Size Presses
Surface sizing is commonly used on grades of paper and board that will be coated and/or printed. The traditional purposes of surface sizing have been to improve the sheet’s resistance to the penetration of fluids and to improve certain sheet properties. Traditionally, a starch-based sizing solution is applied to both sides of a fully dried sheet in a two-roll nip at a “size press” that is located between drying sections. This course discusses the design and functions of a size press.
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Learning Objectives
• List the two traditional purposes of surface sizing • List some of the materials that can be used in surface sizing solutions • Identify and describe pond-style size press designs, including vertical, horizontal, and inclined size presses • List sheet variables that affect the performance of pond-style size presses • List sizing solution variables that affect the performance of pond-style size presses • List equipment variables that affect the performance of pond-style size presses • Identify and describe film-type size press designs • List the advantages of film-type size presses over pond-style size presses • Identify and describe safety hazards and safety guidelines for size presses
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, French, Polish, Russian |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What is the purpose of surface sizing?
The purpose is to improve the sheet’s resistance to the penetration of fluids like ink, and improve certain sheet properties, such as surface strength, internal bond, stiffness, and porosity
Where is surface sizing usually applied to the sheet?
Traditionally, surface sizing is applied at a “size press” that is located between drying sections, though it can also be applied at a calender stack
How is cationic starch different from regular starch?
Cationic starch is starch that has been treated to produce cationically-charged starch that better adheres to the anionically-charged fibers in the sheet
Where is surface sizing usually applied to the sheet?
It is the weight of surface size picked up by the sheet per unit area. You must know the sheet weight before and after the size press in order to calculate it.
Why do sheet breaks often occur at the size press?
Because the sheet is re-wetted at the size press, there is an increased possibility of sheet breaks here, especially if there is a weak spot or hole in the sheet.
Sample Video Transcript
A conventional pond-style or flooded nip size press utilizes two driven rolls pressed together in a vertical, horizontal, or inclined arrangement. The goal in each is to flood the ingoing nip with sizing solution on both sides of the sheet. The sheet absorbs some of the solution and the excess is removed by the nip. The solution is allowed to overflow or is collected in a pan and is continuously recirculated. The vertical size press provides the easiest sheet run but size application is unequal on the two sides of the sheet. The horizontal size press solves the problem of unequal application but has an awkward sheet run. The inclined size press is a compromise of the other two.
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