Selection and use of compound cooking bag ink

The homogenization of flexible packaging manufacturing industry is becoming more and more obvious, especially the relatively low technical threshold of ordinary composite packaging, such as BOPP / / PE and other structures, a large number of companies can only take the scale of production, barely maintain meager space. At present, high-temperature cooking bags used for the packaging of meat and other contents, especially three- or four-layer composite bags such as NY//AL//CPP, PET//AL//NY//CPP and so on, due to technical difficulty Higher, still have a relatively considerable profit margins. In the long-term contact with color printing customers, it is obvious that it is not difficult for enterprises to produce a batch of high-temperature cooking bags that meet the requirements of food companies, but it is not easy to provide long-term stable supply. Summarizing the appearance of quality failures, often the raw materials are unqualified or inconsistently occupy a considerable part, mainly in the NY film, CPP film, and ink and adhesive are mostly.

There are generally three types of cooking compound bags: boiled and sterilized packaging at about 100°C, retort sterilization packaging at 121°C and high temperature cooking and sterilization packaging above 125°C. The corresponding packaging bag structures are: NY/CPP or CPE, NY/ /AL//RCPP, PET//AL//NY//RCPP (RCPP stands for cooking grade polypropylene). In the past five years, high-temperature composite inks have developed rapidly. At present, domestic common high-temperature resistant composite inks include single-component polyester inks and two-component polyurethane inks. Well-known ink manufacturers have corresponding ink products. For example, Toyo's Lamistar, Dainippon Ink's Univure, Zhejiang New Oriental's 300LM, and Yip's inks' GLP, etc., have greatly increased the number of brands selected by domestic flexible packaging manufacturers. 98 years ago, this type of ink was not available ( Not DIC, or Toyo). This scenario is similar to NY film suppliers. In previous years, the average price of NY film was around 40,000, not Foshan Dongfang, or imported parallel imports (Toyobo or Unidjico). In the past two years, the domestic new film was launched. BOPA production lines include: Tianjin Yuncheng, Xiamen Changhua, Zhanjiang Minghe, Shandong New Dongli, Hyosung (Jiaxing), Shanghai Zidong, Wenzhou Jintian, etc. No less than ten, the sales price of nylon film has a lot of fall, available for selection There are many raw material manufacturers, and the supply price is low, but it needs a bit more effort to determine the best price/performance ratio.

For two-layered boiled pouches (eg NY/CPP), one-component polyester composite inks, such as New Oriental 321F, or Yip's GLP, Yongcheng's Type 99 ink, can be selected. Or four layers of high-temperature cooking bag, ink in the selection, use caution. At present, the domestic market is generally recognized as Dongyang's Lamistar, DIC's Univure, Zhejiang New Oriental's 300LM, the best confirmation test before use, In particular, the compatibility of the ink and the NY film, the compatibility of the ink and the adhesive is a very important concern. For example, the properties of the resin used in the ink and the main agent of the adhesive are similar. Due to the reactivity of the curing agent in different types of adhesives, there is a large difference in the margin of use, and when the ink is mixed with the large-format ink printing pattern, it may occur after cooking. Tendency or delamination. For another example, ink red color, such as pink, primary red, ultramarine, or pink spot color, will cause bleed when printed with NY film as the outer layer material, causing serious quality problems. Due to the high value-added factors of high-temperature cooking bags, cooking-resistant inks would rather be expensive to buy. Buying a brand with good stability is not cheap. As a result, it has suffered a big loss. Now many small-scale ink factories can also provide resistance to cooking. Ink, but its stability, as well as its integrity can not be completely convinced.

Polyurethane inks are slightly different from the chloric-based inks currently used in BOPP printing on the market, and their performance is also different. First, the dilution solvent composition is different. Chlorine-based inks are benzene-based solvents, supplemented with esters and ketones to adjust the volatilization rate. The retort-resistant ink uses butanone as the main solvent and acts as a dissolving resin. Since the butanone volatilizes faster than toluene, when the polyurethane ink is used, the solubility caused by the excessive volatilization of the true solvent is not good, or the ink is used. The deterioration of metastasis and other phenomena ensures that the amount of butanone in the solvent composition accounts for a certain proportion. For example, New Oriental Ink Co., Ltd.'s 300LM ink, the butanone requirement in the solvent is not less than 30%. Second, polyurethane inks have a two-liquid reaction type. When the production of retort pouches requires high-temperature sterilization above 121°C, polyurethane ink must be used, and an appropriate amount of hardener must be added before mixing. The two-fluid reaction type uses the remaining ink to be filtered first, and then is partially added to the new ink, or used as a diluting solvent, but cannot be used when the remaining ink shows agglomeration or severe swelling. Third, the polyurethane ink has good composite properties and has a fairly high peel strength. The chlorinated polypropylene ink has a composite strength of 1.5~4.0N/15mm, while the polyurethane ink peel strength can reach 3~8N/15mm. Moreover, after the steaming ink has been sterilized at 121 DEG C, the peeling strength does not decrease.

In the summertime, when printing NY film or PET using high-temperature composite inks, anti-sticking phenomenon may occur, especially in the south of high humidity. Due to the strong hygroscopicity of the NY film, when the relative humidity reaches 80% or more, it is prone to quality failures, and it is necessary to control the workshop environment. Otherwise, do not produce highly demanding retort pouches. There are two major influencing factors for anti-sticking: one is the adhesion of the ink itself to the substrate, and the other is the residual amount of solvent in the printed pattern. The overall adhesion fastness of polyurethane ink to NY film is not as good as the adhesion of PET to PET, and it is not as fast as the adhesion of chlorinated and acrylic inks to BOPP film. I. When it is unable to meet a good printing environment in the workshop, NY film absorbs moisture. After shrinking after winding, when the NY film is printed in summer, the diameter of the film to be taken should not be too large (3000 meters), and when it cannot be compounded, it is wrapped in aluminum foil and placed in a vertical damp-proof manner. The anti-adhesion caused by excess solvent residue often appears on the medium and low-speed printing presses. Due to its own poor drying capacity, the ink has a high printing viscosity and a large amount of ink, the printing pattern “dry” phenomenon is more serious, some packaging patterns, In particular, the overlap of the side lines and the large degree of tightness of the film roll also tend to cause the anti-sticking phenomenon. Polyurethane inks require inks to be printed at low viscosities due to the phenomenon of ink anti-sticking caused by the ink layer being “dry”. In the low-viscosity state, the printing ink consumption is small and the ink layer is thin. Under the effect of a large amount of dilution solvent, the polyurethane ink connecting material molecules are relatively loose, and the shielding ability against solvent volatilization is weak. When the ink is transferred to the film, the solvent can quickly and completely separate from the ink layer in the drying tunnel, and it is not easy to produce a "dry surface" phenomenon.

In the production of retort pouches, there is a possibility of “bleeding” that is not easy to prevent, resulting in greater economic losses, since problems often occur late in processing and even the contents have been packed. The author touched a lot of this type of color penetration accident, and through a lot of comparative tests, I found that the performance of the nylon membrane and the ink itself have serious effects on the color penetration.

1, color penetration occurs in the nylon film as the outer material of the packaging bag, when the replacement of the outer film is polyester or BOPP film (other conditions remain unchanged), the color penetration will not occur.
2, the appearance of the infiltration of the hue is red, purple as much, for this reason, we have chosen different grades of red-violet pigments for comparison, when the nylon membrane defects, the color penetration phenomenon can not be completely ruled out, can only be the degree of penetration of the difference .

3. Temperature and water are two basic elements that cause color penetration. Under the same temperature conditions, the same packaging bag will not be infiltrated in the oven; below 70 °C, the conventional time of sterilization will not appear color penetration.

The analysis of the above three results appears: Nylon resin is a semi-crystalline to amorphous thermoplastic polymer, the lower the degree of crystallization, when the temperature increases, the greater the arrangement changes between molecules, making the possibility of pigment migration The bigger. On the market, nylon film biaxially stretched nylon film (ONY) and unstretched nylon film (CNY), the water vapor permeability of unstretched nylon film is 5 to 10 times that of biaxially stretched nylon film. The water vapor permeability of ONY is 20-40 times that of BOPET. During the boiling of water, water molecules continuously enter and exit the nylon, washing and taking away the pigment components in some printing inks (relatively water-soluble). Pigments such as red) cause color penetration. The moisture permeability of the inner film CPP (or PE) of the packaging bag and the polyurethane adhesive layer is only 1/20 to 1/40 of that of the NY film. The combined effect of the two causes the penetration of water molecules into the inner layer of the packaging bag to be prevented. When the infiltration of water molecules is limited to the two layers of the NY outer membrane that are in close contact with each other, a small amount of dissolved pigment particles (the amount of dissolved pigments differs depending on the grade of the pigment) infiltrates with the water molecules, so we It is always seen that there is color penetration or color spread between the bag and the bag, and color penetration into the inner layer is rarely seen unless the production bag is printed using ordinary printing ink that is not resistant to boiling or cooking.

Due to the relative high technology of retort pouch production and high added value, it is necessary to establish a relatively complete set of inspection procedures for raw materials, accumulate production experience, and write into the best production process route. In order to ensure the qualification of the final product, this article only uses a simple empirical analysis of cooking-resistant compound inks for manufacturers' reference.

Reprinted from: New Oriental Ink Author: Yu Yongyue