The Guardian Scanning Frame Profile System monitors and controls moisture and coating profiles
The GSFPS is the most economical, simple and reliable web measurement solution on the market; comprising a scanning frame, control box, non-contact Near Infrared Sensor and Profile display hardware and software. The software displays current and historical web profiles, Zone average profiles and MD trend plots. Analogue outputs, alerts and alarms are easily configured via the software.
The GSFPS is designed for first time Users, customers who are searching for a cost effective scanning solution and those buying multiple scanners. Installation and set-up of the scanning frame and sensor parameters using two independent recipes within the intuitive S/W package couldn’t be easier. This approach reduces the total number of recipes, saving time and effort. Pricing is attractive as the GSFPS is sold as a standard package and unit cost decreases with additional Scanners, up to four Scanning frames can be controlled and monitored through the S/W. Both the sensor and scanning frame hardware and software have evolved over the last 15 years resulting in a superb reliable scanning system with a rapid ROI.
The Near Infrared measurement principle is based on the fact that different heterogeneous molecular bonds; O-H, C-H and N-H absorb NIR energy over different specific wavelength regions. Absorbance of energy is directly proportional to the concentration of the molecules within the sample matrix. Narrow bandpass filters are selected according to the measurement required and fitted within a filter wheel inside the sensor. When powered, the filter-wheel spins, generating pulses of NIR energy which illuminate the product. Back scattered energy is collected and focused onto a detector which converts the energy to electrical signals. These are processed to provide a proportional output which once calibrated, delivers a direct measurement in % or other engineering units.
The GFSFPS outputs moisture %, coat weight or thickness. Accuracy of on-line measurement is dictated by the accuracy of the primary reference technique used in calibration, also by the composition of the coating relative to the substrate.
Knowledge of the moisture content and distribution within paper and board substrate is critical to the efficient operation of the converting process and quality of the final product; as little as 0.3% variation in relative humidity during storage of the paper stock will affect flatness and cause wrinkling during printing and folding operations, similarly too dry a paper results in static build-up and problems with feed. Moisture content is not only important in ensuring the smooth running of the Converting line, it is also critical in a lamination process. If moisture levels are too high, steam will expand between the foil and printed varnished finish causing the paper to separate from the molten PE laminate. Moisture is sometimes measured following the final drying stage to ensure product quality and storage properties. The substrate is typically, but not exclusively paper.
Coat-weight and thickness
Various coatings can be applied in the converting process; these range from extruded, 100% solids, organic solvent to aqueous coatings. Aqueous coatings on paper ,board, textiles and plastic films will deliver more accurate results when measured immediately following application as there’s no interference from the substrate and signal response from water relative to organic material is greater per molecule , additionally the % SR (Solids ratio) is typically below 50% so the most abundant material is measured. Wet end measurements require %SR to be maintained at a constant level or known so that compensation can be factored in. Organic coat-weight can be measured at the dry end, this may be necessary owing to space constraints at the wet end, poor solids ratio control, or the fact that the coating is 100% solids or extruded. Sometimes it’s beneficial to install a second static sensor to measure organic content of the substrate prior to coating, especially if a low coat weight is applied, i.e. ≤ 10 gsm. In instances where the solid material is non-organic there is no option to measure at the dry end, e.g. clay coating on paper.
Aqueous and organic coatings are also applied to metallised film, steel and aluminium foil. NIR, once again is ideally suited to making these coat-weight measurements as there’s no interference from the substrate matrix. Such applications might include: flexible packaging, aseptic packaging, can stock and conversion coatings on aluminium and steel.
A scanning frame isn’t always the optimum measurement solution; there would be little point in purchasing a scanning system if control options are severely limited. In some instances it may be more practical to purchase two static MCT sensors and install these at either side, or above and below the web, e.g. Control of board flatness at the exit of a double-backer in the production of corrugated board.