Method for improving evenness of two-side offset paper

Abstract

The invention discloses a method for improving evenness of two-side offset paper, and relates to the technical field of papermaking, the freeness of each sizing agent is accurately controlled, and a mixed sizing agent ratio is adopted; a ternary retention system is adopted, and cationic polyacrylamide, anionic polyacrylamide and silica sol are added; a forming net is adopted, uniform fiber distribution is promoted by delaying the dehydration speed, and meanwhile the speed of a paper machine is stably controlled to avoid speed fluctuation; squeezing, pre-baking, sizing, post-baking and calendaring; and a coiling process. The method is suitable for the production and manufacturing process of the two-side offset paper, the produced two-side offset paper can be widely applied to multiple scenes such as printing and writing, and the problems that in existing two-side offset paper production, the uniformity index is low, the product quality consistency is poor, fibers are prone to flocculation to form pulp balls in the production process, the paper structure uniformity is affected, the unit consumption of chemicals is too high, and the production cost is low are solved. Therefore, the problems of high production cost, insufficient operation stability of a paper machine, large fluctuation of technological parameters and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and more specifically to a method for improving the uniformity of double-sided offset paper. Background Technology

[0002] Offset paper, a commonly used type of cultural paper, is widely used in book publishing, official document printing, and daily writing due to its advantages such as smooth writing and good printing results. With the continuous development of printing technology and the upgrading of market demands, high-end applications are placing increasingly higher requirements on the physical properties of offset paper, such as uniformity. Uniformity is one of the core quality indicators of offset paper, directly affecting its printability. Paper with poor uniformity is prone to problems such as uneven ink coverage and blurry images during printing.

[0003] However, current offset paper production technology suffers from several shortcomings that urgently need to be addressed. Firstly, the uniformity index is low; under conventional production processes, the uniformity index of offset paper is only about 66.4%, which is insufficient to meet the demands of high-end printing and writing. Secondly, fibers easily flocculate, forming clumps, which not only affects the paper's appearance but also leads to uneven internal structure. Thirdly, chemical consumption is high; traditional production processes require the addition of large amounts of chemical additives to ensure paper performance, increasing production costs. Fourthly, paper machine operation stability is insufficient; process parameters fluctuate easily during production, resulting in poor product quality consistency and a high scrap rate. These problems severely restrict the high-quality development of the offset paper industry. Therefore, developing a technology that can effectively improve the uniformity of offset paper, reduce production costs, and enhance the stability of paper machine operation has become an urgent need for the paper industry. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings and deficiencies of existing technologies by providing a method for improving the uniformity of offset paper. This method is applicable to the production process of offset paper and can be widely used in printing, writing, and other applications. It solves problems such as low uniformity index, poor product quality consistency, easy fiber flocculation and pulp clumping during production, affecting the uniformity of paper structure, excessive chemical consumption leading to high production costs, insufficient paper machine operation stability, and large fluctuations in process parameters in existing offset paper production.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: its operation method is as follows: Step 1: Pulping process; Step 2, Pulping Process: Precisely control the freeness of each pulp, with the freeness of softwood bleached sulfate pulp (NBKP) controlled at 300-320ml, hardwood bleached sulfate pulp (LBKP) at 320-340ml, bleached chemithermomechanical pulp (BCTMP) at 210-230ml, and waste pulp at around 351ml; Step 3, Pulp Preparation: A mixed pulp ratio is adopted, in which NBKP accounts for 10-15%, LBKP accounts for 45-60%, BCTMP accounts for 30-40%, and waste paper accounts for 5-15% of the total mixed pulp. Step 4, Chemical Addition Process: A ternary retention system is used to add cationic polyacrylamide, anionic polyacrylamide, and silica sol; the surface sizing agent dosage is adjusted simultaneously to not exceed 6.00 kg / t, the upper roller sizing amount is 1.00-1.25 kg / t, the lower roller sizing amount is 1.00-1.25 kg / t, and the filler adopts a ratio of 70-80% heavy calcium carbonate and 20-30% light calcium carbonate, with a dosage of 260-270 kg / t per ton of paper; Step 5, Web forming process: A forming web is used to promote uniform fiber distribution by slowing down the dewatering speed, while stabilizing and controlling the paper machine speed to avoid speed fluctuations; Step 6: Pressing - Pre-drying - Sizing - Post-drying - Calendering process; Step 7, Winding Process: During the production process, record the uniformity index, tensile strength, tear strength, smoothness, first pass retention rate and ash retention rate every hour, and fine-tune the process parameters according to the actual situation.

[0006] Furthermore, in the pulping process, after the degree of freeness of each pulp is precisely controlled, the fiber dispersion effect is significantly improved, effectively avoiding fiber flocculation and the formation of pulp clumps.

[0007] Furthermore, in the pulping process, the mixing ratio of the pulp has been verified through small-scale tests to balance fiber characteristics and production costs, taking into account both product quality and economic benefits.

[0008] Furthermore, in the dosing process, the parameter adjustment of the ternary retention system reduces the chemical consumption per unit while ensuring the retention rate.

[0009] Furthermore, the forming net in the web forming process makes the dehydration speed easier to control and greatly improves the uniformity of fiber distribution.

[0010] Furthermore, the real-time monitoring indicators of the winding process provide data support for adjusting process parameters, ensuring the stable operation of the paper machine.

[0011] Furthermore, the pulping process employs existing mature pulping technology to crush and dissociate waste paper and raw material pulp, providing basic pulp for subsequent processes.

[0012] Furthermore, the pressing-pre-drying-sizing-post-drying-calendering processes all adopt existing technologies. The pressing process removes excess moisture from the paper, the pre-drying and post-drying processes gradually dry the paper, the sizing process improves the paper's water resistance and surface strength, and the calendering process improves the paper's smoothness.

[0013] Furthermore, in step four, both CPAM and APAM are added after being diluted to a concentration of 0.25%.

[0014] Furthermore, in step four, the silica sol stock solution is added directly.

[0015] Furthermore, the chemical addition amounts in step four are 400-450 g / t of cationic polyacrylamide (CPAM), 320-350 g / t of anionic polyacrylamide (APAM), and 4.00-5.00 kg / t of silica sol.

[0016] Compared with the prior art, the beneficial effects of the present invention are: the present invention provides a method for improving the uniformity of offset paper, which is applicable to the production and manufacturing process of offset paper. The offset paper produced can be widely used in printing, writing and other scenarios. It solves the problems of low uniformity index, poor product quality consistency, easy fiber flocculation to form pulp clumps during the production process, affecting the uniformity of paper structure, excessive chemical consumption, resulting in high production costs, insufficient paper machine operation stability and large fluctuations in process parameters in the production of existing offset paper. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below. The preferred embodiments described are only examples. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1:

[0018] This embodiment was conducted on a PM6 paper machine at a pilot-scale production scale. The raw materials included bleached softwood sulfate pulp (NBKP), bleached hardwood sulfate pulp (LBKP), bleached chemithermomechanical pulp (BCTMP), and waste paper generated during the production process. The chemicals included CPAM, APAM, silica sol, surface sizing agents, heavy calcium carbonate, and light calcium carbonate, all of which are commonly used chemicals in the papermaking industry and comply with relevant national standards.

[0019] The operation steps in this embodiment are as follows: Step 1, Pulping: Using existing pulping equipment, raw paper pulp and waste paper are fed into the pulper and crushed and separated according to conventional process parameters to obtain qualified base pulp; Step 2, Refining: Different types of pulp are refined separately using a refiner. The freeness of each pulp is controlled by adjusting parameters such as the speed and pressure of the refiner. Specifically, the freeness of NBKP is controlled at 310ml, LBKP at 330ml, BCTMP at 220ml, and waste paper at 351ml. Step 3, Pulp Mixing: Mix the pulps according to the ratio of NBKP 13%, LBKP 51%, and BCTMP 36%, and add 14% waste paper as the total amount of mixed pulps. Stir thoroughly in the pulp mixing tank to ensure that the pulps are mixed evenly. Step 4, Chemical Addition: During the pulp conveying process, add chemicals according to the following proportions: CPAM is diluted to a concentration of 0.25% and added at a dosage of 420 g / t; APAM is diluted to a concentration of 0.25% and added at a dosage of 348 g / t; silica sol stock solution is added directly at a dosage of 4.98 kg / t; in the sizing stage, the dosage of surface sizing agent is controlled at 5.69 kg / t, and the parameters of the sizing rollers are adjusted so that the sizing amount of the upper roller is 1.24 kg / t and the sizing amount of the lower roller is 1.23 kg / t; the filler is mixed according to the ratio of 80% heavy calcium carbonate and 20% light calcium carbonate and added at a dosage of 265 kg / t per ton of paper. Step 5, Forming on the wire: Using a forming wire, the treated pulp is transported to the wire section of the paper machine. The paper machine speed is controlled to be stable, and the dewatering speed is slowed down so that the fibers are evenly distributed on the wire section to form a wet paper sheet. Step 6, Pressing - Pre-drying - Sizing - Post-drying - Calendering: The wet paper sheet goes through the pressing, pre-drying, sizing, post-drying and calendering processes in sequence, and each process adopts existing mature process parameters; Step 7, Winding: During the winding process, the uniformity index, tensile strength, tear strength, smoothness, first pass retention rate, and ash retention rate are tested every hour. Based on the test data, parameters such as grinding pressure and chemical addition amount are finely adjusted to ensure stable production.

[0020] After pilot production, the produced double-sided offset paper exhibited excellent performance indicators, with a uniformity index of 72.6%, a tensile index of 61.5 N·m / g, a smoothness of 23s, a first-pass retention rate of 82.3%, and an ash retention rate of 63.1%. All indicators were superior to existing production technologies, and the paper machine operated stably with a significant reduction in scrap rate, fully achieving the expected results. Example 2:

[0021] The process steps in this embodiment are the same as those in Embodiment 1, except that some process parameters are different. See the following differences for details: In the pulping process, the freeness of NBKP is controlled at 300ml, the freeness of LBKP is controlled at 320ml, the freeness of BCTMP is controlled at 210ml, and the freeness of waste paper is 350ml. In the pulping process, NBKP accounts for 10%, LBKP for 60%, BCTMP for 30%, and waste paper accounts for 10% of the total mixed pulp. Chemical dosing process: A ternary retention system is adopted, adding 400g / t of cationic polyacrylamide, 320g / t of anionic polyacrylamide, and 4.00kg / t of silica sol; the surface sizing agent dosage is adjusted to 5.00kg / t, the upper roller sizing amount is 1.00kg / t, the lower roller sizing amount is 1.00kg / t, and the filler adopts a ratio of 70% heavy calcium carbonate and 30% light calcium carbonate, with a dosage of 260kg / t per ton of paper.

[0022] After pilot production, the produced double-sided offset paper exhibited excellent performance indicators, with a uniformity index of 72.5%, a tensile index of 61.4 N·m / g, a smoothness of 23s, a first-pass retention rate of 82.1%, and an ash retention rate of 63.0%. All indicators were superior to existing production technologies, and the paper machine operated stably with a significant reduction in scrap rate, fully achieving the expected results. Example 3:

[0023] The process steps in this embodiment are the same as those in Embodiment 1, except that some process parameters are different. See the following differences for details: During the pulping process, the freeness of NBKP was controlled at 320ml, the freeness of LBKP was controlled at 340ml, the freeness of BCTMP was controlled at 230ml, and the freeness of waste paper was 349ml. In the pulping process, NBKP accounts for 12%, LBKP for 56%, BCTMP for 32%, and paper waste accounts for 10% of the total mixed pulp. Chemical dosing process: A ternary retention system is adopted, adding 420g / t of cationic polyacrylamide, 330g / t of anionic polyacrylamide, and 5.00kg / t of silica sol; the surface sizing agent dosage is adjusted to 6.00kg / t simultaneously, the upper roller sizing amount is 1.1kg / t, the lower roller sizing amount is 1.1kg / t, and the filler adopts a ratio of 80% heavy calcium carbonate and 20% light calcium carbonate, with a dosage of 265kg / t per ton of paper.

[0024] After pilot production, the produced double-sided offset paper exhibited excellent performance indicators, with a uniformity index of 73.1%, a tensile index of 63.1 N·m / g, a smoothness of 23s, a first-pass retention rate of 81.5%, and an ash retention rate of 62.1%. All indicators were superior to existing production technologies, and the paper machine operated stably with a significant reduction in scrap rate, fully achieving the expected results.

[0025] Compared with the prior art, the beneficial effects of the present invention are: 1. Significantly improved uniformity: Pilot-scale results show that the uniformity index of the double-sided offset paper produced using the technology of this invention reaches 72.6%, which is 9.3% higher than the 66.4% of the existing technology. It fully meets the target requirement of 65%-80% uniformity for double-sided offset paper in high-end application scenarios, and is better than the uniformity result of 71.3% in the small-scale test. The consistency of product quality is greatly improved, and the core problem of poor paper uniformity in the existing technology is effectively solved. 2. Stable physical properties: The tensile index of the paper is increased to 61.5 N·m / g, which is slightly better than the existing technology's 60.7 N·m / g, further ensuring the strength of the paper; the smoothness reaches 23s, which is 15% higher than the existing technology's 20s, improving the printability of the paper and better meeting the requirements for paper surface flatness during the printing process. Moreover, all physical properties are within the qualified range and fully meet the usage requirements. 3. Outstanding economic benefits: In terms of slurry, the proportion of the more expensive NBKP was reduced, while the proportion of the relatively cheaper BCTMP was increased; in terms of chemicals, the CPAM consumption was reduced from 0.48 kg / t in the existing technology to 0.42 kg / t, while the amount of surface sizing agent was also reduced, significantly reducing the cost of slurry and chemicals; in addition, the first pass retention rate was increased to 82.3%, the ash retention rate was increased to 63.1%, and the scrap rate was significantly reduced, further reducing production costs and enhancing the company's market competitiveness; 4. Strong industrial applicability: The technical solution of this invention has been tested on a PM6 machine. The paper machine runs stably and the process parameters are easy to adjust. There is no need to make large-scale modifications to existing production equipment. It can be directly applied to large-scale production. The technology is easy to operate and workers can easily master it. It has high promotion value and can bring significant economic and social benefits to offset paper production enterprises.

[0026] For those skilled in the art, modifications can be made to the technical solutions described in the foregoing embodiments, and equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A method for improving the uniformity of offset paper, characterized in that: Its operation method is as follows: Step (1), pulping process; Step (II), Pulping Process: Precisely control the freeness of each pulp, with the freeness of softwood bleached sulfate pulp controlled at 300-320ml, the freeness of hardwood bleached sulfate pulp controlled at 320-340ml, the freeness of bleached chemithermomechanical pulp controlled at 210-230ml, and the freeness of waste paper controlled at around 351ml; Step (3), Pulp Preparation: A mixed pulp ratio is adopted, in which NBKP accounts for 10-15%, LBKP accounts for 45-60%, BCTMP accounts for 30-40%, and waste paper accounts for 5-15% of the total mixed pulp. Step (IV) Chemical Addition Process: A ternary retention system is adopted, adding cationic polyacrylamide, anionic polyacrylamide and silica sol; the surface sizing agent dosage is adjusted to not exceed 6.00 kg / t, the upper roller sizing amount is 1.00-1.25 kg / t, the lower roller sizing amount is 1.00-1.25 kg / t, the filler adopts a ratio of 70-80% heavy calcium carbonate and 20-30% light calcium carbonate, and the dosage per ton of paper is 260-270 kg / t; Step (5), forming process: A forming wire is used to promote uniform fiber distribution by slowing down the dewatering speed, while stabilizing the paper machine speed and avoiding speed fluctuations. Step (six): Pressing-pre-drying-sizing-post-drying-calendering process; Step (VII), winding process: During the production process, record the uniformity index, tensile strength, tear strength, smoothness, first pass retention rate and ash retention rate every hour, and fine-tune the process parameters according to the actual situation.

2. The method for improving the uniformity of double-sided coated paper according to claim 1, characterized in that: The pulping process employs existing mature pulping technology to break down and dissociate waste paper and raw material pulp, providing basic pulp for subsequent processes.

3. The method for improving the uniformity of double-sided coated paper according to claim 1, characterized in that: The pressing-pre-drying-sizing-post-drying-calendering processes all adopt existing technologies. The pressing process removes excess moisture from the paper, the pre-drying and post-drying processes gradually dry the paper, the sizing process improves the paper's water resistance and surface strength, and the calendering process improves the paper's smoothness.

4. The method for improving the uniformity of double-sided coated paper according to claim 1, characterized in that: In step (iv), both CPAM and APAM are added after being diluted to a concentration of 0.25%.

5. The method for improving the uniformity of double-sided coated paper according to claim 1, characterized in that: In step (iv), the silica sol stock solution is added directly.

6. The method for improving the uniformity of double-sided coated paper according to claim 1, characterized in that: In step (iv), the chemical addition amounts are 400-450 g / t for cationic polyacrylamide, 320-350 g / t for anionic polyacrylamide, and 4.00-5.00 kg / t for silica sol.