1. Overview

1. 1 The Kind of Paper

Cultural paper: Newspaper, Printing paper (including Art paper), Carbon paper, Double-sided adhesive paper

Packaging paper: Kraft paper, Corrugated paper/Flute paper, White cardboard, Oil resistant paper

Household paper: Toilet paper, Napkins

Special paper： Filter paper, Insulation paper, Decorative paper

1.2 Physical standards for paper

1.2.1Basis Weight

   Also known as quantitative or grammage, the unit is g/㎡. For example,100gsm indicates a base weight of 100 grams per square meter.

1.2.2Uniformity

Meaning of Nouns

  Uniformity is an important physical property of paper, which affects the appearance, physical and optical properties of the paper, as well as the paper’s pressing, drying, and calendering operations. Different papers have different requirements for uniformity

Judgment method

 ①Visual inspection method: 

   Observe the paper in front of the light. If there is an appearance like frosted glass, it is considered to have good uniformity; If there is a cloud flower appearance, it is called poor uniformity.

②Machine measurement：

1.2.3Thickness

Meaning of Nouns

The thickness of the paper was measured directly between two measuring plates under a certain pressure.

1.2.4Mositure

Meaning of Nouns

  The percentage of moisture content in paper to its weight.

Measuring Method

  First, weigh the paper, then dry it at 10 ℃ for 2 hours, take it out and cool it down for weighing, then dry it for 1 hour and cool it down for weighing until the paper reaches a constant weight. Subtract the weight before drying from the weight after drying to calculate the weight of moisture, and then calculate the proportion.

Of course, although this method calculates results accurately, it is too slow. We can use a rapid measuring device.

1.2.5Glue Application Degree

Meaning of Nouns

 The ability of paper or cardboard to resist moisture, penetration, and diffusion.

Measuring Method

Ink streaking

  The ink marking method is a technique that uses standard ink to mark lines on paper to indicate the water resistance of the paper or paperboard by the maximum width of the lines that do not penetrate or spread after air drying. It is suitable for most paper and paperboard, especially for general writing paper and cultural paper.

Liquid permeation method

  The liquid permeation method is used to determine the water resistance based on the time required for the liquid to pass through the paper.

The impact of glue application on paper

1.2.6Smoothness

Meaning of Nouns

  The time required for a certain volume of air to pass through the gap between the sample surface and the glass surface under a certain vacuum degree.

Measuring Method

  The mechanical method is to move a needle on the surface of a paper, and the needle moves up and down according to the unevenness of the paper surface;

 Optical methods measure the degree of diffuse reflection of light.

1.2.7Cobb: refers to the ability of paper or paperboard to resist water wetting, penetration and diffusion. There are many methods for determination, such as ink streaking method, surface absorption method, liquid penetration method, etc.

2. Paper Raw Materials and Chemicals

2.1The Kind of Paper Pulp

 2.1.1Classified by Production Method

2.1.2Classified by Pulp Yield

2.2Common Pulp Kind

 ①Long Fiber： Bleached sulfate coniferous wood pulp, abbreviated as bleached needle pulp, abbreviated as NBKP. It is a type of chemical pulp made from coniferous wood using the sulfate method for cooking and bleaching. It is the most widely used commodity pulp, and according to different coniferous trees, cooking and bleaching processes, and operating conditions, bleached needle pulp is the “king of pulp”, which can be used to produce almost all types of paper (except for special varieties).

②Short Fiber： Bleached sulfate broad-leaved pulp, abbreviated as bleached broad-leaved pulp, abbreviated as BLKP. It is also produced using the sulfate method, but the raw material used is broad-leaved trees. The most famous one is the eucalyptus oar sold in Brazil, which can be used alone or in combination with bleaching needle paste to make various high-end printing papers.

③CMP： Chemical mechanical pulping is a pulping method that uses chemical pretreatment and mechanical grinding post-treatment. First, mild pretreatment (impregnation or steaming) is carried out with chemicals to remove some hemicellulose from the wood chips. Lignin is less dissolved or hardly dissolved, but softens the intercellular layer. After further processing by a disc mill, the softened wood chips (or grass chips) are ground to separate the fibers into pulp, abbreviated as CMP.

2.3Chemicals used in the papermaking process

  2.3.1Filler

Function:  Fill the gaps between fibers, make the surface of the paper smoother, increase the adaptability of paper printing, increase opacity, and save fiber usage.

Type 

①PCC： precipitated calcium carbonate

②GCC： ground calcium carbonate

The difference between ① and ②

There is a significant difference in the shape of PCC and GCC particles. GCC particles have a prismatic structure, which is a common crystal form of calcite. PCC is an unequal edged structure, sometimes referred to as a rose shaped structure. Due to the fine and long crystal structure, which aggregates into clusters and surrounds the core particles, it has a larger specific surface area than GCC prisms, thus possessing greater light scattering ability, resulting in higher whiteness and opacity of the paper. However, this rose shaped structure also creates a large number of gaps within or between particles, which affects the bonding between fibers. When the filling in the paper exceeds a certain threshold, the strength of the paper decreases, gaps are generated, and the speed of the vehicle decreases, becoming a serious problem. This problem can be overcome by mixing PCC and GCC for filling. PCC manufacturers are working hard to develop and replicate particles that resemble natural polyhedra, in order to overcome the limitations of high filling amounts of unequal sided polyhedra PCC.

In order to achieve good glossiness and smoothness, it is required that the solid content of the coating be high. As mentioned earlier, PCC unequal sided prismatic particles are composed of a rose shaped nucleus and needle shaped crystals surrounding it. When making high solid content coatings, the strong dispersing effect causes the needle shaped and rose shaped nuclei to split, resulting in a decrease in optical performance and an increase in adhesive dosage. Generally speaking, PCC’s application in coatings cannot compete with GCC. PCC has an advantage in the paint market in North America, while GCC is mainly used in paint formulations. Due to the fact that the filling amount of PCC cannot exceed 15%, the benefits of switching to alkaline papermaking are reduced. Only GCC can operate stably when the filling amount is high (sometimes up to 30%).

③Talc

④Bentonite

2.3.2 Dye

Function: Due to the different sources of pulp raw materials, there may be differences in paper color. Adjusting the dyes allows the paper color to stabilize without color difference problems.

2.3.3 Sizing

①Internal Sizing

Internal sizing is the process of mixing sizing agents into pulp during pulping or batching, allowing fibers to adsorb the gum and then converting it into paper.

 Function： Endowing paper with the ability to inhibit the penetration of water or water-based ink.

Types: Rosin sizing agent, synthetic sizing agent, paraffin sizing agent, neutral sizing agent, etc.

②surface sizing

Surface gluing is a process in the processing of paper or cardboard, usually located at the end of the drying section of the paper machine, to spray a layer of glue solution on the paper sheet before it is completely dried but has a certain strength. After subsequent drying, a layer of glue film is formed on the surface of the paper and cardboard, thereby achieving the goal of changing the surface properties of the paper or cardboard.

Function And Advantage

1) Improve the printing performance of paper and cardboard;

2) By selecting different types of surface adhesives, the surface strength or water resistance of paper can be improved;

3) Improve the physical strength of paper and cardboard;

4) Surface glue can reduce the difference between the two sides of the paper;

5) Not affected by the water quality and temperature of the papermaking process, the adhesive effect is relatively stable;

6) The retention effect of the adhesive material is good, and the cost of glue application is low;

7) Simultaneous use with internal glue can compensate for some of the shortcomings of internal glue

Types: Oxidized starch, casein, wax, CMC, dialdehyde starch, PVA, etc.

2.3.4Retention Aids

Function: Improve the retention rate of fine fibers and fillers in the mesh during the process of early detection.

Categories: cationic starch, polyacrylamide (PAM), polyethyleneimine (PEI), polyethylene oxide (PEO), etc.

2.3.5 Fungicide

Function: Control the amount of sediment and bacteria in the wet end chemistry of the papermaking process, and reduce perforation and paper breakage.

Add points: streaming system, offline white water pool.

2.3.6 Dry strength/wet strength additive

Function: By increasing the bonding force between fibers, the paper strength can be improved.

Types: Polyacrylamide, positive starch, carboxymethyl cellulose, wet strength agent, etc.

3. Paper production process

One of China’s the Four Great Inventions – papermaking

3.1Pulping Machine

 3.1.1Convey System

Function： Cut iron wire, open pulp and paper bags.

                  Transport pulp and waste paper bags to the pulper.

 Charter flight

Chain conveyor

3.1.2Pulper

Function:It is used to treat OCC, AOCC, etc., so that the plastic, styrene foam and other light and heavy impurities in the slurry can be removed from the tank of the hydraulic pulper before passing through the sieve plate of the pulper without being broken, improving the production capacity and the quality of good pulp.

D-Pulper

Medium Consistency Pulper

3.1.3High Consistency Cleaner 

Function:It is used to remove all kinds of heavy impurities in pulp, so as to reduce the wear of follow-up equipment, essence sauce, and improve product quality.

3.1.4Coarse Screen

 Function:Coarse screen is a commonly used screening equipment placed in front of fine screening and mesh screening in pulp-making systems, used to remove larger impurities in pulp, such as shredded paper, plastic sheets, etc.

3.1.5Light Slag Sepatator

Function： Mainly used for processing light slag and tail slurry in the coarse screening process.

3.1.6Reject Sorter

Function: Processing the screening tail slurry of the light slag separator in the waste paper processing system.

3.1.7Medium Consistency Cleaner

 Function: Further processing impurities in medium concentration pulp to reduce the burden on subsequent equipment and purify the pulp.

3.1.8Fiber Fractionating Screen

Function: Fiber grading screening technology separates the long and short fibers in waste paper pulp, reducing equipment investment, simplifying processing procedures, saving energy, and improving product quality.

3.1.9Fine Screen

Function:Fine screening is a commonly used screening equipment in papermaking and pulp systems, which is placed after coarse screening and before mesh screening

The screened slurry is further selected and processed to remove residual small impurities, coarse fibers, and adhesive substances contained in the waste paper, thereby improving the Quality of finished paper.

3.1.10Low Consistency Cleaner

Function: Mainly used to remove heavy impurities and some light impurities from pulp. The key equipment for waste paper recycling uses the ratio of fibers to impurities to separate heavy impurities from pulp, achieving the purpose of purifying pulp. This device has a wide range of applications, not only for rough selection and purification of high-concentration pulp, but also for paper machines that use low-concentration pulp for purification.

3.1.11Vibrating Screen

Function:Mainly used for removing impurities from chemical pulp, mechanical pulp, and coarse screening of waste paper pulp, the vibrating frame flat screen can effectively remove coarse impurities such as metals, plastics, rubber, etc. from waste paper pulp when used in the waste paper processing process.

3.1.12Refiner

Function： Mainly used for pulping, improving the tapping degree of pulp, and meeting the needs of papermaking. Multiple tooth-shaped grinding discs can be installed, with a wide range of material adaptability, suitable for wood pulp, chemical pulp, chemical pulp, waste paper pulp, etc.

3.1.13Agitator

Function： Mainly used for circulating mixing in the pulp tank to keep the pulp in a suspended state and ensure that the components of the paper are evenly distributed in the pulp.

3.1.14Disc Thickener

Function: Disc Thickener is mainly used for washing and concentrating low-concentration slurry; The combination disc filter drum greatly increases the filtration area, occupies a small area, and has a large production capacity; Adopting stainless steel filter screen, with a long service life; Reasonable cleaning and stripping structure, filter screen is not easily clogged, and has strong dehydration ability.

3.1.15Impurity Separator

Function：Used in the waste paper pulping system to remove a large amount of light and a small amount of heavy impurities from the pulper.

3.1.15Drum Screen

Function: Mainly used for pulp making from waste paper, removing light impurities with larger shapes from the waste paper pulp.

3.1.16FIber Separator

Function:Used for further separation of fibers after being crushed by a hydraulic pulper, while utilizing the difference in specific gravity of fibers to remove various impurities from waste paper raw materials.

3.2Paper Machine 

3.2.1Headbox

Function： As the junction of “flow” and “forming” in paper machines, the basic task of the flow box is to provide good prerequisites for paper sheet forming, that is, to evenly distribute the paper material along the width direction of the paper machine, ensuring uniform pressure distribution, velocity distribution, flow rate distribution, concentration distribution, as well as controllable and uniform fiber orientation; Effectively disperse pulp fibers, prevent fiber agglomeration, and provide and maintain stable sizing head and pulp web ratio according to process requirements.

 In the long-term development of pulp and paper technology, although various structural forms of headboxes have emerged, their main functions remain unchanged, namely pulp spreading, homogenization, and spraying.

3.2.2The Kind of Paper Machine

According to the dehydration form of the net, it can be divided into circular net paper machine, long net paper machine, clamped net paper machine, and multi-layer stacked net board paper machine.

Circular Wire Paper Machine

Long Wire Paper Machine

 clamped wire paper machine

 multi-layer stacked net board paper machine

3.2.3Wire Section

Function: The wire section is mainly used to remove water from the pulp, and it undertakes the majority of the dehydration task. In addition, it also needs to cause some disturbance to the pulp, while ensuring good paper forming.

Wire dehydration component

Forming Felt

3.2.4Press Section

Function： The main function of the paper press section is to use mechanical extrusion to remove as much, evenly, and stably as possible moisture from the wet paper web. The dryness of the wet paper web from the forming section is usually 18% -20%, and after dehydration in the pressing section, the dryness of the wet paper web can be increased to 40% -50%.

Press Felt

Pressing section Felt Structure

3.2.5Drying Section

Function： The main function is to heat the wet paper after pressing, evaporating excess water to meet the requirements of product quality, while improving the strength of the paper, enhancing some physical properties of the paper, and completing processes such as sizing and dyeing.

3.2.6Glue Application Section

Function： Improving paper quality: The glue application department can evenly apply glue to the surface of the paper, thereby improving the strength and durability of the paper. In addition, glue can improve the glossiness and smoothness of paper, making it look more beautiful.

Comparison of the effect after magnifying coating

3.2.7Calendering Section

Function： The repeated processing process between the surface of the light roller and the surface of the coarse paper after the paper comes out of the drying section. Improve the smoothness, glossiness, tightness, and uniformity of thickness of the paper web.

Effect of Calendering On surface of Coated paper

3.2.8Curly Section

Function： The curling department rolls the paper into paper rolls, and the performance of the paper winding machine directly affects the curling tightness and quality of the paper, as well as the storage and processing performance of the paper in the next step.

Rewinder

4. Process Control System

4.1Distribute Control System（DCS）

Function：

① All devices can be started and stopped according to the program in the control room.

② All equipment of the paper machine can be monitored online.

③ Automatically record and save the operating status of the device.

④ Abnormal automatic alarm, reminding operators.

4.2 Quality Control System(QCS)

Function：

① Automatically detect and adjust basis weight/thickness

② Paper color adjustment

③ Various physical property adjustments

④ Automatic copying

4.3Web Image System(WIS)

Function: To detect different types of surface defects in the paper industry and provide real-time feedback in the form of images on defects such as hair, mosquitoes, holes, black spots, dark spots, pulp spots, bright spots, damages, impurities, folds, wrinkles, and uneven uniformity.