(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected)
Manuscript to win: Wang Shuangxi
Editor's note: With the specification of the packaging market, the requirements of post-processing procedures for packaging products are becoming more and more standardized. We often find discussions about post-press processing on our forums. In order to meet everyone's needs, we must win. I came to a master who has been engaged in die-cutting for many years, and made another issue of molding technology with another college student we invited. If there are any inaccuracies or questions in the article, please welcome to discuss in the Bisheng forum.
The molding process of printed products mainly refers to the special technology of making the printed products into the required shape or producing some special effects on the surface based on the Yin and Yang molds by mechanically applying a certain pressure. According to the different molds used in the processing and the final processing effect, it can be generally divided into two process technologies: concave and convex embossing and die cutting indentation.
The concave and convex indentation process is to use two corresponding female and male stencils to imprint a three-dimensional relief pattern on the surface of the printed product through the action of pressure. Its processing effect is that the surface of the printed product is deformed to a certain extent.
The die-cutting and creasing process uses steel knives and steel wires to form a template, and under pressure, the printed product is rolled and formed. The processing effect is that the surface of the printed product is both deformed and broken.
With the development of production and the continuous improvement of people's cultural and living standards, people's requirements for the packaging of products, in addition to quality, have also increased. Molding processing is more and more widely used in the surface processing of various types of printed products due to its unique process advantages, so as to become an indispensable process technology for the surface finishing of printed products.
1. Analysis of the principle of molding process
1. Molded size
Practice has proved that when the paper thickness increases, the shear stress decreases; otherwise, the shear stress increases. In fact, when the thickness of the paper changes, the main role is not exactly the thickness of the paper, but also the ratio of the molded size to the thickness of the paper. The relationship between the changes is shown in the figure:
Change trend of molded size / molded thickness and shear stress
Note: 1, 2, 3, 4 are printed products of different thickness. 4> 3> 2> 1
2. Pressure calculation
In the molding process, due to the different processing objects and various requirements, the force required for molding should be calculated in advance in order to select and adjust the machine and guide the molding process.
Mold pressure F1 can be calculated by the following formula: F1 = K * α * A
Where: F1-force required for molding, shear stress value per unit area in α-molding, actual area of ​​A-molded separation surface, calculated according to the thickness and circumference of the printed matter, K-considering the actual conditions and a series of molding process Coefficient of technical factors.
Production of two die-cut version
The production of die-cut version, commonly known as row knife. The so-called row knife refers to the process operation of assembling the steel knife, steel wire and lining material into the template according to the specified requirements. In the production of die-cutting and creasing, the quality of the row of knives is the key to ensuring the quality of the processing.
1. Plate-making materials
※ Backsheet material. Including wood block, PVC board and steel plate
â‘ The wood block first requires the wood block to have a high hardness and pressure resistance. The wood block must be uniform in wood, neatly cut and uniform in tightness. The installed knife and thread are even and tight. There is no stress on the whole plate, the die-cut paper will be evenly stressed, and will not break. The wear of the knife is small, which can extend the service life of the die-cut plate. In addition, the board needs to have good flexibility, which can alleviate the bending knife. The wood plate stress caused by non-adherence is not only better for sturdy blades, but also has a certain buffering effect during die cutting, making the blade more durable. The boards suitable for making die-cut plates are birch and beech. At present, the best quality boards are Finnish boards, with even wood, high hardness and good flexibility. The quality of die-cutting plate is good. However, it is an expensive imported plate and is only suitable for die-cutting plates with high quality requirements. Among the domestic products, Shanghai board has the best quality, uniform texture, high flexibility and white surface. Northeast board wood is not uniform enough, it is only suitable for general corrugated boxes, medium-sized packaging boxes, larger curve graphics and other products. Plywood die-cutting plates are of high quality and light-weight. Therefore, plywood is commonly used for wooden floor. The commonly used wooden boards are 18mm and 15mm birch. Die-cutting general products use 18mm thick wood board, die-cutting corrugated paper or sponge products use 15mm thick wood board. 20mm wood board is used to make die-cut version of film and self-adhesive products, and the commonly used waste version is 12mm or 8mm wood board.
â‘¡ The commonly used thickness of PVC board is 8mm, 5mm, 3mm, 3mm thick board to make a composite 18mm knife template, that is, the upper and lower layers are 3mm plastic boards, and the middle layer is 12mm wooden boards. The rivet is riveted and the knife line is installed. Due to the high cutting cost and difficulty in installing the knife, the cost is higher than that of the die-cutting board. In addition, the PVC plastic board will emit toxic gases during cutting, which is harmful to the metal parts of the equipment and the human body, and is not suitable for promotion.
â‘¢ Steel plates that are too thick are not easy to cut, and the cost of the plates is high, so the steel plates are also used to make composite die-cut plates. That is, the upper and lower layers are 3mm thick thin steel plates, and the middle is 12mm thick wooden boards. Although the cost is returned, the die-cut plate made is strong and durable, and the tool can be changed multiple times. The cost can be reduced, and because of the good quality of the die cutting, it can be used to do it.
The life of the die-cut version mainly depends on the number of tool changes, and the durability of different base plates is different.
※ Commonly used knives and threads
Steel wire. The steel wire is used as an indentation line in die cutting and indentation processing. There are two kinds of round mouth line and fast mouth line. 23mm high and 0.7mm thick.
Steel knife. The steel knife is used as a die-cutting line in die-cutting indentation. Steel knives are divided into single-sided mouth, double-sided mouth and other specifications, generally 23.8mm high and 0.7mm thick. Commonly used knives and threads are products of Sweden, Austria, and Japan. In order to adapt to the processing of various die-cut products, the materials of steel knives are hard, medium hard, and soft. The rigid steel knife has high hardness and wear resistance, but has low elasticity and low molding flexibility, so it is suitable for processing products with large processing volume, thick cardboard and simple shape; soft steel knife has low hardness, but good elasticity and molding The degree of curvature can be large, so it is suitable for processing small batches, thin paper and complex shapes; medium hardness steel knives are in between.
The length of the steel knife guillotine cutting should be less splicing, and it is generally not suitable to perform guillotine cutting after forming; the formed steel knife steel wire should have its cutting edge and the bottom of the knife perpendicular to each other to maintain the extension of the steel knife steel wire cutting edge Every point on the is in the same plane.
※ Eraser plug. It uses the elastic elastic restoring force of rubber on both sides of the main steel blade of the stencil to push the cardboard separated from the die from the blade. Its original height is 7mm, the rubber should be 3mm ~ 5mm higher than the blade.
As shown:
Sticky rubber sketch. 1. Lining material 2. Steel knife 3. Rubber
The rubber is generally made of synthetic polymer materials, and the elasticity is divided into three kinds of rigidity, softness and neutrality. It should be reasonably selected according to the specific situation when it is used.
※ Commonly used processing tools.
Wire bending machine. Special tool for steel knife and steel wire modeling. It can bend the steel knife and steel wire into an arc of any arc and a folding angle of 30 degrees to 90 degrees. In order to expand the scope of use and facilitate operation, this type of machine is equipped with commonly used forming molds, a set of commonly used angle die and a set of commonly used round diameter die. (There are about 20 species in each group)
Saw board machine. Saw board machine is a special tool for sawing wood board. Generally, it also has drilling function. The thickness of the commonly used saw blade is 0.7mm and 1.07mm. The selection depends on the thickness of the die-cutting steel knife, steel wire and the processed material.
Guillotine machine. It is a special tool for die-cutting and creasing. The main function is to turn the steel wire and steel knife into the required size.
With the development of the molding process, a combination machine for making die-cutting plates appeared. It has the functions of sawing template, cutting steel wire, knife, corner, and circle and ellipse.
※ Material of bottom mold.
Its main function is to make the fold line of the pressure-bearing product clear and beautiful, without wrinkle cracks and accurate shape after folding. The material of the bottom mold is generally made of kraft paper adhered to the steel bottom plate. The kraft paper is soft and easy to grooving by hand without pressure resistance and imperviousness. At present, a large number of imported bottom mold lines have entered the domestic market. Most of these lines are adhesive, fast and convenient, with full creasing lines and high printing resistance. There are different bottom mold lines for different thick paper suppliers, and its basic structure consists of crimping molds, positioning rubber strips, and protective films.
2. Drawing and layout design
※ Drawing
Draw the black-and-white draft of the molded product, that is, the unfolded view of a single carton container before making the molded plate. Generally, the expanded drawing of the molded product is drawn on a plane, the size of the plate is marked with a pencil, the size of the finished product is marked with a color pen, and the broken line of the indentation is marked with other colored pens (to avoid confusion). This picture is the basis for plate making and printing, as well as the basis for molding. It requires straight and precise lines. Use a high-precision drawing table or plotter to draw.
※ Design of the molded version
The structure of the molded version depends on the product structure. The content of the layout design includes: the size of the embossed layout, which should match the specifications and working capacity of the selected equipment, not only to ensure the processing quality, but also to give full play to the ability of the equipment; determine the type of embossed layout; select the stencil materials and specifications; The grid position should be consistent with the printing grid position; the working part should be located in the center of the printing plate; the transplantation of lines and graphics must ensure the accuracy required by the product; the plate cutting lines should be straight, and the longitudinal die cutting lines should be at right angles to each other and The side of the template is parallel, and the broken knife and broken line should be aligned.
In order to make the steel knife and steel wire of the template have better adaptability to die cutting, the technology of die cutting should be considered when designing the product:
â‘ The knife line of the hole should use the whole line as much as possible, and the corners of the line should be rounded to prevent the splicing of steel knifes that are perpendicular to each other.
â‘¡ The joints of the lines should be protected from sharp corners.
â‘¢ To avoid the connection of multiple adjacent narrow waste edges, the connecting parts should be enlarged to make them into one piece, so as to eliminate waste.
â‘£ To prevent continuous sharp corners, the sharp corners required for reactive power performance can be changed to rounded corners.
⑤ Prevent the sharp angle line from ending in the middle section of another straight line, which will make it difficult to fix the knife, the steel knife is easy to loosen, and reduce the die-cutting suitability.
3. Make a template
Before making, the layout should be transferred to the plywood. There are two methods of transfer, one is manual drawing, and the other is photocopying. Hand drawing is less accurate than photographing, and it is more troublesome.
※ Production of the bottom plate
The production of the base plate is based on the product design or sample requirements. Slots inlaid with knife lines are made on the plywood along the lines of the figure. The accuracy of pattern copying and the quality of caulking are the key factors affecting the quality of molding process.
There are many ways to groove the bottom plate: lead block row to make die groove; manual wood board saw groove; mechanical boundary plate die groove; laser cutting die groove.
※ Assembly of knives and threads
â‘ Cutting and forming of steel knives and steel wires. According to the design requirements, the knives and lines used are cut into the largest forming line, and then processed into the required geometric shape.
â‘¡ Open the connection point. In mold making, opening connection points is an indispensable process. Opening the connection point is to make a small opening of a certain width at the cutting edge of the die-cutting knife. During the die-cutting process of the carton, the part of the carton and the waste edge are still partially connected after die-cutting, so that the next paper feed , Smooth paper collection. To make the connection point, use a special equipment knife edge punching machine to grind and open the connection point with a grinding wheel. The hammer should not be used to open the connection point, causing damage to the knife line and the corner, the connection point part has burrs, and the die cutter passes the bridge Because the location is floating, do not open a connection point at this location.
※ Discharge knife and thread.
The knife arrangement is based on the product design specifications and shape, after planning the specifications and proofreading with the printed graphics, you can start the knife arrangement operation. Depending on the lining material used, the knife arrangement is slightly different.
When using plywood as a liner for lining materials, steel knives and steel wires should be inserted into the slit of the base plate perpendicular to the plane of the base plate. The gap is appropriate, and there should be no deformation or twisting during embedding or processing.
When using the metal empty lead arranging knife, it is necessary to fix the knife shape at the specified position of the molding board with the empty lead according to certain process requirements, and complete the knife arranging operation, which is very similar to the typesetting operation in movable type printing. Flexible use of various types of empty lead, the discharged template can not be loosened or threaded during work. Especially when arranging various types of geometric figures, it is necessary to ensure not only the specifications of the figures but also the proper tightness.
When arranging the knives, the interfaces of the steel knives and steel wires should be arranged in appropriate positions, and the clearance of the interfaces should be appropriate. The phenomenon of overlapping of the knives and lines or excessive gaps at the interfaces due to pressure should not occur. After the arrangement, the vertical and horizontal lines of the template should be at an angle of 90 degrees to each other, and the sides should be parallel to each other, so that the layout will be flat.
※ Adhesive die cutting tape
The die-cutting rubber strip is mainly to prevent the die-cutting knife and the indentation line from sticking to the paper during die-cutting and indentation, and to make the paper flow smoothly. When die cutting, the die will be compressed and deformed, which will affect the die cutting effect. If it is too close to the knife line, the rubber strip will be pressed to produce a lateral force component, which is easy to pull the paper edge during die cutting; if it is too far from the die cutting line, it will not function as its own. Generally, the distance is preferably 1-2 mm.
※ Die-cut bottom template production
Wash the steel bottom plate, then paste a layer of insulating paper on it, then put a layer of carbon paper, cover with another layer of cardboard, and carry out indentation. According to the imprint, cut the base mold paper into strips and stick to the indentation on both sides to form an indentation groove. Generally, the thickness of the bottom mold is less than or equal to the thickness of the printed substrate. The indentation effect will be different according to the arrangement direction of the indentation line and the direction of the fiber. The indentation line perpendicular to the fiber direction is full after folding, so In case of threading, the indentation line in the straight grain direction is preferably 0.1 mm narrower.
※ Pad version
After the stencil production is completed, the stencil must be installed on the die-cutting machine for trial cutting. In this process, the trial-cut sample is partially normal, and some parts are not cut through. At this time, it is necessary to pad the part.
Use 0.05mm thick backing paper to stick to the bottom of the stencil and cut the die to compensate for the height.
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