Paper reflective brightness

The object of this study in 1971 was to assess the potential permanence characteristics of selected commercially available copy papers. Physical tests included folding endurance at 500-g tension (10) and reflective brightness (9). Sixty replicate measurements of folding endurance and 10 replicate measurements of reflective brightness were made on each paper in the fresh state and after each withdrawal time from each oven. Only three oven temperatures (60°, 70°, and 80°C) were used in this rate study with humidities adjusted as in Table II for moisture control. Comparison tests were also made using the TAPPI method (16), and the values obtained at 96 hr in the 80°C oven were used as a single-temperature, single-withdrawal moist oven comparison. 

Initial brightness values for the papers in Study No. Ill are listed in Table XV also listed are the post color numbers, activation energy values, and estimated rates of change at room temperature. In this instance, loss of reflective brightness for the two single-withdrawal pro-... 

Table XVI. Reflective Brightness Ranking Order (Papers in Study No. Ill)...

Folding endurance under tension (10) is a favorite physical property for research on paper permanence and is the basis for the TAPPI method (16). Application of the mechanism involved in this test procedure, however, is unknown in practical uses for paper. Comparisons among product choices and estimates of their useful life should be based upon tests that assess physical properties of practical interest. Retention of reflective brightness, tear strength, tensile energy absorption, and... 

Optical Properties. Brightness, or visual whiteness of paper, can be defined as the degree to which light is reflected uniformly over the visible spectmm. Since pulp and typical impurities tend to be yellowish, blue dye is sometimes added in addition to appropriate fillers. The percentage reflectance is usually measured in the blue end of the spectmm at or near 457 nm (14). 

Brightness Meter. A special type of reflection meter for evaluating the brightness of paper and similar products by measuring the diffuse... 

The distinction is fairly clear so far as emitted light and reflected light are concerned. To an observer, a lamp may have about the same color as that of the image of the lamp seen in some mirror. If the mirror is replaced by a piece of white paper, the viewer will see only the paper, but it will appear to be of about the same color as was the light, although less bright and modified by the whiteness of the paper. If the paper is colored, its apparent color will be a combination of the colors of the paper and the source of illumination. 

Transparent materials interact with light only by absorption. This interaction is formulated quantitatively in the Bouguer-Lambert and Beer s Laws (c.f. i). In paper, however, surface reflection is the dominating type of interaction. This results in very desirable properties like high brightness and opacity, but complicates the interpretation of optical tests with regard to absorption data. The Kubelka-Munk theory attempts to separate the two types of... 

Here, n and n2 are the refractive indices of the interfacing materials. The surface reflectivity R, Equation 5, used by Robinson is the Fresnel reflectivity for normal light incidence (c.f. 4). Robinson s interpretation explains the well-known linear relationship between the specific surface area of a paper, as measured by gas adsorption, and its scattering coefficient (15. 28, 32). It also rationalizes the observed decrease in scattering and brightness of wet compared to dry pulp (33, 34). 

Determination of Physical Properties of Paper. BRIGHTNESS. The brightness was measured with a Photovolt model 670 reflectance meter. Measurements were made at 10 different places on both sides of the sheet, and the readings were averaged. 

Brightness is a measure of overall reflectivity of a paper to white light, or whiteness. It is based on a scale of 100 for pure magnesium oxide and 8 for carbon black, when the reflectance of a beam of light, of wavelength 457 nm, is compared at angle of 45° from the axis of the incident light. 

ASTM D 985-93. Brightness of pulp, paper, and paper board (directional reflectance at 457 nm). 

Planes of atoms will only give bright images on sensiti e paper when the reflected waves do not diminish their intensity by interference, but are in... 

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