Dark colors splotchy

[carlathebluegeckoprinting.]

STS Mutoh VJ628D - 90% white under CMY, 50% under K.  Dark colors inconsistent, see pics I uploaded.  

I switch rolls of cold peel film to new roll different lot, to rule out bad film.  Problem is consistent over different films.

Nozzle tests come out perfect.  Temperature in the shop is 69 degrees F. 

The issue is the way the dark blue on the letter A fades to a magenta on the bottom of the legs.  But on the light box and on the film everything looks good.

I have grown to absolutely hate this STS printer.  Any ideas?

[johnson4]

Have you tried printing a few large blocks of solid color? See how it does with that?

[carlathebluegeckoprinting.]

Yes.  I did several tests prints with large areas of solid color and the splotchiness runs over from one color to the next making me believe that is has something to do with the white under.  The white looks solid and even to the eye.

[johnson4]

31 minutes ago, carlathebluegeckoprinting. said:

Yes.  I did several tests prints with large areas of solid color and the splotchiness runs over from one color to the next making me believe that is has something to do with the white under.  The white looks solid and even to the eye.

Usually when I print a color block of each individual color C M Y K with and without an under base it will show if there is an issue and what is causing that issue if it's related to the ink or jetting. 

 

Could be a film issue too.

Edited January 26, 2023 by johnson4

[carlathebluegeckoprinting.]

I had a film issue previously - uneven blacks with or without white under. It turned out to be that my printer does not like hot peel film, tried different rolls with same result.  Went back to the economy cold peel and everything was perfect.

The print I am doing now is onw we have done quite a few of.  It printed perfectly on beginning of roll of cold peel earlier this month. Then today, it began with the splotchiness again.  It was the end of the roll so I assumed maybe film issue.  But new roll, different lot, and different brand and issue is exactly the same, so I am ruling out the film for now.

RIP settings are the same. Only difference is we have had a rare cold spell here in AZ, and it is all we can do to get the shop up to 70 degrees, and I am thinking this has something to do with it.

[johnson4]

41 minutes ago, carlathebluegeckoprinting. said:

I had a film issue previously - uneven blacks with or without white under. It turned out to be that my printer does not like hot peel film, tried different rolls with same result.  Went back to the economy cold peel and everything was perfect.

The print I am doing now is onw we have done quite a few of.  It printed perfectly on beginning of roll of cold peel earlier this month. Then today, it began with the splotchiness again.  It was the end of the roll so I assumed maybe film issue.  But new roll, different lot, and different brand and issue is exactly the same, so I am ruling out the film for now.

RIP settings are the same. Only difference is we have had a rare cold spell here in AZ, and it is all we can do to get the shop up to 70 degrees, and I am thinking this has something to do with it.

It could, more important than temperature is your humidity depending on what method you are using to heat the area. Over here I don't have to worry about it, even when it's cold it's humid. If your humidity is less than 45-50% that can cause issues as well, but generally you would see that on a nozzle check.  Humidity is more important than temperature in my eyes, as that is what will determine the rate at which the ink dries/clogs as it sits in the head waiting to be jetted. 

 

Does that machine use STS inks?

Edited January 26, 2023 by johnson4

[carlathebluegeckoprinting.]

Yes, we use STS inks.  Our climate control was not working, finally fixed it today - so now can maintain a constant 72 degrees.  It was dropping to the low 60's at night - and I know that is not good for the white inks.

Humidity is now 15% which is about the best we can get in the AZ desert other than during monsoon.  A water distillation system is going to run around $1000 if we wanted to install a humidifier - simply no way to use our water in a humidifier out of the faucet or with a cheap filter - coats everything with a white mineral deposit. 

Anyway - with the temp control fixed, on Monday I will run some tests to see if the machine prints any better.

[johnson4]

5 hours ago, carlathebluegeckoprinting. said:

Yes, we use STS inks.  Our climate control was not working, finally fixed it today - so now can maintain a constant 72 degrees.  It was dropping to the low 60's at night - and I know that is not good for the white inks.

Humidity is now 15% which is about the best we can get in the AZ desert other than during monsoon.  A water distillation system is going to run around $1000 if we wanted to install a humidifier - simply no way to use our water in a humidifier out of the faucet or with a cheap filter - coats everything with a white mineral deposit. 

Anyway - with the temp control fixed, on Monday I will run some tests to see if the machine prints any better.

Wow, that’s really low humidity compared to what I am used to. 
 

I run my printers from 50F-80F without issue, as long as I keep the humidity the 45%+. Anytime my humidity drops below 40 I get clogging mid print, and one heck of a time when sitting over night or the weekend. 
 

I don’t know “ scientifically” but to me the temperature only really changes the viscosity of the ink, which hasn’t been a big deal until it hits in the 40’s in my workspace.
 

The lower the humidity the faster the ink carrier evaporates since the air is drier pulling the moisture from it quicker. 
 

for me it’s hard in the summer to keep humidity up when I run the A/C since it inherently removes moisture from the air, winter time is a blessing, everything just works lol. It’s almost always over 50 percent humidity here, unless in an air conditioned space so I’m lucky in that aspect. 
 

I wish you luck and hope you can figure it out, hopefully that fixes your issue.