Raw paper for food paperboard, preparation method of raw paper and surface layer slurry

Abstract

The invention provides base paper for food card paper and a preparation method thereof. The surface layer pulp comprises bleached sulfate softwood pulp, bleached sulfate hardwood pulp and finely ground bleached sulfate hardwood pulp, and the proportion of the bleached sulfate softwood pulp is 30 + / -5%, the proportion of the bleached sulfate hardwood pulp is 50-60%, and the proportion of the finely ground bleached sulfate hardwood pulp is 10-20%. According to the surface layer slurry of the body paper for the food paperboard, provided by the embodiment of the invention, on the premise that a production process of the body paper for the food paperboard is not greatly changed, a process of water adhesion of the food paperboard can be improved only by changing and optimizing the proportion of the surface layer slurry, so that the surface layer slurry has a relatively high cup beating yield, and the production cost is reduced. And meanwhile, the requirements of customers on strength, printing and other properties can be met, and the market application prospect is great.

Description

Technical Field

[0001] This application relates to the technical field of papermaking, specifically to a base paper for food-grade cardboard, its preparation method, and surface pulp. Background Technology

[0002] As people's pursuit of a better material life increases, the sales of beverages such as milk tea and coffee are rising, leading to a corresponding increase in market demand for cups and other containers. The manufacturing process for milk tea cups is as follows: 1. Apply a double-sided or back-sided lamination to the corresponding food-grade cardboard; 2. Print the logo on the front and die-cut into cup pieces; 3. Roll the cup pieces into a cylindrical shape using a paper cup forming machine and seal the seams with heat pressing; 4. Seal the separately cut cup bottom to the cup body with heat pressing. However, issues such as bursting, warping, and water adhesion during paper cup manufacturing are major factors contributing to the increased scrap rate. During the manufacturing process, the cup rim needs to be rolled, but the food-grade cardboard has high bending stress, creating significant resistance to this process. Therefore, before paper cup forming, the edges of the cup sheet at the rolled edge need to be moistened (also known as watering or wetting). The core function is to regulate the humidity and flexibility of the cup sheet edges. Controlling the moisture content at the edges to 7.0-9.0% is beneficial for cup forming, stabilizing the cup sheet dimensions, and reducing shrinkage and deformation. However, the moisture content cannot be controlled too high, otherwise it will affect the bonding strength between the paper layers, resulting in problems such as curling and delamination.

[0003] Therefore, without changing the existing cup-making process and cup-making rate, to increase the quantity of finished paper cups, it is necessary to improve the finished product qualification rate and reduce the cup-making scrap rate to achieve the goal of increasing paper cup production. Bursting and curling can be addressed by softening the cup edges with water or optimizing the cup-making process. However, besides the amount of water applied, the surface properties of the paper are a key influencing factor for water adhesion. Therefore, to reduce the probability of water adhesion during cup making, it is necessary to start with the surface properties of the base paper and related sizing processes. However, such process adjustments may affect the printability of the finished paper. Summary of the Invention

[0004] The first aspect of this application provides a surface pulp for food-grade cardboard base paper, the surface pulp comprising: bleached sulfate softwood pulp, bleached sulfate hardwood pulp, and refined bleached sulfate hardwood pulp, wherein the bleached sulfate softwood pulp accounts for 30±5%, the bleached sulfate hardwood pulp accounts for 50-60%, and the refined bleached sulfate hardwood pulp accounts for 10-20%.

[0005] In some optional embodiments, the freeness of the finely milled bleached sulfate hardwood pulp is 200 ± 20 ml.

[0006] In some optional embodiments, the freeness of the bleached sulfate softwood pulp is 360±20 ml, and the freeness of the bleached sulfate hardwood pulp is 390±20 ml.

[0007] Secondly, embodiments of this application provide a method for preparing base paper for food-grade cardboard, the preparation method comprising: Papermaking base paper, wherein the base paper comprises a surface layer, a core layer and a bottom layer stacked in sequence, and the pulp of the surface layer is the surface layer pulp described in the above embodiments; Surface sizing is applied to both opposite sides of the base paper; The base paper, after surface sizing, is then calendered.

[0008] In some optional embodiments, the quantitative amount of the surface layer is 28-36 g / m³. 2 .

[0009] In some optional embodiments, in the step of applying surface sizing to opposite sides of the base paper, the sizing amount on the front side is 2.0 ± 0.4 g / m². 2 .

[0010] In some optional embodiments, in the step of applying surface sizing to opposite sides of the base paper, the viscosity of the sizing solution on the front side is 180-220 cps.

[0011] In some optional embodiments, in the step of applying surface sizing to opposite sides of the base paper, the starch solid content of the sizing solution on the front side is 8.5-10.5%.

[0012] In some optional embodiments, in the papermaking step, the core pulp comprises 55-65% chemimechanical pulp, 10-20% bleached sulfate hardwood pulp, 0-10% bleached sulfate softwood pulp, and 10-30% waste pulp.

[0013] Thirdly, this application provides a base paper for food-grade cardboard, which is prepared using the preparation method described in the above embodiments.

[0014] The surface slurry for food cardboard provided in this application embodiment can improve the water adhesion process of food cards simply by changing the ratio of the surface slurry without making significant changes to the production process of food cardboard base paper. This results in a higher cup-making yield and can meet customers' requirements for strength and printing performance, thus having great market application prospects. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing the base paper for food-grade cardboard according to this application; Figure 2 This is a schematic diagram of the laminated structure of one embodiment of the original paper of this application; Figure 3 This is a schematic diagram of the laminated structure of the base paper for food-grade cardboard after sizing. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0018] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. 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 may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0019] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0020] This application provides a method for preparing base paper for food-grade cardboard. Please refer to [link / reference]. Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the preparation method of the base paper for food-grade cardboard according to this application. The preparation method includes, but is not limited to, the following steps.

[0021] Step S100: Making the original paper.

[0022] Please see Figure 2 , Figure 2 This is a schematic diagram of the stacked structure of a base paper according to an embodiment of the present application. In this embodiment, the base paper includes a surface layer 110, a core layer 120, and a bottom layer 130 stacked sequentially.

[0023] The surface layer pulp includes: bleached sulfate softwood pulp (NBKP), bleached sulfate hardwood pulp (LBKP), and finely ground bleached sulfate hardwood pulp. The bleached sulfate softwood pulp accounts for 30±5%, with specific percentages of 25%, 26%, 28%, 30%, 32%, 35%, etc.; the bleached sulfate hardwood pulp accounts for 50-60%, with specific percentages of 50%, 51%, 52%, 54%, 55%, 58%, 60%, etc.; and the finely ground bleached sulfate hardwood pulp accounts for 10-20%, with specific percentages of 10%, 12%, 15%, 17%, 18%, 20%, etc.

[0024] Optionally, the freeness of refined bleached sulfate hardwood pulp is 200±20ml, the freeness of bleached sulfate softwood pulp is 360±20ml, and the freeness of bleached sulfate hardwood pulp is 390±20ml. The freeness of refined L-pulp (bleached sulfate hardwood pulp) is controlled at 200±20ml. This utilizes its higher degree of fibrillation and shorter fibers to fill the larger voids generated during molding, enhancing interlayer bonding strength while controlling the pore size of the surface layer. This helps reduce the surface sizing solids content or viscosity, allowing for more uniform penetration of surface starch and ensuring the printing strength of the paper.

[0025] Optionally, in this embodiment, the quantitative amount of the surface layer is 28-36 g / m³. 2 Specifically, it can be 28g / m 2 29g / m 2 30g / m2 32g / m 2 33g / m 2 35g / m 2 36g / m 2 Equal values.

[0026] In this embodiment, the core pulp comprises 55-65% chemimechanical pulp, 10-20% bleached sulfate hardwood pulp, 0-10% bleached sulfate softwood pulp, and 10-30% waste pulp. The proportions of the bottom layer pulp will be shown in the tables in subsequent specific embodiments.

[0027] Please refer to 1. In this embodiment, the preparation method of the base paper for food cardboard also includes step S200, which involves applying sizing to the surfaces of the base paper on both sides.

[0028] Please see Figure 3 , Figure 3 This is a schematic diagram of the laminated structure of the base paper for food-grade cardboard after sizing. In the diagram, 210 represents the front sizing layer, and 220 represents the back sizing layer. Optionally, the sizing amount of the front sizing layer 210 is 2.0 ± 0.4 g / m². 2 Specifically, it can be 1.6g / m 2 1.8g / m 2 2.0g / m 2 2.2g / m 2 2.3g / m 2 and 2.4g / m 2 Equal values.

[0029] Optionally, the viscosity of the top-side sizing agent in this embodiment is 180-220 cps, specifically 180 cps, 190 cps, 195 cps, 200 cps, 210 cps, 220 cps, etc. The starch solid content of the top-side sizing agent is 8.5-10.5%, specifically 8.5%, 8.6%, 9%, 9.5%, 9.8%, 10.0%, 10.2%, 10.5%, etc.

[0030] The preparation process of surface-sizing starch is one of the important factors affecting the printing performance of paper. However, the higher the solid content of the surface-sizing starch, the less effective its penetration becomes, resulting in a relatively larger amount of starch remaining on the paper surface. This leads to more severe water absorption and sticking of food cards during cupping, thus increasing cupping losses. Therefore, to ensure the printing performance of paper, it is necessary to increase or maintain the viscosity of the sizing starch, reduce the solid content and amount of sizing, decrease the actual starch content on the paper surface, and prevent water absorption and sticking caused by excessive water absorption.

[0031] The back adhesive layer 220 has a back adhesive application rate of 1.8-2.0 g / m². 2 In this embodiment, the ash content of the base paper used for food-grade cardboard is controlled at 10-13%. The TV16 of the front side of the food-grade cardboard base paper is controlled to be ≥1.0 times for simulated offset printing, and the interlayer bonding strength is ≥200 J / m. 2 .

[0032] Please refer to 1. In this embodiment, the preparation method of the base paper for food cardboard also includes step S300, which involves calendering the base paper after surface sizing.

[0033] In step S300, the calendering pressure is controlled to be ≥40KN / m, specifically ranging from 40KN / m to 60KN / m, such as 40KN / m, 42KN / m, 45KN / m, 48KN / m, 50KN / m, 55KN / m, 58KN / m, and 60KN / m. The hot roller temperature is controlled between 180-200℃, specifically 180℃, 185℃, 188℃, 190℃, 195℃, 197℃, and 200℃. The function of hard calendering is to control the paper thickness and improve the uniformity of the paper's width. When the calendering pressure is higher, the uniformity of the paper's width is relatively better, which is beneficial to improving the paper's smoothness. The increase in the hot roller temperature also plays a complementary role.

[0034] This invention improves the adhesion problem of food cardboard during cup making without affecting its strength or printing quality, thereby increasing the yield of finished cups. Therefore, the production process of the food cardboard base paper cannot be significantly adjusted; instead, the sizing process and its effect can be optimized to reduce the scrap rate caused by cup adhesion during cup making.

[0035] The following will introduce several specific comparative embodiments to illustrate the technical effects of the technical solution of this application.

[0036]

[0037] The above comparison shows that adding refined LBKP to the surface layer enhances the strength indicators of the paperboard, such as IGT, TV16, and interlayer bonding, and also prevents the paper from sticking together after water application. However, as the proportion of refined LBKP increases further, the paper begins to stick together after 1 minute of water application, indicating that the addition of 30% refined LBKP is too high and not conducive to improving water application and sticking. Therefore, it is necessary to control the amount of refined LBKP added.

[0038] The following table compares the effects of adhesive penetration.

[0039]

[0040] As can be seen from the comparison between Examples 4 and 5 above, increasing the viscosity of the sizing starch and reducing its solid content can significantly improve the penetration effect of the sizing starch, thereby improving the sizing effect and contributing to the improvement of paper strength.

[0041]

[0042] As can be seen from the comparison of Examples 6-10 above, increasing the viscosity of the sizing starch and reducing the sizing solids content significantly improves IGT and TV16 (comparison between Examples 6 and 7), and also significantly improves water adhesion. After reducing the sizing amount (comparison between Examples 8, 9 and 10), IGT and TV16 show a slight decrease, but there is no obvious water adhesion phenomenon, which can reduce the cost per ton of paper. In addition, the effect of adding an appropriate proportion of fine grinding LBKP to the surface layer is even better in improving paper strength and improving water adhesion.

[0043] The technical solution of this application is a process to improve the adhesion of food cards when water is applied. The key technical problem to be solved is that when water is applied to the coated cups, the uncoated surface or edges of the paper absorb water, causing the paper edges to swell or the starch on the surface to absorb moisture, making the adjacent cups more tightly contacted. When water is then applied, the cups stick together, affecting the operation and cupping speed when the cups are being processed.

[0044] The method for preparing the base paper for food-grade cardboard in this application improves the adhesion phenomenon when food cards are used to make cups, without affecting their strength and printing quality, thereby increasing the yield of finished cups. Therefore, the production process of the food-grade cardboard base paper cannot be significantly adjusted; instead, the sizing process and sizing effect can be optimized to reduce the scrap rate caused by cup adhesion during cup making.

[0045] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A surface layer pulp for a base paper used in food-grade cardboard, characterized in that, The surface slurry includes: bleached sulfate softwood pulp, bleached sulfate hardwood pulp and finely ground bleached sulfate hardwood pulp, wherein the bleached sulfate softwood pulp accounts for 30±5%, the bleached sulfate hardwood pulp accounts for 50-60%, and the finely ground bleached sulfate hardwood pulp accounts for 10-20%.

2. The surface slurry according to claim 1, characterized in that, The freeness of the finely ground bleached sulfate hardwood pulp is 200±20 ml.

3. The surface slurry according to claim 1, characterized in that, The freeness of the bleached sulfate softwood pulp is 360±20ml, and the freeness of the bleached sulfate hardwood pulp is 390±20ml.

4. A method for preparing base paper for food-grade cardboard, characterized in that, The preparation method includes: Papermaking base paper, wherein the base paper comprises a surface layer, a core layer and a bottom layer stacked in sequence, and the pulp of the surface layer is the surface layer pulp as described in any one of claims 1-3; Surface sizing is applied to both opposite sides of the base paper; The base paper, after surface sizing, is then calendered.

5. The preparation method according to claim 4, characterized in that, The quantitative amount of the surface layer is 28-36 g / m³. 2 .

6. The preparation method according to claim 4, characterized in that, In the step of applying sizing to the opposite sides of the base paper, the sizing amount applied to the front side is 2.0 ± 0.4 g / m². 2 .

7. The preparation method according to claim 6, characterized in that, In the step of applying sizing to the opposite sides of the base paper, the viscosity of the sizing solution on the front side is 180-220 cps.

8. The preparation method according to claim 7, characterized in that, In the step of applying surface sizing to opposite sides of the base paper, the starch solid content of the sizing solution on the front side is 8.5-10.5%.

9. The preparation method according to claim 4, characterized in that, In the papermaking process, the core pulp comprises 55-65% chemimechanical pulp, 10-20% bleached sulfate hardwood pulp, 0-10% bleached sulfate softwood pulp, and 10-30% waste pulp.

10. A base paper for food-grade cardboard, characterized in that, The base paper is prepared using the preparation method described in any one of claims 4-9.

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