Filler effect for paper properties

1. Filler Effect for Paper
properties
By Audrey Zahra
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Relatively components used in paper and board

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4. Mineral Characteristics
• Hardness (1-7 Moh’s)
• Refractive index (relatively about 1.5-1.65)
• Solubilty (2-4 grams per liter) lower solubility is better
• Wettability (500-700 mNm-1)
• Crytal structure
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5. Filler Properties Controlled by the Supplier
Brightness
Determination of filler particle shape
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6. Particle size
In industrial practice it is convenient to express particle size as an “equivalent spherical diameter,” making it
possible to deal with a variety of particle shapes. In principle, the concept of “equivalent spherical diameter” can
be applied to data based on sedimentation, surface area determination, or projected area in microscopic images
Filler content in paper
X-ray diffraction for type and content of filler
Abrasion
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7. NATURAL, MINED FILLER PRODUCTS 7

8. SYNTHETIC, PRECIPITATED FILLER PRODUCTS
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9. Why Use Fillers?
Fillers are applied to the paper mainly
• to improve the optical properties, such as brightness and opacity
• to improve the smoothness of the sheet surface (i. e. decreased roughness, especially after calendering)
• to improve the sheet formation by filling the voids between the fiber matrix
• to enhance printability in the various printing processes due to a more uniform paper surface, higher
opacity and better ink receptivity. The latter resulting in reduced printing ink penetration, wicking and ink
strike-through to the opposite side of the sheet
• to improve the dimensional stability of the paper as most fillers remain inert
when wetted, unlike the natural fibers usually used in papermaking.
• to improve the permanence of the paper (alkaline papermaking, calciumcarbonate (CaCO3) filler)
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11. Problems associated with filler use
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12. HOW FILLER AFFECTS PAPER PROPERTIES
Optical and Strength Properties
According to Page’s theory (1969), paper’s tensile strength depends on both the strengths
of the fibers and also the strength of the bonds between the fibers. In the case of a typical
sheet of paper for printing or packaging, the inter-fiber bonds are expected to be the main
point of failure when strips of paper are pulled past their point of breakage. Page proposed
that the strength of inter-fiber bonds depended on a variety of factors. Two of the most
critical factors, related to bonding, are the relative bonded area between fibers and the
adhesive strength per unit of bonded area. In principle, fillers can be expected to affect
each of these two factors.
Bøhmer, in his review article (1981), states that addition of 10 percent filler by mass
is expected to result in 20 to 25% loss in tensile or burst strength of paper. Experience has
shown, however, that there can be wide variations from this rule of thumb. Some paper
properties, such as folding endurance, appear especially vulnerable to the effects of filler
addition. Also, the degree of strength loss depends on many variables, including the
properties of the filler.
Filler Content vs. Paper Strength
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13. Light Scattering vs. Bonding in Filled Paper 13

14. Achieving a “Peppered” Filler Distribution to Enhance Opacity 14

15. Dimensional Stability
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16. High-Filler Strategies Focusing on the Fiber
Lumen loading
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17. Amount of filler (loading)
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18. Typical filler loading levels in different European paper grades
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19. Fig. Brightness (Tappi R-457) of various paper fillers and highly bleached mechanical and chemical pulp (source:OMYA).
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20. Characteristic chemical and physical data of regular fillers and specialty pigments. 20

21. Particle Morphology
The particle morphology has an impact also on the packing of the filler particles in flocculates usually formed during
the papermaking process. The results are morphology related differences in sheet drainage, drying behavior, and in
paper properties such as bulk, porosity, ink receptivity, strength, dusting, etc. The sheet surface roughness and
paper gloss after calendering, as well as the sheet compressibility (important in rotogravure printing) are also
influenced by the morphology of the filler or specialty pigment applied.
Figures 2.12 and 2.13 show some typical particle size distribution curves (measured by the sedigraph method) of GCC and PCC
based fillers.
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22. Particle Size and Particle Size Distribution
Figure 2.14 indicates the size relation between the GCC filler particles and the fibers in the sheet. the filler particles are much
finer than the fiber and, in particular, much smaller than the voids between the fibers.
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23. The pigments can be classified as:
• Main pigments:
– ground calcium carbonates (GCC)
– kaolin clays
– precipitated calcium carbonates (PCC) (recently
switching from a special pigment to a main
pigment)
• Special pigments:
– talc
– gypsum (calcium sulfate)
– plastic pigments (e. g. polystyrene)
– satin white (calcium sulfoaluminate)
– barium sulfate
• Additional pigments:
– calcined clays (kaolins)
– titanium dioxides
– alumina trihydrates
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24. overview and comparison of the most important physical and optical properties of coating pigments 24

25. The following simplifies how different quality parameters of coated paper can be
improved by changing specific pigment properties:
• better gloss by increase in platiness and/or decrease in particle size
• higher opacity by increase in refractive index and/or decrease in particle size
• higher brightness by decrease in light absorption
• higher porosity and ink absorption by decrease in packing (less compact pigment
layer), e.g. through mixing of different particle shapes
• higher bulk and better coverage by decrease in packing (decrease in density)
through mixing of different particle shapes.
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26. Wire Section
The main objectives of the wire section are:
1. Extensive separation of fibers from water (drainage)
2. Well-ordered deposition of the fibers on the wire (oriented shear)
3. Prevention of too much fiber flocculation (turbulence).
In paper web forming filtration prevails. The water extracted from the suspension contains fines,
fillers and fibers and is called white water.
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29. Drainage is opposed by the resistance to filtration, which depends on the degree of beating, chemical treatment, and
type of stock, as well as on the amount of fines and fillers present. The dry content after the wire section in most cases
is about 18–20 %. The water removed in the filtration process (white water) carries away fibers, fines and fillers.
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31. Drainage is opposed by the resistance to filtration, which depends on the degree of
beating, chemical treatment, and type of stock, as well as on the amount of fines and
fillers present. The dry content after the wire section in most cases is about 18–20 %. The
water removed in the filtration process (white water) carries away fibers, fines and fillers.
The percentage of solids of the suspension retained on the wire, also called retention, can
be increased by the addition of retention aids. The white water is reused to dilute the
thick stock in the stock approach flow system. Figure 6.42 shows the filler distribution in
the z-direction (across the web thickness) for dewatering the stock to only one side and
symmetrically to both sides.
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32. Coating of Paper and Board
The main purpose of coating is to improve the surface quality of paper or board. The quality
improvement can be aimed at optical properties such as brightness, gloss or opacity, at tactile
properties such as smoothness, but, most importantly, at printability and print image quality.
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33. In the center of the sheet, the fibers can be seen. The lighter and more densely packed structure on
the outside of the paper sheet is the pigments of the coat layers. The caliper of the coat layer varies
according to the changing thickness of the base sheet. The surface is smooth so, by coating, paper and
board can be upgraded to a higher quality level with added value.
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35. Coating Colors 35

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38. Most pigments are significantly cheaper than chemical pulps so increasing both
the proportion of coated paper in general and the coating layer(s) compared to
fibers (Fig. 3.12) is an important economic factor.
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45. 감사합니다
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46. Reference
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Holik Bert. 2006. Handbook of Paper and Board. WILEY-VCH Verlag GmbH & Co.KGaA. Weinheim, Germany
Hubbe, Martin A. and Gill, Robert A. (2016). “Mineral fillers for paper,” BioResources 11(1), 2886-2963.
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