1. Types of Paper bags
a. Kraft paper bags: Made from a chemical pulp produced in the Kraft process. Pulp produced by the Kraft process is stronger than that made by other pulping processes; acidic sulfite processes degrade cellulose more, leading to weaker fibers, and mechanical pulping processes leave most of the lignin with the fibers, whereas Kraft pulping removes most of the lignin present originally in the wood. Low lignin is important to the resulting strength of the paper as the hydrophobic nature of lignin interferes with the formation of the hydrogen bonds between cellulose in the fibers. Kraft pulp is darker than other wood pulps, but it can be bleached to make very white pulp. Fully bleached kraft pulp is used to make high quality paper where strength, whiteness and resistance to yellowing are important.
b. Wood free paper bag: is paper created exclusively from chemical pulp rather than mechanical pulp. Chemical pulp is normally made from pulpwood, but is not considered wood as most of the lignin is removed and separated from the cellulose fibers during processing, whereas mechanical pulp retains most of its wood components and can therefore still be described as wood. Wood-free paper is not as prone to yellowing as paper containing mechanical pulp. Even though the name says wood free wood is still used to make these bags.
c. Art paper bag: Thicker, stronger, and more stylish than other types of paper bags, these more expensive bags often have ribbon handles and are used in high end shops.
2. Advantages of Paper Bags
-Recyclable -Many sizes, styles, shapes, and colors available
-Easy to print on -Can be made from recycled materials
-Biodegradable -Can be laminated for extra strength
-Collapsible -Can be printed on all sides
-Stack-able -Can have twisted paper, rope, or ribbon handles
-Economical -Takes less energy to produce than PET bags
-Can be printed with up to 4 colors -Can be glossy or matte (if laminated)
-Can be embossed
Disadvantages of Paper Bags
-Damaged easily -Flammable
-Disintegrates when wet -Production produces many toxic chemicals
-Not very reusable -Can’t be tied shut
-Requires many resources for production -Not stretchable
-Not very strong
-Generally in Natural and White but can be in colors
A) Screen Printing: Screen printing uses a water like gelling agent with ink mixed in. A screen or stencil is placed over the bag and the ink is applied in the desired colors. The screen is then removed and the bag is left to dry. Since screen printing does not involve chemical solvents, the screen stencil can be washed with just water. The advantages of this printing technique are the image can be in almost any color, it is long lasting, water resistant, odorless and works well on many materials. The disadvantage is that as this method is usually done by hand, for multicolored printing, the positioning may not be accurate which can create smudged or distorted images. As well only solid colors can be screen printed, you cannot show gradations or shading with screen printing.
B) Offset Printing: is a commonly used printing technique in which the inked image is transferred (or “offset”) from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water based film, keeping the non-printing areas ink-free.
C) Foil or Stamp: is the application of pigment or metallic foil to paper where a heated stamp is pressed onto the foil, making it adhere to the surface leaving the design of the stamp on the paper. Foil stamping can be combined with embossing to create a more striking 3D image.