A high-strength polypropylene filament and its preparation process

Abstract

The invention discloses a high-strength polypropylene filament and a preparation process thereof, belonging to the technical field of polypropylene filament preparation, comprising: using nano-scale calcium carbonate and wollastonite powder as reinforcement materials, taking polypropylene slices as a base material and mixing them with the reinforcement material in proportion, adding a nucleating agent to mix them evenly, heating them to a molten state, spinning them, and obtaining ultrafine fibers; twisting the ultrafine fibers into high-strength polypropylene filaments by using eddy current airflow; taking a plurality of sizing agents to alternately perform sizing treatment on the polypropylene filaments, gradually establishing a uniform sizing film, and performing corona treatment on the sizing positions; performing heat setting treatment on the sizing-treated polypropylene filaments; the invention uses the sizing agent in combination with the corona treatment to alternately coat the polypropylene filaments, reduces the permeability of the sizing agent to the polypropylene filaments, improves the adhesion performance of the sizing film, significantly reduces the strength loss of the sizing agent to the polypropylene filaments, and simultaneously prepares high-strength polypropylene filaments with excellent mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene filament preparation, and in particular to a high-strength polypropylene filament and a preparation process thereof. Background Art

[0002] Polypropylene filament, as an important form of polypropylene (PP) fiber, is a continuous polypropylene filament product made by processing polypropylene raw materials through a specific spinning process. This fiber has been widely used in many industrial fields such as textiles, construction, medical treatment, and automobiles due to its excellent wear resistance, chemical corrosion resistance, good insulation, and relatively low cost. However, with the advancement of science and technology and changes in market demand, the performance requirements for polypropylene filaments are becoming higher and higher, especially the requirements for their strength are becoming increasingly stringent, so the preparation technology of high-strength polypropylene filaments is particularly important.

[0003] In the preparation process of high-strength polypropylene filaments, sizing treatment is a key link. The main purpose of sizing is to form a uniform sizing film on the fiber surface to improve the fiber's wear resistance, antistatic properties and weavability. However, during the sizing process, the penetration of the sizing liquid may have an adverse effect on the strength of the polypropylene filament.

[0004] Therefore, it is necessary to design a high-strength polypropylene filament and a preparation process thereof to solve the above problems. Summary of the invention

[0005] The invention overcomes the deficiencies of the prior art and provides a high-strength polypropylene filament and a preparation process thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a preparation process of high-strength polypropylene filament, comprising the following steps:

[0007] Step S1, using nano-scale calcium carbonate and wollastonite powder as reinforcement materials, and mixing polypropylene slices as base materials and the reinforcement materials in a uniform proportion;

[0008] Step S2, adding a nucleating agent to the mixed material in step S1, mixing evenly, heating to a molten state, and spinning to obtain ultrafine fibers;

[0009] Step S3, using vortex airflow to twist the ultrafine fibers into high-strength polypropylene filaments, and adjusting the twisting speed and tension to obtain a yarn structure;

[0010] Step S4, using a plurality of sizing agents to alternately perform sizing treatment on the polypropylene filaments, gradually establishing a uniform sizing film, and performing corona treatment on the sizing position before each sizing;

[0011] Step S5, performing heat setting treatment on the sizing-treated polypropylene filaments.

[0012] In a preferred embodiment of the present invention, in step S1, the particle size of calcium carbonate is 50-80 nm, the particle size of wollastonite powder is 30-60 nm, and the mass ratio between calcium carbonate and wollastonite powder is 1-2:0.6-1;

[0013] The molecular weight of the polypropylene chips is 400,000-800,000 polypropylene, and the mass ratio between the reinforcement material and the base material is 1:4-8.

[0014] In a preferred embodiment of the present invention, in step S2, the nucleating agent is talcum powder, and the mass ratio between the reinforcement material and the nucleating agent is 1:0.2-0.4;

[0015] The mixed materials in step S1 are added with a nucleating agent and mixed evenly. Specifically, the mixed materials in step S1 and the nucleating agent are stirred at a speed of 1000-1200 r / min for 5-10 min, and acetone is added to reduce the surface tension of the nucleating agent particles.

[0016] In a preferred embodiment of the present invention, in step S2, the following sub-steps are included:

[0017] Step S21, mixing the nucleating agent, the base material and the reinforcement material uniformly, and heating to 190-230° C. to a molten state;

[0018] Step S22, controlling the spinning temperature at 200-240° C. so that the material can be stably transformed from a molten state into polypropylene primary fibers;

[0019] Step S23, subjecting the polypropylene primary fiber to a multi-stage stretching treatment, wherein the stretching multiple in the first stage is 4-6 times, and the stretching multiple in the second stage is 8-10 times, to finally obtain ultrafine fibers.

[0020] In a preferred embodiment of the present invention, in step S3, high-strength polypropylene filaments are twisted, specifically, a plurality of ultrafine fibers are twisted in a clockwise direction at an air flow speed of 25-40 m / s and an air flow pressure of 0.5-1.5 MPa to obtain polypropylene filaments.

[0021] In a preferred embodiment of the present invention, in step S4, the plurality of sizing agents include: 1-3% pure epoxy resin, 2-4% epoxy resin mixed with 0.5-1.5% polyester, and 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane.

[0022] In a preferred embodiment of the present invention, in step S4, the corona treatment is specifically performed at a voltage range of 6-12 kV, and the processing speed of the polypropylene filament is controlled to be 5-20 m / min.

[0023] In a preferred embodiment of the present invention, step S4 includes the following sub-steps:

[0024] Step S41, preparing 1-3% pure epoxy resin, 2-4% epoxy resin mixed with 0.5-1.5% polyester, 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane sizing agent, and adding silica nanoparticles to the sizing agent, and the ratio between each sizing agent and silica nanoparticles is 1:0.3-0.6;

[0025] Step S42, performing corona treatment on the polypropylene filaments, and immersing the corona treated polypropylene filaments in 1-3% concentration of pure epoxy resin for 2-5 minutes;

[0026] Step S43, drying the impregnated polypropylene filaments, specifically at a temperature of 50-80° C. for 15-20 minutes, to form a one-third size film on the surface of the polypropylene filaments;

[0027] Step S44, repeating steps S42 and S43 in sequence on the polypropylene filaments after forming one-third of the sizing film, so as to form two-thirds of the sizing film on the surface of the polypropylene filaments.

[0028] In a preferred embodiment of the present invention, in step S4, the thickness of the slurry film is 1.5-3 µm.

[0029] A high-strength polypropylene filament is prepared by the preparation process of the high-strength polypropylene filament.

[0030] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0031] The present invention provides a high-strength polypropylene filament and a preparation process thereof. The polypropylene filament is alternately coated with a sizing agent in combination with a corona treatment, thereby reducing the permeability of the sizing agent to the polypropylene filament and improving the adhesion performance of the sizing film. The strength loss of the polypropylene filament caused by the sizing agent can be significantly reduced, and high-strength polypropylene filament with excellent mechanical properties can be prepared.

[0032] The present invention can form a large number of bonding points on the surface of the film by adding silicon dioxide nanoparticles, thereby increasing the contact area and bonding force between the films. In combination with corona treatment, the nanoparticles can more easily penetrate into the micropores and defects on the surface of the film to form a tighter bonding layer, which not only improves the adhesion of the film, but also enhances the overall strength of the film.

[0033] The present invention twists ultrafine fibers into high-strength polypropylene filaments by utilizing eddy airflow. The eddy airflow tightly entangles the fibers through the uniform airflow action to form a more solid yarn structure, which can better reduce the gaps and defects between the fibers, thereby significantly improving the tensile strength and fracture resistance of the polypropylene filaments. At the same time, the uniform airflow causes each fiber to be subjected to the same force, which helps to produce polypropylene filaments with uniform structure, thereby ensuring the consistency and reliability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 This is a process flow chart of preparing a high-strength polypropylene filament of the present invention;

[0036] Figure 2 It is a bar graph of the strength loss of the polypropylene filament of the present invention. DETAILED DESCRIPTION

[0037] 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.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0039] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, "multiple" means two or more.

[0040] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0041] like Figure 1 As shown, a preparation process of high-strength polypropylene filament comprises the following steps:

[0042] Step S1, using nano-scale calcium carbonate and wollastonite powder as reinforcement materials, and mixing polypropylene slices as base materials and the reinforcement materials in a uniform proportion;

[0043] The particle size of calcium carbonate is 50-80nm, the particle size of wollastonite powder is 30-60nm, and the mass ratio between calcium carbonate and wollastonite powder is 1-2:0.6-1;

[0044] The molecular weight of the polypropylene chips is 400,000-800,000 polypropylene, and the mass ratio between the reinforcement material and the base material is 1:4-8;

[0045] Calcium carbonate and wollastonite powder can form a uniform reinforcement network in polypropylene to improve the mechanical properties of the fiber.

[0046] Step S2, adding a nucleating agent to the mixed material in step S1, mixing evenly, heating to a molten state, and spinning to obtain ultrafine fibers;

[0047] In step S2, the following sub-steps are included:

[0048] Step S21, mixing the nucleating agent, the base material and the reinforcement material uniformly, and heating to 190-230° C. to a molten state;

[0049] Step S22, controlling the spinning temperature at 200-240° C. so that the material can be stably transformed from a molten state into polypropylene primary fibers;

[0050] Step S23, subjecting the polypropylene primary fiber to a multi-stage stretching treatment, wherein the stretching multiple in the first stage is 4-6 times, and the stretching multiple in the second stage is 8-10 times, to finally obtain ultrafine fibers.

[0051] Step S3, using vortex airflow to twist the ultrafine fibers into high-strength polypropylene filaments, and adjusting the twisting speed and tension to obtain a yarn structure;

[0052] Twisting into high-strength polypropylene filaments, specifically, twisting a plurality of ultrafine fibers in a clockwise direction at an air flow speed of 25-40 m / s, maintaining an air flow pressure of 0.5-1.5 MPa, and twisting times of 1000-2000 times / minute to obtain polypropylene filaments;

[0053] The vortex airflow makes the fibers tightly entangled through the uniform airflow to form a stronger yarn structure, which can better reduce the gaps and defects between the fibers, thereby significantly improving the tensile strength and fracture resistance of the polypropylene filament. At the same time, the uniform airflow makes each fiber subject to the same force, which helps to produce polypropylene filaments with uniform structure and ensure the consistency and reliability of the product.

[0054] Step S4, using a plurality of sizing agents to alternately perform sizing treatment on the polypropylene filaments, gradually establishing a uniform sizing film with a sizing film thickness of 1.5-3µm, and performing corona treatment on the sizing position before each sizing;

[0055] The various sizing agents include: 1-3% pure epoxy resin, 2-4% epoxy resin mixed with 0.5-1.5% polyester, and 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane.

[0056] The corona treatment is specifically carried out at a voltage range of 6-12 kV and a processing speed of the polypropylene filament is controlled to be 5-20 m / min.

[0057] In the step S4, the following sub-steps are included:

[0058] Step S41, preparing 1-3% pure epoxy resin, 2-4% epoxy resin mixed with 0.5-1.5% polyester, 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane sizing agent, and adding silica nanoparticles to the sizing agent, and the ratio between each sizing agent and silica nanoparticles is 1:0.3-0.6;

[0059] Step S42, performing corona treatment on the polypropylene filaments, and immersing the corona treated polypropylene filaments in 1-3% concentration of pure epoxy resin for 2-5 minutes;

[0060] Step S43, drying the impregnated polypropylene filaments, specifically at a temperature of 50-80° C. for 15-20 minutes, to form a one-third size film on the surface of the polypropylene filaments;

[0061] Step S44, repeating steps S42 and S43 in sequence on the polypropylene filaments after forming one-third of the sizing film, so as to form two-thirds of the sizing film on the surface of the polypropylene filaments.

[0062] By combining corona treatment with sizing process, the polypropylene filaments are alternately coated with sizing agents, which reduces the permeability of the sizing agent to the polypropylene filaments and improves the adhesion of the sizing film. The strength loss of the polypropylene filaments caused by the sizing agent can be significantly reduced, and high-strength polypropylene filaments with excellent mechanical properties can be prepared.

[0063] Adding silica nanoparticles to the sizing agent can form a large number of bonding points on the surface of the film, thereby increasing the contact area and bonding force between the films. Combined with corona treatment, the nanoparticles can more easily penetrate into the micropores and defects on the surface of the film to form a tighter bonding layer, which not only improves the adhesion of the film, but also enhances the overall strength of the film.

[0064] Step S5, performing heat setting treatment on the sizing polypropylene filaments, the main purpose of which is to set the molecular chains in the polypropylene filaments by heating, thereby fixing their physical structure and properties; the heat process will change the crystallinity and orientation of the polypropylene molecular chains, and by controlling the temperature and time, the internal stress in the fiber can be eliminated, the size and shape of the fiber can be stabilized, and the strength and durability of the fiber can be enhanced;

[0065] Specifically, the sizing-treated polypropylene filaments are placed in a heat-setting furnace and heated at 150-200°C for 5-10 minutes, thereby effectively fixing the size and shape of the fibers and preventing shrinkage or deformation caused by temperature changes during subsequent use.

[0066] By corona treating the surface of polypropylene filaments, the polarity and activity of the surface of polypropylene filaments are improved, more reaction points are provided for the functional groups in the sizing agent, and the formation of more chemical bonds is promoted. The epoxy groups in the epoxy resin, the carboxyl groups or hydroxyl groups in the polyester, and the carbamate groups in the polyurethane react chemically with the active groups on the surface of the polypropylene filaments to form strong chemical bonds of epoxy groups, ester bonds, and carbamate bonds, which not only improve the adhesion between the sizing film and the polypropylene filaments, but also enhance the structural stability of the sizing film, thereby improving the overall mechanical properties of the polypropylene filaments and the sizing film; and after the corona treatment, the surface of the polypropylene filaments becomes rougher and more polar, so that the nanoparticles can be better embedded in the micropores and defects on the surface of the polypropylene filaments to form a tighter bonding layer;

[0067] In the process of alternating sizing combined with corona treatment, the formed sizing film is subjected to corona treatment, and a large number of free radicals and polar groups, such as hydroxyl and carboxyl groups, are generated on the surface of the sizing film, which react with the functional groups in the adjacent sizing films and with the polar groups such as hydroxyl groups on the surface of the silica nanoparticles, thereby promoting the formation of a three-dimensional network structure, thereby improving the bonding force between the sizing films. At the same time, the high specific surface area of ​​the nanoparticles enables more epoxy resin molecules to be adsorbed on their surface, forming a physical entanglement and interlocking structure, further enhancing the bonding force and improving the overall tensile and tear resistance.

[0068] And because silica nanoparticles play a filling role in the sizing agent, they can fill the tiny pores and defects in the sizing film formed by the sizing agent. The filling effect makes the sizing film denser, thereby reducing the permeability of the sizing film. The damage to the polypropylene filament during handling and use is reduced, effectively reducing the contact between the fiber and the external environment and reducing the possibility of strength loss.

[0069] In the present invention, in step S2, the nucleating agent is talcum powder, and the mass ratio between the reinforcement material and the nucleating agent is 1:0.2-0.4;

[0070] The mixed material in step S1 is added with a nucleating agent and mixed evenly. Specifically, the mixed material in step S1 and the nucleating agent are stirred at a speed of 1000-1200 r / min for 5-10 min, and acetone is added to reduce the surface tension of the nucleating agent particles;

[0071] In order to ensure that the nucleating agent promotes the formation and improvement of the fiber crystal structure, it is necessary to detect the mixture after the mixed material in step S1 is added with the nucleating agent and the uniformity of the mixture is detected. When the difference in the nucleating agent content between any two test points in the mixture does not exceed ±5%, it is considered to be uniformly mixed;

[0072] If the mixing is not uniform, repeat the above stirring process until the conditions are met;

[0073] Randomly select no less than 5 test points from the mixture; measure the content of the nucleating agent at each test point; calculate the difference in the content of the nucleating agent between any two test points; and determine whether the difference satisfies the condition of not exceeding ±5% by weight;

[0074] Preferably, for any two test points A and B, the difference in nucleating agent content ΔW = WA - WB is calculated; if |ΔW|≤±5%, it is considered that the difference in nucleating agent content between the two test points is within the allowable range; if |ΔW|>±5%, it is considered that the difference in nucleating agent content between the two test points exceeds the allowable range; repeat this process until all test point pairs meet the conditions.

[0075] For the test point pairs that are beyond the allowable range, record their position information; re-stir the mixture and select the test points for measurement again; repeatedly calculate the difference ΔW and determine whether it meets the condition of |ΔW|≤±5%; until the difference in nucleating agent content of all test point pairs is within the allowable range.

[0076] Experimental example:

[0077] 1. Prepare polypropylene filaments with different densities and determine the influence of various parameters on density.

[0078] 1. Detection method

[0079] Density test: Take a polypropylene filament sample, use a precision balance to measure the mass m of the sample, immerse the polypropylene filament sample completely in water, measure the displacement, the volume is equal to the displacement, use the formula: density = mass (m) / volume (V) to get the density.

[0080] (II) Implementation Examples

[0081] Example 1: Calcium carbonate of 50-80 nm and wollastonite powder with a particle size of 30-60 nm are taken as reinforcement materials, the mass ratio between calcium carbonate and wollastonite powder is 1:0.7, polypropylene with a molecular weight of 400,000-800,000 is taken as the base material, the mass ratio between the reinforcement material and the base material is 1:5, and the nucleating agent is talcum powder, and the mass ratio between the reinforcement material and the nucleating agent is 5:1;

[0082] Example 1: Wollastonite powder, calcium carbonate, polypropylene chips and talcum powder were stirred and mixed at a speed of 1000 r / min for 8 minutes, and acetone was added and heated to 230°C to be in a molten state. The spinning temperature was controlled at 240°C to generate polypropylene primary fibers. The polypropylene primary fibers were subjected to multi-stage stretching treatment, wherein the first stage stretching multiple was 4 times, and the second stage stretching multiple was 8 times, and finally ultrafine fibers were obtained;

[0083] A number of ultrafine fibers were twisted in a clockwise direction, passed through an air flow velocity of 25 m / s, the air flow pressure was maintained at 0.5 MPa, and the twisting frequency was 1000 times / min to obtain polypropylene filaments, and the density of the obtained polypropylene filaments was tested.

[0084] Example 2: Wollastonite powder, calcium carbonate, polypropylene chips and talcum powder were stirred and mixed at a speed of 1000 r / min for 8 minutes, and acetone was added and heated to 230°C to be in a molten state. The spinning temperature was controlled at 240°C to generate polypropylene primary fibers. The polypropylene primary fibers were subjected to multi-stage stretching treatment, wherein the first stage stretching multiple was 4 times, and the second stage stretching multiple was 8 times, and finally ultrafine fibers were obtained;

[0085] A number of ultrafine fibers were twisted in a clockwise direction, passed through an air flow velocity of 30 m / s, the air flow pressure was maintained at 1 MPa, and the twisting frequency was 1500 times / min to obtain polypropylene filaments, and the density of the obtained polypropylene filaments was tested.

[0086] Example 3: Wollastonite powder, calcium carbonate, polypropylene chips and talcum powder were stirred and mixed at a speed of 1000 r / min for 8 minutes, and acetone was added and heated to 230°C to be in a molten state. The spinning temperature was controlled at 240°C to generate polypropylene primary fibers. The polypropylene primary fibers were subjected to multi-stage stretching treatment, wherein the first stage stretching multiple was 4 times, and the second stage stretching multiple was 8 times, and finally ultrafine fibers were obtained;

[0087] A number of ultrafine fibers were twisted in a clockwise direction, passed through an air flow velocity of 35 m / s, the air flow pressure was maintained at 1.5 MPa, and the twisting frequency was 2000 times / min to obtain polypropylene filaments, and the density of the obtained polypropylene filaments was tested.

[0088] 2. Different sizing treatments are performed on embodiments with different densities

[0089] 1. Detection method:

[0090] 1. Tensile strength test: Use an electronic tensile testing machine to clamp the polypropylene filament sample in the fixture of the tensile testing machine, stretch it at the standard test speed, and record the maximum load at break;

[0091] 2. Elongation at break test: The electronic tensile testing machine is equipped with a displacement measurement function, which records the elongation of the sample during the stretching process and calculates the elongation at break;

[0092] 3. Wear resistance test: Place the polypropylene filament sample in a Taber wear tester for wear test, and measure the mass loss or surface change before and after wear;

[0093] 4. Strength loss test: The tensile strength of polypropylene filaments was tested using Shimadzu AXG-10 universal material testing machine in accordance with ISO 10618:2004 (E) standard and recorded as S0. Then, the FWA 1 / 5 / 1 filament winding machine produced by EHA Composite Machinery GmbH in Germany was used to perform spiral winding at a line speed of 20 m / min and tensions of 20, 30 and 40 N, respectively. The wound polypropylene filaments were carefully removed from the mandrel, and their strength was measured and recorded as S1. The strength loss q of the polypropylene filaments due to fiber damage during the winding process was calculated according to the formula: q=(S0-S1) / S0*100%;

[0094] 5. Adhesion test: Use the pull-out test to clamp the polypropylene filament in the fixture, gradually apply tension until the serous film peels off, and record the peeling force;

[0095] (II) Implementation examples:

[0096] Example 4: Prepare 1.5% pure epoxy resin, 3% epoxy resin mixed with 1% polyester, 2% epoxy resin mixed with 2% polyurethane, and add silica nanoparticles to the above three sizing agents, and the ratio between each sizing agent and silica nanoparticles is 1:0.3;

[0097] The polypropylene filaments obtained in Example 2 were subjected to corona treatment, and the polypropylene filaments after the corona treatment were immersed in a 1.5% concentration of pure epoxy resin for 2.5 minutes, and the immersed polypropylene filaments were dried, specifically at a temperature of 60° C. for 15 minutes, to form a one-third slurry film on the surface of the polypropylene filaments;

[0098] The surface of the polypropylene filaments with one-third of the sizing film formed was subjected to corona treatment, and then immersed in 3% epoxy resin mixed with 1% polyester for 2.5 minutes. The impregnated polypropylene filaments were dried, specifically at a temperature of 60°C for 15 minutes, to form one-third of the sizing film on the surface of the polypropylene filaments;

[0099] The surface of two-thirds of the polypropylene filaments was corona treated and immersed in a 2% concentration of epoxy resin mixed with a 2% concentration of polyurethane for 2.5 minutes. The impregnated polypropylene filaments were dried, specifically at a temperature of 60°C for 15 minutes, to form one-third of the size film on the surface of the polypropylene filaments, and finally a size film with a thickness of 3µm was obtained, completing the formation of the size film.

[0100] Example 5: The same as Example 4, except that the ratio between each sizing agent and the silicon dioxide nanoparticles is 1:0.4.

[0101] Example 6: The same as Example 4, except that the ratio between each sizing agent and the silicon dioxide nanoparticles is 1:0.5.

[0102] Example 7: The same as Example 4, except that the ratio between each sizing agent and the silicon dioxide nanoparticles is 1:0.6.

[0103] The performance of the polypropylene filaments obtained in Examples 4 to 7 above was tested, as shown in Table 1;

[0104] Table 1

[0105] Tensile strength(MPa) Elongation at break (%) Wear resistance (mass loss%) Strength loss (%) Adhesion(MPa) Embodiment 4 411.3 21.2 0.054 6.3 80.5 Embodiment 5 423.2 22.6 0.041 4.1 87.4 Embodiment 6 453.7 24.1 0.023 2.7 94.6 Embodiment 7 437.5 23.7 0.031 3.4 89.1

[0106] By comparing Example 4 to Example 7, it can be concluded that as the proportion of silicon dioxide nanoparticles increases, the overall performance of the size film and the polypropylene filament obtained by alternating sizing with three sizing agents and corona treatment on the surface of the polypropylene filament is significantly enhanced. This is mainly because the polarity and activity of the surface of the polypropylene filament are improved by corona treatment on the surface of the polypropylene filament, providing more reaction points for the functional groups in the sizing agent, and promoting the formation of more chemical bonds. The epoxy groups in the epoxy resin, the carboxyl or hydroxyl groups in the polyester, and the carbamate groups in the polyurethane react chemically with the active groups on the surface of the polypropylene filament to form strong chemical bonds of epoxy groups, ester bonds, and carbamate bonds, which not only improves the adhesion between the size film and the polypropylene filament, but also enhances the structural stability of the size film, thereby improving the overall mechanical properties of the polypropylene filament and the size film; and after the corona treatment, the surface of the polypropylene filament becomes rougher and more polar, so that the nanoparticles can be better embedded in the micropores and defects on the surface of the polypropylene filament to form a tighter bonding layer;

[0107] In the process of alternating sizing combined with corona treatment, the formed sizing film is subjected to corona treatment, and a large number of free radicals and polar groups, such as hydroxyl and carboxyl groups, are generated on the surface of the sizing film, which react with the functional groups in the adjacent sizing films and with the polar groups such as hydroxyl groups on the surface of the silica nanoparticles, thereby promoting the formation of a three-dimensional network structure, thereby improving the bonding force between the sizing films. At the same time, the high specific surface area of ​​the nanoparticles enables more epoxy resin molecules to be adsorbed on their surface, forming a physical entanglement and interlocking structure, further enhancing the bonding force and improving the overall tensile and tear resistance.

[0108] And because the silicon dioxide nanoparticles play a filling role in the sizing agent, they can fill the tiny pores and defects in the sizing film formed by the sizing agent. The filling effect makes the sizing film denser, thereby reducing the permeability of the sizing film. The damage to the polypropylene filament during the processing and use process is reduced, which effectively reduces the contact between the fiber and the external environment and reduces the possibility of strength loss.

[0109] However, when the proportion of silica nanoparticles is too high, the silica nanoparticles may aggregate with each other to form larger particle agglomerates. The agglomerated nanoparticles cannot be effectively dispersed in the slurry membrane, resulting in reduced uniformity and density of the slurry membrane. The agglomerated particles form an uneven distribution in the slurry membrane, which will cause uneven layers to form on the surface of the slurry membrane, thereby reducing the overall performance of the slurry membrane. At the same time, it also increases the permeability of the sizing agent and the porosity of the slurry membrane, making it easier for the sizing agent to penetrate into the interior of the polypropylene filaments, thereby increasing the strength loss of the polypropylene filaments.

[0110] By comparing the sizing treatment of polypropylene filaments with different sizing agents, and testing the overall performance of polypropylene filaments obtained with different sizing methods;

[0111] Comparative Example 1: Prepare pure epoxy resin with a concentration of 1.5%, divide it into three portions of sizing agents, and add silica nanoparticles to the three portions of sizing agents respectively, and the ratio between each portion of sizing agent and silica nanoparticles is 1:0.5;

[0112] The polypropylene filaments obtained in Example 2 were corona treated, and the corona treated polypropylene filaments were immersed in one portion of 1.5% pure epoxy resin for 2.5 minutes. The impregnated polypropylene filaments were dried, specifically at a temperature of 60°C for 15 minutes, to form one-third of a slurry film on the surface of the polypropylene filaments, and the same operation was performed on the remaining two portions of the polypropylene filaments in turn, and finally a slurry film with a thickness of 3 µm was obtained, thereby completing the formation of the slurry film.

[0113] Comparative Example 2: 3% epoxy resin and 1% polyester were prepared and divided into three sizing agents, and silica nanoparticles were added to the three sizing agents respectively, and the ratio between each sizing agent and the silica nanoparticles was 1:0.5;

[0114] The polypropylene filaments obtained in Example 2 were corona treated, and the corona treated polypropylene filaments were immersed in one portion of a 3% concentration of epoxy resin mixed with a 1% concentration of polyester for 2.5 minutes. The impregnated polypropylene filaments were dried, specifically at a temperature of 60°C for 15 minutes, to form one-third of a slurry film on the surface of the polypropylene filaments, and the same operation was performed on the remaining two portions of the polypropylene filaments in turn, and finally a slurry film with a thickness of 3 µm was obtained, thereby completing the formation of the slurry film.

[0115] Comparative Example 3: Prepare 2% epoxy resin mixed with 2% polyurethane, divide it into three sizing agents, and add silica nanoparticles to the three sizing agents respectively, and the ratio between each sizing agent and silica nanoparticles is 1:0.5;

[0116] The polypropylene filaments obtained in Example 2 were corona treated, and the corona treated polypropylene filaments were immersed in one portion of 2% epoxy resin mixed with 2% polyurethane for 2.5 minutes. The impregnated polypropylene filaments were dried, specifically at a temperature of 60°C for 15 minutes, to form one-third of a slurry film on the surface of the polypropylene filaments, and the same operation was performed on the remaining two portions of the polypropylene filaments in turn, and finally a slurry film with a thickness of 3 µm was obtained, thereby completing the formation of the slurry film.

[0117] Control group 1: prepare pure epoxy resin with a concentration of 1.5%, add silica nanoparticles, and the ratio between the sizing agent and the silica nanoparticles is 1:0.5, perform corona treatment on the polypropylene filaments obtained in Example 2, immerse the polypropylene filaments after the corona treatment in the sizing agent for 8 minutes, dry the immersed polypropylene filaments, specifically at a temperature of 60°C, dry for 25 minutes, form a sizing film with a thickness of 3µm on the surface of the polypropylene filaments, and complete the formation of the sizing film;

[0118] Control group 2: 3% epoxy resin and 1% polyester were prepared, and silicon dioxide nanoparticles were added, and the ratio between the sizing agent and the silicon dioxide nanoparticles was 1:0.5. The polypropylene filaments obtained in Example 2 were subjected to corona treatment, and the polypropylene filaments after the corona treatment were immersed in the sizing agent for 8 minutes. The immersed polypropylene filaments were dried, specifically at a temperature of 60°C for 25 minutes, and a sizing film with a thickness of 3µm was formed on the surface of the polypropylene filaments, thereby completing the formation of the sizing film;

[0119] Control group 3: Prepare a 2% concentration of epoxy resin mixed with a 2% concentration of polyurethane, add silica nanoparticles, and the ratio between the sizing agent and the silica nanoparticles is 1:0.5, perform corona treatment on the polypropylene filaments obtained in Example 2, and immerse the polypropylene filaments after corona treatment in the sizing agent for 8 minutes, and dry the immersed polypropylene filaments, specifically at a temperature of 60°C, and dry for 25 minutes, to form a sizing film with a thickness of 3µm on the surface of the polypropylene filament, thereby completing the formation of the sizing film.

[0120] The polypropylene filaments obtained by sizing are subjected to performance tests, such as Figure 2 ;

[0121] In summary, by comparing Example 6, Comparative Example 1 and Control Group 1, Comparative Example 2 and Control Group 2, Comparative Example 3 and Control Group 3, it can be concluded that the strength loss of the polypropylene filaments after multiple sizing to form a sizing film by the alternating sizing method is significantly lower. This is mainly because the layers of sizing films formed by the alternating sizing method are usually thinner than the integrated sizing films formed by direct sizing. The thinner sizing films reduce the accumulation of slurry, and the slurry will not excessively penetrate into the interior of the filaments, thereby maintaining the structure and strength of the filaments. In contrast, direct sizing may cause the slurry to penetrate deeper and affect the original strength of the filaments. In summary, Example 6 is the optimal solution.

[0122] The polypropylene filaments of different densities obtained in Examples 1 to 3 were subjected to the operation of Example 6, and the obtained polypropylene filaments were tested for performance, as shown in Table 2;

[0123] Table 2

[0124] Density (g / cm³) Tensile strength(MPa) Elongation at break (%) Wear resistance (mass loss%) Strength loss (%) Adhesion(MPa) Embodiment 1 0.91 442.6 23.1 0.029 3.2 89.2 Embodiment 2 1.07 453.7 24.1 0.023 2.7 94.6 Embodiment 3 0.96 446.3 23.4 0.030 3.1 90.4

[0125] By comparing Examples 1 to 3, it can be concluded that the higher the density of the prepared polypropylene filaments, the better the overall performance of the polypropylene filaments obtained after sizing treatment. This is mainly because the high-density polypropylene filament structure reduces the permeability of the sizing agent, because the film layer formed by the sizing film on the surface of the polypropylene filaments is relatively uniform and dense, which reduces the penetration of the sizing film into the fibers, thereby reducing the strength loss caused by penetration.

[0126] A high-strength polypropylene filament is prepared by the preparation process of the high-strength polypropylene filament.

[0127] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A process for preparing high-strength polypropylene filament, characterized in that: The following steps are involved: Step S1, using nano-scale calcium carbonate and wollastonite powder as reinforcement materials, and mixing polypropylene slices as base materials and the reinforcement materials in a uniform proportion; Step S2, adding a nucleating agent to the mixed material in step S1, mixing evenly, heating to a molten state, and spinning to obtain ultrafine fibers; Step S3, using vortex airflow to twist the ultrafine fibers into high-strength polypropylene filaments, and adjusting the twisting speed and tension to obtain a yarn structure; Step S4, taking a plurality of sizing agents and mixing them with silica nanoparticles, and alternately sizing the polypropylene filaments with the plurality of sizing agents mixed with silica nanoparticles to gradually establish a uniform sizing film, and performing corona treatment on the sizing position before each sizing; Step S5, performing heat setting treatment on the sizing-treated polypropylene filaments; In step S4, the various sizing agents are: 1-3% epoxy resin, 2-4% epoxy resin mixed with 0.5-1.5% polyester, and 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane.

2. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S1, the particle size of calcium carbonate is 50-80 nm, the particle size of wollastonite powder is 30-60 nm, and the mass ratio of calcium carbonate to wollastonite powder is 1-2:0.6-1; The molecular weight of the polypropylene chips is 400,000-800,000, and the mass ratio between the reinforcement material and the base material is 1:4-8.

3. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S2, the nucleating agent is talcum powder, and the mass ratio between the reinforcement material and the nucleating agent is 1:0.2-0.4; The mixed materials in step S1 are added with a nucleating agent and mixed evenly. Specifically, the mixed materials in step S1 and the nucleating agent are stirred at a speed of 1000-1200 r / min for 5-10 min, and acetone is added to reduce the surface tension of the nucleating agent particles.

4. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S2, the following sub-steps are included: Step S21, mixing the nucleating agent, the base material and the reinforcement material uniformly, and heating to 190-230° C. to a molten state; Step S22, controlling the spinning temperature at 200-240° C. so that the material can be stably transformed from a molten state into polypropylene primary fibers; Step S23, subjecting the polypropylene primary fiber to a multi-stage stretching treatment, wherein the stretching multiple in the first stage is 4-6 times, and the stretching multiple in the second stage is 8-10 times, to finally obtain ultrafine fibers.

5. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S3, high-strength polypropylene filaments are twisted, specifically, a plurality of ultrafine fibers are twisted in a clockwise direction at an air flow speed of 25-40 m / s and an air flow pressure of 0.5-1.5 MPa to obtain polypropylene filaments.

6. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S4, corona treatment is performed at a voltage range of 6-12 kV, and the processing speed of the polypropylene filament is controlled to be 5-20 m / min.

7. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S4, the following sub-steps are included: Step S41, preparing 1-3% epoxy resin, 2-4% epoxy resin mixed with 0.5-1.5% polyester, 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane sizing agent, and adding silica nanoparticles to the sizing agent, and the ratio between each sizing agent and silica nanoparticles is 1:0.3-0.6; Step S42, performing corona treatment on the polypropylene filaments, and immersing the corona treated polypropylene filaments in 1-3% concentration epoxy resin for 2-5 minutes; Step S43, drying the impregnated polypropylene filaments, specifically at a temperature of 50-80° C. for 15-20 minutes, to form a one-third size film on the surface of the polypropylene filaments; Step S44, after forming one-third of the sizing film, the polypropylene filaments are corona treated, and then immersed in 2-4% epoxy resin mixed with 0.5-1.5% polyester sizing agent, and step S43 is repeated. After forming two-thirds of the sizing film, the polypropylene filaments are corona treated, and then immersed in 1.5-3% epoxy resin mixed with 0.5-1.5% polyurethane sizing agent, and step S43 is repeated.

8. The process for preparing high-strength polypropylene filament according to claim 1, characterized in that: In step S4, the thickness of the slurry film is 1.5-3µm.

9. A high-strength polypropylene filament, characterized in that: The high-strength polypropylene filament is prepared based on the preparation process of any one of claims 1-8.

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