Thank you Xavier.
I was not aware that invoice and shipping invoice shared the same view.
In case someone wuld llike to know how to do it.
In order to deactivate a column in shipping invoice it is necesary to add a php code to all correspondent th and td tags you wanted to dissappear.
Example:
Original:
<th class="title iva" style=" border: none ">
<?php echo JText::_('VAT'); ?>
</th>
Changed to:
<?php if($this->invoice_type=='full'){?>
<th class="title iva" style=" border: none ">
<?php echo JText::_('VAT'); ?>
</th>
<?php } ?>