344
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 344-350
Wear of Anodized Aluminum-Polymer Lithographic Printing Plates John W. Noble, 111, and Henry Leldhelser, Jr.” Center for Surface and Coatings Research, Lehigh University, Bethlehem, Pennsylvania 180 15
An accelerated test for determining the wear resistance of polymer-coated, anodized aluminum lithographic plates has been developed. The test involves a cyclic backand-forth motion of a weighted block against a lithographic plate immersed in an aqueous solution typical of that used commercially and suspended 0.3-pm alumina particles. The number of cycles to reduce the image quality significantly, as determined by a manual printing test, determines the resistance to wear of the plate samples. A number of commercial and experimental lithographic plates was studied, and their comparative wear resistance was determined. Lithographic plates deteriorate by wear and/or corrosion by three main mechanisms: (1) loss of adhesion of the photopolymer to the substrate; (2) pitting of the anodized aluminum in non-image areas; and (3) abrasive loss of material from both the polymer and anodized aluminum.
Introduction One of the important criteria in appraising the quality of a lithographic plate is the duration of good image reproduction on the press. The loss of a high-quality image by deterioration of the plate is characterized as wear. Wear appraisal consumes large quantities of press time, paper, and labor since the deterioration of high-quality polymer-aluminum plates occurs at upwards of 500 000 impressions. Lithography is a widely used printing technique and considerable technology is involved in the development of new plates. A rapid laboratory test would be of great value in the preliminary appraisal of new and existing plates. Such an accelerated test has been developed and is discussed in the following report. Published information on the mechanism of wear of lithographic plates and accelerated wear tests for studying lithographic plates is scant. Studies of plate wear are performed largely on press-run plates. Often plates are “overpacked” on the press by adding additional backing to the plate during in-press operation. This modification decreases the time of the press run to deteriorate the plate but still involves considerable expense. Previous examinations of press-worn plates have been accomplished primarily by optical and electron microscopy. Conventional metallographictechniques such as imbedding in plastic and replication supplemented these studies (Dean et al., 1972; Dean and Ford, 1973). An unpublished test is used by the ink industry in the appraisal of lithographic inks and their effect on the wear of plates. This laboratory wear test is one in which a rotating disk cut from a plate is pressed against a pad containing ink. The experimental parameter is the weight loss under specific operating conditions. The test also includes exposure of the sample to solvents or fluid carriers used in the formulation. Experimental Procedures Characterization of Wear. In order to develop an accelerated laboratory test, characterization of wear is absolutely essential. The value of such a test is dependent on its ability not only to reproduce the wear obtained in practice, but also its ability to give quantitative and reproducible results. The quantitative evaluation of worn lithographic plates is subjective in nature since the viewer sets the standards for the quality of image reproduction on the press. Early experiments involved examination of new and press-worn commercial plates. The characterization of press wear not only aids in understanding but also serves
Table I
plate designation commercial diazo plate commercial Plate A commercial plate B commercial plate C commercial plate D
anodized surface roughness, in. 24 (mech. grain) 40 (etch)
type of anodization
post treatment silicate hot H,O
17 (etch)
silicate
20 (etch)
silicate
35 (etch)
22 (mech. experimental plate no. 1 grain) experimental 22 (mech. plate no. 2 grain) experimental 22 (mech. plate no. 3 grain) positive plate E 22 (mech. grain) positive plate F 39 (etch) positive plate G 15 (etch) positive plate H 1 7 (etch)
silicate silicate silicate silicate
silicate silicate
as a reference against which laboratory test data can be compared. Topographical features and chemical nature of the plates were emphasized and were studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray fluorescence analysis, and surface roughness as detected by a traveling stylus. Table I lists the different materials included in the study. Both normal and overpacked press-worn plates were studied. Microstructure. A reflectance optical microscope was used for low magnification (up to 500X) examination. Samples were as large as 6 X 6 in., and no special sample preparations were required. Both the anodic oxide and polymer areas were observed and photographs were taken to illustrate typical observations. Scanning electron microscopy (SEM) provides images with detail, magnification, and depth of field unavailable from optical microscopy. Samples were sheared so as to be less than 2 cm square and were mounted on studs with a conductive carbon paste. Accelerating voltages of 20 kV and large tilt angles (40’) gave the best results. Conductivity was poor in the presence of oxide or polymer films and graphite films deposited by evaporation were occasionally used to enhance conductivity. A magnification of 3000X was found useful for comparisons, although a
0196-4321/81/1220-0344$01.25/00 1981 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev.. Vol. 20. No. 2, IS81 S46
f
Figure 1. Side n e w of modified accelerated wear apparatug
variety of magnifications was used. Photomicrographs were recorded in the secondaryelectron mode of the SEM. X-ray fluorescencedata were obtained and the "pition of the sample was determined at various locations on the sample. Semiquantitative data on chemical composition were thus obtained. Transmission electron microscopy (TEM) enabled isolated oxide filmsto be studied at very high magnifications of the order of 1OOOOOX. Maximum potentials of 100 kV were required to penetrate the relatively thick oxide f i i . Many unworn specimens were too thick and needed to be lightly abraded with diamond paste. Films were isolated by use of a saturated mercuric chloride solution (ASTM method B137). Scribing a plate sample with a sharp instrument to produce 2-3 mm squares and subsequent immersion of the scribed sample in the above solution allowed the small squares of undamaged anodic film to be released from the aluminum substrate. The floating samples were picked up on stainless steel transmission microscope grids. Sandwiching of the film with a second grid was necessary due to lack of adhesion of the sample to the grid. Surface roughness as determined by a traveling stylus (Brush Surfindicator) aided in the quantification of wear. Data were generated from both the polymer and anodic oxide areas of the plates. In some cases, averaged data from areas of low halftone dot density were used. Changes in surface roughness during press and laboratory test exposure were recorded. Changes in surface gloss during wear were noted by a Gardner multiangle glossmeter, Model GS-9095,at incident (or reflected) angles of 20,45,60,75,and 85O from the vertical. Correlations of gloss with surface roughness data were obtained as outlined later. The instrument was zeroed with a black felt pad at 45' and percentage reflectance was recorded as a function of wear time. T h e Wear Test. Selection of a wear test method was based on the following requirements: (1) Data from the laboratory test should correlate with press performance. (2) The test should allow determination of effects of pressure, ink properties, solvent, and fountain solution on plate wear. (3) The test results should be able to be compared against a standard. (4)The test should generate data in 60 min or less. The following types of testa were considered in the preliminary stages of this work (A) ball-mill method-a plate sample is attached inside a rotating cylinder containing an abrasive material and pressure-producing material such as steel balls; (B)an abrasive material is dropped on a lithographic plate inclined from the vertical; (C) rotation of a disc cut from a lithographic plate while pressing against an abrasive medium; (D) rotation of a disc cut from a lithographic plate in an abrasive medium with vibration. The test is a modification of a metallographic polishing device; (E) back and forth motion of a weighted block over a lithographic plate while in an abrasive medium. This test is a modification of the Gardner Washa-
Fig" 2. Photograph showing top n e w of modified aealerated wear apparatus.
Table 11. W e i h t Combinations block (wt) aluminum (96.5 g) aluminum (96.5 g) hrass(1164g) hrass(1164g)
presaure
added
total
applied,
wt, g
wt, g 521 997 1589 2064
g/m' 9.0 17.2 21.4 35.2
425 900 425 900
bility Apparatus; Method E was adopted on the basis of preliminary results. Wear Test Adopted. The apparatus that waa finally adopted is shown schematically in Figure 1 and a photograph is given in Figure 2. A crankshaft, A, is connected to a steel bar, B, which slides in a dovetail, C. Attached to this bar is a vertical, slotted freemoving shaft, D, to which weights of various size can be added. To the bottom of this shaft a weighted block is attached. Two such blocks were used. An aluminum block, 7.5 cm long, 7.5 cm wide, and 0.6 cm high was used for light weight tests. Another block made of brass was used for heavier weight testing. This block was 7.5 em long, 7.5 cm wide, and 2.5 cm high. Table I1 gives the combinations of weights and blocks used. The bottom of each block was covered with metallographic felt padding. To the reservoir, F, was added 30 mL of Rmos fountain solution a t pH 4.0 and 1.0 g of 0.3-pm alumina polishing abrasive. The wear block covered a minimum area, 16.5 cm by 7.5 cm of plate sample, at 34.5 cycles/min. The wear stroke could be adjusted to cover up to 23 cm of sample length, and speeds were adjusted by changes in drive pulley ratios. Comparisons. The character of wear of press-wom plates was used as a standard against which the character of wear in the accelerated test was compared. A manual printing proof test was developed in order that comparisons could be more complete. Relative performances of press and laboratory-worn samples were compared and rankings of performance resulted. A manual printing press was modified in order that printing from laboratory samples could be accomplished. This press takes the image from the inked plate sample and transfers it to the paper using one rubber roll. The plate is ilat during printing and pressure between the plate and the impression roller is adjusted. Ink is applied by a hand-held quick peek roller and kit supplied by Twing and Albert Co. Ink follows application of the fountain solution. Considerable trial and error is involved in achieving the proper water-ink balance and f h thickness. Exact specification of the ink and fountain solution is not practical and a subjective feel for the proper balance on the basis of experience is necessary. When a suitable ink
346
Ind. Eng.
Chem. Prod. Res. Dev., Vol. 20,No. 2, 1981
Table I11 relative X-ray fluorescence intensity element aluminum sulfur silicon iron manganese nickel copper
unpitted anodized surface
bottom of pit
82 8
88 5 1.5 1.5 1 0.6
4 2.5 2.5 0.5 trace
-.-
impression was made on the roller, it was transferred to the paper. The proof test was performed on laboratory test samples periodically (generally after each 200 cycles) during the wear test until loss of image quality was observed. Low magnification examination by a magnifying glass or optical microscope supplemented this evaluation. The number of cycles required for inferior image quality was recorded. Measurements of surface roughness were also made simultaneously with the proof tests.
Results and Discussion Examination of press-worn plates by optical and scanning electron microscopy revealed three major types of deterioration by wear and/or corrosion: (1)loss of adhesion of the photopolymer to the substrate; (2) pitting of the anodized aluminum in the non-image areas; (3) abrasive loss of material from both the polymer and the anodized aluminum. Loss of adhesion was found primarily in the deterioration of the commercial diazo plates. SEM studies showed the loss of fragments of polymer from a solid image area of the plate. The “pick out” of fragments of polymer of the order of 1-10 pm2 in area was not observed on any of the other types of plates examined; it was only observed on the diazo plates. A more typical type of loss of adhesion was observed on the commercial photopolymer plate A and experimental plates in which fragments at the edge of halftone dots were broken away. In some cases the fragments were associated with a score mark within the polymer dot, but in other cases no such association could be made. Pitting of the anodized aluminum surface was observed particularly in the commercial plates A and D. It is hypothesized that the loss of aluminum oxide on this plate was a consequence of a combination of corrosion and fracture of the oxide during the wear process. Cracks are known to exist in the surface of an unused plate of this type and the shapes of some of these cracks appear to outline what is observed as a pit on a worn plate. The topography of the roughened surface may be significant to the cracking problem. It has been reported (Cochran and Sprowls, 1979) that growth of anodic films on angular surfaces is irregular due to limited film growth on angled or pointed surfaces. These locations would be susceptible to cracking or fracture during wear. Evidence supports the view that the structural features identified as pits were depressions below the outer surface of anodic oxide. That is, thinning of the oxide is present at these points. X-ray fluorescence data are summarized in Table I11 and the relative intensity of the signal for several elements in an unpitted region as compared to the bottom of a pit is presented. The important point is that the aluminum signal is greater at the bottom of the pit and that the sulfur signal is less at the bottom of the pit. The sulfur signal originates
from sulfate that is occluded in the oxide during anodization. Thus, the higher aluminum signal and the lower sulfur signal at the bottom of the pit suggest that the bottom of the pit has only a thin coating of oxide. It should also be noted that the electron beam which gives rise to the X-ray fluorescence cannot be focused sharply enough that it is confined exclusively to the very center of the bottom of the pit, so that some of the fluorescence probably originates from oxide on the side of the pit and from the actual volume from which the radiation originates. With the possible exception of the diazo plate where adhesion loss is significant, abrasion was the primary mode of deterioration by press wear. Abrasion of both the polymer and anodic oxide films was found. In non-image areas where no polymer dots occur, abrasion is so severe that regions of anodic oxide are completely abraded away. In areas where polymer dot density was low, severe abrasion also occurred, with smoothing of the roughened surface peaks. The anodic oxide from an area of high dot density showed a lesser abrasive loss of anodic oxide than areas of lower dot density. Changes in surface roughness corresponding to the above SEM results are summarized in Table VI found in a later section of this report. Abrasive wear of the polymer surfaces was observed in some cases. Penetration of the polymer film by the substrate oxide occurred. This type of deterioration of the polymer is believed to be less critical to image reproduction than adhesion-related problems. In most cases observations by SEM and surface roughness show little change in appearance of the polymer during normal press exposure. Resistance to wear of the polymer during normal press operation might result from: (1)a lubricating effect of the greasy inks used in lithography or (2) the fact that the polymer is more elastic than the brittle aluminum oxide surfaces and there is less deteriorating effect on the polymer image areas. Overpacked,Press-Worn Plates. Many of the plates studied were worn by overpacking of the plate backing, thus yielding higher pressure between the plate and the mating roller. Accelerated wear of the plates was thus purposely caused by the increased pressure and the use of an abrasive ink. Overpacking resulted in two types of wear not found to any major extent on normal press-worn plates, namely cracking of the anodized aluminum oxide film and rupture of the polymer film at the peaks of the underlying grained aluminum substrate. As mentioned earlier, rupture of the polymer was found occasionally on normal press-run samples. It should also be mentioned that some commercial plates exhibited cracks in the oxide even though the plate was not used. X-ray fluorescence analysis, which is discussed in more detail later, provided further information about the cracking. Relative intensities of the X-ray fluorescence radiation developed by a highly focused electron beam is tabulated in Table IV. Evaluation of these data shows that the aluminum signal is very much higher at the center (bottom) of the crack than it was on the adjacent anodized aluminum surface. These observations suggest that the cracks extend deeply into the oxide. Qualitative Analysis of the Anodized Aluminum Surface. The plate types characterized earlier have been studied in the scanning electron microscope and were subjected to qualitative chemical analysis using a nondispersive energy analyzer for the X-rays generated by the focused electron beam. Table V summarized some of these results. The major conclusions of the analysis are the following: (1) Commercial plate A and all experimental
Id. Eng. Cham. Rod. Res. Dav.. VOI. 20, NO. 2, 1981 947
Table 1V relative X-ray fluorescence intensity on anodized at bottom surface of crack
element aluminum phosphorus
_82_
98.6 0.6
I
Sulfur silicon
0.8
... ... ... ... ...
4 2.5 2.5 0.5
iron
manganese nickel copper
trace
Table V. Qualitative Chemical Analysis of Anodic Oxide on the Surface of Aluminum Lithographic Plates as Determined by X-ray Fluorescence Analysis in the Scanning Electron Microscope relative intensity of emitted X-rays comcomcommercial exptl mercial mercial element plate A plate plate B plate C aluminum 82 91.4 95 90.5 I 4.7 --6.2 sulfur silicon
phosphorus iron
manganese nickel
copper
4
--2.5 2.5 0.5
trace
_ 1.4 __ 1.7
-------
1.4 1.6 0.9
---
__ 1.3 __ __
__ __ __
Figure 3. Optical microscope view of halftone dots on a commercial plate A after 400000 impressions on a commercial press.
1.4 0.75 1.1
plates were anodized in a sulfuric acid electrolyte. (2) Commercial plate B was anodized in phosphoric acid since the phosphorus signal was high. (3) Commercial plate C showed the presence of both sulfur and phosphorus, indicating that a mixed sulfate-phosphate electrolyte was used for anodizing. (4) The iron, manganese, and silicon probably represent alloying elements in the aluminum substrate although silicate is introduced in mechanical graining and post-anodizing sealing treatments of the experimental plates. (5)The presence of nickel in the anodic coating on Commercial plate A suggests that the anodic coating was sealed in a solution containing nickel salts. Transmission Microscopy. Isolated anodic aluminum oxide films were subjected to transmission electron microscopy. Wom samples generally contained regions which were sufficiently thinned by abrasion to allow transmission of the electron beam. Unused plates were abraded using the procedure described in the Experimental Section. TEM studies were made of an unused commercial plate A at 65000X magnification. Pores were observed in the cellular oxide. The cellular structure of all plates with the exception of commercial plate B had similar appearance and pore sizes. The pore sizes are large on commercial plate B. The following conclusions were drawn from these data: (1) Those samples anodized in sulfate or sulfatephosphate electrolyte contained pores on the order of 200 A diameter. (2) The phosphate electrolyte produced pore diameters of the order of 500 A. Commercial plate B was the only plate of this type studied. (3) TEM of unabraded or unworn samples was possible in the case of the experimental formulations. The oxide films were thin relative to the oxides on commercial plates A and C. (4) Transmission through the oxide on unused commercial plate B samples was possible. The presence of a thin oxide was indicated. T h e Wear Test. Deterioration of the anodic oxide in the accelerated wear test was primarily by abrasion as was found to be the case with plates worn on the press. A similar area on a press-worn plate showed likenesses in-
Figure 4.
Opticid microscope view uf hnlfinne dots on B commercial plate A after 1XIH) cycles in the accelerated wear test. Circle wm d r a w on plate after the experiment in order to identify a specific region on plate.
eluding (a) wear of high spots and (b) pitting of the anodic oxide. Abrasive wear of the edges of the polymer dot, a characteristic found in ordinary press deterioration of a similar sample, was also observed. Further similarities between press-wom plates and those worn in the accelerated laboratory test were obtained from optical microscope studies. Figure 3 is a micrograph of a commercial plate A after 400000 impressions on a commercial press, the history of which is otherwise unknown. Figure 4 is a similar micrograph of the same plate type after 1800 cycles a t a pressure of 13 g/cm2 in the accelerated test apparatus. Both photographs show abrasive rupture of the polymer a t high spots and loss of polymer a t the dot edges. Loss of image quality of the laboratory tested sample was noted at 1800 cycles by use of the proof test, and the two photographs represent the appearance of halftone dots after a plate has reached the end of its useful life. SEM photographs demonstrated abrasive flattening of the peaks of the grained anodic oxide surface and loss of polymer in both laboratory and press exposure tests. Applications of the Accelerated Wear Test. The laboratory accelerated test apparatus has provided a means by which performance of commercial and experimental plates could be compared. Determination of the point a t which wear limits the usefulness of a plate is a problem not only in the laboratory but also in the pressroom. This
348
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20,No. 2, 1981
Table VI. Relative Wear Properties of Nine Types of Lithographic Plates in Low Dot Density Areas as Determined by the Accelerated Wear Test no. of wear cycles before image area was seriously plate affected, as determined designation by proof test experimental plate no. 1 commercial plate A commercial plate B positive plate (baked) positive plate (baked) experimental plate no. 3 commercial plate C positive plate (unbaked) positive plate (unbaked) experimental plate no. 2
Table VII. Relative Wear Properties of Five Types of Lithographic Plates in High Dot Density Areas as Determined by the Accelerated Wear Test
plate designation experiment plate no. 1 commercial plate A commercial plate B commercial plate C experimental plate no. 2
2400a 1800
1800 H
1800
F
1500 1500
1400
E
1200
H
1100
1000
no. of wear cycles before image area was affected, as determined by proof test
a
q,
1500a 1300 1200 1000 500
Best performance.
I
0
m
I
.Oo8 0
L
m
00
c
10
a
Best performance.
0
u1 0 (0
(3
end of usefulness is determined by loss in quality of the print, and the range of life selected is dependent upon the discriminating ability of the operator of the press. It was decided that a printing proof test was the most suitable means for determining the end point in the accelerated wear test. The end of the useful life was considered to be the point at which dots in the center of the proof became very fuzzy or were absent. A standard test target was used in testing the negative-working plates. A photographic image of an outdoor pavillion was used to develop the positive-working plates. This scene contained a variety of solid and intermediate tone areas. Exposed and developed plates of this type were tested and evaluated primarily in the intermediate tone areas. Evaluation of performance for nine different types of lithographic plates was accomplished in the accelerated tests. Data which represent the best estimate for several tests, or in some cases single tests, are summarized in Table VI. These data represent loss of fidelity in the low-density (0 to 50%), halftone dot regions only. The longest test (2400 cycles) took less than 70 min to conduct at 34.5 cyclesjmin. Similar experiments were conducted on the high-density halftone dot regions. Proof tests of these areas of a plate are difficult due to scumming or filling-in of the non-image areas with ink. These data are probably less reliable and are found in Table VII. It should be noted that relative rankings of the plates are similar for experiments on lowdensity and high-density regions of the plates. Highdensity test targets were unavailable for the positive working plates. Surface Roughness Correlations. Changes in surface roughness were noted during press wear. It was decided to compare roughness changes for accelerated test samples with the data obtained from plates worn to exhaustion on the press. These data are summarized in Table VIII. The first entry is for a commercial plate A from a printer and the history of this plate is unknown. The other entries represent lithographic plates that were run under overpacked conditions until unacceptable image quality was noted. Original roughnesses of press-worn plates (column 1)were actually made on different plates than those run
I 10
20
Surface
I
I
30
I
I
I
I
,
40
Roughness (
Inches)
Figure 5. Relationship between gloss and surface roughness at 85'.
on the press, but good reproduction of these data has been noted for different plates of the same type. Column 2 gives the roughness of the plate after press deterioration and column 3 gives data for similar samples worn in the laboratory accelerated test with an approximate pressure of 13 g/cm2. A few data on positive working plates were available. Several conclusions can be made from the results summarized in Table VIII. (1)Commercial plates A are considerably rougher than other plates studied and changes in roughness during wear are therefore greater. (2) Overpacked press-wear of the commercial plate A produces excessive changes in surface roughness of polymer image area when compared to ordinary press exposure. (3) The end point in the accelerated wear test for the roughness in the image area was in the range of 7-11 pin. for all six samples. (4) The end point in the accelerated wear test for the roughness in the non-image area was in the range of 10.5-14 pin. for 4 samples and was considerably higher (24 pin.) for commercial plate A. ( 5 ) The accelerated wear tests of commercial plate A and the experimental plates yield comparable roughness end point data for the roughness of the non-image areas for both on the press and wear in the accelerated test. (6) The accelerated wear testa of commercial plates B and C yield comparable roughness end point data for the roughness of the image area for both wear on the press and wear in the accelerated test. (7) The high value of the roughness of commercial plate A after use under overpacked conditions is probably a consequence of the cracking of the anodized aluminum surface. (8) Some correlations exist between roughness data generated in the accelerated test and data obtained from the press. Surface gloss data (reflectance) as detected by a gloss meter at various angles were found to correlate with surface roughness measurements at 85' from the vertical. An inverse relationship was found between roughness and gloss or reflectance at only 85O, as shown in Figure 5. Other angles showed considerable scatter in the data.
Ind. En$. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 349
Table VIII. Roughness Measurements on Lithographic Plates Subject to Wear on the Press and in the Accelerated Wear Test (2) roughness after ( 3 ) roughness at end point ( 1 ) original roughness wear on press in accelerated wear test plate designation commercial plate A (worn on press)
non-image area, p in. 48
image area, p in. 22
non-image area, p in. 24
image area, p in. 22
non-image area, p in.
48
22
48
6
22
9
14.5
6
20
18
17
13
13
17
15
15
12
10.5
20 39 17 15
3 29 9 11
16.5 38 17 13.5
4.5 35 15 11
12 32
20 39 17 15
60 32 7 14
12.5 39 17 14
2.2 33 12.5 12
image area, p in.
24 commercial plate A (overpacked) experimental plate no. 1'" (overpacked)
12
experimental plate no. 2a (overpacked) commercial plate C (overpacked) commercial plate B (overpacked) unbaked
14
E F G
H baked E
F G
H a
--
11 12 32
-lo
Data supplied for press-worn sample did not specify what experimental plate was used. I5 0
75
o
I 200
I a
I
1 600 Ctcl.6
tn
aoo
I 1000
Aicilerotad
I
I
I
1200
14w
1600
I
lam
I
I
2000
2200
I
W e ~ r Tee1
Cycles
Figure 6. Rate of wear of commercial plate B.
in
Accelerated
Wear
Test
Figure 7. Rate of wear of commercial plate C.
Surface contamination by residual films, such as ink, interfere with reflectance to a much greater extent than surface roughness. For these reasons gloss measurements were abandoned as a quantitative measure of lithographic plate wear. Rate of Wear. The rates of wear on plates in the accelerated test apparatus were determined at different pressures by varying the weight of the block which supplies the abrasion in the apparatus. Plots of surface roughness vs. the number of cycles in the accelerated apparatus for a few plates resulted and are found in Figures 6 , 7, and 8. Since the range in values for surface roughness in a 20% halftone dot area was not great, it was decided to use this area for measurements of surface roughness. This roughness measurement shows combined effects of wear on polymer dots and the non-image area. Data were generated to a point beyond the normal end point of lost image quality. The plots show a decrease in surface roughness during wear. Since periodic surface roughness measurements of plates on the press are unavailable, comparisons were not made with rate-of-wear data in the accelerated wear test.
'70r
o
I
I
I
200
400
600
Cyclos
I aw
I IWO
1
I
I
I
1200
1460
,600
Wear
Test
in AccaIerated
1
1x0
1
zoo0
I ZLDS
Figure 8. Rate of wear of experimental plate no. 3.
The surface roughness at the end of usefulness of these plates as determined by the proof test was noted. The number of cycles to accomplish this end point roughness can be found at different pressures from the above plots.
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 350-354
350
showed little difference in the rate of wear over a range of high pressures. The curves corresponding to three high pressures in Figure 6 lie close together. The other plates show greater differences in rate of wear at the same three high pressures. Further experiments should be conducted in order for one to understand the pressure effects on the rate of wear as a function of initial surface roughness. Acknowledgment Appreciation is expressed to the Photo Products Department of the DuPont Company for the support given this research. Literature Cited
b A
aa
KO I Cycles
’ ’ ’ ’
nw in
1000 12w 1400 1660 Acceleroled Weor Test
I
1800
zom
‘ 1
2x0
Figure 9. Effect of pressure on wear end point. Figure 9 shows the effect of pressure on the end point. The unusual shape of the commerical plate B curve may be due to fracture of larger particles of anodic oxide film from the plate which may prevent polishing of the surface. The rate of wear of the plates studied in the accelerated test was related to the initial surface roughness, expecially at high pressures. Commerical plate B, which had the lowest initial surface roughness of the plates studied,
ASTM 8137-45. ”Standard Method of Test for Weight of Coatlng on AncdC cally Coated Alumhum”, Annual Book of ASTM Standards, American Soclety for Testing and Materials: PhlladelpMe, 1972, p 85. Cochran, W. C.; Sprowls, D. 0. “Anodic Coatlngs for Alumhum”, "Corrosion Control by Coatings”, Leidhelser, H., Jr., Ed.; Sclence Press: Prlnceton, N.J. 1979; p 179. Dean, S. W., Jr.; Clerk, D. G.; Friberg, L. S.; Seese, R. G. Roc. Tech. AsSOC. Graphic Arts 1972, 235-48. Dean, S. W., Jr.; Ford, J. A. Roc. Tech. Assoc. Graphic Arts 1973, 198-210.
Received for review July 22, 1980 Accepted September 12,1980
This paper was presented at the 54th Colloid and Surface Science Symposium,June 16-18,1980, at Lehigh University, Bethlehem, Pa.
Anion-Exchange Resins from Copolymers of Styrene and Hexahydrotriacryloyl-s-triazine Sofia Belfer Division of Membranes & Ion-Exchangers, Research & Development Authority, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Abraham Warshawsky Department of Organic Chemktry, The Weizmann Institute of Science, Rehovot, Israel
The properties of anion-exchange resins in relation to conditions of their preparation from styrene-hexahydrotriacryloyl-s-triazine cross-linked and chioromethylated via a Friedel-Crafts reaction are described. Resins with different porous structures can be prepared in accordance with the synthetic conditions. The selection and control of the chloromethylationconditions facilitate the designing and synthesis of tailor-made resins for particular purposes.
Introduction Most anion-exchange resins in use today in water treatment and purification are derived from styrene-divinylbenzene (DVB) copolymers. They are classified (Davankovet al., 1977) 89 either gel or macroporous resins, the latter type consisting of several subtypes according to the synthetic route by which they have been prepared. The gel copolymer is characterized by a network, which swells only in solvating liquids, whereas the macroporous polymer is able to absorb or swell in nonsolvating solvents as well. This advantage of the macroporous structure, combined with the functionality of ionogenic groups, 0 196-4321/81/1220-0350$0 1.25/0
constitutes the basis for the specific adsorbtivity of the macroporous resins. The porous structure of the commercial styrene-DVB copolymer is formed by the precipitation polymerization of mono- and divinylmonomers in the presence of a considerable amount of DVB (Kun and Kunin, 1968; Sederel and Yong, 1973; Tager et al. 1971). The formation of a porous structure by an alternative route, requiring only a small amount of cross-linking agent, could broaden the range of adsorption properties of macroporous resins. Such a synthetic route could also result in a considerable saving in production costs. 0 1981 American Chemical Society
