A method for preparing high-strength paper

Abstract

The invention discloses a method for preparing high-strength paper, comprising the following steps: (1) NBKP, LBKP, chemical mechanical pulp and damaged paper pulp are mixed and then enter into a core layer pulp pool, wherein the PCD range of the chemical mechanical pulp after being squeezed by a pressing screw is ‑3500 to ‑2900 u / L; (2) the core layer pulp and the surface and bottom layer pulps are sprayed onto a forming net through a headbox for forming; (3) the formed wet paper web is squeezed and dried and then enters a sizing machine; (4) the paper web after sizing is dried and coated to form paper; the interlayer bonding force of the paper prepared by the method of the invention is increased by 20‑30 J / m 2 , the folding resistance is increased by 5-10 times; this method improves the medicinal effect of the raw materials and achieves the effect of saving costs; reducing the viscosity of the rubber can also increase the life of the metering rod in the sizing machine, reduce the replacement frequency of the metering rod, and improve work efficiency.

Description

Technical Field

[0001] The invention relates to a paper making method, in particular to a paper making method for improving paper strength. Background Art

[0002] In the existing technology, the printing performance of coated white cardboard is good, but its interlayer bonding strength and other paper strength indicators are difficult to improve. Therefore, white cardboard is generally used for mid-to-high-end packaging boxes, handbags, etc.; some white cardboard is also used to make playing cards, which can reduce the cost of playing cards, but the paper used to make playing cards not only has high requirements for printing performance, but also requires high folding resistance and interlayer bonding strength to ensure the number of times the playing cards are used and the feel. Because the interlayer bonding strength and folding resistance of ordinary coated white cards cannot meet the requirements of playing cards, they are limited in use. The interlayer bonding strength of coated white cardboard prepared by the existing process meets the summer standard of ≥125J / m 2 , winter standard ≥145J / m 2 , the horizontal and vertical folding resistance is ≥12 times to be qualified, which is far from meeting the use requirements of playing cards. Using white cardboard to make playing cards will result in poor playing resistance, few uses, waste of paper resources, and indirectly affect the waste of raw materials.

[0003] Therefore, in order to expand the use of cheap white cardboard, it is necessary to improve the strength of existing paper. In order to improve the paper strength index, the amount of chemicals or the amount of core layer coniferous pulp is usually increased. The use of a large amount of chemicals and coniferous pulp in this method has aggravated environmental degradation; and this method greatly increases the cost of raw materials, while the improvement in paper strength is very limited. Therefore, the existing technology for improving paper strength indicators has the problem of high cost investment and the paper strength cannot be significantly improved. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for preparing high-strength paper with low cost to improve interlayer bonding strength and transverse and longitudinal folding times.

[0005] Technical solution: A method for preparing high-strength paper according to the present invention comprises the following steps:

[0006] (1) NBKP, LBKP, chemical mechanical pulp and broken pulp are mixed and then enter the core layer pulp pool. Among them, the PCD range of chemical mechanical pulp after the pressing screw is -3500~-2900u / L;

[0007] (2) The core layer slurry and the surface and bottom layer slurries are sprayed onto the forming net through the headbox for forming;

[0008] (3) The formed wet paper web is pressed and dried before entering the sizing machine;

[0009] (4) After sizing, the paper web is dried and coated to form paper.

[0010] Furthermore, in step (1), the torque range of the pressing screw is 80 kN·m-120 kN·m; the PCD of the chemical-mechanical pulp is increased, reducing the impact of anionic waste on chemicals and thus improving the effect of chemicals.

[0011] Furthermore, in step (1), a dry strength agent is added to the core layer pulp pool, and the solid content of the dry strength agent is 15-20%; under the same flow rate, the strength additive with a higher solid content has a higher effective ingredient and a better effect on improving the strength of the finished paper. Due to process and cost limitations, the optimal dry strength agent solid content is preferably selected.

[0012] Furthermore, in step (2), the headbox controls the web concentration to be 1.35-1.55%; by increasing the web concentration, more fine fibers are ensured to remain in the paper sheet, and sufficient fine fibers are more likely to form hydrogen bonds, thereby improving the strength of the paper.

[0013] Furthermore, the vertical lip plate at the flow channel outlet of the headbox has an opening range of 12mm-18mm.

[0014] Furthermore, in step (3), the sizing machine has a sizing viscosity of 102-126 cps; reducing the viscosity of the sizing agent improves the penetration performance of the sizing agent, and more sizing agent penetrates into the interior of the paper sheet to increase the strength.

[0015] Furthermore, alpha amylase is added to the sizing material used in the sizing machine.

[0016] Furthermore, the dosage of the α-amylase is 85ppm-120ppm.

[0017] Furthermore, the preparation step of the broke pulp comprises:

[0018] A: Broken paper is fully shredded and collected in the broken paper tower;

[0019] B: After the pulp coming out of the broke tower is concentrated, its concentration is increased to more than 3.8%;

[0020] C: After the concentration, the high-concentration pulp is graded and impurities are removed through the broke paper pressure screen and then collected in the broken paper pre-beating tank;

[0021] D: Put the pulp from the pulp tank before the broken paper is knocked into two sets of grinding mills connected in series for grinding. After grinding by the grinding mills, the broken paper pulp with a freeness of 260-280ml is formed and enters the pulp pool of the paper machine.

[0022] Furthermore, the specific energy consumption of the two groups of mills is consistent and is 45-55 kwh / t. Under the premise of not affecting the operation of the equipment, the specific energy consumption of the broke mill is increased, the freeness of the broke pulp is reduced, the beating degree of the broke pulp is increased, and the strength of the broke pulp can be increased within a certain range. After being added to the pulp tank of the paper machine, the folding resistance and interlayer bonding strength of the finished paper can be improved.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The strength of the paper prepared by the method of the present invention is greatly improved, and the interlayer bonding force can be increased by 20-30 J / m 2 , the folding endurance can be increased by 5-10 times; 2. By changing the equipment parameters and the material concentration to improve the chemical effect, the interlayer bonding strength of the paper can be increased. The process improvement replaces the increase in the amount of chemical pulp to achieve the effect of saving costs; 3. Reducing the viscosity of the glue can also increase the life of the metering rod in the sizing machine, reduce the replacement frequency of the metering rod, and improve work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart for broke pulp preparation;

[0025] Figure 2 Prepare a flow chart for the paper. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below in conjunction with embodiments.

[0027] The specific material ratio and parameters of papermaking are shown in Table 1. During papermaking, the process adjustment is strictly controlled. If an abnormality that affects the operation occurs, the operation is guaranteed first, and the experiment is continued after it returns to normal. The raw materials and chemical additives used in Table 1 are as follows:

[0028] NBKP uses the common Yinxing conifer pulp on the market, LBKP uses the common Goldfish broadleaf pulp on the market, and BCTMP uses a pulp made by mixing 50% eucalyptus and 50% acacia (hereinafter referred to as chemical mechanical pulp). Chemical additives used are common chemical additives on the market, specifically dry strength agent: polyacrylamide; retention agent: polyacrylamide; filter aid: polyacrylamide; cationic starch: corn starch.

[0029] Table 1

[0030]

[0031]

[0032] Example 1

[0033] In the process of paper preparation, Figure 1 and Figure 2 As shown, the specific steps are as follows:

[0034] The first step is to prepare the broke pulp:

[0035] 1.1 Broken paper produced by paper breaking and back copying is fully broken down in the pulper under the machine and collected in the broken paper tower;

[0036] 1.2 Broken pulp is concentrated to a concentration of more than 3.8% by a broken paper thickener;

[0037] 1.3 After the concentration, the high-concentration broke pulp is graded and impurities are removed through the first, second and third broken paper pressure screens, and then collected in the broken paper pre-beating trough;

[0038] 1.4 The broken paper pulp in the pulp tank before the broken paper knocking is refined by two mills connected in series. The freeness of the broken paper pulp after the mill is 283ml. The specific parameters are set to set the specific energy consumption of the mill to 45kwh / t;

[0039] 1.5 After being refined by two groups of broken paper mills, the broken paper pulp gathers in the broken paper post-beating trough and is finally stored in the paper machine pulp pool waiting for standby.

[0040] Step 2: Prepare the paper

[0041] 2.1 After the chemical-mechanical pulp enters the pressing screw for extrusion, it enters the BCT knocking tower for standby use. According to the proportion of the core layer pulp in Table 1, NBKP, LBKP, chemical-mechanical pulp and broken paper pulp are mixed and enter the core layer pulp pool for sizing;

[0042] 2.2 The dry strength agent adding pump is connected to the core layer slurry tank, and dry strength agents with different solid contents are prepared for standby use. According to the data of Example 1 in Table 2, the solid content of the dry strength agent is set to 15%;

[0043] 2.3 The core layer pulp after adding dry strength agent is deslagging and de-slagging by the deslagging device and pressure screen and then enters the core layer attenuation tank. The surface and bottom layer pulps are also deslagging and pressure screen and then enter the corresponding attenuation tank. The surface, core and bottom three layers of pulp are sprayed onto the forming net through the corresponding surface, core and bottom flow boxes. The vertical lip plate opening on the flow channel of the core layer flow box is set to 15mm; the formed net concentration is about 1.35%, forming a uniform formed wet paper web;

[0044] 2.4 The formed wet paper web enters the press section. The line pressure of the press section is set according to the range in Table 1. The first line pressure is 780 kn / m, the second line pressure is 790 kn / m, and the third line pressure is 800 kn / m.

[0045] 2.5 The pressed paper is dried in the front drying section, where the front drying section improves the dryness of the paper sheets through the combined action of the steam cooling system and the ventilation system. Through the drying action of the front drying section, the dryness of the paper sheets is increased from 55% to 85%;

[0046] 2.6 Control the liquid level of the glue storage tank, add 70ppm of α-amylase, adjust the glue viscosity to 135cps, and pass the paper through the sizing machine. The sizing machine uses a metering rod to apply glue to the surface of the paper. The amount of glue applied on the front side is controlled at 5.0gsm, and the amount of glue applied on the back side is controlled at 2.5gsm.

[0047] 2.7 After sizing, the paper enters the post-drying section for drying. The post-drying section improves the dryness of the paper through the combined action of the steam cooling system and the ventilation system. After the drying action of the post-drying section, the dryness of the paper increases from 80% to 90%;

[0048] 2.8 The dried paper is then passed through a hard calender, with the pressure controlled at 20 kN / m and the temperature controlled at 160°C. The hard calendered paper is pre-coated, mid-coated, top-coated, and back-coated. The specific data are shown in Table 1;

[0049] 2.9 Then enter the soft calender, the soft calender pressure is controlled at 10kn / m, the temperature is controlled at 160℃, and the final paper is formed. The strength index of the paper is tested, and the specific test instructions are as follows:

[0050] Test conditions: Ambient temperature and humidity: (23±3)℃, (50±5)%RH

[0051] Interlayer bonding test method:

[0052] Testing steps: ① Cut the sample to a size of 130×25.4mm, and mark the front, back, horizontal and vertical sides of the sample respectively; ② Tighten the 3M interlayer bonding tape parallel to the 5 reference surfaces; ③ Carefully place the sample with the back side facing down on the tape to keep the sample parallel to the tape, and stick another layer of double-sided tape on the sample, and pay attention to keep the bonding flat; ④ Put the angle steel back frame back, turn the sample pressure device inward to drive the pressure ring (the standard clamping pressure is 100psi (pounds per square inch); ⑤ Pneumatic pressure, the green display light CYCLE will turn off, and the clamping pressure will cycle from 0-100-0; ⑥ Turn the sample pressure device to the open position, and remove the angle steel back frame along the direction of the sample angle steel. 7. Cut the sample into 5 parts with a paper cutter, and cut off the excess parts at both ends; 8. Press the sample table on the stage with your left hand, and press the black clamping button with your right hand. Note that there is only one way for the sample to rotate on the stage, that is, the long hole of the sample is on the right, and the vertical part of the sample angle is on the left; 9. Press and immediately release the green pendulum down button to break the sample, and grab and suck it horizontally during the pendulum swing back. If the paper is not completely separated, press the DEL switch to eliminate the record input; 10. Press AVG to read the average interlayer bond strength of a group of 5 samples, and press SD to get the standard deviation of the sample bond strength.

[0053] Quality judgment criteria: interlayer bonding value ≥ 125 is qualified.

[0054] Folding test method:

[0055] Testing steps: Cut the finished paper longitudinally to obtain a 1.5 cm wide paper sample. Under a spring pressure of 9.81 N, fold the paper sample repeatedly at approximately 180° between rollers until it breaks, thereby determining the maximum number of folds the sample can withstand when it breaks.

[0056] Quality judgment criteria: The more times the measurement is taken, the better.

[0057] The test results of paper strength index obtained in Example 1 are shown in Table 2.

[0058] Example 2

[0059] The preparation method is basically the same as that of Example 1, except that, when preparing broke pulp in the first step, the specific energy consumption of the mill is controlled to be 50 kwh / t; the test results of the obtained paper strength index are shown in Table 2.

[0060] Example 3

[0061] The preparation method is basically the same as that of Example 1, except that, when preparing broke pulp in the first step, the specific energy consumption of the mill is controlled to be 55 kwh / t; the test results of the obtained paper strength index are shown in Table 2.

[0062] Comparative Example 1

[0063] The preparation method is basically the same as that of Example 1, except that, in the first step of preparing broke pulp, the specific energy consumption of the mill adopts 40 kwh / t in the prior art; the test results of the obtained paper strength index are shown in Table 2.

[0064] Table 2

[0065]

[0066] Example 4

[0067] The preparation method is basically the same as that of Comparative Example 1, except that in the second step, the solid content of the dry strength agent used is 17%; the test results of the obtained paper strength index are shown in Table 3.

[0068] Example 5

[0069] The preparation method is basically the same as that of Comparative Example 1, except that in the second step, the solid content of the dry strength agent used is 20%; the test results of the obtained paper strength index are shown in Table 3.

[0070] Comparative Example 2

[0071] The preparation method is basically the same as that of Comparative Example 1, except that in the second step, the solid content of the conventional dry strength agent in the prior art is used, specifically 15%; the test results of the obtained paper strength index are shown in Table 3.

[0072] Table 3

[0073]

[0074] Example 6

[0075] The preparation method is basically the same as that of Example 5, except that the viscosity of the sizing agent used is different, the viscosity of the sizing agent is controlled to be 126 CPS, and the α-amylase added is 85 ppm; the test results of the strength index of the prepared paper are shown in Table 4.

[0076] Example 7

[0077] The preparation method is basically the same as that of Example 5, except that the viscosity of the sizing agent used is different, the viscosity of the sizing agent is controlled to be 115 CPS, and the amount of α-amylase added is 100 ppm; the test results of the strength index of the prepared paper are shown in Table 4.

[0078] Example 8

[0079] The preparation method is basically the same as that of Example 5, except that the viscosity of the sizing agent used is different, the viscosity of the sizing agent is controlled to be 102 CPS, and the amount of α-amylase added is 120 ppm; the test results of the strength index of the prepared paper are shown in Table 4.

[0080] Table 4

[0081]

[0082]

[0083] Example 9

[0084] The preparation method is basically the same as that of Example 8, except that the core layer pulp PCD is controlled to be -3450u / L, specifically, the torque of the pressing screw is set to 80kN·m; the test results of the strength index of the prepared paper are shown in Table 5.

[0085] Example 10

[0086] The preparation method is basically the same as that of Example 8, except that the PCD of the core layer pulp is controlled to be -3300u / L, specifically, the torque of the pressing screw is set to 100kN·m; the test results of the strength index of the prepared paper are shown in Table 5.

[0087] Embodiment 11

[0088] The preparation method is basically the same as that of Example 8, except that the PCD of the core layer pulp is controlled to be -2950u / L, specifically, the torque of the pressing screw is set to 120kN·m; the test results of the strength index of the prepared paper are shown in Table 5.

[0089] Table 5

[0090]

[0091] Example 12

[0092] The preparation method is basically the same as that of Example 11, except that the online concentration is controlled to be 1.39%, specifically, the vertical lip opening is set to 18 mm; the test results of the strength index of the prepared paper are shown in Table 6.

[0093] Embodiment 13

[0094] The preparation method is basically the same as that of Example 11, except that the online concentration is controlled to be 1.45%, specifically, the vertical lip opening is set to 12 mm; the test results of the strength index of the prepared paper are shown in Table 6.

[0095] Table 6

[0096]

[0097]

Claims

1. A method for preparing high-strength paper, comprising the following steps: (1) NBKP, LBKP, chemical mechanical pulp and broken pulp are mixed and then enter the core layer pulp tank, where: The PCD range of chemical mechanical pulp after screw extrusion is -3500~-2900u / L; (2) The core layer slurry and the surface and bottom layer slurries are sprayed onto the forming net through the headbox for forming; (3) The formed wet paper web enters the sizing machine after being pressed and dried; (4) After sizing, the paper web is dried and coated to form paper; In step (1), the torque range of the pressing screw is 80 kN·m-120 kN·m, a dry strength agent is added to the core layer slurry pool, and the solid content of the dry strength agent is 17-20%; The preparation steps of the broken pulp include: A: Broken paper is fully shredded and collected in the broken paper tower; B: After the pulp coming out of the broken paper tower is concentrated, its concentration is increased to more than 3.8%; C: After the concentration, the high-concentration pulp is graded and impurities are removed through the broke paper pressure screen and then collected in the broken paper pre-beating tank; D: Put the pulp from the broken paper pre-beating trough into two sets of grinding mills connected in series for grinding. After being refined by the grinding mills, the broken paper pulp with a freeness of 260-280ml is formed and enters the pulp pool of the paper machine; In step (2), the headbox controls the screen concentration to be 1.35-1.55%, and the vertical lip opening range of the headbox flow channel outlet is 12mm-18mm.

2. The preparation method according to claim 1, characterized in that: In step (3), the viscosity of the sizing agent used in the sizing machine is 102-126 cps.

3. The preparation method according to claim 2, characterized in that: Alpha amylase is added to the size used in the size press.

4. The preparation method according to claim 3, characterized in that: The dosage of the α-amylase is 85ppm-120ppm.

5. The preparation method according to claim 1, characterized in that: The specific energy consumption of the two groups of mills is consistent and is 45-55 kwh / t.

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