Gravure Printing in Pharmaceutical Compound Flexible Packaging (I)

There are many printing methods in the entire packaging printing market, of which lithographic printing still dominates, but in the composite flexible packaging printing industry such as medicine and food, gravure and flexo occupies a considerable proportion, especially in gravure printing.

The content of gravure printing is quite extensive, and there are many factors that affect the quality of gravure printing. This paper mainly discusses the printing substrate, ink, and gravure printing process elements and controls in gravure printing in the pharmaceutical composite flexible packaging industry.

First, printing substrate

Due to the special nature of the contents of medical flexible packaging, the requirements for surface gravure printing substrates are relatively high. The basic requirements are:

1. Good transparency (except paper, special effects, matting film, etc.)

2. The surface of the printing substrate should be smooth and smooth, free from impurities and damage, and has good printability;

3. The surface of non-polar materials should be treated to increase the surface energy, and the surface tension of the printed substrate film is generally required to be more than 38mN/m.

4. The printing substrate should not be too loose, especially when it is tight and one side is loose;

5. The shrinkage elongation and deformation rate of the substrate is preferably less than 1%;

6. The printing substrate has a certain tensile strength and rigidity;

7. Good heat resistance and heat deformation can not be too large, such as BOPP film will be deformed by heat, resulting in bags when the bag size, pattern is not uniform;

8. With abrasion resistance, puncture resistance, can play a protective role for the middle layer;

9. When the double-layer composite film is used, the surface layer also preferably functions as a barrier.

Commonly used surface materials are: BOPP, BOPET, BOPA, PT (glassine paper), paper and so on.

(1) BOPP film is an anterior film obtained by longitudinal and transverse stretching of polypropylene after melt extrusion, and is one of the most widely used film materials for packaging. BOPP has high tensile strength and large elastic modulus but low tear strength. Good rigidity, outstanding ductility and bending fatigue resistance, can be folded millions of times; chemical stability is good, except for strong acid (such as fuming sulfuric acid, nitric acid) has a corrosive effect on it, insoluble in other solvents, only part Hydrocarbons have swelling effect on them and good water resistance. They are one of the best materials for moisture and moisture resistance, and their water absorption is less than 0.01%.

(2) PET is commonly referred to as vinegar, commonly known as "polyester," a colorless, transparent, extremely tough material that is odorless and non-toxic. It is known for its strength, toughness and transparency. It has good rigidity, hardness, abrasion resistance, folding and dimensional stability, good odor-proof permeability, airtightness and moisture resistance, and good heat and cold resistance. It maintains its excellent physical and mechanical properties over a wide temperature range. The disadvantage is that it is easy to carry static electricity in the gravure printing process, and is prone to blockage, fluffing, and scraping (knife) phenomenon.

(3) Polyamide (PA, commonly known as nylon) is a generic name for a class of polymers containing a large number of repeating guanamine groups on a primary bond, and nylon is commonly used as its trade name. Nylon molding process and printing performance is good, not easy to accumulate static electricity, oil resistance is good, but easy to damp, so nylon in the shop after opening the packaging of the remaining raw materials are required to be sealed moisture-proof packaging, to prevent its moisture deformation and affect the next use.

(4) Cellophane, also known as transparent paper, is a very high-grade transparent packaging paper. It uses high-grade bleached sulphate wood pulp as raw material and is treated with sodium hydroxide to make alkalized cellulose. Then it is made into a viscose solution by a series of treatments such as carbon disulfide and alkali, and then it is formed in a sulfuric acid bath. After washing, etc. made. Cellophane has excellent transparency, gloss, printability and non-conductivity. Unlike many plastic films, it does not accumulate static charges on the surface, so it is not easy to adhere to dust and has excellent dust resistance. In addition, because it is a paper fiber material, it has good tearability and is generally used as a surface printing layer of an easily tearable film product. It should be noted that cellophane is easier to absorb moisture and affect the printing accuracy. Therefore, it is also necessary to pay attention to sealed moisture-proof packaging when storing, similar to nylon.

(5) The paper has excellent printing adaptability, is foldable, can be sterilized by high temperature and high pressure, and is one of the best printing substrates. Moreover, the paper packaging materials can be recycled and the cost is low. As waste, the treatment method is easy and no pollution is generated. Most green packaging now uses paper as raw materials. For example, Tetra Pak is now popular on the market, and a large proportion of its basic raw materials are paper.

Second, gravure printing ink

Ink is a very important material in the gravure printing process, and its quality directly affects the printing quality.

The selection of ink mainly considers five factors:

1. The properties of the printed substrate. Variety of printing substrate types, we must choose the most suitable ink according to the characteristics of the printing substrate, to consider the temperature resistance of the substrate, the adhesion with the substrate and the dissolution and swelling of the substrate, etc. .

2. Printing conditions. Consider the condition of drying and printing speed of gravure printing equipment.

3. Printing effect. For superimposition, color inks with good transparency should be selected.

4. Post-processing conditions. After printing, it needs to be compounded by glue and should be printed with compound ink. To boil or high-temperature cooking, pay attention to the temperature resistance and water resistance of the ink.

5. Use. The inks used in food and pharmaceutical packaging require no toxicity and odor, and secondly, the properties such as retort resistance, freezing resistance, and ultraviolet light sterilization must be considered.

The inks that are often used in pharmaceutical compound packaging mainly include nitrocellulose systems, polyurethane, and polypropylene. Polyurethane resin contains many functional groups and has high-grade groups, so it can bond most plastic films, and it also has excellent film properties. Therefore, as a gravure printing ink, polyurethane ink has been widely used, polyurethane ink for polyester, nylon, OPP, cellophane and other packaging films can be applied, and less residual solvent prints, R Fuk domain God Gu Cooked C, imine AC-PEEL dry compound, NS adhesive can adapt. In the case of two-component reactive inks, they have a longer pot life than other resins and can be printed with low-roughness, making them suitable for high-speed printing of modern packaging.

Grafted polypropylene is generally used primarily for OPP printing inks. Its adhesion to polypropylene should be attributed to its polypropylene backbone. For OPP films, chlorinated polypropylene inks have good adhesion whether processed or not. Sex, compound strength is also very good. In addition, OPP ink itself is not suitable for steaming or cooking process, so chlorinated polypropylene ink is not used for this purpose.

50g coated paper in medical composite paper aluminum-plastic packaging mostly uses nitrocellulose paper ink. The solvent is mainly mixed solvent of ethyl acetate and alcohol solvent.

Since the polarity of the substrate used in the gravure printing is different, the selected inks are also different. For example, Duofu ink is suitable for the printing of Pu-Ming and sex materials, You-Li-Fu is suitable for the printing of polar materials, and Wanter is suitable for the printing of aluminum foils. Paper has a special ink, anti-cooking type requires a particularly high peel force, you must add a curing agent in Uniforce ink.