Highly transparent paper and method for producing the same

Abstract

The application provides a kind of high transparent paper and its preparation method, its preparation method includes using whole coniferous wood pulp, the process steps of pulping, beating, pulp mixing and auxiliary material adding, wet paper sheet making, squeezing, drying, wetting, super calendering, rewinding and packing, wherein, (1) pulp mixing ratio: 100% bleached kraft coniferous wood pulp; (2) pulp beating conditions: beating consistency is controlled at low consistency, beating degree is controlled at 91±1 °SR, wet weight is controlled at 2.0~3.5g; (3) the basis weight of the prepared base paper is 28±1g / m 2 ; (4) base paper wetting conditions: single-sided wetting is carried out by using a drum wetting machine, and wetting water is added, the moisture balance time of the wetted base paper is at least controlled for 4 hours, and the moisture content of the paper is controlled at about 20±1%; (5) super calendering conditions: a super calendering machine is used, and the vehicle speed is not higher than 50m / min; the high transparent paper prepared by the method has qualified and stable quality, high transparency, environmental protection and easy recycling; and is suitable for the field of papermaking technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of papermaking, in particular to a high transparent paper and a preparation method thereof. BACKGROUND

[0002] The high transparent paper is a food-grade high-end packaging special paper with the characteristics of "using paper bags instead of plastic bags", environmental protection and easy recycling, which has important significance for the implementation of "limiting and reducing plastic bags, using paper bags instead of plastic bags" in China and meets the requirements of green development in China. The product is prepared through a series of processes such as beating, paper machine papermaking, wetting and super-calendering. The high transparent paper has the characteristics of certain oil and water resistance, good tensile strength, no fluorescence and high transparency. The product is mainly used for the packaging and protection of high-end precision instruments and meters, the packaging and decoration of luxury goods and high-end clothing, etc.

[0003] Through investigation, most customers require the transparency of the high transparent paper to be more than 85%. The quality and yield of the high transparent paper produced in China cannot be compared with the international advanced level, and cannot meet the needs of people. At present, the demand for high transparent paper in China is mainly imported, and the product is expensive. In addition, plastic film and semi-transparent paper are often used instead of high transparent paper, which is not environmentally friendly and not easy to recycle, and the grade is not high. Therefore, it is an urgent problem to develop high transparent paper with qualified and stable quality. SUMMARY

[0004] The present application provides a high transparent paper and a preparation method thereof to solve the problems of low transparency, poor quality stability and even unqualified of the existing high transparent paper.

[0005] In order to achieve the above purpose, the present application provides the following technical scheme:

[0006] The preparation method of the high transparent paper provided by the present application comprises the process steps of using whole coniferous wood pulp for pulping, beating, pulp preparation, addition of auxiliary materials, wet paper sheet papermaking, pressing, drying, wetting, super-calendering, rewinding and packaging, wherein (A) the pulp ratio is 100% bleached kraft coniferous wood pulp; (B) the pulp beating conditions are that three double-disc mills are connected in series for circulation beating, the pulp beating concentration is controlled at a medium-low concentration, the beating degree is controlled at 91±1°SR, and the wet weight is controlled at 2.0-3.5g; (C) the basis weight of the prepared base paper is 28±1g / m 2 ; (D) the base paper wetting conditions are that a drum wetting machine is used for single-sided wetting of the prepared base paper, and wetting water prepared is added to the drum wetting machine; the moisture balance time of the wetted base paper is controlled at least for 4 hours, and the moisture content of the paper is controlled at 20±1%; (E) the super-calendering conditions are that a 12-roll super-calendering machine is used, the width is 1880mm, and the speed is not higher than 50m / min; (F) the basis weight of the high transparent paper prepared after super-calendering is 28g / m2 moisture 6.0-7.0%, longitudinal breaking length≥8.0km, water absorption≤15g / m 2 smoothness≥1000S, transparency≥85%, color phase pure white.

[0007] Preferably, the specific conditions of the process steps further comprise: (G) the dosage of the additives to the absolute dry pulp: the dosage of the retention agent is 0.02-0.04% by weight, the dosage of the low-chlorine wet strength agent is 0.8-1.0% by weight, the dosage of the neutral sizing agent is 1.2-1.5% by weight, and the dosage of the defoaming agent is adjusted according to the white water foam; (H) the wet paper sheet making conditions: the wire speed is 250-280m / min, the width is 1880mm, and the lip opening of the headbox is 9.7mm; (L) the press section conditions: the first press line pressure is 500kN / m, and the second press line pressure is 550kN / m; (M) the drying conditions: drying is performed by using multiple drying cylinders, and the last drying cylinder is a cold cylinder through which normal temperature clean water is passed; (N) the winding conditions: the winding tension is 280kN / m.

[0008] Preferably, in the pulp proportioning of (A), the bleached kraft softwood pulp is Canadian northwood pulp.

[0009] Preferably, in the pulp beating conditions of (B), the beating consistency is 3.8-4.0%.

[0010] Preferably, in the wetting conditions of (D), the wetting water contains 2kg / ton of paper of the oil and water repellent agent.

[0011] Preferably, in the super-calendering conditions of (E), the speed is controlled at 40-50m / min.

[0012] Preferably, in the dosage of the additives to the absolute dry pulp of (G), the neutral sizing agent is alkyl ketene dimer AKD.

[0013] Preferably, in the wet paper sheet making conditions of (H), the wire speed is 0.17%.

[0014] Preferably, in the drying conditions of (M), there are 10 drying cylinders, and the last drying cylinder through which the wet paper sheet passes is a cold cylinder.

[0015] The application further provides a high-transparency paper prepared by the preparation method described in any of the above.

[0016] The preparation method of the high transparent paper provided in the embodiments of the present application focuses on improving the transparency of the paper from the aspects of pulp selection, beating process, base paper wetting process, super-calendering process, etc. Finally, the high transparent paper with qualified and stable quality, high transparency, environmental protection and easy recovery, and high cost performance is obtained. In the preparation method, 100% bleached kraft softwood pulp is used as the pulp, which is beneficial to improving the transparency of the paper. No filler is added in the papermaking process, so that the transparency of the base paper is high after super-calendering. No chemical containing fluorescent substances is added, so that the high transparent paper prepared reaches the food grade. The pulp is beaten by three double-disc mills in series circulation, and the beating consistency is controlled at a medium-low consistency, so that the fiber has good cutting effect and good fibrillation. The beating degree is controlled at 91±1°SR, and the wet weight is controlled at 2.0-3.5 g, so that the uniformity is good, and the transparency of the base paper is high after super-calendering. The base paper is adjusted in humidity by the humidifier with humidifying water, and the moisture balance time after humidification is controlled at at least 4 hours, so that the moisture is uniform, the moisture content of the paper is controlled at 20±1%, the paper is completely wetted, the transparency of the paper is improved, and the intermolecular tension and oil resistance of the paper surface are also improved. The super-calendering is performed by using a 12-roll super-calendering machine, and the speed is not higher than 50 m / min, so that the transparency of the paper after super-calendering by the super-calendering machine is more than 85%. DETAILED DESCRIPTION

[0017] The embodiments of the present application disclose a high transparent paper and a preparation method thereof, to solve the problems of low transparency, poor quality stability, and even unqualified of the existing high transparent paper.

[0018] In order to make the technical solutions and advantages of the embodiments of the present application clearer, the following further describes the exemplary embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0019] The raw materials used in the embodiments are commercially available raw materials without special instructions. The methods in the following embodiments are conventional methods in the art without special instructions.

[0020] The width of the paper machine in the present application is 1880 mm, and the smoothness is the average smoothness of the front surface of the paper and the back surface of the paper.

[0021] The embodiments of the present application provide a preparation method of a high transparent paper, which comprises the processes of full softwood pulp beating, pulp preparation, wet paper sheet making, pressing, drying, wetting, super-calendering, rewinding and packaging, and specifically comprises the following steps:

[0022] S1, beating: 100% bleached kraft pulp is placed in a hydraulic beater for disintegration, and the disintegrated pulp is circulated through three double-disc mills in series for beating, with a beating consistency of 3.8-4.0%, until the beating degree of the pulp is 91±1°SR and the wet weight is 2.0-3.5g, and then pumped to a post-beating pulp tank;

[0023] S2, pulp preparation: the pulp in the post-beating pulp tank is directly pumped to a pulp preparation tank, and 0.8-1.0% by weight of a low-chlorine wet strength agent and 1.2-1.5% by weight of a neutral sizing agent are added to the pulp preparation tank, which is stirred uniformly to obtain a mixed pulp, and the mixed pulp is pumped to a pulp tank and then to a pre-coating tank;

[0024] S3, pulp dilution: the mixed pulp from the pre-coating tank is pumped through a pulp feeding pump, a head tank and a constant flow valve, and then enters a pulp dilution pump, and the mixed pulp is diluted by the pulp dilution pump and then enters a debris remover and a pressure screen in sequence, and 0.02-0.04% by weight of a retention agent is added at the outlet of the pressure screen;

[0025] S4, wet paper sheet making: the mixed pulp after the debris remover is fed to a headbox, and a defoaming agent is added to a white water tank in the headbox, and the amount of the defoaming agent can be adjusted according to the white water foam, and the flow rate is adjusted, and the consistency of the pulp on the wire is 0.17%, and the basis weight of the paper sheet is 28±1g / m 2 , the wire speed is 250-280m / min, the lip opening of the headbox is 9.7mm, and a wet paper sheet is obtained;

[0026] S5, pressing: the wet paper sheet after the wire is subjected to pressing treatment in a compound press section, and the pressure of the first press line is 500kN / m, and the pressure of the second press line is 550kN / m;

[0027] S6, drying: drying is performed by using multiple drying cylinders, and the last drying cylinder through which the wet paper sheet passes is a cold cylinder, and normal temperature water is circulated in the cold cylinder, and the dryness of the paper is 94%;

[0028] S7, winding: the dried paper web is wound to obtain a base paper with a basis weight of 28±1g / m 2 , and the winding tension is 280kN / m;

[0029] S8, base paper wetting: the wound base paper is installed on a drum wetting machine provided with wetting water for single-sided wetting, and after the base paper is wetted, a plastic film is wrapped outside the base paper, and the water balance time is controlled for at least 4 hours, and at the same time, the water content of the paper is controlled to be 20±1%;

[0030] S9, super-calendering: super-calendering is performed by using a super-calender, and when the wetted base paper is subjected to super-calendering, the speed of the super-calender is not higher than 50m / min, and a high transparency paper with a basis weight of 28±1g / m 2 is obtained.

[0031] S10, rewinding and packing.

[0032] In step S4, the combined action of the forming wire and the shaking ensures uniform dispersion of the fibers and ordered arrangement and uniform distribution of the fibers in the longitudinal and transverse directions. In step S6, the last dryer through which the wet paper sheet passes is a cold dryer, which can make the paper have good flatness.

[0033] Further, in step S2, the neutral sizing agent is alkyl ketene dimer AKD.

[0034] Further, in step S3, the type of retention aid is polymin sk.

[0035] Further, in step S6, there are 10 dryers in total. In specific operation, the temperature of the dryers is adjusted and optimized according to the general dryer temperature curve and according to the flatness and drying of the paper, and the last dryer through which the wet paper sheet passes is a cold dryer through which normal temperature clean water flows.

[0036] Further, in step S8, the speed of the wetting machine is 300 m / min.

[0037] Further, in step S8, the wetting water includes 2 kg / ton of paper of oil and water repellent agent for improving the water and oil repellency of the paper.

[0038] Further, in step S9, the speed of the super calender is controlled at 40-50 m / min.

[0039] Specifically, the oil and water repellent agent is OnGuard KST oil and water repellent agent.

[0040] Further, the surface sizing process and soft calendering technology are not used in the production of the base paper. The surface sizing process not only reduces the production cost, but also reduces the steam consumption without affecting the transparency of the paper sheet in the later stage. The soft calendering technology is not used in order to make the water more easily penetrate into the base paper when it is wet, which is helpful for the super calendering of the wet base paper, thereby improving the transparency of the paper sheet.

[0041] Examples 1-3 and Comparative Examples 1-17 were prepared according to the content of each auxiliary and the preparation conditions specified in Tables 1 and 2 below.

[0042] Table 1

[0043]

[0044] The application adds low-chlorine wet strength agent in the pulp mixing tank. On one hand, the low-chlorine wet strength agent forms a staggered chain network structure around the fibers, preventing the fibers from water absorption and swelling to maintain the original fiber combination. On the other hand, the low-chlorine wet strength agent crosslinks with the pulp fibers to form new water-resistant bonds such as covalent bonds and hydrogen bonds, thereby enhancing the fiber combination strength and improving the paper wet strength, which can effectively reduce the wet part paper breakage. Adding neutral sizing agent AKD in the pulp mixing tank can improve the sizing degree and water resistance of the paper, so that the base paper will not absorb a large amount of water when wet, causing excessive wet water and other problems, and can also improve the printing adaptability of the paper. Adding retention agent in the pressure screen outlet pipeline can effectively improve the retention rate of fibers and small particles in the paper machine net part. Adding defoaming agent in the net part white water tank can quickly remove the fine bubbles entrained between the fibers, inhibit the generation of foam, make the paper have better uniformity, and improve the quality of the paper.

[0045] Table 2

[0046]

[0047] As can be seen from Table 2, the difference between Example 1 and Comparative Examples 1 to 5 is that the types and proportions of the pulp are different. As can be seen from the table, as the proportion of bleached kraft softwood pulp increases, the transparency of the paper continuously improves, and only when the pulp is 100% bleached kraft softwood pulp, can the transparency of the paper after super calendering reach more than 85%. The difference between Example 1 and Comparative Examples 6 to 10 is that the beating degree is different. As can be seen from the table, as the beating degree of the pulp increases, the transparency of the paper continuously improves, and only when the beating degree is increased to 91±1°SR, can the transparency of the paper after super calendering reach more than 85%. The difference between Example 1 and Example 3 and Comparative Examples 11 and 12 is that the moisture content of the base paper after wetting is different. As can be seen from the table, after the base paper is wetted, the moisture content increases from 17% to 20%±1, and the transparency of the paper continuously improves. When the moisture content exceeds 21%, although the transparency can reach more than 85%, at this time, the paper pressed by the super calender is easy to collapse, causing the super calender to break paper and the production to be abnormal. As can be seen from the above, during the wetting process of the base paper, the moisture content of the wetting water is 20±1%, which can not only ensure that the transparency of the paper meets the requirements, but also ensure that the production is normal. The difference between Example 1 and Example 2 and Comparative Examples 13 to 17 is the speed of the super calender. As can be seen from the table, as the speed of the super calender gradually decreases, the super pressure time relatively increases, and the transparency of the paper continuously improves. When the speed of the super calender decreases to below 50 m / min, the transparency of the paper can reach 85.5-89, thereby meeting the needs of customers.

[0048] From the above comparison, it can be seen that in the process range claimed in the present application, the transparency of the paper can reach more than 85%. From the above comparative examples, it can be seen that only the change of the pulp, or the change of the beating degree, or the change of the moisture content in the wetting of the base paper, or the change of the speed of the super calender, cannot reach the transparency requirement in the examples, and cannot meet the growing customer demand.

[0049] In summary, the preparation method of the high transparency paper provided in the examples of the present application focuses on improving the transparency of the paper from the aspects of pulp selection, beating process, base paper wetting process, super calendering process, etc. Finally, a high transparency paper with qualified and stable quality, high transparency, environmental protection and easy recycling, and high cost performance is obtained. Among them, the pulp is 100% bleached kraft softwood pulp, and the bleached kraft softwood pulp is selected from Canadian Northwood pulp. The fiber is long and thin, and the paper strength is high, which is beneficial to improve the transparency and evenness of the paper. No filler is added in the papermaking process to ensure that the base paper has high transparency after super calendering. No chemicals containing fluorescent substances are added to ensure that the prepared high transparency paper meets the food grade; the pulp is circularly beaten by three double-disc mills in series, and the beating consistency is controlled at medium-low consistency, which can ensure good cutting effect and better fibrillation of the fiber. The beating degree is controlled at 91±1°SR, and the wet weight is controlled at 2.0-3.5g to ensure good evenness and high transparency of the base paper after super calendering; the base paper is adjusted by the humidifier with wetting water, and the moisture balance time after wetting is controlled at least 4 hours to make the moisture uniform. The moisture content of the paper is controlled at 20±1%, which ensures that the paper is completely wet and improves the transparency of the paper. At the same time, it also improves the intermolecular tension and oil resistance of the paper surface; the super calendering uses a 12-roll super calendering machine with a speed not higher than 50m / min, which can ensure that the transparency of the paper after super calendering reaches more than 85%.

[0050] In order to better understand the essence of the present application, the performance tests of the base paper obtained during the preparation process of the examples and the finally prepared high transparency paper are carried out, and the performance tests are shown in Table 3.

[0051] Table 3

[0052] Item Base paper High transparent paper Quantitative / g / m 2 ]]> 28±1 28±1 Moisture / % 6.0 6.5 Hue Intrinsic white Intrinsic white Fluorescence 84% no fluorescence No fluorescence Longitudinal breaking length / Km 9.8 9.9 Absorbency / g / m 2 ]] 14.6 13.2 Smoothness / S / 1286

[0053] From Table 3, it can be seen that in the process range claimed in the present application, the basis weight of the base paper without wetting and super calendering treatment is 28±1g / m 2 , the moisture is 6.0%, the longitudinal breaking length is 9.8Km, the water absorption is 14.6g / m 2 , the color phase is white, and 84% has no fluorescence. In addition, the paper sheet is uniform and smooth, and the hand feeling is good. The quality indicators of the base paper can meet the expected requirements, and can meet the requirements of the following wetting and super calendering; the basis weight of the prepared high transparency paper is 28±1g / m 2, moisture content is 6.5%, longitudinal breaking length is 9.9 Km, water absorption is 13.2 g / m 2 , smoothness is 1286S, transparency is 86.3%, color is white, and no fluorescence, reaches food grade, in addition, the prepared high transparent paper has good evenness and flatness, and meets the needs of customers.

[0054] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the embodiments by those skilled in the art once they learn of the basic inventive concepts. Therefore, the appended claims are intended to encompass within their scope all such variations and modifications as are included within the scope of the application.

Claims

1. A method for preparing high-transparency paper, comprising the following steps: pulping, beating, mixing, adding auxiliary materials, wet papermaking, pressing, drying, wetting, supercalendering, rewinding, and packaging using whole softwood pulp; characterized in that: (A) Pulp mix ratio: 100% bleached sulfate softwood pulp; (B) Pulping conditions: Three double-disc mills are used for series circulation pulping. The pulp concentration is controlled at a medium to low concentration, with a pulp concentration of 3.8~4.0%, a freeness of 91±1°SR, and a wet weight of 2.0~3.5g. (C) The basis weight of the prepared base paper is 28±1 g / m³. 2 ; (D) Base paper wetting conditions: The prepared base paper is wetted on one side using a roller wetting machine, and the prepared wetting water is added to the roller wetting machine; the wetting water includes 2 kg / ton of oil and water resistant agent; The moisture balance time of the base paper after wetting should be controlled at least 4 hours, and the moisture content of the paper should be controlled at 20±1%. (E) Supercalendering conditions: Use a 12-roll supercalender with a width of 1880mm and a machine speed not exceeding 50m / min, with the machine speed controlled between 40 and 50m / min; (F) The basis weight of the high-transparency paper obtained after supercalendering is 28±1 g / m³. 2 Moisture content is 6.0~7.0%, longitudinal fracture length is ≥8.0km, and water absorption is ≤15g / m³. 2 Smoothness ≥1000S, transparency ≥85%, hue pure white.

2. The method for preparing high-transparency paper according to claim 1, characterized in that, The specific conditions for the process steps also include: (G) The dosage of auxiliary materials for oven-dry slurry is as follows: retention aid 0.02~0.04% by weight, low-chlorine wet strength agent 0.8~1.0% by weight, and neutral sizing agent 1.2~1.5% by weight; (H) Wet paper sheet production conditions: wire speed 250~280m / min, width 1880mm, headbox lip opening 9.7mm; (L) Pressing section conditions: First press line pressure: 500 kN / m, Second press line pressure: 550 kN / m; (M) Drying conditions: Multiple drying cylinders are used for drying, and the last drying cylinder through which the wet paper sheet passes is a cold cylinder, which is filled with room temperature water; (N) Winding conditions: Winding tension: 280kN / m.

3. The method for preparing high-transparency paper according to claim 1, characterized in that, In the pulp formulation (A), the bleached sulfate softwood pulp is Canadian Northwood Pulp.

4. The method for preparing high-transparency paper according to claim 2, characterized in that, In the (G) auxiliary materials for oven-dry slurry usage, the neutral sizing agent is alkyl ketene dimer AKD.

5. The method for preparing high-transparency paper according to claim 2, characterized in that, In the (H) wet paper sheet production conditions, the on-grid concentration is 0.17%.

6. The method for preparing high-transparency paper according to claim 2, characterized in that, In the (M) drying conditions, there are a total of 10 drying cylinders, and the last drying cylinder through which the wet paper sheets pass is the cold cylinder.

7. A highly transparent paper, characterized in that, It is prepared according to any one of claims 1-6.

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