UV-ışınları ile sertleştirilen polimerik filmlerin hazırlanması, karakterizasyonu ve uygulama alanları

Abstract

UV-IŞINLARI İLE SERTLEŞTİRİLEN POLİMERİK FİLMLERİN HAZIRLANMASI, KARAKTERİZASYONU VE UYGULAMA ALANLARI ÖZET 1970'lerde ortaya çıkan enerji ve çevre sorunlarına çözüm bul mak amacı ile kaplama endüstrisinde yapılan araştırma ve geliştirme çalışmaları yeni kaplama tekniklerinin doğmasına yol açmıştır. Bu tekniklerden biri olan UV (ultraviyole) - ve EB (elektron demeti) - ışınları ile sertleşebilen kaplamalar pekçok alanda yaygın olarak kullanılmaktadır. İlk olarak 1960'larda Batı Almanya'da mobilya en düstrisinde kullanılan UV-ışmları ile sertleşebilen kaplamaların en önemli uygulama alanları; ahşap, metal, kağıt, karton ve plastik en düstrisi gibi alanlardır. Uygulanmasında çözücü veya inceltici gerekmediği için maliye ti, ilk yatırımı, ayrıca çevre kirliliğini ve sağlık sorunlarını azaltmaktadır. UV-ışınları ile sertleşebilen bir kaplama formülasyonunda en az üç bileşen bulunmaktadır; doymamış oligomerler, reaktif seyrelti- ciler ve fotobaşlatıcılar. Bunların yanında pigmentler, boyalar, kö pük bastırıcılar, ıslatıcılar gibi reaktif olmayan özel kimyasal kat kı malzemeleri de kullanılmaktadır. Bu çalışmanın ilk aşamasında, izosiyanatoetil metakrilattan (IEM) çıkılarak üç değişik poliglikolden, polietilen glikol (PEG-200), poliester poliol (T-1136), polikaprolakton poliol (PCP-0310) ve ayrıca izoforon diizosiyanat (IPDI) ile polipropilen- glikol monometakrilat (PPGMM) tan akrillenmiş poliüretan oligomerleri hazırlanmış ve İR- ve 1 H-NMR-spektrum yöntemleri ile karakterize edilmiştir. İkinci aşamada, reaktif seyrelticilerin tip ve konsantrasyon larının ve ayrıca fotobaşaltıcı konsantrasyonunun filmlerin fiziksel özelliklerine etkileri 33 değişik örnek hazırlanarak incelenmiştir. Elde edilen filmlerde polimerizasyonun yürüyüşü IR-spektrum yöntemi ve Soxhlet ekstraksiyonu ile jel miktarının bulunması ile incelenmiş tir. Serbest film örneklerinde tensilon kullanılarak gerilme-şekil değiştirme testleri, kaplanmış sac plakalarda ise yapışma, esneklik, darbe direnci, sertlik, parlaklık gibi testler uygulanarak hazırlanan örneklerin kaplama malzemesi olarak etkinlikleri incelenmiştir. Bu çalışmaların sonunda, hazırlanan polimerik filmlerin meka nik özelliklerinin, reaktif seyreltici ve fotobaşlatıcı konsantras yonlarına ve ayrıca seyreltici tipine bağlı olduğu gözlenmiştir. Yukarıda belirtilen mekanik test sonuçlarından bu çalışmada hazırlanan UV-ışınlarma duyarlı bazı örneklerin çeşitli alanlarda kaplama malzemesi olarak kullanılabileceği bulunmuştur. - v

THE PREPARATION, THE CHARACTERIZATION, AND VARIOUS APPLICATIONS OF UV-CURED POLYMERIC FILMS SUMMARY Coatings have been used since prehistoric man applied mineral pigments bonded with fats to create their cave printings. Today coating industry is an important segment of the chemical industry and coatings are produced from a wide variety of organic resins, metals and inorganic materials using techniques of increasing technological sophistication. Energy related and ecological events of the 1970s have significantly influenced research and development activities in the coating industry. The industry reacted to these problems by introducing new coating technologies, such as high solids waterborne, powder and radiation curable coatings. Despite the relative newness of radiation curable coatings, which was designed for use under ultraviolet (UV) or electron beam (EB) radiation have made important penetration into various sectors of the coating industry by displacing conventional coating materials. UV-curable coatings was first commercialized in West Germany in the 1960s for furniture finishing. The major markets for UV-curable coating in the world are for: o Wood (fillers, sealers, top coats) o Metal (base coats, clear coats, coatings for can, bottle caps, metal furniture) o Paper and paperboard (clear, overprint varnishes) o Flexible and rigid plastics o Miscellaneous (magnet wire, magnetic tape, adhesive, dental applications, optical fiber and others) - viThe main advantages of UV-curing include; o Elimination of solvents or thinners for application o Great minimisation of the pollution and health hazards o Elimination of the cost of such solvents o Very rapid cure at ambient temperatures, requires very low energy o Ability to coat heat sensitive substrates such as polyethylene, polypropylene without detrimental effects due to heat o Low capital investment o Less plant floor space requirement o Excellent film properties and performance A UV-curable coating formulation include at least the fololwing components; unsaturated oligomers, reactive diluents, photoinitiators, nonreactive speciality additives. The most important of these components in determining mechanical properties is the reactive oligomer: For this reason, most of the desired coating properties must be built in the oligomer. Therefore, the molecular design of radiation sensitive oligomers has been a major concern in the recent years. Most of the oligomers contain an acrylate functionality since this type of unsaturation provides the highest response to actinic light compared to methacrylate, vinyl or ally functionality. Acrylated urethanes, as a class, combine the well known properties specific to conventional urethane coatings, such as high abrasion resistance, thoughness, tear strength and good low temperaure properties with the superior optical properties and weatherability of poly- acrylates. Although the unsaturated oligomer is the most important component in determining the ultimate properties of the coatings, it usually can not be used alone. Most of the oligomers have high viscosities, low curing speeds, low cross-link densities, or deficiencies in their performance. Therefore various reactive diluent systems are used to overcome above shortcomings. For this - vii -purpose generally two types of reactive diluents are used; monofunctional and multifunctional. In general, they improve substrate wetting and for this reason, may improve adhesion. Relatively non volatile multifunctional monomers, are used to influence curing rate, cross-link density and viscosity. These monomers are types of acrylate and methacrylates. The following multifunctional acrylates are widely used in many formulations: 1,4 butanediol diacrylate (BDODA), tetraethyleneglycol diacrylate (TTEGDA), trimethylolpropane triacrylate (TMPTA), 1,6 hexanediol diacrylate (HDODA), thiodiethyleneglycol diacrylate (TDGDA), pentaerythritol triacrylate (PETA), glycerol propoxy triacrylate (GPTA). The principal function of monof unctional monomers is to reduce viscosity, however it is not their only function, they may modify the final properties of the cured film. Some commonly used monof unctional monomers are: phenoxyethyl acrylate (PEA), isobornyl acrylate (IB A), N-vinyl pyrrolidone (NVP), tetrahydrof urf uryl acrylate (THFA). The photoinitiators, as is apparent from their nane, start the whole curing reaction, on exposure to UV-light. The major classes of photochemical reactions used to prepare polymers are polycondensation and active center polymerizations. The photoinduced active center polymerizations are radical, cationic or anionic. In radical polymerizations, the photoinitiator initiate the curing reaction by forming free radicals after absorbing the UV energy. There are two major groups of photoinitiator systems. In the first group UV energy is absorbed by a molecule which undergoes intramolecular photocleavage to form free radicals, absorbing molecule is called as photoinitiator. Such as, benzoin ethers (isopropyl benzoin ether, isobutyl benzoin ether, methyl phenyl- glyoxylate), benzil ketals (2, 2-dimetoxy-2-phenyl acteophenone and hydroxy cyclohexyl phenyl ketone), acetophenone derivatives (diethoxy acetophenone and l-phenyl-2-hydroxyl-2-methylpropan-l-on), ketoxime esters [l-phenyl-1,2 propane dione-2-( o-ethoxy carbonyl) oxime]. In the second group, the excited molecule transfers its energy to another molecule which, dissociates and produces free radicals. The initial absorber is called a photosensitizer, and the dissociat ing molecule is called as coinitiator. - vxxx -Other components which often appear in radiation curable-systems are nonreactive speciality chemicals such as pigments, dyes, extender pigments, defoamers, wetting agents, flatting agents, adhesion promoters, slip aids. Commercial acrylated urethane oligomers are normally prepared by a two step procedure. Polyether or polyester based macroglycols are sequentially tipped by an aromatic diisocyanate such as toluene diisocyanate (TDI), xylidine diisocyanate (XDI), cycloaliphatic isophorone diisocyanate (IPDI) and then by a hydroxyalkyl acrylate such as 2-hydroxyethyl acrylate (HEA), 2-hydroxy- ethyl methacrylate (HEMA), etc. Isocyanatoethyl metha- crylate (IEM) combines the acrylate and isocyanate functionality into one molecule, thereby eliminating one step in the oligomer synthesis. At the first stage of our work, four series of acrylated urethane oligomers have been prepared based on four different polyols namely, polyethyleneglycol (PEG-200), polyester polyol (T-1136), polycaprolactone polyol (PCP-0310), polypropyleneglycol monomethacrylate (PP?MM). IEM based acrylated urethane oligomers were synthesized by slowly adding two moles of IEM into a nitrogen-purged, dried reaction flask containing one mole of vigorously dried polyols (PEG-200, PCP-0310, T-1136). The temperature was kept at 35±2 C to avoid thermal poly merization of unsaturated acrylate groups. After IEM addition was completed, about 0.08% (by weight) stannous dilaurate (T-12) was added and eight hours were allowed to complete the reaction. During this reaction period, reaction flask was purged with dried oxygen as an additional precaution to stop polymerization. Similar method was used for the preparation of IPDI/PPGMM type of acrylate polyurethane. Before UV-curing, to ensure stable shelf life, less than 100 ppm of hydroquinone (HQ) was added into the product as an inhibitor. Acrylated polyurethane structures were characterized by investigation of IR-and -4i- NMR-spectra. In IR-spectra, the complete disappearance o_£ assymmetric stretching vibration bands at 2275 cm which is characteristic for -NC0 _group and disappearance of hydroxyl bands at 3600 cm and finally appearance of stretching vibration band of ^N-H at 3350 cm` which is characteristic for urethanes, were all used to monitor the extend of reaction in prepolymer preparations. In the H-NMR~spectra of products disappearance of hydroxyl protons signals and appearance of ^NH carbamide protons at ^6 ppm showed that the reaction has been completed. - ix -At the second stage of our work, the effects of reactive diluent type and concentration and photoinitiator concentration on the physical properties of the UV-cured acrylated polyurethane films and coated cold rolled steel were investigated. When radiation curable coatings were first introduced to industry, cured film properties were generally characterized in terms of surface film dryness, solvent resistance and tape adhesion. As the use of radiation curable coating has broadened over the years, more extensive test procedures have been required to determine cured film performance. For this purpose 33 different formulations were prepared and systematically investigated. In these formulations acrylated polyurethane oligomer content was kept as high as 78-99% (by weight) and photoinitiator concentration was kept around 1-3% (by weight), and the reactive diluent content was varied between 5-20% (by weight). Homogeneously mixed liquid samples were poured into teflon coated molds to obtain free films for tensile tests and some of them were also used as a coating material on sand blasted cold rolled steel in order to find out coating performances. These samples were irradiated for 2.5 minutes from one side, using a 300 W Osram Ultravitalux lamp as the UV- source. The gel fraction of the cured free film samples were determined by Soxhlet extraction using acetone and gel contents were found above 95% in all samples. Infrared spectra of thin polymer films cast on KBr plates and covered with thin clear Teflon film were taken before and after UV-irradiation. The rate of polymeriza tion was followediy noting the rate of disappearance of the `olefinic` 810 cm peaks in the infrared with the use of a Teflon film in the reference cell, and calculating absorbance from the peak height by the baseline technique. Stress-strain measurements were obtained at room temperature by using table and floor models Instron tensile testing machines. Also, film thickness, gloss retention, adhesion test, conical mandrel film flexibility test, cupping test, reverse and direct impact test, and pendulum hardness test were applied onto coated substrate. In this work it has been shown that mechanical properties of all the polymeric films prepared were depend - x -on the concentration and type of the reactive diluent used as well as on the concentration of the photoinitiator. Stress-strain and Young modulus values of the polymeric films showed that these films were suitable as coating materials. Performance tests on coated substrates were also indicated that some of the formulations developed in this work, can be used as coating materials in various fields. xi -