Poor machine adaptability of slim cigarette packs? This process solves the problem
In recent years, slim cigarette packs have become the driving force behind the scale and structural growth of many cigarette brands. An increasing number of cigarette brands are continuously iterating and upgrading their products centered on consumer demand, jointly promoting the accelerated development of the slim cigarette pack category. As the market share of slim cigarette packs continues to grow, the speed of slim cigarette packing machines is also increasing, reaching 600–700 packs per minute. The die-cut forming effect of cigarette packs will greatly limit their adaptability on machines. Through tests and comparisons on cigarette packing machines, round-to-round die-cut slim cigarette packs have better machine adaptability compared to flat-to-flat die-cut slim cigarette packs.
Selection of Die-Cutting Process
In terms of die-cutting processes, slim cigarette packs are more difficult to produce compared to standard cigarette packs. Comparing the dimensions of cigarette pack box types, as shown in Figure 1, slim pack boxes measure 260.3mm × 77.0mm, while standard pack boxes measure 245mm × 98mm. Slim pack boxes are longer, with a paper web width generally exceeding 770mm, and horizontal imposition is 50–60mm wider than standard pack boxes. The increase in horizontal layout affects the accuracy of die-cut dimensions. From the perspective of vertical imposition, slim pack boxes are narrower, and excessive vertical imposition makes alignment between the box tabs and the printing ends more difficult.
As can be seen from Figure 1, the minimum crease line spacing for slim pack boxes is 8mm, which is 4mm smaller than that of standard pack boxes. The smaller the crease line spacing, the more difficult it is to uniformly control the crease depth due to the 'force competition' factor. The distance between the crease line and the die-cut edge is 11mm for slim pack boxes and 21.5mm for standard pack boxes. The closer the crease line is to the die-cut edge, the greater the force that tends to open the pack during forming. If the crease depth is insufficient or the adhesive performance is poor, frequent packing machine stoppages will occur. Currently, domestic slim pack boxes are all produced with a flat-to-flat die-cut method. To better control the die-cut forming effect and ensure stable machine adaptability, our company has conducted test verification using a round-to-round die-cutting method.
Fig.1 Schematic diagram of the size of standard (top) and fine (bottom) box cigarette packs
In the early process planning and analysis, we compare with the flat and flat die-cutting method, and the circular die-cutting method has the following five advantages.
01/ High production efficiency of circular die-cutting
According to the die-cutting machine speed of 210,000 sheets/hour, it is twice the efficiency of flat sheeting of 105,000 sheets/hour.
02/ Using the same length of paper, the output rate of circular die-cut products is higher
The circular die-cutting adopts the roll feed method, which does not need to leave a mouthpiece and a tip position during typesetting, and can also be continuously cross-nested, which can save about 6% of the paper. According to the width of the cigarette pack box of 77mm, every 10,000 boxes of products will produce 1.48 million more small products.
03/ The pressure of the creasing line and die cutter is more uniform, and the die cutting quality is better
Since the circular pressing and circular die cutting and pressing method is line contact, the die-cutting roll is equipped with a high-precision four-axis machining center to ensure that the dimensional accuracy of the product is controlled within 0.2mm, and the plane shape is accurately converted into a three-dimensional processing pattern. Because it adopts a line pressing method with less pressure, the pressure uniformity of indentation and die-cutting is much higher than that of flattened surface pressing, and the molding of cigarette pack products is more stable.
04/ High die-cutting accuracy
The circular die-cutting machine is equipped with a high-precision registration device and a die-cutting phase adjustment device, which can obtain a fairly high die-cutting accuracy. The tension control system can improve the positioning accuracy of printing, die-cutting, and indentation. The error between the entire die-cutting, indentation plate circumference and the printing process plate circumference can be evenly distributed to each cigarette box in the circumferential direction, which can eliminate the problem of large differences in the tail die-cutting sleeve of the flattened die-cut bite plate, and the size of a single box is more accurate.
05/ High print resistance of die-cut plates
Reduce the adaptability of cigarette packs caused by changing die-cut plates. The circular die-cutting plate has a long service life, the die-cutting roller can be re-ground 3 times, and it can also run 5 million ~ 10 million revolutions after each regrinding, which is much higher than the flat flattening die-cutting method.
Risk points of circular pressing and circular die-cutting process
The fine branch box type cigarette pack round pressing round die-cutting tool is basically made of imported powder steel, and then vacuum quenched after rough machining, and the hardness can reach more than HRC60. Whether the circular die-cutting box cigarette pack process can meet mass production and whether it can maintain effective and stable machine adaptability on the cigarette machine for a long time, we need to consider the following four risk points when planning the process.
01/ The risk of "breaking the knife" with sharp corners of the dovetail
As shown in Figure 1, the sharp angle of the fine box type cigarette pack is 35.86°, which is much smaller than the 60° of the standard box type cigarette pack. The smaller the angle, the more likely it is to be squeezed by the paper after die-cutting and pressing, and the sharp corners are very prone to the risk of "chipping".
02/ Selection risk of indentation line width and depth
As shown in Figure 2, according to the different types of paper transfer paper, laminated paper, and white cardboard, different paper thicknesses, and the difference in the depth and width of the indentation required at different positions of the box type, the appropriate indentation edge and indentation groove width, angle and height should be selected. Once the choice is unreasonable, it is easy to form the problem of "oblique mouth", "sky and earth" or "earth covering the sky" after molding.
Figure 2: Schematic of Indentation Blade and Groove
03/ Risks in Choosing Die-Cutting Blade Width and Angle
As shown in Figure 3, different blade widths and angles need to be designed and selected according to the type of paper and ink, in order to meet sufficient printing durability and die-cut edge smoothness. The die-cut blade angle ranges from 35° to 55°, and the blade width ranges from 0.02 to 0.05 mm; paper types can generally be divided into coated paper, transfer card, and laminated card; ink types can generally be divided into regular ink, white ink, and UV ink. Different papers and inks also require different selections of die-cut blade widths and angles.
Figure 3 Schematic Diagram of the Die-Cutting Blade
04/ Risks in Selecting the Number of Cigarette Packs in the Circumferential Direction for Die-Cutting
The number of cigarette packs in the circumferential direction for die-cutting should first be chosen based on the difficulty of controlling the printed card position, preferably matching the number of packs in the circumferential direction of printing; second, it is necessary to fully consider the roller's self-weight caused by the roller diameter. The fewer the number of packs in the circumferential direction, the lighter the roller's self-weight. The layout of thin cigarette packs is longer in the horizontal direction compared to standard cigarette packs, making it more prone to insufficient die-cutting and creasing pressure in the middle packs. Although adding a single-axis or four-axis setup as shown in Figure 4 can compensate for insufficient pressure, the larger the die-cutting roller diameter, the more beneficial it is for stabilizing the pressure in the middle of thin cigarette packs if the self-weight is adequate.
Figure 4 Schematic of the Round-Pressure Round Die-Cutting Workstation
In addition to maintaining better and more stable machine adaptability for slim-pack cigarette boxes, round-pressure round die-cutting can also expand downstream connections to inspection equipment, automatic collection equipment, automatic turning equipment, automatic bundling equipment, and automatic palletizing equipment, and can be integrated with AGV automatic guided vehicles to achieve an intelligent production mode. The application of round-pressure round die-cutting on slim-pack cigarette boxes has proven its high efficiency and stability. In the future, we will also pursue broader applications.