conventional epoxy impregnation process to prepare modified meta-aramid paper (typical scheme of prior art), and the specific steps are as follows: the same specification of raw meta-aramid paper (thickness 100 μm, basis weight 80 g / m 2 , original porosity 26%) as the substrate, and the commercially available bisphenol A type epoxy resin is used as the impregnating agent, and the acetone is used as the diluent solvent, and the epoxy impregnating solution with solid content of 40% is prepared; the substrate is completely immersed in the impregnating solution for 15 min, and after being taken out, it is pre-dried at 80°C for 10 min to remove the solvent, and then it is cured at 150°C and 1.5 MPa pressure for 20 min to obtain the epoxy impregnated modified aramid paper product.

[0072] The test results show that the porosity of the modified product of the prior art is 18%, which is only reduced by 30.8% compared with the raw paper; the tear strength is 7.5 N / mm, which is increased by 10.3% compared with the raw paper; the breakdown voltage is 16 kV / mm, which is increased by 23.1% compared with the raw paper; the volume resistivity is 1.2 x 10 14 Ω·cm; due to the limited heat resistance of the epoxy resin (long-term use temperature ≤ 150°C), after aging at 350°C for 100 h, the epoxy resin is severely carbonized and brittle, and is peeled off from the aramid paper substrate, and the product completely loses the use performance, and the densification effect and the comprehensive performance are far inferior to the present application.

Claims

1. A low porosity metaplyme paper characterized by The aramid paper is coated with arnosulfonic acid pulp, the porosity of the coated aramid paper is less than 13.2%, the coating amount is 15-25 g / m2, and the penetration depth of the coating is 30%-60% of the thickness of the uncoated base paper.

2. The low porosity metaplymer paper of claim 1, wherein The low-porosity meta-aramid paper has a tear strength of not less than 9.5 N / mm, which is increased by more than 30% compared with the uncoated base paper; the low-porosity meta-aramid paper has a breakdown voltage of not less than 17.5 KV / mm, which is increased by more than 40% compared with the uncoated base paper; and the strength retention rate of the low-porosity meta-aramid paper is not less than 85% after aging at 350℃ for 100 hours.

3. A method of making the low porosity meta-aramid paper of claim 1 or 2, characterized in that The method comprises the steps of: S1, preparation of high-solid-content arnosulfonic acid pulp: arnosulfonic acid fibers are dissolved in N-methyl pyrrolidone (NMP) or N,N-dimethylacetamide (DMAC) to prepare a slurry with a concentration of 25wt%-40wt%, polyvinylpyrrolidone (PVPK30) is added as a dispersant, a polyimide precursor PAA with a Tg>280℃ after curing is selected as a binder, and the slurry is stirred and ultrasonically dispersed to obtain a uniform slurry with a viscosity of 800-2500 mPa·s; S2, pretreatment of meta-aramid base paper: plasma treatment and pre-impregnation treatment in a silane coupling agent (KH-560); S3, gradient coating: the first layer is coated by a micro-gravure roll; the second layer is coated by a doctor blade; S4, gradient drying and hot-pressing curing: the coated meta-aramid paper is first pre-dried, then hot-pressed and cured, and finally calendered to make the surface roughness Ra of the modified aramid paper less than 1.0 μm; vacuum degassing is performed to remove residual solvents and obtain a low-porosity modified meta-aramid paper.

4. The method of claim 3, wherein the low porosity meta-aramid paper is prepared by In the step S1, the length of the arnosulfonic acid fibers is 0.5-2.0 mm, and the fiber diameter is 5-10 μm; the mass percentage of the polyvinylpyrrolidone (PVPK30) is 0.3wt%-1.0wt%; and the addition amount of the PAA is 3wt%-8wt%.

5. The method of claim 3, wherein the low porosity meta-aramid paper is prepared by the steps of In the step S2, the thickness of the meta-aramid base paper is 80-150 μm, the basis weight is 60-100 g / m2, and the porosity of the base paper is 20%-28%.

6. The method of claim 3, wherein the low porosity meta-aramid paper is prepared by the steps of In the step S3, a third layer spraying process is further included, the coating thickness of the third layer spraying process is 5-10 μm, and the coating amount is 3-6 g / m 2 .

7. The method for preparing a low-porosity meta-aramid paper as described in claim 3, characterized in that... In the step S3, the micro gravure roll coating has a coating thickness of 8-15 μm and a coating amount of 5-12 g / m 2 .

8. The method for preparing a low-porosity meta-aramid paper as described in claim 3, characterized in that... In the step S3, the coating thickness of the blade coating is 10 to 20 μm, and the coating amount is 8 to 12 g / m 2 .

9. The method for preparing a low-porosity meta-aramid paper as described in claim 3, characterized in that... In the step S4, the pre-drying temperature is 100-120℃, and the pre-drying time is 5-10 min; the hot-pressing curing temperature is 260-300℃, the pressure is 2.0-5.0 MPa, and the curing time is 3-6 min; the calendering temperature is 150-180℃, the pressure is 1.0-2.0 MPa, and the time is 1-2 min.