Flexo Plate: Photopolymer vs Elastomer, Shore Hardness & Mounting Tape Spec

Overview #

Flexographic plate selection is one of the most consequential pre-press decisions on any flexible packaging or label job — get it wrong and you are chasing dot gain, ink skip, and registration drift through an entire production run. The choice between photopolymer and elastomer plates, combined with Shore A hardness specification and mounting tape compressibility, determines whether your brand’s 2% highlight dots hold cleanly or plug solid by the third colour station. This guide covers the quality parameters we control on our flexo lines, the measurement methods we use, and the compliance requirements that apply when plates contact food-grade substrates or inks. Brand partners specifying corrugated, flexible film, or label packaging with us will find the most relevant detail here.

Plate Material Selection: Photopolymer vs Elastomer #

The first question we ask when a new flexo job is briefed is: what substrate, what screen ruling, and what ink system? Those three answers determine whether we specify a photopolymer plate or a conventional elastomer (rubber) plate.

Photopolymer plates — both analogue and digital (direct laser engraving or LAMS-based) — are our standard specification for process colour work, fine line detail, and any job requiring screen rulings above 100 lpi. Digital photopolymer plates produced on our CDI (Cyrel Digital Imager) system hold a minimum dot size of 10 microns and support flat-top dot geometry, which reduces ink spread on film substrates and keeps highlight dot gain within our target of ≤12% at 40% tint on BOPP. We specify Dupont Cyrel or Flint nyloflex plates at 1.14 mm or 1.70 mm total plate thickness depending on the press sleeve diameter and repeat length.

Elastomer (rubber) plates remain the right choice for solid flood coats, simple line work on corrugated board, and high-abrasion applications such as kraft paper bags where the substrate surface roughness would accelerate photopolymer wear. Rubber plates on our corrugated post-print line run at Shore A 35–45 for medium-density corrugated and Shore A 50–60 for solid fibreboard. Below Shore A 35, the plate face deforms under impression pressure and ink spread becomes uncontrollable on uneven board surfaces.

Shore A hardness is measured per ASTM D2240 using a Type A durometer. We test every plate batch at goods-in — our acceptance threshold is ±3 Shore A units from the specified value. A plate arriving at Shore A 62 when we specified Shore A 65 for a fine-screen film job will be quarantined and returned; the 3-unit deviation shifts dot gain by approximately 2–4% at midtone, which is outside our G7 process control tolerance.

Mounting Tape Specification and Compressibility Control #

Mounting tape is not a consumable afterthought — it is a precision component of the plate stack. The total plate stack height (plate thickness + tape thickness + sleeve or cylinder wall) must match the press-specified printing gap to within ±0.025 mm. We use a digital micrometer to verify stack height on every plate mount before the sleeve goes to press.

We stock three tape compressibility grades for different applications:

• Open-cell foam tape (high compressibility, ~0.56 mm compressed thickness): Used for corrugated post-print and uneven substrate surfaces. The compressible layer absorbs board caliper variation of ±0.3 mm without causing impression bounce.
• Closed-cell foam tape (medium compressibility, ~0.38 mm compressed thickness): Our standard specification for flexible film and label jobs. Provides controlled ink transfer with minimal plate bounce at press speeds up to 400 m/min.
• Solid adhesive tape (low compressibility, ~0.10 mm compressed thickness): Specified for hard-dot photopolymer plates on smooth film substrates where maximum dimensional stability is required. We use this for jobs with register tolerance tighter than ±0.15 mm.

Tape adhesion must hold through a full production run without plate lift at the leading edge — a failure mode that causes ink skip and register loss. We specify a minimum peel adhesion of 40 N/25mm (tested per ASTM D3330) for all mounting tapes used on our high-speed lines. Any tape showing edge lift during a run is flagged as a non-conformance and the root cause (contamination, incorrect tape grade, sleeve surface condition) is documented in our NCR system before the job resumes.

Compliance and Food-Contact Considerations #

When flexo plates are used to print food packaging — whether direct-contact flexible film or indirect-contact outer cartons — the plate material and associated chemistry must comply with applicable food safety regulations. This is an area where we apply strict incoming material controls.

For jobs destined for the EU market, photopolymer plate chemistry must be compatible with EU Regulation 10/2011 on plastic materials in contact with food, and any UV-curable ink system used with those plates must comply with Swiss Ordinance SR 817.023.21 (the Swiss Ordinance on Materials and Articles), which is the de facto standard for low-migration UV inks in European food packaging. We require a migration compliance declaration from our ink supplier for every food-contact UV flexo job.

For the US market, ink and plate chemistry must be consistent with FDA 21 CFR 175.300 (resinous and polymeric coatings) and 21 CFR 176.170 (components of paper and paperboard in contact with aqueous and fatty foods) where applicable. We maintain a current SDS and compliance letter file for all plate chemistries used on food-contact jobs.

Plate washout solvents and processing chemistry are managed under our ISO 14001:2015 environmental management system. Solvent recovery units on our plate processing lines achieve >90% solvent recovery, and waste photopolymer is segregated and disposed of through a licensed hazardous waste contractor — documentation available on request for brand partners with supply chain sustainability requirements.

For FSC-certified packaging jobs, our plate production process is covered under our FSC Chain of Custody certification (FSC-C[our CoC number on file]) — the plate itself is not an FSC-controlled input, but the job tracking and material flow documentation must be maintained to support the CoC audit trail.

Our inline colour measurement system on flexo lines uses a Techkon SpectroDens spectrodensitometer, and all process colour jobs are controlled to G7 Grayscale and Targeted (G7T) methodology per IDEAlliance G7 Master Colorspace specification. Our standard ΔE tolerance for brand colour approval is ΔE 2000 ≤ 2.0 for spot colours and ≤ 3.0 for process builds.

Specification Notes for Brand Partners #

When you brief us on a flexo printing job, the most useful information you can provide upfront is: substrate type and caliper, ink system preference (water-based, UV, or solvent), screen ruling or artwork complexity level, and whether the packaging has any food-contact surface. These four inputs let us specify the correct plate type, hardness, and tape grade before we even open the artwork file.

The most common brief gap we see is brands supplying artwork without specifying minimum positive text size or minimum reverse knockout width. On a digital photopolymer plate at 133 lpi, we can hold positive text down to 4pt and reverse knockouts down to 0.3 mm line width — but only if the artwork is built to those limits. Text supplied at 3pt in a reverse knockout on a mid-tone background will fill in on press regardless of plate quality. We flag this at pre-press and work with your design team to adjust before plate output.

Our standard process: digital proof review in 3–5 working days, physical press proof (if required) in 10–15 working days, production lead time 15–25 working days after approved press proof. Plate files are archived for 24 months, so repeat orders do not require new plate costs unless artwork changes.

Frequently Asked Questions #

Q1: What Shore A hardness should I specify for a fine-screen flexo label job on BOPP film?
A: For process colour work at 133 lpi or above on BOPP, we specify digital photopolymer plates in the Shore A 60–70 range. Below Shore A 55, the plate face compresses too readily under impression load and dot gain at 40% tint exceeds our 12% threshold, which visibly shifts midtone colour from your approved proof.

Q2: What is your typical lead time for new flexo plates, and do repeat orders require new plates?
A: New plate sets are typically ready in 5–7 working days from approved pre-press files. We archive all plate files for 24 months, so repeat orders with no artwork changes can go straight to production without new plate costs — this is a meaningful saving on short-run repeat packaging.

Q3: Do your flexo plates and inks comply with EU food packaging regulations?
A: Yes. For EU food-contact flexible packaging, we use UV ink systems with migration compliance declarations aligned to EU Regulation 10/2011 and Swiss Ordinance SR 817.023.21. We can provide the full compliance documentation package — ink supplier declarations, SDS files, and our own food-contact job specification sheet — as part of the pre-production approval package.

Q4: Can you combine photopolymer plates for process colour with rubber plates for solid flood coats on the same job?
A: We do this regularly on combination jobs — for example, a flexible pouch with a photopolymer plate set for the process image area and a Shore A 45 rubber plate for the white flood coat on the reverse. The key is that both plate types must be mounted to achieve the same total stack height within ±0.025 mm, which we verify with a digital micrometer before the job goes to press.

Q5: What happens if a plate fails mid-run — how do you handle the non-conformance?
A: If a plate shows edge lift, wear, or register drift beyond ±0.20 mm during a run, we stop the press and log a non-conformance report. The affected output since the last good inspection point is quarantined and inspected at AQL Level II per ISO 2859-1 before any decision on rework or scrap. A replacement plate is output and the root cause — whether tape adhesion failure, incorrect hardness spec, or sleeve surface contamination — is documented and corrected before the run resumes.

Planning a flexo packaging project? Contact our team to request a complimentary specification review and sample quote.