I was employed as a Researcher for Millennium Chemicals (formerly SCM Chemicals) in Bunbury for their Titanium Dioxide processing plant. I was primarily researching finishing processes for the pigment to aid both production and quality improvements.
High Gloss Pigment Coatings – Millennium Chemicals
Gloss of a pigment is the gloss development of the resin and binder that the pigment is in. Gloss development can be measured by a reflectance type meter as the amount of light reflected from the coated surface at a specified angle. Pigment gloss is affected by many factors including pigment passivation, coating type, pH etc. I undertook an investigation into the state of the art, including tests on the current market products. Based on this data, I designed a set of experiments to reproduce the properties important in the market pigments (gloss, durability etc). My research further indicated that some gloss gains were made from adding trace heavy transition metals. I discounted some of these as they were not available in the market in production quantities but I was able to identify four metal salts that were earmarked for laboratory experimentation. I formulated a series of laboratory scale tests that concentrated on the main parameters. I was able to demonstrate the benefits of the trace metal additions, but not the cost, as to obtain any benefit, the addition amounts were excessive. The second part of the research was looking at process issues, such as mixing, pH, addition order, addition rates etc. The aim was to change the nature of the existing coating chemistry to improve the gloss. From this research a matrix of experimental work was formulated. The experimental work was all laboratory based, with little engineering in this task.
Multi-Disk Grinding Mills – Millennium Chemicals
The largest consumer of energy in the pigment process was the wet fine grinding process. Traditionally this was achieved using Sand Mills, which were essentially attrition mills with silica sand as the media. The energy efficiency of these mills was very low, as many attrition millings are. Contamination of the final product by silica was also an increasing problem as production was under pressure to improve product quality. I headed a small team assembled to look at sand milling from both an engineering and chemistry point of view with the aim of reducing silica carryover and improving energy efficiency. I conducted research into the best practices of attrition milling and their suitability to grinding to below 2 micron particle size and to retrofitting to the existing process infrastructure, which was an important design constraint. I was able to focus on two areas (1) the mill engineering and (2) the grinding media. My research was also a detailed study of the present production, including particle sizes, silica content, power inputs and physical properties of the pigments, comparing with standards and set targets at all phases. I conducted a mill-wide analysis of particle sizes and gloss/durability analyses, including historical data. I published the research along with recommendations for plant trials. The outcome of my research was to trial in the laboratory spherical Zirconium Oxide pellets. These had a higher density than the silica sand and were of a more uniform particle size distribution. The higher density was to help with the attrition efficiency and to stop the upflow of the media which was common with sand. Zirconium Oxide was also much harder than silica, leading to less attrition of the media and less carryover with the product pigment. The drawback was the cost of Zirconium versus that of sand, but this was justified because of the longer life as a media, which was extended by up to 10 times. I designed a series of laboratory scale trials that showed that there were definite advantages in this media, including less carryover, improved particle size and similar power inputs to that of sand. I was able to demonstrate that the “fluidization” of the regularly shaped Zirconium was easier, possibly leading to better attrition efficiency, which matched my research. From the laboratory trials, I designed and build a pilot-scale mill with multiple shafts (4). My research indicated that having more than one rotor and baffling should also increase the mixing and fluidization, leading to better attrition and to a reduction in per-tonne power usage. I also purchased and installed specialised instrumentation to measure power input and control rotor speeds. With this mill, I was able to analyse both the single shaft and multi-shaft hypotheses along with both the sand and Zirconium. I ran many laboratory trials using the single shaft mill first to analyse the effect of the Zirconium media. From this data, I designed a full-scale plant trial. I engineered the installation of new piping and pumping circuits in the grinding mill to isolate two mills. These two mills were then filled with the zirconium beads and run as per the trial matrix. The extra piping allowed the pigment product to be loaded separately for transport to the finishing plant where I also isolated a whole section of the plant (storage, washing, coating and micronising) for the trial material. At the end, I blended the trial pigment back into the normal production in a controlled way such that the production was not affected. All testing for physical and chemical parameters was done on pre, during and post trial pigments. The results of the plant trial, run over a week period, were very successful, demonstrating the efficiency of the zirconium media. All key parameters improved over the standard pigments. Further benefits were found in micronising since the pigment feed had a better particle size and less silica content. I was able to demonstrate savings in steam and wear in the micronisers due to the lower silica content of the final pigment, and the finer particle size of the feed. In parallel with the above, I ran laboratory trials with the 4-shaft mill with both sand and zirconium media. The aim of the trials was to show that 1 large mill was more efficient than 4 standard size mills, with the added benefits of the zirconia media. Power inputs, shaft speeds and media loadings were all varied in a controlled matrix to test the above hypothesis. The results of these trials were analysed and compared to all of the standard pigments. I was not able to demonstrate that power efficiency of the 4 shaft mill was improved over the single shaft mill however, I was able to demonstrate that the fluidity of the pigment in a multi-shaft mill was much improved.
Deposition of Phosphate in Pigment Coatings – Millennium Chemicals
This project was a chemistry task, designed to find the mechanism of Phosphate (Sodium Hydrogen Phosphate) deposition onto the surface of Titanium Dioxide pigment. Phosphate was the best and most effective additive for the improvement of durability in paint pigments. The accepted theories ranged in views of how, where and when the Phosphate ions were precipitated during the treatment process. What was known was that the durability (passivating) of the pigment surface was improved by the addition of Phosphate to the treatment scheme. I first carried out research into current Phosphate –containing pigment formulations and demonstrated that there were many differing views on the mechanism, addition chemistry and addition conditions required for an optimum improvement using Phosphates. I was also able to demonstrate in this project how good experimental technique is important and can yield solid, defendable data. I designed an experimental scheme to show the definitive point or points where the Phosphate precipitated into the pigment surface and what, if any, were the conditions and other ions that were involved in this precipitation. I designed the experiment so that small samples could be extracted from the reaction vessel at all points during the treatment process. I used four different treatment recipes and these were analysed in the experiment, with samples taken at every change in conditions (eg. pH, temperature, chemical addition, hold time, etc.). I analysed the samples using XRF, C/S and XRD to determine the total mineral contents. I was able to demonstrate that the Phosphate mechanism was in two stages. One stage was just after heating and initial pH adjustment, the second stage was the last in the process, where the remaining Phosphate ions precipitated with the Alumina. These results both reinforced the theories at the time.
Ceramic Micronisers – Millennium Chemicals
Micronisers are sub-micron size grinding machines utilizing super-sonic steam in a vortex to achieve attrition of very small particles of pigment. The traditional material of the machine is high carbon steel. The fundamental design problem, bot in materials and engineering is that titanium pigments erode the steel, limiting production rates and discolouring the white pigment. The erosion also limits the life of the machine and increases maintenance costs. As pressures were put on production and quality a new material or process was needed. I was part of a team, including engineers, production personnel and suppliers that was looking at ceramic wear liners. The problems that had o be overcome in the project were to do with cost, vibration and the accuracy of the moulding of the ceramic. I researched the ceramics to find easily mouldable materials that could withstand vibration, or that could be made to withstand vibration by supporting the internal liner. I was able to identify two ceramics that had many of the features required, one that was expensive but fitted the criteria almost fully and one cheaper material that matched 80%. I recommended that both should be evaluated, as the extra cost could be offset by other parameters. I designed the basic wear liner for the laboratory microniser and managed the manufacture of these by a subcontractor. The outer casing was stainless steel and this was designed by another engineer. I designed a matrix of experiments to compare the three micronisers for a variety of parameters including production rate, pigment quality, iron carryover and wear rates. I was able to demonstrate that, in all of the pertinent areas, the ceramic was superior except that it was vulnerable to vibration damage. The vibration was a fundamental characteristic of the machine, and my research showed that it was caused by the super-sonic shock waves that built up in the steam jetstream. The decision was made to go ahead with a full scale trial of the ceramic in the plant and to control the vibration to a minimum. The ceramic was in service for two weeks before being removed and checked for dimensions, wear and any evidence of cracks. The use of ceramics was justified from the wear statistics alone however the vibration problems at start-up and shutdown created some cracking. The vibration would have to be controlled to ensure the life of the ceramic liners.
Ceramic Washing & Filtration – Millennium Chemicals
Traditionally, pigment washing machinery has focussed on large, fabric covered vacuum washers which have low throughput and an average efficiency. Washers were classified “efficient” if the product was low in salts and of high solids content. New technology was released, primarily for the mining and minerals processing market, utilising vertical, porus ceramic disks. This technology claimed that it could achieve much higher throughputs for much smaller machine footprints. With the porus ceramic material, maintenance was claimed to be lower and easier. Working with the supplier, I was able to obtain a sample disk for laboratory evaluation. I trialled this disk on all of the production grades, with good results for dewatering and washing. In parallel I undertook further research into ceramic disk filters. I was able to determine that it was an established technology in other industries, but not in pigments. I published the results of my research with recommendations for plant trials based on my short laboratory trials. I then evaluated the supplied disk segments further in the laboratory, with a recommendation of two segments that could be trialled in a pilot plant. I selected two disks based on throughput, washing efficiency and dewatering ability. A pilot scale (1 disk rotor) filter was installed in the plant by the supplier and I evaluated this over the next few months on a continuous basis. I was not able to demonstrate any efficiency in the plant. The results of the pilot plant were not encouraging due to the thixotropic nature of some pigment grades. These grades did not adhere to the disks sufficiently to allow for any throughput. This was further complicated by the scheduling of production. To be fully efficient, the disks would have to be changed to suit each grade, resulting in down-time. No one disk was suitable for all grades. After the plant trial, the idea was abandoned.
Low Abrasion Pigments – Millennium Chemicals
Printing inks for the Gravure Offset process require low abrasive pigments to prevent wear of vital press components. The mechanism by which pigment becomes abrasive or not in this process needed much research as there were many theories. In reality it was an engineering problem in the gravure process that required an elegant solution from the pigment manufacturers. I was responsible for the project to investigate the mechanism and to suggest how the abrasion problem could be tackled. There were many pieces of apparatus available in the market to test the abrasive properties of inks. I undertook a full review of all of the available machines, however the research showed that only one machine filled all of the criteria. I also carried out research into acceptable standards for test pieces and the methods of evaluation. I found that, although there were many empirical standards, there were few quantitative measures of abrasion for pigments. I recommended to purchase the selected machine and to purchase some useful empirical test pieces that could be evaluated and used in a quantitative method. I was able to find a baseline for abrasion in one of the competitive pigments. My research showed that one particular grade was accepted as being the benchmark and I was able to match this to the results collected from the testing machine. I then designed a set of experiments to reproduce the abrasion noted in my research on the Gravure press. I compared both production pigments and pigments from the market with the baseline I established, along with a matrix of laboratory samples that I prepared of various treated pigments. A key outcome of this matrix was the difference between “Blue Tone” and “Neutral Tone” base pigments. Produced using different TiO2 reactors, this outcome was the most significant. The challenge then was to produce “Neutral Tone” pigment using the “Blue Tone” reactor, and I designed a plant trial for this outcome. This project was still on-going when I left Millennium Chemicals.