Process method for improving back smoothness of coated ivory board and ivory board thereof

Abstract

The invention provides a process method for improving the smoothness of the back surface of a coated ivory board and the ivory board. The process method comprises the following steps: controlling the particle size grade of calcium carbonate in the back coating to be greater than or equal to C70; and the mass fraction of the latex in the back coating is controlled to be 5-7%. According to the process method for improving the back smoothness of the coated ivory board provided by the embodiment of the invention, the effect of improving the back smoothness is finally achieved by optimizing the freeness of the bottom layer slurry, the ratio of the NBKP slurry, the moisture before hard pressing, the particle size of coating calcium carbonate, the number of latex parts and the like at the same time.

Description

Technical Field

[0001] The present application relates to the technical field of papermaking, and in particular to a process for improving the smoothness of the back side of coated white cardboard and the white cardboard. Background Art

[0002] For white cardboard with both front and back coated, if the back side is not smooth enough, when the paper is cut, the back side of the paper will rub against the front side, which will cause light spots on the front side and cause poor printing. How to improve the back side smoothness to avoid the impact of the rough back side on the front side has become a technical problem that needs to be solved urgently. Summary of the invention

[0003] The first aspect of the embodiment of the present application provides a process method for improving the smoothness of the back side of coated white cardboard, the process method comprising: controlling the particle size grade of calcium carbonate in the back side coating to be greater than or equal to C70; controlling the mass fraction of latex in the back side coating to be 5-7%.

[0004] In some optional embodiments, the mass fraction of latex in the back coating is controlled to be 6±0.5%.

[0005] In some optional embodiments, the process further includes controlling the back coating amount to 21-22 g / m 2 .

[0006] In some optional embodiments, the process method further includes controlling the dynamic water retention time of the back coating to be less than or equal to 600 seconds.

[0007] In some optional embodiments, the process further comprises controlling the freeness of the bottom pulp, wherein the NBKP freeness is 360±10 ml.

[0008] In some optional embodiments, the LBKP freeness is controlled to be 370±10ml.

[0009] In some optional embodiments, the process method further comprises controlling the slurry proportion of NBKP to be 10±5%.

[0010] In some optional embodiments, the process further comprises increasing the moisture content of the paper product to 10-11% before entering the hard matte finish.

[0011] In some optional embodiments, the process method further comprises controlling the temperature of the hard pressing hot roller to be 100±10° C. and the hard pressing linear pressure to be 14-15 kN / m.

[0012] In a second aspect, an embodiment of the present application provides a white cardboard, which is prepared by the process method described in the above embodiment.

[0013] The process method for improving the smoothness of the back side of coated white cardboard provided in the embodiment of the present application is achieved by simultaneously optimizing the freeness of the bottom slurry and the NBKP slurry ratio, the moisture before hard pressing, the particle size of calcium carbonate in the coating and the amount of latex, thereby ultimately achieving the effect of improving the smoothness of the back side. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 It is a schematic diagram of a laminated structure of a coated white cardboard in the present application;

[0016] Figure 2 This is a schematic diagram comparing the silk saponification of slurry at different freeness levels;

[0017] Figure 3 is a graph of moisture, temperature and pressure during hard calendering in an embodiment of the present application;

[0018] Figure 4 It is a structural schematic diagram of the cross-section comparison of uncoated base paper. DETAILED DESCRIPTION

[0019] The present application is further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present application, but are not intended to limit the scope of the present application. Similarly, the following examples are only some embodiments of the present application rather than all embodiments, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0020] The terms "first", "second", and "third" in the embodiments of the present application are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second", and "third" can expressly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the embodiments of the present application, all directional indications (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. The terms "including" and "having" in the embodiments of the present application and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or components inherent to these processes, methods, products, or devices.

[0021] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] In the past production process, we found that the back smoothness is not affected by a single factor, which also increases the difficulty of improving the back smoothness. The bottom slurry ratio, freeness, coating calcium carbonate particle size and latex content, paper web moisture content before hard calendering and other processes all have a certain impact on the back smoothness.

[0023] ① The particle size of calcium carbonate in the back coating is relatively coarse;

[0024] ②The amount of latex in the back coating is too low;

[0025] ③The freeness of the bottom slurry is too high and the NBKP ratio is too large;

[0026] ④ The moisture content of the paper web before hard calendering is too low.

[0027] See also Figure 1 , Figure 1It is a schematic diagram of the laminated structure of a coated white cardboard in this application. Among them, the label 101 in the figure represents the core layer, the label 102 represents the surface layer, the label 103 represents the bottom layer, the label 104 represents the front sizing layer, the label 105 represents the back sizing layer, the label 106 represents the front coating layer, and the label 107 represents the back coating layer.

[0028] Specifically, the process method in the embodiments of this application mainly optimizes the freeness of the bottom layer pulp, the ratio of NBKP pulp, the moisture before entering the hard press, the particle size of the coating calcium carbonate, and the amount of latex simultaneously, and finally achieves the purpose of improving the back smoothness.

[0029] When the particle size grade of calcium carbonate used in the back coating layer 107 is only ground to C55, the maximum particle size reaches 10 μm; when the calcium carbonate grade is ground to C70, the maximum particle size is only 6 μm. The smaller the particle size grade in calcium carbonate, the smaller the large particle size, which can make the back coating more delicate, reduce the friction on the front coating, and effectively avoid the generation of front surface spots.

[0030] The process method in this embodiment: the particle size grade of calcium carbonate in the back coating is increased from C55 in the conventional technical solution to above C70, such as numerical values like C70, C90, C98, etc.

[0031] Latex plays a very important role in the coating of the back coating layer 107. It has a significant impact on the performance of the coating. Increasing the amount of latex can improve the smoothness. The greater the amount of latex in the coating, the higher the smoothness of the coating film usually is. The principle is mainly based on the following points:

[0032] ① Film-forming performance: Latex is one of the film-forming substances of water-based coatings. Increasing its content helps to form a more continuous and uniform coating film. Latex particles polymerize and form a continuous film during the drying process. The higher the content, the stronger the ability to polymerize and form a smooth film;

[0033] ② Levelling property: With a high latex content, the coating has better levelling property during coating. Good levelling property means that the coating can be more evenly distributed on the substrate surface, reducing the depressions and protrusions in the coating layer, thereby improving the smoothness of the coating film;

[0034] ③ Reducing shrinkage: The coating will shrink during the drying process. Excessive shrinkage will cause cracks and depressions in the coating film. The coating with a high latex content shrinks less during drying, so the coating film is smoother;

[0035] ④ Filling effect: Latex particles play a filling role in the coating film, and can fill into the tiny pores between pigment particles and the substrate surface, reducing the roughness of the coating film;

[0036] ⑤Reduce pigment agglomeration: Latex helps stabilize pigment dispersion and reduce pigment particle agglomeration, so that after the coating dries, the pigment distribution is more even and the coating surface is smoother.

[0037] Although increasing the amount of latex can improve the smoothness of the coating, there is also an optimal amount. Excessive use of latex may lead to a decrease in other properties of the coating, such as mechanical properties, water resistance, etc., and will also increase costs.

[0038] The comparison of the physical properties of the back coating is shown in the following table:

[0039]

[0040] As the amount of latex increases, the dynamic water retention becomes better, and other properties of the coating are not much different. As the amount of latex increases, the coating retains water too well, which can easily lead to the coating not being able to be dried when the cloth is dried, and will also lead to increased costs.

[0041] Optionally, in the process method of the embodiment of the present application, the coating amount on the back side is 21-22 g / m 2 The dynamic water retention time of the back coating is less than or equal to 600s, so as to ensure that the coating does not carry material. In the process method in the embodiment of the present application: the mass fraction of latex is increased from 4.0% in the conventional technical solution to 5-7%, and in some embodiments, it can be specifically 6±0.5%.

[0042] Another thing is to optimize the freeness of the NBKP / LBKP slurry of the bottom layer 103

[0043] ① The slurry freeness is beaten in the laboratory, and the parameters are shown in the following table.

[0044]

[0045] According to laboratory pulping, as the freeness decreases, the folding times of NBKP and LBKP increase, and the dynamic water filtration also deteriorates. If the dewatering capacity of the paper machine is sufficient, the freeness can be reduced for reinforcement.

[0046] The process method in the embodiment of the present application: the freeness of NBKP is reduced from 400 in the conventional technical solution to 360±10ml, the freeness of LBKP is reduced from 390 in the conventional technical solution to 370±10ml, and the proportion of NBKP in the slurry of the bottom layer 103 is reduced from 20 in the conventional technical solution to 10±5%.

[0047] Comparison of silk saponification of slurry at different freeness Figure 2 As shown, Figure 2 This is a schematic diagram comparing the saponification of pulp at different freeness levels.

[0048] Microscopic observation shows that NBKP pulp fibers are coarser than LBKP pulp fibers. In addition, as the freeness decreases, the silk saponification of NBKP and LBKP becomes better. Under the condition of satisfying the dehydration of the paper machine, the freeness is reduced for reinforcement, and under the condition of maintaining the same folding resistance of the finished paper, the proportion of NBKP addition is reduced, the amount of crude fiber used in the bottom layer is reduced, and the smoothness of the back surface is further improved.

[0049] Lifting into hard calendering moisture test. See Figure 3 , Figure 3 It is a curve diagram of moisture, temperature and pressure during hard calendering in the embodiment of the present application. When other processes remain unchanged, the process method in the embodiment of the present application controls the temperature of the hard calendering hot roller to 100±10℃, the hard calendering line pressure to 14-15kN / m, and the moisture before hard calendering is increased from the original 9.0-10.0% to 10.0-11.0%.

[0050] Uncoated base paper cross section comparison Figure 4 As shown, Figure 4 It is a structural schematic diagram of the cross-section comparison of uncoated base paper.

[0051] The cross-section was analyzed and compared using an electron microscope (150 times), and the bottom fiber layer was denser and smoother at 10.7% moisture than at 9.1% moisture.

[0052] The specific implementation cases of this application are shown in the following table.

[0053]

[0054] Adjustment test time points for each plan in 2024:

[0055] ① January 8: NBKP / LBKP freeness decreased from 400 / 390 to 360 / 370 (±10) ml;

[0056] ② February 3: The NBKP ratio in the primer was reduced from 20% to 10%;

[0057] ③ March 15: The particle size grade of calcium carbonate in the back coating was increased from C55 to C70;

[0058] ④ April 12: The latex content in the back coating increased from 4% to 5%; May 2: The latex content in the back coating increased from 4% to 5%;

[0059] ⑤ On July 8, the moisture content of hard calendering increased from 9.0-10.0% to 10.0-11.0%;

[0060] After the above adjustment and testing on July 8, 2024, the back BEKK smoothness was improved from 13~14s to 26~27s.

[0061] The process method for improving the smoothness of the back side of coated white cardboard provided in the embodiment of the present application optimizes the bottom slurry freeness and NBKP slurry ratio, the water content before hard pressing, the particle size of calcium carbonate in the coating, and the number of latex, thereby ultimately achieving the effect of improving the smoothness of the back side. With this process method, since the smoothness of the back side is greatly improved, the light spot problem caused by friction on the front side is completely eliminated when the paper is stacked and cut, which greatly improves the product quality and reduces the customer complaint rate caused by the above problem to zero.

[0062] The above descriptions are only some embodiments of the present application, and do not limit the protection scope of the present application. Any equivalent device or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A process for improving the smoothness of the back side of coated white cardboard, characterized in that: The process method comprises: controlling the particle size of calcium carbonate in the back coating to be greater than or equal to C70; and controlling the mass fraction of latex in the back coating to be 5-7%.

2. The process according to claim 1, characterized in that: The mass fraction of latex in the back coating is controlled to be 6±0.5%.

3. The process according to claim 1, characterized in that: The process also includes controlling the back coating amount to 21-22 g / m 2 .

4. The process according to claim 1, characterized in that: The process method also includes controlling the dynamic water retention time of the back coating to be less than or equal to 600 seconds.

5. The process according to claim 1, characterized in that: The process also includes controlling the freeness of the bottom pulp, wherein the NBKP freeness is 360±10 ml.

6. The process according to claim 5, characterized in that: Control the LBKP freeness to 370±10ml.

7. The process according to claim 5, characterized in that: The process method also includes controlling the slurry proportion of NBKP to be 10±5%.

8. The process according to claim 5, characterized in that: The process also includes increasing the moisture content of the paper product to 10-11% before entering the hard matte finish.

9. The process according to claim 8, characterized in that: The process method also includes controlling the temperature of the hard pressing hot roller to be 100±10° C. and the hard pressing linear pressure to be 14-15 kN / m.

10. A white cardboard, characterized in that: The white cardboard is prepared by the process method described in any one of claims 1 to 9.

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