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Technical communication: paper knowledge Twenty Questions
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1.What are the raw material of modern paper?

A: Modern papermaking raw materials are plant fibers(wood、bamboo、grass etc.)、mineral fibers (asbestos、 glass、etc.)、other fibers (nylon, wire, etc.)and polymer materials from petroleum cracking. Currently the paper used for writing、printing、 packaging is still made mainly from plant fibers as main raw material.

  2.What are the types of paper-making plant fiber raw materials?

A: The plant fiber raw materials used in papermaking industry can be divided into two types :
   Wood fiber raw materials:  fiber obtained directly from the trees.
   Non-wood fiber raw materials: divided into the grass fibers raw material 、bast fibers material   and seed hair fiber material.

  3.  What is the composition and function of paper accessories ?

A: The accessories are the various additives added to the meet the different usage of the paper properties . Accessories include the filler、rubber、pigment and other chemical additives.

    The filler can improve the smoothness of paper and opacity; rubber can improve the water resistance of paper ; pigment can increase the paper whiteness; colorant can give color to paper; other chemical additives can change the nature of the paper to provide paper for some special purpose.

 4. What is the role of rubber?

A: The paper made of plant fiber , because there are a large number of pores between the fiber itself and between the fiber,and cellulose, hemicellulose contain a large number of hydrophilic hydroxyl , they are able to absorb water or other liquids. In order to make the paper not infiltrated by water or other liquids ,we need to add the anti-liquid colloidal material or film-forming substances in the paper,that is the rubber material, giving the paper the performance of resistance to liquid penetration and diffusion.  in the paper industry adding rubber process is called sizing.

  5. What are the methods of Sizing ?

A: According to the different effects,the sizing methods are divided into two kinds of internal sizing and surface sizing. Internal sizing is to add rubber into the pulp to make  and cardboard. The common  rubber include rosin material and synthetic material. Surface sizing is to coat with a thin layer of plastic material on the paper surface to make the paper , The Common rubber includes starch、 gelatin、 and synthetic rubber materials. Surface sizing is mainly used for offset paper, writing paper and hydrophobic requirements of wrapping paper and cardboard.

  6.What is the influence of surface sizing on the performance of the printing paper?

A: ① to increase the ability of water-resistant and surface strength ,and can reduce the phenomenon of hair loss of the offset printing paper ; ② to improve printability, if the surface rubber is too less, printing paper will absorb too much link material in the ink, resulting in imprinted dull. On the contrary, if the surface rubber is too much, will slow down the drying rate of ink, resulting in soiled and light stain; ③ increase the paper erasability, surface sizing can reduce the penetration of ink, then easy to wipe off the ink, increase paper anti-friction ability; ④ increase the strength of the paper, such as bursting strength, folding endurance and tensile strength; ⑤ reduce the sides difference of paper and deformation.

  7.What is the role of filler?

A: Filler is to to make the paper get specific performance, such as whiteness, opacity, smoothness, and fillers make the paper internal voids become smaller and thinner, thereby increasing the paper's ink absorbent, and makes the ink change evenly. Normally we add filler of insoluble or slightly soluble material, containing about 10% -25% in the printing paper, and may vary greatly in different paper.

 8.What characteristics  should the printing paper have ?

A: The printing paper filler should have high whiteness, high refractive index, small particles, low water-soluble, low density and good chemical stability, in addition better resource-rich and with low prices.

 9.What are the common filler used in printing paper?

A: The most commonly used inorganic filler are talc、clay、 titanium dioxide and calcium carbonate.  titanium dioxide is expensive and good quality filler; the organic synthesis is polymer material.

10. What is the influence to printing paper performance by filler?

A: The printing paper fillers can improve the printability of the paper, such as increased whiteness of the paper, smoothness, opacity, stiffness. To improve the paper ink affinity, flexibility and stability, thus contributing to the improvement of the quality of presswork. Of course,if the filler amount is too high ,it will bring some adverse effects, mainly of the reduction of paper strength and sizing effect, is prone to lose powder and hair, the filler particles delivered to the printing plates and rubber cloth will form paste version  phenomenon; the filler will wear the plate for its friction, but calcium carbonate (PCC) can make the reduction of wearing plates to a minimum (Jindong currently used).

11 What is the degree of the paper opacity ?

A: The degree of paper opacity is the opaque nature of the paper .The opacity depends on the paper light scattering capacity and the quantity of the internal light scattering interface (ie, the number of independent internal particles) and the size of the scattering interface refractive index difference. Light scattering interface is more, the greater the refractive index difference between the scattering interface is, the larger the paper light is scattering, the higher the opacity is.

12. How does the filler affect the opacity of the paper?

A: The paper without filler are composed with fiber and air. The air is in the pores between the fibers, the refractive index of the fiber and the air is different, when the beam shines to the paper surface, some of the light scatters in interface between the fiber and the air, to give the paper a certain (lower) opacity ,reflected in the printing, Main show is extremely easy to print through. After adding filler whose refractive index is greater than the cellulose in the paper, the scattering interface gets more, there are three different types of interfaces of fiber and air,the filler and the fiber, the filler and the airs ,among the three fillers the refractive index difference between the filler and the air is the biggest, Therefore the light between the filler and the air interface scatters the biggest, leading to increased opacity.

13. How does the filler improve the paper surface smoothness?

A: The network formed by intertwined fibers always has a large number of pores and  surface uneven points,  the small particles filler can improve the flexibility and plasticity, capable of better pressing process, which can improve the smoothness after the paper polishing .

14. How about the influence to the paper strength by the filler?

A: The combination of the fiber is the base of the strength of paper, fillers reduce the combination of the fiber, so a lot of filler makes the paper strength decrease significantly. The degree of tensile strength、folding and bursting decline larger,the degree of the tear declines less, there is restriction for the amount of filler using .

15. How does the filler affect the bulk of the paper?

A: The density of paper fiber is about 1g/cm3,the density of filler is mostly about 2.5-3.0g/cm3. So the fillers will reduce the bulk of paper. But if small amount of filler added, the bulk increases with the amount of adding, especially short fiber paper.

16 How does the filler affect paper stiffness?

A: The paper stiffness is a function of paper thickness and elastic modulus. We should consider the combined affect of the bulk and tensile strength caused by the the filler.  When the filler is stiffness plus filler loadings, hours, fillers basically does not affect the paper, plus filler loadings increase, the stiffness increased with the filler volume significantly reduced.

17 What is the role of pigment in the paper?

A: Even after bleaching the pulp fiber is slightly yellow or gray, this is because the fiber lignin contained in the pulp tends to absorb purple and blue light wavelengths in the 400-500nm , the more the fiber lignin in the pulp ,the deeper its color will be . Therefore, to make the paper has a higher whiteness, we often add blue-purple or red-blue dye in the bleached pulp. Production of colored paper must also be dyed.

18.What's the composition of the pigment?

A: The pigment is used for paper dyeing and color . Most pigments are inorganic and do not dissolve in water; dyes divides into natural dyes and synthetic dyes, synthetic dyes have been completely replaced natural dyes, most dye can dissolve in water,or soluble in water after chemical treatment.

19. What are the other paper accessories in the chemical additives and their effects?

A: In order to meet the needs of the paper for some special use, we often add various types of non-fibrous additives in the pulp or paper. According to their use, they can be divided into the following categories:
① wet strength agent. The wet strength agent is added to increase the wet strength of paper sheets and additives, such as urea-formaldehyde resin and phenolic resin.
② dry strength agents. Such as cationic starch, and polyacrylamide.
③ retention aid. Additives added to reduce the loss of fillers and fine fibers in the papermaking process, such as polyacrylamide, polyethylene oxide and polyethylene imine and so on.
④ defoamer. Used to eliminate foam in the papermaking process. Such as silicone oil, turpentine, tridecanol, phosphoric acid, butyl, amyl alcohol, octanol, and so on.
⑤ anti-water agent. Mainly used in the paper with higher requirements against water . Such as paraffin wax, metal soaps, glyoxal, melamine A wake resin and acrylic acid dimethyl amine acetate.

20. How to classify paper simply?

A: The paper can usually be divided into cultural paper, industrial paper, household paper and special paper according to use, cultural paper can be simply divided into non-coated paper and coated paper. Without the coating processing the paper is called the non-coated paper such as newsprint, offset paper, electrostatic copy paper and writing paper; after coating processing the paper is called coated paper, such as coated paper, calendars, paper, Asia glossy paper, glass and cardboard.