| Abstract | Istraživanja materijala tehnologija aditivne proizvodnje uglavnom su fokusirana na istraživanja mehaničkih svojstava. Primjena ovih tehnologija u području gdje su bitna vizualna svojstva zahtijeva dodatna istraživanja definiranja boja 3D otiska. U disertaciji se definira utjecaj UV zračenja i debljine materijala stereolitografske tehnologije na kolorimetrijska svojstva otiska. Fotopolimerne smole će se pomiješati s pet bojila grafičke reprodukcije (cijan, magenta, žuta, bijela, crna) te izmjeriti spektralne vrijednosti, izraditi spektralne krivulje uzoraka i definirati kolorimetrijske vrijednosti u CIE Lab i LCh sustavu. Za pojedine debljine i boje 3D otisaka odredit će se refleksijske i transmisijske kolorimetrijske vrijednosti te razlike i smjer promjene boje tijekom UV zračenja. Temeljem provedenih ispitivanja se definirat će se ovisnost kolorimetrijskih vrijednosti 3D otisaka o vremena UV zračenja i debljin materijala u svrhu optimizacije stereolitografske aditivne proizvodnje. |
| Abstract (english) | Materials research in additive manufacturing is mainly focused on the study of mechanical properties. The application of these technologies in an area where visual properties are essential requires additional research on colors defining of 3D prints. The effect of UV radiation and the thickness of stereolithographic resin on the colorimetric properties of the print is defined in the dissertation. The materials will be mixed with five graphic reproduction dyes (cyan, magenta, yellow, white, black) and spectral values measured, producing samples spectral curves and defining colorimetric values in the CIE Lab and LCh system. For individual thicknesses and colors of 3D prints, the reflection and transmission colorimetric values, the differences and direction of color change during UV radiation will be determined. Based on the performed tests, the dependence of the colorimetric values of 3D prints on the UV radiation time and the material thickness will be defined to optimize stereolithographic additive production.
Methodology
In order to confirm the set hypotheses, 3D sample models will first be created using a CAD computer program. A CAD environment is used to meet the need for strict measurement tolerances of the samples. After creating a computer 3D model, the file is saved in STL format. The measuring samples are designed as a series of tiles from 0.8mm to 5mm thick. The thickness of the measuring samples increases by 0.2 mm, so a total of 22 measuring samples are obtained.
For research purposes, the addition of dyes to the base polymer defines five base colors wich are cyan, magenta, yellow, black and white. The test specimens are first washed in a solvent that removes the unpolymerized material, and then additional drying of the 3D prints by UV radiation is required. In order to investigate in detail the influence of drying on the colorimetric properties using a spectrophotometer, the spectral information of each sample is measured while in the green state. Then each sample is dried at time intervals of 15 minutes. Drying of the samples takes place in a UV chamber under controlled measuring conditions. After each interval, the spectral information is measured again in order to determine the effect of drying on the colorimetric properties of the material. Based on the measured spectral and chromatic data, an analysis of the influence of changes in material thickness and time intervals of UV radiation on the colorimetric properties of 3D prints is performed. The color change is displayed as a value of ΔE00, with a description of the direction of change.
Main results
The hypothesis that the change in material thickness in the process of stereolithographic additive production affects the colorimetric properties of a 3D impression has been confirmed. Test specimens have very large color changes when looking at the transmission properties of the specimens. If the reflection properties of the samples are observed, a noticeable change is in thinner materials while thicker samples have a much smaller color change. Each combination of the base photopolymer and dye has different colorimetric characteristics, but in general, we look at the color change values the largest changes occur in thinner samples. The effect of 3D print drying on colorimetric properties was investigated.
Drying changes the colorimetric properties, the biggest changes are noticed after the first drying intervals. In general, observing the measurement results, it can be seen that the brightness and chromaticity decrease. The direction of the tone change depends on the dye. Analyzing the transmission and reflection characteristics of the test specimens, the color changes that occur are most noticeable in the thinnest specimens. The total color change is the least in black dye, while the largest changes are seen in transmission and reflection in test dyes with white dye. The direction of color change was determined for each group of dye test specimens. The test samples with black dye have the least total color changes, and the value of ΔE2000 does not exceed the value of 0.15, which is a negligible change. A total color change with a vrijednostiE2000 value greater than 4 was obtained for white dye samples. |
