Some questions about printed materials (10)

What is cellophane ?
Cellophane, also known as cellophane, is also known as transparent paper because of its softness and transparency. Invented in France in 1900, it was widely used in the late 1920s and became an important packaging material. In the mid 30's, the use of composite coating improved the moisture resistance and heat-sealability of common cellophane papers and became the “glass paper packaging age”.

Cellophane is made of cellulose, just like paper. Its main raw material is wood. However, paper is made of wood fiber directly, which maintains the structure and structure of fiber. Cellulose is made of highly purified wood pulp. Regenerated cellulose. The process is as follows.

The natural cellulose pulp is immersed in an alkaline solution of 18-20% sodium hydroxide to prepare alkali cellulose, and the excess alkaline solution is pressed and placed in a 32-35% difluidized carbon solution to be stirred and disagglomerated into fibers. The sodium sulphonate sodium salt is dissolved in dilute sodium hydroxide solution and becomes mucus. The mucus is squeezed into the coagulation liquid consisting of sulfuric acid, zinc sulphate and sodium sulphate through the slit of the die to solidify and form the cellophane membrane.

Ordinary cellophane is soft, odorless, odorless, non-toxic, high gloss, strong transparency, can penetrate about 92% of visible light, less oil and acid resistance, alkali resistance, strong hygroscopicity, high humidity environment The lower moisture absorption elongation, dry and brittle and easy to break, usually water content of 9 ~ 10% is appropriate. Ordinary cellophane can not be moisture-proof, that is, it has great transparency. Every 24 hours, per square meter of cellophane can permeate 10 to 20 g of water. Therefore, in the current packaging materials, the amount of the common cellophane paper only accounts for a small part of the amount of cellophane, and widely used is a moisture-proof cellophane coated with other substances on the surface of the cellophane paper. The purpose of the coating is to enhance the heat sealability of the cellophane in addition to the moisture resistance of the cellophane in order to facilitate the heating of the cellulase during the bagging process. According to the different uses of paper, there is a single-sided coating and two-sided coating points. When printing single-side coated moisture-proof cellophane, it is undoubtedly necessary to pay attention to the surface printing ink that needs to be printed when the cellophane is rolled up.

The types of cellophane vary depending on the type and nature of the coating material, and the amount, type, and specifications of the cellophane. But from the perspective of flexo printers, there are three basic types of printing surfaces:
1 Uncoated other common cellophane 2 Nitrocellulose coated moisture-proof cellophane 3 Polymer-coated moisture-proof cellophane.