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Rhopoint ID In-line Transparent Appearance Analysis
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Rhopoint ID In-line Transparent Appearance Analysis

  • Camera-based system
  • Quantify product transparency with parameters that are highly correlated to human perception
  • Short or long focal distance versions available to suit customer production line

Industries and Applications

Category:

Description

Why measure the appearance of transparent materials with an inline solution?

The functionality of a manufactured product or its perceived quality is often linked to its transparency. Matt shipping labels require good contact clarity which allows QR codes to be read on high-speed conveyor lines, while recycled salad trays are preferred with low haze so the consumer can appreciate the vibrant colours of packed vegetables.

To optimise and improve transparency, a constant inline measurement of key parameters is more efficient than occasional offline measurements. Instant feedback from an sensors allows fine tuning of a process, ultimately achieving a better-quality product, with measured consistency throughout every production run.

The Rhopoint ID measurement technology (patent pending) was jointly developed with Eidgenössische Technische Hochschule (ETH) Zürich.

What is the Rhopoint ID-Inline?

The Rhopoint ID-Inline is a camera-based system which fully quantifies product transparency with parameters that are highly correlated to human perception.

Step 01

A backlit, high accuracy, reference target graticule functions as the viewed object, creating a highly defined pattern of light intensities with optimally sharp transitions between the backlit and masked areas.

Step 02

The camera works like the human eye quantifying changes in the transmission of the light caused by a test material.

Step 03

Image analysis techniques are used to characterise these effects into parameters which correlate closely with human perceptions.

Versions of the Rhopoint ID-Inline

There are two versions of the Rhopoint ID-Inline. A short focal length version which has a separation distance of 45mm between the camera and graticule, or the long focal distance version which has a separation distance of 170mm.

What software integrations are available for the Rhopoint ID-Inline?

Flexible software allows single or multiple ID sensors to be combined with compatible measurement devices and tabulated in the Rhopoint ID laboratory software.

Measurement Parameters of the Rhopoint ID-Inline

Haze

Haze: quantifies the loss of contrast for objects viewed through a material.

When a material has haze, it changes the appearance of both the material and any objects viewed through it. This can lead to a reduction in perceived quality.

  • The product viewed through the material appears lifeless and dull – but details remain sharp
  • The colour of a viewed object appears washed-out and faded
  • The material itself appears cloudy or milky.

Measure Haze with the Rhopoint ID to ensure visibility of products are at their best and can be seen properly by the customer.

What affects Haze?

Haze can be affected by factors such as the choice of resin, the moulding process and any surface textures. Haze can be caused by:

Raw material choice

For example, a plastic with an incorrect melt viscosity for a particular process.

Process parameters

Cooling a plastic material too quickly can introduce micro textures onto the surface of the film or structures in the bulk which reduce optical quality.

Machine wear

Wear and tear in moulds, chill rollers and slip dies can induce visible surface defects in the material.

Measuring Haze with the Rhopoint ID

  • Haze is measured directly by evaluating contrast of black and white areas on graticule
  • Measurements made with the Rhopoint ID are fully comparable with those made on an ASTM D1003 haze meter
  • Automatically operates when ASTM Haze platen (8 mm thickness) is placed in position on instrument between the graticule and a sample
  • Factory calibrated to ASTM standards for a quantitative match.

Sharpness quantifies the loss of perceived detail for objects viewed through a material.

What are the effects of reduced Sharpness?

When viewed through a material with high sharpness, an object appears sharp and distinct. As material sharpness decreases, the object appears blurry and obscured.

Anisotropic Sharpness. Only available with Rhopoint ID-L version.

A material can often exhibit optical effects which are directional. These phenomena are often induced in plastic parts by specific processing faults.

Visible texture is a common feature of plastic films and causes a significant reduction in their see- through quality.

Directional Effects

The Rhopoint ID is the only instrument that can measure directional effects in materials using the ID laboratory analysis software.

The images to the right show the visual impact of different ID Sharpness (S) values in vertical and horizontal directions.

Measuring directional effects can be used in advanced optical quality control and for adjusting processing parameters to obtain optimal transparency.

Quantifies the blurriness of an object when viewed through a material, results are proportionate with Sharpness, but the measurement scale is compressed and the measurement resolution is reduced.

Clarity is a scale used by traditional haze and clarity meters. When measured using the 8mm adaptor plate, Rhopoint ID Clarity data conforms to specifications written for these meters.

Inter-instrument Clarity agreement between Rhopoint ID and traditional sphere instruments for commercial plastic films (<1000μm) is typically <0.4% C (SD).

Inter-instrument Clarity agreement between traditional sphere instruments and Rhopoint ID for thick transparent plastic materials (<6mm) is typically <0.5% C (SD).

What is Waviness?

Waviness is an optical effect caused by large structures (0.1-2mm) on the surface of the material. If the structure is homogeneous it is often described as orange peel – the surface resembles the peel of an orange.

If the effect is anisotropic, visible lines can often be seen when looking through the material.

Unlike sharpness, these larger structures can cause dynamic distortion when the film is moved over a target image/object which has straight edges – the edges appear to distort and wave as the material is moved.

How is Waviness measured?

Waviness measures the visible distortion of the ID graticule edges through the material. W is the standard deviation of the edge deformation in μm.

Waviness homogeneity is assessed by comparing W (average waviness) with WH (horizontal waviness) and Wv (vertical waviness) using Rhopoint ID software available with the Rhopoint ID-L version.

Many materials exhibit a variation of transparency depending on whether the material is in contact with a viewed object, or separated by an ‘air gap’ distance between them.

 

Why is Distance Dependence important?

Matching the material exactly to the application allows quality improvements and production cost savings.

To match a specific material application the Rhopoint ID can measure ID Haze at any distance within 0–40 mm.

Using the ID it is possible to identify the air gap distance at which maximum Haze is obtained (typically <25 mm).

Haze and Distance

The images below show the effect of air gap distance for a hazy plastic film held in front of an image.

Direct measurement of haze from transmission image contrast

Measured in contact or at user-defined distance between material and object (0–40 mm)

Measures distance dependence on the same scale as ASTM Haze

Direct measurement of transparency via contrast of black and white areas on target graticule

Measure and understand distance dependent haze

When considering how material is perceived by a consumer it is important to consider how bright an object viewed through it will appear.*

Visible Transmission to human observer
  • Rhopoint Transmittance (TID) quantifies the amount of light passing through the material and reaching the camera/eye of the observer
  • This measurement describes the brightness/ luminosity of the viewed object and is correlated to how one perceives the quality of the material.

*Traditional hazemeters measure total transmission which is related to light absorption not visual perception

Sensor features

The Rhopoint ID has been designed to measure samples for haze, transmittance and sharpness quickly and safely.

Specifications

Free extended warranty

Free extended 2 year warranty: Requires registration at www.rhopointinstruments.com/help-services/forms-feedback/instrument-registration/ within 28 days of purchase. Without registration, 1 year standard warranty applies.

Calibration and service

Fast and economic service via our global network of accredited calibration and service centres. Please visit www.rhopointinstruments.com/help-services/calibration-servicing/ for detailed information.

Downloads

Rhopoint ID Inline Datasheet

Rhopoint ID Application Notes – Agricultural Film

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