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Author Topic: OBA free vs. RC resistance to UV  (Read 9833 times)

pcm81

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OBA free vs. RC resistance to UV
« on: August 22, 2015, 01:15:28 PM »

Good day all.
I am curious about your opinion on RC papers vs OBA free papers. I realize that usually OBA free criteria is most critical for fine art matte papers; but indulge me for this discussion.

About a year ago I did some black light tests for relative OBA content in various papers. Among the papers tested I looked at HP Premium Plus and Canon glossy papers. What I found to be interesting is that the back side of these papers lit up like a Christmas tree under the black light; yet the printing face covered with RC was one of the darkest I've seen. It makes sense if the resin used blocks UV; so no surprise there. What I am curios about is the practical aspect of these papers and if they can be treated as if they were OBA free. Since resin coat does not allow UV light to brighten the paper byOBA loaded base, then in theory the brightness of the paper will not shift either, since OBAs in base are not contributing to brightness anyways...

what do you all think?
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #1 on: August 22, 2015, 02:48:56 PM »

In my RC paper measurements for SpectrumViz there are papers that give a higher fluorescence value at the back and there are that have it at the front but none of the OBA content RC papers is blocked by the resin coating / polyethylene barrier that there is no fluorescence to measure. In fact there are very few RC papers without an OBA effect at the front and/or back.

My best guess is that your lamp has a UV output in a restricted spectral range, not triggering the specific OBA used at the front of the papers you measured. There is even a small chance that the spectral output of your lamp matches 1:1 the UV absorption of TiO2, quite often used as a normal whitening agent in the PE barrier, the TiO2 absorbed UV energy is emitted as heat beyond the visual red so not as a visible blue light. The spectrometer I use has a tungsten lamp that covers a wider spectral range in UV starting from the visual spectrum and going downwards, though it still might be cut for the shortest UV wavelengths that can trigger certain OBAs.

I do not see why paper manufacturers would use a resin coating / polyethylene film to block the OBA effect, they could have started from an OBA free (RC) paper base right away if their intention was to reduce the OBA effect. However they want the OBA effect as customers want cool papers. OBAs can be found in the paper base, in the barrier and in the inkjet coating, sometimes in all but few papers give an identical OBA effect at front and back.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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Tim Lookingbill

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Re: OBA free vs. RC resistance to UV
« Reply #2 on: August 22, 2015, 03:31:37 PM »

Maybe it's my misunderstanding but I thought "UV blocking" was essential for archival purposes in preventing fading and paper yellowing from oxidation over time.

UV blocking properties doesn't necessarily translate to seeing bluish brightening agents which I've never seen in any paper unless I place one paper brand next to another and in that case there will always be one yellower and bluer.

And there's something else on this subject I've been wanting to mention in that I've been noticing the more we as photographers become so over concerned about OBA papers the more I see us become interior decorators and designers when what we should be more focused on is what the image on the print communicates.

Let the interior and architectural designers decide what color of paper they like as a compliment to their interior designs (including museums). I have never had to deal with this issue of color of paper in my days as a graphic designer. This obsession with inkjet paper OBAs is getting ridiculous.

As a hobbyist photographer in the past what I didn't like were my prints from negatives I got back from the lab yellowing with age which they have as I see them today. So if a paper manufacturer has to put anti-aging agents in the paper to reduce or prevent oxidation or whatever yellows paper when exposed to the elements like my living room then as long as I see white paper I really don't care about OBAs.
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pcm81

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Re: OBA free vs. RC resistance to UV
« Reply #3 on: August 22, 2015, 08:38:57 PM »

OBAs basically absorb invisible UV light and emit light in far blue, but still visible, spectrum. Shining UV light, black light, on OBA full paper will make it seem blue, because there is not enough light in full visible spectrum to show the paper white. Normally this "extra" blue light adds to normal white hence making it appear whiter.

My train of thought is that if RC coat stops the  paper from glowing blue under UV light then either it blocks UV light or that RC coat blocks the far blue visible light that is reemitted by OBAs. In either case the visual brightness of paper is the brightness without the OBA contribution. Hence the crazy thought that with those RC coating the OBAs do not actually matter even if they are in paper base. 
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #4 on: August 23, 2015, 07:42:45 AM »

OBAs basically absorb invisible UV light and emit light in far blue, but still visible, spectrum. Shining UV light, black light, on OBA full paper will make it seem blue, because there is not enough light in full visible spectrum to show the paper white. Normally this "extra" blue light adds to normal white hence making it appear whiter.

My train of thought is that if RC coat stops the  paper from glowing blue under UV light then either it blocks UV light or that RC coat blocks the far blue visible light that is reemitted by OBAs. In either case the visual brightness of paper is the brightness without the OBA contribution. Hence the crazy thought that with those RC coating the OBAs do not actually matter even if they are in paper base.  

Which papers exactly did you measure? As written RC papers without Optical Brightening Agents are rare and RC papers with OBA content somewhere in their construction not showing any fluorescence effect of OBAs are even more rare. I measured hundreds of RC papers, can not recall one that fits the last description.

I'm interested in your blacklight description too. Which wavelength does it generate? It might be a tool to discover TiO2 in inkjet papers.

Edit: As there is no reply yet on the questions I asked here I could as well add an assumption. Reading back the docs on LILIS it could actually be the LILIS effect you observe. If the sheets you checked have been exposed to light a long time (as prints?) and then archived in the dark the PE layer containing TiO2 + OBAs can have the deteriorated OBA as yellow stain in that layer. That could act as a filter for your UV lamp to a degree that even the OBA in the paper base is not excited and if excited the emitted blue light from the paper base may not get through that yellow filter on its way back to the front. A way to see whether the first filtering happens is to shine through the sheet and look at the back, if you see more blue then the UV is not blocked but the emitted blue light coming from the paper base is filtered on its way to the front. The PE barrier at the back of the paper has no influence, it is transparent. If this is the case you see the worst effect of OBA deterioration and not a wonderful property of PE layers that counteracts the paper manufacturer's intention to deliver a cool white paper. For LILIS see http://forum.luminous-landscape.com/index.php?topic=102676.20

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots



« Last Edit: August 24, 2015, 09:18:12 AM by Ernst Dinkla »
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #5 on: August 23, 2015, 08:50:13 AM »

Maybe it's my misunderstanding but I thought "UV blocking" was essential for archival purposes in preventing fading and paper yellowing from oxidation over time.

UV blocking properties doesn't necessarily translate to seeing bluish brightening agents which I've never seen in any paper unless I place one paper brand next to another and in that case there will always be one yellower and bluer.

And there's something else on this subject I've been wanting to mention in that I've been noticing the more we as photographers become so over concerned about OBA papers the more I see us become interior decorators and designers when what we should be more focused on is what the image on the print communicates.

Let the interior and architectural designers decide what color of paper they like as a compliment to their interior designs (including museums). I have never had to deal with this issue of color of paper in my days as a graphic designer. This obsession with inkjet paper OBAs is getting ridiculous.

As a hobbyist photographer in the past what I didn't like were my prints from negatives I got back from the lab yellowing with age which they have as I see them today. So if a paper manufacturer has to put anti-aging agents in the paper to reduce or prevent oxidation or whatever yellows paper when exposed to the elements like my living room then as long as I see white paper I really don't care about OBAs.

My view on this is that the artist, photographer, should decide what paper color he wants for the print's content.  When I print for customers like that I will tell them what the consequences are of selecting a neutral to very cool paper with the then inevitable OBA content. From more "metamerism" in varying light conditions, dampened OBA effect when framed behind normal glass and no OBA effect behind UV blocking glass, up to the paper white color shift issues when exposed to UV, visible light and/or oxygen. Maybe when they are still interested I would even mention the LILIS effect. I would mention some OBA papers that stand time better according Aardenburg-Imaging tests. I then express my hope that OBA content papers will appear without said issues as there is rightly a demand for cool papers.

There are some ideas I have for using OBAs in a sensible way, even a way that create the effect and will protect prints against UV light. There are also quality differences in OBAs, white textiles can have better OBAs in the fibres; https://en.wikipedia.org/wiki/Optical_brightener
Before OBAs were introduced papers could get a bluish tint in their white by adding blue etc. With the consequence that the overall white reflection dropped. This is what makes OBAs so attractive, the total white "reflection" can go beyond the amount of visible light falling on the paper. Given their low price they are also used to compensate lower quality paper base and paper coating components that give a low white reflection. There are some weird paper white spectral plots in SpectrumViz that show papers depending on OBA fluorescence + some reflection at the red side of the visible spectrum, little in between. Ideal paper to show color inconstancy in changing light conditions.

The UV blocking with thin layers of UV blocking varnishes on prints is questionable. Test results show improvement in fade resistance of the inks and (OBA) paper whites, both in Wilhelm and Aardenburg tests. The thin layer of varnish is more likely preventing gas fading of the ink colors and OBA dyes. Thicker UV blocking varnishes on canvas is another matter, in that case both gas and UV blocking can be achieved with consequently less OBA effect if there are OBAs in the canvas.

Good paper bases will not yellow in time due to oxygen or UV. Your experience with yellowed prints is more likely the result of OBA content, it has been used in most photo papers (silver halide, chromogenic, inkjet) since the 1950's, possibly earlier, the warm portrait papers not included. What has been described as bad developing practices causing yellowing, darkening, of photo papers in time may well be a wrong observation and the paper color shift could be more related to the LILIS effect, at least Mark McCormick mentioned that possibility. Something that has to be researched too.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
« Last Edit: August 24, 2015, 09:12:42 AM by Ernst Dinkla »
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Tim Lookingbill

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Re: OBA free vs. RC resistance to UV
« Reply #6 on: August 23, 2015, 03:48:07 PM »

I then express my hope that OBA content papers will appear without said issues as there is rightly a demand for cool papers...

What has been described as bad developing practices causing yellowing, darkening, of photo papers in time may well be a wrong observation and the paper color shift could be more related to the LILIS effect, at least Mark McCormick mentioned that possibility. Something that has to be researched too.

My hope is not for cool looking papers but just plain white. But in real world print substrate viewing conditions there appears to be as many versions of OBA hues as their are white light viewing conditions that it makes it futile to obsess over for photographers who should be more concerned about archival issues and making sure their work is presented in the best light. Below is an example of all the hues of the rainbow presented by an OBA paper that appears to change hue according to the light it's viewed under.

If all a photographer can do to insure this is to only hang their work in strictly controlled viewing conditions as in museums and galleries,  not too many folks are going to see their work.

What is the LILIS effect. I tried to look it up but got nothing.
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #7 on: August 24, 2015, 06:52:15 AM »


What is the LILIS effect. I tried to look it up but got nothing.

Tim, there will be more on this subject but a good start:
http://forum.luminous-landscape.com/index.php?topic=102676.20

Yes, I try to avoid OBAs in papers too. I look for the highest paper white reflection papers without OBAs as their warmth is less prominent that way but they are still warmer than neutral and when a paper has to be neutral or cool on customer's request I check the ones with the lowest OBA content and a high white reflectance based on the other paper components. The total of the spectral plot close to 100% reflection, without hills and peaks, covering the visible spectrum from 400-800 nm. Plain white is Lab 100 0 0 for me, with a straight spectral plot running from 400-800 nm. It does not exist, one might print on Teflon sheets but the ink bond will be horrible. For most users a plain white paper is near Lab 97 0 -5 or beyond, OBA territory. With galleries that use halogen display lights below 3000K they might find a paper with Lab b -10 more suitable. Yes, after that color can be all over the place if the next gallery has LEDs of whatever spectral output installed. Better fade resistant OBAs will not solve that problem but tirades against the use of OBAs will not change public opinion on plain white either.

Archival is an ambiguous term, I go to the Aardenburg-Imaging tests results and look for the paper white changes in time, check Mark's UV and UV-cut spectro measurements to compare them with my spectral plots and hope for the best in the end if it has to be an OBA paper. So far every 3 or 4 years a new fading phenomenon appears and over the 15 years I saw a change from bad inks that improved so much that now papers have to be examined. That is progress. I expect that the inkjet coating bond to the paper base is the next "archival" issue that has to be tackled, could be the weakest link.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
« Last Edit: August 24, 2015, 09:09:26 AM by Ernst Dinkla »
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Paul Roark

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Re: OBA free vs. RC resistance to UV
« Reply #8 on: August 24, 2015, 11:28:36 AM »

[... I expect that the inkjet coating bond to the paper base is the next "archival" issue that has to be tackled, could be the weakest link. -- Ernst [/quote]

Ernst, you may have noticed my post in the B&W Digital Print forum at https://groups.yahoo.com/neo/groups/DigitalBlackandWhiteThePrint/conversations/messages/108596 .  Premier Imaging's "Platinum Rag" paper is a glossy/luster paper that is OBA free and has no polyethylene barrier between it and the paper base.  Almost all glossy papers use these barriers to achieve their smoothness, but I also suspect those barriers are a major factor in the glossy papers' very poor performance in "Shadowblade's" well done test of papers at http://forum.luminous-landscape.com/index.php?topic=87926.0 .  (See also http://www.dp3project.org/preservation#crackinginkjetlight ).

One of the interesting possibilities of a paper with no barrier between the inkjet receptor coating and the base is the use of a post-printing spray or other coating that penetrates the paper and helps lock the layers together.  I sprayed the Platinum Rag with Premier Art Print Shield, and it was clear that the solvent was, in fact, reaching the paper base.  A lower viscosity spray like Lascaux would probably do so even more readily.  Whether any water-based coating can do this is more questionable.  And, of course, it would be good to see comparative aging tests after treatment to see if this will affect the problem.  (Note that I don't put much if any faith in the standard aging tests that do not cycle the temperature and humidity, thus avoid the differential expansion and contraction of the layers that is probably a major cause of the issues deterioration of the coated papers.)

Paul
www.PaulRoark.com
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #9 on: August 25, 2015, 04:50:20 AM »

Paul,

When coating canvas I deliberately spray a 1:1 dilution of Lascaux (water based) varnish to get more penetration of the varnish. Aiming at the same anchoring of the coating like you describe. It means I have to spray more layers for a build up with drying in between but I have a silkscreen dryer tunnel to speed that up. I have not done tests to verify whether that method works though but customers have not complained either.

There are more papers gloss and matte without a PolyEthylene foil barrier or a Resin Coated spray/coated layer, that does not describe all possible barriers though. We generalize with the term RC papers, there are differences within that group as a technician from Sihl rightly told me. I have checked most of the RC papers (foil + spray layers) in SpectrumViz by splitting the layers of hot water soaked strips and put only the PE layer variants in the RC map. Should rename that map. There may be some left there that I did not check. The rest, with or without sprayed resin coats, went into the ordinary inkjet paper map, most with the sprayed resin in the glossy, satin categories. There are glossy and matte papers without any visible ink medium barrier. Visible as based on my method of dissection which is not perfect.

So it is not that simple. Non RC papers with several layers of coating will have a kind of ink medium barrier/membrane (possibly PVA but could be something else) right on top of the paper base, an ink medium absorbent layer on top of that (say cat litter type) and a pigment catching layer on top of that. Not mentioning whitening agents etc mixed in on one or more layers. PVA exists in varieties, mainly grades of hydrolization so the membrane can act as a blocker at print time keeping the paper base flat but allowing the water, glycol, glyzerine to evaporate in time after printing. PE + RC papers have only one way to escape, through the front and we know what happens then when framed too early.

If you want a penetrating varnish etc to get a bond to the paper fibers there has to be a bond to PVA too and I expect that the PVA has already a good bond to the fibres. PVA though is quite inert to aromatic solvents used in sprays. For example it is used as a separation layer in polyester molding, as a masking emulsion in silkscreen printing, less hardened for aromatic solvents and more for water based inks. Alcohols, glycols, water (in time) should dissolve it though. If the membrane is of another kind of polymer that could get a bond to spray varnish it may work. I just do not know what kind of membranes are used and I doubt the better quality papers go without a membrane. Maybe soaking a strip of paper in different solvents could show what barrier is used and the varnish then selected on compatibility.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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Paul Roark

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Re: OBA free vs. RC resistance to UV
« Reply #10 on: August 25, 2015, 11:40:15 AM »


When coating canvas I deliberately spray a 1:1 dilution of Lascaux (water based) varnish to get more penetration of the varnish. Aiming at the same anchoring of the coating like you describe. ...

One issue that concerns me regarding the water-based coatings and glossy inkjet papers/substrates is whether the coating material, as opposed to just the water, is actually penetrating the micro-porous coating.  I've been told that water-based coatings are suspensions of what one of the company's technical people described as "gooey golf balls" of coating material.  They are like the pigment inks themselves in that they are suspensions.  The micro-porous coatings, as I understand them, allow the water through but hold the pigment particles on the surface.  Is the same thing happening with water-based coatings?  The fact that the base gets wet does not mean the "glue" that we hope would help hold the material together is getting to where we want it to get.

On the other hand, with a solvent based coating, it's like a dye.  The coating is dissolved in the fluid.  So, if the fluid gets through the material, the binder is also.

From a user perspective, it may be that the only way we'll be able to test this is to do something like you describe in terms of actually trying to separate the layers of the materials.  If we knew the size of the suspended "particles" in the coatings compared to the "holes" in the paper coating, that information may also help determine if this is an actual issue or not.  However, I don't think I've ever seen that information.

Paul
www.PaulRoark.com
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Some Guy

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Re: OBA free vs. RC resistance to UV
« Reply #11 on: August 25, 2015, 12:22:06 PM »

A quick "penetration comparison test" might be to take a lacquer (solvent) like Premier Art's "Print Shield" and spray it onto a thin paper stock like tissue or typing paper, and compare it to the same with a sprayed water-base over-coating.  Might be the solvent penetrates to the back of the paper, and the water-based remains on one side?

If it remains on one side, I would think it would also tend to cracking easier on wrapping.  I've used the Art Shield and rolled and stretched it and never seen cracking occur, but some roll-on water-based and clean-up brands that appear as a thin jelly have been awful on cracking.

SG
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #12 on: August 25, 2015, 05:58:16 PM »

One issue that concerns me regarding the water-based coatings and glossy inkjet papers/substrates is whether the coating material, as opposed to just the water, is actually penetrating the micro-porous coating.  I've been told that water-based coatings are suspensions of what one of the company's technical people described as "gooey golf balls" of coating material.  They are like the pigment inks themselves in that they are suspensions.  The micro-porous coatings, as I understand them, allow the water through but hold the pigment particles on the surface.  Is the same thing happening with water-based coatings?  The fact that the base gets wet does not mean the "glue" that we hope would help hold the material together is getting to where we want it to get.

On the other hand, with a solvent based coating, it's like a dye.  The coating is dissolved in the fluid.  So, if the fluid gets through the material, the binder is also.

From a user perspective, it may be that the only way we'll be able to test this is to do something like you describe in terms of actually trying to separate the layers of the materials.  If we knew the size of the suspended "particles" in the coatings compared to the "holes" in the paper coating, that information may also help determine if this is an actual issue or not.  However, I don't think I've ever seen that information.

Paul
www.PaulRoark.com

Not all water based coatings are dispersions and if we consider PVA as a possible barrier polymer then alcohols or glycols could dissolve it too. The old method to fix drawings was done with schellac and spirit, PVA  can be used dissolved in water/alcohol and there are more. I think there are polyurethanes that can be dissolved in water, not just used in dispersions. Soluble glass is still at the back of my mind as a binder/fixer for inkjet prints. I recall a sign printer who claimed he could make outdoor signs weatherproof that way despite the fact that he used an Encad dye printer at that time, more than ten years ago. It is correct that a dispersion with for example an acrylic polymer is not a real solution and behaves differently. The flow is different, primers were the first usable water based car paints as the top layers required a better flow that was harder to achieve with dispersions.


Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots


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Paul Roark

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Re: OBA free vs. RC resistance to UV
« Reply #13 on: August 26, 2015, 11:13:01 AM »

One response from a representative of a popular water based coating confirmed my suspicions that the binding property of the coating (cross linking technology) that gives it strength to protect Canvas from cracking when doing a gallery wrap, will also prevent it from flowing through the micro-porous coatings.

As I read the Wiki entry on PVA, it looks like that is the same type of suspension or emulsion that I'm talking about.  See https://en.wikipedia.org/wiki/Polyvinyl_acetate and follow the link to the article on "emulsions."

I'm skeptical that the water-based materials are going to help the adhesion of the inkjet receptor coating to the base.  They are designed to and do protect the surface of the print, but they may not get at the issue we're discussing. 

Paul
www.PaulRoark.com
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MHMG

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Re: OBA free vs. RC resistance to UV
« Reply #14 on: August 26, 2015, 11:34:14 AM »


I'm skeptical that the water-based materials are going to help the adhesion of the inkjet receptor coating to the base.  They are designed to and do protect the surface of the print, but they may not get at the issue we're discussing.  

Paul
www.PaulRoark.com

I'm skeptical that any "penetrating" varnish can improve the bond of any of the sub layers to the layer right beneath them. That bond is dictated by the chemical adhesion at the molecular level and also the original micro surface characteristics of the two layers forming the interface. Penetrating varnishes tend to improve their own bond to the top layer they have been applied to, nothing more, unless they are actually dissolving components in the sublayers thus reflowing one or more sublayers, but that's a very risky proposition for any printed image which usually leads to lesser not greater image quality.  Varnishes do indeed offer both protective and decorative properties to the piece as a whole, but again, consolidation of any flake prone layers is not usually all that successful unless there is serious cracking and flaking to begin with in the artwork, and one is trying to find some way to consolidate the existing loose debris.

The water based emulsified acrylic varnishes form films that are more porous and thus don't typically achieve as high a vapor barrier for molecules like water, oxygen, etc. as their non aqueous solvent based counterparts, but they are typically less toxic and more convenient to apply for the enduser, so they have a nice role to play in the market for protective overcoats.

Additionally, one really does need to check the compatibility of any varnish with some longevity testing.  Even the water base variety have additional chemistry (like ammonia) in that water that can attack the integrity of the inkjet ink's encapsulation polymers thus actually reducing the light fade and ozone resistance rather than improving it as is often claimed by the manufacturer of the coating.


cheers,
Mark
http://www.aardenburg-imaging.com
« Last Edit: August 26, 2015, 01:55:09 PM by MHMG »
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pcm81

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Re: OBA free vs. RC resistance to UV
« Reply #15 on: August 28, 2015, 10:21:10 PM »

Sorry for taking so long to reply to my own thread; I had to go on a work assigned road trip with limited access o internet.

As a nuclear engineer and a physicist, who is a mere hobbyist printer this is how i understand the archivability situation:
1. Acid present in paper will eat away the papers flexibility, causing it to become brittle; hence archival paper must be acidically neutral ph=7.
2. Some substances like lignin can produce acid over time, hence also needs to be eliminated from paper to satisfy criteria #1 above.
3. Optical brighteners are chemical compounds that absorb invisible UV light and re-emit it in far blue, but visible spectrum. This causes paper to appear whiter than it really is when a UV source is present.  This process consumes the optical brightener resulting in condition knows as OBA burn-out at which point paper shows its true white color without the OBA contribution.

What this means is that in absence of UV light OBAs neither contribute to brightness of the paper not do they burn out (they could still evaporate or chemically fall apart). In presence of UV light rate of OBA burnout will be proportional to UV light concentration (Flux Density) on surface of the paper (this is why accelerated testing is possible).

Now is the interesting part, If we block all UV light from reaching OBA in base of the paper, the paper will show white "equivalent to" its OBA free version.

This is why i am wondering about RC coated papers like HP Premium Plus, which glow very bright blue under UV light from the back, but present equivalent dark grey color as Archival OBA Free fine art papers like Breathing Color Pura Smooth.

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Alan Goldhammer

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Re: OBA free vs. RC resistance to UV
« Reply #16 on: August 29, 2015, 09:01:59 AM »

Lignin causes premature yellowing of paper and it's not a result of an acid effect as it's a poly phenolic compound that provides structural integrity to cell walls.  It's oxidized to various chromophores that give rise to the yellow color.  The process is free radical mediated and not an acidic process.  It is routinely removed during the paper making process and the reason that cotton is preferred in paper making is because of the very low lignin content.
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MHMG

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Re: OBA free vs. RC resistance to UV
« Reply #17 on: August 29, 2015, 09:25:17 AM »


Now is the interesting part, If we block all UV light from reaching OBA in base of the paper, the paper will show white "equivalent to" its OBA free version.

This is why i am wondering about RC coated papers like HP Premium Plus, which glow very bright blue under UV light from the back, but present equivalent dark grey color as Archival OBA Free fine art papers like Breathing Color Pura Smooth.



I have not encountered any RC paper that doesn't have relatively high levels of OBA in the paper base. That base is then sandwiched between two Polyethylene (PE) layers. The PE layer just below the image bearing layer is also filled with TiO2 and with rare exceptions more OBA as well. The PE layer facing the back is often just clear PE, so your UV lamp is going to activate the paper base OBA and its fluorescence easily shines through the clear PE. The TiO2 in the image side PE layer impedes the penetration of the UV radiation from the front side and blocks the fluorescence of the OBAs in the paper base from reaching the viewer, not entirely which is why the manufacturer still puts OBAs in the paper core, but to a significant degree. So, to get the whitening boost from OBAs, RC papers often incorporate quite a significant amount of OBAs in the paper base, the PE-TiO2 layer, and even the ink receptor layer of RC inkjet media at times. Now here's the big catch-22 for archival properties of RC media. Depending on it's structure TiO2 has varying  photo reactive properties that create free-radicals in the PE layer which in turn promote serious PE degradation over time. The manufacturer typically adds additional anti-oxidants to counter the problem, and this approach extends the "life" of the PE layers significantly, but it's not a perfect answer.  There also appears to be another serious degradation reaction, namely a reaction between the TiO2 and the OBAs such that when the OBAs do degrade they don't remain colorless. They form additional yellowish stain over and above the yellowing due to loss of fluorescence. This phenomenon is one I've taken to calling the LILIS effect, i.e., low intensity iight induced staining. This problem has been under reported in the conservation literature and print longevity ratings because the stain is also a light bleachable stain, but it takes relatively high light levels  on display (or those encountered in accelerated light fade test units) to suppress this additional stain from appearing. However, within weeks after placing in dark storage the stain will begin to reappear, so the light bleachable behavior of the LILIS effect is not a practical solution to this staining issue, IMHO.  What appears to be a promising fix to the LILIS problem is for the manufacturers of RC media to start giving us  RC papers with OBA free PE-TiO2 layers. The PE layers will still eventually degrade, but the LILIS stain formation will probably not occur. This tentative conclusion is based on my recent testing of Epson Proofing Paper white Semimatte RC paper. It has no OBAs in it's PE-TiO2 layer and yet still delivers a beautiful neutral white finish. All other RC media I have tested contain OBAs in the TiO2-PE layer including the famous Fuji Crystal Archive II paper used in traditional photo finishing, and all of them exhibit varying degrees of the LILIS effect now that I know how to look for it in my accelerated light fade studies.

Thus, no free lunch for RC media on continuous display. As such, I now consider RC prints to require more special care compared to many non RC media in order to extend the life of the image. RC media should primarily be stored in albums, folios, document boxes, etc., and curated on display with discretion rather than used in a constantly displayed situation if the print is deemed to have long term historic, artistic, or sentimental value. Cool and cold storage is also recommended for museums and archives.  UV block glazings will also slow down the rate of OBA burnout (but not entirely eliminate it), but the visual appearance of the print may shift undesirably when using said glazings as the media color and image highlights shift to the more  native "yellow" appearance without the OBA fluorescence.

regards,
Mark
http://www.aardenburg-imaging.com
« Last Edit: August 29, 2015, 09:30:10 AM by MHMG »
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Ernst Dinkla

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Re: OBA free vs. RC resistance to UV
« Reply #18 on: August 29, 2015, 11:30:22 AM »

Sorry for taking so long to reply to my own thread; I had to go on a work assigned road trip with limited access o internet.

As a nuclear engineer and a physicist, who is a mere hobbyist printer this is how i understand the archivability situation:


No measurements for HP Premium Plus in SpectrumViz so I can not compare your observations with my measurements. I think there were two versions of that paper, a swellable type for dye ink printers and today it is a mordant? type for dye inks but more universally usable. Aardenburg-Imaging has 5 tests for HP Premium Plus, all indicate OBA content with a YES. and A-M only measures at the printing side of the papers! They date back to 2008 so will be of the swellable type I guess.

Paper base properties are not really relevant if other components are more prone to degradation, Resin Coating + the added TiO2 whitening agent has been a weak link in the past for this kind of papers, PE cracks in time. Inkjet coating bond as already described in the other messages is probably a weak property too. All of a chemo-mechanical character. The RC papers will normally contain a chemically stable paper base but more important the two PE or RC barriers, at front and back of the paper slow down any paper base degradation you describe here, yellowing of the paper base between the two barriers is unlikely a first problem to happen. Even the OBA in the paper base survives longer there than at the open inkjet coating side.

With inks that have a good fade resistance, the OBA content in different layers of the paper becomes the real thing to worry about before any mechanical or chemical aspects become an issue if there has to be an 'archival' label on a print. The idea that in time after degradation of the OBAs any OBA paper will fall back to a non-OBA paper state is an illusion. Many OBA papers will degrade and the OBA dyes do not disappear or become transparent in that process, they produce a stain. Few may not. The degradation of OBAs happens on UV light, visible light, oxidation to O3 and oxygen etc like all dyes are prone to. As already mentioned in this thread. So by just blocking UV light you are still not there to keep your OBAs throughout time. And why would you like to preserve your OBAs if they do not have to function. We have OBA papers to get that cooler paper white when UV light is part of the viewing light. If the last is not adding that coolness + pulling up the total paper white reflectance you are better off with a high quality white reflectance sans OBAs.

Your return to the logic that a potential preservation of a print happens by the RC barrier UV filtering is one I do not see the logic or the benefits off, both for practice. If your HP Premier Plus printing paper side shows no OBA effect and the back side shows it, it is either your UV lamp or an already degraded OBA layer stain at the printing side that causes that effect.  The last can be made translucent, more or less, by exposure to UV containing sunlight for example and then your UV lamp might stir up the remaining OBAs in the paper base even from the front. Just a guess.

I share your wondering about that paper in your last line, what you actually have there that shows the effect you describe. I do not see a practical use of it though. Beaten a dead horse for too long in this thread so this is the last reply on this subject from this graphic industry pro.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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Alan Goldhammer

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Re: OBA free vs. RC resistance to UV
« Reply #19 on: August 29, 2015, 01:02:13 PM »

The PE layer just below the image bearing layer is also filled with TiO2 and with rare exceptions more OBA as well. The PE layer facing the back is often just clear PE, so your UV lamp is going to activate the paper base OBA and its fluorescence easily shines through the clear PE. The TiO2 in the image side PE layer impedes the penetration of the UV radiation from the front side and blocks the fluorescence of the OBAs in the paper base from reaching the viewer, not entirely which is why the manufacturer still puts OBAs in the paper core, but to a significant degree. So, to get the whitening boost from OBAs, RC papers often incorporate quite a significant amount of OBAs in the paper base, the PE-TiO2 layer, and even the ink receptor layer of RC inkjet media at times. Now here's the big catch-22 for archival properties of RC media. Depending on it's structure TiO2 has varying  photo reactive properties that create free-radicals in the PE layer which in turn promote serious PE degradation over time. The manufacturer typically adds additional anti-oxidants to counter the problem, and this approach extends the "life" of the PE layers significantly, but it's not a perfect answer.  There also appears to be another serious degradation reaction, namely a reaction between the TiO2 and the OBAs such that when the OBAs do degrade they don't remain colorless. They form additional yellowish stain over and above the yellowing due to loss of fluorescence. This phenomenon is one I've taken to calling the LILIS effect, i.e., low intensity iight induced staining. This problem has been under reported in the conservation literature and print longevity ratings because the stain is also a light bleachable stain, but it takes relatively high light levels  on display (or those encountered in accelerated light fade test units) to suppress this additional stain from appearing. However, within weeks after placing in dark storage the stain will begin to reappear, so the light bleachable behavior of the LILIS effect is not a practical solution to this staining issue, IMHO.  What appears to be a promising fix to the LILIS problem is for the manufacturers of RC media to start giving us  RC papers with OBA free PE-TiO2 layers. The PE layers will still eventually degrade, but the LILIS stain formation will probably not occur. This tentative conclusion is based on my recent testing of Epson Proofing Paper white Semimatte RC paper. It has no OBAs in it's PE-TiO2 layer and yet still delivers a beautiful neutral white finish. All other RC media I have tested contain OBAs in the TiO2-PE layer including the famous Fuji Crystal Archive II paper used in traditional photo finishing, and all of them exhibit varying degrees of the LILIS effect now that I know how to look for it in my accelerated light fade studies.
Interesting comment.  Do you know what the relative reactivity might be for barium sulfate versus TiO2?  Both are commonly used whitening agents though I believe TiO2 is less expensive on a bulk basis than barium sulfate.  It has been a lot of years since I studied this stuff in college and I know that some of the reactivity is dependent on the crystal structure of the compound.  I wouldn't wait around for manufacturers to reformulate OBA free papers since there are lots of users that just like the performance.  I have a friend whose comment back is, "I'll just reprint if there is a fading/color problem."
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