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Melamin d.d. Kočevje že vrsto let izdeluje AKD klejiva za klejenje papirja in kartona. AKD klejiva so vodne disperzije voska alkilketen dimera velikosti delcev okoli 1µm. V letošnjem letu smo v Melaminu d.d. Kočevje nabavili aparaturo za določanje porazdelitve velikosti delcev. Aparatura omogoča določitev velikosti delcev tako suhih kot tudi tekočih vzorcev v območju med 0,04 in 2000 µm. Namen diplomske naloge je bil določiti porazdelitev velikosti delcev AKD disperzij rednim industrijskih šaržam kot tudi analizirati laboratorijske vzorce v fazi razvoja novih tipov AKD klejiv. Pri svojem praktičnem delu sem ugotovila, da ima stabilna AKD disperzija delce velikosti pod 1 µm. Večina delcev ima velikost v območju med 0,1 in 0,7 µm. Je pa lahko v disperziji prisoten tudi manjši del večjih delcev velikosti 100 in več µm. Ti delci so posledica nerednega čiščenja proizvodne linije in skladiščnih posod in se odstranijo s filtracijo produkta. Ugotovila sem, da pri določanju velikosti delcev stabilne disperzije ni potrebna posebna priprava vzorca. Vzorca ni potrebno homogenizirati, rezultati so neodvisni od mesta vzorčenja (dno ali vrh posode). Dovolj je tudi, da določitev izvedemo v dveh paralelkah. Pokazalo se je, da je podatek o velikosti delcev pomemben zlasti v primeru okvar na dispergatorju med procesom izdelave disperzije ali napak v tehnološkem procesu. Velikost delcev je prvi pokazatelj, ali bo disperzija dovolj stabilna ves čas zagotovljene stabilnosti, to je vsaj 2 meseca, ali bo morda po določenem času prišlo do ločevanja disperzije, to je koncentriranja AKD voska na površino. Ugotovila sem, da v kolikor ima večina delcev velikost nad 1 µm, obstaja velika verjetnost, da bo prišlo po določenem času skladiščenja do ločevanja disperzije. Največkrat se to opazi šele potem, ko je izdelek že pri kupcu. Z določitvijo porazdelitve velikosti delcev pa je mogoče preprečiti morebitne reklamacije zaradi nestabilnosti disperzije. ABSTRACT For several years Melamin d.d. Kočevje has been producing cationic AKD sizing agents for sizing paper and cardboard. AKD sizing agents are water dispersions of alkyl ketene dimer wax, particle size approximately 1 µm. This year Melamin d.d. Kočevje purchased equipment for determination of particle size. It allows determination of particle size both in dry and liquid samples, within the range between 0.04 and 2000 µm. The aim of my thesis is to test the distribution of particle size in AKD dispersions for regular industrial batches, and to analyze laboratory samples during the phase of development of new types of AKD sizing agents. Through practical tests it was established that within a stable AKD dispersion the size of particles is below 1 µm. Most of the particles range between 0.1 in 0.7 µm. The dispersion can include a smaller number of larger particles of size 100 µm or more. These particles are a result of inadequate cleaning of the production line and storage containers, and can be removed by filtering. It was established that at determination of particle size of stable dispersion no special preparation of samples is necessary. The sample needs no homogenisation, and the results do not depend on the position from which the sample was taken (bottom, or top of the container). Double particle determination is enough. I established that the data regarding particle size is important mainly in case of dispergator malfunction during the process of preparation of dispersion, or faults in the technological process. The particle size is the first indication whether the dispersion will remain stable during the assured stability period, i.e. at least two months, or the separation of dispersion is to be expected after a certain period of time, due to the surface concentration of AKD wax. I also established that if the size of most of the particles measure more than 1 µm, the probability that after a certain time the separation of the dispersion will occur is large, which is most often observed after the product has already been delivered to the customer. By determining the particle size we can prevent eventual claims due to unstable dispersion. Ključne besede alkyl ketene dimer dispersions, particle size distribution, laser granulometer, dispersion stability |
