Substrates- play role in process color printing.
Provide the foundation and background for the ink film.
Substrate absorption- influence the resulting process color.
Substrate that absorbs more ink –results in reduction of gloss.
Less absorption- increased ink holdout- increased gloss.
Variety of uncoated groundwood papers
Paper Committee GAA-classification system 1982
Classification based on: brightness, color, roughness
Brightness- measure of ability to reflect light ( reflectivity at different wavelengths
Color- perceived shade, hue. Color cast- yellow, blue, red
Smoothness- levellness of paper surface
Basis weigth: Newsprint – ream 24x36 in (500 sheets)
Other paper grades – ream 25x38 in (500 sheets)
Basis weight : terminology based on paper sizes standard for sheetfed presses
Grammage : g/m2 ISO (International Standards Organization)
5 categories of Roto News
Empiric measurements of paper samples, not intended to be recommended specifications for buying
Group E: Newsprint
The lowest price grade, used in gravure
Lowest brightness, greatest roughness, high color saturation
Group D: Standard Roto News
D- most economical grade of groundwood paper for gravure
Slightly brighter and smoother than newsprint, color saturation the same
Group C: Premium Machine Finished (MF) Roto
Originally: Tappi Brightness 58-62, PPS smoothness 2.5 - 3.6
Recent years: Brightness 60-66, PPS 1.8 - 2.8
New development: Soft nip calendering- improved smoothness
Soft-nip= running paper web through series of paired cylinders, one is made of heatable hard metal and the other cylinder has soft covering
Varying temperatures and nip pressures, number of sequences
Most common: 33 and 35 lb. / ream (25x38 in); lighter, heavier- less frequent
Quality of MF- between newsprint and supercalendered grades
Price: based on brightness, smoothness
Before 1989- Major use- Sunday magazines, now- newsprint
High quality MF- inserts, flyers, also heatset offset
Producers: Boise-Cascade, Canadian Pacific Forest Products, Champion, Kimberley-Clark, Macmillan Bloedel, Stone Container Corp.
Group B: Hibrite Roto News
B grades- better in brightness, smoothness- superior brightness
SC-B 64-65 TAPPI brightness
PPS smoothness below 2.0 micron
Brightness and smoothness- improved with fillers addition
Group A: Supercalendered Roto News
Supercalendering- method of sheet smoothening and polishing its surface
to higher gloss through friction and pressure
Stack of alternating fiber-filled rolls and chilled iron rolls
Supercalendering- polishes paper through pressure of iron and cotton rolls-“ironing” both sides of sheet- smooth finish, high gloss
Steam showers-moisten the sheet
SCA Roto News- superior quality –70 TAPPI Brightness, bellow 2.0 micron PPS smoothness
SC-A+ grade current high-tech newest SC grade
New gap-former technology – distributing filler material close to paper surface- ink holdout and printability better than SC-A
1994- USA consumption of SC papers- 1.9 million tons.
Uncoated supercalendered- resemble Roto News, but contain high content
of bleached chemical pulp, and fillers
Basis weight- 30-50 lb./ream (25x38in)
Gravure printed catalogues, newspaper inserts, magazines
2 major categories- groundwoods and freesheets.
Coated- more expensive than uncoated- higher quality, richer image
Publication papers for magazine, catalog- coated to improve printability: increased ink holdout, smoother surface, color, gloss, brightness, compressibility, enhances color fidelity
Coating: pigment: calcium carbonate, clay, Titanium dioxide
Binder: starch, latex- anchor the pigment to base stock
Coating: improves brightness, gives more pleasing shade, more even reflectivity, higher opacity
On-machine coating, off-machine coating, combination of the two
Off- machine- better quality
Coated papers: dull, mate, glossy
Multiple layers of coating (double coated sheet)
1994 –U.S. consumption of all coated groundwood grades- 5.2 million
Principal papers – magazine printing
Coated Groundwood: 30-60% chemical pulp, reminder mechanical pulp, groundwood or TMP
Recycled, deinked pulp- in varying amount
Low to moderate pigment filler
Coating- 25-35% total weight
Basis weight: 28-70 lb./ream ((25x38in)
Light weight coated 40 lb./ream- majority
Brightness: 67-71 #4
Hunter Gloss: 45-60
Opacity : 87-92 (basis weight, mechanical fiber content) (MF-superior opacifying properties)
Blade-coated-coating similar to latex house paint,
White kaolin clay from Georgia.
Latex binders hold kaolin particles
Coated groundwood- #4 or #5 increasing brightness
Coated groundwood grades:
ULWC Ultra Light Weight Coated 32 lb.
LWC- Light Weight Coated up to 40 lb.
MWC- Medium Weight Coated over 40 lb.
Heavy Weight Coated HWC
No groundwood, (freesheet, wood-free). Less than 10% mechanical pulp.
Higher brightness, gloss, grades 1-4 according to brightness
The highest quality (price) magazine papers ,
Heavier basis weight- 35-100 lb./ream (25x38in)
#1 and #2 76-82 , and over brightness, 60-110 lb./ream-annual reports, high-end commercial printing
#3 and #4 76-82 brightness, 45-80 lb./ream – catalogs, magazines, commercial printing
Coated freesheet- high basis weight, superior brightness, printed gloss
Mixture of hardwood , softwood kraft pulps, low to moderate filer pigments, some recycled fiber
Blade coated predominantly, roll coating, kaolin clay, calcium carbonate, latex resin.
In-between grades SC-LWC in brightness and gloss
New manufacturing technologies- new properties
FCO- Film coated offset- mechanical pulp, very thin film of starch with clay pigment. Film metered by blades onto a rubber roll, transferred onto paper.
Improved ink holdout
MFC- machine finished coated- coated with rolls or blades
Soft-nip calendering, all on paper machine.