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What is Paper Whiteness?

Whiteness can be seen as the flatness of the radiation curve as compared to the light reflectance of the ideal white standard. A paper that radiates equal amount of light in 360-780nm wavelengths is defined as white paper. Whiteness is therefore directly related to absence of color. ISO whiteness can reflect the amount of OBA. Blue shade gives a higher whiteness value than yellow shade. Therefore this method allows the calculation of the fluorescent components present on the papers. There are two methods for whiteness measurement in ISO: they are ISO 11475 and ISO 11476. The greater the whiteness of the paper, the greater the contrast and the readability of the ink. Whiteness indices are single numbers which are based on the total visible spectrum because they derive from the CIE values. This test is done according to ASTM E313 by the simple formula: Whiteness Index (WI) = 4B-3G B and G refer to the blue and green reflectance values.

What is Brightness?

Within the paper industry, the term brightness refers to the brightness value clearly defined in ISO 2470. This ISO brightness is defined as the total amount of light that a paper reflects at 457nm. ISO brightness is also called the R457 reflectance factor or the blue reflectance factor. ISO brightness is excellent for characterizing the effect of bleaching of pulp. Also, it permits the yellowing of paper to be easily gauged.

What is Gloss?

ISO 8254-1:1999 is carried out usually on supercalendered art paper or board. It is determined by the intensity of an angled beam of light (typically 75) which is reflected from the sheet of paper or board. The result is expressed as %. The usual result for a glossy board should be 60% or more. For paper with very high gloss, both the illuminating angle and measuring angle are placed at 20 either side of the paper measured. For the majority of papers, there is a greater degree of diffuse reflectance, and angles of 60 or 75 are considered to be appropriate. Other relevant standards for 20, 60, and 75 are ISO 2813 and TAPPI 480.

What is Smoothness?

The smoothness level is a measure of the surface characteristics of paper. The flatter or more even the surface, the higher the level of smoothness. High smoothness stock can provide a fully-shaped ink dot resulting in a sharper and higher quality image. The commonly used testing will be Bendtsen and Gurley. Each is based on different observations. Bendtsen (ISO 8791-2:1990) is based on the extent to which the surface of the paper deviates from a plane. The measuring head will allow no air to escape when placed on a smooth plane hard surface; however, air will escape when a piece of rough paper is measured. The amount of air that escapes is measured in milliliters per minutes (ml/min). The higher the smoothness, the lower the reading. The other method, using the Gurley Smoothness Tester, leaks air at a specified pressure between a smooth glass surface and a paper sample. The time (in second) for a fixed volume of air to seep between these surfaces measures the smoothness of the paper. The smoother the paper, the more time is required.

What is Porosity?

This is a measure of the extent to which a paper surface allows the penetration of a gas or liquid through its surface. Surface sizing, costing, calendaring and supercalendering all work to seal or compress surface fibers and reduce the paper’s porosity. Different printing methods require papers to have different degrees of porosity. Porosity will affect how thoroughly and how quickly inks are absorbed into the paper. Paper too high in porosity will have an increased risk of show-through. If a paper has too-low porosity, it will cause ink holdout. Also, low porosity will cause the paper to curl and cause great problems with dimensional stability as a result of changing moisture content. Porosity can be measured by the Gurley methods (ISO 5636-5:2003) in which the length of time is measured for a quantity of air to pass through a paper sample. The lower the reading, the higher the porosity.

What is Surface Strength?

It is important to ensure that the paper surface should have sufficient strength to withstand the splitting force created during the separation of the blanket and paper. Dennison wax pick (TAPPI T459 om-93) determines the highest value of wax that can be applied to the sheet and pulled away without rupturing the surface. Dennison wax is numbered from 1 (least tack) to 23 (greatest tack). Offset printing paper should have a Dennison wax number greater than 11 in order to withstand the splitting force. IGT is a Dutch manufacturer of testing instrument. ISO 3782-3, which determines the printing velocity at which surface picking occurs, uses a complicated procedure involving low viscosity oil and a special printing unit applied at an ICT testing instrument which works at accelerating speed. The normal requirement is that 4-color offset printing paper has no picking at a minimum reading of 135 cm/s.

What is Opacity?

The opacity of a paper determines the extent to which printing on a particular side of paper will be visible from the reverse side. Tinting and dyeing of paper will increase the opacity. Increasing a paper’s whiteness tend to decrease its opacity. Opacity is the ratio of the reflectance of a single sheet of paper with a black backing, to the reflectance of a wad if the same paper thick enough to be completely opaque. The result is expressed as a percentage: 91-93% is typical. Opacity can be measured by the contrast ratio method or the diffuse opacity method. The greater the transmittance, the lower the opacity and vice versa. The 0-100% contrast ratio opacity scale is used for paper measurement.

What is Moisture Content?

All paper naturally contains a certain amount of moisture, typically about 3-7% in paper intended for printing and writing, and as much as 10% in newsprint. Paper that is too dry is hard and brittle and will reduce the quality of the printed impression. If the paper is too moist, it will blister during heatset drying. The moisture content is determined by taking a representative sample and placing it in a sealed container to be weighed. The sample is then again placed in an oven for a minimum of four hours at 105 degree Celsius, then place in the same sealed container and re-weighed. The difference in weight (i.e. the moisture content) is expressed as a percentage of the original weight: loss in weight x 100/ weight of original sample.

What is pH value?

The pH value is the degree of acidity or alkalinity of a substance. Most European papers are now neutral or alkaline. The materials used in the paper’s coating will also affect pH. For example, calcium carbonate, which produces alkalinity as the coating material, has been known to have deleterious effects when particles of coating contaminate a press’s dampening system. Low pH can interfere with the proper drying of quickset and drying-oil inks while high-pH paper can interfere with the acidic dampening system of the press. Acid-free paper: Type of paper which has no acidity and no residual acid-producing chemicals. Acid-free papers may also be slightly alkaline to resist the harmful effects of an acidic environment and provide greater longevity. Bleached board is produced with acid pH of 4-5. Alkaline paper: paper using calcium carbonate as the filler and a synthetic material, compatible with the alkaline process, as a sizing agent. This process increases the longevity, overall brightness, opacity, and printing characteristics of the paper without added cost. In addition, the life expectancy for alkaline papers is about 200 years compared to 50 years for acid papers.

Reclaimed Water
Waste water which, after being treated to a certain standard, can be re-used for other purposes.
Points of Caution on Material Purchasing
Regulations to comply with: If the final products are for export, then it is necessary to be aware of regulations that must be complied with, e.g. heavy metal (ASTM D963, EN71), RoHS, etc. These regulations are getting more and more stringent, and we must continue to pay close attention to regulatory issues. List of materials banned in the packaging for the electronic industry includes: lead and lead compounds, cadmium and cadmium compounds, mercury and mercury compounds, hexavalent chromium (chromium VI) and hexavalent chromium compounds, PBB, PBBEs and PBBOs, PCBs, PCTs, asbestos and asbestos materials, brominated dioxins / furans, chlorinated dioxins / furans.
Post-Consumer Waste
Utilise used consumer items collected for recycling from homes and businesses with the intention of incorporating these materials into new products.
Pre-Consumer Waste
Materials generated during manufacturing, such as scraps (including damaged or obsolete products, overruns and trimmings) that can be incorporated into the manufacture of new products.
Chemical Oxygen Demand (COD)
Under certain conditions, the amount of strong oxidants used to treat water samples.
Greenhouse Gas(GHG)
Gas that can absorb visible light and give off infrared radiation, including CO2, CH4, N2O, HFC3 and PFC3, etc.
Climate Change
Change in climate which is attributed directly or indirectly to human activities to alter composition of the global atmosphere, is in addition to natural climate variability.
Elemental Chlorine Free(ECF)
Elemental Chlorine Free (also known as chlorine dioxide bleaching) is a pollution prevention technology. Its bleaching agent eliminates persistent and toxic substances in mill waste-water. Chlorine dioxide is also an essential component for producing the highest quality pulp and paper products.
White Water
Water screened by the paper machines during the papermaking process with small/short fibers etc. which give it a white appearance.
Black Liquor
Liquid produced from the pulp washing and cooking using kraft and soda. It is black in color and contains inorganic substances of cooking materials dissolved from lignin and semi-cellulose of the raw material/plant fiber and biodegraded substance and organic acid of cellulose.