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Rezultaty
A LAN was designed and constructed for controlling the UFMWE unit. The ellipsometric measurement and modeling calculation of the coated layer is carried out by the UFMWE and the set of layer relevant data (e.g., calculated thickness) and status data (e.g., error codes) is sent to the network of the coating machine (PLC, EB gun control system). For the closed loop PID control of the thickness, the web-speed or EB power will be controlled. For other layer parameters other machine parameters can be used for control purposes. The UFMWE unit installed on a lab scale coater was further tested and improved. A final version of DP2 software was installed and checked in order to verify the ability of controlling the EB deposition processes. Afterwards, the system was installed on the LAV machine (coater).SiOx coatings were EBE deposited on PET substrates using as evaporated source material the standard SiO18, which showed the best barrier properties measured after retortability tests. The first point of interest was to investigate the accuracy in thickness calculation by altering the web speed. A correlation formula has been established between web speed and resulting SiOx coating thickness, by applying the standard deposition conditions. However, upon the installation of the UFMWE unit on the coater, this correlation is no longer fully valid due to the alterations that need to be done in the deposition processes.
The parameters tested and monitored within this task were:
- Thickness
- Optical properties
- The accuracy in the modelling procedure applied when during the deposition process
- It was attempted to investigate the effect of the in vacuum and in air oxidation of the deposited SiOx layers.
The accuracy in the modeling procedures, the initial fitting parameters as well as the acquisition parameters set in the recipe mode were tested.
The adaptation of the UFMWE unit to LAV machine was installed in the part were the pretreatment procedure was performed on the PET web prior the SiOx barrier coating deposition. Also, due to the position of the UFMWE, it was necessary to run the appropriate pretreatment of the PET membrane and the EBE deposition processes in a non-standard mode. As a result, two main points emerged showing that the whole barrier coating deposition process is not optimal. First, there is a time delay between the pretreatment and the coating deposition, which may cause adhesion failures of the SiOx coatings on the PET. Second, the quality of the initially deposited SiOx layers is not optimal due to the reverse running mode of the EBE, and thus the initial layers of the SiOx coatings deposited on PET have different composition and stoichiometry properties. It is very possible that these layers have a considerably lower density than the bulk of the SiOx coatings.
All these factors resulted in poorer barrier properties than the SiOx films produced and characterised by TransMach. As a consequence, it was considered more meaningful to work on the optimisation of the barrier coating deposition processes, using UFMWE controlling, in the technical scale EBE coater at AF. Representative results on these activities are presented in the final report of the project.
The development of UFMWE has been approached to meet the specific requirements and demands (in-line monitoring and control of very fast vacuum web coating processes). The reasons for designing a new monochromator FUV200:UT 300 and using a new light source (150 Watts Xenon) include one of the main UFMWE unit requirements, that is high data acquisition speed for following processes in real time, yielding exploitable results in a total time of less than 100ms and over a 32 wavelength range, and the spectral range of 190-830 nm. The new approach made use of a new ultra fast acquisition board (DSP inside) which can simultaneously convert up to 32 channels at a rate of 800kHz per channel combined with a hybrid multi-channel detector including a photodiode coupled with a photo cathode. The new monochromator FUV200 has a focal length 200 nm single grating, the calibration is automatic with opto-switch, and the spectral range is: 1.5 6.5eV. In order to cover the 190-830 nm spectra range, two PMT for the ViS and UV energy ranges are used. The need for the FUV range led to the design of a dedicated light source. In order to overcome the problem of the strong absorption of the atmosphere, a Nitrogen purge system was incorporated with the safety requirement for ozone evacuation. Since the life time of the Xenon source is around 2000h in the FUV range, a time counter was inserted in the block source. For an accurate measurement, any perturbations from the external environment need to be taken into account. A microshutter is incorporated to this end.
The spectrograph is based on a specific holographic fixed grating specifically designed and manufactured by JY for this project. A flat field spectrum of 150mm width is obtained with a dispersion of around 2 nm/mm. In this spectrum field, 16 wavelengths were selected as defined by AUTh. This corresponds to the optimised wavelength of the project. The selection is done by optical fibre, using the optical demultilplexing technology already developed by JY and then coupled to 32 photomultiplier tubes (provided by the Hammatsu Company). The detectors and the spectrograph were designed to achieve a high level of integration in an industrial standard rack (height: 3U, width: 19").
The Integrated Spectroscopic Detector is fully integrated into a PC based platform and is based on the use of the CAUTH40 spectrograph and a linear CCD detector (2048 pixels). The software is based on Windows 2000. The work on firmware included the communication of the ellipsometric unit with sensors through ultrafast acquisition boards to perform acquisition, modelling, local database support, data management and statistics. In addition to the selected technical requirements concerning the proper spectral range and the number of wavelengths, a new ultra fast acquisition board (DSP inside) has been optimised in order to meet the basic demand for high data acquisition. The board can simultaneously convert up to 32 channels at a rate of 800 kHz per channel combined with a hybrid multi-channel detector including a photodiode coupled with a photo cathode.
Fibre optic was not used to connect the Xe-lamp with the Analyser housing in order to increase the intensity & accuracy and to reduce the cost. The software delivered with the prototype UFMWE was basic software (DP1 version), which was optimised during the project. Aspects of the software, such as: i) the industrial communication, ii) the full parallelism and iii) its total integration, were finalised in the second version of the software (DP2).
Thin silicon oxide films (SiOx) were produced using electron-beam evaporation (EBE) technique. Different types of source evaporated materials were used, such as standard silicon monoxide (SiO) and silicon dioxide (SiO2), as well as mixed materials of silicon (Si), SiO2 and SiO, in order to obtain all possible stoichiometries. Depending on the applied deposition conditions and the different evaporation processes, SiOx coatings of different stoichiometry, properties, and thickness, were formed.
A number of SiOx coatings, grown on polymeric membrane substrates, were studied in terms of their optical properties either ex situ or in situ and in real-time during the evaporation processes, using the Spectroscopic Ellipsometry (SE) and the Multi-Wavelength Ellipsometry (MWE) techniques, respectively. For the evaluation and the determination of the specified optical parameters an appropriate modeling and fitting procedure was carried out.
This allowed the calculation of the Penn Gap (the energy where the strong electronic absorption takes place) and of the static dielectric constant or refractive index n. On the basis of the work carried out so far, these two parameters have proved to be the two most important optical parameters correlated to the final functional properties, such as the barrier properties (i.e., oxygen transmission - ORT and water vapour transmission - WVTR) of the SiOx coatings. The latter were determined with the appropriate permeation tests.
In addition, the strong correlation between the SiOx films' thickness and their barrier properties was verified. A precise determination of the thickness of coatings was achieved by analysing SE and MWE data, even in a real-time analysis mode. The latter is very important if we take into account that there is a complexity in the accurate calculation of the thickness of the SiOx films, which are grown onto polymeric membranes. SE and MWE results for thickness were compared with the respective values deduced either theoretically, by means of calibrated deposition rates of the evaporation processes, or experimentally by means of i) XRF, ii) EDX, and iii) SEM techniques, which were applied ex situ.
Wyniki nadające się do wykorzystania
The TransMach project was led by the current and future market needs for packaging films (i.e. current food and medical), optical coatings on flexible substrates, barrier layers for solar modules, and flexible displays, where cost efficient production and high quality transparent coatings produced by large area vacuum (LAV) coating machines are the two drivers.
The current required barrier properties of transparent coatings (e.g., for gases) for packaging films are below 0.2 and in order to support the new technical applications (i.e. solar modules) should be well below 0.02 for the production of flexible displays systems. These requirements could not be solved with that state-of-the-art because the following issues had to be managed:
- The technical difficulties of the LAV processes such as high coating speed, large moving surface areas coated in each run, two step processes during each run (surface treatment and then coated, important to control product quality and achieve cost and waste reduction),
- The technical demands for functional coatings in new applications,
- The requirements for material and energy reduction (i.e. by controlling coating thickness and its uniformity over the surface), and
- Repeatability and high quality of products and cost efficiency, in a systematic approach and call for an intelligent and reliable in-line monitoring and control LAV machinery.
Control units available today for metallisation cannot be used at all for transparent ones whereas the state-of-the-art technique to monitor LAV transparent coating's thickness, X-ray fluorescence is of low reliability and cannot be used for close-loop control of the fast process in LAV machines. In addition, costs a factor of 10 more and is lower in speed by a factor of 100, than the ultra-fast multi wavelength ellipsometric-UFMWE unit (sensor) developed in the TransMach.
The TransMach project was aiming at providing a new generation of LAV production equipment at the European level, with emphasis on highly reliable and integrated approach, focusing on three aspects: The component technology aspect, the system design and integration aspect and the assessment/measurements aspect.
The technical demands for transparent functional coatings were:
- Good adhesion of the deposited coating to the substrate in all applications,
- Well defined optical properties (in general transparency in the VIS region) depending on the application area,
- Well defined barrier properties depending on the application area (today is ~1cm³/m² day bar for gases in packaging, but for future must be below 0.2, 0.1 and 0.02cm³/m² day bar for food and medical packaging, solar modules and flexible display systems, respectively),
- Good wear resistance for displays, climatic and light stability for solar modules, anti-counterfeit devices.
The objectives of TransMach were to develop, procure and test the requisite component technology in order to achieve:
- Verification of method to screen transparent coatings properties
- Development of a UFMWE unit, faster & cheaper, suitable to assess transparent coatings properties
- Validation of unit in-line monitoring on very fast moving flexible substrates
- Technical applicability of unit in LAVE
- Demonstration of prototype LAVE with intelligent in-line control
- Applicability to new high barrier/transparent LAV product
- Substantial overall reduction of LAV process waste and product cost
The main achievements of the project are:
-- The development of a methodology for screening functional coating (thickness, uniformity, composition and interface) properties by UFMWE
-- The development of a novel, UFMWE unit - to monitor very fast processes, an ambitious and beyond the state-of-the-art novelty
-- The incorporation in an integrated approach, UFMWE monitoring units, managed by a local area network (LAN) and an intelligent in-line control of processes and properties of the LAV machines.
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