Paper product and method for controlling volatile organic compounds in production process of paper product

Abstract

The invention provides a paper product and a control method for volatile organic compounds in the production process of the paper product. The control method comprises the following steps: the pH value of the mechanical pulp is adjusted to 6.0-7.5 by using an acidic material, and the concentration of the adjusted mechanical pulp is 3.0-5.0%. According to the method for controlling the volatile organic compounds in the paper product production process provided by the embodiment of the invention, the content of the volatile organic compounds in the paper pulp can be effectively reduced by controlling the pH value range of the mechanical pulp, so that the amount of the volatile organic compounds in a finished paper product is reduced; the method has the characteristics of low cost, convenience in operation, small change in the papermaking process and the like.

Description

Technical Field

[0001] The present application relates to the technical field of papermaking, and in particular to a paper product and a method for controlling volatile organic compounds in a production process thereof. Background Art

[0002] Since most volatile organic compounds (VOCs) have varying degrees of harmful effects on the environment and human health, some packaging materials have formulated regulations on the VOC limits allowed in various products, especially cigarette rod and box packaging materials. The production of most tobacco packaging materials is inseparable from printing, and its printing methods cover a variety of processes such as gravure printing, offset printing, screen printing, and flexographic printing. In addition to the VOCs that remain in the packaging materials due to ink, fountain solution, car wash water, etc. during the printing process, the VOC content of the base paper of the cigarette pack itself will also have a great impact on the VOC content of the printed product.

[0003] Since VOC in cigarette packs mainly comes from the back-end printing process, such as the volatilization of solvent-based inks, alcohol-based inks, and diluents used in gravure printing products, and fountain solutions and car wash water used in offset printing products, the existing technology mainly focuses on the research of the printing section, such as low-VOC inks, low-VOC organic solvents, fountain solutions, etc. At present, there are few technologies that study which factors will affect the VOC content of base paper and how to produce paperboard with low VOC content. Summary of the invention

[0004] A first aspect of an embodiment of the present application provides a method for controlling volatile organic compounds in a paper production process, the control method comprising: using an acidic substance to adjust the pH value of mechanical pulp to a range of 6.0 to 7.5, wherein the concentration of the mechanical pulp after adjustment is 3.0 to 5.0%.

[0005] In some optional embodiments, the control method further comprises: using an acidic substance to adjust the pH of the mixing tank and the paper machine pulp tank to be within the range of 7.0 to 8.0.

[0006] In some optional embodiments, the acidic substance includes any one of acetic acid, citric acid, sulfuric acid, and aluminum sulfate, or a combination of more than one thereof.

[0007] In some optional embodiments, the control method further comprises: in the hard calendering stage, the hard calendering temperature is controlled at 120-180° C.; and the pressure is controlled at 50-60 kN / m.

[0008] In some optional embodiments, the control method further comprises: during the coating stage, controlling the volatile organic compound content in the coating latex to be no greater than 30 ppm.

[0009] In some optional embodiments, during the coating and drying stage, a drying method combining infrared light and a hot air box is used.

[0010] In some optional embodiments, the control method further comprises: in the soft calendering stage, the temperature of the soft calendering is controlled at 80-120° C., and the line pressure is 20-40 kN / m.

[0011] In some optional embodiments, after soft calendering, the paper product is cooled by a cooling device so that the paper product winding temperature is less than or equal to 52°C.

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

[0013] In some optional embodiments, the paper product includes a surface layer, a surface lining layer, a core layer and a bottom layer stacked in sequence; wherein the fiber ratio of the surface layer, the surface lining layer and the bottom layer is: 12-20% of coniferous wood bleached chemical pulp, 80-88% of hardwood bleached chemical pulp; the fiber ratio of the core layer is: 30-50% of hardwood bleached chemical pulp; 40-60% of chemical mechanical pulp; and 0-20% of damaged pulp.

[0014] The method for controlling volatile organic compounds in the paper production process provided in the embodiment of the present application can effectively reduce the content of volatile organic compounds in the pulp by controlling the pH value range of the mechanical pulp, thereby reducing the amount of volatile organic compounds in the finished paper product. This method has the characteristics of low cost, easy operation and small changes in the papermaking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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 paying any creative work.

[0016] Figure 1 It is a schematic diagram of the production process structure of the paper product of the present application;

[0017] Figure 2 It is a schematic diagram of the stacking structure of an embodiment of the paper product of the present application. DETAILED DESCRIPTION

[0018] 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.

[0019] 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.

[0020] 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.

[0021] According to research, the VOC components in cigarette pack (base) paper are mainly methanol, xylene, toluene, etc. Among them, methanol has the highest content. How to reduce the methanol content in the production process, thereby reducing the VOC content in cigarette pack base paper, is the main technical problem solved by the present invention. The fiber raw materials account for 70-80% of the paperboard components, which mainly include bleached chemical pulp and chemical-mechanical pulp. In the pulping process, the bleaching and delignification process of wood chips will produce a certain amount of methanol more or less. In addition, in order to ensure the box-making effect, the cigarette pack base paper requires a higher bulk thickness, generally 1.3-1.5, and the mechanical pulp content accounts for 50% or more of the total fiber amount. Compared with bleached chemical pulp, chemical-mechanical pulp contains relatively more lignin. In the subsequent papermaking process, the methoxyl group in lignin is broken and removed due to alkalinity, high temperature and other conditions, and some methanol is still easily produced. In addition, the VOC content of latex, the main component of the coating, will also affect the VOC content of the finished paper.

[0022] The production method of low-VOC paper products in the embodiments of the present application mainly includes the following aspects: selection and processing of raw materials, control of system conditions during the production process, and selection and parameter control of equipment.

[0023] Generally speaking, the initial VOC (mainly methanol) content in the raw material has a great influence on the VOC (mainly methanol) content of the final paper. The higher the lignin content and VOC content in the raw material, the higher the VOC of the finished paper. When the VOC content of the raw material (mainly methanol) is low, there is a large space for controlling the system conditions of the production process, as well as the selection and parameter control of the equipment. When faced with a high VOC (mainly methanol) content in the raw material, the control method of the present invention is as follows.

[0024] See also Figure 1 , Figure 1 It is a schematic block diagram of the production process structure of the paper product of the present application, wherein the production process includes but is not limited to the following process nodes or equipment: mechanical pulp 101, bleached coniferous chemical pulp 102, bleached broadleaf chemical pulp 103, mixing tank 104, paper machine pulp tank 105, headbox 106, pressing section 107, pre-drying 108, sizing 109, post-drying 110, hard calendering 111, coating 112, drying 113, soft calendering 114, cooling cylinder, cold air box 115 and paper reel 116.

[0025] The control method in the embodiment of the present application is mainly carried out from the following aspects.

[0026] 1. pH control: Use acidic substances to adjust the pH value of mechanical pulp to the range of 6.0 to 7.5. The specific values ​​of the pH value can be 6.0, 6.1, 6.5, 6.8, 7.0, 7.2, 7.5, etc. The acidic substances include any one or a combination of acetic acid, citric acid, sulfuric acid, and aluminum sulfate. The concentration of the mechanical pulp after adjustment is 3.0 to 5.0%. Among them, sulfuric acid, acetic acid, and citric acid need to be prepared into a concentration of 3 to 6% or added by online dilution, and aluminum sulfate can be added as a stock solution. The pH of the clean water is controlled at 6.0 to 7.5, and the pH of the mixing tank 104 and the paper machine pulp tank 105 is controlled at 7.0 to 8.0. If the pH of the mixing tank and the paper machine pulp tank is too high, a certain amount of acetic acid, sulfuric acid, and aluminum sulfate should be added to the mixing tank to ensure that the core layer head box is 7.0-8.0, specifically 7.0-7.5, that is, the pH of the white water circulating in the system can also be stably controlled between 7.0 and 8.0. The various fiber raw materials are mixed in the mixing tank from the pulp storage tower, and then to the paper machine pulp tank, and diluted to a concentration of 0.9-1.8% by the pulp pump and white water to the headstock box for composite molding. After pressing, drying, sizing and drying on the front and back sides. The pH is controlled here mainly because if the pH is too high, the lignin content in the pulp, especially the mechanical pulp, is high. Under alkaline conditions, the methoxyl group and the hydroxide ion in the lignin structure react to produce methanol; if the pH is too low, it will affect the strength of the pulp and the use effect of some chemicals.

[0027] 2. In the hard calendering 111 stage, the hard calendering temperature is controlled at 120-180°C, and can be specifically 120°C, 125°C, 130°C, 150°C, 165°C, 170°C, 172°C, 180°C and other values. The pressure is controlled at 50-60kN / m. Specifically, it can be 50kN / m, 51kN / m, 52.5kN / m, 54kN / m, 55kN / m, 56kN / m, 58kN / m, 60kN / m and other values. The purpose of controlling the hard calendering temperature and pressure is to achieve a better calendering effect, compact the paper, and reduce the voids inside the paper, which can reduce the diffusion rate of water vapor and oxygen in the paper, thereby reducing the possibility of methanol generation.

[0028] 3. During the coating 112 stage, the latex, which accounts for a relatively large proportion of the coating, controls the VOC content to ≤30ppm.

[0029] 4. Temperature control: High temperature can increase the reaction rate of methoxyl groups in lignin under alkaline conditions, thus facilitating the production of methanol. In the drying process 113 after coating, a combination of IR (infrared light) and hot air oven is used to dry the coating quickly and reduce the temperature of the paper. After coating and drying, soft calendering 114 is performed. The soft calendering temperature is generally 80-120°C, and can be specifically 80°C, 85°C, 90°C, 100°C and 120°C. Line pressure is 20-40 kN / m, and can be specifically 20 kN / m, 25 kN / m, 28 kN / m, 30 kN / m, 33 kN / m and 40 kN / m.

[0030] Generally, the temperature of the paper after soft calendering is 70-80℃, and 4-6 cold cylinders or 3-5 groups of cold air boxes need to be installed after soft calendering. The temperature of each cold cylinder is set to ≤40℃, generally 35-40℃. The temperature of the cold air box is 0-30℃, and the temperature of the cold cylinder or cold air box is ≤55℃. The cold air box has the best effect, because the surface is easily exposed when the temperature of the cold cylinder is low, which causes the paper to get damp and easily cause adhesion problems. The winder adopts a steel winder with cooling water inside. The water temperature is set at 30-35℃ to reduce the temperature of the paper during the winding process, and the final temperature of the paper machine is controlled to be ≤52℃. The reason for controlling the temperature of the paper: During the storage of paper, the methoxyl group in the lignin may still break due to oxidation reaction in the presence of oxygen and certain temperature and humidity conditions to produce methanol, especially inside the paper roll, where the paper temperature is high.

[0031] Through the selection and processing of the above raw materials, the control of the production process system conditions, and the selection and parameter control of the equipment, the final paper products produced have a total VOC content of ≤0.8ppm after leaving the machine and rewinding, of which the methanol content is ≤0.5ppm.

[0032] Several specific embodiments of the present application are shown in the following table. In the following embodiments, a four-layer fourdrinier paper machine with a speed of 1080 m / min, a mechanical pulp concentration of 3.8%, a raw pulp pH of 7.5-8.0, and a clear water pH of 6.8-7.2 are used as an example of system pH control using citric acid as an acidic substance.

[0033]

[0034]

[0035] From the above comparison, we can see that in Comparative Scheme 1, when the methanol content of mechanical pulp raw material is high, the system pH and paper temperature are high, the methanol content of cigarette pack (base) paper reaches 1.29ppm, and after being placed for 1 month (sealed with coated kraft paper), the methanol content reaches 2.79ppm. The general market requires that the methanol content of cigarette pack base paper should be controlled below 1ppm, and a very small part can be relaxed to 1.5ppm.

[0036] Example 1: When the methanol content of mechanical pulp raw material is low, the system pH is high, and the paper temperature is controlled at ≤52°C, the methanol content of cigarette pack paper can be reduced to less than 1.0ppm, and after being placed for 1 month (sealed with coated kraft paper), the methanol content is 1.23ppm.

[0037] Example 2: When the methanol content of the mechanical pulp raw material is high, by controlling the pH of the system and the paper temperature to ≤52°C, the methanol content of the cigarette pack base paper can be as low as 0.58ppm. After being placed for 1 month (sealed with coated kraft paper), the methanol content is 0.73ppm.

[0038] In Example 3, the methanol content of the mechanical pulp raw material is low. By controlling the pH of the system and controlling the paper temperature to ≤52°C, the methanol content of the cigarette pack base paper is 0.32ppm. A lower methanol content can be achieved, and after being placed for 1 month (sealed with coated kraft paper), the methanol content is 0.4ppm.

[0039] The method for controlling volatile organic compounds in the paper production process in the embodiment of the present application studies the technical points of each section through the selection and processing of raw materials, the control of system conditions in the production process, and the selection and parameter control of equipment, and provides a production method for producing low-VOC paperboard that is practical and operable. This method is not only applicable to cigarette pack (base) paper, but also to other paperboards with higher VOC requirements. The total VOC content of paperboard produced using this method can be lower than 0.8ppm, and the methanol content can be lower than 0.5ppm.

[0040] The method for controlling volatile organic compounds in the paper production process provided in the embodiment of the present application can effectively reduce the content of volatile organic compounds in the pulp by controlling the pH value range of the mechanical pulp, thereby reducing the amount of volatile organic compounds in the finished paper product. This method has the characteristics of low cost, easy operation and small changes in the papermaking process.

[0041] In addition, the present application also provides a paper product, which can be used in packaging paper with strict requirements on VOC, such as cigarette packaging paper. Figure 2 , Figure 2 : is a schematic diagram of the stacking structure of an embodiment of the paper product of the present application. The paper product in this embodiment may include a surface layer 201, a surface lining layer 202, a core layer 203 and a bottom layer 204 stacked in sequence. Optionally, the fiber ratio of the surface layer 201, the surface lining layer 202 and the bottom layer 204 in this embodiment may be: 12-20% of coniferous wood bleached chemical pulp, 80-88% of hardwood bleached chemical pulp; the fiber ratio of the core layer 203 may be: 30-50% of hardwood bleached chemical pulp; 40-60% of chemical mechanical pulp; 0-20% of damaged paper pulp. Among them, the paper product in this embodiment may be prepared by the method in the aforementioned embodiment. For the preparation process of the paper product, please refer to the description of the aforementioned embodiment, which will not be repeated here. In addition, other parameter characteristics of the paper product may be conventional selections, which are within the scope of understanding of those skilled in the art and will not be repeated here.

[0042] It should also be noted that this embodiment only illustrates a four-layer stacked paper product solution. In some other embodiments, the paper product can also have other stacked numbers (such as three layers, five layers, and multiple layers, etc.), which will not be listed and described in detail here.

[0043] The paper product provided in the embodiment of the present application can reduce the content of volatile organic compounds during the preparation process, thereby enabling the paper product to meet the requirements of special packaging paper products and be suitable for more scenarios and ranges.

[0044] 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 method for controlling volatile organic compounds in a paper production process, characterized in that: The control method comprises: using acidic substances to adjust the pH value of the mechanical pulp to a range of 6.0 to 7.5, wherein the concentration of the mechanical pulp after adjustment is 3.0 to 5.0%.

2. The control method according to claim 1, characterized in that: The control method further comprises: using acidic substances to adjust the pH of the mixing pulp tank and the paper machine pulp tank to a range of 7.0 to 8.

0.

3. The control method according to claim 2, characterized in that: The acidic substance includes any one of acetic acid, citric acid, sulfuric acid, and aluminum sulfate, or a combination of multiple thereof.

4. The control method according to claim 1, characterized in that: The control method further comprises: in the hard calendering stage, the hard calendering temperature is controlled at 120-180° C.; and the pressure is controlled at 50-60 kN / m.

5. The control method according to claim 4, characterized in that: The control method further comprises: during the coating stage, controlling the content of volatile organic compounds in the coating latex to be no greater than 30 ppm.

6. The control method according to claim 5, characterized in that: During the coating and drying stage, a drying method combining infrared light and hot air box is used.

7. The control method according to claim 5, characterized in that: The control method further comprises: in the soft calendering stage, the temperature of the soft calendering is controlled at 80-120° C. and the line pressure is 20-40 kN / m.

8. The control method according to claim 7, characterized in that: The control method further comprises: cooling the paper product by using a cooling device after soft calendering so that the paper product winding temperature is less than or equal to 52°C.

9. A paper product, characterized in that: The paper product is prepared by the control method according to any one of claims 1 to 8.

10. The paper product according to claim 9, characterized in that: The paper product comprises a surface layer, a surface lining layer, a core layer and a bottom layer which are stacked in sequence; wherein the fiber ratio of the surface layer, the surface lining layer and the bottom layer is: 12-20% of coniferous wood bleached chemical pulp, 80-88% of hardwood bleached chemical pulp; the fiber ratio of the core layer is: 30-50% of hardwood bleached chemical pulp; 40-60% of chemical mechanical pulp; and 0-20% of broken paper pulp.

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