Quality control suggestions for Tip-On® sheets by Tom Rittman, Technical Service Manager Email: rittman@plasticsuppliers.com

Control and uniformity of moisture content are vitally important if TIP-ON sheets are to perform well on a sheet fed press.  The paper section of a TIP-ON sheet will change dimensionally when it is exposed to a drier or damper atmosphere than the air with which it is in equilibrium.  If the sheet is exposed to a damper atmosphere, it expands.  If exposed to a drier atmosphere, it contracts.  Wavy and tight edges originate when paper is exposed to air that has higher or lower relative humidity than that of the paper.

STORAGE AND WAREHOUSING
TIP-ON sheets have a limited storage life and should be used within 30 days of shipment.  An inventory control system should provide for an orderly inventory rotation to prevent older stock from accumulating.  The sheets should never be stored next to radiators or other heated objects, cold walls, or areas subject to sudden and drastic temperature changes.

MOVEMENT FROM STORAGE TO PRESSROOM
The temperature and relative humidity of the storage room may be quite different from that of the pressroom.  When moving sheets from a cold warehouse to a pressroom, never unwrap the skid.  Also, stage the pallet in the pressroom 72 hours prior to printing.  The temperature of the sheets must reach equilibrium with the pressroom.  If not, it will cause the paper to take on moisture on the edge of the sheet.  Always temperature-condition all sheets to pressroom temperature before unwrapping.

PRESSROOM HAVING HUMIDITY CONTROLS
If the relative humidity (R.H.) of the pressroom is controlled to a constant level (in the range of 35 % - 50 % R.H.), the paper will be in reasonable balance.  This is because most paper in the United States is produced in the above range.

PRESSROOM WITHOUT HUMIDITY CONTROL
It is impossible to produce paper that meets the R.H. requirements of the changing and widely different conditions of pressrooms that are not humidity controlled.  When paper is not in balance with the pressroom R.H., the sheets should remain wrapped until ready to be printed.  Nothing is to be gained by exposing paper to an atmosphere that is not in balance.