ISO Brightness Tester for Paper

What is the ISO Brightness Tester for Paper?

An ISO brightness tester measures the diffuse blue reflectance factor at 457 nm under illuminant C using a defined geometry. It is the standard instrument for pulp and paper brightness specification testing and for mill process control.

Overview

The instrument consists of an integrating sphere or equivalent diffuse illumination system, a photodetector with a filter set that defines the effective 457 nm wavelength, and a pressure pad or aperture to hold the specimen flat. Measurement is normally made on a pad of sheets stacked to opacity behind the specimen, and the scale is set with a certified white standard and a black trap before each series. Because the reading is in the blue region, the instrument is directly sensitive to fluorescent whitening agents, and a UV cut-off filter or a controlled ultraviolet content in the source is used to define whether fluorescence is included. Some models also measure opacity by contrast ratio, which is convenient on the same specimen pad.

How does it work?

A brightness or reflectance instrument illuminates the specimen diffusely and measures the light reflected at right angles, using a defined geometry, illuminant and observer so that results are reproducible between laboratories. ISO brightness is the diffuse blue reflectance factor measured with an effective wavelength of 457 nm under illuminant C, and it is highly sensitive to fluorescent whitening agents. Whiteness is a single number derived from the full colour coordinates under illuminant D65 or C, while yellowness, tint and shade are obtained from the same measurement. Opacity is the ratio of reflectance of a stack-backed specimen to that of an infinite stack, and can be determined by diffuse reflectance or by the contrast ratio of luminous reflectance. Gloss is measured separately at a fixed angle of incidence, because it depends on surface finish rather than on bulk optical properties.

What are the key features?

• Effective wavelength of 457 nm under illuminant C
• Diffuse illumination with defined geometry
• Certified white standard and black trap
• UV cut-off filter or controlled UV content
• Pad clamp for the specified number of sheets
• Optional contrast ratio opacity function

What are the technical specifications?

A typical iso brightness tester for paper configuration offers effective wavelength of 457 nm under illuminant C, measurement geometry of Diffuse illumination, 0° viewing, measuring area of About 30 mm diameter, scale range of 0–100% reflectance, repeatability of ±0.1% reflectance and sheets in pad of Per the method, often 10 or more. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The ISO Brightness Tester for Paper is used in pulp and paper brightness specification testing, mill process control of bleaching and dye addition, fluorescent whitening agent effect checks and incoming inspection of recovered paper brightness. Across the wider Brightness Testing class, laboratories also deploy it for brightness verification of printing and writing papers, whiteness and shade control for coated papers and opacity checks for lightweight printing grades.

Which standards and certifications apply?

Relevant standards and methods include ISO 2470-1, ISO 2470-2, ISO 2471, ISO 11475, ISO 11476, ISO 5631-1, TAPPI T452, TAPPI T525 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Keep the instrument calibrated with certified standards traceable to a national laboratory, and check the white standard and black trap at the start of each measurement series. Stack at least the number of sheets the method requires behind the specimen to ensure an opaque backing, because too few sheets allow the backing plate to influence the reading. Condition specimens to the standard atmosphere and protect them from light and heat, since fluorescent whitening agents bleach and papers yellow on exposure. Clean the measuring aperture and the standard regularly, avoid touching the measurement area of the specimen with fingers, and record the geometry, illuminant and observer with every result.

How do I select the right ISO Brightness Tester for Paper?

Select a dedicated brightness tester when ISO brightness is the specification parameter and throughput is high, because it is simple, fast and directly aligned with the standard. Confirm the geometry, the ultraviolet condition and the pad clamp, and check whether opacity measurement on the same instrument is useful for your product range.

How does it compare with other Brightness Testing variants?

Match the instrument to the parameter named in the product standard. ISO brightness requires a 457 nm effective wavelength with the specified geometry, while D65 whiteness, colour and yellowness require a spectrophotometer covering the visible range under standard illuminants and observers. Opacity is measured with either a dedicated contrast ratio instrument or a spectrophotometer able to compute it from reflectance data. Gloss needs a dedicated meter with the correct incidence angle for the paper grade. Where the laboratory also verifies print appearance or matches shades, a benchtop spectrophotometer with both measurement geometries and a full set of illuminant and observer combinations is more useful than a single purpose meter, even though it costs more.