بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم (وَقُلِ اعْمَلُواْ فَسَيَرَى اللّهُ عَمَلَكُمْوَرَسُولُهُ وَالْمُؤْمِنُونَ ) التوبة (105) صدق الله العظيم

2. Coating of Paper and Paperboard By Dr. Essam Saber Abd. El -Sayed Cellulose and Paper Department Organic Chemical Industrial Research Division National Research Center Oct, 2006

3. Coating of paper and paperboard »»Definition of Coating (Coating Process) »» Coated Paper and Board Grades »» Requirements of Coated Paper »» Components of Coating Colors »» Pigments »» Dispersing Agents »» Binders or Adhesives »» Other Additives »» Coating Color Formulations »» Coating Color Preparation »» Types of Coating Machines

4. Paper defined by a felted sheet formed on a fine screen from a water suspension of fibers and non-fibers materials.

5. Paper is made by: • Pulping and bleaching, to separate and clean the fibers • Beating and refining the fibers • Forming a web of fibers on a thin screen • Drying to remove the remaining moisture • Finishing, to provide a suitable surface • Converting processes, to produce different paper products.

6. Wet Converting »Coating » Laminating » Corrugating » Impregnating » Embossing » Wet creping Dry Converting » Bag making » Box making » Envelope making » Cutting & Folding » Hot pressing » roll winding Paper Converting

7. Coating of Paper and Board »Coatingis a process by which a mixture of water, white pigments, binder, and various additives are applied to one or both sides of paper sheet. »The main objectivesof coating process for paper and paperboard are to improve their appearance, and printability. »Coating impartsmoothness, gloss, brightness, and opacity to the base sheets for improved appearance, and provide them with enhanced printability. Coating Processes On-Machine Off-Machine

8. Factors Affecting on Coated Sheet Properties 1-The base sheets (fiber types, sheet formation, internal sizing, and basis weight) 2- Coating materials(pigment types, binder types, water retention aids, lubricant, and defoamers) 3- Coating formulations(ratios of coating components, solids, and pH’s) 4- Coating process(coating application types and speed) 5- Coating weights 6- Drying conditions(dryer types, drying temperature, drying time, and final moisture level.) etc.

9. Coated Paper and Board grades Classification of coated grads has not yet been standardized. However, certain terms are recognized throughout Europe as: • Art paper • Chromo-papers • Machine-coated papers • Light-weight coated (LWC) papers • Cast-coated papers • Folding boxboard and chromo-board

10. Art paper Chromo-paper This term refers to: • wood-free or slightly wood containing paper • That is coated on both sides • The weight of the coating exceeds 20g/m2 per side • Art paper is used for high quality printed product Chromo paper is coated only on one side • the weight and quality of the coating correspond to that of art paper. • Much of this paper is employed for packaging purposes

11. Requirements of Coated papers Coating must have: 1- adequate stiffness 2- good brightness 3- low yellowing tendency 4- good aging resistance 5- good compressibility 6- high degree of smoothness 7- adequate receptivity for the ink solvent 8- low odor, flexibility, glueability, and crease resistance 9- alkali resistance (labels) 10- washability (wallpaper) 11- solvent resistance

12. Properties and components of coating colors Coating colors are fairly complicated multi-components systems, which all water-based components. The main components of a coating color are • Pigment coating, • binders, in addition to, a variety of auxiliary agents such as: • Dispersing agents for the pigments • Additives for reducing wet abrasion • Products for control of viscosity and water retention • Foam control agents • Shading dyes • Optical brighteners • Lubricants to improve paper calendaring

13. Coating colors are classified according to their solids content:

14. Factors affected in the coating process • Solids contentgreatly influences the runability of the coating color in the machine • Viscosityof the coating color and its flow behavior at varying shear stress in coating machine • pHof the coating color which processed at range 7.5-11.5 • The water retention capacityof the coating color i.e., the ability of the coating color to retain water in spite of the sucking action of the coating base paper.

15. Pigments • The pigment is a highly important component of coated paper. Pigments form the actual "body" of paper coatings. They usually account for at least 80% of the total dry coating weight. Thus, pigments largely determine the quality and cost of the coating. • The principle function of the pigment is to fill in the irregularities of the paper surface, to produce an even and uniformly absorbent surface for printing and to improve the appearance of the coated sheet.

16. Be continued A good pigment should posses all or most of the following properties: • Good dispersibility in water • Small particle size distribution • High opacifying power • High brightness • Low water absorption • Chemical inertness • Compatibility with other coating component • low adhesive demand

17. Be continued Types of Pigments The most important types of pigments are • Clay, • Ground and precipitated calcium carbonate, • Calcium sulfoaluminate (satin white), • Titanium dioxide, • Talc, • Barium sulfate, • Gypsum (calcium sulfate ), • Calcined and delaminated clays and synthetic pigments based on aluminum silicateare employed for special applications. • Zinc Pigments (Zinc oxide, zinc sulfide and zinc composite), • Calcium sulfide, • Calcium sulfate

18. Specialty types of pigment coating * Luminescent Pigments • Fluorescent pigment[Sulfides of Zn, Cd, Strantium or calcium] • Phosphorescent pigment[ Combination of Zn & Cd sulfides, Ca & Strontium sulfides] * Colored Pigments • Zn, Cd, iron oxides for yellow color • Iron oxides for brown color • Cobalt greens for green color • Sienna, red lead for red color • Carbon for black color

19. Dispersing Agents • The first stage in the production of coating colors is the conversion of the coating pigments, into a flowable and pumpable aqueous slurry. This dispersion process consists of two steps: • The mechanical dispersion of the coarse pigment agglomerates in an aqueous medium, and • The chemical stabilization of the slurry towards reagglomeration. • Suitable dispersing agents areordinary alkali as NaOH, Na2CO3, Sodium silicate, trisodium phosphate, and polyanions. e.g.. salts of polyphosphoric acids (pyrophosphates, hexametaphosphates) or poly(acrylic acids).

20. Binders *The function of the binder or adhesive is to bind the pigment particles to each other and to fix the coat to the base paper. *In spite of their low proportion by weight in the coating color (generally 5 -25% based on the pigment), binders have a large influence on the coating and processing properties of the coating color.

21. Be continued Properties necessary in coating adhesives An adhesive, to be satisfactory, should have: ›A high pigment bonding adhesive • Good color • The correct viscosity for the solid content • Strong filming properties to prevent excessive penetration of coating • Compatibility with the pigment • Enough plasticity

22. Be continued Binders Natural binders Synthetic binders The most widely employed binders of this Types are: Animal glue, gum arabic, Starch & Its Derivatives (oxidized, etherified, esterfied and hydrolyzed starches) Cellulose ethers (CMC, hydroxyethyl- Cellulose) Soybean protein, casein, and alginate. Polymer dispersion give the coat a higher Water resistance, better flexibility, higher Gloss and better printability. For example: copolymers of several Monomers, e.g., Styrene-butadiene Acrylic & ester Vinyl acetate and acrylonitrile Acrylamide, acrylic acid, maleic acid, and Methacrylamine used as modifier agents.

23. Other Additives • Waterproofing agents, such as water-insoluble polymer dispersions to make the coating be resistance to water. • Hardening agents to harden the coating. Three main classes of products are employed as hardening agents: melamine-formaldehyde resins, urea-formaldehyde resins and bifunctional aldehydes such as glyoxal, which is added only to coatings containing starch. • products based on ammonium zirconium carbonate or epoxides are being used as cross-linking agents in some cases. • Anti-Foam agent to prevent the formation of foam • Defomer agent to destroy or kill the foam bubbles. • Defoamersinclude mixtures of higher alcohols, salts of fatty acids, and water-emulsible phosphate esters.

24. Other additives • Titanium dioxide, and blue-violet dyes(shading dyes) are often used to increase the brightness, • Optical brighteners such as diaminostilbenedisulfonic acid are added to increase the brightness and the luminosityof coating. • polyvinyl alcohol, carboxymethyl cellulose, casein, starch, and some synthetic cobindersused as stabilizing agent for attached of optical brighteners. • calcium or ammonium stearateare used in many illustration paper as lubricantsto reduce dusting on the calender and produce a higher paper gloss.

27. Coating machines • Brushes coater • Distributor coater • Air knife • Bar Coater • Size Press • Film Press • Bill Blade • Inverter Blade • Roller Blade • Rod Blade

28. Coating color Formulations

29. Dr. Essam saber Thank You