By Kemira’s Clay Campbell, global business development, senior mgr. Kemira, and Lucyna Pawlowska, tissue process application specialist, Kemira
A great deal of information can be ascertained through in-depth diagnostics of the structure of the parent roll and/or converted finished sheet. Some of the key process variables that effect the sheet structure include: variations in the CD sheet profile, the creping process and blade changes, and the effect of changes in fibre source and wet end chemistry. Changes in sheet structure can significantly impact tissue softness.
There are different roads one can take to achieve tissue softness. The key is to be able to determine how to get there and when you are at your target destination. An easy and reliable measurement of sheet properties that determine softness will help to choose the most effective path and set a measurable sheet quality target.
Paper manufacturers can utilise a variety of process tools to improve overall surface softness, formation and appearance. The most significant factor is the fibre type and ratios, followed by machine type and creping process configurations. Each process change impacts the sheet structure in positive or negative ways.
The key to improving and maintaining final sheet softness is to measure how each process factor change impacts the sheet structure and then how each change in sheet structure impacts the softness.
KemView™ Sheet Structure Analyser (SSA) description / features
Kemira’s KemView Gen II unit is an easy to use, fast response, sheet structure analyser that provides a diverse array of sheet measurements and can be effectively used as a laboratory and field support tool assisting in the diagnostics of paper sheets. KemView SSA consists of a digital optical detector positioned at the top of the unit. Multiple LED light emitters illuminate the sheet sample. Analysis of a sheet sample is easy by simply placing the KemView Gen II unit on top of the sheet and clicking the analysis button. Generating images at several different sheet locations takes seconds, and the data can easily be exported to an Excel file for comparative analysis.
Kemira’s KemView Gen II unit has diverse features that are beneficial for a new grade development, external product benchmarking, comparison of the same product manufactured on different machines, and troubleshooting sheet quality issues. It provides quick feedback allowing for optimisation of creping, softening and strength programs.
A variety of sheet surface properties can be measured by utilizing KemView SSA and emtec Tissue Softness Analyser* (TSA). Combined results from these two measurements in conjunction with physical properties sheet testing provides a comprehensive insight into the sheet structure and softness and allows for comparative analysis of various tissue products.
KemView SSA is a novel image-based measurement tool that provides in depth 3D analysis of the sheet with the ability to easily measure the following parameters:
• Crepe bar count (#/ inch)
• Crepe bar width, length and height
• Crepe bar uniformity and distribution
• Sheet roughness and intensity (crepe visibility)
• Number of free fibre ends (FFE)
• Markings (sheet patterns and embossed marks).
Typically, a sheet structure that has a high crepe bar count and low crepe bars intensity (visibility) provide softer tissue. The higher free fibre ends (FFE) count, the softer or more velvety hand feel surface. However, if the FFE count is too high in the sheet, it could lead to dusting and linting conditions.
Two retail facial tissue samples were analysed using the KemView SSA, emtec TSA and physical properties testing. As shown in Table #1 and photos, branded facial tissue has significantly higher crepe bar count and produces lower surface roughness, while private label (P/L) facial tissue has lower crepe bar count and higher intensity (bars are more visible). In addition, the FFE count is quite higher than normal and may contribute to sheet dusting and linting.
Sheet properties testing was performed (as shown in Table #2) with branded facial having lower dry tensile strength, basis weight and bulk.
In Table #3 subjective hand feel panel and emtec TSA softness results clearly indicate that the branded facial has higher overall softness then the private label facial.
In conclusion, if private label was looking to compete against the branded facial to achieve closer hand feel softness results, then several chemical and process actions can be considered:
• Decreasing sheet dry tensile strength via the use of wet end softener, reduced refining or a reduced crepe release/adhesive ratio.
• Increasing crepe adhesive dosage will increase crepe bar count with slight reduction in bulk, but an increase in overall sheet surface smoothness.
• Utilising a dry strength agent that allows for reduced refining while maintaining strength and providing opportunity to reduce overall basis weight. In addition, certain dry strength agents provide a secondary benefit by anchoring free fibre ends into the sheet and reducing overall sheet dusting and linting.
Examples of KemView SSA application in the tissue mill
• Evaluation of new products in a creping program
• Evaluation of blades at different bevels
• Blade wear effect on sheet
• Effect of dry strength resins application on creping
• Effect of softeners on creping process and the impact to the sheet
• Comparison of sheets creped at different sheet moistures
• Measurement of sheet structure profile in cross machine direction
• Degradation of crepe at the felt seam mark
• Effect of basis weight reduction
• Replacement of virgin fibre with recycle fibre.
Kemira’s KemView Gen II Sheet Structure Analyser is an effective field support tool allowing quick testing feedback, troubleshooting for sheet quality and production issues, and optimisation of the creping process.
This article was written by Kemira’s Clay Campbell, global business development, senior mgr. and Lucyna Pawlowska, tissue process application specialist, for TWM.