In recent years, the use of additives in the papermaking industry has become increasingly common. Whether in foreign and domestic markets, as well as in laboratories or production practices, various papermaking additives have shown significant advantages and have received special attention from the papermaking industry. This article comprehensively introduces the application effects of several papermaking additives in the papermaking industry.

1. Polyethylene oxide

To maintain high opacity in low weight paper, additives should be added to the wet end of the paper machine to increase the retention of fines. Many paper mills in North America and Scandinavia use high molecular weight polyethylene oxide to improve fines retention in 45g/m2 newsprint, resulting in an increase of 1.7% in page opacity and 2.8% in 37g/m2 telephone book paper. Polyethylene oxide can be used alone or together with phenolic resin reinforcing agents. The retention aid should be added just in front of the mesh box.

By adding 0.27kg of polymer to one ton of air dried slurry, the retention rate of fine fibers increased from 53% to 74%, the retention rate of porcelain clay increased from 36% to 75%, and the retention rate of titanium dioxide increased from 8% to 60%.

2. Urea formaldehyde resin

The addition of urea formaldehyde resin can greatly improve the strength of paper, with an optimal dosage of 1.0% -3.0% (for dry fibers). For example, adding this additive to the pulp of copper plate base paper can provide a sufficiently high interlayer strength for high-speed offset printing.

3. Aluminum compounds

Production of low quantity paper and paperboard requires high mechanical strength. If aluminum sodium sulfate (2.5%) is added, it can increase the fracture length by 32.5%, compressive strength by 25.5%, and bonding strength by 39%. For example, the kraft pulp of a mixture of larch (70%), birch (15%), and poplar (15%) has a beating degree of 17SR, and a pulp sheet of 130g/m2 is prepared by adding 0.5% brown gum and 2.5% sodium aluminate at pH 8.5. The mechanical strength index increases sharply: the fracture length increases by 90%, the circular stiffness strength increases by 47%, and the flexural strength increases by almost 20 times.

In addition, adding sodium aluminate to the beating process can shorten the beating time by 20% -25%, and increase the ash content of the paper by 3%. Therefore, when the quantity remains unchanged, 1 ton of product can save 2-30kg/fiber.

4. Polyvinyl alcohol

Polyvinyl alcohol has excellent film-forming properties, which can improve tear resistance, tensile strength, folding resistance, and roller adhesion.

If polyvinyl alcohol (PAVL) and trimethyl alcohol melamine (TMM) are used together to generate a cationic complex with a PAVL/TMM ratio of 1/1, the optimal fine material retention and paper strength can be achieved at a dosage of 0.2%, and the effect is good in acidic, neutral, and slightly alkaline media. The use of this additive can increase the sizing degree by 4-6 times, significantly improve the surface strength of IGT, and greatly reduce the phenomenon of hair loss, powder loss, and plate pasting in printing paper. In addition, with an increase in drying speed, steam consumption can be reduced by 25%. The addition point of additives should be close to the front box of the mesh, so that the wet end additives and pulp have a contact time of at least 10 seconds.

If used with coating, this additive can make the finished paper have good opacity, whiteness, glossiness, and smoothness.

5. Applying sulfate lignin to increase paper strength

Industrial sulfate lignin can be used for sizing and improving the strength of paper, such as sulfate pulp with a beating degree of 28.5SR, adding 2% lignin adhesive (concentration of 11.5%) for sizing, and adjusting the pH to 5.5 with bauxite. The addition of adhesive enables the distribution of lignin in the porous structure of fiber materials, such as polymer connections that can enhance the strength of paper in contact between fibers. For example, the maximum increase in fracture length is 23%, the maximum increase in fracture resistance is 17%, the maximum increase in ring compression strength is 41%, the bending stiffness is 15%, but the tearing strength is reduced by 10%.

————————————

Label paper application

The commonly used self-adhesive labels on barcode machines consist of three parts: base paper, face paper, and adhesive used as the bonding agent between the two. The surface of the backing paper is oily and has an isolating effect on the adhesive, so it is used as an attachment for the backing paper to easily peel off the backing paper.

The base paper is divided into regular base paper and GLASSINE base paper. The ordinary base paper is rough and thick, with colors such as yellow and white. The commonly used adhesive base paper in the printing industry is an economical yellow base paper; GLASSINE paper substrate is dense and uniform, with good internal strength and transparency, making it a commonly used material for making barcodes. It is commonly used in white and blue.

Facial paper is the carrier of label printing content, which is divided into several types according to material, such as coated paper, thermal paper, PET, PVC, etc. The back of the face paper is coated with adhesive, which not only ensures a moderate adhesion between the base paper and the face paper, but also ensures that after the face paper is peeled off, it can have strong adhesion with the adhesive.

PET Advanced Label Paper

PET is the abbreviation for polyester film, which is actually a polymer material. PET has good hardness and brittleness, and common colors include silver, white, and bright white. Due to its excellent dielectric properties, such as anti fouling, scratch resistance, and high temperature resistance, PET is widely used in various special occasions. In fields such as electronic parts, mobile phone batteries, electrical products, automotive parts, chemicals, outdoor advertising, textile printing, etc;

Copper coated paper (snow copper) label

It is a commonly used material for barcode printing, and its thickness is generally around 80g. Widely used for barcode printing purposes in supermarkets, retail, clothing tags, logistics labels, inventory management, railway tickets, drug labels, product printing, etc;

PVC premium label paper

PVC is the abbreviation for vinyl, and it is also a polymer material. Common colors include sub white and pearl white. PVC has similar properties to PET, and it has good flexibility and a soft feel compared to PET. It is often used in high-end occasions such as jewelry, watches, electronics, and metal industries. However, PVC has poor degradability and has a negative impact on environmental protection. Some developed countries abroad have begun to develop alternative products in this regard.

Thermosensitive paper

Thermal paper is a paper material treated with a high thermal sensitive coating, and the surface material with high sensitivity can be used for low voltage printing heads, thus minimizing wear and tear on the printing heads. Heat sensitive paper is a type of heat sensitive paper specifically used in electronic scales and cash registers. The simplest method to test heat sensitive paper is to use your fingernail to scratch the paper with force, leaving a black scratch. Heat sensitive paper is suitable for labeling shelves such as cold storage and refrigerated cabinets.

Washing label

Mainly used in the clothing industry.

Corrugated Paper Applications

Flexographic printing has developed rapidly abroad, especially in packaging printing. In the United States, flexographic printing accounts for 75% of the packaging printing market, while 35% of the total printing volume in Europe uses flexographic printing, and this market share is still expanding. Relatively speaking, flexographic printing in China started relatively late, but with its unique process and characteristics, it has emerged in the packaging and printing industry and is being promoted and popularized.

The application characteristics of flexographic printing in corrugated cardboard boxes

Currently, environmental awareness is constantly increasing and resource conservation is receiving attention. Flexographic printing is considered a widely used printing method in the printing of multiple varieties, small batches, short cycles, and low costs of ordinary paper boxes and cardboard boxes. Flexographic printing has the following advantages in corrugated box printing.

(1) Good environmental friendliness. Flexographic printing uses water-based ink that meets international environmental requirements, which is pollution-free during the production process and greatly improves the qualification rate of printed products. When making plates, non volatile and environmentally friendly solvents can be used, and waste solvents can be recycled using a recycling device to minimize pollution.

(2) Low loss, short cycle, and high efficiency. Flexographic printing usually uses drum type materials, with a width of up to 2.5cm and several meters. In terms of printing cost, flexographic printing is 15% lower than offset printing; In terms of paper consumption, the scrap rate of flexographic paper is 1%, while that of offset printing is 5%; In addition, flexographic printing can integrate various functions such as printing, die-cutting, and polishing. The production process of flexographic corrugated cardboard boxes is 2-3 fewer than offset printing. Therefore, in the printing cycle, flexographic printing takes 2-3 days to complete live parts, while offset printing takes 7-8 days to complete. After offset printing, equipment such as a backmounting machine, die-cutting machine, and polishing machine need to be equipped, which increases investment. In short, flexographic printing can greatly shorten the printing cycle, reduce energy consumption, and cost, Enable users to occupy a leading position in the fiercely competitive market.

(3) Easy to operate, low noise, and pollution-free. Compared with other printing machines, the structure of the flexographic printing machine is relatively simple, making it easy to operate and maintain. The transmission mechanism of the machine operates with low noise, and the water-based ink used is pollution-free to the environment.

(4) There is no flying ink phenomenon. Due to the use of water-based ink in flexographic printing, which is environmentally friendly and equipped with a reverse ink scraper, there will be no ink flying phenomenon. After printing, the corrugated cardboard box will not fade or deink.

(5) Enhance the compression resistance and load-bearing capacity of corrugated cardboard. Flexographic corrugated cardboard, after high-temperature treatment and hot adhesive bonding, has significantly better compressive strength than offset cold adhesive composite. Moreover, after flexographic printing and UV polishing, the corrugated cardboard box has functions of wear resistance, dirt resistance, and moisture resistance.

Although flexographic printing machines have various advantages and are simpler in structure than offset printing machines, there are many factors involved in flexographic printing, such as plate material, anilox roller, ink, and imprint structure, which all affect and constrain each other during the flexographic printing process. Therefore, flexographic printing is a highly technical process, and practitioners must master relevant knowledge from the pre press plate making process to the printing process. In addition, as a relatively mature printing process, offset printing and gravure printing have some recognized or nationally established standards and specifications to follow. However, there are currently no universal guidelines, parameters, or guiding process specifications for flexographic printing, which requires practitioners to have a solid accumulation of knowledge.

Flexographic direct printing

The production process of using flexographic printing for corrugated cardboard boxes is corrugated cardboard production → direct flexographic printing of cardboard → die cutting and slotting → adhesive nailing of boxes. The biggest advantage of direct printing with flexographic printing is that it can be produced online, that is, printing, polishing, die-cutting, slotting, gluing, and bundling can be completed on one machine. The newly built corrugated cardboard factory only needs to be equipped with a corrugated cardboard production line and a flexographic printing machine to be put into production, while using offset printing and pre printing methods requires multiple equipment.

There is a certain degree of excessive packaging problem in China's packaging market, which hinders the promotion of flexographic printing technology. However, there are still some factors that will promote the promotion of flexographic printing technology in the corrugated box industry. If the product undergoes frequent revisions or version additions, the flexographic printing method of printing directly on corrugated cardboard has the advantages of fast speed, low cost, and good quality; The market is developing towards intensification and scale, and customer inventory is decreasing. More and more packaging materials are required to be directly used after delivery, and flexographic printing has a faster customer response speed.