Thermochromic (TC) printing inks change their colour regarding the change in temperature. One of ... more Thermochromic (TC) printing inks change their colour regarding the change in temperature. One of the most frequently used TC material in printing inks are leuco dyes. This TC composite usually consists of a colour former (leuco dye), a colour developer and a solvent, protected in polymer capsules. The colour of TC prints is dynamic, it is not just temperature dependend, but also depends on thermal history. The effect is described by colour hysteresis. Leuco dye-based TC inks are known for their short pot life, poor lightfastness and low resistivity to high temperatures and many chemicals. The effect of UV light and high temperatures on dynamic colour properties was tested. The effect was evaluated by total colour difference between fully coloured states of exposed and unexposed samples, by the total colour contrast between fully coloured and totally discoloured states of the samples and by the sample discolouration ability.
Leuco dye-based TC inks have short pot life, poor lightfastness, low resistivity to high temperat... more Leuco dye-based TC inks have short pot life, poor lightfastness, low resistivity to high temperatures and many chemicals. Polymer envelopes are much more stable than the polymer binder in TC ink5. However, lightfastness and chemical stability of TC capsules in the applied vehicle were considered to be the origin of poor stability of TC inks6. The lightfastness of leuco dye-based TC samples might be increased simply by applying a protective layer. For this reason, two transparent lacquers were tested. Special commercial TC ink with intrinsically improved lightfastness (the so-called UV-protected ink) was used without protective layer as a comparison. The effect was evaluated by total colour differences between exposed and unexposed samples and by the total colour contrast between fully coloured and totally discoloured states.
Slovenian female physicists are organized in an informal network that incorporates more than 100 ... more Slovenian female physicists are organized in an informal network that incorporates more than 100 women working in research, academia, government, and industry. In the past three years we have accomplished several actions in order to motivate young girls and students to pursue physics. Our main achievement was publishing the monograph Physics-My Education in September 2007. The book includes 79 autobiographic
Summary Evaluating our experiments performed so far the industrial grass proved to be a hopeful y... more Summary Evaluating our experiments performed so far the industrial grass proved to be a hopeful yearly renewable raw material for energetic as well as for industrial application. It can be concluded from results of pilot and industrial scale production that the industrial grass cellulose was equivalent or even better in quality and value with papers produced from traditional resources. Acknowledgement Authors are very thankful to the National Develop
The present study investigates the preparation of the copper phthalocyanine pigment for inkjet pr... more The present study investigates the preparation of the copper phthalocyanine pigment for inkjet printing inks. The pigment particle size distribution was measured with laser diffraction at different times of wet milling. Simultaneously, the absorbance spectra in a visible-near infrared spectral region of the corresponding diluted pigment dispersions were measured. At the beginning of the milling process, the particle size distribution is bimodal, showing the presence of aggregates and agglomerates. During the second hour of milling, the particle size distribution changes to unimodal due to the breaking of agglomerates, and the corresponding absorbance spectra change accordingly. Further milling diminishes the size of pigment aggregates up to the steady state value of around 130 nm, where also the absorbance in the corresponding spectra does not increase. A detailed analysis of intensity and position of the absorbance peak at 340 nm in dependence on the milling time and pigment concentration confirms the idea that an optical spectroscopy could be used for the assessment of optimal milling time required for the preparation of pigments with the maximum absorption ability.
Optical security takes advantage of complex gonioapparent effects of diffractive samples having s... more Optical security takes advantage of complex gonioapparent effects of diffractive samples having strong angular and spectral dependence of reflected light. However, resolving the full angular and spectral properties of these kinds of targets might be a tremendous task. Preferably, one would like to measure a more limited number of illumination-viewing directions, using a multiangle goniometer, and still reveal the complex and unique properties of the target. In this study, we use a method for converting the full angular reflection data into reduced goniospectrometric space and further on into an xDNA graph, which we find to show good potential as a fingerprint for gonioapparent surfaces when limited measurement geometries are available. For the evaluation of the xDNA graph, we use two goniometric devices with a 45° incident angle illumination, a high-resolution bidirectional spectrometer, and a portable multiangle goniometer. This study tests the xDNA graph by evaluating the effects of geometry count and spectral resolution in goniometric measurements and further finds that the xDNA graph indeed works best with a reduced count of geometries and is not sensitive to lowered spectral resolution.
The colour of some samples is easily seen by naked eye, but is badly or completely wrongly evalua... more The colour of some samples is easily seen by naked eye, but is badly or completely wrongly evaluated by measurements. Such examples are thin layers with interference effect and liquid-crystal-based thermochromic printing ink. The directional illumination - directional viewing measurement geometries which are most frequently applied in graphic art fail completely or to a large extent and integrating sphere measurements are required to describe the effect by colorimetry. Various parameters of a selected measuring geometry are also important. The consequences of using integrating sphere with different diameter and sample openings on the derived colour were investigated. The investigated samples include directional-occurring phenomena and those which are directionally independent. This is clearly revealed in colorimetric results. When the samples are observed by naked eye, we often have to change illuminationviewing conditions to get the best vision. Thus, measuring conditions should be of large importance.
Temperature has critical impact on food quality and safety within food supply chain, therefore, f... more Temperature has critical impact on food quality and safety within food supply chain, therefore, food should be kept at the defined storage temperature range. Final consumer should be assured when buying food about actual temperature and thermal history of the selected food product and this is why it should be indicated on the packed or prepacked item. The chromogenic temperature indicator for cold food chain was prepared from suitable active material packed in the properly structured holder. When temperature rises above the defined storage temperature, the active material changes colour and physical state (solid/liquid). Simultaneously, special packaging structure enables irreversible recording of the time exposed to the elevated temperature. The active material was made of thermochromic composite, consisting of dye, developer and solvent. It changes colour at its melting point, being coloured below and discoloured above it. The temperature is called activation temperature of the composite. Its value was adjusted by appropriate solvent and additives used for preparation of the composite, to reach the desired value. The temperature dependent colour change of the composite was determined by colorimetric measurements. The conditions for best observation of the change by naked eye were also examined. The structure of the active material’s holder was analyzed for best displaying of the time spend at high temperature (above the activation temperature). Functioning of the indicator was examined with growth of pathogens as a function of migration of the active material at temperature above the required storage temperature of the food. It was found out that the described chromogenic temperature indicator for cold food chain shows the thermal history of food storage by colour-, phaseand migration changes of the active composite material and consequently would be reliable as indicator in cold food chain to indicate temperature abuse and would disclose potential growth of psychrophilic microorganisms.
UV-curable leucodye-based thermochromic inks with activation temperature of 31 °C in blue, red an... more UV-curable leucodye-based thermochromic inks with activation temperature of 31 °C in blue, red and black shades were analysed. The colour of samples does not depend only on their temperature but also on thermal history – they show colour hysteresis. Similar hysteresis loops were obtained for the red and blue samples and narrower for the black sample, as measured by cycling in 14–40–14 °C region. The blue and black samples have approximately closed loops but a small colour difference was obtained even after one cycle for the red one thus the loop remains slightly opened. The colour of all samples also depends on the UV dose applied at curing. This difference was followed over the whole hysteresis loop. The largest values were measured for the red sample where the CIEDE2000 total colour difference rises above 4 and remains well observable all over the temperature region applied for cycling. One of the possible reasons for this effect might be different degree of polymerisation of the polymer matrix achieved by different UV curing.
Thermochromic (TC) printing inks change their colour regarding the change in temperature. One of ... more Thermochromic (TC) printing inks change their colour regarding the change in temperature. One of the most frequently used TC material in printing inks are leuco dyes. This TC composite usually consists of a colour former (leuco dye), a colour developer and a solvent, protected in polymer capsules. The colour of TC prints is dynamic, it is not just temperature dependend, but also depends on thermal history. The effect is described by colour hysteresis. Leuco dye-based TC inks are known for their short pot life, poor lightfastness and low resistivity to high temperatures and many chemicals. The effect of UV light and high temperatures on dynamic colour properties was tested. The effect was evaluated by total colour difference between fully coloured states of exposed and unexposed samples, by the total colour contrast between fully coloured and totally discoloured states of the samples and by the sample discolouration ability.
Leuco dye-based TC inks have short pot life, poor lightfastness, low resistivity to high temperat... more Leuco dye-based TC inks have short pot life, poor lightfastness, low resistivity to high temperatures and many chemicals. Polymer envelopes are much more stable than the polymer binder in TC ink5. However, lightfastness and chemical stability of TC capsules in the applied vehicle were considered to be the origin of poor stability of TC inks6. The lightfastness of leuco dye-based TC samples might be increased simply by applying a protective layer. For this reason, two transparent lacquers were tested. Special commercial TC ink with intrinsically improved lightfastness (the so-called UV-protected ink) was used without protective layer as a comparison. The effect was evaluated by total colour differences between exposed and unexposed samples and by the total colour contrast between fully coloured and totally discoloured states.
Slovenian female physicists are organized in an informal network that incorporates more than 100 ... more Slovenian female physicists are organized in an informal network that incorporates more than 100 women working in research, academia, government, and industry. In the past three years we have accomplished several actions in order to motivate young girls and students to pursue physics. Our main achievement was publishing the monograph Physics-My Education in September 2007. The book includes 79 autobiographic
Summary Evaluating our experiments performed so far the industrial grass proved to be a hopeful y... more Summary Evaluating our experiments performed so far the industrial grass proved to be a hopeful yearly renewable raw material for energetic as well as for industrial application. It can be concluded from results of pilot and industrial scale production that the industrial grass cellulose was equivalent or even better in quality and value with papers produced from traditional resources. Acknowledgement Authors are very thankful to the National Develop
The present study investigates the preparation of the copper phthalocyanine pigment for inkjet pr... more The present study investigates the preparation of the copper phthalocyanine pigment for inkjet printing inks. The pigment particle size distribution was measured with laser diffraction at different times of wet milling. Simultaneously, the absorbance spectra in a visible-near infrared spectral region of the corresponding diluted pigment dispersions were measured. At the beginning of the milling process, the particle size distribution is bimodal, showing the presence of aggregates and agglomerates. During the second hour of milling, the particle size distribution changes to unimodal due to the breaking of agglomerates, and the corresponding absorbance spectra change accordingly. Further milling diminishes the size of pigment aggregates up to the steady state value of around 130 nm, where also the absorbance in the corresponding spectra does not increase. A detailed analysis of intensity and position of the absorbance peak at 340 nm in dependence on the milling time and pigment concentration confirms the idea that an optical spectroscopy could be used for the assessment of optimal milling time required for the preparation of pigments with the maximum absorption ability.
Optical security takes advantage of complex gonioapparent effects of diffractive samples having s... more Optical security takes advantage of complex gonioapparent effects of diffractive samples having strong angular and spectral dependence of reflected light. However, resolving the full angular and spectral properties of these kinds of targets might be a tremendous task. Preferably, one would like to measure a more limited number of illumination-viewing directions, using a multiangle goniometer, and still reveal the complex and unique properties of the target. In this study, we use a method for converting the full angular reflection data into reduced goniospectrometric space and further on into an xDNA graph, which we find to show good potential as a fingerprint for gonioapparent surfaces when limited measurement geometries are available. For the evaluation of the xDNA graph, we use two goniometric devices with a 45° incident angle illumination, a high-resolution bidirectional spectrometer, and a portable multiangle goniometer. This study tests the xDNA graph by evaluating the effects of geometry count and spectral resolution in goniometric measurements and further finds that the xDNA graph indeed works best with a reduced count of geometries and is not sensitive to lowered spectral resolution.
The colour of some samples is easily seen by naked eye, but is badly or completely wrongly evalua... more The colour of some samples is easily seen by naked eye, but is badly or completely wrongly evaluated by measurements. Such examples are thin layers with interference effect and liquid-crystal-based thermochromic printing ink. The directional illumination - directional viewing measurement geometries which are most frequently applied in graphic art fail completely or to a large extent and integrating sphere measurements are required to describe the effect by colorimetry. Various parameters of a selected measuring geometry are also important. The consequences of using integrating sphere with different diameter and sample openings on the derived colour were investigated. The investigated samples include directional-occurring phenomena and those which are directionally independent. This is clearly revealed in colorimetric results. When the samples are observed by naked eye, we often have to change illuminationviewing conditions to get the best vision. Thus, measuring conditions should be of large importance.
Temperature has critical impact on food quality and safety within food supply chain, therefore, f... more Temperature has critical impact on food quality and safety within food supply chain, therefore, food should be kept at the defined storage temperature range. Final consumer should be assured when buying food about actual temperature and thermal history of the selected food product and this is why it should be indicated on the packed or prepacked item. The chromogenic temperature indicator for cold food chain was prepared from suitable active material packed in the properly structured holder. When temperature rises above the defined storage temperature, the active material changes colour and physical state (solid/liquid). Simultaneously, special packaging structure enables irreversible recording of the time exposed to the elevated temperature. The active material was made of thermochromic composite, consisting of dye, developer and solvent. It changes colour at its melting point, being coloured below and discoloured above it. The temperature is called activation temperature of the composite. Its value was adjusted by appropriate solvent and additives used for preparation of the composite, to reach the desired value. The temperature dependent colour change of the composite was determined by colorimetric measurements. The conditions for best observation of the change by naked eye were also examined. The structure of the active material’s holder was analyzed for best displaying of the time spend at high temperature (above the activation temperature). Functioning of the indicator was examined with growth of pathogens as a function of migration of the active material at temperature above the required storage temperature of the food. It was found out that the described chromogenic temperature indicator for cold food chain shows the thermal history of food storage by colour-, phaseand migration changes of the active composite material and consequently would be reliable as indicator in cold food chain to indicate temperature abuse and would disclose potential growth of psychrophilic microorganisms.
UV-curable leucodye-based thermochromic inks with activation temperature of 31 °C in blue, red an... more UV-curable leucodye-based thermochromic inks with activation temperature of 31 °C in blue, red and black shades were analysed. The colour of samples does not depend only on their temperature but also on thermal history – they show colour hysteresis. Similar hysteresis loops were obtained for the red and blue samples and narrower for the black sample, as measured by cycling in 14–40–14 °C region. The blue and black samples have approximately closed loops but a small colour difference was obtained even after one cycle for the red one thus the loop remains slightly opened. The colour of all samples also depends on the UV dose applied at curing. This difference was followed over the whole hysteresis loop. The largest values were measured for the red sample where the CIEDE2000 total colour difference rises above 4 and remains well observable all over the temperature region applied for cycling. One of the possible reasons for this effect might be different degree of polymerisation of the polymer matrix achieved by different UV curing.
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