Blocking

The Cause

Blocking is a problem common to a wide range of printing and finishing processes. It describes the tendency of stacked graphics to stick to one another, often leaving an imprint on the bottom of the next stacked graphic. Although the term applies to both laminated and unlaminated graphics, in many cases lamination can prevent blocking in printed graphics. Blocking also applies to adhesion between rolled layers of the same material, and also to adhesives in which the backing paper sticks to the adhesive layer. Various examples are discussed below.

Problem 1

Unfinished graphics: Printed image does not dry or re-wets.

Solution 1

This is a common problem caused by incompatibility between inks and substrates. It is typical of inkjet printing with aqueous inks.

Problem 2 

Vinyl Plasticizers

Solution 2

Inexpensive vinyl substrates, especially those used in screen printing, contain monomeric plasticizers that can rise to the surface, rewetting printed inks and causing the vinyl and inks to fuse to stacked sheets. This problem is made worse by heat, humidity and pressure. If vinyl materials are used, then large stacks should be avoided.

Problem 3  

Vinyl Overlaminates

Solution 3

Vinyl films which use monomeric plasticizers may block when stored in large stacks. Check with your material supplier if you have concerns about this scenario. This problem is more likely to occur in high temperature/humidity conditions.

Problem 4

Blocking in Rolls During Storage

Solution 4

This problem can often be prevented by stocking films rolls vertically rather than laying them on their sides.