Paper bag indentation process.

What is the indentation of a paper bag?

Indentation is the use of a wire pressing knife or die to press a line mark on the sheet metal through pressure, or a wire roller is used to roll a line mark on the sheet metal, so that the sheet metal can be bent and formed according to the predetermined position. Most of the marks pressed out by this method are straight lines, so they are also called pressing lines.

Indentation is also known as press-cut forming, buckle knife and so on. When the paper bag needs to be folded and punched, it can be done through the indentation process of the indentation machine.

During die-cutting, steel blades are arranged into different shapes such as molds and frames, and the paper is cut into a certain shape on the indentation machine. during indentation, the steel wire installed on the die-cutting board is used to press marks on the paper through the indentation machine. or leave grooves that provide bending.

The factory that makes the paper bag generally uses the opposite indentation machine, using the special knife plate to indentation on the printed paper, usually a bag knife plate, if complex, several knife plates will be used.

How to make the indentation version?

To make the indentation version, you should first make the bottom plate, and then make the wire according to the required knife shape, which is placed in the bottom plate, and there are two kinds of metal base plate and wood base plate.

1. Metal base plate.

 Metal base plate has lead empty typesetting, pouring lead plate, steel plate engraving, steel plate engraving and so on. Lead empty typesetting is made up of lead empty groups of different sizes. The cast lead plate is made of molten lead alloy as the base plate. This method first bends the steel wire into the required shape, leaving the edge of the 10mm around, and the periphery is fixed with wooden strips.

Then pour the molten lead alloy into it and cool it into a die-cutting knife plate. Steel engraving is to first bend the steel strip into a curved closed frame similar to the die cut mark, the joint is welded firmly, and the two sides are ground to the height of 30mm or so. Then accurately plane the frame line of the cut figure, file out the knife edge according to the line, and finally heat-treat it to make a die-cutting plate. This kind of die-cutting is difficult to make and the process is complicated.

Steel plate engraving is generally selected slightly larger than the printing picture and text, the thickness of the 25mm steel plate, the need to process the side of fine grinding, and then coated with photosensitive liquid, turn the sun. The parts outside the knife edge line needed by the picture and text are milled, then the knife edge is carved out, and finally heat treated. Although the cost of this kind of die-cutting knife plate is very high, it can be used repeatedly for a long time, and it is generally suitable for stereotyped products with small and complex graphics. At present, lead empty typesetting is widely used.

2. The bottom plate of the plank.

There are several kinds of plywood on the bottom plate, such as plywood, plywood, zinc wood nailboard and so on. The plywood is generally 9-13 layers with a thickness of 18~20mm. It is to transfer the design pattern to the plywood, drill holes and saw seams in the lines, and then embed the die-cutting knife line and indentation line to make a die-cutting indentation plate.

The quality of die-cutting in this method is higher, and the weight of die-cutting plate is lighter, which is shorter than that of blank lead knife. The bottom plate of the board is the hardwood board that is directly sawed as the bottom plate. The zinc wood nailboard is to make a negative picture of the die-cutting pattern on the zinc plate, nail the zinc plate to the wood, and after trimming, it can be installed on the die-cutting machine with a steel knife. Plywood is commonly used in the bottom plate of the plywood.

Why do paper bags need indentation?

With people’s higher and higher requirements for packaging, the purpose of indentation on the paper bag is to facilitate the folding of the paper bag, so as to make the formed paper bag look more beautiful.

Indentation is in the later process of making paper bag, the paper bag needs to go through the process of cutting paper, printing, coating, bronzing and so on, and then it is indentation. After indentation, the paper bag is folded manually to fold the paper into the finished product style of the paper bag.

What does the principle of indentation make?

Indentation causes permanent tensile deformation of paper fibers by extrusion of punches and concave dies.

What happens if the paper bag is not indented?

If the indentation of the paper bag is too light, the crease of the paper bag is not clear and the paper bag is not beautiful.

If the indentation of the paper bag is too heavy, the color will burst and the paper fiber will break.

If the paper used for printing is already very brittle, or the humidity in the workshop is low and too dry, it will affect the effect of indentation.

What are the ways of indentation?

There are three ways of indentation:

 AdvantagesShortcomingCommon equipment
Flat pressureEasy to achieve, with ready-made knife mold; the best indentation effect, especially thick paperThe limit speed is not high, and different tool dies need to be replaced for different thickness of paper.Manual indentation machine.Die-cutting indentation machine.Digital indentation machine
Roll pressureThe utility model has high efficiency and can realize the functions of drilling and cutting at the same time.It can only be indented longitudinally, and the width of the machine is too large. Too thick, too brittle paper indentation effect is not good.Electric rolling machine
Rotary pressureIt not only has a good indentation effect, but also can achieve faster speed.The structure of the machine is complex, and it is the most difficult to realize.A few high-end adhesive equipment

What kind of equipment does the current indentation machine have? What is the scope of application?

 PrincipleSpeedApplicable scope
Manual indentation machineFlat pressure300 sheets per hour1-500 sheets / batch
Die-cutting indentation machineFlat pressure800 sheets per hour50-2000 sheets / batch
Electric rolling machineRoll pressure6-1500 sheets per hour of advanced equipment can reach1800050-20000 sheets / batch
Digital indentation machineFlat pressure3000-8000 sheets per hour100-20000 sheets / batch

Thus it can be seen that manual indentation machine and die-cutting indentation machine are not suitable for fast and mass production orders.

In today’s society, labor costs are getting higher and higher, and the speed of making paper bags required by customers is getting faster and faster, which requires the use of efficient electric rolling machines and digital indentation machines.

What is the production process of die-cutting indentation version?

Die-cutting indentation version of the production, commonly known as row knife. The so-called row knife refers to the technological operation of assembling steel knives, steel wire and hollow lining materials into die-cutting indentation plates according to the prescribed requirements. At present, the domestic knife row operation basically uses two kinds of blank lining materials: metal hollow lead and plywood.

Glued plate as a lining material template, the first to make the base plate, other operations are basically the same.

(1) The manufacture of the base plate.

 It means that according to the design requirements of the product, the die outline is drawn or drawn on the base plate in a certain way, and then the narrow groove is sawed out according to the outline line after different technological treatment. In the manufacture of the bottom plate, the drawing of the outline of the stamping die and the quality of the saw seam are the key to affect the quality of the printing plate.

At first, the manufacture of the bottom plate is all done manually, and the accuracy of the stamping die depends entirely on the individual’s technical level. You must first draw the die figure on the board by hand, and then saw the seam along the graphic line manually with a wire saw. At present, there has been a laser plate making system, in which the automatic operation until the last working procedure, as long as the parameters such as the outline size and paper thickness of the die-cutting product are input into the electronic computer, the electronic computer can control the base plate making system, which makes the base plate move automatically under the laser beam according to the die pattern.

(2) Guillotine cutting and forming processing of steel knife (line).

The guillotine cutting and forming processing of steel knife (line) refers to the process of cutting die-cutting steel knife and steel wire into the largest forming line segment according to the design specifications and requirements, and then processing it into the required geometric shape. When forming the shape of the knife, great attention should be paid to the selection of steel knife and steel wire. The hard steel knife has high mechanical strength and poor elasticity, so it can be used as a straight line knife as far as possible, and it can not be bent too much; a soft steel knife with good elasticity should be used as an arc knife with large curvature as far as possible.

When selecting steel knives and steel wires, factors such as the thickness of the material of the die-cut products and the width of the indentation line should also be taken into account. The general rule is: the thickness of die-cutting products is different, the height and thickness of steel wire should be different, with the decrease of paper thickness, the height of steel wire increases and the thickness decreases.

(3) Rows of knives.

According to the product design specification and shape, after drawing the specification sample and checking with the printed picture and text correctly, you can start the knife arrangement operation. According to the different lining materials used, the operation of the row cutter is slightly different, and the technical requirements and process difficulty of the metal empty lead row cutter are generally slightly higher than that of the plywood lining material. When using metal empty lead typesetting knife, according to certain technological requirements, the knife shape is directly fixed in the specified position of the molded plate with empty lead, and the typesetting operation is completed, which is very similar to the typesetting operation in movable type printing.

In the metal empty lead row knife, the operator is required to be able to use various specifications of air lining materials flexibly and freely, and the embossed plate can not be loosened or strung in the die-cutting process. Especially in the layout of all kinds of geometric figures, it is necessary to ensure that the graphics are standardized, and that the tightness is appropriate. When there are multiple pictures in one page, they should be consistent with each other, and should not be different because of the different lead ratios added.

In addition, the vertical line of each point on the opposite side of the printing plate should be equidistant to facilitate clamping and fastening when fixing the knife. In the operation of arranging cutters with plywood lining material, after steel knives and steel wires are embedded in the saw seams of the bottom plate, they should be hung on the same plane as the bottom plate, and the clearance should be appropriate, and there should be no deformation or twisting in the embedding or processing. If the layout is composed of multiple soleplates, the single soleplate should be arranged and formed first, then arranged one by one, and finally clamped and fixed uniformly.

After the printing plate is arranged, its vertical and horizontal lines should be 90 °angle to each other, and the edges should be parallel to each other, so that the whole layout can be flat. In addition, the steel knife and steel wire interface should be placed in the right position, the interface gap should be appropriate, and the phenomenon of overlap or excessive gap should not occur due to the action of pressure.

(4) check and fix the knife.

Fixed knife is also known as playing plate or card plate, that is, the arranged printing plate is stuck in the plate frame. After the knife row is completed, do a comprehensive check again, and check it correctly before you can officially start fixing the knife. The printing plate fixing knife with empty lead as the hollow material should be fastened directly with the fixed plate lock after adding the wood bar around the plate frame; using plywood as the die-cutting plate of the hollow lining material should be clamped and fastened by the fixed plate lock according to the specific conditions of the whole layout.

In order to make the handheld paper bag easy to fold without fracturing, we need to pay attention to the following points.

(1) The backing paper should have sufficient thickness.


(2) Press the cushion paper out the groove before molding.


(3) The pressure during formal molding should be appropriate.

Along the strand direction of the paper, the paper is easier to fold, the molding pressure can be smaller, while perpendicular to the strand direction of the paper, the paper is more difficult to fold, can increase the molding pressure locally.

The problem that the indentation line is not clear:

Two situations generally occur when the indentation line is not clear, one is called dark line, which refers to the indentation line that should not have, and the other is called explosion line, mainly because the pressure of die-cutting indentation is too large, which exceeds the range of pressure on the material, causing the product to break. And what caused this phenomenon.

The main reasons are:

First, the choice of indentation line and indentation die is not ideal, so we should choose the correct indentation die type and indentation line height. When selecting the die-cutting material, the bad depth of the indentation die should be the same as the thickness of the die-cutting material; the width is 1.5 times the thickness of the paper plus the thickness of the indentation line; ensure that the height of the indentation line is the same as that of the die-cutting knife.

Second, the pressure of the molding machine is not accurate, so the pressure regulating part of the die-cutting machine should be properly adjusted to ensure that the pressure reaches the appropriate standard.

The problem of producing too many rough edges and ash shavings in the die-cutting process:

1. The edge of the die-cutting knife is not sharp enough.

If the edge of the die-cutting knife is not sharp enough and the quality of the body is not up to standard, the edge may not be smooth, resulting in more rough edges and ash shavings, so as to ensure the quality of die-cutting products, it is necessary to choose a steel knife with good quality to improve the suitability of die-cutting.

2. Serious wear of die cutter.

Die-cutting due to frequent use, the degree of wear of the die-cutting knife is often ignored, if the wear is too serious, not timely replacement, it will not be able to play the role of steel knife. Therefore, whenever it has been used for a period of time, it is necessary to check the steel knife edge regularly to see whether the wear has reached the replacement condition and replace it in time.

3. The choice of die cutter and sponge strip is not reasonable.

Because the sponge strip must reach a certain hardness in order to make the die cutting to the smooth cutting of the paper, therefore, it is necessary to choose different sponge strips according to different paper. At the same time, it is also necessary to ensure that the installation position of the sponge strip should have a certain distance from both ends of the die cutter, generally at least the distance of 2mm. If the distance between the two ends is not suitable, the sponge strip may be subjected to uneven force after being pressed by the die cutter, resulting in the sponge strip being pulled off before the product is completely cut, resulting in a large amount of paper dust and paper hair. In addition, it is also necessary to ensure that the number, hardness and height of the sponge strips are evenly distributed on the whole template to ensure that the operation process is standardized.

The problem of adhesion between the product and the knife plate:

In the actual production and processing, there is often the problem of adhesion between the product and the knife plate, the main reason is that the hardness of the sponge strip is too small, so that the paper can not bounce back, so it is necessary to reasonably use the sponge strip of different hardness or locally add the sponge strip according to the actual situation. It is also possible that the edge of the die-cutting knife is not sharp enough, and the thickness of the product is indeed too large, resulting in adhesion between the product and the blade, so it is necessary to check the wear of the blade in time and replace it in a timely manner. There may also be a problem with the angle of the blade. There are three kinds of blade: double-sided knife, straight inside and straight outside, and there will be adhesion if the blade used is incorrect.

The position of the die-cutting indentation line does not match the position of the product.

The main results are as follows:

(1) There are errors in the production process of the die-cutting knife plate itself, and the manual plate-making can not achieve the ideal die-cutting indentation accuracy due to the limitation of the level of technicians and operating equipment. For some products that require high die-cutting precision, laser plate making can be used instead.

(2) The product rules are different. If the product specification error is large, then it may be that the post-positioning (also known as secondary positioning) poking distance of the die-cutting machine is too small, which can be solved by adjusting the post-positioning and increasing the post-positioning poking distance.

(3) The die-cutting indentation is not aligned with the position of the product. The solution is to recalibrate the die-cutting plate and correct the product and die-cutting indentation position according to the product requirements.

(4) In addition, die-cutting indentation is different from the working environment will cause material deformation or stretch, but also produce die-cutting indentation grid position is not correct. The solution is to ensure that die-cutting indentation and production are carried out in the same working environment or the identity of the working environment (that is, the same temperature, humidity, etc.).


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