Test 3 Flashcards
Refining, Paper machine, etc
Retention Aid
used as a glue for fines and filler particles to fibers so they don’t pass through the paper machine
Types of retention aids
cationic starch, polyacrylamides
Sizing Agents
makes fibers/sheet water-repellent for improved printing and better stability in humidity
What kinds of sizing agents are needed for different grades?
Linerboard- liquid resistance
Printing and writing- controlled penetration
What are the goals of fillers?
improve sheet opacity by providing light-scattering surfaces
improve sheet smoothness and printability
What are fillers?
inorganic material added to improve certain characteristics
What are strength agents?
polymers that improve the dry or wet strength of sheets. polymers bridge across bonding areas between fibers
Dry strength agent examples
starches, gums, synthetics
Wet strength agent examples
PAE, GPAM, resins
Alum
Al2(SO4)3, improves drainage, additive effectiveness
Chest types
Dump chest, mix/blend chest, machine chest
Dump chest purpose
recives the raw fiber, may be a hydrapulper
Blend chest
receives stock and furnish components, often feeds the refiners
Machine chest
receives refined stock, feeds the stuff box
Headbox consistency
.5-1%
What is refining?
physical treatment performed on pulp fibers to improve their papermaking characteristics
What does refining do to the individual layers?
Removes P and S1 layers, collapses S2 layers
What is the Canadian Freeness Test?
Most common North American Test, measures the dilution of pulp
How does refining improve grades?
Better tensile/burst strengths, formation, smoothness, and printability
How does refining hurt grades?
Worse tear strength, bulk, drainage rate, air porosity, yield, and opacity
Stuff box function
overflow box, providing constant pulsation above basis weight valve
Basis weight valve funtion
scanner, meters thick stock to set sheet basis weight
Fan pump function
huge pump which mixes thin stock and white water to produce thick stock
Headbox cleaners function
used fro grades that require low level of contaminants, centrifugal force used to remove dense contaminants
Headbox pressure screen function
induces pulsations in the stock to bust up fiber flocs and ensure good formation
Three sections of the wet end
Gravity, vacuum and press
Goals of wet end
distribute the paper stock uniformly across the machine, remove most of the water, press the dewatered sheet
Fourdrinier strengths and weaknesses
strengths: simple, good retention
weakness: limited rate, two sidedness can occur
Top wire former strengths and weaknesses
strengths: permits water removal on both sides, can be easily added to existing fourdrinier
weaknesses: lower retention of fines and filles, two wires to maintain
Gap former types
S, C or crescent former
Gap former strengths and weaknesses
strengths: good for fragile sheets, high speed, no two sideness
weaknesses: complex, two wires to maintain, formation set in the headbox, poor retention
6 Ds of papermaking
Dose: thick stock to achieve basis weight
Dilute: use white water, used for formation
Disperse: put high shear to break up flocs
Distribute: dilute uniformly
Dewater: remove free liquid
Dry: use heat to evaporate water
Gravity section
set formation of sheet, 85% of total water, sometimes involves microturbulence
Headbox function
provides pressure necessary to deliver correct amount of thin stock
Slice funtion
opening at the lip of the headbox, can be adjusted to change basis weight
Basis weight CD profile
dilution headbox uses a series of water injector tubes to dilute heavy spots
Forming fabric
moving wire that supports the stock/sheet and allows water drainage
Breast roll
support roll for fabric, usually has a shower under the headbox to keep clean, may have a shake mechanism
What is formation?
a general term that describes how well fibers are distributed in finished paper sheets
Forming board
supports wire where the stock first comes in contact with the wire
table rolls
rotating devices which removes water and supports the wire
causes pressure pulse on the front end and vacuum spike on back end
Hydrofoils
static drainage devices, similar to table rolls, less intense pulse
Foils
front end of each foil, strips off the water from the previous foil
Vacuum Section
15% removal, goal is to do so without harming gross sheet structure
Vacuum foils
foils attached to a vacuum header to extend the vacuum zone after the foil blade
Vacuum boxes
perforated or slotted boxes under the wire, water removed from passing sheet through holes
The Dry Line
a line separating the glossy draining sheet from the duller dewatered sheet
The Dandy Roll
wire, mesh covered roll which rides lightly on top of sheet, near the first flat box, levels wet paper surface, improving formation and smoothness
Steam Boxes
usually placed over the top of flatboxes, allowing more water to be drained
Trim Squirt
high pressure water nozzles, used to trim off the ragged outer edge, trimmed edges fall into couch pit and are recycled
The Couch Roll
place where paper is released from the forming wire and onto the first press felt, has some suction
Press section
removes water without crushing sheet
Press felts
nylon based fabric used to form fluffy surface, cover the rolls that are on the press nip
Dry End
uses heat to remove .5% of water, dried while the sheet is stretched
Steam Economy
Lbs steam used/ lbs water evaporated
Surface Sizing
On the size press, improves strength and smoothness of
Calendering
a mechanical treatment carried out on the sheet after drying, flattens out the sheets ridges, reduces thickness
Dry End Scanning
pass different rays through the sheet to measure properties, such as caliper and strength
Reels
where the paper is stored, at the end of the machine
Slitter-Rewinder
cutes reel into desired roll sizes, is designed to run fast
Multi-Headbox Fourdinier
first headbox is followed by gravity and vacuum section, then a second headbox is dewatered
Multiple Fourdrinier
multiple headboxes and lines formed together before press section
Multi-layer headboxes
multiple streams feed into a single headbox, usually good for tissue
Why coat paper?
coating fills in the remaining micro pores on the surface of the sheet
Pigments
Clay, calcium carbonate, TiO2, Al2O3. All used for color purposes
Binders
latex, starch, proteins. add mechanical strength to the dry coating
Typical Coating Operations
dry paper
use size press
dry again
use calendrer stack
apply coating
dry using steam
calendaring again
How to get premium softness (tissue)
80% bleached eucalyptus kraft, 20% bleached northern softwood kraft.
new way: combine hard and soft wood
Twin wire gap former
stock is injected into a gap formed between two forming wires.
advantages: compact, fast, both sides identical
S wrap former
stock injected horizontally or inclined, then goes through an s motion in-between wires
C wrap
stock jet directly vertically between forming wires and moves up and around
advantages: good for two ply sheets, can go faster, less stress on the sheet
Cresent Former
horizontal headbox injects between a felt and wire
advantages: no transfer wire, low cost, high efficiency, good quality
Yankee Dryer
uses creping, sheet is dried while supported and restrained, scaped off at the end then creping is induced
Through Air Drying
forced hot air through wet sheet, can be done on a Yankee dryer
Drying terms
LDC - lightweight dry creping
TAD - through air drying
CTAD - creped through air drying
UCTAD - uncreped through air drying
Market Pulp
one fiber type, no additives, not refined, formation not important, dried unrestrained, sold in bales
Critical Attributes of Market Pulp
brightness, uniform fiber length, cleanliness, high viscosity
Fluff Pulp
southern softwoods make the best fluff, good at transporting and holding liquid
Super Absorbent Polymers
most common: polyacrylic acid, used for hygiene, spill clean up and bandages
Gel blocking
a group of SAP particles, also used in many absorbent heavy products
Hammermill
uses rotating hammers to beat apart fluff pulp, creates a fiberized pulp
Fluff pulp characteristics
intermediate product, heavy, weak, only softwood, high cleanliness, no surface, lightly calendared, uniform caliper
Big 7 for Fluff Pulp
- fiberization energy
- low dirts
- high brightness
- high viscosity
- uniform caliper
- water absorption
- reel moisture
Cellulose Acetate
acts like a plastic, found in phones, cigarettes
