A process for producing a gypsum board facing paper

Abstract

The present application relates to a kind of gypsum board facing paper production process, comprising the following steps: making natural needle leaf wood pulp board and waste paper into pulp respectively, and waste paper pulp is divided into long fiber pulp and short fiber pulp;Wood pulp pulp, long fiber pulp and short fiber pulp are mixed, after pressure screen, into flow system dispersion after spraying net forming, get finished paper.The present application is provided with pressure screen before flow system, and the dispersion effect of fiber can be improved by pressure screen, wood pulp, long fiber pulp and short fiber pulp after using pressure screen can get better mixing effect, reduce wood pulp long fiber flocculation, improve the uniformity of mixing effect, and the strength of paper is improved and stabilized.

Description

Technical Field

[0001] This invention belongs to the technical field of gypsum board facing paper, and specifically relates to a production process for gypsum board facing paper. Background Technology

[0002] Gypsum board is a material made primarily from building gypsum. It is a lightweight, high-strength, thin, and easy-to-process building material with good sound insulation, heat insulation, and fire resistance properties, making it one of the new lightweight building materials currently under development. Gypsum board is widely used in various buildings such as residences, office buildings, shops, hotels, and industrial plants for interior partitions, wall cladding (replacing plaster layers), ceilings, sound-absorbing panels, floor baseboards, and various decorative panels.

[0003] The breaking load of gypsum board is one of its important performance indicators, directly related to its quality and safety. According to the current national standard GB / T 9775-2008 "Paper-faced Gypsum Board," the average longitudinal breaking load of paper-faced gypsum board should be ≥400N, with a minimum of ≥360N; the average transverse breaking load should be ≥160N, with a minimum of ≥140N. This standard ensures that gypsum board maintains a certain strength under external forces, making it less prone to cracking or breaking, thus guaranteeing the safety and stability of building structures.

[0004] 60% of the breaking load strength of gypsum board comes from the tensile strength of the gypsum board facing paper covering both sides. Therefore, with market development and changes, gypsum board facing paper is developing towards lower basis weight and higher strength. The tensile strength of the facing paper is a decisive indicator for measuring the quality of the product. The main factors affecting tensile strength are: the strength of the fiber itself, the bonding strength between fibers, and uniformity.

[0005] To improve the tensile strength of gypsum board facing paper, paper mills generally need to add a certain proportion of softwood long fibers. However, the inventors found in production that the long fibers of wood pulp are prone to flocculation, which affects the mixing of wood pulp and waste paper pulp, thereby affecting the strength and uniformity of the finished paper. Summary of the Invention

[0006] The purpose of this invention is to provide a gypsum board facing paper production process that can reduce the flocculation of long wood pulp fibers and achieve a better mixing effect between wood pulp and waste paper pulp.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A process for producing gypsum board facing paper includes the following steps:

[0009] (1) Pulping: The unbleached softwood pulp board and waste paper are made into pulp separately, and the waste paper pulp is divided into long fiber pulp and short fiber pulp;

[0010] (2) Papermaking: Wood pulp, long fiber pulp and short fiber pulp are mixed, passed through a pressure screen, dispersed in a flow system and sprayed onto a wire mesh to form finished paper.

[0011] Preferably, in step (1), the process of making unbleached softwood pulp board into pulp includes the following steps: conveying unbleached softwood pulp board with a wet weight ≥15g to a pulper to add water and break it down to make a pulp with a concentration of 4~5%, then removing impurities through a high-consistency deslagging device, and then grinding it in a disc mill until the beating degree is 35±2°SR.

[0012] Preferably, in step (1), the waste paper is made into pulp, and the waste paper pulp is divided into long fiber pulp and short fiber pulp, including the following steps: the waste paper is fed to a pulper and water is added to break it down to make a pulp with a concentration of 3.5% to 4%, impurities are removed by a high-consistency desander and a coarse screen, and the pulp is separated into long fiber pulp and short fiber pulp by fiber grading screen with a screen gap of 0.15 mm.

[0013] Preferably, the long fiber pulp, after passing through a low-consistency separator and a fine screen, enters a multi-disc thickener to be concentrated to a concentration of 8-10%, and then is transported to a thermal dispersion treatment, and then pulped to 30±2°SR by a double-disc refiner; the short fiber pulp, after passing through a low-consistency separator, enters a multi-disc thickener to be concentrated to a concentration of 8-10%.

[0014] Preferably, the aperture of the pressure screen is 8 mm.

[0015] Preferably, in step (2), the mixed slurry enters the conveying system to form a slurry with a concentration of 0.4%-0.8%, and is dispersed and sprayed onto the web through the headbox.

[0016] Preferably, in step (2), the mixed slurry used in the lining of the mesh part is 10%~40% wood pulp slurry, 20%~50% long fiber slurry and 0%~20% short fiber slurry, the mixed slurry used in the core layer of the mesh part is 10%~40% wood pulp slurry, 0%~30% long fiber slurry and 20%~40% short fiber slurry, and the mixed slurry used in the bottom layer of the mesh part is 10%~40% wood pulp slurry, 20%~50% long fiber slurry and 0%~20% short fiber slurry.

[0017] Preferably, sizing agent, retention aid, aluminum sulfate and starch are added to the headbox, and the amount of aluminum sulfate added is adjusted to ensure that the pH of the headbox does not exceed 6.8.

[0018] Preferably, in step (2), the mixed pulp is dispersed in the flow system and sprayed onto the wire surface. It is dehydrated by gravity or vacuum at the wire section to achieve a dryness of 10%-14%. After pressing, pre-drying, surface sizing, post-drying, and winding, the finished paper is obtained.

[0019] The present invention sets a pressure screen before the flow system. The pressure screen can improve the fiber dispersion effect. The wood pulp, OCC long fiber and OCC short fiber after the pressure screen can achieve a better mixing effect, reduce the flocculation of wood pulp long fiber, improve the uniformity of the mixing effect, and improve and stabilize the paper strength. Attached Figure Description

[0020] Figure 1 A schematic diagram of the structure for feeding wood pulp, long fiber pulp, and short fiber pulp into a pressure screen. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] This invention discloses a process for producing gypsum board facing paper, comprising the following steps:

[0023] (1) Pulping: The unbleached softwood pulp board and waste paper are made into pulp separately, and the waste paper pulp is divided into long fiber pulp and short fiber pulp.

[0024] Specifically, the raw material is unbleached softwood pulp board with a wet weight of ≥15g. It is conveyed to a pulper via a chain conveyor and broken down with water to produce a pulp with a concentration of 4-5%. Then, it passes through a high-consistency desander to remove some heavy impurities such as sand and to prevent impurities such as iron wire from entering the system. After passing through the high-consistency desander, the wood pulp is sent to the pre-pulping tower. Finally, it is pulped by a disc mill to a freeness of 35±2°SR. After being properly cut and filamentized by the disc mill, the wood pulp is stored in the post-pulping tower for use in the pulping of each layer of papermaking.

[0025] Specifically, the OCC waste paper is conveyed to the pulper via a chain conveyor and then pulverized with water. In this embodiment, the Kaden D-type pulping system is used to produce pulp with a concentration of 3.5% to 4%. Some heavy impurities in the waste paper are removed by a high-consistency desander and a coarse screen. The pulp is then separated into long fiber pulp and short fiber pulp by fiber grading screening. The fiber grading screen has a sieve opening of 0.15 mm and a grading ratio of 40% short fiber + 60% long fiber.

[0026] More specifically, the long-fiber pulp undergoes further processing via a low-consistency separator and a fine screen to remove impurities such as foam, plastic, and adhesives. The fine screen consists of three stages: after passing through the low-consistency separator, the long-fiber pulp sequentially enters three pressure screens, then enters a multi-disc thickener to be concentrated to 8%, and is then conveyed by an inclined screw conveyor to a thermal dispersion treatment to disperse the adhesives in the pulp to a level invisible to the naked eye. Afterward, it is pulped to 30±2°SR by a double-disc refiner, and the refined pulp is stored in a pulp tower for papermaking pulp preparation. The short-fiber pulp, after passing through the low-consistency separator, enters a multi-disc thickener to be concentrated to 8% and is then stored in a pulp tower.

[0027] (2) Papermaking: Wood pulp, long fiber pulp and short fiber pulp are mixed, passed through a pressure screen, dispersed in a flow system and sprayed onto a wire mesh to form finished paper.

[0028] Specifically, such as Figure 1 As shown, wood pulp, long fiber pulp, and short fiber pulp from the pulping workshop are fed into the feed pipe of the pressure screen. The pressure screen is a perforated screen with an 8mm aperture. The large aperture allows the pressure screen to primarily function as a dispersing device rather than a screening device. During the rotation of the rotor and screen drum, the pulp is thoroughly mixed from the inlet to the outlet. Positive and negative pressure pulses are formed at the front and rear of the rotor blades, improving the fiber dispersion effect. At this time, the pressure screen no longer removes impurities from the pulp, and the discharge port of the pressure screen no longer discharges impurities. The wood pulp, OCC long fiber, and OCC short fiber after using the pressure screen achieve a better mixing effect, as shown in Table 1. This reduces the flocculation of long wood fibers, improves the uniformity of the mixing effect, and enhances and stabilizes the strength of the paper.

[0029] The three types of slurry are fed into the slurry tank after passing through a pressure screen. Then, they are processed by the flow system, namely the slurry pump and the pre-screen, to form a slurry with a concentration of 0.4%-0.8%. Functional additives such as sizing agent, retention aid, filter aid, aluminum sulfate and starch are added to the flow system. The amount of aluminum sulfate added is adjusted to ensure that the pH of the slurry in the headbox does not exceed 6.8.

[0030] The headbox evenly sprays the head onto the mesh surface along the entire horizontal direction. The mesh consists of four layers (face, liner, core, and bottom). The face layer is coated with ONP slurry, while the liner, core, and bottom layers are made of the aforementioned mixed slurry. The liner uses a mixed slurry of 30% wood pulp, 50% long fiber pulp, and 20% short fiber pulp. The core layer uses a mixed slurry of 30% wood pulp, 30% long fiber pulp, and 40% short fiber pulp. The bottom layer uses a mixed slurry of 30% wood pulp, 30% long fiber pulp, and 40% short fiber pulp. The pulp consists of 50% wood pulp, 50% long fiber pulp, and 20% short fiber pulp. It is dewatered by gravity or vacuum dewatering at the wire section to achieve a dryness of 10-14%. After pressing, pre-drying, surface sizing, post-drying, calendering, and winding, the pressing section consists of two shoe presses. The dryness of the pressing section is about 48%. The surface sizing is controlled by starch with a sizing concentration of 18% on the front and 8% on the back. Finally, it is rewound by a rewinder into paper rolls of the required specifications and diameter, and then stored in the warehouse via a chain conveyor.

[0031] Table 1

[0032]

[0033] As shown in Table 1, after the pressure screen was put into use, the strength of the same paper type increased and the strength fluctuation decreased, thus improving the stability of product quality.

Claims

1. A process for producing gypsum board facing paper, characterized in that, Includes the following steps: (1) Pulping: The unbleached softwood pulp board and waste paper are made into pulp separately, and the waste paper pulp is divided into long fiber pulp and short fiber pulp; (2) Papermaking: Wood pulp, long fiber pulp, and short fiber pulp are fed into the feed pipe of a pressure screen, which is an 8mm perforated screen. After passing through the pressure screen, the three pulps enter the pulping tank, are then dispersed by a conveying system, and sprayed onto a wire mesh to form the finished paper. In step (1), the process of making unbleached softwood pulp board into pulp includes the following steps: unbleached softwood pulp board with a wet weight ≥15g is transported to a pulper and water is added to break it down to make a pulp with a concentration of 4~5%. Then, impurities are removed by a high-consistency deslagging device and then the pulp is put into a disc mill to be beaten to a beating degree of 35±2°SR. In step (2), the lining of the mesh section uses a mixed slurry of 30% wood pulp slurry, 50% long fiber slurry and 20% short fiber slurry, the core layer of the mesh section uses a mixed slurry of 30% wood pulp slurry, 30% long fiber slurry and 40% short fiber slurry, and the bottom layer of the mesh section uses a mixed slurry of 30% wood pulp slurry, 50% long fiber slurry and 20% short fiber slurry.

2. The gypsum board facing paper production process according to claim 1, characterized in that, In step (1), waste paper is made into pulp, and the waste paper pulp is divided into long fiber pulp and short fiber pulp, including the following steps: waste paper is fed to a pulper and water is added to break it down to make pulp with a concentration of 3.5% to 4%. Impurities are removed by a high-consistency deslagging device and a coarse screen, and the pulp is divided into long fiber pulp and short fiber pulp by fiber grading screening.

3. The gypsum board facing paper production process according to claim 1 or 2, characterized in that, The long fiber pulp, after passing through a low-consistency separator and fine screening, enters a multi-disc thickener to be concentrated to a concentration of 8-10%, and then is transported to a thermal dispersion treatment, and then pulped to 30±2°SR by a double-disc refiner; the short fiber pulp, after passing through a low-consistency separator, enters a multi-disc thickener to be concentrated to a concentration of 8-10%.

4. The gypsum board facing paper production process according to claim 1, characterized in that, In step (2), the mixed slurry enters the flow system to form a slurry with a concentration of 0.4%-0.8%, which is then dispersed and sprayed onto the web through the headbox.

5. The gypsum board facing paper production process according to claim 1 or 4, characterized in that, Add sizing agent, retention and filtration aid, aluminum sulfate and starch into the headstock to the headstock system, and adjust the amount of aluminum sulfate added to ensure that the pH of the headstock in the headstock does not exceed 6.

8.

6. The gypsum board facing paper production process according to claim 1, characterized in that, In step (2), the mixed pulp enters the flow system and is dispersed before being sprayed onto the wire surface. It is then dehydrated by gravity or vacuum to achieve a dryness of 10%-14%. After pressing, pre-drying, surface sizing, post-drying, and winding, the finished paper is obtained.

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