Figure 4-4 shows a table detailing the effects of varying stylus angle on cell volume
`
`whilst keeping cell width and length constant. As the stylus angle is increased, the
`
`volume and cross sectional area of the cell decreases significantly, with a 140° stylus
`
`engraving a cell with only approximately half of the cross sectional area of a 110°
`stylus and two thirds ofthe volume. 15
`
`Stylus Angle Volume (~m3)
`
`120°
`
`130°
`
`140°
`
`81192
`
`65590
`
`51192
`
`Assummg I 50 ).1m cell, wrdth and length
`
`Figure 4-4 -Comparison of CSA of cells
`
`Graph 4.26 details the effects of volume on density as stylus angle changes.
`
`Maximum density is achieved for a specified volume using a 130° stylus engraved
`
`cell. As with the results examining screen ruling, a specified volume cell will be at
`different points on the coverage range for different stylus angles. 16 No significant
`variation was observed when examining specific volume due to the number of
`
`cells/unit area being maintained as stylus angle is changed.
`
`15 Styli with angles as small as 90" and as large as 150° are used, with the majority of engraving work
`using styli between I I 0° and I 40°.
`16 A 100% 140° cell has a similar volume to a 90% 130° cell and a 75% 120~ cell.
`
`106
`
`FAST FELT 2010, pg. 121
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`IPR2015-00650
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`

`
`1.6
`
`1.4
`
`1.2
`1.0
`-~
`~ 0.8
`0.6
`
`0
`
`0.4
`
`0.2
`
`0.0
`
`0
`
`50000
`
`1 00000 150000 200000 250000 300000
`Volume (uml}
`
`Graph 4.26 -Volume and Density
`
`The effect of stylus angle at different coverages is shown in Graph 4.27. Volume
`increases significantly at each coverage level as the stylus angle is reduced.
`
`350000
`
`300000
`
`250000
`
`M'
`.§,200000
`II
`E
`= c >
`
`150000
`
`100000
`
`50000
`
`0
`0%
`
`20%
`
`40%
`60%
`Coverage
`
`----120°----130°----140°
`
`80%
`
`100%
`
`Graph 4.27- Stylus angle effects on volume and coverage
`
`107
`
`FAST FELT 2010, pg. 122
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`IPR2015-00650
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`

`
`c
`
`c
`
`c
`
`(
`
`Although volume increases as stylus angle decreases, by considering the results as
`
`shown in Graph 4.26, the solid density is not merely a function of this volume, but is
`
`also affected by the ink release process.
`
`45.00 I
`
`40.00
`35.00
`
`Q)
`
`e 3o.oo
`2. 25.00
`.t::. c. 20.00
`c 15.00
`10.00
`5.00
`0.00
`0%
`
`180.00 1
`160.00 i
`140.00 ;
`e 12o.oo jj
`
`2-100.00
`~
`~ 80.00
`§ 60.00 1
`40.00
`20.00 .
`0.00 -
`0%
`
`50%
`
`100%
`
`l
`
`50%
`
`100%
`
`Graph 4.28a - Depth
`
`Graph 4.28b - Width
`
`Graph 4.28 - Effects of Stylus Angle on depth and width
`
`The effect of varying the stylus angle on the depth and width of the cells is shown in
`
`Graph 4.28. There are differences between the two sets of curves. Previously when
`
`comparing depth and width results, the effects of changing the diamonds were
`
`averaged out through the data reduction associated with the orthogonal array
`
`technique. Although three diamonds were used for the engraving, a set of cells using
`
`each diamond was measured, analysed and averaged. It is clear that by increasing the
`
`stylus angle, shallower cells are obtained, but that changing the stylus angle has not
`
`significantly altered the width of the cells.
`
`The effects of stylus angle on length and open area are also shown in Graph 4.29.
`
`Varying the stylus angle makes no significant difference to the external dimensions of
`
`the cells being analysed, as required by the engraver.
`
`108
`
`FAST FELT 2010, pg. 123
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`IPR2015-00650
`
`

`
`250 I
`
`200
`
`2.150
`
`-E
`.c -g' 100
`
`G>
`..J
`
`50
`
`0
`0%
`
`- 18()(X)
`16000
`cg1400J
`a 12000
`m 10000
`~8()(X)
`c 6000 .
`G>
`Q. 400J
`02000
`0
`
`50%
`
`100%
`
`50%
`
`100%
`
`Graph 4.29a - Length
`
`Graph 4.29b - Open Area
`
`Gr aph 4.29 - Effects of stylus angle on Length and Area
`
`Graph 4.30 details the effects of stylus angle on tone gain, compared to the tonal
`
`reproduction normalised with respect to the 130° stylus.
`
`Stylus Angle effects on tone gain
`
`12
`
`8
`
`-8
`
`Graph 4.30 - Effects of stylus angle on tone gain
`
`109
`
`FAST FELT 2010 , pg. 124
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`IPR2015-00650
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`

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`0
`
`0
`
`As stylus angle increases, generally tone gain decreases. This is the same finding as
`with the effects of screen ruling, and is also attributed to the physical dot gain. The
`larger printed dots spreading out more, giving near identical performance for each
`stylus angle. At lower coverages the tone gain decreases as stylus angle increases.
`
`4.3.3.1 Stylus angle summary
`
`The decrease in density with stylus angle appears to be non-linear, with the largest
`decrease occurring in the gap between 130° and 140° (Graph 4.25). This trend is
`reversed however, when comparing stylus angle with volume, where the largest
`difference occurs between 120° and 130°. This trend also holds with length, width and
`depth. Ink transfer, similarly increases (slightly) as stylus angle increases. The reasons
`for this apparent discrepancy are unclear. It is considered that this is due to the
`different release characteristics of conjoined dots (where the dots have merged
`together to produce a continuous layer of ink on the substrate) compared with the
`necessary use of individual dots observed at 30-50% coverage, as used when
`calculating ink release. It is believed that this is a function of the geometry of the cell
`
`It should be noted that at stylus angle increases, the depth of the cell engraved
`decreases, but that the external dimensions (width, length etc) of the cells are retained.
`As stylus angle increases, the printed density, both solid and in the tonal regions
`decreases. This is due to the significantly reducing volume of the cells, making a
`much smaller quantity of ink available to the substrate, and thus leading to reduced
`printed densities.
`
`4.3.4 Summary of geometric parameters effects
`
`In general, as cell volume increases, printed density increases.
`
`As screen ruling increases, printed density decreases, both in terms of solids and of
`tonal reproduction. This is largely due to the reduced specific volume available at
`higher screen rul ings. As screen ruling increases, tone gain decreases. This has been
`
`110
`
`FAST FELT 2010 , pg. 125
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`0
`
`0
`
`0
`
`(
`
`attributed to the viscosity of the ink allowing larger dots to spread out further, which
`was borne out by analysis of the physical dot gain of the system. It has been shown
`that as screen ruling is changed, the shape of the cell remains unchanged, as is the
`engravers intention, and that the cells are merely scaled down as screen ruling is
`increased.
`
`As compression ratio increases, the depth of the cells decreases along with the width,
`whilst the length of the cells increases, thus approximately maintaining volume, while
`allowing the external shape of the cells to be changed to approximate changing the
`screen angle, and thus allowing the prevention of Moire. The printed density, both
`solid and in tonal regions decreases as compression ratio increases, although no
`significant difference is observed as the compression ratio is increased from 37°-45°.
`This is because the volume remains approximately constant between 3 7° and 45°
`before decreasing as the compression ratio is increased beyond 45°, despite the
`engravers intention to maintain volume as compression ratio is increased.
`
`The decrease in density with stylus angle is non-linear, with the largest decrease
`occurring in the gap between 130° and 140°. This trend is reversed however, when
`comparing stylus angle with volume, where the largest difference occurs between
`120° and 130°. This trend also holds with length, width and depth. Ink transfer,
`similarly increases (slightly) as stylus angle increases. It is likely that this is due to the
`different release characteristics of conjoined dots (where the dots have merged
`together to produce a continuous layer of ink on the substrate) compared with the
`necessary use of individual dots observed at 30-50% coverage, as used when
`calculating ink release. This is a function of the geometry of the cell. It should be
`noted that at stylus angle increases, the depth of the cell engraved decreases, but that
`the external dimensions (width, length etc) of the cells are retained, as intended by the
`engraver. As stylus angle increases, the printed density, both solid and in the tonal
`regions decreases, due to the decreased volumes
`
`Ill
`
`FAST FELT 2010 , pg. 126
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`0
`
`0
`
`(
`
`c
`
`(
`
`4.4 Calculation of printed dot volumes
`
`The calculation of the volume of ink transferred to the substrate required the use of
`
`two distinct stages, the first - thermal desorption - gas chromatography - mass
`
`spectrometry (TDGCMS) and the second - white light interferometry. By knowing the
`
`volume of notionally 'dry ink', (using interferometry) and the quantity of retained
`
`solvents in the 'dry ink' (using TDGCMS), coupled with the known solvent content of
`
`the ink as supplied, it is possible to calculate the total volume of ink, which was
`
`released from the cell. This section details the results from this two stage analysis
`
`procedure.
`
`4.4.1 TDGCMS results
`
`The TDGCMS was used in order to ascertain the quantity of solvent in the raw
`
`substrate, the ink and the printed substrate. TDGCMS analysis is a three-stage
`
`process. Thermal desorption strips the volatile component of a sample by heating. Gas
`
`chromatography separates the volatile components from the mix supplied from the
`
`thermal desorber, and mass spectrometry identifies the components from their
`
`molecular weight and measures their abundance in the measurement sample.
`
`Although there is no literature suggesting that this technique has been used previously
`
`to precisely quantify retained solvents in printed material, the manufacturers of the
`
`equipment specify that it is suitable for this sort of testing (23] (29] [35], and similar
`
`experiments have been performed, as discussed in section 2.2.
`
`4.4.1.1
`
`Inks
`
`Due to the nature of the test, it is not possible to test for methanol, and so the results
`
`from the TDGCMS were complemented by analysis of a detailed breakdown of the
`
`ink supplied by the manufacturer, and a simple dry weight analysis.
`
`All inks were analysed, covering both colour inks used in the experiment (cyan and
`
`magenta) and both reduction techniques (conventional viscosity reduction and
`
`112
`
`FAST FELT 2010, pg. 127
`Owens Corning v. Fast Felt
`IPR2015-00650
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`

`
`_,.........u........
`
`
`
`................
`
`............“.......
`
`
`
`
`
`......”u....:..::_..........._...........nuu....n......._.....u.....
`
`
`
`
`
`
`
`..u..._..........,
`
`
`
`.._"...............:.”.......
`
`
`
`
`
`...:W...............
`
`
`
`..."..m.n.._”.._m...v..._._...r......._.\....y...m"...u..
`
`
`
`
`
`
`
`
`

`
`0
`
`0
`
`0
`
`c
`
`c
`
`of retaining it. As a result, the precise breakdown was used to calculate volatile
`
`content of the supplied ink. It was ascertained that the raw ink base (in each case)
`
`contained 69% ±0.5% by weight solvent. Ratios for additional solvent added (to
`
`reduce the viscosity to press-ready levels) were also supplied, the solvent levels
`
`ranging from 80% - 86% by weight.
`
`Values for solvent content were confirmed by solid analysis. Three phials were
`
`weighed, and 1 cc of ink was added to each. The ink was allowed to dry in a warm,
`
`well-ventilated place for two weeks before it was reweighed. Theoretical calculation
`
`of solids concentration indicates that there should be 0.32g of solids per cc of ink.
`
`Average solids weight measured was found to be 0.34g of solids per cc of ink.
`Substrate analysis was performed approximately 18 months following the trial, and
`
`solvents were still found in the prints, so it is unlikely that all the solvent has been
`
`removed from the ink - this accounts for the excess 0.02g of solids, and validates the
`
`measurements.
`
`Acetic acid does not appear in the breakdown of the ink, and this is either
`
`contamination (for example, it occurs in small quantities in fingerprint oils) or the
`
`product of a reaction. It does however appear in sufficiently small quantities to be
`
`safely ignored without altering the results.
`
`4.4.1.2 Substrate
`
`Patches were measured from each ink trial, and of unprinted substrate. No significant
`
`variation in the quantities of retained solvent were observed in the results between
`
`different viscosities or reduction methods, although variation was observed between
`
`the cyan and magenta inks.
`
`The sample size was 40x l Omrn. The total retained solvent/sample is listed in ng ( 10·
`9g) I measurement strip. Results are shown below, in Graph 4.31 for the breakdown of
`
`cyan printed substrate, magenta printed substrate, and unprinted substrate.
`
`114
`
`FAST FELT 2010, pg. 129
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`Ill E aoo~----------------~:~
`"' 5 600 ~--------------~
`0
`; 4oor-----------------~~·~
`c
`
`m
`::T
`Q)
`:::s
`2.
`
`)> m
`::T
`'<
`)>
`(')
`('0
`Q)
`
`('0
`c;·
`Q)
`~-
`
`1\..)
`
`I
`
`- (') - I ~
`-
`:::J
`...
`-c
`-
`-c
`0
`a. -
`-c
`C1)
`~ :::J
`0 - Q)
`('0 - 9:
`Q)
`Q)
`:::s
`Q) - 0
`C1)
`
`:::s
`C1)
`• magenta • cyan 0 unprinted
`
`C1)
`
`Graph 4.31 - Retained solvents in printed substrate
`
`It was identified that n-propyl acetate occurs in both the printed and unprinted
`
`substrate. The quantities of n-propyl acetate found are small in any case, and were
`deducted from the solvents found in the printed substrate.
`
`No propanol or isopropyl alcohol were observed in any samples of the prints. It is
`
`assumed
`
`therefore
`
`that
`
`these
`
`two components had fully evaporated before
`
`measurement occurred. The volume of solvent retained was calculated from the
`
`densities of the solvents observed, giving a value of I% for retained solvent volume.
`
`Thus I% of the total volume of dry ink on the substrate is made up of unevaporated
`
`solvents, the remaining 99% being made up from the dry components of the ink.
`
`4.4.2
`
`Interferometry results
`
`Prints were examined using white light interferometry to measure the precise amount
`
`of solid ink deposited on the substrate (see 3.4.3). A film was used to eliminate
`
`penetration of the ink into the substrate. Measurements were taken at 30% , 40% and
`
`50% coverage for reasons detailed in section 3.4.3.1. A three dimensional image of a
`
`115
`
`FAST FELT 2010, pg. 130
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`

`
`gravure dot is shown in Figure 4-6. A matrix showing the range of dots examined is
`given in Figure 4-7.
`
`(
`
`(
`
`... :::=
`<.) c..
`0 .......
`
`... t::
`<.) c..
`0
`'0
`
`0 or
`'T
`E
`0 c..
`§
`
`tOOpm
`
`Figure 4-6 - 3D image of gravure printed dot (40% coverage, 701pcm, 45°
`
`compression ratio, 130° stylus angle)
`
`" " Sf
`
`" 0
`0 or,
`
`IOOpm
`
`Figure 4-7 - Range of dot sizes
`
`116
`
`FAST FELT 2010 , pg. 131
`Owens Corning v. Fast Felt
`IPR2015-00650
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`

`
`0
`
`0
`
`0
`
`c
`
`4.4.2.1 Optimisation of sample size
`
`A set of measurements was taken, totalling 20 dots, from a patch. A moving average
`
`analysis was performed, indicating that measurement of 12 dots would give
`
`acceptable accuracy on the printed dot size. The calculation is as detailed in Section
`3.6.
`
`4.4.2.2 Solid ink volumes - effects of cell characteristics
`
`Orthogonal array techniques were used to analyse the volumes of the printed dots,
`
`analysing the way in which the dots change as screen ruling, stylus angle,
`compression ratio, etc are changed 17
`volume with compression ratio, screen ruling and stylus angle are shown in Graph
`
`• Histograms showing the variation of printed dot
`
`4.32. From analysis of these graphs, it can be seen that as screen ruling and stylus
`
`angle increase, printed dot volume decreases. As compression ratio increases from
`
`37°-45°, there is a slight increase in the printed dot volume, but the printed dot
`
`volume decreases as compression ratio is increased further from 45°-57°. This
`
`correlates with the results measured for volume and open area, where there is little
`
`change in volume (albeit a slight decrease), but an increase in open area observed in
`
`the change between 37° and 45° compression ratio. It should be noted that these
`
`measured values are highly accurate and relate the release from an individual cell
`
`rather than an averaged release over a large area. As a result, this work is significantly
`
`more accurate than previous studies in the field. [25] [29] [41) [42) [43] [44] [53]
`
`[56]
`
`17 A worked example of this analysis is shown in appendix 3, for volume analysis of L9. 1.
`
`117
`
`FAST FELT 201 0 , pg. 132
`Owens Corning v. Fast Felt
`IPR2015-00650
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`

`
`4500
`4000 r- r-
`3500 r-
`3000
`-r-
`2500
`2000 r-
`r--
`1500 f- 1 - i--
`-
`1000 r-
`r--
`-
`500 1-
`0
`
`r-
`
`r--
`
`':"'""
`
`' - -
`
`r--
`
`M E
`:::2
`
`~
`
`.,......
`
`......
`
`1 -
`
`1 -
`
`1 -
`
`1 -
`
`r--
`
`-
`-
`-
`-
`-
`
`_r
`-
`---- 1 - r-
`-
`-
`
`i--
`
`r--
`
`,_
`
`-
`
`1 - i -
`
`60
`
`70
`
`80
`
`37
`
`45
`
`57
`
`120 130 140
`
`Screen Ruling (Jpcm) Compression Ratio (0
`
`)
`
`Stylus Angle (0
`
`)
`
`Graph 4.32 - Average dot volumes for different conditions
`
`As detailed in section 4.2 changing the defining characteristics of the engraved cells
`(the screen ruling, compression ratio and stylus angle) can change the length, depth,
`volume etc of the cells. As a result, printed dot volumes were plotted against the
`various characteristics of the cells, in order to investigate correlations between them.
`This demonstrated that larger cells made larger dots -
`the entire principle of
`engraving. As a result of this, the data was reanalysed in terms of release.
`
`4.4.2.3 Effects of Ink
`
`Histograms of ink release (solid content and released volume) are given in Graph
`4.33. Prints were made using inks at three different viscosities, termed high (24s,
`Zahn 2), medium (20s, Zahn 2) and low ( 17s Zahn 2). Results given are for magenta
`ink, using conventional reduction means (adding solvent to higher viscosity inks,
`lowering both the viscosity and colour strength). It can be seen from Graph 4.33a that
`as the viscosity increases, the volume o f solid ink on the substrate increases. This is
`partly a transfer effect, and partly an effect caused by the dilution of the ink at lower
`
`118
`
`FAST FELT 2010 I pg. 133
`Owens Corning v. Fast Felt
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`

`
`viscosities. Also, as viscosity rises, the total quantity of ink released from the cells
`also increases, with the largest changes being observed between mid and high
`viscosity ink. This is caused by the significant quantities of solvent required to lower
`the viscosity to the l 7s (Zahn 2) that was required for the low viscosity trial, since by
`adding solvent, the surface tension of the ink is reduced, aiding adhesion, but reducing
`the amount of ink being pulled out of the cell, as shown in [57]. This trend was
`maintained with changes in coverage. Large differences were observed in the shape of
`the printed dots as the viscosity of the ink was changed. High viscosity ink produced
`dots with much sharper, well defined edges, whilst low viscosity ink sp read more,
`providing less well defined cells. Examples of this are shown in Figure 4-8.
`
`9200
`
`9000
`
`8800
`
`8600
`
`....
`E
`
`2000
`1800
`1600
`1400
`1200
`1000
`800
`600
`400
`200
`0
`
`..,
`E
`::I
`
`~
`
`-
`
`r---"
`
`I
`
`Low Mid High
`
`::I 8400 :oo
`
`8200
`
`8000
`
`Low Mid High
`
`Graph 4.33a - Solid ink release
`
`Graph 4.33b - Total ink released
`
`Graph 4.33 - lnk release with viscosity
`
`11 9
`
`FAST FELT 2010 I pg. 134
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`Figure
`
`4-Sa
`
`High Figure
`
`4-Sb
`
`Mid Figure
`
`4-Sc
`
`Low
`
`viscosity
`
`Viscosity
`
`viscosity
`
`Figure 4-8 - Different viscosity dots (50% coverage, 70lpcm, 45° Compression
`ratio, 130° stylus angle)
`
`This is likely to be caused by the slumping mechanisms of the drying ink. As the low
`viscosity ink has a higher quantity of solvent related to each individual dot, the drying
`time of that dot will be higher than the drying time of a higher viscosity dot, which
`has a lower amount of solvent associated with it. As a result, this extended drying
`time has led to the low viscosity ink dots spreading further.
`
`4.4.2.4 Discussion of errors in dot volumes
`
`As detailed in section 3.6, the random variation in dot sizes is significant, and
`relatively large numbers of dots needed to be measured in order to have confidence in
`the measurements. Appendix 6 details the variation in dot sizes, and demonstrates that
`size variations of the level observed are caused by process variation with 99.999%
`confidence.
`
`120
`
`FAST FELT 2010 I pg. 135
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`

`
`4.4.2.5 Dot volumes and printed density
`
`The printed dot volumes of all dots, from all available coverages (30-50%), 60, 70
`
`and 80lpcm screen rulings, 37°, 45° and 57r:. compression ratios and 120°, 130° and
`
`140° stylus angles, as taken from the orthogonal array matrix were also plotted against
`
`density (Graph 4.34). An increase in printed dot volume leads to an increase in printed
`
`density, although the correlation band is not particularly close.
`
`0.6
`
`0.5
`
`0.4
`
`~ 03
`(/)
`c:
`Q) 0.2
`0
`
`0 1
`
`00
`
`•
`
`0
`
`1000
`
`2000
`
`3000
`
`4000
`
`5000
`
`Volume (um3)
`
`Graph 4.34 - Printed dot volume and density. (30-50% coverage, all screen
`
`rulings, all stylus angles, all compression ratios. Magenta ink, conventional
`
`reductions)
`
`Density is a measure of the reflectance of the sample, and as such an increase in
`
`transferred volume would be expected to lead to a decrease in reflectance, and thus an
`
`increase in density. This can be seen generally, although it would be expected for data
`
`to fit more closely to the correlation. The Jack of a simple, clear line indicates that
`
`something other than volume is important in producing the printed density. This is
`
`largely due to the spreading effects of the ink. Under certain conditions, for example,
`
`with lower viscosity inks, as identified in 4.4.2.3,the ink spreads out more, providing
`
`a larger, thinner ink covering. These in tum lead to an increase in the printed density.
`
`12 L
`
`FAST FELT 2010, pg. 136
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`IPR2015-00650
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`

`
`The volumes of dots are also skewed by the presence of entrained particles, which do
`
`not significantly affect the printed density.
`
`4.4.2.6 Total released volume
`
`Total released volume is the sum total of the printed dot volume (the solids remaining
`
`after solvent evaporation), and the solvents evaporated from that quantity of solids.
`
`The TDGCMS experiments indicated the presence of 1% (volume) of solvents
`
`remaining in the solid ink, and that the raw printing ink was made up of 80%-86%
`
`solvent, depending on the ink in use (82% for magenta ink at mid viscosity). From
`
`this it was established that the total volume of ink released (for mid viscosity,
`
`conventional reduction ink) could be calculated from:
`
`0.99 x (Printed dot volume) I 0.18 =Total released volume
`
`Equation 4.2 -Ink release calculation
`
`As shown in section 4.3, printed density on tonal reproduction is affected by screen
`
`ruling, stylus angle and compression ratio. Thus the volume of ink released is likely to
`
`be affected in a similar manner.
`
`-.....
`
`25000
`
`,-...
`
`..,
`e :::1.
`.._..
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`Q)
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`§
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`
`25000
`
`20000
`
`15000
`
`10000
`
`5000
`
`............
`
`"'
`
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`.......,
`"'0
`Q)
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`
`10000
`
`15000 ~
`
`5000
`
`0
`110 120 130 140 150
`
`0 - . , -
`50
`60 70
`
`80 90
`
`- -30%-- 40%
`
`50% Coverage
`
`-
`
`3{J!Ja-- 4CJ>Io
`
`5(J>; o Coverage
`
`Graph 4.35a - Stylus angle (0
`
`)
`
`Graph 4.35b - Screen ruling (lpcm)
`
`122
`
`FAST FELT 2010, pg. 137
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`-.....
`25000
`E 20000
`::1.
`-
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`
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`
`500/o Coverage
`
`Graph 4.35c - Compression ratio(")
`
`Graph 4.35- Effects of variables on release
`
`In each case, the trends regarding the total volwne of ink release correlate with the
`
`measurements of cell volume in section 4.2. A larger cell contains a larger quantity of
`ink and thus more of it is available to be released. Hence the higher release volumes
`
`observed with the larger cells engraved at lower screen rulings, stylus angles and
`
`(generally) compression ratios.
`
`4.5 Calculation of ink release ratio
`
`This section is one of the focal points of this work. Other investigators have used a
`
`variety of techniques to investigate the proportion of ink released from gravure cells,
`
`but their methods have been limited by the measurement techniques that were
`
`available at the time. In each experimental work the cell volume has been
`
`theoretically calculated. This, as shown in section 4.2 significantly underestimates the
`
`cell volume compared to those which have been measured using interferometry. In
`
`addition, the analysis techniques used involve averaging over large areas, rather than
`
`investigating the release from individual cells. Furthermore, the accuracy of the
`
`averaging techniques for films of the thickness under investigation is in question. As a
`
`result, this work provides the fi rst, accurately quantified value for ink release from
`
`123
`
`FAST FELT 2010, pg. 138
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

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`gravure cells, utilising highly accurate cell volume measurements and highly accurate
`
`dot volume measurements. The latter also accounts for retained solvent quantities and
`
`an accurate breakdown ofthe ink to produce these values.
`
`As demonstrated in 4.4.2.6 the total volume of ink released from a given cell has been
`
`calculated. The volume of a cell was measured and calculated in section 3.2.5.
`
`As discussed in section 2.3.1, previous work performed by Kunz (25] has indicated
`
`that the cells are not completely full after doctoring, and that some ink is removed by
`
`the doctoring process. No method is readily available to quantify the filling state of
`
`the cells, particularly when using production inks. Kunz [25] gives cross sections of
`
`cells indicating the filling state at various times after doctoring. From analysis of these
`
`diagrams, a filling state of 95% is indicated. This was calculated using an early
`
`interferometric technique identifying a meniscus in the fluid surface within the cell,
`
`and although the trial was performed using unrealistic inks it is reasonable to assume
`
`that a small amount of the ink is 'scraped out' by the doctoring process.
`
`The percentage ink release was thus calculated for each of the conditions to examine
`
`the effects of the different variables. The results account for the filling state [25] and
`
`they are shown in Graph 4.36. A relatively wide spread of results are observed due to
`
`the large number of conditions being examined with the orthogonal array matrices.
`
`However, a simple linear regression trendline was plotted to indicate how the data
`
`changes with respect to the screen ruling, stylus angle and compression ratio.
`
`0
`
`0
`
`c
`
`c
`
`124
`
`FAST FELT 201 0 , pg. 139
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`

`
`25 - - - - - - - -
`
`23
`
`•
`
`•
`
`* 21
`
`"0
`Q)
`~
`~
`
`Q)
`
`19
`
`17
`
`15
`50
`
`•
`70
`Screen RulinQ
`Graph 4.36b - Effects of Screen ruling
`
`90
`
`25
`
`23
`
`21
`
`•
`
`•
`•
`
`•
`
`17 / .
`• •
`
`•
`
`•
`•
`•
`
`15
`
`~tvlus Angle
`
`Graph 4.36a - Effects of stylus angle
`
`25
`
`23
`
`"'d
`Q)
`~
`Q)
`
`p::
`
`17
`
`* 21
`•
`19 ~ Q)
`I
`
`•
`•
`
`•
`•
`
`•
`•
`•
`4cf
`C'omnression Ratio
`
`Graph 4.36c - Effects of compression ratio
`
`Graph 4.36- Percentage release from cells
`
`Most dramatically1 it can be seen that the percentage release of ink from cells is
`
`typically approximately 18%. The release is also affected to some extent by stylus
`
`angle, screen ruling and compression ratio.
`
`125
`
`FAST FELT 2010, pg. 140
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`These values are all significantly lower than most previously published results, both
`
`theoretical and practical [25] [29] [41] [42] [43] (51] [52] [53], although they are
`
`comparable to the work of Kapur, Gaskell and Bates [54] and Benkreira and Cohu
`
`[52] who calculated release at between 15% and 20%.
`
`It is widely held in the gravure industry, that the release of ink from cells is
`
`significantly higher than that observed in this study. It has been suggested that the low
`
`figures for ink release presented here are as a result of significant evaporation
`
`occurring between doctoring and the printing nip.
`
`Evaporation is a function of many different variables, including temperature,
`
`air/surface interfacial speed, humidity, vapour and partial pressures, volatility etc.
`
`Stefan's law (Equation 4.3) defines evaporation in terms of diffusion, where;
`
`m" = DpMA .In (p- Pu2)
`(P-Put)
`R0 T.!1X
`
`Equation 4.3 - Stefan's law
`
`As a first approximation, given that the solvent used is made up of many different
`
`components, considering for the most volatile component (Methanol - CH30H) will
`give a 'worst case' scenario for evaporation - calculated to be at the rate of 6g of
`
`methanoVhr. It is assumed that a layer of 1 urn of ink is passed under the blade for
`lubrication. 6g/hr equates to a loss of 1.6mg/s or 2 X 1 0"3 cc/s. The time delay between
`doctoring and printing is approximately 60ms, thus the total solvent evaporated
`between the blade and the nip is equal to 0.13 x 1 o-3 cc - or a total of 0.4% of the
`available ink. Considering that this is a 'worst case' scenario, the actual evaporation
`will be lower than this, and thus evaporation is not a significant source of error in the
`
`release calculations.
`
`In order to explore the impact of cell geometry on the ink release process, results were
`
`calculated to investigate the effect of changing cell length, depth and open area and
`
`126
`
`0
`
`0
`
`0
`
`c
`
`FAST FELT 2010, pg. 141
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`these results are presented in Graph 4.37, with linear regressions imposed to identify
`
`trends.
`
`r
`
`~
`
`•
`
`25
`24
`23
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`22
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`17
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`16
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`15
`70 90 110 130 150 170
`Lenlrth (urn)
`
`~
`
`.#
`
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`
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`
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`16
`15
`
`• •
`30
`20
`Denth(um)
`
`40
`
`10
`
`Graph 4.37a - Length (J.I.m)
`
`Graph 4.3 7b - Depth (~-tm)
`
`;::R
`0
`'0
`t1.)
`en
`cd
`
`t1.) -Q)
`
`~
`
`•
`
`25
`24
`23
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`•
`22 1
`•
`• •
`21
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`20 J
`~· ....
`• • •
`•
`19
`••
`18
`• • • • • •
`17
`• ••
`•
`16
`•
`•
`15 .
`2000 6000 10000 14000
`Open Area (J.Im2
`)
`Graph 4.37c - Open area (~-tm2)
`
`#+•
`
`Graph 4.37- Cylinder parameter effects on ink release
`
`127
`
`FAST FELT 2010, pg. 142
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`c
`
`In each case, the trends observed are indicative of the way in which these variables
`will affect the ink release behaviour.
`
`The cell length has no significant effect on the release characteristics of that cell.
`However, as compression ratio increases, the ink release increases. As the effect of
`increasing the compression ratio is to decrease the depth/width of the cells and to
`increase their length, a closer correlation was expected. As compression ratio
`decreases, the depth of cells increases in line with the width, in order to compensate
`for the reduced length of the cells. As depth increases, release decreases, and also that
`as compression ratio decreases, release decreases. The same trends were observed
`between open area and screen ruling.
`
`As cells get deeper, the release of ink from that cell drops (Graph 4.3 7b ). This is
`inconsistent with previous theoretical work, which suggests that larger cells should
`allow more ink to be released. Kunz however demonstrates that cells with pointed
`bases retain more ink than those with rounded bases. As a deeper cell will lead to a
`more pointed base, it therefore follows that a deeper cell should retain more ink. It can
`also be seen in Graph 4.3 7c that as the open area of a cell increases, the release from
`that cell decreases. Schwartz [56] suggests that this may be due to refilling of the cell
`due to ink being squeezed out of the cell under impression. Kunz also suggests that
`this may be due to flow within the cell.
`
`Benk.reira and Patel [55] observed in models of ink transfer from several different
`types of cell, that release was independent of cell shape at approximately 30% of cell
`volume. They also observed that at lower Reynolds numbers (Equation 4.4) the ink
`transfer increases, but that under normal operating conditions the release is equal to
`1/3 specific cell volume.
`
`0
`
`0
`
`(
`
`128
`
`FAST FELT 2010 I pg. 143
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`0
`
`0
`
`0
`
`c
`
`Equat