It is well known [1-3] that the m e c h a n i c a l p r o p e r t i e s of polymers, as of other solid m a t e r i a l s , can be substantially affected by the surrounding medium. The changes produced are e x t r e m e l y diverse and are due not only to c h e m i c a l r e a c t i o n s but also to r e v e r s i b l e physicochemical p r o c e s s e s . In this case, the selectivity of the effect of the working medium is determined by the m o l e c u l a r nature of the m a t e r i a l s , by the i n t e r m o l e c u l a r interaction of the chains of the m a c r o m o l e c u l e s , and by p r o c e s s e s taking place over the c o u r s e of time, such as penetration of the medium into the p o l y m e r under investigation (by volumetric diffusion and by m i g r a t i o n along defects), swelling of the material, orientation of the m a c r o m o l e c u l e s , and other s t r u c t u r a l changes . Consequently, the stability of the p r o p e r t i e s of photopolymeric printing f o r m s which, under the conditions of their use, are subjected to the combined action of mechanical s t r e s s e s and liquid media (coloring agents, solvents and their binders, moisture, etc.), m a y vary, which has a substantial effect on the quality of the printing. T h e r e f o r e , an investigation of the effect of the working media used in printing on the deformability, the s e r v i c e life, and other p r o p e r t i e s of photopolymeric f o r m s is of g r e a t importance for the polygraphic industry. T h e r e are p r a c t i c a l l y no papers devoted to this problem since, at the p r e s e n t time, photopolymeric printing f o r m s are undergoing s e m i - w o r k s t e s t s in s e v e r a l polygraphic e n t e r p r i s e s in the Soviet Union. We give below the r e s u l t s of a study of the effect of working media on some of the p r o p e r t i e s of printing f o r m s made of mixed polyamides, developed at the I. Fedorov Ukrainian P o l y g r a p h i c Institute. The kinetics of the deformation of photopolymeric printing f o r m s , held previously in various media, as well as under various a t m o s p h e r i c conditions, were investigated using a method proposed e a r l i e r . The objective indices of the deformation p r o p e r t i e s of the printing f o r m s were calculated on the basis of data obtained in
~ t, days Fig. 1
Fig. 1. Relative maximal deformation of photopolymeric printing forms, held in various media: 1) water; 2) 96% ethyl alcohol; 3, 4, 5) turpentine, kerosene, mixture of turpentine and kerosene (1 : 1); 6, 7, 8) weak drying oil, medium drying oil, GLF11-300 drying oil. Fig. 2. Change in the fraction of the elastic-resilientdeformation of photopolymeric printing forms, held in various media: 1, 2, 3) turpentine, kerosene, mixture of turpentine and kerosene (1 : 1); 4, 5, 6) weak drying oil, medium drying oil, GLFll-300 drying oil; 7) water; 8) 96% ethyl alcohol.
I. Fedorov Ukrainian Polygraphic Institute; L'vov. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 8, No. 2, pp. 102-104, March-April, 1972. Original article submitted March 9, 1971. 9 Consultants Bureau, a division of Plenum Pu.blistling Corporation, 227 I~'est 17th Street, .Vow }or/,, Y. Y. )0012. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any .form or D) any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the p~b/isher. I copy of this ortiele is available from the publisl~er for $15.00.
a study of the kinetics of deformation under a load (30 k g / c m 2) and after r e m o v a l of the load (1 kg/cm2). The change in weight of the photopolymeric f o r m s and the profile of a printing element were also determined. In a m a j o r i t y of the working media (Figs. 1 and 2), the deformation p r o p e r t i e s of photopolymeric printing f o r m s , i.e., the relative maximal deformation emax, the fraction of elastic eelas, r e s i l i e n t e r e s deformations (in %, r e f e r r e d to emax) varied only slightly. Thus, for example, with testing of samples in kerosene, turpentine, a mixture of turpentine and kerosene (1 : 1),and in other media, during the f i r s t 24 h there is observed a certain d e c r e a s e 5 ~ t, days in the plastic deformations of the m a t e r i a l and a corresponding Fig. 3. Kinetms of the swelling of i n c r e a s e in the e l a s t i c - r e s i l i e n t d e f o r m a t i o n s , while in water and photopolymeric printing f o r m s in in 96% ethyl alcohol there is an appreciable i n c r e a s e in emax and the binders of coloring agents and in the fraction o f e r e s . The r e s u l t s of swelling tests c o r r e l a t e with in their solvents: 1) water; 2) 96% these data (Fig. 3): in a m a j o r i t y of working media there is a ethyl alcohol; 3) mixture of turpensmall limited swelling, and in 96% ethyl alcohol and water a contine and kerosene (1 : 1); 4) turpensiderable degree of swelling. The change in the e l a s t i c o - e l a s t i c tine; 5) kerosene; 6, 7, 8) weak p r o p e r t i e s of a m a t e r i a l under the effect of the media is obviously drying oil, medium drying oil, connected with facilitation of the slipping of individual elements G L F l l - 3 0 0 drying oil. in the links of the m a c r o m u l e c u l a r chains, included between the nodes of a joint, with r e s p e c t to one another; this is the r e s u l t of an i n c r e a s e of the i n t e r m o l e c u l a r interaction in the m a t e r i a l in the presence of a sorbed substance, tn addition, the affinity of ethyl alcohol for polyamide, and its ability to form single-ended hydrogen bonds, explain the r e a s o n s for the r e l a t i v e l y high deformability of photopolymeric printing f o r m s held in this medium.
Natural and synthetic binders for coloring agents have practically no effect on the deformation p r o p e r ties of the f o r m s (Figs. 1 and 2), although these media are in continuous cbntact with the photopolymeric printing f o r m s during the printing p r o c e s s . Thus, the stability of the mechanical c h a r a c t e r i s t i c s of photopolymeric f o r m s can vary, depending on the duration of the contact between the m a t e r i a l and the liquid, and on the physicochemical p r o p e r t i e s of the forms. However, since in use the photopolymeric printing f o r m s are, as a rule, subjected only for a s h o r t period of time to the action of wetting agents, i.e., benzene, kerosene, a mixture of kerosene and turpentine, etc., they should not be expected to have any significant effect on the deformation p r o p e r t i e s of the f o r m s , which could be reflected to any considerable extent in the quality of the printing. Actually, an industrial tests of the printing capacity of photopolymeric f o r m s has shown that after 500,000-600,000 i m p r e s s i o n s the quality of the printing r e m a i n s sufficiently high. On the basis of what has been said above, the conclusion m a y be drawn that the physicochemical media used in printing do not worsen the physicomechanical p r o p e r t i e s of photopolymeric f o r m s after 500,000-600,000 i m p r e s s i o n s . LITERATURE 1. 2. 3. 4.
A . N . Tynnyi and A. I. Soshko, Fiz.-Khim. Mekhan. Mat., No. 3 (1965). A . N . Tynnyi, N. A. Oltkhovich-Novosadyuk, A. I. Soshko, N. G. Kalinin, and O. A. Mikityuk, F i z . Khim. Mekhan. Mat., No. 4 (1969). E . D . Shchukin, A. I. Soshko, O. A. Mikityuk, and A. N. Tynnyi, Fiz.-Khim. Mekhan. Mat., No. 2 (1971). F . S . Savitskii, V. M. T r e m u t , S. F. Mikhailishin, and F. S. Martynyuk, Modern Flexographic P r i n t i n g [in Russian], Moscow-Kiev (1969).