PACKAGING PAPER SUBSTRATES

Paper-25-60 lb./ream
Packaging- specialty papers specially designed for given end use
Several categories

Uncoated Stock

Papers made without any surface treatment – (only light surface sizing)
Uncoated –not sufficient smoothness, ink holdout

Supercalendered Paper

Smoother, denser than uncoated- fine halftone reproduction
Supercalendered- loss of strength, opacity, bulk

Coated Papers

Most widely used in gravure packaging
C1S, C2S, multiple coated
Mostly- blade coated – on paper machine, off paper machine, or combination of the two
Sometimes- coating + supercalendering
Gravure packaging- printed one side
Reverse side- required various properties on reverse side. Special quality-multiple blade coating.

Label Stock

Chemical wood pulp
Smooth machine or supercalendered finish- good printing, gumming characteristics
Clay coated on 1 side- C1S
Basis weight 40-80 lb./ream (25x38 in.)
C1S- variety applications
Usually supercalendered  or multiple coated-high gloss smooth finish
Base sheet  - needs sizing (or backside coating) to control curl
Curl- problem during sheeting, cutting, dye cutting, customer application process
Specific coating formulations: using delaminated clay, soft latex, blade coating
Uncoated- machine glazed, machine finish- to avoid blistering
Coated >uncoated in print quality
Uncoated- laminated structures

Specialty Label Papers

Citrus paper- withstand citrus juice packaging- free of pin holes
Can wraps- withstand high speed can wrapping operations
35-55 lb./ream (24x36 in)

Beer label paper- white, good wet and dry opacity
Highly sized- wet storage
40-55 lb./ream (neck-body of the bottle- differs)

Oil and grease resistant paper- OGR- treated with fluorochemicals- prevent penetration of oil, grease
Products: corn, cooking oils, salad dressings, cosmetic bottles

Paperboard

Heavier in basis weight, thicker, more rigid than paper- 0.012 in caliper
(Exceptions)

SBS

Solid Bleached Sulfate- 100 % bleached, virgin pulp
White sheet clay coated one side- improved printability
High quality performance, appearance – cosmetics, toiletries, pharmaceuticals
SBS- range of thickness, caliper, more smooth consistent in quality than other grades

Coated Unbleached Board

(or Natural kraft) variety of characteristics for specialty product needs
Made for variety of printing processes
Smoothness = f (n physical properties)
Increase of smoothness negatively affects: tear, basis weight, bulk, long fiber content
These properties- required for high speed folding, glueability, tear, stiffness

Recycled Paperboard

Clay coated recycled paperboard- from recycled fibers
Detergent cartons, cereal boxes, diaper cartons, tissue boxes
Manufactured in layers top liner, filler, back (bottom) liner, chemical additives according to required properties (grease, water-resistant grades)
Appearance-vary from manufacturer to manufacturer
Recycled Paperboards- vary in smoothness
Recycled Paperboards- compressible- printability- impression pressure (maybe increased)
- reduction of missing dots, snowflaking
Impression pressure- monitored (deforming the board)

Outside Wax Laminated Paperboard (OWL)

Packaging the products that require high degree of moisture vapor protection
 (powdered, granulated dry bleach)
OWL –made by wax laminating a coated two side litho grade paper to an uncoated recycled paper board
Caliper- customer specification
Printing surface depending on paper surface, amount of the wax adhesive, surface of recycled board
High quality graphic reproduction
Temperature of gravure press dryers- excess T- delamination (wax melts)

RUNNABILITY TESTS

Physical properties – strength, durability- made according to standard test procedures
TAPPI- Technical Association for Pulp and Paper Industry
CPPA- Canadian Pulp and Paper Association
GATF- Graphic Arts Technical Foundation
ASTM- American Society for Testing Materials
 
Burst

Resistance of paper to puncture
Perkins Mullen instrument
Bursting pressure- applied by rubber diaphragm at controlled increasing rate
30.5 mm diameter
Bursting strength [kPa]
TAPPI T 403 OM-85

CALIPER

Thickness of the paper- perpendicular distance between top and bottom surfaces
Value given in micrometers, or thousands of inch
Pressure 50 ?2 kPa during 3 sec- determination of caliper
TAPPI  T411 OM – 84

HUCK-GRI PRINTABILITY TESTER

Simulate gravure printing- evaluate smoothness- skipped dots, ink holdout, print through, print gloss
TAPPI Useful Method 561

MOISTURE

Loss of weight measured after being dried to a constant weight at 105 ? 2 oC

BASIS WEIGHT

Mass in pounds of ream of paper ream can be 480-500 sheets
Sheet can have 13 different sizes (traditionally from 19th century)
Grammage- ISO - air-dry basis: 23 ? 1 oC, 50?% relative humidity
 

PRINT QUALITY TESTS (PRINTABILITY)

BRIGHTNESS

Amount of light reflected by a substrate [% standard]
Spectrophotometer- 457 nm diffuse illumination and normal viewing- ISO brightness (diffuse brightness)
TAPPI T452 OM-87

OPACITY

Show-through- of print from back side
Measure of hiding power (light scattered and absorbed) of the sheet
Amount of light reflected from a single sheet placed over a black backing, expressed as a % of reflection from the same sheet backed by effectively opaque pile of the same paper
TAPPI T452 OM-87

COLOR

Can be measured with 3 well-known systems: Dominant wave length and purity, Hunter l,a,b and CIE L*a*b* values- spectrophotometer
L* Lightness [%] ranging: 100% - perfect white 0%-perfect black
a* redness (+a) or greenness (-a)
b* yellowness (+b) or blueness (-b)
Standard TAPPI T 524 OM-86

GLOSS

Paper surface reflectance- smooth papers will give shiny, lustrous appearance
Specular gloss- the angle of incident light is equal to angle of reflected light
20, 45, 60, 75-degree specular gloss, 75 deg – paper specially
TAPPI T 480 OM-85

POROSITY AND INK HOLDOUT

Porous material- gaps- pores- passage of fluids (inks)
Porosity- measured as air permeability
Gurley Densometer TAPPI T460
Sheffield Porosity tester
Porosity by forcing air through paper, measuring the rate of the flow
Gurley- the time it takes for 100 cubic centimeters of air to pass through the sheet
Higher value- denser sheet
Sheffield- the rate of flow at continuous flow of air.
Parker Print Surf- the same principle
Here- the higher the number- the lower paper density
Porosity- high enough to allow vehicle to penetrate, pores small enough not to allow pigment to soak in. Ink holdout- indirectly- gloss, density

SMOOTHNESS/ ROUGHNESS

Smoothness-top priority for gravure, offset
Smooth- free of irregularities
Measure smoothness- measure the extent of irregularities
Roughness- deviation of the surface from the ideal plane
Tests: smoothness of “free” surface vs. smoothness under pressure (mimic printing nip)
Air leak tests: paper pressed against annulus (ring) with flat surface
Flow of air between paper and annulus –measure of roughness
Sheffield Roughness – most widely used in USA
Clamps paper using 2 concentric annular lands  (rings with indentations permitting air flow) against glass surface
Air-constant pressure, fills space between lands and paper surface
The air flow across the paper surface is determined
TAPPI OM-518
Parker-Print-Surf Roughness- widely accepted in last years
PPS- roughness under pressure