Influencing factors of the hottest dry papermaking

2022-08-12
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Influencing factors of dry papermaking production

wanshizhe Ningxia Wuzhong Ruite paper company, 751100

dry papermaking adopts air sedimentation. The government team will also continue to adhere to the post reduction technology and dry processing method, so that the fluff pulp is strongly glued, or it is formed by melting hot-melt chemical fiber and fluff pulp. It will not produce waste water and waste gas in the production process, which is easy to treat and meets the requirements of environmental protection. It will not produce fines in the process of use, and can be used both dry and wet, so its tensile strength and wet strength are particularly important. Now, the factors affecting various physical indexes of dry process paper in the production process are analyzed as follows:

I The main process flow of the production of glued dust-free paper (fluff pulp + latex)

glued dust-free paper is:

(electrostatic treatment) air feeding

pulp board → fiber separator → forming box → hot pressing → hot embossing → upper glue spraying → 1 oven → lower glue spraying → 2 oven → ripening box (expansion box) → finishing → calendering → coiling → slitting → packaging → warehousing

1. The influence of fluff pulp

the best dust-free paper is pine sulfite fluff pulp with 100% pure natural plant fiber. The fiber polymerization degree of sulfite pulp is higher than that of sulfate pulp, and its fiber cavity is flat, while the fiber cavity of sulfate pulp is open. The selection of fluff pulp mainly considers whether to treat (treated with softener) the pulp, the average length of the fiber, the dry elasticity (expressed by the height of the dried fluff pulp sample under the pressure of 1.3kpa), the fluid stagnation rate, the energy required for crushing, moisture, whiteness and the content of fine fibers. The dust-free paper produced by treated pulp is soft and comfortable, and the paper surface is flat and smooth; Untreated pulp is rough and straight, but has good liquid absorption and air permeability; The main index affecting the paper strength is the average length of the fiber. The longer the fiber, the better the strength, the higher the degree of fine fibrosis, and the better the strength. Generally, the length of 2.0 ~ 3.0mm is the best; The moisture content is more than 7%, and the whiteness (ISO)> 80%; The fully treated pulp is treated with softener in the production process, which has high fluffy degree, easy fiber separation and low separation energy. The produced dust-free paper appears fluffy, that is, the thickness increases and the hand feel is particularly good. The electrostatic treatment of pulp board is also particularly important. Adding 1% antistatic agent to pulp board can ensure that there will not be many pulp clusters due to fiber separation and formation in the process of dry forming, which will affect the quality of products

2. Influence of forming 4 Limit protection

the separated fluff pulp is dredged into a single fiber and sent into the screen cylinder of the forming box by air. The nail roller equipped with dense mixing nail teeth further separates the fiber mass into a single fiber, which is evenly settled on the moving forming through the screen under the action of air flow. Adjust the air flow and vacuum degree through the inlet fan and vacuum suction fan, and adjust the product quantity. When the paper sheet is just formed, its strength is very low and its density is small. The paper sheet is initially shaped by hot pressing. The dust-free paper produced by high mesh forming has good density, flat paper sheet, large liquid absorption, high retention rate of fine fibers and reduced flow charges. When settling the fibers, pay special attention to the fact that the fibers should be arranged more longitudinally (i.e. in the direction of sub operation) and less horizontally. Avoid vertical arrangement, and the strength of dry paper and pages can be guaranteed. According to different quantitative products, the negative pressure of forming (i.e. the pressure difference between air inlet and vacuum exhaust) should be adjusted in production, so as to facilitate paper forming and reduce the loss of fine fibers and workshop dust, which is also the key of air sedimentation technology

adjust the air volume and wind speed in the middle layer of the forming box to prevent air vortex from affecting the uniform settlement of fluff pulp. In order to fully disperse the fluff pulp, the direction of the screen barrel is designed to be opposite to that of the nail roll. It is particularly important to prevent static electricity in the forming process. Forming is an antistatic material, and the surface of the forming box must also be an antistatic material. The surface should be smooth and flat, without bulges or grooves, so as to prevent slurry hanging and affect the appearance of the paper

3. Influence of hot pressing

the formed paper web first enters the pressing roller at about 140 ℃ for preheating and pressing, so that the fiber layer is compact, and a certain number of fiber interlacing points are generated at the same time, and the paper begins to have tightness. Then it is introduced into the embossing area by transmission, and then enters the high hot pressing area at about 180 ℃. After high temperature and high pressure treatment again, the fibers are more compact, and the fiber nodes increase. The grain of the transfer paper can be adjusted and selected according to needs, and various flower squares can be pressed out. The purpose of hot pressing dry paper is to adjust the tightness and quantity of paper; The second is to press out various patterns, such as plain, twill, diamond, etc. At the same quantity, plain paper has higher strength, better softness and feel than other paper

4. Influence of adhesive (latex) and spray system

water soluble latex is used in the production of dust-free paper, which should be prepared according to the requirements of production process. At present, we use en429 from Germany, ul-101 and ul-102 from Japan, kt-711 from Taiwan, and vae-05 series special latex for dust-free paper in China. Its main components are ethylene vinyl acetate, ethylene acetate copolymer, styrene propylene copolymer (ACR) and SBR. Among them, en429 latex is the best. Its latex particle size is 0.2 microns, the minimum film-forming temperature is 0 ℃, pH value is about 4, the transverse connection temperature is higher than 130 ℃, and the curing temperature is about 180 ℃. Wet strength agent, penetrant and other additives are added to the latex to make the paper have dry strength and high wet strength. The latex is a hydrophilic material, otherwise the paper will not absorb water. In order to make the produced paper acid free, the polymerization degree of latex meets the requirements, and there must be no free acid. Latex cannot be denatured, aged and condensed, and the glass transition temperature, minimum film-forming temperature and high elastic state (a mechanical state of amorphous linear polymers with slightly bonded structure within a certain range, also known as rubber colloidal state) must meet the requirements

the glue spraying system uses a porous spray nozzle to spray water-soluble latex into the paper with air atomization. The glue spraying amount depends on the different types of products. The spray nozzle is generally annular and fan-shaped. The annular spray nozzle has good atomization, and the fan-shaped spray nozzle has strong penetration ability. Directly below the glue spraying system is a vacuum suction box, which is used to suck air to make the glue penetrate or penetrate into the core layer of the paper, prevent delamination and ensure the strength of the paper. The concentration of latex should not be too high, the particles should be clean, and the vacuum suction effect should be better, otherwise the latex will quickly form a film on the surface of the paper, resulting in the delamination of the paper and affecting the strength

5. Influence of drying

after spraying wet paper, it enters the oven at about 180 ℃ for drying. The first purpose is to make the adhesives chemically interact and cross connect with each other through the action of hot air, which has strength; Second, latex particles and fibers are bonded to each other, resulting in many nodes. This process is the key to the dry and wet strength of dust-free paper. The dried paper sheets also enter the expansion box to make the paper sheets fluffy and soft. The temperature of the oven should not be too high, otherwise the latex will age and lose its adhesion and elasticity. The relationship between air supply and exhaust should be adjusted to make the hot air penetrate the paper to ensure the final strength of the paper and improve the softness and other physical properties of the paper

II. The production process of heat sealed dust-free paper (hot-melt fiber + fluff pulp)

the production process of heat sealed dust-free paper only needs to add hot-melt fiber in the transportation process after the fluff pulp is crushed into fibers, and the rest is the same as the glued dust-free paper. The application of heat sealed dust-free paper is more extensive, and its liquid absorption, padding, softness and fluffy are better than those of glued dust-free paper, which has the characteristics of fast speed, smooth interface and simple operation

1. Influence of hot-melt fiber

the hot-melt fiber used is generally polyethylene and polypropylene (PE/pp:1) skin core structure, and its skin melting point temperature is 135 ℃. There is a certain temperature difference between the skin layer and the core layer of the hot-melt fiber, so it is only necessary to melt the skin layer in production. The requirements for hot-melt fibers are mainly fiber length (4 ~ 10mm), tensile strength, electrostatic treatment, crimp, moisture regain, oil content and so on

2. The effect of hot pressing

the formed paper sheet is a mixture of cellulose fiber and hot-melt fiber of fluff pulp. After hot roller hot pressing, the two fibers are preliminarily fused and cross connected, and the hot-melt fiber PE/PP is evenly geothermal fused in the fiber, making the paper sheet more compact. The temperature of the hot roll should not be too high, otherwise the roll sticking phenomenon will occur or the core of the hot-melt fiber will melt

3. Influence of drying

the hot pressed paper sheet enters the hot air drying oven, and the hot-melt fiber is heated to the melting point temperature of the two-component fiber coating 135 ~ 150 ℃, forming a thermal bonding point with the fiber with its surface melting and flow generated in the heating process. At this time, the strength has reached the requirements. However, it should be noted that the strength of heat bonded paper mainly depends on the amount of hot-melt fiber and the appropriate temperature

the dried paper is treated with foam like surface treatment agent to prevent wool and powder from falling, and then calendered and rolled

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