Discussion on Paper Cup Printing Technology (Part 2)
2. Composition of paper cups
Paper cup paper is made by extruding and composite of paper cup base paper and plastic resin particles. Plastic resin generally uses chat resin. The paper base paper is coated with single-sided PL film or double-sided film. Becomes single PE paper cup paper or double PL paper cup paper.
PE itself is non-toxic. Odorless, odorless, hygienic performance, reliable, stable chemical performance, good physical and mechanical properties, good cold resistance, water and moisture resistance, certain oxygen barrier, good oil resistance, excellent molding performance and good heat sealing performance. The team has a large production volume and convenient sources. The price is low, but it is not suitable for high temperature cooking. If there are special performance requirements for the paper cup, the resin with the corresponding performance should be selected when coating.
Printability of paper cup materials
1. Surface requirements of paper cup base paper
Directly printed paper cup base paper should have a certain surface strength (wax stick value ≥ 14A) to prevent fluffing and powdering during any printing. At the same time, the base paper of the paper cup must have a good surface fineness to ensure uniform printing ink.
2. Surface treatment before printing
The surface of the base paper or base film to be printed must be clean. Dry and smooth without dust or oil. For non-polar PE materials with dense and smooth surface, the surface tension value is only 2 days ~ 31mN / m, so corona treatment is required before printing to change the surface state, and the surface tension value is increased to 40mN / M, at least 38mN / m. Only in this way. Only printing ink can achieve a certain adhesion fastness on the substrate surface.
After corona treatment of double-sided composite paper, the treatment effect of PE film will exponentially disappear with the extension of storage time. The speed of fading depends on various factors such as the temperature of the storage environment, the grade of raw materials, and the thickness of the film. The higher the storage temperature, the faster the subside speed and the more thorough. For example, when stored in an environment below 20 ° C, the critical surface tension of the film can be maintained for a month or even half a year from 30 to 42mN / m. However, when the ambient temperature is above 36 ° C, no matter how the original film is processed, the material is placed for a month. The surface tension will subside below 38mN / m. Generally speaking. The surface tension of thick films fades faster than thin films. Therefore, the material is best printed immediately after corona treatment to obtain the best wettability and adhesion.
Paper cup printing process
1 Ink
The heat sealing performance and printing suitability of the Pc film surface required for continuous forming of paper cups. Factors such as ink composition, residual solvent amount, and drying conditions must be adapted to the performance of the paper cup.
The quality of paper cup printing is spoiled, which is the result of a reasonable combination of printing machinery and printing process substrates and inks. As long as one of them is not well coordinated, it will affect the printing quality of the paper pocket or malfunction during the printing process.
Usually paper cup paper printing uses flexographic water-based ink. For water-based ink. Ink adhesion performance is critical. In order to avoid losses, a large number of tests are generally done before the official printing in order to select inks with better adhesion. Only by choosing the appropriate ink can the printed matter get good light resistance, heat resistance, friction resistance and other properties.
Therefore, the ink used for paper cup printing requires good visibility, and the surface of the printed matter has good acid resistance. Alkali resistance, water resistance, heat resistance, light resistance will not fade due to external factors such as acid and alkali. Discoloration, ink layer peeling and other phenomena. Also. Paper cup prints should have good scratch resistance, gloss, semi-matting and matting.
The components of the ink must comply with the Food Sanitation Law and the corresponding food packaging hygiene standards.
2. Solvent
The selected ink solvent should not swell the film as much as possible, nor can it contain water in the solvent to prevent curling of the printed matter. As much as possible, choose an ink containing a plasticizable free carrier to prevent the ink film and the PE film from shrinking due to different shrinkage rates due to temperature changes. The curled printed matter will be warped after die cutting into fan-shaped pieces. Difficulties are brought about during the cup making process and the crimp forming process.
The amount of residual solvent should be less. In order to prevent the paper cup from smelling after printing, the back of the printed matter is dirty. The solvent adheres to the substrate or base film at the seal. Poor heat sealing will result in poor adhesion at the seal or poor solid adhesion, causing curling and popping.
3. Drying temperature
After printing. The drying temperature of the printed matter should not be too high. When the temperature is too high, the surface of the base film will undergo an oxidation reaction, resulting in poor heat sealing. However, it is also necessary to prevent the printing ink from drying poorly to avoid the smell of paper cups.
4. Environment temperature and humidity
The relative humidity in the workshop is too high. It will also cause the printed matter to curl. In the environment where the temperature is too high after printing, the film will stick between the upper and lower layers, which will also affect the subsequent paper cup forming.
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