Mahindra Plastic Industries

Bag making machines produce bags / pouches that are used to package various types of goods in food and beverage, pharmaceutical and consumer product industries. In general these machines are fully automatic and require operator intervention only to replenish the raw material and remove the finished products. Bag making typically has certain main functions which make up of material feeding, sealing, cutting and stacking. In the Feeding section, roll-fed flexible packaging film is unwound from a feeder roll. Feeder rollers are used to move the film through the machine to carry out the required operations. Feeding is usually an intermittent operation and other operations like sealing and cutting are carried out when feeding has stopped. Dancer systems are used to maintain a constant tension on film web. Feeders and dancers are required for maintaining tension and critical accuracy in feed. In the Sealing section, temperature controlled sealing elements are brought into contact with the film for a specified amount of time to appropriately seal the material. The sealing temperature and sealing time is dependent on the type of material and they need to be maintained constant for different speeds of the machine. The sealing element configuration and thereby the machine format is dependent on the sealing type dictated by the bag design. In most machine formats, sealing is accompanied by cutting and both of these are carried out only when feeding has come to stop. In the Cutting and Stacking operations, like sealing are typically done during the non-feeding time of the machine cycle. Similar to sealing, the cutting and stacking also would determine the ideal machine format. In addition to these basic functions additional operations like zipper, hole punch, handle punch, tamper proof seal, spout, cap etc. might be carried out depending on the bag design. Accessories attached to the base machine are used to carry out the additional operations.

Flexographic printing is a common printing method in the packaging field. The printing method is characterized primarily by the flexible printing plate and the low viscosity inks which make it suitable for use on almost any substrate. The object of this study was to obtain further knowledge of some important mechanisms of flexographic printing and how they influence the print quality. The thesis deals with printing primarily on board and liner but also on newsprint with water-borne ink using a fullscale flexographic printing press. Several printing trials have been performed with a focus on the chemical interaction between the ink and substrate and the physical contact between the inkcovered printing plate and the substrate. Multicolour printing exposes the substrate to water from the watercontaining ink. The emphasis was to investigate the relation between print quality and water-uptake of the paper surface with heat and water. Printing trials was carried out on substrates possessing a hydrophobic, and also a rather hydrophilic surface using a regular commercial water-borne ink. The favorable effect which water or surfactant solution had on the hydrophobic substrate with regard to print mottle could depend on its surface compressibility in combination with the hydrophobic nature of its surface that could affect the wetting properties. Conventional printing involves physical contact between plate and ink and between ink and substrate. A method for measuring the dynamic nip pressure using thin load cells is presented. Print quality was influenced by the plate material. A correction procedure taking into account the size of the sensor was developed in order to estimate the maximum dynamic pressure in the printing nip. An attempt was made to identify essential mechanical and chemical parameters, and also geometrical properties of the plate that affected print quality. Laboratory printing trials were carried out and a multivariate analysis was applied for evaluation of print density data.