1 And combinations of rubber and plastics are used in some instances。The rubbers are specially compounded，and are supplied in unvulcanized sheet form。

The type，line engravings，coarse halftones，or combinations of these which are to be duplicated，are carefully selected to make sure they have sufficient depth of relief，no undercutting in the engravings，and are of accurate height，ordinary letterpress engravings usually do not possess sufficient depth。Powderless etching methods have been found to give the best results，photopolymer originals also are coming into use，

In addition to specially made deep etch engravings for making rubber plates，several type foundries have recently placed on the market specially made foundry type for rubber plate making。The type has much deeper relief than regular type，and is slanted from the face down to the shoulder for effective release from the plastic matrix。

Type and engravings are locked up on a chase or frame，

With bearers all around，the same as they would be for making ordinary electrotype molds。Bearers often are a part of engraving，as noted above。

2 The from is placed in a molding press and a sheet of thermosetting plastic material is placed over it.The heated upper

Platen of the molding press is placed over it。The heated upper plated of the molding pressing is brought down，pressing the matrix material onto the from，and a reverse（female）mold or matrix，made from the master plate or type，can be used to made many identical rubber plates，because it retains its shape and stability under later operations involveing heat and pressure。

Matrices normally shrink slightly in processing，and this is allowed for in preparing the copy for reproduction。In cases where exact size must be retained，for tight color register，etc，a non-shrink matrix can made by the incorporation of a then（010）sheet of perforated metal between sheets of the matrix material。Molding operations are carried out the same as with ordinary material。

The next step is to plate a sheet of unvulcanized rubber，or other from which the plate is to be made，in contact with the matrix。They are again plated in the molding press where they are pressed together under great pressure and heat，which makes a rubber relief plate like the original master form，and vulcanizes the rubber into a stable material。The operations are done with great accuracy，and plate thickness is controlled to meet the requirements of the flexographic printing presses。plates most commonly are ·125（one-eight）inch thick。

Rubber plates for fibre box printing，usually called rubber dies，are basically the same as the foregoing，but usually are made in thicknesses of·250（one-quarter）inch，in order to achieve a much deeper relief image。Much of this printing，using slow drying，oil base letterpress ink，is done with presses using wood cylinders to which plates are tacked or taped。

3 Usually flexographic printing is followed by some kind of package fabricating，such as bag-making，sheeting， or roll feeding into wrapping or form-fill machinery where great accuracy of the printing is required。Proofs offer the flexographer and customer an opportunity to check the accuracy and positioning of all elements in the job before printing begins

Flexographic presses，while utilizing rather simple basic principles，usually are quite complex，precision machines。As in most printing presses，the rollers cylinders which carry the printing plates and move the web or substrate。The printing unit of the flexographic process consists of four rollers or cylinders。

First is the fountain roll which is usually rubber and rotates in the tray-like fountain which holds the fluid ink。This roller is in contact，often at a different speed，with the transfer roller。This roller，usually called the Anilox10（10为次方）roller

Is of metal and carries a fine mechanically engraved surface，providing thousands of minutes intaglio cells。These cells hold a measured and controlled amount of ink，and provide the main ink control factor in the system。A typical steel transfer roll might have from 165 to 180 cells to inch and 25 to 40 microns deep。A doctor blade is sometimes used on this roll to remove excess ink