A polyester fiber pulp, its preparation method and application

Abstract

The present invention belongs to the technical field of papermaking, and relates to a polyester fiber pulp, a preparation method thereof and an application. The preparation method is to mix short fibers, water and inorganic salts and then carry out beating to obtain the polyester fiber pulp; the preparation method of the short fibers is as follows: first, spin using a spinning melt containing coated and modified titanium dioxide, then carry out alkali etching treatment and cutting; the coated and modified titanium dioxide includes titanium dioxide and oligomers coated on its surface through covalent bonds; the preparation method of the coated and modified titanium dioxide is as follows: first, carry out organic modification on titanium dioxide using an amino-containing coupling agent to obtain coupling agent-modified titanium dioxide, and at the same time prepare oligomers, and then mix the oligomers with the coupling agent-modified titanium dioxide and react. The polyester fiber pulp of the present invention can maintain stable dispersion and can be applied to the preparation of paper. The preparation method of the present invention does not need to use a dispersant, saves costs, reduces environmental pollution and the amount of waste water, and is beneficial to the recycling of waste paper in the later stage.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and relates to a polyester fiber pulp, a preparation method thereof, and an application thereof. Background Art

[0002] The papermaking industry is an important basic raw material industry closely related to the development of the national economy and social undertakings. At present, chemical fibers have been widely used in papermaking for making various special-purpose papers such as high-temperature resistant, flame-retardant, insulating, and wear-resistant papers. However, chemical fibers generally have a smooth surface, poor wettability to water, and are prone to agglomeration in water, resulting in disadvantages such as difficulty in dispersion, easy flocculation, and low bonding strength between paper fibers during the process of mixing chemical fibers with other fiber raw materials for papermaking. Simply by adjusting the fiber type and fiber mixing ratio, the improvement of fiber dispersibility and wettability is limited, which restricts the application of chemical fibers in papermaking.

[0003] To solve the problems of the dispersibility and wettability of chemical fibers, some methods have been proposed in the prior art.

[0004] The most commonly used method is to add substances such as polyvinyl alcohol, sodium hexametaphosphate, methoxypolyethylene glycol, polyethylene glycol dimethyl ether, polyacrylamide, sodium polyacrylate, sodium silicate, guar gum, methyl pentanol, etc. as dispersants to increase the paper wetness and diffusion coefficient. For example, a quick-drying thermal sublimation transfer paper disclosed in patent CN220700751U, an acetic acid cellulose fiber / plant fiber composite paper and its preparation method and application disclosed in patent application CN117604804A, and a preparation method of a special titanium white pulp for papermaking disclosed in patent application CN115678316A.

[0005] There is also a method of coating chemical fibers with additives such as fatty acid salts on the surface to improve the hydrophilicity and wettability of the fibers. For example, a preparation method of a high-strength packaging chemical fiber paper disclosed in patent application CN107419573A.

[0006] There is also a method of improving the wettability difference of paper by adjusting the fiber type and fiber mixing ratio while adding a dispersant. For example, a polyphenylene sulfide ultrafine fiber and ultra-short fiber and its preparation method disclosed in patent application CN114481354A, and a synthetic fiber paper applicable to an ultra-low concentration inclined screen forming process and its preparation method disclosed in patent application CN118461354A.

[0007] The common feature of the above existing methods is the use of a large amount of dispersants or additives. Although adding dispersants or additives to the pulp facilitates papermaking and improves the properties of the paper, it is easy to cause environmental pollution, and a large amount of wastewater will be generated during the production process, increasing the difficulty of sewage treatment. Moreover, chemical fiber waste paper is not easily degraded. With the demand for sustainable development, it is necessary to consider recycling waste chemical fiber products through recycling. Since these dispersants or additives will be mixed with the chemical fibers, it greatly affects the recycling of chemical fiber waste paper. Most of them can only be degraded by composting, and this degradation method is inefficient and causes waste of resources.

[0008] Therefore, there is an urgent need for a polyester fiber pulp that can both improve the dispersibility of the pulp and facilitate the recycling of waste paper, as well as a preparation method thereof. Summary of the Invention

[0009] The purpose of the present invention is to solve the problems existing in the prior art and provide a polyester fiber pulp, a preparation method thereof, and an application.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A preparation method of polyester fiber pulp, which is obtained by mixing staple fibers, water and inorganic salts and then beating them.

[0012] The preparation process flow of the staple fibers is as follows: the spinning melt is extruded from the spinneret → oiling → bundling (i.e., gathering the filaments from different spinnerets together) → texturing (using a pair of gear discs to deform the fibers so that they are easy to interlock and improve the mechanical properties of the paper) → preheating (since the filament bundle is thick after bundling and it is difficult to fully contact with the hot roller during the drawing process, thus unable to ensure the drawing effect, so preheating is required) → drawing → heat setting → alkali etching treatment → cutting.

[0013] The spinning melt contains 15-20 wt% of coated and modified titanium dioxide; the D50 particle size (i.e., the median diameter or the median particle size) of the coated and modified titanium dioxide is 50-900 nm; the coated and modified titanium dioxide includes titanium dioxide and oligomers coated on its surface through covalent bonds. The oligomers and the matrix of the spinning melt only have different average degrees of polymerization, and the average degree of polymerization of the oligomers is 40-60.

[0014] The preparation method of the coated and modified titanium dioxide is as follows: first, the titanium dioxide is organically modified with an amino-containing coupling agent (such as γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, etc.) to obtain the coupling agent-modified titanium dioxide, and at the same time, the oligomers are prepared, and then the oligomers and the coupling agent-modified titanium dioxide are mixed and reacted.

[0015] The preparation process of the spinning melt is as follows: First, polyester and coated modified titanium dioxide are melt-blended to obtain masterbatch, then the masterbatch is subjected to solid-phase viscosity increase, and then the masterbatch after solid-phase viscosity increase is melt-blended with polyester to obtain the spinning melt. During the solid-phase viscosity increase process, the oligomers coated on the surface of titanium dioxide react with polyester, improving the binding fastness between titanium dioxide and the fiber body in the subsequently prepared fibers and preventing titanium dioxide from falling off during the alkali etching treatment process;

[0016] The drawing ratio is 5.5 to 6.5;

[0017] The inorganic salt is one or more of potassium salts, sodium salts and calcium salts;

[0018] The principle for the pulp of the present invention to maintain stable dispersion is as follows:

[0019] (1) By controlling the content of coated modified titanium dioxide, the particle size of coated modified titanium dioxide, and the drawing ratio in the spinning melt, a large number of protrusions can be formed on the fiber surface, forming a rough surface different from the smooth surface of ordinary chemical fibers. A large number of capillary-like channels are formed between the protrusions of fibers. Water molecules quickly spread on the fiber surface and quickly penetrate between fibers by capillary action, improving the wettability of water molecules between fibers and enabling the fibers to be quickly dispersed into a single fiber state;

[0020] (2) The alkali etching treatment can remove the oligomers on the protruding part of the coated modified titanium dioxide on the fiber surface, exposing titanium dioxide. An amino-containing coupling agent is grafted on the surface of titanium dioxide, and the amino-containing coupling agent combines with metal ions in the inorganic salt, so that the surface of the fiber is positively charged. After the fibers in the slurry are all positively charged, the fibers repel and separate from each other, are not easily agglomerated and settled, and maintain stable dispersion for a long time.

[0021] As a preferred technical solution:

[0022] For the preparation method of a polyester fiber pulp as described above, the preparation steps of the coated modified titanium dioxide are as follows:

[0023] (a) The titanium dioxide is organically modified with a coupling agent to obtain coupling agent-modified titanium dioxide;

[0024] (b) Add a dibasic acid and a diol to a reaction kettle, stir and heat up to 200 - 230 °C, control the pressure of the reaction system to be 0.2 - 0.3 MPa, add a catalyst after reacting for 3 - 5 h, control the reaction system to gradually heat up to 260 - 270 °C, evacuate to a vacuum degree lower than 80 Pa, and cool down to 230 °C after reacting for 2 - 3 h to obtain oligomers;

[0025] The dibasic acid is terephthalic acid; the diol is one or more of ethylene glycol, propylene glycol and butanediol; the catalyst is antimony glycolate or tetrabutyl titanate; the molar ratio of the dibasic acid to the diol is 1:0.9 - 0.95; the mass of the catalyst is 0.01 - 0.1% of the mass of the dibasic acid;

[0026] (c) Add coupling agent-modified titanium dioxide to the reaction system in step (b), stir at high speed to make it fully mixed, keep the temperature for reaction for 0.5 - 1 h, continuously evacuate, discharge, cool, pre-crush, and air-crush to obtain coated and modified titanium dioxide;

[0027] The mass ratio of the coupling agent-modified titanium dioxide to the oligomer is 5 - 8:1.

[0028] For the preparation method of a polyester fiber pulp as described above, solid-phase viscosity increase is carried out under a nitrogen or inert gas atmosphere, the temperature is 190 - 210 °C, and the time is 24 - 48 h.

[0029] For the preparation method of a polyester fiber pulp as described above, the preheating temperature is 70 - 80 °C, and the preheating can be carried out by means of water bath heating.

[0030] For the preparation method of a polyester fiber pulp as described above, four pairs of drafting rollers are used for drafting; the temperature of the first pair of drafting rollers is 100 - 120 °C, the temperature of the second pair of drafting rollers is 130 - 150 °C, the temperature of the third pair of drafting rollers is 180 - 200 °C, and the temperature of the fourth pair of drafting rollers is 200 - 240 °C; the spinning speed of the first pair of drafting rollers is 400 - 500 m / min, the spinning speed of the second pair of drafting rollers is 1200 - 1500 m / min, the spinning speed of the third pair of drafting rollers is 2400 - 2600 m / min, and the spinning speed of the fourth pair of drafting rollers is 2600 - 2800 m / min.

[0031] For the preparation method of a polyester fiber pulp as described above, the heat setting temperature is 100 °C, and the heat setting can be carried out by means of steam treatment.

[0032] For the preparation method of a polyester fiber pulp as described above, the process of alkali etching treatment is as follows: place the fiber in an alkali solution, heat it to 130 °C at a heating rate of 2 °C / min in an infrared dyeing machine, keep it warm for 40 min, and then carry out post-treatment (washing, drying, drying at 105 °C for 2 h), wherein the ratio of the fiber to the alkali solution is 1 g:50 mL, the alkali solution is composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6 g / L, and the concentration of benzyl alcohol is 3 mL / L.

[0033] A preparation method of polyester fiber pulp as described above. After cutting, the proportion of fibers with a length of 5 - 10 mm in the short fibers is 50 - 60 wt%, the proportion of fibers with a length of 11 - 18 mm is 30 - 40 wt%, and the remaining part is fibers with a length of 19 - 24 mm. Since the pulp contains fibers in three length ranges, which respectively play the roles of being soft and delicate, maintaining the stiffness of the paper, and entangling to enhance the strength of the paper, it is beneficial to the comprehensive mechanical properties of the finally prepared paper.

[0034] A preparation method of polyester fiber pulp as described above. The beating degree is 40 - 60 °SR, the content of inorganic salts in the slurry is 0.5 - 1 wt%, and the content of short fibers is 30 - 50 wt%.

[0035] The present invention also provides a polyester fiber pulp prepared by using the preparation method of a polyester fiber pulp described in any one of the above. The sedimentation volume fraction Vs / V of the polyester fiber pulp is 90 - 95%, and the ζ potential is 8 - 12 mV, indicating that the pulp has good stability and dispersibility.

[0036] The present invention also provides an application of the polyester fiber pulp as described above. After sending the polyester fiber pulp to a paper machine for papermaking, the wet paper sheet is pressed by a press roll to remove excess water, and dried in a blast drying oven at 70 °C for 2 h to finally make a paper; the thickness of the paper is 0.2 ± 0.02 mm, and the grammage is 200 ± 20 g / m 2 , and the tensile strength is 11 - 13 N / mm 2 , and the water contact angle is 3 - 5 °, indicating that the paper prepared from the pulp of the present invention has good mechanical strength and wettability. This may be because the fiber-coupled agent modified titanium dioxide on the surface of the fiber has a large number of amino functional groups, and when the paper is formed, a large number of hydrogen bonds are formed between the fibers by means of the amino groups.

[0037] Beneficial effects:

[0038] (1) A large number of protrusions are distributed on the surface of the fibers of the present invention, forming a rough surface of the fibers. A large number of capillary-like channels are formed between the protrusions of the fibers. These capillary-like channels enhance the capillary action on the fiber surface, enabling water molecules to spread rapidly on the fiber surface and also facilitating the rapid penetration of water molecules between the fibers, improving the wettability of water molecules between the fibers, and enabling the fibers to be rapidly dispersed into a single-fiber state.

[0039] (2) The alkali etching treatment of the present invention can remove the oligomers protruding from the surface of the fiber in the coated and modified titanium dioxide, exposing the titanium dioxide. The surface of the titanium dioxide is grafted with a coupling agent containing amino groups, and these amino groups combine with metal ions in the inorganic salt, so that the surface of the fiber is positively charged. After the fibers in the pulp are all charged with the same kind of charge, the fibers repel and separate from each other, are not easily agglomerated and settled, and maintain stable dispersion for a long time.

[0040] (3) The paper prepared from the pulp of the present invention has good mechanical strength and wettability.

[0041] (4) The present invention does not need to use a dispersant, which saves costs, reduces environmental pollution and waste water volume, and is also beneficial to the recycling of waste paper in the later stage. Specific Embodiments

[0042] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0043] The following are the test methods for relevant performance indicators in each example and comparative example:

[0044] Average degree of polymerization: Tested by gel permeation chromatography (GPC).

[0045] Sedimentation volume fraction Vs / V: Tested by sedimentation method. The specific steps are as follows: Take 100 ml of pulp and put it into a beaker. Set the stirring speed to 200 rpm. After stirring for 10 minutes, immediately transfer the pulp to a graduated cylinder, and record the scale value corresponding to the highest liquid level of the fibers in the suspension in the graduated cylinder at this time, which is recorded as the initial volume V; Let the suspension stand for 30 minutes, and record the scale value corresponding to the highest liquid level of the fibers in the suspension at the end of standing, which is recorded as the volume Vs after standing; Calculate the sedimentation volume fraction Vs / V.

[0046] ζ potential: Tested by a Zeta potential analyzer.

[0047] Tensile strength: Tested by a paper tensile testing machine; among them, the tensile speed is set to 300 mm / min.

[0048] Water contact angle: Tested by a contact angle tester.

[0049] Example 1

[0050] A method for preparing paper, the specific steps are as follows:

[0051] (1) Preparation of raw materials;

[0052] Coupling agent: γ-aminopropyltriethoxysilane;

[0053] Titanium dioxide;

[0054] Dicarboxylic acid: terephthalic acid;

[0055] Diol: ethylene glycol;

[0056] Catalyst: antimony glycolate;

[0057] Polyester: PET with an average degree of polymerization of 600;

[0058] Water;

[0059] Inorganic salt: potassium chloride;

[0060] Alkali solution: composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6 g / L, and the concentration of benzyl alcohol is 3 mL / L;

[0061] (2) Prepare the spinning melt;

[0062] (2.1) In a high-speed mixer, under the conditions of a rotation speed of 3000 r / min and a temperature of 80 °C, the titanium dioxide is organically modified with a coupling agent for 2.5 h to obtain coupling agent-modified titanium dioxide; among them, the mass of the coupling agent is 5% of the mass of the titanium dioxide.

[0063] (2.2) Add the dicarboxylic acid and the diol to the reaction kettle, stir and heat up to 200 °C, control the pressure of the reaction system to be 0.2 MPa, add the catalyst after reacting for 4 h, control the reaction system to gradually heat up to 270 °C, evacuate to 75 Pa, and cool down to 230 °C after reacting for 2.5 h to obtain an oligomer with an average degree of polymerization of 40; among them, the molar ratio of the dicarboxylic acid to the diol is 1:0.95; the mass of the catalyst is 0.1% of the mass of the dicarboxylic acid.

[0064] (2.3) Add the coupling agent-modified titanium dioxide to the reaction system in step (2.2), stir to make it fully mixed, keep the temperature for reaction for 0.5 h, continuously evacuate, discharge, cool, pre-crush, and air-crush to obtain coated and modified titanium dioxide with a D50 particle size of 50 nm; among them, the mass ratio of the coupling agent-modified titanium dioxide to the oligomer is 5:1.

[0065] (2.4) First, melt-blend the polyester and the coated and modified titanium dioxide to obtain a masterbatch with a concentration of 65 wt%, then solid-phase viscosity-increase the masterbatch at 190 °C in an atmosphere of nitrogen or inert gas for 48 h, and then melt-blend the solid-phase viscosity-increased masterbatch with the polyester to obtain a spinning melt containing 20 wt% of the coated and modified titanium dioxide.

[0066] (3) Prepare staple fibers;

[0067] The preparation process flow of staple fiber is as follows: the spinning melt is extruded from the spinneret → oiling → bundling → texturing → preheating → drawing (using four pairs of drawing rollers) → heat setting → alkali etching treatment (placing the fiber in the alkali solution at a mass-to-volume ratio of 1 g:50 mL, heating to 130 °C at a heating rate of 2 °C / min, holding for 40 min, and then performing post-treatment) → cutting;

[0068] Among them, the preheating temperature is 80 °C, the temperature of the first pair of drawing rollers is 100 °C, the temperature of the second pair of drawing rollers is 135 °C, the temperature of the third pair of drawing rollers is 180 °C, and the temperature of the fourth pair of drawing rollers is 200 °C; the spinning speed of the first pair of drawing rollers is 400 m / min, the spinning speed of the second pair of drawing rollers is 1250 m / min, the spinning speed of the third pair of drawing rollers is 2500 m / min, the spinning speed of the fourth pair of drawing rollers is 2600 m / min, and the heat setting temperature is 100 °C;

[0069] After cutting, the proportion of fibers with a length of 5 - 10 mm in the staple fiber is 55 wt%, the proportion of fibers with a length of 11 - 18 mm is 35 wt%, and the remaining part is fibers with a length of 19 - 24 mm;

[0070] (4)Prepare polyester fiber pulp;

[0071] Mix the staple fiber, water and inorganic salt and beat to a beating degree of 55 °SR to obtain polyester fiber pulp; among them, the content of inorganic salt in the slurry is 0.7 wt%, and the content of staple fiber is 40 wt%;

[0072] The sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 93.8%, and the ζ potential is 9.7 mV;

[0073] (5)Prepare paper;

[0074] Send the polyester fiber pulp to a paper-making machine for papermaking, then press to remove excess water, and dry to obtain paper.

[0075] The thickness of the finally prepared paper is 0.21 mm, the grammage is 212 g / m 2 , the tensile strength is 12.5 N / mm, and the water contact angle is 3.8°.

[0076] Comparative Example 1

[0077] A method for preparing paper is basically the same as that in Example 1, the difference is only that: the inorganic salt is replaced by an equal mass of water.

[0078] In step (4), the sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 46%, and the ζ potential is 3.9 mV; the tensile strength of the finally prepared paper is 5.4 N / mm, and the water contact angle is 4.8°.

[0079] Comparing Example 1 with Comparative Example 1, it can be seen that the stability and dispersibility of the polyester fiber pulp prepared in Comparative Example 1, as well as the mechanical strength and wettability of the paper, have significantly decreased. This is because in Comparative Example 1, an equal mass of water was used to replace the inorganic salt, resulting in the inability of the fiber surface to carry a positive charge by binding with metal ions in the inorganic salt through an amino-containing coupling agent. There is a lack of repulsive interaction between the same charges among the fibers, which makes it easier for them to agglomerate and settle, leading to a significant decrease in the stability and dispersibility of the polyester fiber pulp. At the same time, the decrease in the stability and dispersibility of the polyester fiber pulp will further affect the entanglement between the fibers during the paper preparation process, resulting in a decrease in the mechanical strength and wettability of the paper.

[0080] Comparative Example 2

[0081] A method for preparing paper is basically the same as that in Example 1, except that: in step (2.3), the D50 particle size of the coated and modified titanium dioxide is 40 nm.

[0082] In step (4), the sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 73%, and the ζ potential is 6.2 mV; the tensile strength of the finally prepared paper is 9.6 N / mm, and the water contact angle is 7.9°.

[0083] Comparing Example 1 with Comparative Example 2, it can be seen that the stability and dispersibility of the polyester fiber pulp prepared in Comparative Example 2, as well as the mechanical strength and wettability of the paper, have significantly decreased. This is because the D50 particle size of the coated and modified titanium dioxide in Comparative Example 2 is too small, making it difficult to form a sufficient number of convex structures on the fiber surface. This will result in the inability to form enough and effective capillary-like channels between the fibers, which is not conducive to the rapid spreading of water molecules on the fiber surface and the rapid penetration between the fibers by capillary action. Furthermore, it affects the state of the fibers being rapidly dispersed into single fibers, leading to a significant decrease in the stability and dispersibility of the polyester fiber pulp. At the same time, the decrease in the stability and dispersibility of the polyester fiber pulp will further affect the entanglement between the fibers during the paper preparation process, resulting in a decrease in the mechanical strength and wettability of the paper.

[0084] Example 2

[0085] A method for preparing paper is as follows:

[0086] (1) Preparation of raw materials;

[0087] Coupling agent: γ-aminopropyltriethoxysilane;

[0088] Titanium dioxide;

[0089] Dicarboxylic acid: terephthalic acid;

[0090] Diol: ethylene glycol;

[0091] Catalyst: antimony glycolate;

[0092] Polyester: PET with an average degree of polymerization of 600;

[0093] Water;

[0094] Inorganic salt: sodium chloride;

[0095] Alkali solution: composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6 g / L, and the concentration of benzyl alcohol is 3 mL / L;

[0096] (2) Prepare the spinning melt;

[0097] (2.1) In a high-speed blender, under the conditions of a rotation speed of 2800 r / min and a temperature of 100 °C, the titanium dioxide is organically modified with a coupling agent for 2.8 h to obtain coupling agent-modified titanium dioxide; among them, the mass of the coupling agent is 3% of the mass of the titanium dioxide;

[0098] (2.2) Add the dicarboxylic acid and the diol to the reaction kettle, stir and heat up to 200 °C, control the pressure of the reaction system to be 0.2 MPa, add the catalyst after reacting for 3.5 h, control the reaction system to gradually heat up to 265 °C, evacuate to 78 Pa, and cool down to 230 °C after reacting for 2.5 h to obtain an oligomer with an average degree of polymerization of 45; among them, the molar ratio of the dicarboxylic acid to the diol is 1:0.92; the mass of the catalyst is 0.04% of the mass of the dicarboxylic acid;

[0099] (2.3) Add the coupling agent-modified titanium dioxide to the reaction system in step (2.2), stir to make it fully mixed, keep the temperature for reaction for 0.7 h, continuously evacuate, discharge, cool, pre-crush, and air-crush to obtain coated and modified titanium dioxide with a D50 particle size of 200 nm; among them, the mass ratio of the coupling agent-modified titanium dioxide to the oligomer is 8:1;

[0100] (2.4) First, melt-blend the polyester and the coated and modified titanium dioxide to obtain a masterbatch with a concentration of 65 wt%, then solid-phase viscosity-increase the masterbatch at 195 °C in an atmosphere of nitrogen or inert gas for 30 h, and then melt-blend the solid-phase viscosity-increased masterbatch with the polyester to obtain a spinning melt containing 15 wt% of the coated and modified titanium dioxide;

[0101] (3) Prepare staple fibers;

[0102] The preparation process flow of staple fiber is as follows: the spinning melt is extruded from the spinneret → oiling → bundling → texturing → preheating → drawing (using four pairs of drawing rollers) → heat setting → alkali etching treatment (placing the fiber in the alkali solution at a mass-to-volume ratio of 1 g:50 mL, heating to 130 °C at a heating rate of 2 °C / min, holding for 40 min, and then performing post-treatment) → cutting;

[0103] Among them, the preheating temperature is 75 °C, the temperature of the first pair of drawing rollers is 100 °C, the temperature of the second pair of drawing rollers is 130 °C, the temperature of the third pair of drawing rollers is 180 °C, and the temperature of the fourth pair of drawing rollers is 210 °C; the spinning speed of the first pair of drawing rollers is 400 m / min, the spinning speed of the second pair of drawing rollers is 1200 m / min, the spinning speed of the third pair of drawing rollers is 2400 m / min, the spinning speed of the fourth pair of drawing rollers is 2600 m / min, and the heat setting temperature is 100 °C;

[0104] After cutting, the proportion of fibers with a length of 5 - 10 mm in the staple fiber is 60 wt%, the proportion of fibers with a length of 11 - 18 mm is 30 wt%, and the remaining part is fibers with a length of 19 - 24 mm;

[0105] (4)Prepare polyester fiber pulp;

[0106] Mix the staple fiber, water and inorganic salt and beat them to a beating degree of 40 °SR to obtain polyester fiber pulp; among them, the content of inorganic salt in the slurry is 0.5 wt%, and the content of staple fiber is 30 wt%;

[0107] The sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 95%, and the ζ potential is 8.5 mV;

[0108] (5)Prepare paper;

[0109] Send the polyester fiber pulp to a paper-making machine for papermaking, then press to remove excess water and dry to obtain the paper.

[0110] The thickness of the finally prepared paper is 0.2 mm, the grammage is 204 g / m 2 , the tensile strength is 12.2 N / mm, and the water contact angle is 3.5°.

[0111] Comparative Example 3

[0112] A method for preparing paper is basically the same as that in Example 2, the difference is only that: in step (2.4), the content of coated modified titanium dioxide in the spinning melt is 12 wt%.

[0113] In step (4), the sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 84%, and the ζ potential is 7.7 mV; the tensile strength of the finally prepared paper is 10.8 N / mm, and the water contact angle is 5.2°.

[0114] Comparing Example 2 with Comparative Example 3, it can be seen that the stability and dispersibility of the polyester fiber pulp prepared in Comparative Example 3, as well as the mechanical strength and wettability of the paper, have decreased significantly. This is because the content of coated modified titanium dioxide in the spinning melt in Comparative Example 3 is too low, resulting in a reduction in the number of convex structures formed on the fiber surface and an insufficiently dense distribution. It is difficult to form a sufficient number of effective capillary-like channels between the fibers, and the effect of water molecules spreading rapidly on the fiber surface and penetrating rapidly between the fibers by capillary action becomes poor, which is not conducive to the rapid dispersion of the fibers into single fiber state, and thus leads to a significant decrease in the stability and dispersibility of the polyester fiber pulp. At the same time, the decrease in the stability and dispersibility of the polyester fiber pulp will further affect the entanglement between the fibers during the paper preparation process, resulting in a decrease in the mechanical strength and wettability of the paper.

[0115] Example 3

[0116] A method for preparing paper, the specific steps are as follows:

[0117] (1) Preparation of raw materials;

[0118] Coupling agent: γ-aminopropyltriethoxysilane;

[0119] Titanium dioxide;

[0120] Dicarboxylic acid: terephthalic acid;

[0121] Diol: propylene glycol;

[0122] Catalyst: antimony glycolate;

[0123] Polyester: PET with an average degree of polymerization of 720;

[0124] Water;

[0125] Inorganic salt: calcium chloride;

[0126] Alkali solution: composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6 g / L, and the concentration of benzyl alcohol is 3 mL / L;

[0127] (2) Preparation of spinning melt;

[0128] (2.1) In a high-speed blender, under the conditions of a rotation speed of 3000 r / min and a temperature of 100 °C, the titanium dioxide is organically modified with the coupling agent for 2 h to obtain the coupling agent-modified titanium dioxide; wherein, the mass of the coupling agent is 3.5% of the mass of the titanium dioxide;

[0129] (2.2) Add a dibasic acid and a diol into a reaction kettle, stir and heat up to 210 °C, control the pressure of the reaction system to be 0.23 MPa, add a catalyst after reacting for 3 h, control the reaction system to gradually heat up to 268 °C, evacuate to 70 Pa, and cool down to 230 °C after reacting for 2 h to obtain an oligomer with an average degree of polymerization of 60; wherein, the molar ratio of the dibasic acid to the diol is 1:0.9; the mass of the catalyst is 0.01% of the mass of the dibasic acid;

[0130] (2.3) Add coupling agent-modified titanium dioxide into the reaction system of step (2.2), stir to mix it evenly, keep the temperature for reaction for 1 h, continuously evacuate, discharge, cool, pre-crush, and air-flow crush to obtain coated and modified titanium dioxide with a D50 particle size of 500 nm; wherein, the mass ratio of the coupling agent-modified titanium dioxide to the oligomer is 7:1;

[0131] (2.4) First, melt-blend the polyester and the coated and modified titanium dioxide to obtain a masterbatch with a concentration of 55 wt%, then solid-phase viscosity-increase the masterbatch at 200 °C in an atmosphere of nitrogen or inert gas for 24 h, and then melt-blend the solid-phase viscosity-increased masterbatch with the polyester to obtain a spinning melt containing 18 wt% of the coated and modified titanium dioxide;

[0132] (3) Prepare staple fibers;

[0133] The preparation process flow of the staple fibers is as follows: the spinning melt is extruded from a spinneret → oiling → bundling → texturing → preheating → drawing (using four pairs of drawing rollers) → heat setting → alkali etching treatment (place the fibers in an alkali solution according to a mass-to-volume ratio of 1 g:50 mL, heat up to 130 °C at a heating rate of 2 °C / min, keep the temperature for 40 min, and then perform post-treatment) → cutting;

[0134] Among them, the preheating temperature is 75 °C, the temperature of the first pair of drawing rollers is 120 °C, the temperature of the second pair of drawing rollers is 150 °C, the temperature of the third pair of drawing rollers is 200 °C, and the temperature of the fourth pair of drawing rollers is 240 °C; the spinning speed of the first pair of drawing rollers is 430 m / min, the spinning speed of the second pair of drawing rollers is 1300 m / min, the spinning speed of the third pair of drawing rollers is 2500 m / min, the spinning speed of the fourth pair of drawing rollers is 2800 m / min, and the heat setting temperature is 100 °C;

[0135] After cutting, the proportion of fibers with a length of 5 - 10 mm in the staple fibers is 50 wt%, the proportion of fibers with a length of 11 - 18 mm is 40 wt%, and the remaining part is fibers with a length of 19 - 24 mm;

[0136] (4) Prepare polyester fiber pulp;

[0137] Mix staple fibers, water and inorganic salts, and then beat them to a beating degree of 48°SR to obtain polyester fiber pulp; among them, the content of inorganic salts in the slurry is 0.85wt%, and the content of staple fibers is 40wt%.

[0138] The sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 90.6%, and the ζ potential is 10 mV;

[0139] (5)Prepare paper;

[0140] Send the polyester fiber pulp to a paper machine for papermaking, then press to remove excess water, and dry to obtain paper.

[0141] The finally prepared paper has a thickness of 0.18 mm and a grammage of 193 g / m 2 , and the tensile strength is 11.5 N / mm, and the water contact angle is 4.2°.

[0142] Example 4

[0143] A method for preparing paper, the specific steps are as follows:

[0144] (1)Preparation of raw materials;

[0145] Coupling agent: γ-aminopropyltrimethoxysilane;

[0146] Titanium dioxide;

[0147] Dicarboxylic acid: terephthalic acid;

[0148] Diol: butanediol;

[0149] Catalyst: tetrabutyl titanate;

[0150] Polyester: PET with an average degree of polymerization of 720;

[0151] Water;

[0152] Inorganic salt: sodium chloride;

[0153] Alkali solution: composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6 g / L, and the concentration of benzyl alcohol is 3 mL / L;

[0154] (2)Prepare spinning melt;

[0155] (2.1)In a high-speed mixer, under the conditions of a rotation speed of 2500 r / min and a temperature of 90 °C, use a coupling agent to organically modify titanium dioxide for 3 h to obtain coupling agent-modified titanium dioxide; among them, the mass of the coupling agent is 4.5% of the mass of titanium dioxide;

[0156] (2.2) Add the dibasic acid and the diol into the reaction kettle, stir and heat up to 230 °C, control the pressure of the reaction system to be 0.3 MPa, add the catalyst after reacting for 5 h, control the reaction system to gradually heat up to 270 °C, evacuate to 65 Pa, and cool down to 230 °C after reacting for 3 h to obtain an oligomer with an average degree of polymerization of 55; wherein, the molar ratio of the dibasic acid to the diol is 1:0.92; the mass of the catalyst is 0.1% of the mass of the dibasic acid;

[0157] (2.3) Add the coupling agent modified titanium dioxide into the reaction system of step (2.2), stir to make it fully mixed, keep the temperature for reaction for 0.8 h, continuously evacuate, discharge, cool, pre-crush, and air-crush to obtain the coated and modified titanium dioxide with a D50 particle size of 700 nm; wherein, the mass ratio of the coupling agent modified titanium dioxide to the oligomer is 6:1;

[0158] (2.4) First, melt-blend the polyester and the coated and modified titanium dioxide to obtain a masterbatch with a concentration of 60 wt%, then solid-phase viscosity increase the masterbatch at 205 °C under an atmosphere of nitrogen or inert gas for 30 h, and then melt-blend the solid-phase viscosity increased masterbatch with the polyester to obtain a spinning melt containing 15 wt% of the coated and modified titanium dioxide;

[0159] (3) Prepare staple fibers;

[0160] The preparation process flow of the staple fibers is as follows: the spinning melt is extruded from the spinneret → oiling → bundling → texturing → preheating → drawing (using four pairs of drawing rollers) → heat setting → alkali etching treatment (place the fibers in the alkali solution according to the mass-to-volume ratio of 1 g:50 mL, heat up to 130 °C at a heating rate of 2 °C / min, keep the temperature for 40 min, and then carry out post-treatment) → cutting;

[0161] Among them, the preheating temperature is 78 °C, the temperature of the first pair of drawing rollers is 105 °C, the temperature of the second pair of drawing rollers is 135 °C, the temperature of the third pair of drawing rollers is 190 °C, and the temperature of the fourth pair of drawing rollers is 220 °C; the spinning speed of the first pair of drawing rollers is 450 m / min, the spinning speed of the second pair of drawing rollers is 1200 m / min, the spinning speed of the third pair of drawing rollers is 2400 m / min, the spinning speed of the fourth pair of drawing rollers is 2650 m / min, and the heat setting temperature is 100 °C;

[0162] After cutting, the proportion of fibers with a length of 5 - 10 mm in the staple fibers is 55 wt%, the proportion of fibers with a length of 11 - 18 mm is 38 wt%, and the remaining part is fibers with a length of 19 - 24 mm;

[0163] (4) Prepare polyester fiber pulp;

[0164] Mix staple fibers, water and inorganic salts, and then beat them to a beating degree of 60°SR to obtain polyester fiber pulp; wherein, the content of inorganic salts in the slurry is 1 wt%, and the content of staple fibers is 50 wt%.

[0165] The sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 91%, and the ζ potential is 12 mV.

[0166] (5)Prepare paper.

[0167] Send the polyester fiber pulp to a paper-making machine for papermaking, then press to remove excess water, and dry to obtain the paper.

[0168] The finally prepared paper has a thickness of 0.19 mm, a grammage of 198 g / m 2 , a tensile strength of 12 N / mm, and a water contact angle of 4.5°.

[0169] Example 5

[0170] A method for preparing paper, the specific steps are as follows:

[0171] (1)Preparation of raw materials;

[0172] Coupling agent: γ-aminopropyltrimethoxysilane;

[0173] Titanium dioxide;

[0174] Dicarboxylic acid: terephthalic acid;

[0175] Diol: butanediol;

[0176] Catalyst: tetrabutyl titanate;

[0177] Polyester: PET with an average degree of polymerization of 720;

[0178] Water;

[0179] Inorganic salt: sodium chloride;

[0180] Alkali solution: composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6 g / L, and the concentration of benzyl alcohol is 3 mL / L;

[0181] (2)Prepare the spinning melt;

[0182] (2.1)In a high-speed mixer, under the conditions of a rotation speed of 2800 r / min and a temperature of 90 °C, use a coupling agent to organically modify titanium dioxide for 2.5 h to obtain coupling agent-modified titanium dioxide; wherein, the mass of the coupling agent is 4% of the mass of titanium dioxide.

[0183] (2.2) Add the dibasic acid and the diol into a reaction kettle, stir and heat up to 200 °C, control the pressure of the reaction system to be 0.28 MPa, add the catalyst after reacting for 4 h, control the reaction system to gradually heat up to 260 °C, evacuate to 75 Pa, and cool down to 230 °C after reacting for 2.8 h to obtain an oligomer with an average degree of polymerization of 60; wherein, the molar ratio of the dibasic acid to the diol is 1:0.95; the mass of the catalyst is 0.08% of the mass of the dibasic acid;

[0184] (2.3) Add the coupling agent-modified titanium dioxide into the reaction system of step (2.2), stir to make it fully mixed, keep the temperature for reaction for 0.5 h, continuously evacuate, discharge, cool, pre-crush, and air-crush to obtain the coated and modified titanium dioxide with a D50 particle size of 900 nm; wherein, the mass ratio of the coupling agent-modified titanium dioxide to the oligomer is 8:1;

[0185] (2.4) First, melt-blend the polyester and the coated and modified titanium dioxide to obtain a masterbatch with a concentration of 50 wt%, then solid-phase viscosity-increase the masterbatch for 24 h in an atmosphere of nitrogen or inert gas at a temperature of 210 °C, and then melt-blend the solid-phase viscosity-increased masterbatch with the polyester to obtain a spinning melt containing 20 wt% of the coated and modified titanium dioxide;

[0186] (3) Prepare staple fibers;

[0187] The preparation process flow of the staple fibers is as follows: the spinning melt is extruded from a spinneret → oiling → bundling → texturing → preheating → drawing (using four pairs of drawing rollers) → heat setting → alkali etching treatment (place the fibers in an alkali solution according to a mass-to-volume ratio of 1 g:50 mL, heat up to 130 °C at a heating rate of 2 °C / min, keep the temperature for 40 min, and then carry out post-treatment) → cutting;

[0188] Among them, the preheating temperature is 70 °C, the temperature of the first pair of drawing rollers is 110 °C, the temperature of the second pair of drawing rollers is 145 °C, the temperature of the third pair of drawing rollers is 195 °C, and the temperature of the fourth pair of drawing rollers is 235 °C; the spinning speed of the first pair of drawing rollers is 500 m / min, the spinning speed of the second pair of drawing rollers is 1500 m / min, the spinning speed of the third pair of drawing rollers is 2600 m / min, the spinning speed of the fourth pair of drawing rollers is 2800 m / min, and the heat setting temperature is 100 °C;

[0189] After cutting, the proportion of fibers with a length of 5 - 10 mm in the staple fibers is 60 wt%, the proportion of fibers with a length of 11 - 18 mm is 32 wt%, and the remaining part is fibers with a length of 19 - 24 mm;

[0190] (4) Prepare polyester fiber pulp;

[0191] Mix staple fibers, water, and inorganic salts, and then beat them to a beating degree of 50°SR to obtain polyester fiber pulp; among them, the content of inorganic salts in the slurry is 1 wt%, and the content of staple fibers is 45 wt%.

[0192] The sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 92.5%, and the ζ potential is 11.3 mV.

[0193] (5)Prepare paper.

[0194] Send the polyester fiber pulp to a paper-making machine for papermaking, then press to remove excess water, and dry to obtain paper.

[0195] The thickness of the finally prepared paper is 0.22 mm, and the grammage is 216 g / m 2 , the tensile strength is 12.7 N / mm, and the water contact angle is 4.3°.

[0196] Comparative Example 4

[0197] A method for preparing paper is basically the same as that in Example 5, except that: in step (3), the spinning speed of the fourth pair of drafting rollers is 2600 m / min.

[0198] In step (4), the sedimentation volume fraction Vs / V of the prepared polyester fiber pulp is 82%, and the ζ potential is 7.4 mV; the tensile strength of the finally prepared paper is 9.5 N / mm, and the water contact angle is 6.5°.

[0199] Comparing Example 5 with Comparative Example 4, it can be seen that the stability and dispersibility of the polyester fiber pulp prepared in Comparative Example 4, and the mechanical strength and wettability of the paper have decreased significantly. This is because in Comparative Example 4, the drafting is insufficient, so that the fibers cannot be fully refined and an ideal fiber surface structure cannot be shaped during the drafting process, resulting in a decrease in the number of convex structures formed on the fiber surface and an insufficiently dense distribution. It is difficult to form enough and effective capillary-like channels between fibers, and the rapid spreading of water molecules on the fiber surface and rapid penetration between fibers by capillary action will be hindered, which is not conducive to the rapid dispersion of fibers into single-fiber states, thus resulting in a significant decrease in the stability and dispersibility of the polyester fiber pulp; at the same time, the decrease in the stability and dispersibility of the polyester fiber pulp will further affect the entanglement between fibers during the paper preparation process, resulting in a decrease in the mechanical strength and wettability of the paper.

Claims

1. A method for preparing polyester fiber pulp, characterized in that: The short fibers, water and inorganic salts are mixed and then beaten to obtain polyester fiber pulp; The polyester fiber pulp does not require the use of a dispersant; The preparation process of staple fibers is as follows: spinning melt is extruded from the spinneret → oiling → bundling → extrusion deformation → preheating → drawing → heat setting → alkali etching → cutting; The spinning melt contains 15-20wt% of coated modified titanium dioxide; the D50 particle size of the coated modified titanium dioxide is 50-900nm; the coated modified titanium dioxide includes titanium dioxide and oligomers coated on the surface thereof by covalent bonds, and the oligomers are different from the matrix of the spinning melt only in average polymerization degree, and the average polymerization degree of the oligomers is 40-60; The preparation method of the coated modified titanium dioxide is as follows: firstly, an amino-containing coupling agent is used to organically modify titanium dioxide to obtain coupling agent-modified titanium dioxide, and at the same time, an oligomer is prepared, and then the oligomer and the coupling agent-modified titanium dioxide are mixed and reacted; The preparation steps of coated modified titanium dioxide are as follows: (a) organically modifying titanium dioxide with a coupling agent to obtain coupling agent-modified titanium dioxide; (b) adding the dibasic acid and diol into a reaction kettle, stirring and heating to 200-230°C, controlling the pressure of the reaction system to be 0.2-0.3MPa, adding a catalyst after reacting for 3-5h, controlling the temperature of the reaction system to gradually rise to 260-270°C, evacuating to a vacuum degree of less than 80Pa, reacting for 2-3h, cooling to 230°C, and obtaining an oligomer; (c) adding the coupling agent modified titanium dioxide to the reaction system of step (b), stirring to fully mix, keeping the temperature for reaction for 0.5 to 1 hour, continuously evacuating the vacuum, discharging, cooling, pre-crushing, and airflow crushing to obtain coated modified titanium dioxide; The mass ratio of coupling agent-modified titanium dioxide to oligomer is 5-8:1; The preparation process of the spinning melt is as follows: firstly, the polyester and the coated modified titanium dioxide are melt-blended to obtain a masterbatch, then the masterbatch is solid-phase thickened, and then the masterbatch after solid-phase thickening is melt-blended with the polyester to obtain a spinning melt; The draft multiple is 5.5~6.5; The inorganic salt is one or more of potassium salt, sodium salt and calcium salt.

2. The method for preparing polyester fiber pulp according to claim 1, characterized in that: The solid phase adhesion is carried out in a nitrogen or inert gas atmosphere at a temperature of 190-210°C for 24-48 hours.

3. The method for preparing polyester fiber pulp according to claim 1, characterized in that: The preheating temperature is 70~80℃.

4. The method for preparing polyester fiber pulp according to claim 1, characterized in that: Four pairs of drafting rollers are used for drafting; the temperature of the first pair of drafting rollers is 100~120℃, the temperature of the second pair of drafting rollers is 130~150℃, the temperature of the third pair of drafting rollers is 180~200℃, and the temperature of the fourth pair of drafting rollers is 200~240℃; the spinning speed of the first pair of drafting rollers is 400~500m / min, the spinning speed of the second pair of drafting rollers is 1200~1500m / min, the spinning speed of the third pair of drafting rollers is 2400~2600m / min, and the spinning speed of the fourth pair of drafting rollers is 2600~2800m / min.

5. The method for preparing polyester fiber pulp according to claim 1, characterized in that: The process of alkali etching treatment is: placing the fiber in alkali solution, heating it to 130°C at a heating rate of 2°C / min, keeping it warm for 40 minutes, and then performing post-treatment, wherein the ratio of fiber to alkali solution is 1g:50mL, the alkali solution is composed of NaOH, benzyl alcohol and water, the concentration of NaOH is 6g / L, and the concentration of benzyl alcohol is 3mL / L.

6. The method for preparing polyester fiber pulp according to claim 1, characterized in that: After cutting, the fibers with a length of 5 to 10 mm account for 50 to 60 wt% of the staple fibers, the fibers with a length of 11 to 18 mm account for 30 to 40 wt%, and the remaining fibers are fibers with a length of 19 to 24 mm.

7. The method for preparing polyester fiber pulp according to claim 1, characterized in that: The beating degree is 40~60°SR, the content of inorganic salt in the slurry is 0.5~1wt%, and the content of short fibers is 30~50wt%.

8. The polyester fiber pulp prepared by the method for preparing polyester fiber pulp according to any one of claims 1 to 7, characterized in that: The sedimentation volume fraction Vs / V of polyester fiber pulp is 90~95%, and the ζ potential is 8~12mV.

9. The use of polyester fiber pulp according to claim 8, characterized in that: After the polyester fiber pulp is sent to the papermaking machine for papermaking, it is squeezed to remove excess water and dried to finally make paper; the thickness of the paper is 0.2±0.02mm and the gram weight is 200±20g / m 2 , tensile strength is 11~13N / mm 2 , the water contact angle is 3~5°.