Analysis of influencing factors on the production

2022-08-05
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Analysis of factors affecting the production quality of plastic flexible packaging (II)

printing control and quality:

when receiving the processing order issued, the printing operators should first carefully understand their product requirements and determine the printing method. There are two printing methods for plastic film: surface printing and internal printing. Table printing is similar to all kinds of paper, with white as the first color, which is arranged from light color to dark color; Inner printing is a unique printing method of transparent plastic film. It is a printing method that uses reverse graphic printing to show positive images on the front of the printed material. It is arranged from dark color to light color. Because the inner printing is more bright and beautiful, with bright colors, and after composite processing, it is firm and wear-resistant, without fading and adhesion. Therefore, the inner printing process is basically used in flexible packaging printing

in the daily production process, printing is the first process of the product, and the surface tension detection of the printing film is very important. Of course, most manufacturers have completed this inspection in the incoming inspection of materials. However, in order to prevent the occurrence of printing problems, it is best to test again when using each roll of printing substrate, because the surface tension has a direct impact on the ink adhesion and the production of the subsequent process, Therefore, the surface corona detection is required for the general film production

generally, the printing operator can only inspect the appearance quality of the printing plate. The real quality of the printing plate depends on the internal control and quality control of the plate making supplier to meet the requirements of the printing quality. The printing enterprise can only inspect the appearance quality of the printing plate. The chromium layer inspector only needs to swallow one intelligent "capsule" to see if there are any scratches and bumps on the appearance, and the surface should be smooth and smooth, Finish to be Δ 8~ Δ Level 10. The concentricity of the printing plate after the machine is put into operation. When the printing plate pattern and printing effect cannot meet the needs of the product, it is only necessary to rework to meet the printing and customer needs. The hardness of the chromium layer is related to the printing resistance of the printing plate cylinder, and the chromium plating hardness of the printing plate should reach HV

the selection of ink is the focus of the quality control of plastic gravure. The inspection of ink quality is based on the printing requirements. The quality status of ink in plastic products is of paramount importance. Good ink produces good products, which is the consensus of the plastic upholstery printing industry. When selecting gravure printing ink, first of all, it is necessary to confirm the printed substrate - printing conditions - printing effect - processing conditions - final product use and many other factors. How to control the ink quality depends on the ink manufacturer, so the printing manufacturer should take the initiative to test and control its color hue, viscosity, fineness, adhesion, applicability and other indicators in the selection and use, Only in this way can we meet the needs of printing

overprint error, knife thread, mimeograph, etc. are common defects in printing. The phenomenon is that in the process of multi-color overprint, each color cannot be completely overlapped, and there is a certain deviation. If the deviation exceeds the specified requirements (GB front pattern ≤ 0.3mm, back pattern ≤ 0.5mm), it will become unqualified. The above error factors are caused by personnel factors - equipment factors - printing plate factors - operation process and other factors. Because these errors exist objectively, to control them within a certain range, the operating staff must have strong working ability

printing is a meticulous work, which must be done:

there are three hearts: heart, heart and care

three quick: quick eye (staring at the stage and finding out in time), quick leg (finding problems and reaching the position in time), quick hand (paying attention to safety and adjusting in time)

three times: frequently add (regularly check the viscosity and timely add solvent), frequently check (frequently check the quality and observe the equipment operation status), and frequently look (check against the standard sample)

three inspections and three signature samples:

self inspection: the printer captain shall check the printed samples against the incoming samples, standard samples and instruction sheets, check whether the size, text, pattern and color meet the requirements, and sign after confirmation

first inspection: after passing the self inspection, the process inspector or production management personnel shall conduct the first inspection and confirmation, and sign for confirmation after all requirements are met

re inspection: the inspector shall re inspect the standard samples and incoming samples. If any problem is found, the inspector shall timely notify the platform personnel for rectification, sign after confirmation, and make inspection basis according to all signed samples. We call it the printing sample signing system. If one party fails to sign, the platform shall not have the right to produce. In this way, the quality loss caused by inadequate process audit and printing adjustment can be eliminated

institutionalized and standardized management shall be formed for three fast, three diligent, three inspection and three signature samples

the control of printing pressure, printing tension, oven temperature adjustment, diluent allocation, ink viscosity control, printing color difference control, etc. are all related to the skills of printing operators. Some of these aspects of control involve professional knowledge, and the vast majority rely on our experience in daily operation. It is suggested that we should "write diligently and think carefully", that is, we should record the problems we usually encounter, the solutions, and the success or failure samples one by one. When we encounter the same problems, we can learn from them in time

dry compounding and quality:

compounding process is the soul of plastic flexible packaging. It lies in the superposition of performance, which is also the core of compounding production technology. As the key process of plastic flexible packaging, the quality of composite process is directly related to the product input and product qualification rate. Its process is complex and requires high operating skills

let's learn about the process flow of dry compounding for the first time (see the figure below):

after understanding the above process, we should first test whether the surface tension of the substrate meets the requirements, whether the unwinding tension system - composite tension system - winding tension system meets the quality requirements, and tension control is one of the most important process conditions in the compounding process, It includes three parts: the first is the setting of the initial value of tension, the second is the tension matching relationship, and the third is the setting of taper. Improper tension control may cause quality problems such as film curling, wrinkling, difficult bag making, reduced peel strength, bag making deformation, etc

the selection of adhesive is one of the important links in the quality control of dry composite, because the adhesive used is to bond two or more substrates together after coating. The amount of adhesive used in the dry composite production is small, but it has an important impact on the quality and performance of the composite film, which determines the peel strength, transparency, heat sealing strength, heat resistance, medium resistance, etc. of the composite film. Therefore, we should determine the use of adhesives according to the final performance of products when selecting adhesives

after the adhesive is determined, the coating system shall be controlled to ensure that the dry base solid content of the product coating shall be about 3g/m2

oven drying control is the main factor in dry compounding. Drying directly affects the peel strength and transparency of compounding. The solvent in the adhesive coated on the substrate is heated, evaporated and extracted through the drying system. The drying temperature setting is mainly based on the heat resistance of the substrate and the mechanical linear speed. Generally, the temperature is set to three stages: the first stage is 50~60 ℃; The second stage is 65~75 ℃; The third section is 75~80 ℃, and the temperature must increase step by step. Generally, the temperature of the hot cladding roll should be controlled between 85 ℃ and 90 ℃ at the 101st western international plastic industry exhibition to be held in Chongqing on April 16, 2015. If necessary, it should be adjusted according to the actual situation

it is common for products to be scrapped due to improper selection of adhesives and operation. The corresponding substrate indicators shall be checked according to the product's internal content and packaging requirements, and the peel strength shall be tested after ripening. The detection of these indicators is often ignored by some flexible packaging enterprises. The relationship between the final quality of the composite and the peel strength and the strength of bag making and sealing welding. The key to this kind of alloy is to deal with the post crystallinity of pet

curing is also called curing, which means putting the composite film into the curing room (drying room) to make the main agent of polyurethane adhesive and curing agent react and cross-linked and interact with the surface of composite substrate. The purpose of curing is to make the main agent and curing agent fully react within a certain period of time to achieve the best composite strength. Ripening control mainly includes temperature and time. In order to meet the delivery time requirements of customers, some enterprises increase the curing temperature and shorten the curing time to deliver in advance, and some lead to unqualified product quality and scrap. Because the quality and characteristics of the adhesive manufacturers are different, it is recommended to control the temperature and time required in the adhesive manual, and it is not advisable to leave the curing room in advance

the ambient temperature has a certain influence on the volatilization of solvent and the coating state of glue solution in the composite process, and the optimal ambient temperature is 20~28 ℃. Humidity has a great influence on dry compounding. Generally, it is appropriate to control the humidity at 50~75%. When the humidity is too low, it is easy to generate electrostatic sparks, which is very dangerous. When the humidity is too high, it volatilizes with the ethyl ester, causing the temperature of the coating roller, rubber disc, guide roller, etc. to drop and form large water vapor to condense into water droplets, which will greatly affect the performance of the adhesive. Too high humidity will also consume a large amount of curing agent, resulting in the decline of peel strength or insufficient curing agent. Therefore, when the humidity is too high, Control the environment and properly add some curing agent to make it meet the product requirements

(to be continued)

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