At present, the homogeneity phenomenon in the flexible packaging industry is more and more obvious, especially for the common composite packaging bags with relatively low technical threshold, such as BOPP / / PE and other structures, the competition is very fierce. Many flexible packaging manufacturers can barely maintain a low profit level only through large-scale and mass production. High temperature cooking packaging bags for meat and other products, especially three-layer or four layer composite bags such as BOPA / / AI / / CPP, BOPET / / AI / / BOPA / / CPP, still have relatively considerable profit margin due to the high technical difficulty. Therefore, many flexible packaging manufacturers hope to increase the order of cooking packaging products. However, due to the high production technology of cooking resistant packaging bags, it is necessary to establish an optimized production process route to ensure that the final products are qualified. This paper only from the cooking resistance of composite ink, a simple analysis, for your reference.
Selection of cooking resistant composite ink
Before 1998, there were few manufacturers who could manufacture cooking resistant composite ink in China, mainly DIC and Toyo ink. In the past five years, the development of cooking resistant composite ink is quite fast. Domestic well-known ink manufacturers have corresponding ink products supply, such as lamistar of Toyo, univure of DIC, 300lm of Zhejiang New Oriental, GLP of Ye's ink, etc., which greatly increases the choice of domestic flexible packaging manufacturers.
At present, the common cooking resistant composite inks in China include one component polyester ink and two-component polyurethane ink. For the two-layer structure of 100 ℃ boiling sterilization packaging bags (such as BOPA / / CPP), one component polyester composite ink can be selected, such as 321f of Zhejiang New Oriental, lglp of Ye's ink, 99 type of Yongcheng ink, etc. If it is to produce three-layer or four-layer structure of 121 ℃ or above high-temperature cooking bag, generally choose two-component polyurethane ink. At present, the most widely used in domestic market are Oriental lamistar, DIC's univure, Zhejiang New Oriental 300lm.
In a word, as cooking bags are high value-added products, flexible packaging manufacturers in the choice of cooking resistant composite ink, it is best to buy brand products with a slightly higher price but good stability. It is absolutely impossible to buy inferior ink for a short time, which will cause quality accidents and economic losses. Now there are many small-scale ink manufacturers can also provide cooking resistant composite ink, but the product quality and stability is poor, flexible packaging manufacturers should be cautious when purchasing.
Main characteristics of polyurethane ink
The performance of polyurethane ink is slightly different from that of chlorinated polypropylene ink used in BOPP printing, and the use method is also different.
First, the composition of the diluent is different. The dilution solvent of chlorinated polypropylene ink is mainly benzene, supplemented by esters and ketones. Polyurethane ink with butanone as the main solvent, plays a role in dissolving resin. Because butanone volatilizes faster than toluene, so when using cooking resistant polyurethane ink, it is necessary to ensure that the content of butanone in the mixed solvent reaches a certain proportion in order to prevent the poor solubility of the ink caused by excessive volatilization of the true solvent or the poor ink transfer. Taking the 300lm cooking resistant composite ink of New Oriental ink company as an example, the content of butanone in the mixed solvent is required to be no less than 30%.
Secondly, polyurethane ink has two liquid reaction type. When it is necessary to produce cooking packaging bags which have been sterilized by high temperature above 121 ° C, two liquid reactive polyurethane ink must be used, and proper amount of hardener should be added, and the printing can be carried out after mixing evenly. After use, the remaining two-liquid reactive ink should be filtered first, and then partially added to the new ink, or used as a diluting solvent. However, when the residual ink appears caking or serious swelling phenomenon, it can not continue to be used.
Third, the polyurethane ink composite performance is good, composite peel strength is quite high. Generally speaking, the peel strength of chlorinated polypropylene ink is 1.5 ~ 4.0n/15mm, while that of polyurethane ink is 3 ~ 8N / 15mm. Moreover, the peel strength of the composite product printed with cooking resistant polyurethane ink after sterilization at 121 ℃ does not decrease but increases.
The following is about the cooking resistance of composite ink in the use of a few points for attention:
First of all, the printing ink should be distinguished from the ordinary cooking type, high temperature cooking type and ultra-high temperature cooking type, which should be selected according to the actual needs.

Secondly, it is better to conduct confirmatory test before using cooking resistant composite ink, especially the compatibility of cooking resistant composite ink and BOPA film, and the compatibility of cooking resistant ink and composite adhesive, so as to avoid affecting the printing and composite quality. For example, the performance of the resin used in cooking resistant ink is similar to that of the two-component polyurethane adhesive. Due to the different reaction activity of curing agent in different adhesives, there is a big difference in use. When it is compatible with large printing ink printing patterns, wrinkle or delamination of the composite packaging bag after cooking may occur.

Thirdly, the design of cooking bags should be simple and the color number should not be too much. In addition, if the inner printing method is adopted, considering the composite strength and heat sealing strength of the follow-up process, the full page printing should be avoided when designing the manuscript, especially the heat sealing part of the packaging bag should be designed to be transparent without printing patterns.
Analysis of anti sticking phenomenon
When using cooking resistant composite ink to print BOPA film or BOPET film in summer, the phenomenon may appear, especially in the south of high humidity. Because of the strong hygroscopicity of BOPA film, when the relative humidity in the air reaches more than 80%, it is easy to cause quality failure. Therefore, it is necessary to control the ambient temperature of the workshop, otherwise, it is impossible to produce high-quality cooking bags.
There are two main reasons for the phenomenon
One is the poor adhesion fastness of the composite ink itself to the substrate. The adhesion fastness of polyurethane ink on BOPA film is not as high as that on BOPET film, and it is not as good as that of chlorinated polypropylene ink on BOPP film. If the winding is too tight, it is easy to cause anti adhesion. Especially when the environment humidity of printing workshop is high, the BOPA film will shrink after moisture absorption and winding, which will cause anti adhesion. Therefore, when printing BOPA film in summer, the winding diameter should not be too large, and the printing length of film roll should be about 3000 meters. In addition, if the printed BOPA film does not composite immediately, it must be wrapped with aluminum foil and placed upright in a dry place to prevent the BOPA film from absorbing moisture.
Second, the high residual solvent in the printed matter causes anti sticking, which often occurs in low and medium speed printing machines. Due to the low drying capacity of low and medium speed printing, the printing viscosity of cooking resistant composite ink is high, and the amount of ink is large. The phenomenon of "surface dryness" of printing pattern is serious. With the gradual volatilization of residual solvent after winding up, it will cause anti sticking phenomenon. Some patterns, especially the part with more overlapping edge lines, have thicker ink layer and uneven tightness of film roll after winding up, which is also easy to cause anti sticking phenomenon.
Polyurethane ink due to the "surface dry" phenomenon caused by the phenomenon of anti adhesion, the ink viscosity can be adjusted to make it printed at low viscosity. At this time, the amount of ink on the printing is small and the ink layer is thin. Under the action of a large amount of diluted solvent, the molecules of polyurethane ink binder are relatively loose, and the shielding ability of solvent volatilization is relatively weak. When the ink is transferred to the film, the solvent can be quickly and completely separated from the ink layer in the drying channel, which is not easy to produce "surface dry" phenomenon.
Analysis of color penetration
When using red cooking compound ink (such as pink, magenta or pink ink) to print high temperature cooking packaging bag with BOPA film as outer material, the phenomenon of penetration often occurs, which leads to serious quality accidents. Moreover, because the problems often appear in the later stage of processing, even after the contents have been packed, the economic losses caused are relatively large.
The author has been exposed to many color penetration accidents of this type. Through a large number of comparative tests, it is found that the performance of BOPA film and the characteristics of cooking resistant composite ink itself have a significant impact on color penetration.
(1) Color penetration often occurs in cooking bags with BOPA film as the outer layer. If the outer printing film is replaced by BOPET film or BOPP film, the color penetration phenomenon will disappear.
(2) Red and purple are the main colors of ink with color penetration phenomenon. Therefore, we have selected different grades of red and purple pigments for comparison. When the moisture permeability of BOPP film is too high, the phenomenon of color penetration can not be completely eliminated, but the degree of penetration is different.
(3) Temperature and water are the two basic factors of color penetration. Under the same temperature conditions, the cooking bag will not appear color penetration phenomenon when it is heated in the oven; when the temperature is lower than 70 ℃, the cooking packaging bag will not appear color penetration phenomenon after conventional sterilization treatment.
The results of the above three points were analyzed: nylon resin is a kind of thermoplastic polymer from semi crystalline to amorphous. The lower the degree of crystallization is, the greater the change of molecular arrangement will be when the temperature is increased, which makes the migration possibility of pigment greater. The water vapor permeability of BOPA film is 20-40 times higher than that of BOPET film. In the process of boiling, water molecules constantly enter and leave the BOPA film, washing and taking away some pigment components in printing ink (relatively water-soluble pigments, such as red pigments), resulting in color penetration. At the same time, the moisture permeability of CPP film and polyurethane adhesive layer is only 1 / 20 ~ 1 / 40 of that of BOPA film Under the joint action of the two, the water molecules are prevented from penetrating into the inner layer of the packaging bag. When the water molecule's penetration is limited between two layers of BOPA outer membrane which are in close contact, a small amount of dissolved pigment particles (the dissolved amount varies with the grade of the pigment) permeate each other with the activity of water molecules, so we always see the color penetration or color diffusion between the bags, And rarely appear color to the inner layer of penetration, unless the use of ordinary non cooking composite ink printing production of packaging bags.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service. The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries. We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.