Conformance of extruded and laminated card substrates to the dimensional requirements of ISO/IEC 7810:2019 is determined at the final cut-card level but is engineered through the entire flat-film extrusion, lamination, and die-cutting sequence. For the ID-1 card body, the nominal width is 85.60 mm, the nominal height is 53.98 mm, and the nominal thickness is 0.76 mm. Table 1 of ISO/IEC 7810:2019 sets bilateral tolerances of ±0.12 mm for width and height and ±0.08 mm for thickness, thereby establishing a width envelope of 85.48 mm to 85.72 mm, a height envelope of 53.86 mm to 54.10 mm, and a thickness envelope of 0.68 mm to 0.84 mm. Because extruded PVC, PETG, and polycarbonate sheet is produced with anisotropic orientation, and because press lamination superimposes additional thermal and mechanical history, the measured dimensions of a finished ID-1 card are not equal to the arithmetic sum of the incoming layer calipers. Thickness is governed by core stock gauge variation, overlay film thickness, adhesive or heat-seal layer thickness, and viscoelastic flow under lamination pressure. Width and height are governed by film shrinkage, panel layout, cutting die dimensions, and post-cut relaxation. The measurement environment specified in ISO/IEC 10373-1:2020, with conditioning at 23 °C ± 2 °C and 50 % ± 5 % RH per ISO 291:2008, is mandatory because the substrates are hygroscopic and thermoplastic. A card may pass measurement in an uncooled press shop and fail after conditioning in the standard atmosphere. The evaluation of dimensional conformity must therefore separate deviations that are recoverable through conditioning from those that are permanent because of frozen-in orientation, moisture swelling, or die-cutting damage.

At the sheet extrusion stage, the core stock is characterized by transverse thickness profile, machine-direction thickness variation, surface temperature at the polishing stack, and residual shrinkage measured after a free-shrink test. In laminated card production, the core stock is typically 0.60 mm to 0.68 mm thick, with overlay films of 0.04 mm to 0.10 mm on each face. The finished card must fall within the 0.68 mm to 0.84 mm thickness envelope. If the core sheet has a local thin band below 0.58 mm, no practical overlay thickness can restore the finished card to the lower thickness limit, and the affected pockets must be rejected or diverted. Conversely, if the core sheet has a thick band above 0.72 mm, the finished card may exceed 0.84 mm after two overlays and lamination flow. Width and height are established later, but thickness nonuniformity can also influence localized cutting force and final edge geometry. The same logic applies to laminated structures made with polycarbonate or PETG cores and overlays; the tolerance budget remains fixed, while the individual material contributions shift according to their shrinkage, thermal expansion, and flow behavior.

What Gauge Instability in Extruded PVC Core Stock Does to ID-1 Thickness Conformance?

Rigid PVC core stock for laminated card bodies is typically produced on a single-screw extruder with a screw diameter of 120 mm and an L/D ratio of 30:1, feeding a flexible-lip sheet die of 900 mm working width. Suspension PVC with a K-value of 57 to 60 is extruded at a die melt temperature of 180 °C to 195 °C. Below this range, melt fracture and die-lip deposit formation increase; above this range, dehydrochlorination accelerates and creates black specks, gel particles, and local gauge bands. The melt enters a vertical three-roll polishing stack with roll surface temperatures of 55 °C to 80 °C. The middle roll gap sets the final sheet caliper, and the speed differential between the last two rolls controls machine-direction orientation. A transverse thickness profile is measured before trimming with a beta gauge or x-ray gauge at 1 mm to 2 mm intervals. On a well-maintained extrusion line, the central 700 mm of the web can be held within ±0.03 mm of target caliper, but the untrimmed edge bead frequently exceeds ±0.10 mm. Edge bead is removed by in-line slitting, but the adjacent zone may still show a thickness gradient that later becomes the outer card pockets on a nested panel. Core sheet panels are conditioned for at least 24 h at 23 °C ± 2 °C and 50 % ± 5 % RH before lamination to release short-term orientation and stabilize moisture content. The core sheet thickness is recorded before lay-up because it is the largest single contributor to finished card thickness.

Thermal shrinkage of extruded PVC core sheet measured according to ASTM D1204-14 at 100 °C for 30 min typically ranges from 0.2 % to 0.8 % in the machine direction and 0.1 % to 0.3 % in the transverse direction. The exact values depend on haul-off tension, roll temperatures, and die-lip alignment. During press lamination at 130 °C to 150 °C, the frozen-in orientation relaxes; the core sheet loses length in the machine direction and increases in thickness. If the panel is not laid out with machine-direction shrinkage in mind, the laminated sheet can be too small for the die-cutting layout, and the outer card pockets may fall below the 85.48 mm width lower limit after cutting. In addition, the thickness of the card body after lamination follows a relation of t_card = t_core + t_overlay1 + t_overlay2 − t_flow, where t_flow is the thickness lost through edge flash and viscoelastic flow under pressure. For a construction with a 0.68 mm PVC core and two 0.06 mm PVC overlays, the incoming stack is 0.80 mm; a flow loss of 0.04 mm during lamination brings the finished card to the nominal 0.76 mm thickness. The flow loss is not uniform. It is larger at the panel edges, where material can escape to flash, and smaller at the panel center, producing a convex thickness profile across the panel.

Lamination pressure also controls void elimination and edge flow. Multi-opening hydraulic presses used for card lamination operate at platen pressures of 0.8 MPa to 1.4 MPa and platen temperatures of 130 °C to 150 °C. At 140 °C, PVC exhibits viscoelastic flow; the card thickness decreases during the first 2 min to 5 min of dwell and stabilizes as the platens reach thermal equilibrium. Higher pressure reduces void content but increases flash and core squeeze-out. If the press platens are not ground flat or shimmed to compensate for frame deflection, the outer card pockets can be thinner than the center pockets by 0.03 mm to 0.05 mm on a 1000 mm × 1000 mm platen. That degree of thickness variation consumes a large fraction of the 0.16 mm ISO/IEC 7810 thickness tolerance. Published data for a specific press configuration may be limited, but the relationship between platen deflection, pressure distribution, and card thickness variation is well documented in polymer processing literature. The production audit should therefore include a pocket-by-pocket thickness map of the laminated panel before die cutting, not simply an average thickness per card. A core sheet that is within specification on average can still produce reject cards if the transverse thickness gradient exceeds 0.05 mm across a single card pitch.

When a coextruded PETG overlay is laminated to a PVC core under asymmetric heating or unbalanced layer construction, the differential thermal contraction on cooling frequently becomes the dominant cause of warpage. Rigid PVC exhibits a coefficient of linear thermal expansion of approximately 50 × 10⁻⁶ K⁻¹ to 100 × 10⁻⁶ K⁻¹ depending on plasticizer content and orientation; PETG is commonly in the range 60 × 10⁻⁶ K⁻¹ to 80 × 10⁻⁶ K⁻¹; polycarbonate is lower and more isotropic at 65 × 10⁻⁶ K⁻¹ to 70 × 10⁻⁶ K⁻¹. A PVC core with a 0.06 mm PETG overlay on one face and a 0.06 mm PVC overlay on the other will bend upon cooling from 140 °C to 23 °C, even when the in-plane dimensions remain inside the ISO/IEC 7810 width and height envelopes. Warpage is measured in accordance with ISO/IEC 10373-1:2020 by placing the card on a flat reference surface and recording the maximum vertical displacement of the card edge from that surface with a digital height gauge or laser displacement sensor. If the measured displacement exceeds the maximum permitted by ISO/IEC 7810:2019, the card fails the physical characteristics requirement regardless of its width, height, and thickness readings. The measured curl also changes the projected width and height; a card with significant curvature appears shorter on an optical measuring system because the surface is not parallel to the measurement plane.

Asymmetric cooling in the lamination press is a second source of curvature. When the cooling water is activated, the top platen often cools more rapidly than the bottom platen because the press frame and hydraulic cylinder act as a heat sink on the lower side. The lower card surface therefore remains above the PVC glass transition temperature of 75 °C to 85 °C for a longer period and relaxes more orientation, creating a stress gradient through the thickness. A hold-under-pressure step at 0.2 MPa to 0.4 MPa until the sheet surface drops below 60 °C reduces this gradient. After the press opens, the sheets are transferred to a flat cooling plate with a mass of 2 kg to 5 kg per panel to cool to room temperature under constraint. These steps reduce but do not eliminate the locked-in bending moment. The residual curvature is then mapped by measuring the card at four corners and at the center on a granite surface plate. A difference of more than 0.2 mm between the highest and lowest readings is often observed in unbalanced laminates, while a symmetric PETG/PVC/PETG build-up should produce a difference below 0.1 mm if the cooling is balanced. Batch-to-batch variance in warpage is also affected by the overlay film roll-to-roll shrinkage. PETG and PVC overlay films are produced by extrusion or calendering and may carry machine-direction shrinkage values that differ from one shipment to the next. The incoming films are conditioned and tested per ASTM D1204-14; a change of 0.2 % in MD shrinkage between two film lots can alter the final card curvature and the die-cut width by several hundredths of a millimetre. Dimensional conformity is therefore not a fixed die-size problem; the die cavity must be adjusted when the material supplier changes the film source, the core sheet gauge, or the overlay thickness. This type of lot-to-lot variation is the primary reason that laminated card manufacturers retain dimensional history records and run first-piece dimensional inspection after every new material combination.

Die-cutting edge stress, punch clearance, and dimensional bellmouth formation

The die-cutting operation converts the laminated panel into individual ID-1 blanks and simultaneously introduces the final edge geometry. Solid milled male-female dies or steel-rule dies are used in a platen press with a cutting force of 20 t to 80 t depending on panel size, material thickness, and die design. For a rigid PVC/PETG laminated card, a punch-to-die clearance of 0.01 mm to 0.02 mm per side produces a predominantly shear-cut edge; clearances above 0.05 mm shift the process toward tensile fracture and generate edge roll-over, chipping, and a bellmouth profile. The bellmouth localizes deformation at the cut surface and can create a measured width difference between the top surface and the middle plane of several hundredths of a millimetre when the card is inspected on a vision measuring system. After cutting, residual stresses in the core and overlay films cause springback that changes the card width and height relative to the die cavity. The die cavity is therefore offset from the nominal ID-1 dimensions by an amount determined from first-piece measurements under the conditioning atmosphere of ISO/IEC 10373-1:2020. The first cut cards are measured, and the die offset is corrected before production is released. Die-cutting also introduces compressive set at the cut edge; subsequent heating during magnetic stripe application, embossing, or laser personalization can relax that compressed zone and produce a small local expansion. Edge burrs are removed by a vibratory deburring unit or by controlled micro-roughening, and the cards are re-measured to verify that deburring has not reduced the width below 85.48 mm or the height below 53.86 mm.

Under repeated temperature-humidity cycles typical of card service, extruded and laminated substrates exhibit hysteretic dimensional recovery. A card that has been die-cut and deburred may retain residual stress from extrusion orientation, lamination pressure, and cutting. When the card is exposed to 50 °C to 60 °C for 24 h to 48 h in a forced-air oven, PVC-based cards lose additional machine-direction length as the oriented polymer chains relax; the width and height are recorded before and after exposure. Shrinkage values above 0.10 mm indicate that the card may fall below the lower tolerance limit after hot storage. Polycarbonate-based cards show less post-exposure shrinkage because the glass transition temperature of polycarbonate is 145 °C to 150 °C, while PVC relaxes above 75 °C to 85 °C. The conditioning atmosphere defined in ISO/IEC 10373-1:2020 and ISO 291:2008 is 23 °C ± 2 °C and 50 % ± 5 % RH; measurements taken before the card reaches equilibrium can overstate the width by several hundredths of a millimetre. This difference is small but significant near the 85.72 mm upper tolerance limit. Humidity swelling of PVC and PETG is lower than that of paper-based or polyolefin-based core materials, but it is not zero. At 80 % RH, the width of a PETG-laminated card can increase by a few hundredths of a millimetre relative to the 50 % RH conditioned state. A single compliance measurement at standard atmosphere therefore cannot guarantee performance in tropical service, and internal specifications often require a second measurement after a high-humidity soak or after thermocycling.

A dimensional compliance audit of ID-1 card bodies combines the incoming substrate data with the finished card measurements. The table below summarizes the relationship between the standard requirement and the measurement method used on the production floor.