Journal of Photopolymer Science and Technology Volume 5, Number 3 (1992) 453-460 APPLICATIONS OF ROSIN-MODIFIED EPOXIDIZED SOYA BEAN OIL ACRYLATE IN UV CURE COATINGS SHI WENFANG JIANG VU and LIU HEWEN Diepartment o f Applied Chemistry, University o f Science and Technology o f China, Hef ei, Anhui 2300 26, P. R. China The cured films of epoxidized soya bean oil acrylate containing a- bietic group will exhibit a variety of properties by the proper choice of their components' ucture and molecular weight. In this paper, the general properties of the rosin-modified epoxidized soya bean oil acrylate, such as adhesion, cure rate, glossiness, chemical and abrasion resistance, are discussed and compared with other oligomers without abietic group. 1. Introduction Ultraviolet (UV) curable coatings have enjoyed a continued growth since their commercial introduction as wood finishes in the 1960's. The growth is result of the u pique advantages which UV technology offers for the formulators and end users. Initially, energy saving and pollution consideration were of primary importance. Today, the properties of cured films, such as adhesion, glossiness, flexibility, abrasion and chemical resistance and cost have become important considerations. In spite of these advantages, one deficiency associated with UV cure coatings has Received April 20, 1992 Accepted July 11, 1992 453
J. Photopolym. Sci. Technol., Vol. 5, No.3, 1992 has hindered the growth of UV technology. This deficiency centers round the difficulty of obtaining adequate adhesion, rapid curing, high gloss and low cost price in the meantime. In view of high cost of radiation curable oligomers, the development of these oligomers based on the indigenous materials such as rosin and soya bean oil are of prime importance to a country like China. Rosin and dieter rosin, being high molecular weight and produced by dimerization of unsaturated rosin acids, react with epoxidized soya bean oil and were converted further photo-curable oligomers. Therefore, we have studied such systems in this paper involving use of rosin - modified epoxidized soya bean oil acrylate, addition of multifunctional acrylate monomer, a photof ragmenting initiator, and photoinitiation of the cure reaction using UV irradiation. 2. Experimental (1)Materials Epoxidized soya bean oil, rosin and acrylic acid as modifiers are used for synthesis endcapping of abietic group and double bond, respectively. For the curing, vinyl acetate (VAc), trimethylolpropane triacrylate (TMFT'A) and Irgacure 1$ 4 are added as reactive diluent monomers and photoinitiators, respectively. Steel and copper as substratesare used with cleaning or pretreatment as usual. Infra - red spectrum of the curing film is recorded on a Perkin - Elmer 1710 Fourier Transform Spectrometer. (2) Preparation of Rosin-modified epoxidized soya bean oil acylate (RE-resin) The RE - resins are prepared by a two - step condensation reaction. In the first step, rosin reacts with epoxidized soya bean oil, then the residual epoxy groups of e- poxidized soya bean oil react with an excess of acrylic acid which is slowly added during vigorous stirring in the second step. The resultant RE-resin which has following formula is stored under refrigerator until used. CH2 = CHCOO - CHRCHR'C CH2 = CHCOO - CHRCHR'COOCH H2 A - OOC - CHRCHR'CO0CH2 Al - abietic group A2 -hydrogenerated A3 -dimeric abietic group abietic group 454
J. Photopolym. Sci. Technol., Vol. 5, No.3, 1992 The degree of conversion of carboxyl group in two steps are shown in Fig. 1. (3) Processing A given amount of reactive diluent monomer and photoinitiator are added to the RE -resin systems using a glass rod for stirring, and then uniformly coated on different substractes with special coater. The samples are UV irradiated in a W - cure device constructed in our laboratory at a distance of 100mm from the mercury lamp (80w/cm). Fig. 1 The Relationship between Reaction Degree of Garboxyl Groups and Reaction Time in Two Steps (4) Testing methods of general properties. Table 1 shows the testing methods of UV cured coatings. Table l Testing Methods of General Properties 455
j Photopolym. Sci. Technol., Vol. 5, No.3, 1992 3. Results and Discussions (1) Increasing Cure Rate The formulations with RE-resins exhibit increasing cure rates as compared with epoxidized Soya bean oil acrylate (ESOA ) and urethane acrylate (UA ) oligomers alone, and high efficiency to promote curing of the films with RE/UA and RE/ESOA compositions, as shown as Table 2. Tablet Increasing UV cure rates of coatings with RE-resins It is well - known that cure rate of coating is effected seriously by many factors including oxygen inhibition. It was reported that acrylated urethane is a high efficient photopolymerizable oligomer and insensitive to oxygen inhibition. Table 2 shows that the rate of photopolymerization of formula with UA is much high compared to correspondent with ESOA oligomer. However, replacement of UA or ESOA by RE-resin partly in the formula increases cure rate considerably. two times higher. In the case of ESOA, it is even These results show that the conjugate double boud of abietic group provides higher reactivity to photopolymerization compared to acryloyl group of ESOA and are unaffected by the usual inhibition of molecular oxygen which is probably related to particular position of double bonds. on the other hand, the reaction of unsaturated abietic group can be seen from IR measurement (Fig 2). 456
J. Photopolym. Sci. Technol., Vol. 5, No.3, 1992 The IR absorption peaks of the thin film of the RE - resin at 970, 925, 800, 7 3 0 cm4 due to C = CH decreased upon exposure with irradiation time. Fig. 2 The Changes of IR Absorption Peaks of Film with Irradiation Time (2) Film Properties of RE-resin The EB or 1W curing process has some disadvantages, one of which being that the coatings formed have in general poor adhesion to metal substrates. This is probably due to instantaneous formation of three dimentional structure and apparently bigger volume shrinkage. However, the adhesion can be improved by introducing of abietic group which possesses voluminous phenanthrene nucleus into the formula of ESOA oligomer, as shown in Table 3 and Table 4. Table 3 Adhesion of RE-resin and Other Acrylates to Metal 457
J. Photopolym. Sci. Technol., Vol.5, No.3, 1992 Table 4 Effect of RE-resin to adhesion The other properties of paints containing RE - resin, as shown in Table 5 can be explained perfectly on the base of molecular structure. RE - resin contains different types of reactive group ; vinyl group, unsaturated obietic group and acrylate group. Large and hard abietic group containing also vinyl group (except of RE- 2) works as a plasticizer and can be copolymerized with monomer to produce internal plasticization of the crosslink networks. On the other hand, the tight phenanthrene nucleus structure of abietic group can help prevent from chemical penetration. Constantly, obtained tough curing films possess excellent chmical resistance, such as solvent, acid and base. The internal plasticization and copolymerization of the coating permit relaxation to absorb the strain produced by impacting. Table 5 Other properties of the RE-resins 458
J. Photopolym. Sci. Technol., Vol.5, No.3,1992 4. Conclusions The rosin-modified epoxidized soya bean oil acrylate has been developed instead of expensive photopolymerizable materials and upgrade the performance of paint with epoxy and urethane acrylates. The resin exhibits low viscosity, excellent adhesion, rapid curing rate, high glossiness and improved chemical resistance compared to conventional UV polymerizable oligomers. References 1. George Pastemaclc, Radiation Curing (1983) 9. 2. Byron K. Christmas, Radiation Curing (1985) 9. 3. R. C. Whisteside, P. S. Shein and J. L. massinggill, J. of Coatings Technology, 62, zb._a (1990) 61. 4. V. P. Janakey, Z. M. Jazeps, EP. 02735565. 459