1. There are three ways to print corrugated cardboard:
1 Printing directly on corrugated cardboard with a photosensitive flexographic or rubber plate (mostly an array type) is called a post-printing process.
(2) Fine offset printing on reel copperplate paper with an offset or flexo printer, followed by bonding with corrugated paperboard, known as the master table process.
3 In the production of corrugated cardboard, the first version of the reel paper is printed on a flexible version of the satellite machine, and the corrugating medium and the liner are combined to produce corrugated cardboard. This means that the corrugated board produced is a good product to be printed. For preprinting process.
The first post-printing process conforms to the principle of “quickness, convenience, environmental protection, and economyâ€, and it is used more often, accounting for about 70%.
The second type of offset printing has a higher cost for the main table, which is suitable for a small amount of sharpness and requires high-quality, special-shaped corrugated boxes.
The third pre-printing process is suitable for large-volume products and is rarely used in China.
2. Main factors to improve the printing quality of corrugated carton (box) flexo printing
(1) The quality of corrugated paperboard tends to use E-type corrugated paper for printing after the printing; multi-layer composite corrugated paperboard is also used for printing on the E-type corrugated layer, which is conducive to uniform printing pressure, flat mesh, and paper saving. The domestic three-layer corrugated paper is mostly AC (or B) corrugated composite; the five-layer corrugated paper is an AB or BC corrugated composite; the seven-layer corrugated paper is ACB, BAB, BAA, CAC-type corrugated composite, rarely E-type corrugated cardboard or Combined with E-type corrugated.
Printed cable version of the corrugated board to use white paper, foreign generally used paint white cardboard or 85g single coated paper, offset paper. Light-coated and recoated white-white cattle paperboard produced by the Finnish forestry company is a coated type corrugated paper. Compared with non-coated paper, the coated paper has a 63% higher printing ink density; the gloss is 350% higher and can be printed well. Quality and clarity. However, the use of ordinary ink printing coated paper, ink will often appear uneven, slow drying conditions, it is recommended to use a new generation of ink or a flexographic printing machine with drying device. In addition, a small area of ​​graphic and text will be printed first, and a large area of ​​graphic and text will be printed. The sequence of black, cyan, magenta, and yellow may be used. At present, Finnish White Cattle Calf Paper has been used for branded beer, beverages, food, computers, and home appliances.
(2) Equipment factors The improvement of the color printing quality of corrugated paper shall bear the brunt of the technical transformation of the printing equipment, the deployment of a high-level corrugated paper printing machine with more than 3 colors, and the imported high-precision carton printing machine with high printing accuracy. Computer-controlled carton production lines will surely be adopted more and more. Shaanxi Printing Machinery Co., Ltd. is a key enterprise in China's packaging, decorating and printing machinery manufacturing industry. Its leading product YCW series corrugated board printing slotting machine technology ranks the leading domestic level, mainly used for 3 or 7 color printing of corrugated cardboard. , Completion of indentation, slotting, cutting corners, hitting hands, air holes, etc.
(III) High-quality ink, ink and ink systems
1. Flexo inks for corrugated cardboard There are currently three types of flexographic printing inks commonly used at home and abroad:
1 Flexible water-based ink: mainly used for paper printing;
2 flexo alcohol-soluble ink: mainly used for plastic printing;
3 flexo UV ink: general-purpose ink.
China's corrugated board printing uses water-based ink.
More than a decade ago, the domestic production of water-based ink still stays at the level of maleic acid-modified rosin resin. Although this water-based ink has good printability and good storage stability, the printing ink layer The poor gloss, slow drying, and poor resistance make it difficult to stretch the paper.
Hanghua Ink Chemical Co., Ltd. uses a new type of acrylic copolymer resin with good performance as the water-based ink for connecting materials, and introduces WBIBF series water-based flexographic printing inks printed on high-grade corrugated cardboard. Gangu Ink Factory, Tianjin Ink Factory, Shaanxi New Century Material Research Institute and Co., Ltd., and Tianjin Toyo Ink Company have all developed high-quality water-based inks to replace imported water-based inks. At present, the drying speed of water-based ink has reached 200m/min, the resolution has exceeded 150l/in, and the imprinted gloss is no less than solvent-based ink.
Water-based ink control indicators include viscosity, pH, and dryness.
2. Anilox roller Anilox roller is a key component of the flexographic printing press. The heart of the flexo printing machine is made by special means to sculpt the surface of the roller into a specific cell shape. Its role is to use the ink. Uniformly and accurately transferred to the plate, the anilox roller is also called an anilox roller.
1 Chrome-plated Anilox Roller The metal anilox roll is extruded or sculpted by a metal mold or an electric engraving machine on a relatively soft metal roll by a certain number of lines and a mesh cavity shape. To make it hard, it is plated with chromium. The mesh structure of the chrome-plated anilox roller is of the shape of an inverted pyramid, with large openings and small bottoms. In addition, the metal itself has no ceramic wear resistance, and the use of the mesh wall will begin to increase in thickness and the ink load will drop. Under the same squeegee conditions, the color density will drop, and the dots on the printing plate will easily penetrate into the interior of the cell, with excess ink on the side, resulting in blocking of the plate and printing of large ink dots that should not appear. Due to the limitations of metal molds and metal properties, it is difficult for chrome-plated rolls to reach a high number of lines, usually reaching about 400 l/in.
2 Ceramic Anilox Roller The ceramic anilox roll is produced by plating nickel and sprayed ceramics on a metal base roll, and then using a laser to sculpt a certain number of wire and cell shape on the ceramic.
The ceramic anilox roller is very wear-resistant and the loss of ink loading is slow. Under the condition of using a squeegee, a good quality ceramic anilox roller has a lifetime of 10 times that of the chrome-plated roller and can reach a high number of lines ( 800l/in or more).
At present, the CO2 laser engraving ceramic anilox roller is widely used in the carton industry, and the net hole is a deep cup shape. In the printing, the ink at the bottom is not released, so the effective ink transfer amount is low, the rough ink is not released, the effective ink transfer amount is low, and the rough net wall must be polished, not only thick but also uneven. The inner wall of the cell site is also relatively rough, and the ink has poor filling and releasing properties, and the ink is easy to be blocked therein.
The APEX-Ultracell super laser (YAG laser) operated by Hongye Equipment Co., Ltd. engraved ceramic anilox roller with a wide bowl-shaped net space, and the network hole does not need to develop in depth. The effective ink transfer volume is very high, and the net point is straight. Side wall rule, according to the calculation of 1200l/in anilox roller volume the same as the traditional 700l/in, can meet the production requirements of fine, high color intensity products.
Hexagonal and 60° mesh shapes are currently used because the shape of the mesh is the most favorable for ink release. Select the number of anilox roller lines should consider the level of the number of lines. That is, the number of screens: the number of anilox rollers = 1:4 to 1:5. The guarantee that the amount of ink carried by the anilox roller is constant is the maintenance and maintenance of the anilox roller. First, perform daily cleaning. Immediately after shutting down, anilox rolls are sprayed on the surface of the anilox roller with a special cleaning agent. Fine brushes (stainless steel brushes are used for brushing ceramic anilox rollers, and wire brushes are used for cleaning metal anilox rollers) are repeated. Brushing, and secondly, periodic cleaning must be done. It is usually done in the first shift, every week, or at the time of color change. Shanghai Aokeli Printing Machinery Co., Ltd. sells ink cleaning products.
3. Should use reverse (reverse) squeegee ink system
The installation direction of this system squeegee is opposite to the direction of rotation of the anilox roller. Compared with the conventional angle, the pressure between the squeegee and the anilox roller is lighter, the loss is smaller, and it can be more accurately transmitted and controlled. Printing ink to meet the requirements of high-quality printing.