Printing and recycling of milk and juice packaging containers

With the improvement of people's living standards, the consumption of milk and fruit juices has increased dramatically. In order to facilitate storage and transportation and meet the goals of health, environmental protection and promotion, higher requirements have been placed on the packaging of these drinks. This article describes the printing, recycling and development trends of milk and juice packaging containers.

I. Printing of containers for milk and juice packaging paper

(I) Printing process

The printing of milk and juice packaging containers generally needs to go through the following processes: decoration design, plate making, printing, compounding, slitting, and bag making.

1. Decoration Design

The decorating design of the paper container is an important part of the packaging design. It is an important means to facilitate the use, communication of product information, and promotion of sales. With the continuous improvement of the economic and cultural living standards of our people and the increasing expansion of foreign trade, the design and decoration of paper containers is very important. In the interior design, we must first consider the requirements for the packaging of goods and choose the appropriate style. Second, we must consider the correct and appropriate use of patterns, text, and colors. We must follow the principles of “scientific, aesthetic, applicable, economical, and promotional” and strive to have a beautiful design. The sense of the times, decoration and nationality.

At the same time, in order to achieve the above design goals, we must adopt advanced process technologies such as CAD (Computer Aided Design), CAM (Computer Aided Manufacturing), and professional software, such as Flunder - Pack, a specialized software for packaging carton structural design. With good design as a prerequisite, we can shorten the gap with foreign countries as soon as possible, and promote enterprise products to be “up-level”.

2. Plate making and printing

Paper containers can be printed using traditional analog printing and new digital printing. With the development of the printing process, none of the printing methods is only for paper containers, and almost all printing methods can be used in paper container printing. At present, most of them still use analog printing. Different types of printing plates need to be prepared according to different printing methods, and different printing processes are adopted.

In the conventional four major printing methods, lithography is the most commonly used, while the presensitized version of PS is mainly used in lithography. Because the PS version is simple and fast, the plate is light and inexpensive, and with the application of new light sources, new photosensitive materials, and new types of equipment, the quality of platemaking continues to increase.

The second can use gravure. The gravure printing plate is partially concave, and the blank portion is in the same plane. The gravure is often obtained by a photographic method and an electronic engraving method. The gravure image is rich in color and rich in hue. The printing plate has a high printing rate, which is very suitable for the printing of packaging products. However, gravure plate making is difficult, the cycle is long, and the cost is high. However, with the development of the electronics industry and the popularization and application of electronic engraving platesetters, gravure will play a greater role in packaging and printing.

The third is letterpress printing. Toppan printing is suitable for small batches and many types of prints. Printed prints have clear outlines, strong strokes, and bright ink. They are mainly used for text-based prints, but are less widely used on paper-based prints, but China's national conditions, there are a wide range of letterpress printers, so many packaging printed products still use this approach. In addition, the use of adhesive-convex printing technology, printing those existing color patterns, text, lines, background, and a large area of ​​the packaging paper, you can give full play to the advantages of embossing and offset, and avoid weaknesses. Get a good copy effect.

At the same time, the flexo version derived from letterpress developed rapidly in the application of packaging printing. The flexographic plate is a general name for a letterpress made of an elastic solid such as a rubber relief, a photosensitive resin plate, or the like. Flexo printing combines the advantages of embossing, gravure printing and offset printing, as well as high speed, versatility, low cost, and simple equipment. Its main features are: Flexible flexo printing is a direct printing method; ink is supplied by a short ink path system, and the mechanism is greatly simplified; low printing pressure, close to non-pressure printing, can realize lighter printing press; can be used for multiple printing Materials are printed at high speed. At present, the flexographic printing quality is close to that of lithographic offset printing and gravure printing, and the printing ink solvent is alcohol or water, which can be completely non-toxic, and completely volatilize, and the post-press processing is easy to achieve continuity, and generally uses web rotation printing. , Can be die-cut online, paste boxes, bag making, etc., especially suitable for food automated packaging production. At present, flexographic printing in industrialized countries has been widely used for packaging and printing, and it is generally believed that the development of flexible packaging will mainly focus on gravure printing. For example, in the United States, 45% of packaging printing has been adopted. Flexo printing [1]. Although there is still a big gap between the speed of development and the application of flexographic printing in China and in Europe and America, in recent years, more and more applications have been applied to flexible packaging. At present, China has successively introduced 100 flexo production lines [2]. ].

The fourth is stencil printing. The printed part of a stencil is composed of meshes of different sizes or of different sizes but within a unit area. During printing, the ink is applied to the printing plate, the printing material is placed under the printing plate, and the printing material is transferred onto the printing material to form a printed product by scraping the ink through the holes on the plate surface. The printing plate of the stencil printing plate has a thick ink layer and has a wide range of printing. It can be used for the printing of paper packaging containers, but the production efficiency is low, and it is generally not used.

The above is a traditional printing method. With the development of digitization and network technology, digital printing has been widely applied to the printing of paper containers. Digital printing eliminates color separations, simplifies production processes, and enables short-run, fast, practical, elegant, and economical printing processes. The digital printing system mainly includes the following four aspects: (1) Digital Graphic and Text Prepress Processing; (2) Direct Platemaking; (3) Direct Printing; (4) Direct Digital Color Proofing; The traditional printing process from manuscript, plate making to printing has been changed, which not only greatly simplifies the process, shortens the production cycle, but also gives new meaning to “printing”. For example, ink-jet printing, using computer-controlled nozzles to directly print ink on paper to obtain graphic and text information; another example is the Indigo series of digital printers, which incorporates computer, network, data processing, laser imaging, and liquid electronic inks. High-tech and other new technologies are subtly combined to fully meet the personalized and changeable printing requirements of paper containers and meet the needs of the market.

3. Compound

The compounding process is the most important in the entire process because it plays a decisive role in the packaging function of the entire container. For example, the paper container Tetra Pak, the printed semi-finished product is placed on the compounded unwinding rack, and after four times of lamination, the aluminum foil (aluminum foil can be protected against ultraviolet light to ensure the quality of the contents) adheres. Finally, The winding section is wound into a roll shape. Tetra Pak's four-layer plastic is made from outer layer, composite layer, inner layer 1 and inner layer 2 with different thicknesses of polyethylene or modified polyethylene resin, and extruded through four extruders. The wide film is bonded to paper and aluminum foil [3]. The core of the entire compounding process is the bonding force between the layers. If the bonding strength is not good, all the products will have the phenomenon of rising bags and missing packages soon after filling. So before the bonding, two flame processors pre-treat the paper base on both sides, and each layer of plastic has ozone gas jet at the outlet of the extruder die, which can greatly enhance the packaging materials. Adhesion between layers. Secondly, there is a special laser device [4] to monitor the quality of each point in the inner layer, even if it is a small black spot, or a small bright spot, it can accurately measure and remove these defects in the subsequent process. To ensure that the packaging of liquid beverages is intact before filling.

4. Cutting

This process is relatively simple. It cuts the compounded semi-finished products into individual pieces. Each piece is wound into small rolls of a certain diameter at the winding place, wrapped in a shrink film, and finally the several layers are transported in several layers. To wooden platform, wrapped by wrapping film into a finished product [5].

5. Making bags

After liquid beverages such as milk and juice are filled, they are aseptically heat-sealed in a filling machine or a bag making machine. The methods of heat-sealing are mainly side-sealed, palm-closed, and pleated. Sealed packaging does not need to be refrigerated when it is distributed and stored, and the shelf life can be guaranteed.

(b) Printing materials

As a packaging container for milk, fruit juice and other foods, its safety and hygienic properties are increasingly attracting people's attention. Therefore, in the selection, production, and circulation of raw materials, they must meet the requirements of the Food Sanitation Law. The paper container must use pure bleached pulp and can not use waste paper as raw material. At present, generally 100% softwood pulp is used as raw material, and the paperboard is made by a long wire paper making machine. The cardboard banner is required to have the same amount and physical strength; and the production process is The quality of water must comply with the “Standard for the Production of Drinking Water” (GB5749); Additives such as fluorescent whitening agents must not be added; Wax paper or paperboard must be of food grade; Printing ink must be non-toxic, heat-resistant, cold-resistant, solvent-resistant, etc. Oil-resistant, abrasion-resistant, and radiation-resistant, and the ink is not transferred and is conducive to the recovery of paper containers; The solvent in the ink is completely volatilized after printing, and the UV ink must be completely cured; Ink and pigment must not be printed in containers that come into contact with food when printing. Inside; aluminum foil used for paper containers, shall not use recycled aluminum; at the same time, the hygiene of printing workshops and personal hygiene of workers must meet the hygiene standards.

Second, paper container recycling

After the consumption of milk and juice, the responsibilities of the paper containers have been completed. Like other packaging wastes, they become solid waste. Where do these wastes go? According to the basic principles of the “recycling economy” theory, sustainable development is the only way for the future development of humankind. The choice, we want to recycle it, how to recycle and use it? This is an important issue facing the development of paper containers.

For the recycling of milk and juice boxes, the ink contained in the carton, residual milk in the box, juice and polyethylene plastic must be taken into account. At present, for the recycling of milk and juice boxes, one is by collecting and the other by technology [6].

(a) Collection of milk and juice boxes

After the milk and juice boxes are picked up at the point of purchase, they are shredded, disinfected, and dried in a carton shredding and sterilizing device. The shreds are packaged into bales and sent to waste paper processing plants for further processing. The purpose is to Ensure the odor and bacteria count of the final product.

(2) Using related technologies to remove smashed plastics from other de-inking treatment processes, milk and juice boxes need not be de-inked when recycled, because inks are generally printed on plastic films, and plastic film materials are gathered. Ethylene and paper fibers are electrostatically bound together, are relatively easy to separate from the fibers, and have very little fiber loss, so the ink can be removed simultaneously with the polyethylene when the fibers are recycled. Therefore, the recycling of milk and juice boxes is mainly through screening and reverse slag remover to remove the crushed plastic in the pulp. The main process is as follows:

The collected and packaged debris are transported to the pulper for repulping in the reservoir through a conveyor belt, and then the pulp is withdrawn from the orifice plate under the pulper and sent to the high-concentration and impurity-removing unit after removing the larger debris by the demissifier. The device is then processed through a fine hole screen, a long slotted fine screen, and a reversed slag remover, and finally reaches a washing and concentrating machine and is sent to a storage and storage pool for storage.

At the same time, a large piece of polyethylene left in the pulper is flushed from the pulper with water to a round-hole sieve. Better fibers are returned to the hydropulper. The polyethylene film discharged from the end of the cylinder as waste can be packed and delivered to the boiler. Burning treatment. Note that when repulping, add proper caustic soda to the pulper, remove the wet strength agent [7], and perform gentle degassing inside the machine so that separation of the polyethylene from the paper fibers can be achieved as much as possible. Through the above process, generally about 75% of the pulp quality can be obtained, and if it is required to obtain a high brightness pulp, a dithionite bleaching process can be added [8].

Note that the above is only for the recycling of milk and juice cartons containing polyethylene plastic. If the carton contains aluminum foil, besides recycling pulp, metal aluminum should also be recycled. Recycling of metal aluminum can be achieved by using fired carbonized aluminum scrap paper or paper aluminum foil composite materials to recover aluminum particles. Chemically recycled waste paper containing aluminum foil can also be used. The following chemical method is used as an example [9]. When recycling, use an aqueous solution containing an emulsifier, degumming agent, and dispersant to soak the aluminum foil waste paper for 5 to 7 minutes, and then turn the stirrer on and stir it for about 5 minutes to stand still; remove the upper aluminum foil pulp mixture and wash it in water.