Abstract : This paper describes the method of printing carton, carton and other packaging products using offset printing process. The characteristics of offset printing, the method of plate making, the process arrangement and the printing method are introduced.
Keywords: direct printing direct plate making PS plate ink balance
Paper packaging mainly refers to cartons, cartons, paper bags used in the packaging of goods, and corrugated cartons for transportation and packaging.
1 Offset features and process arrangements
1.1 Offset Features
1.1.1 Fine pattern
The product produced by offset printing has a fine pattern, bright ink and clear graphics.
1.1.2 tone: good reproducibility
Comparing offset printing with embossing and screen printing, the reproducibility of tone reproduction is good. Compared with offset printing, offset printing has a short cycle time and low cost.
1.1.3 Ink thickness is small
Offset ink color åˆ; if other printing methods are thick, in the traditional printing, the offset printing ink layer is the thinnest.
1.1.4 Printing pressure
Because offset printing pressure is large, offset printing is generally not easy to directly print corrugated cardboard, and it is not possible to print thick paperboard (an offset press with a print thickness of less than 0.75 mm corrugated cardboard is currently available).
1.2 Process Arrangement for Printing Corrugated Carton (Box)
Offset printing Corrugated paper boxes (boxes) are divided into direct printing and pre-printing. Direct printing, also referred to as primary or post-printing, refers to the direct printing on a formed corrugated board with a print thickness of 0.75 mm or less (E and G type corrugated paper). Pre-printing, also known as secondary processing, refers to printing on cardboard first, followed by corrugated board forming.
Direct printing process arrangement: corrugated cardboard → printing → glazing (laminating) → die-cutting indentation → folding box, gluing box → inspection.
Pre-printing process arrangement: surface board → printing → glazing (laminating) → affixing with corrugated cardboard die-cut indentation box, paste box → inspection.
1. 3 Offset printing machine suitable for printing boxes (boxes)
Offset printing machines suitable for printing boxes (boxes) should meet the following requirements: Generally, a sheet-fed offset press is used; the range of substrate thickness is large: the printing accuracy is high, and the ink path is longer (to prevent the occurrence of ink bars when printing large areas on the ground); There are anti-dirty devices to prevent back.
1. 4 Requirements for carton design
1.4.1 The size of the carton is not too large. If the width of the box exceeds the width of the printing press, the carton should be divided into two halves for printing. In this case, an additional interface is required.
1.4.2 The cardboard thickness should not be too large. If the cardboard thickness of the box exceeds the thickness range of the offset printing machine, thin cardboard should be printed first, and then one or more layers of cardboard should be laid on it.
1.4.3 The printing processability is good. In addition to aesthetic considerations, the design of the pattern should not consider the degree of difficulty and the effect of copying of the printing process at the same time, so as to avoid large-area on-site, flat screens, and to avoid local ink volume differences. Big phenomenon.
1.4.4 The number of registrations should be reduced. The number of registrations should also take into account the beauty of the design, the economic benefits, the number of printing mechanism units and the accuracy of the machine overprint.
2 Offset printing process
2.1 Offset printing plate
2.1.1 PS version
The PS plate was pre-sensitized, and the plate was an aluminum plate with a thickness of 0.15 mm, 0.3 mm, and 0.5 mm. The surface of the PS plate has a diazo or azide-based coating with a high publishing base of about 3u. PS version is divided into positive PS version and negative PS version, positive PS version is photolytic type, blank part of the exposure decomposition, remove the coating in the developer to expose the hydrophilic layer; no part of the picture does not see light decomposition, A oleophilic layer forms. The negative PS version is a photopolymerization type. In the graphic part, light photopolymerization occurs to form a lipophilic layer; the blank part is unreacted, and the coating is removed in a developer to form a hydrophilic layer.
PS plate making process is simple, easy to grasp, and the printing quality is good. It is the most widely used printing plate in offset printing.
2.1.2 Gravure
The gravure plate base is a zinc plate with a coating of polyvinyl alcohol and ammonium dichromate on the surface. Flat gravure is divided into positive and negative editions. When the positive gravure edition is printed, no light is found in the graphic part, no hardening, and the coating is removed in the developer. The etching solution is slightly corroded by the 3-5u, and then the pro Oil-based paint; after exposure of the blank, the hardened layer was washed with a phosphoric acid solution to expose the hydrophilic layer.
Flat tone color tone reproducibility and graphic clarity are not as good as the PS version, the plate making process is not easy to grasp, the plate quality is unstable, and the use is limited.
2.1.3 Multilayer Metal Plate
Multilayered metal plates have double-layered metal plates and three-layered metal plates. The double metal plate consists of a copper base and a chrome layer. The three-layer metal plate consists of a sheet metal base, a copper plating layer and a chrome plating layer.
Multi-layered metal plates can be made into flat and gravure plates and flat plates. The gravure plate method is as follows: coating with a photosensitive liquid, exposure of a positive picture, development, and corrosion. In the graphic part, no light is seen, no hardened, the coating is removed in the developer, etched to the copper layer, the plate is concave, and the copper layer is oleophilic. The hardened layer is washed off in the blank portion to expose the chromium layer and is a hydrophilic layer. Plano-convex version of the surface of the copper layer, plate making methods: coated photosensitive solution, negative pictures, development, corrosion. The blank part is not photo-cured, the coating is removed in the developer, and the chromium layer is etched to form a hydrophilic layer; the hard and soft layer is washed away and the copper layer is exposed to form an oleophilic layer.
Multi-layer metal plate production is complicated, limiting its use.
2.1.4 Protein Plate
The plate of the protein version is a zinc plate with a protein gel and ammonium dichromate coating on the surface, and a negative film on the negative plate. The process flow of plate making is: coating photosensitive adhesive, exposing, developing and washing. Graphic part of the photosensitive, forming a hard film, oleophilic, high publishing base 3-5um; blank part is not sensitive, washed with water, exposed material, for the hydrophilic layer.
Protein plate hardenable protein membrane has poor acid resistance, poor abrasion resistance, low resistance to printing, poor printing quality, and less use.
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