When a screen does not expose correctly, the first thing many printers change is the exposure time.
They add a few seconds. They subtract a few seconds. They change the emulsion, blame the exposure unit or assume the washout pressure is wrong.
Sometimes the real problem is sitting between the light source and the screen.
The film positive.
A film positive may look black when placed on a white table and still fail to block enough exposure light. It may contain soft edges, inconsistent density, missing halftone dots, banding or small gaps that become much more obvious after the screen is exposed.
Your exposure unit can only reproduce the information the film gives it.
If the film is weak, inaccurate or inconsistent, even a properly coated screen and a good exposure unit may produce disappointing results.
That raises an important question:
Are your film positives costing you good screens?
The Film Positive Is Part of the Exposure System
A film positive is not simply a transparent sheet carrying black artwork.
It is an important part of the complete exposure system:
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Light source
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Film positive
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Film-to-screen contact
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Emulsion
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Mesh
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Exposure time
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Washout procedure
All of these elements must work together.
The black areas of the film are intended to block exposure light. The clear areas allow light to reach the emulsion and harden the stencil.
When the image areas are not dense enough, unwanted light can pass through the film. That light may begin exposing the emulsion beneath fine lines, small text and halftone dots that are supposed to wash away.
The result can include:
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Lost detail
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Soft edges
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Closed halftones
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Fine lines that disappear
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Small text that becomes difficult to read
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Inconsistent washout
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Screens that appear overexposed in some areas
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A narrow exposure window
The problem may look like incorrect exposure time, but the exposure unit may simply be revealing a weakness in the film.
“It Looks Black” Is Not a Complete Test
One of the most common mistakes is judging film density only by looking at the film on a table.
Most printed black images will look dark against a white background.
The better question is:
How much exposure light can pass through that black image?
Hold the film in front of a strong light.
A solid black area should appear dense and even. If you can clearly see the light source through the artwork, the film may not be blocking enough light for dependable screen exposure.
Look for:
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Thin or gray-looking black areas
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Pinholes inside solid artwork
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Horizontal banding
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Uneven ink coverage
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Missing portions of fine lines
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Jagged or soft edges
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Incomplete halftone dots
A transmission densitometer provides a more precise measurement, but even a strong backlight and magnification can reveal many obvious problems.
The film does not need to look attractive.
It needs to perform as a light-blocking production tool.
Weak Films Create an Exposure Compromise
When a film positive does not block enough light, printers often shorten the exposure time to make the image wash out.
That may open the image, but it can create a new problem.
The clear areas of the screen may now be underexposed.
This can result in:
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Soft or slimy emulsion
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Premature stencil breakdown
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Reduced chemical resistance
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Emulsion washing away where it should remain
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Shorter screen life during production
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Screens that require excessive touch-up
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Inconsistent reclaiming
The printer becomes trapped between two bad options:
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Expose long enough to properly harden the stencil and lose image detail
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Shorten the exposure enough to open the image and weaken the stencil
A high-density film creates a wider, more dependable exposure window. It allows the clear areas to receive sufficient light while protecting the image areas underneath the black ink.
That is why film density matters so much.
Seven Film Problems That Can Damage Screen Quality
1. Insufficient Black Density
A standard desktop printer may produce an image that looks black but remains too transparent for reliable exposure.
The problem can become more noticeable with:
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Long exposure times
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Powerful LED exposure units
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Fine halftones
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High mesh counts
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Detailed artwork
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Photopolymer emulsions
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Small text and thin lines
Professional film output systems may use RIP software, calibrated settings and all-black ink configurations to increase density and produce more reliable positives.
2. Clogged or Misfiring Printhead Nozzles
A printer can appear to be operating normally while individual nozzles are missing.
This may produce:
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Horizontal lines
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Small gaps
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Inconsistent solid areas
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Distorted halftones
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Missing artwork details
Those defects can expose directly into the screen.
Always perform a nozzle check before printing important production films. If the nozzle pattern is incomplete, correct the printer problem before trusting the output.
3. Printing on the Wrong Side of the Film
Many waterproof inkjet films have a coated printing side designed to receive and hold ink.
Printing on the uncoated side may cause:
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Poor ink adhesion
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Weak density
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Smearing
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Slow drying
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Soft detail
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Ink that scratches away easily
Before loading a new film product, confirm which side should receive the ink. The coated side may feel slightly tackier or react differently when touched with a lightly moistened fingertip, depending on the product.
Follow the film manufacturer’s instructions whenever possible.
4. Incorrect Printer or RIP Settings
Printer settings affect how much ink is deposited and how the image is rendered.
The wrong media setting may reduce ink deposit. Incorrect resolution or screening settings may damage small details. Outputting halftones through an uncontrolled workflow can change dot shape, frequency or angle.
Professional output requires consistent control over:
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Resolution
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Ink deposit
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Halftone frequency
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Halftone angle
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Dot shape
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Image orientation
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Page scaling
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Registration marks
Once you find settings that produce dependable films, document them. Consistency is more valuable than changing settings for every job.
5. Scaling Errors Between Separations
A one-color design may expose correctly even if the film is slightly distorted.
A multicolor job will reveal the problem quickly.
If one separation prints at a slightly different size from the others, the registration marks may line up in one area while the artwork drifts out of registration somewhere else.
Scaling differences can be caused by:
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Different printer settings
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“Fit to page” being selected
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Files printed from different programs
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Incorrect document dimensions
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Printer feed inconsistencies
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Separations output at different resolutions
Print every separation through the same controlled workflow. Verify important dimensions with a ruler before exposing an entire set of screens.
A registration problem created during film output cannot always be corrected with press micros.
6. Poor Edge Definition
Film positives should have clean, well-defined image edges.
Soft or feathered edges can come from:
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Low-resolution artwork
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Excessive ink spreading
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Poor media compatibility
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Incorrect printer settings
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Double-stacked films
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Weak film-to-screen contact
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Artwork that was enlarged beyond its usable resolution
Soft film edges become soft stencil edges.
That can reduce print sharpness, make registration less precise and cause small details to disappear.
7. Damaged or Contaminated Film
Film positives can be damaged after they are printed.
Watch for:
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Scratches
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Fingerprints
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Dust
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Dried ink or emulsion
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Creases
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Tape residue
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Bent corners
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Moisture damage
A scratch through a solid black area may create an unwanted line in the stencil. Dust trapped between the film and screen can interfere with contact or create unwanted marks.
Store completed films flat or in protective envelopes. Label them clearly so they can be reused without unnecessary handling.
Halftones Reveal Film Problems Quickly
Bold spot-color artwork can sometimes tolerate a film that is less than perfect.
Halftones cannot.
A halftone image contains dots of different sizes. The smallest highlight dots and finest shadow openings may be extremely sensitive to:
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Film density
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Output resolution
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Mesh count
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Emulsion thickness
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Exposure time
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Film contact
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Washout technique
If the smallest dots are weak, incomplete or missing on the film, they cannot appear correctly on the screen.
If unwanted light passes through the black dots, they may become smaller or disappear during exposure.
This is why dependable film output becomes especially important for:
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Simulated-process printing
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Four-color process printing
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Photorealistic images
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Fine gradients
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Small text
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Detailed illustrations
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High-mesh screens
Before exposing a complicated separation, examine the film with a loupe. It is much less expensive to find a damaged halftone on the film than after coating, exposing and washing out the screen.
Can You Double Up Weak Films?
Some printers attempt to increase density by stacking two copies of the same film.
For simple, bold artwork, this may occasionally serve as a temporary solution. However, it introduces additional risks.
If the films are not aligned perfectly, the image can develop:
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Soft edges
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Enlarged lines
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Distorted halftones
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Misaligned registration marks
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Loss of fine detail
The second layer also increases the distance between part of the image and the emulsion, especially if dust or air is trapped between the films.
A single properly produced high-density film is usually a more dependable solution than stacking two weak films—particularly for halftones and detailed work.
Film Contact Matters Too
Even a high-quality film can produce a soft screen if it is not held tightly against the emulsion.
Any gap between the film and screen allows light to travel beneath the image edge. This is sometimes called light undercutting.
Poor contact can produce:
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Soft edges
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Thickened or distorted lines
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Lost detail
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Reduced halftone accuracy
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Inconsistent exposure across the screen
Vacuum exposure units are designed to pull the film tightly against the screen. If you are using another contact method, make sure pressure is even and the film remains flat.
Check that:
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The film is positioned against the correct side of the screen
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The glass is clean
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The film is flat
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The vacuum blanket is in good condition
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The screen frame is not interfering with contact
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No dust or debris is trapped between the film and emulsion
Film density and film contact solve different problems. You need both.
An Exposure Calculator Cannot Correct a Bad Film
An exposure calculator is a valuable tool for determining exposure time.
However, it tests the complete exposure system—including the film used during the test.
If you calibrate exposure with a dense film and later expose production screens with weak films, the results may change. If your film density varies from job to job, your exposure time may appear inconsistent even though the exposure unit has not changed.
Use an exposure calculator to establish exposure time, but also maintain a consistent film-output standard.
When troubleshooting, do not ask only:
“How long did I expose the screen?”
Also ask:
“Was this film produced the same way as the film used when I established that exposure time?”
Repeatable screens require repeatable films.
A Simple Film Positive Quality Check
Before exposing a production screen, inspect the film.
Density
Hold solid black areas in front of a strong light. Look for thin areas, gaps, banding and unwanted light transmission.
Detail
Use magnification to inspect:
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Small text
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Thin lines
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Halftone dots
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Fine negative spaces
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Registration marks
Dimensions
Measure the artwork and confirm that it printed at the intended size.
Registration
For multicolor work, stack the films and align the registration marks. Check the artwork in several different areas, not only at one corner.
Orientation
Confirm whether the film should be right-reading or mirrored for your exposure workflow.
Cleanliness
Remove dust and inspect for scratches, fingerprints or damage.
Dryness
Make sure the ink is completely dry before placing the film against the screen.
This inspection may take only a few minutes. Remaking a failed screen takes much longer.
The Hidden Cost of Printing Films In-House
Printing your own film positives can provide speed and control when the system is operating correctly.
The cost, however, includes more than film and ink.
An in-house output system may require:
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A dedicated printer
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RIP software
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Compatible film
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Specialty ink
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Routine nozzle checks
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Printhead cleaning
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Replacement cartridges
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Color-channel maintenance
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Test prints
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Wasted film
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Operator training
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Time spent troubleshooting
Then there are the costs created by a poor film:
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Wasted emulsion
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Additional coating and drying
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Repeated exposure
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Screen reclaiming
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Production delays
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Missed deadlines
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Press-registration problems
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Labor spent correcting preventable issues
The least expensive film is not always the lowest-cost film.
A dependable positive that produces a good screen the first time may be worth far more than the difference in output price.
When Outsourcing Film Output Makes Sense
Outsourcing may be a practical choice when:
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You only need films occasionally
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Your printer is unreliable
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You are struggling with film density
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You need oversized artwork
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You are printing detailed halftones
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You do not want to purchase RIP software
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Printer maintenance is interrupting production
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You need additional capacity during busy periods
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A difficult job requires more dependable output
You do not have to outsource every film.
Some shops use a hybrid workflow. They print basic spot-color films internally and outsource oversized artwork, simulated-process separations, halftones or other demanding jobs.
The goal is not to give up control.
The goal is to prevent film output from becoming the weakest part of the screen-making process.
Professional Film Output From Kolormatrix
Kolormatrix offers Professional Film Positive Output Services for screen printers who need dense, sharp and dependable production films.
Our film-output workflow includes:
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Premium high-resolution inkjet film
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All-black ink systems
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Professional RIP software
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Calibrated wide-format output
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High-density black ink
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Sharp edge reproduction
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Output resolution up to 1200 DPI
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Standard and oversized film options
Oversized film positives are available up to 24 inches wide for larger production artwork.
Our film services support:
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Spot-color printing
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Athletic graphics
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Fine-detail artwork
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Halftones
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Simulated process
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Four-color process
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Small text
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Oversized printing
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Production screen printing
Instead of maintaining another printer, troubleshooting ink density or wasting film on repeated output attempts, you can upload your artwork and receive production-ready positives.
Need More Than Film?
A good film is only one part of making a good screen.
If coating, exposure or washout is also slowing production, Kolormatrix offers Professional Photo Screen Services.
Photo screens arrive:
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Professionally coated
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Exposed with your artwork
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Washed out
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Inspected
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Taped
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Ready for production
You can choose the level of support that fits your shop:
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Print your own films and prepare your own screens
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Order professional films and expose screens in-house
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Order complete production-ready photo screens
A hybrid workflow allows you to keep the steps your shop handles well and outsource the steps causing delays, inconsistency or unnecessary expense.
Start Troubleshooting With the Film
When a screen fails, it is tempting to immediately change the exposure time.
Before doing that, inspect the film.
Ask:
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Is the black image truly dense?
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Are the edges sharp?
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Are the smallest details present?
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Are the halftone dots complete?
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Is there banding or nozzle loss?
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Did the artwork print at the correct size?
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Do all separations register?
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Is the film clean and undamaged?
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Is it making firm contact with the emulsion?
A good exposure unit cannot recreate missing detail.
A premium emulsion cannot correct inaccurate scaling.
Perfect washout technique cannot restore halftones that were never properly printed.
Good screens begin with good preparation—and the film positive is one of the most important pieces of that process.
Are Your Films Helping or Hurting Production?
If you are repeatedly remaking screens, losing fine detail or changing exposure times from one job to the next, your film positives deserve a closer look.
Kolormatrix can help you determine whether the problem is coming from the artwork, film, exposure or screen-preparation workflow.
Explore our Film Positive Output Service, order Production-Ready Photo Screens, or call us at 404-691-0015 to discuss your screen-making challenges.
A better screen may begin with a better film.