Aromatic polyamide surface felt and preparation method thereof

Abstract

The present invention relates to the technical field of fiber fabric materials, and specifically to an aromatic polyamide surface felt and a preparation method thereof, wherein the preparation method comprises: S1, uniformly dispersing a dispersant and a defoaming agent in water to prepare white water; the dispersant comprises an ionic dispersant and a thickening dispersant; S2, dissociating and dispersing aramid fibers in white water to prepare a fiber dispersion slurry; S3, using the fiber dispersion slurry to paper-make a fiber web; S4, applying a wetting agent and an adhesive on the surface of the fiber web; S5, drying and heat-treating to obtain the aromatic polyamide surface felt. The surface felt has good mechanical properties, dimensional stability, chemical stability, flexible and adjustable gram weight, good air permeability, and excellent resin impregnation, and has great application potential in the application field of composite material structural parts.

Description

Technical Field

[0001] The invention relates to an aromatic polyamide surface felt and a preparation method thereof, belonging to the technical field of fiber fabric materials. Background Art

[0002] Aromatic polyamide fiber, or aramid fiber, is known for its excellent properties such as high strength, high modulus, high temperature resistance, and chemical corrosion resistance, and is known as the "all-round fiber." These properties make aramid fiber have a wide range of application potentials in many fields, such as aerospace, military protection, sporting goods, industrial manufacturing, etc. Aramid fiber is especially indispensable in situations where high strength, high temperature resistance, and lightweight materials are required.

[0003] Due to the many performance advantages of aramid fiber, it is widely used in composite structural parts. In the field of aerospace, it is widely used in the manufacture of structural parts such as fuselages, main wings, and tail wings of aircraft and spacecraft. These structural parts need to withstand huge mechanical loads and harsh environmental conditions. The excellent performance of aramid fiber can ensure the stability and safety of the structural parts. In the field of national defense and military, it is widely used in personal protective equipment such as bulletproof vests and bulletproof helmets. Bulletproof equipment with aramid fiber is not only light in weight and small in size, but also has significantly improved bulletproof effect. Aramid fiber is also used in the manufacture of tanks and armored vehicles. Tanks and armored vehicles using "steel-aramid-steel" composite armor can greatly improve their protective capabilities. In the industrial field, it is widely used in tire cords and is currently the most ideal tire skeleton material. Compared with steel wire, aramid cord has a relatively low density, fatigue resistance, and shear resistance. It can significantly improve the rigidity and wear resistance of tires and extend their service life. In addition, aramid is also widely used as a composite reinforcement material in hose materials.

[0004] At present, aramid fibers are mainly used in composite structural parts in the form of filaments, yarns, textile sleeves, woven fabrics, non-woven fabrics and other yarn or fabric structures combined with rubber, resin and other materials to form composite materials. At present, products that enhance the surface of composite materials, make them lightweight and have good resin wettability are still under research.

[0005] Surface felt is usually made of glass fiber, polyester fiber or other synthetic fibers. It plays an important role in composite material manufacturing and industrial applications. It is widely used in the fields of ships, automobiles, construction, wind energy, pipeline storage tanks, etc. At present, most surface felts are made of glass fiber. For example, the patents with publication numbers CN219637152U and CN219214328U all disclose glass fiber surface felts. It is of great value to study how to use aromatic polyamide materials with excellent performance to prepare surface felts. Summary of the invention

[0006] In view of the shortcomings of existing products that cannot meet the requirements of surface enhancement, lightweight and insufficient resin wettability of composite materials, the present invention provides an aromatic polyamide surface felt and a preparation method thereof. The surface felt has good mechanical properties, dimensional stability, chemical stability, flexible and adjustable gram weight, good air permeability, and excellent resin wettability, and has great application potential in the application field of composite material structural parts.

[0007] The technical solution of the present invention to solve the above technical problem is as follows: a method for preparing an aromatic polyamide surface felt, the preparation method comprising:

[0008] S1. Dispersing the dispersant and defoamer evenly in water to make white water;

[0009] S2, dissociating and dispersing the aramid fibers in white water to prepare a fiber dispersion slurry;

[0010] S3, using the fiber dispersion slurry to papermake a fiber web;

[0011] S4, applying a wetting agent and an adhesive to the surface of the web;

[0012] S5, obtaining the aromatic polyamide surface felt after drying and heat treatment.

[0013] Further, in the white water, the mass ratio of the dispersant to water is 1:(200-10000);

[0014] The dispersants include ionic dispersants and thickening dispersants.

[0015] Furthermore, the ionic dispersant is at least one of fatty alcohol polyoxyethylene ether sodium sulfate, sodium dodecyl diphenyl ether disulfonate, hexadecyl trimethyl ammonium bromide, and Remibond A;

[0016] The thickening dispersant is at least one of sodium lignin sulfonate, polyethylene oxide, polyvinyl pyrrolidone, and polyethylene glycol;

[0017] In the white water, the mass ratio of the ionic dispersant to water is 1: (5000-10000); the mass ratio of the thickening dispersant to water is 1: (200-700).

[0018] Further, in the white water, the mass ratio of the defoamer to water is 1:(1000-2000);

[0019] The defoamer is at least one of a polyether modified defoamer, dimethyl silicone oil, a silicon dioxide dispersed defoamer, polydimethylsiloxane, a high carbon alcohol defoamer, and tributyl phosphate.

[0020] Furthermore, in step S2, the aramid fiber is meta-aramid chopped fiber or para-aramid chopped fiber, and the length of the aramid fiber is 6-12 mm; in the fiber dispersion slurry, the weight ratio of aramid fiber to white water is 1: (1000-20000).

[0021] Furthermore, in step S2, the dissociation dispersion is mechanical stirring dispersion, the rotation speed is 1000-2500 rpm, and the number of stirring revolutions is 5000-30000 revolutions;

[0022] In step S3, the screen used in the papermaking process is 70-100 mesh.

[0023] Furthermore, the adhesive is a blocked water-based isocyanate adhesive;

[0024] The isocyanate in the blocked water-based isocyanate adhesive is selected from at least one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate or hexamethylene diisocyanate;

[0025] The blocking agent in the blocked water-based isocyanate adhesive is selected from at least one of n-propanol, n-butanol, sodium bisulfite, methyl ethyl ketone oxime, acetone oxime, cyclohexanone oxime and acetophenone oxime;

[0026] The solid content of the isocyanate in the adhesive is 2-5%.

[0027] Furthermore, the wetting agent is at least one of sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, and fatty acid glyceride polyoxyethylene ether, and the mass ratio of the wetting agent to the isocyanate in the adhesive is 1: (1000-2000).

[0028] Furthermore, in step S5, the drying method is hot air drying, and the drying temperature is 110-130°C;

[0029] In step S5, the heat treatment temperature is 110-185° C., and the heat treatment time is 5-60 min.

[0030] The invention also discloses an aromatic polyamide surface felt, and the aromatic polyamide surface felt is prepared according to the preparation method of the invention.

[0031] The beneficial effects of the present invention are:

[0032] The preparation method of the aromatic polyamide surface felt of the present invention adopts a wet papermaking method, the molding process is efficient, no organic solvents or other hazardous chemicals are used, the process flow is safe and controllable, and no pollution is caused to the environment.

[0033] In order to meet the wettability of composite structural parts to resin, the prepared surface felt needs to have good porosity to achieve high bonding strength of the resin, which requires the surface felt to have as low a gram weight as possible while meeting a certain strength, which will challenge the uniformity of the slurry before papermaking. Due to the surface inertia of aramid fibers, their uniformity of dispersion in water is poor. The present invention coordinates multiple components to regulate the negative charge density of fiber particles and enhance their stability. Due to the directional adsorption of the dispersant to form a hydration film, the fibers are transformed from a hydrophobic state to a hydrophilic state, thereby effectively dispersing the fibers and reducing the tendency of mutual coagulation or precipitation, so as to achieve uniform dispersion of aramid fibers and ensure uniform papermaking of low-gram-weight surface felt.

[0034] The present invention designs a corresponding chemical cross-linking bonding system in view of the characteristics of the aramid fiber surface inertia and insufficient bonding strength with the adhesive component, which can achieve good bonding strength between the fibers to meet the mechanical property requirements of the surface felt. The prepared aramid surface felt has good mechanical properties, dimensional stability, chemical stability, flexible and adjustable gram weight, good air permeability, excellent resin impregnation, can be widely used in composite materials, and has great application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a scanning electron microscope image of the aromatic polyamide surface felt of Example 1;

[0036] Figure 2 This is the thermogravimetric curve of the aromatic polyamide surface felt in Example 1. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is described in detail below. The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0039] A method for preparing an aromatic polyamide surface felt, the preparation method comprising:

[0040] S1. Dispersing the dispersant and defoamer evenly in water to make white water;

[0041] S2, dissociating and dispersing the aramid fibers in white water to prepare a fiber dispersion slurry;

[0042] S3, using papermaking equipment to form the prepared fiber dispersion slurry into a fiber web;

[0043] S4, applying a wetting agent and an adhesive to the surface of the web;

[0044] S5, obtaining the aromatic polyamide surface felt after drying and heat treatment.

[0045] Further, in the white water, the mass ratio of the dispersant to water is 1:(200-10000);

[0046] The dispersants include ionic dispersants and thickening dispersants.

[0047] Specifically, the ionic dispersant is at least one of fatty alcohol polyoxyethylene ether sodium sulfate (low molecular weight type), sodium dodecyl diphenyl ether disulfonate, hexadecyl trimethyl ammonium bromide, and Remibond A;

[0048] The thickening dispersant is at least one of sodium lignin sulfonate (weight average molecular weight: 2000-10000), polyethylene oxide (average molecular weight: 1000000), polyvinyl pyrrolidone (weight average molecular weight: 10000-50000), and polyethylene glycol (weight average molecular weight: 4000);

[0049] In the white water, the mass ratio of the ionic dispersant to water is 1: (5000-10000); the mass ratio of the thickening dispersant to water is 1: (200-700).

[0050] Specifically, in the white water, the mass ratio of the defoamer to water is 1:(1000-2000);

[0051] The defoamer is at least one of a polyether modified defoamer (using HLB of 9-14, weight average molecular weight of 5000-10000), dimethyl silicone oil, a silicon dioxide dispersed defoamer (hexamethyldisilazane (HMDS) modified type), polydimethylsiloxane (viscosity <1000 mPa·s), a high carbon alcohol defoamer (using type with HLB of 6), and tributyl phosphate.

[0052] Specifically, in step S2, the aramid fiber is meta-aramid chopped fiber or para-aramid chopped fiber, and the length of the aramid fiber is 6-12 mm; in the fiber dispersion slurry, the weight ratio of aramid fiber to white water is 1: (1000-20000).

[0053] Specifically, in step S2, the dissociation dispersion is mechanical stirring dispersion, the rotation speed is 1000-2500 rpm, and the number of stirring revolutions is 5000-30000 revolutions.

[0054] Specifically, in step S3, the papermaking process is as follows: the dispersed slurry is evenly dispersed onto the mesh surface of the inclined mesh former (inclination angle 20-30°) through a headbox, and initially dehydrated by gravity of the inclined mesh, and then vacuum dehydrated to a dryness of 15-40%, and the dehydrated white water enters the white water circulation system, and then an adhesive is applied to the formed fiber web.

[0055] More specifically, in step S3, the screen used in the papermaking process is 70-100 mesh.

[0056] Specifically, the adhesive is a blocked water-based isocyanate adhesive;

[0057] The isocyanate in the blocked water-based isocyanate adhesive is selected from at least one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate or hexamethylene diisocyanate;

[0058] The blocking agent in the blocked water-based isocyanate adhesive is selected from at least one of n-propanol, n-butanol, sodium bisulfite, methyl ethyl ketone oxime, acetone oxime, cyclohexanone oxime and acetophenone oxime;

[0059] The solid content of the isocyanate in the adhesive is 2-5%.

[0060] More specifically, the preparation method of the blocked water-based isocyanate adhesive is as follows: adding isocyanate to an ethyl acetate aqueous solution, dripping a blocking agent into the system under heating conditions in an inert gas environment, and stirring to react to obtain the blocked water-based isocyanate adhesive.

[0061] Specifically, the wetting agent is at least one of sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether (low molecular weight type), and fatty acid glyceride polyoxyethylene ether (selected type with EO number 15-20), and the mass ratio of the wetting agent to the isocyanate in the adhesive is 1: (1000-2000).

[0062] More specifically, the wetting agent and the adhesive are applied to the surface of the fiber web in the form of an aqueous solution, and the application method can be conventional methods such as spraying.

[0063] Specifically, in step S5, the drying method is hot air drying, and the drying temperature is 110-130°C;

[0064] In step S5, the heat treatment temperature is 110-185° C., and the heat treatment time is 5-60 min.

[0065] Example 1

[0066] Preparation of an aromatic polyamide surface felt:

[0067] S1. Dispersing sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer in water to prepare white water, wherein the weight ratios of sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer to water are 1:10000, 1:700, and 1:1000, respectively;

[0068] S2, dissociate and disperse 12 mm para-aramid short fibers in white water, with the ratio of fiber to white water being 1:1000. After adding the fibers, mechanical stirring is performed, with the stirring speed set at 1000 rpm, and after stirring at 30,000 rpm, a fiber dispersion slurry is prepared;

[0069] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 70 mesh;

[0070] S4. Apply adhesive and wetting agent to the surface of the formed fiber web.

[0071] The preparation method of the adhesive is as follows: 4,4-diphenylmethane diisocyanate is added to an ethyl acetate aqueous solution with a mass concentration of 50% (the amount of 4,4-diphenylmethane diisocyanate added is 2% of the weight of the ethyl acetate aqueous solution), the solution system is placed in a heating medium at 40°C, and an 84% mass concentration sodium bisulfite aqueous solution is added dropwise thereto, wherein the weight ratio of 4,4-diphenylmethane diisocyanate to the sodium bisulfite aqueous solution is 1:1, nitrogen is introduced and stirred for 3 hours to obtain an adhesive.

[0072] The wetting agent is sodium dodecylbenzene sulfonate, and the weight ratio of sodium dodecylbenzene sulfonate to isocyanate in the adhesive is 1:2000. The adhesive and the wetting agent are mixed and then applied to the fiber web prepared in step S3.

[0073] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 185° C. and heat treated for 5 minutes to obtain an aromatic polyamide surface felt.

[0074] Example 2

[0075] Preparation of an aromatic polyamide surface felt:

[0076] S1. Evenly dispersing sodium dodecyl diphenyl ether disulfonate, polyvinyl pyrrolidone and polydimethylsiloxane defoamer in water to prepare white water, wherein the ratios of sodium dodecyl diphenyl ether disulfonate, polyvinyl pyrrolidone and polydimethylsiloxane defoamer to water are 1:10000, 1:200 and 1:2000 respectively;

[0077] S2. Dissociate and disperse 6 mm meta-aramid short fibers and 12 mm para-aramid short fibers in white water, wherein the mass ratio of meta-aramid short fibers to para-aramid short fibers is 30:70, and the ratio of fiber (total amount of meta-aramid short fibers and para-aramid short fibers) to white water is 1:10000. After adding the fibers, mechanical stirring is performed, and the stirring speed is set to 2500 rpm. After stirring for 5000 rpm, a fiber dispersion slurry is prepared.

[0078] S3, using papermaking equipment to form the prepared fiber dispersion slurry into a fiber web, and the web used is 100 mesh;

[0079] S4. Apply adhesive and wetting agent to the surface of the formed fiber web.

[0080] The preparation method of the adhesive is as follows: dicyclohexylmethane diisocyanate is added to an ethyl acetate aqueous solution with a mass concentration of 50% (the amount of dicyclohexylmethane diisocyanate added is 5% of the weight of the ethyl acetate aqueous solution), the solution system is placed in a heating medium at 40°C, n-propanol is added dropwise thereto (the weight ratio of n-propanol to dicyclohexylmethane diisocyanate is 1:1.35), nitrogen is introduced and stirred for 2 hours to obtain an adhesive.

[0081] The wetting agent is fatty alcohol polyoxyethylene ether, and the weight ratio of fatty alcohol polyoxyethylene ether to isocyanate in the adhesive is 1:1000. The adhesive and the wetting agent are mixed and then applied to the fiber web prepared in step S3.

[0082] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 185° C. and heat treated for 60 minutes to obtain an aromatic polyamide surface felt.

[0083] Example 3

[0084] Preparation of an aromatic polyamide surface felt:

[0085] S1. Dispersing cetyl trimethyl ammonium bromide, sodium lignin sulfonate, and a high-carbon alcohol defoamer uniformly in water to prepare white water, wherein the weight ratios of cetyl trimethyl ammonium bromide, sodium lignin sulfonate, and a high-carbon alcohol defoamer to water are 1:5000, 1:700, and 1:1250, respectively;

[0086] S2, dissociate and disperse 10 mm para-aramid short fibers in white water, the weight ratio of fiber to white water is 1:5000, after adding the fibers, mechanical stirring is performed, the stirring speed is set to 1500 rpm, and after stirring for 20000 rpm, a fiber dispersion slurry is prepared;

[0087] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 80 mesh;

[0088] S4. Apply adhesive and wetting agent to the surface of the formed fiber web.

[0089] The preparation method of the adhesive is as follows: adding hexamethylene diisocyanate to an ethyl acetate aqueous solution with a mass concentration of 50% (the amount of hexamethylene diisocyanate added is 2.5% of the weight of the ethyl acetate aqueous solution), placing the solution system in a heating medium at 40° C., adding methyl ethyl ketone oxime dropwise thereto (the weight ratio of methyl ethyl ketone oxime to hexamethylene diisocyanate is 1:0.95), introducing nitrogen and stirring for 1.5 hours to obtain an adhesive.

[0090] The wetting agent is fatty acid glyceride polyoxyethylene ether, and the weight ratio of the wetting agent to the isocyanate in the adhesive is 1:1500. The adhesive and the wetting agent are mixed and then applied to the fiber web prepared in step S3.

[0091] S5. The formed fiber web is dried with hot air at a drying temperature of 120° C. After drying, the prepared fiber web is placed in an oven at 150° C. for heat treatment for 20 minutes to obtain an aromatic polyamide surface felt.

[0092] Example 4

[0093] Preparation of an aromatic polyamide surface felt:

[0094] S1. Evenly disperse Remibond A, polyethylene glycol, and tributyl phosphate defoamer in water to prepare white water. The weight ratios of Remibond A, polyethylene glycol, and tributyl phosphate defoamer to water are 1:8000, 1:600, and 1:1000, respectively.

[0095] S2, dissociate and disperse 12 mm para-aramid short fibers in white water, the weight ratio of fiber to white water is 1:7000, after adding the fibers, mechanical stirring is performed, the stirring speed is set to 2000 rpm, and after stirring for 15000 rpm, a fiber dispersion slurry is prepared;

[0096] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 80 mesh;

[0097] S4. Apply adhesive and wetting agent to the surface of the formed fiber web.

[0098] The preparation method of the adhesive is as follows: dicyclohexylmethane diisocyanate is added to an ethyl acetate aqueous solution with a weight concentration of 50% (the amount of dicyclohexylmethane diisocyanate added is 2.5% of the weight of the ethyl acetate aqueous solution), the solution system is placed in a heating medium at 40°C, and an acetone oxime aqueous solution with a mass fraction of 56% (the weight ratio of the acetone oxime aqueous solution to dicyclohexylmethane diisocyanate is 1:1) is added dropwise thereto, nitrogen is introduced and stirred for 1.5 hours to obtain an adhesive.

[0099] The wetting agent is fatty alcohol polyoxyethylene ether, and the weight ratio of fatty alcohol polyoxyethylene ether to isocyanate in the adhesive is 1:1500. The adhesive and the wetting agent are mixed and then applied to the fiber web prepared in step S3.

[0100] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 170° C. and heat treated for 15 minutes to obtain an aromatic polyamide surface felt.

[0101] Comparative Example 1

[0102] The aromatic polyamide surface felt was prepared by the same method as in Example 1, except that in this comparative example 1, no adhesive and wetting agent were applied to the surface of the formed web, but a conventional wet papermaking method was used. The specific preparation process is as follows:

[0103] S1. Dispersing fatty alcohol polyoxyethylene ether sodium sulfate, polyethylene oxide, and polyether modified defoamer in water to prepare white water, the ratios of the three substances to water are 1:10000, 1:700, and 1:1000 respectively;

[0104] S2, dissociate and disperse 12mm para-aramid short fibers in white water, the ratio of fiber to white water is 1:1000, after adding the fibers, mechanical stirring is performed, the stirring speed is set to 1000 rpm, and after stirring for 30000 rpm, a fiber dispersion slurry is prepared;

[0105] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 70 mesh;

[0106] S4. The formed fiber web is dried by hot air at a drying temperature of 130°C. After drying, the prepared fiber web is placed in a muffle furnace at 260°C for heat treatment for 60 minutes, and then immediately subjected to hot pressing treatment at a pressure of 100 Pa. After cooling to room temperature, an aromatic polyamide surface felt is obtained.

[0107] Comparative Example 2

[0108] The aromatic polyamide surface felt was prepared by the same method as in Example 1, except that the ionic dispersant fatty alcohol polyoxyethylene ether sodium sulfate was not added in step S1 of this comparative example 2. The specific preparation process is as follows:

[0109] S1. Evenly dispersing polyethylene oxide and polyether modified defoamer in water to prepare white water, wherein the weight ratios of polyethylene oxide and polyether modified defoamer to water are 1:700 and 1:1000 respectively;

[0110] S2, dissociate and disperse 12 mm para-aramid short fibers in white water, with the ratio of fiber to white water being 1:1000. After adding the fibers, mechanical stirring is performed, with the stirring speed set at 1000 rpm, and after stirring at 30,000 rpm, a fiber dispersion slurry is prepared;

[0111] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 70 mesh;

[0112] S4. Apply adhesive and wetting agent to the surface of the formed fiber web.

[0113] The preparation method of the adhesive is as follows: 4,4-diphenylmethane diisocyanate is added to an ethyl acetate aqueous solution with a mass concentration of 50% (the amount of 4,4-diphenylmethane diisocyanate added is 2% of the weight of the ethyl acetate aqueous solution), the solution system is placed in a heating medium at 40°C, and an 84% mass concentration sodium bisulfite aqueous solution is added dropwise thereto, wherein the weight ratio of 4,4-diphenylmethane diisocyanate to sodium bisulfite is 1:1, nitrogen is introduced and stirred for 3 hours to obtain an adhesive.

[0114] The wetting agent is sodium dodecylbenzene sulfonate, and the weight ratio of sodium dodecylbenzene sulfonate to isocyanate in the adhesive is 1:2000. The adhesive and the wetting agent are mixed and then applied to the fiber web prepared in step S3.

[0115] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 185° C. and heat treated for 5 minutes to obtain an aromatic polyamide surface felt.

[0116] Comparative Example 3

[0117] The aromatic polyamide surface felt was prepared by the same method as in Example 1, except that no thickening dispersant polyethylene oxide was added in step S1 of this comparative example 3. The specific preparation process is as follows:

[0118] S1. Dispersing sodium fatty alcohol polyoxyethylene ether sulfate and polyether modified defoamer in water to prepare white water, wherein the weight ratios of sodium fatty alcohol polyoxyethylene ether sulfate and polyether modified defoamer to water are 1:10000 and 1:1000 respectively;

[0119] S2. 12 mm para-aramid short fibers were dissociated and dispersed in white water with a ratio of fiber to white water of 1:1000. After adding the fibers, mechanical stirring was performed with the stirring speed set at 1000 rpm. After stirring for 30,000 rpm, a fiber dispersion slurry was prepared. The fibers in the prepared slurry were severely doubly wired and entangled and could not be processed subsequently.

[0120] Comparative Example 4

[0121] The aromatic polyamide surface felt was prepared by the same method as in Example 1, except that the binder was replaced with polyvinyl alcohol in this comparative example 4. The specific preparation process is as follows:

[0122] S1. Dispersing sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer in water to prepare white water, wherein the weight ratios of sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer to water are 1:10000, 1:700, and 1:1000, respectively;

[0123] S2, dissociate and disperse 12 mm para-aramid short fibers in white water, with the ratio of fiber to white water being 1:1000. After adding the fibers, mechanical stirring is performed, with the stirring speed set at 1000 rpm, and after stirring at 30,000 rpm, a fiber dispersion slurry is prepared;

[0124] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 70 mesh;

[0125] S4. Apply adhesive and wetting agent to the surface of the formed fiber web.

[0126] Among them, the adhesive is polyvinyl alcohol, and the wetting agent is sodium dodecylbenzene sulfonate. Polyvinyl alcohol and sodium dodecylbenzene sulfonate are dissolved in an ethyl acetate aqueous solution with a mass concentration of 50% (the solid content is 3%), and then applied to the surface of the formed fiber web, wherein the weight ratio of sodium dodecylbenzene sulfonate to polyvinyl alcohol is 1:2000.

[0127] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 185° C. and heat treated for 5 minutes to obtain an aromatic polyamide surface felt.

[0128] Comparative Example 5

[0129] The aromatic polyamide surface felt was prepared by the same method as in Example 1, except that no wetting agent was added in step S4 of this comparative example 5. The specific preparation process is as follows:

[0130] S1. Dispersing sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer in water to prepare white water, wherein the weight ratios of sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer to water are 1:10000, 1:700, and 1:1000, respectively;

[0131] S2, dissociate and disperse 12 mm para-aramid short fibers in white water, with the ratio of fiber to white water being 1:1000. After adding the fibers, mechanical stirring is performed, with the stirring speed set at 1000 rpm, and after stirring at 30,000 rpm, a fiber dispersion slurry is prepared;

[0132] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 70 mesh;

[0133] S4. Apply adhesive to the surface of the formed fiber web.

[0134] The preparation method of the adhesive is as follows: 4,4-diphenylmethane diisocyanate is added to an ethyl acetate aqueous solution with a mass concentration of 50% (the amount of 4,4-diphenylmethane diisocyanate added is 2% of the weight of the ethyl acetate aqueous solution), the solution system is placed in a heating medium at 40°C, an 84% mass concentration sodium bisulfite aqueous solution is added dropwise thereto, wherein the weight ratio of 4,4-diphenylmethane diisocyanate to the sodium bisulfite aqueous solution is 1:1, nitrogen is introduced and stirred for 3 hours to obtain an adhesive. The adhesive is applied to the fiber web prepared in step S3.

[0135] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 185° C. and heat treated for 5 minutes to obtain an aromatic polyamide surface felt.

[0136] Comparative Example 6

[0137] The aromatic polyamide surface felt was prepared by the same method as in Example 1, except that no adhesive was added in step S4 of this comparative example 6. The specific preparation process is as follows:

[0138] S1. Dispersing sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer in water to prepare white water, wherein the weight ratios of sodium fatty alcohol polyoxyethylene ether sulfate, polyethylene oxide, and polyether modified defoamer to water are 1:10000, 1:700, and 1:1000, respectively;

[0139] S2, dissociate and disperse 12 mm para-aramid short fibers in white water, with the ratio of fiber to white water being 1:1000. After adding the fibers, mechanical stirring is performed, with the stirring speed set at 1000 rpm, and after stirring at 30,000 rpm, a fiber dispersion slurry is prepared;

[0140] S3, using papermaking equipment to shape the prepared fiber dispersion slurry into a fiber web, and the web used is 70 mesh;

[0141] S4. Apply a wetting agent to the surface of the formed web.

[0142] The wetting agent is sodium dodecylbenzene sulfonate, which is dissolved in water and then applied to the fiber web prepared in step S3, wherein the amount of the wetting agent used is the same as that of the wetting agent in Example 1.

[0143] S5. The formed fiber web is dried by hot air at a drying temperature of 130° C. After drying, the prepared fiber web is placed in an oven at 185° C. and heat treated for 5 minutes to obtain an aromatic polyamide surface felt.

[0144] The aromatic polyamide surface felts prepared in the above examples and comparative examples were subjected to performance tests, and the specific test results are shown in Table 1. The test methods involved are as follows.

[0145] (1) Tensile strength and elongation at break:

[0146] The tensile strength and elongation at break were tested using an INSTRON 34TM-30 electronic tensile testing machine, and the test standard referred to GB / T 24218.18-2014 nonwoven fabric test method.

[0147] (2) Air permeability:

[0148] With reference to GB / T 24218.15-2018, the air permeability of the prepared aromatic polyamide surface felt was tested, and the pressure used during the test was 200Pa.

[0149] (3) Thermal decomposition temperature:

[0150] The aromatic polyamide surface felt sample was placed in an oven at 60°C for 3 hours for drying. Then 100 mg of the sample was weighed and placed in a crucible, and the temperature was raised from room temperature to 800°C at a rate of 10°C / min in a nitrogen atmosphere to obtain the thermal decomposition temperature of the sample.

[0151] Table 1 Performance data of aromatic polyamide surface felt in Examples and Comparative Examples

[0152]

[0153] From the data results in Table 1 above, it can be seen that the aromatic polyamide surface felt prepared by the preparation method of the present invention in Examples 1 to 4 has good mechanical properties and thermal stability. Polyisocyanate is introduced as an adhesive and a cross-linking agent in the preparation process, and a surface wetting agent is added to the adhesive formula to enhance the surface bonding force between the adhesive and the aramid fiber. In addition, since isocyanate is very easy to react with other substances containing active hydrogen atoms, a blocking agent is used to block the polyisocyanate so that it can be stably present in the water dispersion system. After the fiber network is formed, it is dried and heat-treated to remove the blocking group of the polyisocyanate, so that it reacts with the amide bond of the aramid to form a urea bond, and a bonding structure is formed by chemical bonds, which improves the overall strength of the surface felt and makes it have excellent processability in subsequent applications. The aramid surface felt prepared according to the preparation method of the present invention has good mechanical properties, dimensional stability, chemical stability, and the gram weight is flexibly adjustable (the gram weight of the final surface felt can be controlled according to the ratio of white water to aramid fiber, which can bring great convenience to the production of products of different models), good air permeability, and excellent resin impregnation. It can be widely used in composite materials and has huge application potential.

[0154] Figure 1 is a scanning electron microscope image of the aromatic polyamide surface felt of Example 1; Figure 1 It can be seen that the adhesive forms connection points between the fibers, which can effectively improve the overall mechanical properties of the product. Figure 2 The thermogravimetric curve of the aromatic polyamide surface felt of Example 1 is shown in FIG. Figure 2 It can be seen that the first thermal weight loss step appears near 380°C. This is because the adhesive is an amide bond between aramid fibers that produces a cross-linked structure, which effectively improves the temperature resistance of the product.

[0155] Comparison of the data of Comparative Example 1 and Example 1 shows that the product prepared by the conventional wet papermaking process in Comparative Example 1 cannot meet the actual use requirements because the adhesive formulation is not used. Due to the molding characteristics of wet papermaking, the surface felt is often thin and has good air permeability. This porous structure is conducive to a good bonding strength with the resin during subsequent processing, and has a wider application prospect in the field of composite materials.

[0156] Comparison of the data of Comparative Example 2 with that of Example 1 shows that: if no ionic dispersant is added in step S1, the dispersion effect of the fiber in the dispersant is greatly weakened, and the fiber slurry is doubly distributed, which results in uneven fiber distribution in the final product, thereby causing a decrease in mechanical properties.

[0157] Comparison of the data of Comparative Example 3 with Example 1 shows that: if no thickening dispersant is added in step S1, the fibers cannot be dispersed in white water, and the fibers are entangled into balls under stirring, and the subsequent preparation process cannot be carried out. Comparison of the experimental results of Comparative Example 2, Comparative Example 3 and Example 1 shows that the use of ionic dispersants and thickening dispersants in white water together is more conducive to obtaining surface felt products with excellent performance, because the compounding of multiple components can regulate the negative charge density of fiber particles and enhance their stability, and due to the directional adsorption of the dispersant to form a hydration film, the fibers are transformed from a hydrophobic state to a hydrophilic state, thereby effectively dispersing the fibers, and the thickening dispersant will reduce the tendency of mutual coagulation or precipitation, and achieve uniform dispersion of aramid fibers, thereby preparing products with excellent performance.

[0158] Comparison of the data of Comparative Example 4 with that of Example 1 shows that if the adhesive is replaced with the more common polyvinyl alcohol, the mechanical properties of the product will decrease. This is because polyvinyl alcohol forms a film after drying to coat the fibers to produce an adhesive effect, and the mechanical properties are mainly provided by polyvinyl alcohol. The use of a blocked aqueous isocyanate adhesive in the present invention is more conducive to obtaining a surface felt product with excellent performance, because the isocyanate group will react with the amide bond in the aramid to form a urea bond under heating treatment, resulting in chemical crosslinking between the fibers. The essence of this is the bonding strength generated by the reaction between the adhesive and the fibers, which is better than the physical coating of the fibers by the adhesive itself for bonding.

[0159] Comparison of the data of Comparative Example 5 with that of Example 1 shows that if no wetting agent is added in step S4, the mechanical properties of the product decrease. This is because the aramid surface is hydrophobic, and without the effect of the wetting agent, it is difficult for the adhesive to be evenly dispersed on the surface of the fiber web and produce sufficient bonding strength.

[0160] Comparison of the data of Comparative Example 6 with that of Example 1 shows that if no binder is added in step S4, effective strength cannot be generated between the fibers after the fiber web is formed, and the overall mechanical properties of the product are poor and not practical.

[0161] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0162] For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, all of which belong to the protection scope of the present invention. The protection scope of the present invention shall be based on the attached claims.

Claims

1. A method for preparing an aromatic polyamide surface felt, characterized in that: The preparation method is: S1. Dispersing the dispersant and defoamer evenly in water to make white water; S2, dissociating and dispersing the aramid fibers in white water to prepare a fiber dispersion slurry; S3, using the fiber dispersion slurry to papermake a fiber web; S4, applying a wetting agent and an adhesive to the surface of the web; S5, drying and heat treating to obtain the aromatic polyamide surface felt; The dispersant includes an ionic dispersant and a thickening dispersant; The ionic dispersant is at least one of fatty alcohol polyoxyethylene ether sodium sulfate, sodium dodecyl diphenyl ether disulfonate, hexadecyl trimethyl ammonium bromide, and Remibond A; The thickening dispersant is at least one of sodium lignin sulfonate, polyethylene oxide, polyvinyl pyrrolidone, and polyethylene glycol; In the white water, the mass ratio of the ionic dispersant to water is 1: (5000-10000); the mass ratio of the thickening dispersant to water is 1: (200-700); The adhesive is a blocked water-based isocyanate adhesive.

2. The method for preparing an aromatic polyamide surface felt according to claim 1, characterized in that: In the white water, the mass ratio of the defoamer to water is 1:(1000-2000); The defoamer is at least one of a polyether modified defoamer, dimethyl silicone oil, a silicon dioxide dispersed defoamer, a high carbon alcohol defoamer, and tributyl phosphate.

3. The method for preparing an aromatic polyamide surface felt according to claim 1, characterized in that: In step S2, the aramid fiber is meta-aramid chopped fiber or para-aramid chopped fiber, and the length of the aramid fiber is 6-12 mm; in the fiber dispersion slurry, the weight ratio of aramid fiber to white water is 1: (1000-20000).

4. The method for preparing an aromatic polyamide surface felt according to claim 1, characterized in that: In step S2, the dissociation dispersion is mechanical stirring dispersion, the rotation speed is 1000-2500 rpm, and the number of stirring revolutions is 5000-30000 revolutions; In step S3, the screen used in the papermaking process is 70-100 mesh.

5. The method for preparing an aromatic polyamide surface felt according to claim 1, characterized in that: The isocyanate in the blocked water-based isocyanate adhesive is selected from at least one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate or hexamethylene diisocyanate; The blocking agent in the blocked water-based isocyanate adhesive is selected from at least one of n-propanol, n-butanol, sodium bisulfite, methyl ethyl ketone oxime, acetone oxime, cyclohexanone oxime and acetophenone oxime; The solid content of the isocyanate in the adhesive is 2-5%.

6. The method for preparing an aromatic polyamide surface felt according to claim 5, characterized in that: The wetting agent is at least one of sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, and fatty acid glyceride polyoxyethylene ether. The mass ratio of the wetting agent to the isocyanate in the adhesive is 1: (1000-2000).

7. The method for preparing an aromatic polyamide surface felt according to claim 1, characterized in that: In step S5, the drying method is hot air drying, and the drying temperature is 110-130°C; In step S5, the heat treatment temperature is 110-185° C., and the heat treatment time is 5-60 min.

8. An aromatic polyamide surface felt, characterized in that: The aromatic polyamide surface felt is prepared according to the preparation method described in any one of claims 1-7.

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