Superfine polyester staple fiber for specialty paper and its manufacturing process

Abstract

The application relates to the technical field of polyester staple fiber manufacturing, and discloses super-fine polyester staple fiber for special paper and a manufacturing process thereof, which comprises the following steps: Step 1, drying PET chips and PET-PEG master batches; Step 2, melt blending the PET-PEG master batches with antioxidants and heat stabilizers; Step 3, melt blending, homogenizing and devolatilizing the PET chips and active carriers to form a composite melt, and then cooling, solidifying, cutting and granulating; Step 4, drying the composite granular master batches; Step 5, melt spinning; and Step 6, processing and forming the nascent fibers. In the application, the antioxidants and the heat stabilizers are uniformly dispersed in the PET-PEG melt in advance, the thermal oxygen degradation and hydrolysis of PEG segments and a PET matrix are inhibited, the melt rheological property is stabilized, the melt is blended and melted with the PET chips, the hydrophilic segments of the PET-PEG are uniformly dispersed in the PET matrix, selective adhesion of bubbles is reduced, and the fibers are uniformly dispersed in water.

Description

Technical Field

[0001] This invention relates to the field of polyester staple fiber manufacturing technology, specifically to a special paper-grade ultrafine polyester staple fiber and its manufacturing process. Background Technology

[0002] Polyester staple fiber is a short segment of chemical fiber made from polyethylene terephthalate (PET) through processes such as melt spinning, drawing, crimping, and cutting. Ultrafine polyester staple fiber refers to polyester staple fiber with a single filament fineness of less than 1.0 dtex. Its diameter is only a fraction to a dozen times that of ordinary fiber. Due to its extremely large specific surface area and extremely fine fineness, it gives the final product higher softness, density, coverage, and special tactile feel. In the field of specialty paper, ultrafine polyester staple fiber is often added to pulp as a reinforcing skeleton material to improve the strength, uniformity, durability, and dimensional stability of paper. However, ordinary PET polyester staple fiber, due to the lack of a large number of hydrophilic groups in its molecular chain structure and its low fiber surface energy, usually exhibits slow wetting speed, long floating time, easy entanglement between fibers and easy encapsulation of air bubbles in the wet forming process of papermaking, and has problems such as insufficient hydrophilicity and poor dispersion uniformity. To improve the hydrophilicity of PET fibers, the existing technology mainly adopts the blending spinning method, which physically mixes hydrophilic masterbatch (such as PET-PEG) with PET chips to introduce PEG hydrophilic segments into the PET-PEG material. Then, the mixture is directly melt-spun. Through melt blending, the hydrophilic PEG segments are introduced into and retained in the PET fiber matrix in the form of a dispersed phase, thereby improving its hydrophilicity without changing the main polymerization process of PET. However, physical mixing between solid particles cannot achieve uniform dispersion of PET-PEG in the PET matrix, easily leading to uneven distribution of hydrophilic segments within the fiber and the formation of localized hydrophobic points. This makes it prone to entraining air bubbles when dispersed in water, resulting in poor paper uniformity. Furthermore, the thermal stability of PEG segments in PET-PEG is lower than that of PET. During high-temperature melt blending and spinning, it is prone to thermal oxidative degradation and hydrolysis, causing a decrease in melt intrinsic viscosity, an increase in melt flow index, and an increase in terminal carboxyl group content. This not only weakens the hydrophilic effect, but the small molecule gases generated by degradation can also directly form bubbles, causing fluctuations in melt viscosity and affecting fiber fineness uniformity and spinning stability. Therefore, those skilled in the art provide a special paper-grade ultrafine polyester staple fiber and its manufacturing process to solve the problems mentioned in the background art. Summary of the Invention

[0003] The purpose of this invention is to provide a special paper-grade ultrafine polyester staple fiber and its manufacturing process. The process involves preparing an active carrier melt by pre-dispersing antioxidants and heat stabilizers uniformly in a PET-PEG melt to inhibit the thermo-oxidative degradation and hydrolysis of PEG segments and the PET matrix, thereby stabilizing the melt's rheological properties. Then, the active carrier melt is blended and melted with PET chips, allowing the hydrophilic segments of the PET-PEG to be dispersed in a fine and uniform manner within the PET matrix. This avoids the formation of hydrophobic points, reduces selective adhesion of bubbles due to local differences in hydrophilicity and hydrophobicity, and ensures uniform fiber dispersion in water, thus solving the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A manufacturing process for ultrafine polyester staple fiber for specialty paper, comprising the following steps: Step 1: Dry the PET chips and PET-PEG masterbatch separately to reduce their moisture content to below 50 ppm. Step 2: Under the protection of inert gas, the dried PET-PEG masterbatch, antioxidant, and heat stabilizer are simultaneously fed into a single-screw melt for melt blending to form an active carrier melt. Step 3: The active carrier melt is fed into the twin-screw extruder. At the same time, the dried PET chips are fed into the twin-screw extruder to melt, mix, homogenize and devolatilize with the active carrier melt to obtain a composite melt. Then, the composite melt is extruded in strip form from the twin-screw extruder die. After solidification in a cooling water tank, it enters the pelletizer for cutting and granulation to obtain composite granule masterbatch. Step 4: Dry the composite particle masterbatch to reduce its moisture content to below 30 ppm; Step 5: The dried composite granule masterbatch is fed into the spinning screw extruder and melted and filtered at a temperature of 260℃-290℃ to form a composite masterbatch melt. Then, the composite masterbatch melt is transported to the spinning assembly by a metering pump and extruded through the spinneret to form a melt stream. The melt stream is cooled by an annular airflow with a temperature of 20-24℃ and a speed of 0.45-0.70m / s to solidify the melt stream into nascent fibers. Step 6: Apply spinning oil evenly to the surface of the nascent fiber and wind it into a tubular filament cake. Then, arrange the filaments of multiple nascent fiber filament cakes in an orderly manner on the guide frame to form a filament bundle. After stretching, heat setting and cutting, ultrafine polyester staple fiber is obtained.

[0005] As a further aspect of the present invention: the antioxidant proposed in step two includes a primary antioxidant and a secondary antioxidant, wherein the primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the secondary antioxidant is tris(2,4-di-tert-butylphenyl) phosphite.

[0006] As a further embodiment of the present invention: the mass ratio of the primary antioxidant to the secondary antioxidant is 1:0.8-1.2, and the total amount of both added is 0.2%-0.5% of the total mass of the active carrier melt.

[0007] As a further aspect of the present invention: the heat stabilizer proposed in step two is bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, and the amount added is 0.05%-0.15% of the total mass of the active carrier melt.

[0008] As a further embodiment of the present invention: the mass ratio of active carrier melt to PET chips is 5%-15%: 85%-95%, and the mass ratio of PET-PEG masterbatch to PET chips is 4.97%-14.96%: 85%-95%.

[0009] As a further aspect of the present invention: the melting temperature of the single-screw melter proposed in step two is 220℃-250℃, and the inert gas is nitrogen or carbon dioxide.

[0010] As a further embodiment of the present invention: the stretching proposed in step six is ​​two-stage or three-stage hot roller stretching, with a total stretching ratio of 3.5-4.5; the heat setting temperature is 120℃-135℃.

[0011] A special paper-grade ultrafine polyester staple fiber obtained using the above manufacturing process.

[0012] Compared with the prior art, the advantages of the present invention are as follows: The manufacturing process of the special paper ultrafine polyester staple fiber proposed in this application prepares an active carrier melt by pre-mixing and melting PET-PEG masterbatch, antioxidant and heat stabilizer. The antioxidant and heat stabilizer are uniformly dispersed in the PET-PEG melt to inhibit the thermo-oxidative degradation and hydrolysis of PEG segments and PET matrix, reduce small molecule gases generated by degradation, and stabilize the rheological properties of the melt. Then, the active carrier melt is blended and melted with PET chips to disperse the hydrophilic segments of PET-PEG in the PET matrix in a fine and uniform form, avoid the formation of hydrophobic points, reduce the selective adhesion of bubbles caused by local hydrophilic and hydrophobic differences, ensure uniform dispersion of fibers in water, and improve the spinnability and uniformity of fibers. Attached Figure Description

[0013] Figure 1 This is a schematic flow diagram of the manufacturing process of the composite particle masterbatch according to an embodiment of the present invention; Figure 2 A schematic diagram of the process for preparing ultrafine polyester staple fibers from composite particle masterbatch according to an embodiment of the present invention. Detailed Implementation

[0014] Example 1

[0015] Combination Figure 1 and Figure 2 As shown in this embodiment, a manufacturing process for a special paper ultrafine polyester staple fiber includes the following steps: Step 1: Using a vacuum drum dryer, PET chips are dried at 135℃-175℃ for 6-10 hours, and PET-PEG masterbatch is dried at 120℃-140℃ for 4-8 hours to ensure that the moisture content of the dried PET chips and PET-PEG masterbatch is less than 50ppm. The dried PET chips and PET-PEG masterbatch are then temporarily stored in a sealed container filled with dry air or nitrogen to prevent re-absorption of moisture.

[0016] In this embodiment, in step two, under the protection of nitrogen or carbon dioxide, the dried PET-PEG masterbatch, antioxidant, and heat stabilizer are simultaneously fed into the feed inlet of a single-screw melter. In the feeding section before entering the barrel, the PET-PEG masterbatch, antioxidant, and heat stabilizer undergo preliminary physical mixing under the conveying and stirring action of the screw. Then, the mixture enters the heating zone with a melting temperature of 220℃-250℃. At this time, the PET-PEG masterbatch melts first to form a melt base material. The antioxidant and heat stabilizer are uniformly dispersed in the melt base material to form an active carrier melt, which inhibits the thermo-oxidative degradation and hydrolysis of PEG segments and PET matrix, reduces the melt viscosity fluctuation caused by the formation of bubbles from small molecule gases generated by degradation, and stabilizes the melt rheological properties.

[0017] In this embodiment, step three involves conveying the active carrier melt into the main feed port of the twin-screw extruder via a melt pump. Simultaneously, dried PET chips are fed into the side feed port via a loss-in-weight feeder. Inside the twin-screw barrel, the PET chips melt at 245℃-265℃ under the screw's conveying action, and are encapsulated and permeated by the active carrier melt. Then, under the high-intensity shearing, diversion, and recombination action generated by the screw assembly elements, the active carrier melt and the PET chip melt are uniformly mixed, homogenized, and devolatilized to obtain a composite melt. This allows the PET-PEG hydrophilic segments to be dispersed in the PET matrix in a fine and uniform form, avoiding the formation of hydrophobic points and reducing the selective adhesion of bubbles caused by local differences in hydrophilicity and hydrophobicity, thus ensuring uniform dispersion of fibers in water.

[0018] In this embodiment, the composite melt is extruded in strip form from the die of a twin-screw extruder to form a strip. Then, the strip enters a cooling water tank to cool and solidify. The strip is then pulled into a pelletizer to be cut and granulated to obtain composite particle masterbatch.

[0019] In this embodiment, step four involves feeding the composite particle masterbatch into a pre-crystallizer and stirring at low speed for 20-30 minutes at a temperature of 150℃-160℃ to allow initial crystallization on the surface of the composite particle masterbatch, preventing the composite particle masterbatch from sticking together during subsequent high-temperature drying. Then, the composite particle masterbatch is dried uniformly at a constant temperature of 170℃-180℃ with low wind speed for 4-6 hours to ensure that the moisture content of the composite particle masterbatch is below 30ppm. The dried composite particle masterbatch is then temporarily stored in a sealed container or a nitrogen-protected environment at a temperature of 120℃-150℃ to prevent the composite particle masterbatch from regaining moisture or absorbing moisture from the atmosphere.

[0020] In this embodiment, in step five, the dried composite granule masterbatch is fed into a spinning screw extruder and melted and filtered at a temperature of 260℃-290℃ to form a composite masterbatch melt. Then, the composite masterbatch melt is transported to the spinning assembly by a metering pump and extruded through a spinneret to form a melt stream. The melt stream is cooled by a ring-blown airflow with a temperature of 20-24℃ and a speed of 0.45-0.70m / s, so that the melt stream solidifies into nascent fibers.

[0021] In this embodiment, step six involves uniformly coating the nascent fiber surface with spinning oil via a metering pump and nozzle to improve the fiber's bundle properties, smoothness, and antistatic properties. Then, a high-speed winding machine is used to wind the nascent fiber into a tubular filament cake. The filaments from multiple tubular filament cakes are then drawn out and merged on a guide frame to form a filament bundle. The filament bundle is then drawn into a multi-roller drawing machine for two-stage hot roller drawing. The first stage involves preheating and preliminary drawing at a temperature of 70℃-90℃, while the second stage involves main drawing at a temperature of 110℃-130℃. This ensures that the total fiber draw ratio is precisely controlled between 3.5 and 4.5, allowing the PET macromolecular chains to be highly oriented and crystallized along the fiber axis, thereby improving the fiber's breaking strength and modulus.

[0022] In this embodiment, a heat setting machine is used to heat set the drawn filament bundle, eliminate internal stress in the filament bundle, stabilize the fiber structure, fix the elongation and reduce the boiling water shrinkage rate. Finally, according to the product specifications, the continuous long filament bundle is fed into a cutting machine to cut into short fiber segments of a specified length, thereby obtaining the ultrafine polyester staple fiber product and realizing the manufacturing of ultrafine polyester staple fiber.

[0023] In this embodiment, the antioxidant proposed in step two includes a primary antioxidant and a secondary antioxidant. The primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the secondary antioxidant is tris(2,4-di-tert-butylphenyl) phosphite. The primary antioxidant and the secondary antioxidant are compounded at a mass ratio of 1:0.8-1.2 to form a synergistic stabilizing mechanism, which inhibits the thermo-oxidative degradation and hydrolysis of PEG segments and PET matrix, reduces small molecule gases generated by degradation, maintains the stability of melt viscosity, and reduces yellowing caused by degradation.

[0024] In this embodiment, the heat stabilizer proposed in step two is bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite. Bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite captures and decomposes hydrogen peroxide generated by heat and shear, interrupts the oxidative degradation chain reaction of PET and PET-PEG copolymer, inhibits thermal oxidative yellowing and molecular chain breakage of the melt during processing, and maintains the viscosity and color stability of the melt. At the same time, the heat stabilizer and antioxidant synergistically protect the thermal stability of the entire process from composite masterbatch preparation to fiber forming, ensuring the durability of the natural whiteness, mechanical properties and hydrophilicity of polyester staple fiber.

[0025] In this embodiment, the mass ratio of active carrier melt to PET chips is 5%-15%: 85%-95%, and the mass ratio of PET-PEG masterbatch to PET chips is 4.97%-14.96%: 85%-95%. The contents of PET chips, PET-PEG masterbatch, antioxidants and heat stabilizers are configured according to the mass ratio to precisely control the effective content of PET-PEG in the final fiber, ensuring that PET-PEG is highly uniformly dispersed in the fiber and meeting the requirements of fiber hydrophilicity.

[0026] Example 2

[0027] Based on Example 1, using an active carrier melt with a mass ratio of 5:95 and PET chips, a primary antioxidant and an auxiliary antioxidant with a mass ratio of 1:1 and a total addition amount of 0.35% of the PET-PEG masterbatch mass, and a heat stabilizer with an addition amount of 0.1% of the PET-PEG masterbatch mass, the following steps were taken to manufacture ultrafine polyester staple fibers for specialty paper: Step 1: Using a vacuum drum dryer, bright PET chips with an intrinsic viscosity of approximately 0.65 dL / g were dried at 160℃ for 8 hours, and PET-PEG masterbatch with a PEG segment content of 32 wt% was dried at 130℃ for 6 hours. After drying, the moisture content of both PET chips and PET-PEG masterbatch was measured using a coulometric moisture analyzer and found to be less than 40 ppm. Then, the dried PET chips and PET-PEG masterbatch were temporarily stored in a sealed container filled with dry nitrogen for later use. Step 2: Under the protection of continuous high-purity nitrogen, the dried PET-PEG masterbatch, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite are accurately weighed by a loss-in-weight balance and simultaneously fed into the feed inlet of a single-screw melter with a melting temperature of 235°C. After being conveyed, melted, and blended, the materials form a homogeneous active carrier melt. Step 3: The active carrier melt is metered and delivered to the main feed port of the co-rotating twin-screw extruder via a melt pump. At the same time, the dried PET chips are added from the side feed port through another loss-in-weight feeder. Under the action of the high shear, mixing and devolatilization section in the twin-screw extruder at a temperature of 245℃-260℃ and a screw speed of 300rpm, the melt is melted, mixed, homogenized and volatiles are removed. Then, the composite melt is extruded in strip form through the die, solidified in the cooling water tank and then cut into granules by the pelletizer to obtain composite granule masterbatch. Step 4: Put the composite masterbatch particles into the pre-crystallization drying system, pre-crystallize at 155℃ for 25 minutes, and then dry at 175℃ under low dew point dry air conditions for 5 hours to make its moisture content less than 25 ppm. Step 5: The dried composite masterbatch is fed into a spinning screw extruder, melted and filtered at 275℃ to form a composite masterbatch melt. After being filtered by a metering pump and spinning assembly, it is extruded through a spinneret with 144 holes and a single hole diameter of 0.18mm to form a fine melt stream. Then, a ring blower with an air temperature of 22℃ and an air velocity of 0.55m / s is used to uniformly cool the fine stream and solidify it into nascent fibers. Step 6: Apply spinning oil evenly to the surface of the nascent fiber, then wind it into a yarn cake at a speed of 3200 m / min. Combine the yarn bundles from multiple yarn cakes and pass them through a first hot roller at 75°C and a second hot roller at 125°C for two-stage drawing, with a total drawing ratio of 4.0. After drawing, heat set the yarn bundles at 128°C. Finally, cut them into 38 mm long ultrafine polyester staple fibers. The single filament fineness of the ultrafine polyester staple fiber is tested to be 0.85 dtex.

[0028] Example 3

[0029] Based on Example 1, using an active carrier melt with a mass ratio of 10:90 and PET chips, a primary antioxidant and an auxiliary antioxidant with a mass ratio of 1:1 and a total addition amount of 0.4% of the PET-PEG masterbatch mass, and a heat stabilizer with an addition amount of 0.12% of the PET-PEG masterbatch mass, the following steps were taken to manufacture ultrafine polyester staple fibers for specialty paper: Step 1: Using a vacuum drum dryer, bright PET chips with an intrinsic viscosity of approximately 0.65 dL / g were dried at 165°C for 9 hours, and PET-PEG masterbatch with a PEG segment content of 32 wt% was dried at 135°C for 7 hours. After drying, the moisture content of both the PET chips and PET-PEG masterbatch was measured using a coulometric moisture analyzer and found to be less than 35 ppm. Then, the dried PET chips and PET-PEG masterbatch were temporarily stored in a sealed container filled with dry nitrogen for later use. Step 2: Under the protection of continuous high-purity nitrogen, the dried PET-PEG masterbatch, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite are accurately weighed by a loss-in-weight balance and simultaneously fed into the feed inlet of a single-screw melter with a melting temperature of 240°C. After being conveyed, melted, and blended, the materials form a homogeneous active carrier melt. Step 3: The active carrier melt is metered and delivered to the main feed port of the co-rotating twin-screw extruder via a melt pump. At the same time, the dried PET chips are added from the side feed port through another loss-in-weight feeder. Under the action of the high shear, mixing and devolatilization section in the twin-screw extruder at a temperature of 250℃-265℃ and a screw speed of 320rpm, the composite melt is melted, mixed, homogenized and volatiles are removed. Then, the composite melt is extruded in strip form through the die, solidified in the cooling water tank and then cut into granules by the pelletizer to obtain composite granule masterbatch. Step 4: Put the composite masterbatch particles into the pre-crystallization drying system, pre-crystallize at 150℃ for 30 min, and then dry at 180℃ under low dew point dry air conditions for 5.5 h to make its moisture content less than 20 ppm. Step 5: The dried composite masterbatch is fed into a spinning screw extruder, melted and filtered at 280℃ to form a composite masterbatch melt. After being filtered by a metering pump and spinning assembly, it is extruded through a spinneret with 144 holes and a single hole diameter of 0.18mm to form a fine melt stream. Then, a ring blower with a wind temperature of 21℃ and a wind speed of 0.6m / s is used to uniformly cool the fine stream and solidify it into nascent fibers. Step 6: Apply spinning oil evenly to the surface of the nascent fiber, then wind it into a yarn cake at a speed of 3300 m / min. Combine the yarn bundles from multiple yarn cakes and pass them through a first hot roller at 80°C and a second hot roller at 128°C for two-stage drawing, with a total drawing ratio of 4.2. The drawn yarn bundles are then heat-set at 132°C. Finally, they are cut into 38 mm long ultrafine polyester staple fibers. The single filament fineness of the ultrafine polyester staple fiber is measured to be 0.82 dtex.

[0030] Example 4

[0031] Based on Example 1, using an active carrier melt with a mass ratio of 15:85 and PET chips, a primary antioxidant and an auxiliary antioxidant with a mass ratio of 1:1.1 and a heat stabilizer with a mass ratio of 0.45% of the PET-PEG masterbatch, and a heat stabilizer with a mass ratio of 0.14% of the PET-PEG masterbatch, the following steps were taken to manufacture ultrafine polyester staple fibers for specialty paper: Step 1: Using a vacuum drum dryer, bright PET chips with an intrinsic viscosity of approximately 0.65 dL / g are dried at 170℃ for 10 hours, and PET-PEG masterbatch with a PEG segment content of 32 wt% is dried at 140℃ for 8 hours. After drying, the moisture content of both PET chips and PET-PEG masterbatch is measured by a coulometric moisture analyzer and is less than 30 ppm. Then, the dried PET chips and PET-PEG masterbatch are temporarily stored in a sealed container filled with dry nitrogen for later use. Step 2: Under the protection of continuous high-purity nitrogen, the dried PET-PEG masterbatch, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite are accurately weighed by a loss-in-weight balance and simultaneously fed into the feed inlet of a single-screw melter with a melting temperature of 245°C. After being conveyed, melted, and blended, the materials form a homogeneous active carrier melt. Step 3: The active carrier melt is metered and delivered to the main feed port of the co-rotating twin-screw extruder via a melt pump. At the same time, the dried PET chips are added from the side feed port through another loss-in-weight feeder. Under the action of the high shear, mixing and devolatilization section in the twin-screw extruder at a temperature of 255℃-270℃ and a screw speed of 300rpm, the melt is melted, mixed, homogenized and volatiles are removed. Then, the composite melt is extruded in strip form through the die, solidified in the cooling water tank and then cut into granules by the pelletizer to obtain composite granule masterbatch. Step 4: Put the composite masterbatch particles into the pre-crystallization drying system, pre-crystallize at 155℃ for 30 min, and then dry at 182℃ under low dew point dry air conditions for 6 h to make its moisture content less than 20 ppm. Step 5: The dried composite masterbatch is fed into a spinning screw extruder, melted and filtered at 285℃ to form a composite masterbatch melt. After being filtered by a metering pump and spinning assembly, it is extruded through a spinneret with 144 holes and a single hole diameter of 0.18mm to form a fine melt stream. Then, a ring blower with a wind temperature of 23℃ and a wind speed of 0.5m / s is used to uniformly cool the fine stream and solidify it into nascent fibers. Step 6: Apply spinning oil evenly to the surface of the nascent fiber, then wind it into a yarn cake at a speed of 3100 m / min. Combine the yarn bundles from multiple yarn cakes and pass them through a first hot roller at 85°C and a second hot roller at 130°C for two-stage drawing, with a total drawing ratio of 3.8. After drawing, heat set the yarn bundles at 135°C. Finally, cut them into 38 mm long ultrafine polyester staple fibers. The single filament fineness of the ultrafine polyester staple fiber is tested to be 0.88 dtex.

[0032] Comparative Example 1 Set up the following sample groups: Sample A was selected from ordinary PET staple fibers with a single filament fineness of 0.8 dtex; Sample B was selected from PET-PEG masterbatch with a PEG content of approximately 30 wt% that was hot-pressed into a film; Sample C1 was selected from PET and PET-PEG masterbatch directly mixed and melt-spun at a mass ratio of 95:5; Sample C2 was selected from PET and PET-PEG masterbatch directly mixed and melt-spun at a mass ratio of 90:10; Sample C3 was selected from PET and PET-PEG masterbatch directly mixed and melt-spun at a mass ratio of 85:15; Sample D1 was selected from the ultrafine polyester staple fiber manufactured in Example 2; Sample D2 was selected from the ultrafine polyester staple fiber manufactured in Example 3; and Sample D3 was selected from the ultrafine polyester staple fiber manufactured in Example 4.

[0033] Comparative Example 2 Based on Comparative Example 1, the static water contact angle of the fiber web surface was tested with a contact angle measuring instrument for 5 seconds. Then, 0.20g of short fibers were weighed and evenly dispersed on the surface of 500mL of deionized water for sedimentation time testing. The time was started and measured until the fiber bundle was completely submerged and settled to the bottom of the 250ml graduated cylinder. Each sample was tested 5 times and the average value was taken. Table 1 shows the comparative data of hydrophilicity test results for short fibers under the same conditions:

[0034] Table 1 Therefore, under the same conditions, the water contact angle of ordinary PET short fibers is 81.3° and the settling time is 305s, indicating poor hydrophilicity; the water contact angle of short fibers prepared by direct mixing of PET and PET-PEG is 60.4° and the settling time is 132s, indicating improved hydrophilicity; the water contact angle of short fibers prepared by blending active carrier melt with PET is reduced to 51.6° and the settling time is shortened to 54s, indicating high hydrophilicity.

[0035] Comparative Example 3 Based on Comparative Example 1, 0.20 g of short fibers were added to 500 mL of deionized water, stirred at 300 r / min for 2 min, and allowed to stand for 10 s. Immediately after stirring, 50 mL of the dispersion was taken and sheeted on a standard paper forming device and dried at 105 °C. Under a D65 standard light source, the number of fiber flocculation points in an area of ​​100 cm² was counted using image analysis software. At the same time, samples were taken immediately after dispersion and observed under a 100x optical microscope. The number of visible bubbles attached to the surface of 100 fibers was randomly counted. Table 2 shows the comparative data of wet dispersion and bubble adhesion test results of short fibers under the same conditions:

[0036] Table 2 Therefore, under the same conditions, ordinary PET short fibers have 31.6 flocculation points / 100cm² and 21.5 bubbles / 100 fibers, making dispersion difficult; short fibers prepared by directly mixing PET and PET-PEG have 14.9 flocculation points / 100cm² and 9.2 bubbles / 100 fibers, showing improved dispersibility; short fibers prepared by blending active carrier melt with PET have 3.5 flocculation points / 100cm² and 2.1 bubbles / 100 fibers, effectively reducing selective bubble adhesion and ensuring uniform fiber dispersion.

[0037] Comparative Example 4 Based on Comparative Example 1, 20g of composite masterbatch particles from samples C2 and D2 were selected. The composite masterbatch particles from samples C2 and D2 were placed in a Hacker rheometer molten plate at 270℃ and kept at a constant temperature for 20min under nitrogen protection. The intrinsic viscosity, terminal carboxyl content and yellow index of the melt were tested at the initial time and 20min. At the same time, the number of visible bubbles in the melt was recorded at 20min. The data of ordinary PET melt was used as a reference. Table 3 shows the comparative data of melt thermal stability test results for short fibers under the same conditions:

[0038] Table 3 Therefore, under the same conditions, the IV decrease value of short fibers prepared by direct mixing of PET and PET-PEG is 0.052 dL / g, the yellow index b value is 5.8, and there are 28 melt bubbles / 10g, indicating severe melt degradation. The IV decrease value of short fibers prepared by blending active carrier melt with PET is 0.023 dL / g, the yellow index b value is 2.4, and there are 9 melt bubbles / 10g. The pre-dispersion of antioxidants and heat stabilizers in the active carrier melt can effectively inhibit thermo-oxidative degradation and hydrolysis, and stabilize melt properties.

[0039] Comparative Example 5 Based on Comparative Example 1, samples C2 and D2 were selected and spun continuously for 8 hours on the same spinning production line. The spinning production status of samples C2 and D2 was recorded. Table 4 presents comparative data on the continuous spinning stability of short fibers under the same conditions:

[0040] Table 4 Therefore, under the same conditions, the spinning of short fibers prepared by directly mixing PET and PET-PEG resulted in 7 spinning breakages, a module pressure rise of 5.2 MPa, a fineness CV value of 3.8%, and poor spinning stability. The spinning of short fibers prepared by blending the active carrier melt with PET resulted in 2 spinning breakages, a module pressure rise of 2.8 MPa, a fineness CV value of 1.9%, and maintained spinning stability.

[0041] The working principle of this invention is as follows: In the manufacturing process of the special paper ultrafine polyester staple fiber proposed in this application, an active carrier melt is prepared by pre-mixing and melting PET-PEG masterbatch, antioxidants, and heat stabilizers. The antioxidants and heat stabilizers are uniformly dispersed in the PET-PEG melt to inhibit the thermo-oxidative degradation and hydrolysis of PEG segments and PET matrix, reduce small molecule gases generated by degradation, and stabilize the rheological properties of the melt. Then, the active carrier melt is blended and melt-spun with PET chips, so that the hydrophilic segments of PET-PEG are dispersed in the PET matrix in a fine and uniform form, avoiding the formation of hydrophobic points, reducing the selective adhesion of bubbles caused by local hydrophilic and hydrophobic differences, ensuring uniform dispersion of the fiber in water, and improving the spinnability and uniformity of the fiber.

[0042] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A manufacturing process for ultrafine polyester staple fiber for specialty paper, characterized in that, The manufacturing process includes the following steps: Step 1: Dry the PET chips and PET-PEG masterbatch separately to reduce their moisture content to below 50 ppm. Step 2: Under the protection of inert gas, the dried PET-PEG masterbatch, antioxidant, and heat stabilizer are simultaneously fed into a single-screw melt for melt blending to form an active carrier melt. Step 3: The active carrier melt is fed into the twin-screw extruder. At the same time, the dried PET chips are fed into the twin-screw extruder to melt, mix, homogenize and devolatilize with the active carrier melt to obtain a composite melt. Then, the composite melt is extruded in strip form from the twin-screw extruder die. After solidification in a cooling water tank, it enters the pelletizer for cutting and granulation to obtain composite granule masterbatch. Step 4: Dry the composite particle masterbatch to reduce its moisture content to below 30 ppm; Step 5: The dried composite granule masterbatch is fed into the spinning screw extruder and melted and filtered at a temperature of 260℃-290℃ to form a composite masterbatch melt. Then, the composite masterbatch melt is transported to the spinning assembly by a metering pump and extruded through the spinneret to form a melt stream. The melt stream is cooled by an annular airflow with a temperature of 20-24℃ and a speed of 0.45-0.70m / s to solidify the melt stream into nascent fibers. Step 6: Apply spinning oil evenly to the surface of the nascent fiber and wind it into a tubular filament cake. Then, combine the filaments of multiple nascent fiber filament cakes in an orderly manner on the guide frame to form a filament bundle. After stretching, heat setting and cutting, ultrafine polyester staple fiber is obtained. The antioxidants proposed in step two include primary antioxidants and secondary antioxidants, wherein the primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the secondary antioxidant is tris(2,4-di-tert-butylphenyl) phosphite; The heat stabilizer mentioned in step two is bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, and the amount added is 0.05%-0.15% of the total mass of the active carrier melt. The mass ratio of the active carrier melt to PET chips is 5%-15%: 85%-95%, and the mass ratio of the PET-PEG masterbatch to PET chips is 4.97%-14.96%: 85%-95%.

2. The manufacturing process of ultrafine polyester staple fiber for special paper according to claim 1, characterized in that, The mass ratio of the primary antioxidant to the secondary antioxidant is 1:0.8-1.2, and the total amount of both added is 0.2%-0.5% of the total mass of the active carrier melt.

3. The manufacturing process of ultrafine polyester staple fiber for special paper according to claim 1, characterized in that, The melting temperature of the single-screw melter proposed in step two is 220℃-250℃, and the inert gas is nitrogen or carbon dioxide.

4. The manufacturing process of ultrafine polyester staple fiber for special paper according to claim 1, characterized in that, The stretching proposed in step six is ​​a two- or three-stage hot roller stretching, with a total stretching ratio of 3.5-4.5; the heat setting temperature is 120℃-135℃.

5. A fiber, characterized in that, The special paper ultrafine polyester short fiber obtained by the manufacturing process of a special paper ultrafine polyester short fiber according to any one of claims 1-4.

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