The carton is one of the most important forms of sales packaging. In recent years, there has been an unprecedented rapid development in our country. The purpose and performance requirements of paper foods determine the materials, prepress, printing and finishing processes and equipment, and the filling/packaging equipment also has a direct impact on the process and equipment of the carton. The printing and post-processing processes and equipment used in cartons of different uses are quite different, and the focus and direction of development are also different. But overall, the development of carton technology has the following new features:
First, from single-layer materials to multi-layer materials
The shaking of the carton used is from layer 1 to layer 7, but the use of multi-layered materials tends to increase. This is mainly because the field of use of the carton is continuously expanding and the performance requirements are getting higher and higher. The number of carton material layers can be roughly divided into three levels: single-layer material, 2-3 layer material, and multiple layers (4-7 layers). Common cigarette packs, cosmetics boxes, medicine boxes and some food boxes are all made of single-layer materials; most wine boxes and food boxes use two or three layers of materials; paper-based multilayer materials (4-7 layers) ) More and more widely used in paper packaging with higher barrier properties such as beverage boxes, "Tetra bags" (5-7 layers), "Kangmei boxes" (7 layers) and "roof packs" (4) Layers) are typical examples.
Monolayer cardboard is generally 220-450g/m2; 2-3 layers of material have the following structures: cardboard (printing surface) / E corrugated, film / cardboard (printing) / cardboard, film (printing surface) / cardboard / cardboard , film/cardboard (printing)/E corrugated, etc., typically 500-600 g/m2; and an example of a multilayer (7-layer) structure: polyethylene/paper/polyethylene/adhesive layer/aluminum foil/glued The layer/polyethylene can have a basis weight of 600 g/m2 or even 1000 g/m2. The production of multi-layer materials often uses coating and compounding processes. Such as 7-layer composite paperboard adopts the following processes: unwinding (paper selection) - 1st extrusion coating unit 1 (concave roller) coating unit - 2nd extrusion coating/composite unit - 2nd (concave roller) Coating unit - third extrusion coating unit - rewind.
Second, a variety of printing methods coexist, flexographic printing growth
Offset printing, gravure printing, flexo printing, silk screen printing and other printing methods have all been applied in carton processing. Almost 100% of the printing on sheet-fed paper is offset printing, and these methods are used in web printing. The number of carton printing color groups is generally between 2-8 colors, of which 4-6 colors are used most. In recent years, more and more spot colors have been used in folding cartons. Therefore, a large number of printing color groups use 6-8 colors. Sheetfed offset printers generally have no more than 5-6 colors, so their use is being challenged, and the use of web presses (including offset, gravure, flexo, and screen printing) has increased rapidly. Judging from the current situation, in the high-end and high-volume printing, gravure dominates, and its use ratio has remained basically unchanged throughout the 1990s (as in the United States); in the medium and small batches, medium and low-grade printing, the flexographic ratio has increased. The fastest. In addition, gravure and flexo printing do not have certain limitations on materials and processes.
There are two main types of equipment used for the flexo printing of the carton: the unit type flexo press and the satellite type (CI type) flexo press. Because of the low price and flexible function, the unit type flexo printing press has received attention in the country in recent years. Generally, a UV curing device is installed in the last-color group for UV coating. In addition to printing and glazing, narrow-width unit-type flexographic printing presses can also be equipped with units for online bronzing, embossing, die-cutting and conveying and delivery. Since the online bronzing has a great influence on the speed of the whole machine, the on-line embossing and die-cutting tools must be processed abroad. The cycle is long and the price is high, so it is only suitable for printing large-scale, single-type paper boxes, such as cigarette packets. Wine boxes and so on. Taking into account the requirements of flexibility, many domestic manufacturers currently choose to cut large sheets online, and then use a sheet-fed die-cutting hot stamping machine to die-cut hot stamping. Because most printing companies have die-cutting hot stamping machines (one or more), this configuration is a good choice. At present, high-speed automatic delivery of on-line die-cutting has been widely used, and the effect is very good. Wide-range unit type flexographic printing presses are produced in major manufacturing facilities in Europe and the United States, but the number is small. In foreign countries, the carton flexo printing press is based on the CI model. The main reason is that the CI type has the following advantages compared with the unit type: 1 has higher overprint accuracy; 2 more reliable performance; 3 fewer parts and more convenient maintenance; 4 can be equipped with a robot (replacement downtime less); There are better upgrade performance and so on. As flexo printing meets more and more stringent environmental requirements, its own printing quality is also increasing, and the price of CI-type flexo printing presses is relatively low (generally about 25% lower than the price of gravure printing machines of the same color group). It is widely used abroad and gradually recognized and valued in China.
In China, except for the use of offset printing, the Tetra Pak has now been printed in a natural format. "Combibloc" mainly uses gravure printing. For some of the less demanding cartons, such as garment packaging boxes, shoe boxes, etc., flexo printing is becoming its main printing method.
Third, the development of sheet-fed paper to roll paper, stand-alone online production
Sheet-fed printing press was once the main model of carton printing. It has the advantages of simple plate making, standard color printing, and universal versatility. However, the subsequent processing is complex and generally only suitable for small and medium batch production. In the short live production area, it is facing the competition of web flexographic printing presses; in the large-volume printing, web gravure has always been dominant. Due to the increase in the use of online web-cutting, online die-cutting, trimming, compounding and on-line slitting and rewinding equipment for web printing presses, the production process and on-line production equipment of the mechanism carton have become more and more extensive. used.
Of course, carton production is very different from material preparation, printing, post-press processing, molding, filling, and packaging, so the on-line production methods vary from product to product, and the machines used can vary greatly. Such as:
Single-layer boards such as cigarette packs are printed on webs—cross-cut (on-line or off-line)—single-sheet die cut/pressed embossing—bronzing (aluminum) or web-fed—on-line die-cut/embossing.
2-3 layers of paperboard with web-printed film compound - die-cut (on-line or off-line) sheet-fed die-cutting / embossing; roll-foil film-printed paperboard compound - crosscut (online or not) sheetfed Cut/press concave and convex.
In multi-layer materials, the on-line production methods adopted by Tetra Pak are: unwinding-compounding-printing-slicing-rewinding; unwinding (cutting and cutting) cutting-die cutting/pressing and embossing-adhesion Junction forming filling and so on. The "Combibloc" and "roof packs" use the so-called "preformed carton", namely: unwinding compound - printing - cutting - die cutting / embossing - seam joint; flat folding carton - bonded forming irrigation Equipment, equipment, etc. are not the same. Automatic packaging, filling, folding, sealing, assembly and stacking can be realized on the packaging machine, which has high production efficiency.
On-line post-press processing also includes hot stamping, laser holographic anti-counterfeiting, etc., but at present, it is only used on a narrow range flexographic press with a low speed.
4. More and more constrained by environmental protection and health standards
Due to the increasingly strict implementation of environmental protection and hygienic standards, the standards for carton materials, adhesives, inks, solvent residues, waste water and waste gas in production processes, and storage and transportation requirements have increasingly regulated the production of cartons, including water-based oils. The most important development trend, especially in gravure printing, and the promotion and application of solvent concentration control technologies and devices, is also the biggest problem at present.
V. Comprehensive application of various related new technologies to continuously optimize the entire production system
In the carton production process, the most influential processes are printing and die cutting. The quality of printing and die-cutting directly affects the appearance and precise forming of the carton, and the die-cutting also affects the production efficiency and waste of raw materials in the subsequent process. So plates and die-cuts, printers and die-cutting machines are the key to controlling the quality of printing and die-cutting.
Around these aspects, computer design, digital technology, laser processing technology and new materials are continuously applied, and more and more computers and software technologies are used in most of the processes from design, plate making, printing, die cutting, and molding; Continuously improve the machine management system, from single control functions to centralized control, from stand-alone control devices to the entire production line monitoring system; laser engraving technology is widely used in die-cutting manufacturing to improve the production accuracy and speed of die-cutting plates. Reduced workload and scrap rate; more advanced registration technology, substrate size control technology, carton pre-drilling forming technology and mechanical processing technology are also being applied to the carton production. (Text / Zuo Guangshen)