Preparation method of light and thin para-aramid honeycomb paper

Abstract

The invention belongs to the technical field of synthetic fiber paper, and discloses a preparation method of light and thin para-aramid honeycomb paper, which comprises the following steps: preparing meta-aramid fibrid, preparing aramid honeycomb paper pulp, carrying out double-layer inclined wire papermaking molding, preheating, carrying out hot pressing, and annealing. The para-aramid paper is free of pinholes and holes, uniform in dispersion, free of pulp blocks, high in tensile strength and free of cracks through the technologies of wide-film-shaped precipitation raw materials, low-concentration sizing, screening before net feeding and double-net stacking combination, meanwhile, the net stacking design is adopted, the B faces of the paper formed by the bottom net and the face net respectively serve as the two outer surfaces of the final paper, and the paper quality is improved. The upper surface and the lower surface of the finished product para-aramid paper are consistent in character, so that the width and the binding force of core strip glue are kept consistent during honeycomb manufacturing, formed hole grids are regular, the problem of breakage of a paper roll during rolling is prevented, and the yield is improved; the para-aramid paper has the advantages that the temperature of fibrid in the center of the para-aramid paper can reach the melting temperature during hot pressing, and after hot pressing, the fibrid extends and is tiled, so that pinholes are prevented. The annealing process is adopted, so that the stress of the aramid paper can be eliminated after heat treatment, the dimensional stability is kept, and the temperature resistance requirement during subsequent honeycomb manufacturing is met.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic fiber paper, and in particular relates to a method for preparing a light and thin para-aramid honeycomb paper. Background Art

[0002] Aramid honeycomb paper is often used as a sandwich material in aircraft cabin floors, interior decoration parts and some secondary load-bearing components due to its light weight, high specific strength, high specific stiffness, heat insulation, wave transmission and excellent dielectric properties. Aramid fiber is the key raw material for making aramid honeycomb paper. It is made of aramid short fibers and aramid precipitated fibers through wet papermaking and hot rolling technology. The structure and properties of aramid paper will directly affect the performance of the honeycomb. Various aramid paper research and development units have conducted a lot of research on this.

[0003] DuPont patent US 4710432 uses paper-based materials containing meta-aramid fibers for the manufacture of honeycombs; DuPont patent US 5137768 uses para-aramid fibers instead of meta-aramid to manufacture aramid honeycombs with high shear modulus; DuPont patent US20090214818A1 uses 50-85% para-aramid chopped fibers, 10-40% para-aramid pulp, and 5-30% aramid precipitated fibers to manufacture aramid to improve the shear modulus of honeycombs; DuPont patent US 7771811B2 uses high modulus chopped fibers and thermoplastic adhesives to manufacture paper-based materials, the thermoplastic adhesive has a melting temperature of 180-300°C, and contains at least 30% of a film-like component, the thickness of the film-like component is 0.1-5μm, and the length and width are more than 30μm; DuPont patent US 8025949B2 uses para-aramid fiber and aliphatic polyamide fiber to manufacture high-strength aramid honeycomb paper, with a strength of more than 60lb / in, and a high para-aramid fiber content of 80%-98%; DuPont patent US7815993B2 uses high modulus short-cut fiber and flame-retardant thermoplastic adhesive to manufacture aramid paper, the melting temperature of the thermoplastic adhesive is 120-350℃, and the limiting oxygen index is above 26; DuPont patent US 2016 / 0097162A1 discloses a para-aramid paper capable of improving the flat compression strength of honeycombs, wherein the content of para-aramid chopped fibers is 30-70%, the content of aramid fibrils is 30-70%, the air permeability is above 200 seconds / 100 milliliters, and a pressure-resistant reinforcement layer is coated on the outer layer of the honeycomb paper, the total weight of the reinforcement layer is about 5% of the gram weight of the aramid paper, and the chopped fibers can be other high-strength fibers, and the fibrils can be one of para-aramid and meta-aramid fibers or a mixture thereof; Japanese SHOWA Aviation Industry Co., Ltd. patent US 6544622B1 uses para-aramid chopped fibers, para-aramid pulp and meta-aramid fibrillation binder to manufacture honeycomb paper to improve the poor uniformity of papermaking using only para-aramid fiber; Chinese patent CN 101343845B uses para-aramid fiber, meta-aramid fibrid and polyester fiber to manufacture aramid paper, and the obtained honeycomb plane has very high compression strength and shear strength.

[0004] It can be seen from the above patents that honeycombs made of para-aramid paper have higher flat compression strength and shear strength than meta-aramid paper honeycombs. According to research data from the American MCGill Company, the weight reduction of the N636 para-aramid paper honeycomb compared to the T412 meta-aramid paper honeycomb can reach 30%. Therefore, the use of para-aramid paper honeycombs in the aviation manufacturing industry will become a future development trend.

[0005] The conventional lightest and thinnest specifications of existing para-aramid paper are a surface density of 30g and a thickness of 40 microns. If the surface density and thickness of the para-aramid paper are further reduced, especially when its surface density is lower than 21g / ㎡ and its thickness is lower than 0.028mm, pinholes and holes are likely to appear on the paper surface, and glue will seep through when making honeycombs, and the cells cannot be pulled out, resulting in breakage when the paper roll is rolled up, reducing the yield rate. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a light and thin para-aramid honeycomb paper to solve the problems that the existing aramid honeycomb paper is prone to pinholes and holes on the paper surface, glue seepage during honeycomb production, and cells cannot be pulled out, resulting in breakage when the paper roll is rolled up.

[0007] In order to achieve the above object, the present invention provides the following technical solution: a method for preparing a light and thin para-aramid honeycomb paper, comprising the following steps: Sp1: Preparation of meta-aramid fiber precipitate, injecting a resin solution of 15% meta-aramid resin, 77.5% dimethylacetamide, 2% water, and 6.5% calcium chloride into a horizontal precipitator for precipitation, the precipitate ratio is 40% dimethylacetamide, 58% water, 2% calcium chloride, the precipitate fiber is cooled and solidified for 8 hours, and then washed with a pulp washer, and the obtained precipitate fiber has a length of 0.8 mm and a width of 75 microns; Sp2: Prepare aramid honeycomb paper pulp, take 50-70 parts by weight of para-aramid chopped fibers, and then take 30-50 parts by weight of meta-aramid fibrids prepared in Sp1 as standby, mix the para-aramid chopped fibers and meta-aramid fibrids in a proportion in a batching tank to obtain a slurry with a concentration of 0.03%, and store them in a surface mesh slurry tank and a bottom mesh slurry tank respectively; Sp3: Double-layer inclined screen papermaking and forming. The low-concentration pulp obtained by Sp2 is flushed by the surface screen flushing pump, and then sieved by the pressure screen with a screen hole of 0.3mm. Finally, the pulp is distributed through the central pulp distributor. The pulp concentration is 0.3 parts per ten thousand. The pulp then enters the inclined screen headbox through the leveling element, so that the pulp is evenly distributed on the forming screen. The excess pulp overflows into the white water pool. When the pulp runs along the inclined screen forming screen, the water is filtered out from the pulp with the help of the dehydration pressure difference to form Wet paper sheets, the filtered white water enters the vacuum white water tank for pulping, the bottom screen process is the same as the surface screen, and the wet paper sheets with the same surface density are formed. Finally, the two layers of wet paper sheets are overlapped, dehydrated by two pressings on the paper machine, and then dried by the drying cylinder to obtain the rough aramid paper, so that the properties of the upper and lower surfaces of the finished aramid paper are consistent, so as to ensure that the width and bonding force of the core strip glue are consistent when making the honeycomb, and the formed pores are regular, so as to prevent the problem of breakage when the paper roll is rolled up, and improve the yield rate; Sp4: Preheating: preheating the raw paper by electromagnetic preheating roller and infrared preheating box in turn, so that the precipitated fibers in the center of the para-aramid paper can reach the melting temperature during hot pressing. After hot pressing, the precipitated fibers are spread flat to prevent the generation of pinholes. Sp5: hot pressing, introducing the preheated rough paper into a three-roll hot press for hot pressing; Sp6: Annealing: anneal the hot pressed aramid paper with an annealing roller.

[0008] Preferably, the annealing roller temperature in the Sp5 is set to 60°C, and the annealing time is set to 2-4s. The length and fineness of the para-aramid chopped fibers in the Sp1 are set to 6mm and 1.5D respectively, and the length and width of the aramid fibrids are set to 0.8mm and 75µm respectively.

[0009] Preferably, the aramid chopped fibers in the Sp2 are dispersed and decomposed in water to form an aramid chopped fiber slurry with a mass concentration of 0.3-0.8%, the aramid fibrils are dispersed and decomposed in water, and the aramid fibrils are disc-grinded until the beating degree is 50-65SR to form an aramid fibril slurry with a mass concentration of 1-2%.

[0010] Preferably, the motor speed of the horizontal precipitator in Sp1 is set to 3000 rpm, the pulp washer is a horizontal pulp washer, and the cleaning water used by the pulp washer is set to pure water.

[0011] Preferably, the preheating temperature of the preheating box in Sp4 is set to 260-290°C.

[0012] Preferably, the hot pressing temperature and line pressure of the three-roll hot press in the Sp5 are set to 290-310° C. and 180-220 N / m, respectively.

[0013] The beneficial effects of the present invention are as follows: The invention adopts wide film-shaped precipitation raw materials, low-concentration sizing, screening before being put on the net, and double-stacked net superposition combination technology to make the para-aramid paper free of pinholes and holes, and evenly dispersed without pulp blocks, with high tensile strength and without cracks. At the same time, the stacked net design is adopted so that the B surface of the paper formed by the bottom net and the surface net respectively becomes the two outer surfaces of the final paper, so that the properties of the upper and lower surfaces of the finished para-aramid paper are consistent, so that when making honeycombs, the width and bonding force of the core strip glue are consistent, the formed pores are regular, the problem of paper roll breaking when rolling is prevented, and the yield rate is improved. Before hot pressing, electromagnetic rollers and infrared preheating technology are adopted so that the precipitation fibers in the center of the para-aramid paper can reach the melting temperature before hot pressing. After hot pressing, the precipitation is extended and flattened to prevent the generation of pinholes. The annealing process is adopted so that the aramid paper can eliminate stress after heat treatment, maintain dimensional stability, and meet the temperature resistance requirements of subsequent honeycomb production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a flow chart of the present invention; Figure 2 It is a schematic diagram of the bottom net and the surface net AB of the present invention; Figure 3 It is a schematic diagram of the superposition of the bottom mesh and the surface mesh AB of the present invention; Figure 4 It is a schematic diagram of preheating, hot pressing and annealing of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] Example: like Figures 1 to 4 The embodiment of the present invention provides a method for preparing a light and thin para-aramid honeycomb paper, comprising the following steps: Sp1: preparing meta-aramid fiber precipitate, injecting a resin solution containing 15% meta-aramid resin, 77.5% dimethylacetamide, 2% water and 6.5% calcium chloride into a horizontal precipitator for precipitation, the motor speed of the horizontal precipitator is set to 3000 rpm, the precipitate ratio is 40% dimethylacetamide, 58% water and 2% calcium chloride, the precipitate fiber is cooled and solidified for 8 hours, and then washed with a pulp washer, the pulp washer is a horizontal pulp washer, and the washing water used by the pulp washer is set to pure water, and the obtained precipitate fiber has a length of 0.8 mm and a width of 75 microns; Sp2: preparing aramid honeycomb paper pulp, taking 50-70 parts by weight of para-aramid chopped fibers, the length and fineness of the para-aramid chopped fibers are set to 6 mm and 1.5D respectively, the aramid chopped fibers are dispersed and decomposed in water to prepare aramid chopped fiber slurry with a mass concentration of 0.3-0.8%, and then taking 30-50 parts by weight of meta-aramid fibrids prepared by Sp1 as standby, the length and width of the aramid fibrids are set to 0.8 mm and 75 µm respectively, the aramid fibrids are dispersed and decomposed in water, and the aramid fibrids are disc-milled until the beating degree is 50-65SR to prepare aramid fibrid slurry with a mass concentration of 1-2%, the para-aramid chopped fibers and the meta-aramid fibrids are uniformly mixed in a proportion in a batching tank to obtain a slurry with a concentration of 0.03%, and stored in a surface mesh pulp tank and a bottom mesh pulp tank respectively; Sp3: Double-layer inclined screen forming, the low-concentration pulp obtained by Sp2 is flushed by the surface screen flushing pump, and then screened by a pressure screen with a screen hole of 0.3mm, and finally distributed by the central pulp distributor, the slurry concentration is 0.3 parts per ten thousand, and the slurry then enters the inclined screen headbox through the leveling element, so that the slurry is evenly distributed on the forming net, and the excess slurry overflows into the white water pool. When the slurry runs along the inclined screen forming net, with the help of the dehydration pressure difference, water is filtered out from the pulp to form a wet paper sheet, and the filtered white water enters the vacuum white water tank for flushing. The bottom screen process is the same as the surface screen, and a wet paper sheet with the same surface density is also formed. Finally, Two layers of wet paper sheets are overlapped, dehydrated by two pressings in a paper machine, and then dried by a drying cylinder to obtain rough aramid paper. In the double-layer screen forming process, when the single-layer inclined screen is used for paper forming, one side of the pulp, namely the B side, contacts the forming screen and is at the bottom, while the other side, namely the A side, does not contact the forming screen and floats on the upper part of the pulp, thus forming different surface states; and the side where the pulp contacts the screen surface, namely the B side, has very small mesh holes and a smooth screen surface, so that this side is relatively enriched with precipitated fibers; and the other side, namely the A side, is rough and enriched with more short-cut fibers due to the scouring of the pulp flow and the vibration of the inclined screen during operation. Double-layer mesh papermaking is adopted. The rough surface A of the paper formed by the bottom mesh and the surface mesh is pasted together, and the two layers of B face outward to form a layer of composite paper. Since the humidity of the paper is very high at this place, after two pressings, it becomes a tightly combined layer of paper. The stacked mesh design makes the B surface of the paper formed by the bottom mesh and the surface mesh become the two outer surfaces of the final paper, so that the properties of the upper and lower surfaces of the finished aramid paper are consistent. In this way, when making honeycombs, the width and bonding force of the core strip glue are consistent, and the formed pores are regular; Sp4: Preheating: preheat the rough paper by electromagnetic preheating roller and infrared preheating box in turn, and the preheating temperature of the preheating box is set to 260-290℃; Sp5: hot pressing, introducing the preheated embryo paper into a three-roll hot press for hot pressing, the hot pressing temperature and line pressure of the three-roll hot press are set to 290-310℃ and 180-220N / m respectively; Sp6: Annealing: annealing the hot pressed aramid paper with an annealing roller, the annealing roller temperature is set to 60° C., and the annealing time is set to 2-4 seconds.

[0017] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0018] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a light and thin para-aramid honeycomb paper, characterized in that: The following steps are involved: Sp1: preparing meta-aramid fiber precipitate, injecting a resin solution of meta-aramid resin, dimethylacetamide, water and calcium chloride into a horizontal precipitator for precipitation, wherein the precipitate is a mixed solution of dimethylacetamide, water and calcium chloride, cooling and solidifying the precipitate, and then washing it with a pulp washer; Sp2: Prepare aramid honeycomb paper pulp, take para-aramid chopped fibers, and then take meta-aramid fibrids prepared in Sp1 as standby, mix the para-aramid chopped fibers and meta-aramid fibrids in proportion in a batching tank to obtain a mixed slurry, and store them in a surface mesh slurry tank and a bottom mesh slurry tank respectively; Sp3: Double-layer inclined screen papermaking and forming. The low-concentration pulp obtained by Sp2 is flushed by the surface screen flushing pump, then screened by the pressure screen, and finally distributed by the central pulp distributor. The pulp concentration is 0.3 parts per ten thousand. The pulp then enters the inclined screen headbox through the leveling element, so that the pulp is evenly distributed on the forming net. The excess pulp overflows into the white water pool. When the pulp runs along the inclined screen forming net, with the help of the dehydration pressure difference, water is filtered out from the pulp to form wet paper sheets. The filtered white water enters the vacuum white water tank for flushing. The bottom screen process is the same as the surface screen, and wet paper sheets with the same surface density are also formed. Finally, the two layers of wet paper sheets are overlapped, dehydrated by two presses on the paper machine, and then dried by the drying cylinder to obtain the rough aramid paper. Sp4: Preheating, preheating the rough paper through electromagnetic preheating roller and infrared preheating box in turn; Sp5: hot pressing, introducing the preheated rough paper into a three-roll hot press for hot pressing; Sp6: Annealing: anneal the hot pressed aramid paper with an annealing roller.

2. The method for preparing a light and thin para-aramid honeycomb paper according to claim 1, characterized in that: In the Sp5, the annealing roller temperature is set to 60° C., and the annealing time is set to 2-4 s.

3. The method for preparing a light and thin para-aramid honeycomb paper according to claim 1, characterized in that: The aramid chopped fibers in the Sp2 are dispersed and decomposed in water to prepare aramid chopped fiber slurry with a mass concentration of 0.3-0.8%, and the aramid fibrils are dispersed and decomposed in water, and the aramid fibrils are disc-grinded until the beating degree is 50-65SR to prepare aramid fibril slurry with a mass concentration of 1-2%.

4. The method for preparing a light and thin para-aramid honeycomb paper according to claim 1, characterized in that: The motor speed of the horizontal precipitator in the Sp1 is set to 3000 rpm, the pulp washer is a horizontal pulp washer, and the cleaning water used by the pulp washer is set to pure water.

5. The method for preparing a light and thin para-aramid honeycomb paper according to claim 1, characterized in that: The preheating temperature of the preheating box in the Sp4 is set to 260-290°C.

6. The method for preparing a light and thin para-aramid honeycomb paper according to claim 1, characterized in that: The hot pressing temperature and line pressure of the three-roll hot press in the Sp5 are set to 290-310° C. and 180-220 N / m, respectively.

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