What Is Heatset Printing?


Heatset printing is a process that dries printing ink in a heated oven immediately after the ink is applied to the paper. Heat evaporates the oils in the ink and leaves the pigment along with wax resins. The ink is then "set" by means of cold rollers.

Heatset web offset printing is simply a term to describe one of several web 

While some sites provide a very basic description, I will endeavor to give a little more detail on the level that a press operator should know.

Heatset printing also differs from more commonly known forms of printing.  For example, a bubble jet printer works by spraying ink onto paper.  The ink absorbs into the paper and the water based ink will evaporate leaving a dried pigment on the paper.  It behaves in a similar way to

Heatset web printing works differently.  A layer of ink is applied to a usually glossy paper that does not allow the ink to absorb into the paper.  The ink is not water based, but oil based meaning that it must literally boil or evaporate off the paper to dry.


What a heatset printing press looks like.

Heatset web offset printing machine


1. Splicer
This device feeds the web press continuously.  It splices from one roll to the next, usually without slowing down.  Both coldset and heatset web presses uses these.

2. Infeed unit
This keeps the tension steady as the paper runs through the web press. The printing units and the heatset oven can impose forces on the paper and the tension must be kept stead.

3. Printing units
As in the diagram above, there are four printing units. They would normally apply black, cyan, magenta and yellow to make a full color product. 

4. Web catcher
Both heatset and coldset printing presses will have a device that will cut the paper in the event that the paper breaks.  If the paper breaks, then the fourth printing unit will start wrapping up in paper.  It will then pull all the paper back out of the oven and wrap around the cylinders in the printing unit.  To prevent this, a "web catcher" prevents this paper from being drawn back.

5. Hot air dryer or oven
This the the most obvious and unique process to this type of offset printing.

6. Chill roll assembly
After the paper leaves the oven, it will then pass over cold rollers that will set the ink.  The ink does not dry.  Rather it sets as the term 'heatset' emphasizes.  This happens much in the same way that wax solidifies when it is cooled down. The pigment is now solidified into the ink.  A further 5% drying happens in the days that follow as the ink absorbs into the paper and is exposed to air.

7. Silicone applicator 
This is another process that is mostly only found on heatset printing presses due to the speed and paper printed.  The reason is that this type of printing uses mostly glossy paper.  There is almost no absorption of the ink into the paper and so it can rub off easily.  A silicone applicator will apply a small layer of silicone to prevent this.  Adding the silicone will also return some of the moisture back into the paper that was lost in the oven. All of this will help in the next step as it must glide past other bars. 

8. Turner or angle bars
These bars are unique to heatset printing as the paper now needs to be slit and moved to different positions depending on page count and format.

9. Folder
Both coldset and heatset printing share this final step. The paper is folded into the format required by the client.

To see a heatset printing press, take note of each step as shown in the video below.

 

How is heatset different from coldset printing?

Coldset printing press.
Coldset printing press requires less components.
Coldset printing and heatset printing are both web offset printing presses.  However coldset printing differs in that it requires less components than a heatset press.  The diagram above shows only three of the above mentioned components for heatset printing.  

For this reason, coldset printing differs in the following ways:

1. It is less expensive.
2. Quality is lower.
3. The drying process is by absorption into the paper.
4. The paper tends to run vertical. 
 


How heatset printing ink is different

Heatset web offset printing ink consists of varnishes or solvents which make up the oil based portion of the ink.  Pigments are used for color.  In addition, various resins and waxes are added.  Ink companies will also put in various additives to meet the demands of the printing process and customer requirements.

Since heatset printing inks will go through an oven, the solvents in them must have a lower flash point. This means that the oils and solvents in the ink must reach an evaporation or flash point quickly.


What do heatset printing presses print?
The heatset process is expensive.  These printing presses cost about 10 million dollars and require many resources to keep it running.  Thus heatset web printing companies will only use these printing presses for longer run publications.

Though they can print on newsprint and matte papers, they tend to run glossy paper.  Hence all catalogs and magazines will invariably be printing using a heatset printing press. 

While this article discusses the heatset printing process, understanding the

Comments

  1. Good evening sir,

    I have a one question for you.
    What are the inking roller difference between the heatset, coldset and sheetfed printing mechanism.
    Regards
    Rahul

    ReplyDelete

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