With the popularization and application of digitization, intelligence, and networking in the printing field, the printing process has gradually developed from analog to digital, which has opened the prelude to digital printing. Today, the rapid development of digital printing is not only integrated into various fields of printing, but also continuously expands its market share. According to statistics, the current digital printing business in the United States has accounted for more than half of the total printing work, and this trend is still evolving. According to the British Paper Printing and Packaging Technology Research Association, global digital printing will account for more than 25% of the printing business by 2010. In addition, a standard file format based on XML is introduced, regardless of the type of file, and the same procedure can be used to complete the work. The maturity and wide application of PDF files as international standards ensure the consistency of cross-platform operations, which lay the foundation for the development of digital printing. According to the 28-character guideline for the development of the printing industry in China, "pre-press digital, networked, multi-color and efficient printing, exquisite post-printing, automation, high-quality and serialized equipment", it shows that digital printing is now and in the future An important point of development. In digital printing, how to match post-press processing with pre-press and printing is one of the keys to fully improve and develop digital printing.
Digital printing is a completely digital production system. The digital process runs through the entire production process, from information input to printing, and even binding output. Digital printing combines pre-press, printing and post-press into one. From the perspective of system control, it is a seamless all-digital system.
However, in order for digital printing to truly show its superiority, in addition to the pre-press and printing processes, it also requires a better matching of post-press processing. Therefore, attention should be paid to the cooperation of post-press processing of digital printing. Let's talk about the issues that should be paid attention to such as lamination, binding, and cutting, which are closely related to the post-processing of digital printing.
1. Lamination problem
Laminating is a commonly used post-press finishing method for books and periodicals. It has a wide range of applications and is also suitable for digitally printed products. Film processing on the surface of digital prints, especially after printing a large area on the ground, and then film processing will help protect the printed matter during post-press processing, especially when cutting or packaging, and enable printing Products are more beautiful and durable. However, it is not necessarily advantageous to apply a single-sided coating on a double-sided printed product, because the uncoated side may be prone to peeling off of the printing color due to friction in subsequent processing. Many printed products are covered with various bright films, matte films, and matting films in order to pursue distinctive effects. However, it is more appropriate to use thermal lamination for digitally printed products. This method is easy to use and inexpensive. The films used for thermal lamination mainly include polyester films and polypropylene films. Polypropylene films are generally required for thinner films, and thicker polyester films can be used for printed products that require additional protection. Polyester film is more expensive than polypropylene film, but it has high strength and can play a better role in protecting printed products. If both sides of the printed product need to be covered, it is best to use polyester film. In the lamination of digital printing products, it is mainly necessary to avoid the curling of printed products after lamination. Therefore, as far as conditions permit, it is possible to cover the film on both sides of the printing material; if only one side of the paper is coated and the other side is not, it is very easy to curl. However, it should be noted that the cover of the wireless bound book can only be coated on one side. Never cover the second and third covers, otherwise the book block and the cover cannot be firmly bonded. In addition, when the laminating machine is selected, a rod that prevents the lamination of the printed matter from curling can also be selected, so as to ensure that the product after lamination is flat and not curled. Avoiding foaming of products after coating is also a problem that should be paid attention to in coating. When thermally laminating printed products, first ensure that the surface of the printed product to be coated is clean and dust-free, and secondly, note that the temperature must be appropriate. Too high a temperature will easily melt the toner and cause the film to foam. In addition, in order to make the coated product without wrinkles after folding, OPP film can be used. For the selection of laminating materials, laminating may affect the color reproduction of digital prints. This is mainly because the films used in laminating are not necessarily 100% transparent films, so it will affect the color balance. Therefore, for the sake of insurance, you can first try to cover a few samples to the customer, see if the color of the printed product after the coating meets the customer's requirements, and then formally process the coating.
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2. Binding problems
The products that can be printed by digital printing are books, booklets, tenders, calendars, etc. Therefore, the commonly used binding methods are wireless glue binding, saddle stitching, wire binding, wire binding, spiral binding and ring binding. However, it should be noted that it is necessary to decide which binding method to use before starting to print the job, rather than blindly waiting for printing before considering which method to use. Because different binding methods (such as wireless perfect binding and saddle stitching) have different requirements in the page layout of the prepress layout stage. The decision on which binding method to use depends mainly on the customer's requirements, the characteristics of the paper used, the direction of the paper strands, and the final use of the printed product.
Before binding, the printed products are usually folded. When the weight of the printed paper exceeds 120g, pressing the crease before folding can make folding easier, the printed sheet folded out is smoother, and the effect is more beautiful. In fact, no matter what kind of paper, if you press the crease before folding, you can get good results. The creasing can be done on a special creasing machine, this machine has a desktop, but also a larger type of creasing and punching. If there is an indentation mold, the indentation work can also be completed on a flat press. In addition, some folding machines have the function of pressing creases. The occurrence of cracks in the printed image of the printed sheet after creasing or folding may be due to the drying of the paper, and the higher the weight of the paper, the more prone to this failure. Therefore, to avoid cracks, the paper should be kept at an appropriate humidity and not too dry. In addition, when folding the paper in the direction of the paper thread, it can also avoid the phenomenon of breakage at the fold. In the case of processing books and periodicals, when digitally printing, the thread direction of the paper should be parallel to the spine direction of the final book. Of course, covering the printed paper can also avoid cracks at the folding of the printed product. When indenting, it should also be noted that the depth of the indentation should be moderate. If using an indenter, the speed should not be too fast.
At present, domestic digital printing shops use flat binding more, especially in the form of wireless glue binding. The book of glue binding is not only beautiful, but also firmly bound. When designing a flat booklet, first of all, pay attention to leave enough room for binding between the staple and the text. For example, when the hole ratio of the O-spiral is 3: 1 (referring to 3 holes per inch), you should Leave at least 3/8 inch blank; and when the line-to-hole ratio is 2: 1, at least 1/2 inch blank should be left. This blank space refers to the distance between the stitching edge and the nearest line hole edge. In order to clarify the specific position of the bookbinding process, it is best for the designer to understand the changes of the actual printing paper after the digital printing before the digital printing process, which is especially important for digital prints. Most computer design programs do not consider small changes in paper thickness after printing. In digital printing, the color material printed on the paper surface will cause the thickness of the printed sheet to change. When binding dozens of digital printed sheets, the cumulative thickness The changes may make the binding size carefully calculated by the computer meaningless. Therefore, it is necessary to grasp the sample change parameters of the actual production paper after digital printing in order to accurately measure the thickness of the book during the printing design and ensure that the post-press processing obtains a suitable binding size. Similar to the wireless binding process of offset printing, the wireless binding of digital prints also needs to consider the cutting volume of the binding. In addition to leaving a 1 / 8-inch milling back margin on the back of the book, a 1 / 8-inch cutting volume should also be reserved on the other three sides of the book. In addition, a 1 / 4-inch glue area should be left at the bottom of the book cover to prevent glue from seeping into the next book during binding. The wireless adhesive binding process also requires that the printed bleeding cover should be larger than the text size. Wireless adhesive binding hardcover processing is also an important post-press processing method in digital printing and binding. The key to the hardcover process is how to firmly bond the book block to the hard book case to produce a book that can be stored for a long time. Although the cost and time consumed by wireless glue binding hardcover seems to be somewhat unequal to the digital printing for the short version printing market, some post-press binding companies have prefabricated different colors, different styles and different commonly used in digital printing hardcover The size of the hardcover book case is for digital printers to choose. Therefore, wireless adhesive binding hardcover has also become a common binding method for digital printing.
In wireless glue binding, some books or booklets sometimes have the phenomenon of falling pages. There are many reasons for this phenomenon, including glue and machine.
The wireless perfect binding machines used by digital printers generally include milling back, gluing, and bag cover. Some cheap perfect binding machines do not have the process of milling back at all; some of the perfect binding machines have milling back functions. But the back milling of the spine is not in place, which will affect the firmness of the binding. In addition, the type and quality of the glue also have an impact on the fastness of the glue binding. If the temperature is not properly controlled during the glue binding process, it will also cause loose and loose pages of the book. In the binding process, the open time is a very important parameter, which refers to the time required for the glue to make the cover of the book firmly adhere to the book. After the book or booklet is glued on the machine, the glue still needs a certain time to continue curing, sometimes up to several hours. Therefore, don't read the book as soon as the book is bound on the perfect binding machine, at least 15 minutes later, then read and check it.
In addition, saddle stitching is a fast, efficient, and economical method for book and booklet binding. It is also a good choice for most digital prints, especially suitable for guides, brochures, and brochures. Binding of thinner books. This binding method can be carried out online with other processing methods. It can perform post-press processing of collation, folding, binding and online cutting at the same time, which can provide guarantee for the fast delivery required by digital printing. However, the thickness of saddle stitching is limited, generally not more than 4mm.
Although the thread-stitching method has a good binding strength, it is time-consuming and expensive. Therefore, careful design and arrangement of printing work must be done from the beginning to ensure the harmony between printing and post-press processing. The following issues should be noted in binding and post-press processing. First, because the ink color on the digital print only adheres to the surface of the paper, the folding process is prone to breakage. Therefore, it is better to press the crease before folding.
Spiral binding and ring binding also play a role in the binding of digital printing products. Both spiral binding and ring binding require punching first and then binding the printed matter into a booklet. The variety of spirals or loops used is of various specifications, both metallic and plastic; both monochrome and color. The spiral binding is to use a continuous plastic wire or wire to pass from the first hole to the last hole of the printed product; while the ring binding is to use a separate circular iron wire or plastic ring to "clamp" the printed through the round hole Leaflet. The characteristic of spiral binding and ring binding is that the binding cost is low and the flatness is good. Use a manual small desktop punching screw binding or ring binding machine (which can bind a booklet with a thickness of 20 ~ 28mm) to bind an A4 booklet. It takes 5 minutes. If the number of binding is large, it is best to choose a computer-controlled punching and binding machine with a high degree of automation.
Digital printing products can also choose punching or drilling binding method, this binding method is more suitable for binding documents composed of single sheets of paper, it is very suitable for student materials or sales samples. Especially when you need to change some of the content, you only need to reprint the page or pages with changed content, and then add the hole after replacing the old page, without having to reprint the entire document or sample. . When using the hole-punching binding method, pay attention to that the paper punched at one time should not be too much or too thick, otherwise it will affect the quality of the hole punching. During drilling, the drill pin will heat and cause the digitally printed image toner to melt. Care should be taken not to over-drill. When the polyester material is to be punched and bound, the punching process should be used as much as possible instead of drilling, because the heat generated by the drilling is easy to melt and stick the polyester material.
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3. Cutting problems
Cutting is also an important aspect of digital printing post-press processing, first of all is the cutting of paper. Like traditional printing, digital printing also uses a paper cutter to cut the paper or finished product into the required size and shape. At present, there are a variety of paper cutters on the market, both manual and computer-controlled fully automatic. The cutting specifications of single-sided knife cutters are mostly 52-150cm. Generally speaking, a paper cutter with a cutting width of 78cm is more suitable for digital printing. If possible, a computer-controlled paper cutter can better match digital printing because it can store a certain amount of data. When cutting jobs that have been processed, you only need to call up the original program from the computer, which can fully save the time of adjusting the machine. In the use of paper cutters, in order to maintain the sharpness of the blade and prolong the service life of the paper cutter, the thickness of the paper cut at one time is preferably not more than 40mm, and the pressure of the paper on the paper cutter should also be appropriate, generally softer paper The pressure required is higher, and the pressure required for harder materials is relatively lower.
It is critical to keep the blade sharp when using a paper cutter. Care should be taken to maintain and use the blade correctly. Once the blade is dull, the blade should be reground, otherwise it will affect the cutting accuracy. In addition, pay attention to keeping the ambient temperature at 19-23 ° C and the relative humidity at 50%. Under such conditions, the characteristics of the paper are relatively stable, which is conducive to the correct use and maintenance of the paper cutter, because the determination of many cutting parameters depends on the paper being processed.
The die-cutting of digital prints can make the final prints attract people's attention with special shapes or outstanding features, which can increase the added value of the products. Whether a digital printer needs to add a die-cutting machine depends on the amount of live parts it processes. If there is not much work, the die-cutting machine will be idle, causing waste. When choosing a die-cutting machine, it is necessary to pay attention to the processing requirements of printed products. When die-cutting thick paper, you can choose a platform die-cutting machine, and die-cutting thin paper can choose a rotary die-cutting machine.
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