Latest Developments in On-Line Measurement and Control of Multilayer Blown Films: Full Spectrum InfraRed (FSIR) and Air Ring Doug Wright Thermo Fisher Scientific Abstract This paper expands on a previous work that focuses on a new technique of precisely mapping the double-layer lay-flat measurement to the rotating top nip of bubble to provide discrimination of various polymer layers using the Full Spectrum Infra Red sensor technology to the automated air ring. Previous papers discussed the resulting rapid Auto Profile Control (APC) of the annular die to ensure blown film gauge uniformity. Film quality improvements along with significant savings due to down gauging and reduced scrap while improving productivity have been achieved in both the viscosity heaters and with the air ring.

Introduction High barrier multi-layer co-extruded blown films for food packaging and medical packaging is a rapidly growing market. Machinery to manufacture nine to twelve layer co-extruded blown films at high throughput are commercially available. Hence, there exists a critical need for an on-line gauging system to provide fast accurate measurement and control of various polymer layers. The conventional nuclear or thickness gauges that have been used historically for measurement on the bubble cannot provide multi-layer discrimination of the high barrier films. Also, a non-contacting sensor is preferable to a contacting sensor to avoid marking or tearing the film. The application of the Full Spectrum Infra Red (FSIR) technology for measurement of the double-layer lay-flat film after collapsing the bubble at the nip rolls provides fast accurate measurement of the various polymer layers. An FSIR transmission sensor is used for the measurement of double lay-flat multi-layer film.

Challenges Historically, in a blown film process either nuclear backscatter sensors or capacitance sensors were used to measure thickness of the blown film at the bubble. The sensors were either fixed (stationary) to measure the slowly rotating bubble or were mounted on a rotating platform. The measurements provided by these sensors were too slow, anywhere from 2 to 40 minutes per scan. Also, these sensors were incapable of discriminating between various polymer layers and measured only the total thickness of the film.

In addition successful control requires cross direction (CD) measurement data. On the bubble solutions includes machine direction (MD) influences in the measurement data used for any control action causing inaccuracies and therefore not realize the desired resin savings and film quality from a gauging solution.

Two developments were instrumental in overcoming these shortcomings. One was the development of a new technique to precisely map the double-layer lay-flat film measurement to the rotating bubble to control the annular die. The other was a sensor that can discriminate between the various polymers in a multi-layer film structure to precisely control the thicknesses of the layers.

Technological Solutions The technological solutions to the dual challenges of fast and accurate on-line measurement of multi-layer barrier films are two-fold. The first one is a technique of fast accurate measurement of the double-layer lay-flat film. By measuring the lay-flat with a fast scanning gauge head, data collection rate is nearly independent of the bubble oscillation time. A proprietary algorithm allows for the scanning of the collapsed tube by distinguishing between top and bottom layers of the double lay-flat film, thus obviating the need for splitting the tube. The superiority of this technique is in the faster processing of data to precisely map the scanned double lay-flat film to the bubble to facilitate fast effective (APC).

Data Mapping Technique The rotational speed is measured at the collapsing frame with a high resolution quadrature encoder. Accuracy is maintained via a reference input every rotation of the bubble at the home position. Haul-off speed is measured at the winder or at other convenient location with a digital

line speed tachometer. Distance from the rotational point to the measurement point at the scanning gauge is monitored by the digital tachometer. During the startup, the twist angle is measured by the system along with the corresponding speeds and stored with that product recipe. During each scan of the collapsed tube rotational data is saved along with the corresponding measurement point position. The data is rotated into a static standard orientation based on rotational buffer data and the resulting buffer is resegmented into a fixed number of points to allow for bubble breathing. Twist angle compensation is applied, considering the haul-off and rotational speeds. The raw data is then calibrated. The proprietary mapping algorithm is then applied to separate top layer from the bottom layer of the collapsed tube. The mapping algorithm uses current value of pairs of segments at a known position versus the values at the last known positions to “split” the data into top and bottom distribution. The high resolution split data is distributed into a zone profile which is used for APC.

Full Spectrum InfraRed Sensor The second technological solution to address the challenge of the on-line measurement of the double lay-flat multilayer film is the use of FSIR sensor to discriminate the various Polymer layers.

The various currently available sensor technologies such as Nuclear sensors or X-ray or thickness sensors (Optical, laser) or capacitance gauges can measure only the total mass or thickness of the film. These sensor technologies cannot discriminate between the various polymer layers in a multilayer barrier film. On the other hand, InfraRed sensor technology can discriminate between the various polymers.

Historical developments of various sensor technologies for measurement of film thickness or weight in web gauging Historically gamma backscatter sensors or capacitance sensors have been used on the bubble in blown film applications to measure total thickness, while transmission sensors (Beta, Gamma or X-Ray have been used on flat films)

The beta sensor was one of the earliest on-line measurement technologies. A beta transmission gauge utilizes a radioactive source that emits beta particles (high speed electrons) that pass through moving web to a detector placed on the opposite side of the web from the source. The mass (weight/area) of the web determines how many of the beta particles pass through the web to the detector. A characteristic of the beta particles is that to a first order, the response is independent of the composition of the material being measured. The source depends on the weight of the material being measured. The most common source materials are Promethium-147 for the lightest material; Krypton-85 for medium weight materials and Strontium-90 for the heavier materials.

The gamma transmission sensor is similar to the beta transmission sensor except that the gamma radioactive source emits gamma rays which are high energy protons that interact with the material and are reduced in intensity as a function of the weight/area of the material being measured. The interaction is highly dependent upon the atomic number of the material being measured and the energy of the gamma ray. Hence gamma transmission sensors can be used for selective measurements in some applications with a high atomic number coating and a low atomic number substrate. The most common radioactive material used for a gamma source is Americium-241 which emits 60keV photons.

X-Rays are very similar to gamma rays differing only from where they originate. Gamma rays originate from the nucleus of a decaying radioactive material and X-Rays originate from acceleration (deceleration) of high speed electrons. Once created, there is no distinguishing difference between a gamma Ray and an X-Ray. They are both high energy photons. X-Rays are generated by having high speed electrons hit a target material and in the process are rapidly decelerated, giving of photons with an energy that is a function of the velocity prior to hitting the target material. The voltage applied to the X-Ray tube determines the velocity of the electrons and therefore the voltage applied to the tube determines the energy of the X-Rays. X-Ray sensors can be tuned for different measurement sensitivity to the materials being measured by varying the voltage being applied to the tube. X-Rays are non-nuclear; low energy level X-Ray sensors (below 30 keV) are not subject to any regulatory restrictions.

Capacitance sensors are usually single-sided sensors that contact a film web. They work on the principle that plastic materials act as a dielectric. By having the plastic film act as a dielectric for two metal plates contacting the film, the capacitance will vary with film thickness. For a given type

of plastic the dielectric constant is fixed and therefore film thickness can be implied by capacitance.

Capacitance sensors are affected by moisture and therefore are not suitable for measurement of hygroscopic materials such as Nylon.

Infrared (IR) is a selective measurement technology that distinguishes various organic materials at the molecular level. IR Sensors provide a solution for the measurement of individual layer thickness in a multi-layer film. They measure the amount of infrared energy absorbed by the various components in a multi-layer web. Since specific components exhibit characteristic absorption according to their fundamental chemical structure, web composition can be determined by analysis of the amount of source light that reaches the detector after it is either transmitted through the web or reflected back from the web. They can be calibrated to measure thickness or mass.

IR Sensors evolved over time to meet the challenging requirements of a variety of complex applications. The conventional IR Sensors use a ratiometric measurement technique between a few selected wavelengths. Some IR sensors use the beam splitter configuration, while others use the spinning filter wheel configuration. Conventional on-line IR sensors suffer from spatial displacements of individual measurements. Since the spinning filter wheel requires a finite time to rotate, each filter sees a slightly different spot on the web.

Some design improvements have been made to the filter wheels to increase number of wavelengths and increase the speed of the filter wheels. However, some inherent limitations remain in its applications to the manufacturing environment where frequent polymer material changes are common. This requires physical changes of filter wheels that cause production line downtime.

Advanced On-Line IR Sensor Technology To overcome the afore-mentioned limitations, Full Spectrum Infra Red (FSIR) technology was developed. This on-line spectrometer using special optics allows the FSIR sensor to monitor infrared absorption in the near-IR spectrum, 1.35 to 3.4 microns. By simultaneously analyzing the entire near-IR spectrum, the FSIR sensor discriminates between multiple components as well as discern between components that exhibit similar, but not identical IR absorption. Also, full spectrum data allows numerical compensation for variations in the optical density of the web.

The FSIR sensor (SpectraBeam TM) is an on-line infrared spectrometer specifically designed for use in an industrial process. It has the ability to detect the signature of the multi-layer moving web, enabling the quantification of what materials and how much of these materials are present in the web. It simultaneously samples the entire near IR spectrum, eliminating the substrate and background effects that are inherent in sensors that sample a spectrum over a period of time. This also removes the spatial displacement problem demonstrated by conventional IR sensors. High resolution elliptical optics resulted in the ability to measure closer to the edge of a high speed moving web with enhanced streak-detection capability.

Software-based spectral analysis using chemometrics, in contrast to the hardware filtering techniques used by conventional IR sensors, provides a high degree of product measurement flexibility. Chemometrics refers to a broad class of mathematical manipulation techniques used

CAPACITANCE MEASUREMENT PRINCIPLE Measuring head and stray field without film

Measuring head and stray field with film

A

B

A – B = Δ FIELD STRENGTH >> THICKNESS

for quantitative and qualitative analysis of complex overlapping spectra. New component measurements can be easily implemented on-line through recipe-based calibration.

The following table gives a comparison of the various on-line sensor technologies:

Criteria

SpectraBeam TM FSIR Sensor

Conventional IR Sensor

X-Ray Sensor

Beta Sensor

Noise Characteristics

Best Good Good Nuclear

Statistics

Noise Degradation over time

None

None

None

1.5% increase every month

Tolerance to Web Flutter

Best +/- 5 mm

Best +/- 5 mm

Good +/- 3 mm

Fair +/- 1 mm

Temperature Sensitivity

No No Yes Yes

X,Y,Z Sensitivity No No Yes Yes

Composition Sensitivity

No No Yes Some

Dynamic Repeatability

Best Good Good Good

Multi-layer Calibration:

Complexity Moderate Moderate High High

Flexibility Yes No No No

Polymer Discrimination Best Limited No No

Multi-Component Measurement

Yes Yes No No

Auto Profile Control of the Blown Film Fast accurate dynamic measurement of the multilayer film together with precise mapping of the double-layer lay-flat film, provide the basis for the (APC) of the Blown Film. APC ensures gauge uniformity of the blown film bubble by controlling various bolts of the annular die. Past work focused on the viscosity heaters in the annual die. The same APC control technique is now used with an air ring mounted on a manual annular die.

The APC of Thermo Scientific system uses advance algorithms such as Kick & Wait or Accelerated Time Response (ATR) and PI (Proportional-Integral) control. ATR is suitable when the profile deviations are larger, such as at start-ups, and PI is used when deviations are less than a customer-selected profile deviation (CD spread) value. The modes are automatically switched to respond to various levels of profile variations during the production process. Other useful features are the different PI loops available for the heating and cooling modes of APC, as well as randomization to ensure uniformly flat profile without gauge-bands at windup.

Case Study: Customer Results We gathered data on two multi-layer barrier blown film configurations. The first was with an automated annular die using the Thermo Scientific FSIR transmission sensor on a scanning frame with APC on the viscosity heaters. The other was the same gauging configuration but now controlling a manual annular die fitted with an air ring. In the later case the APC controlled the nozzles in the air ring.

Previous Results for Annular Die with Viscosity Heaters

The following figures illustrate the performance of the system in Auto Profile Control

Figure-1: 2 Sigma CD spread = 3% at start of APC

Figure-2: 2 Sigma CD spread = 1.3% after 55 minutes from start-up (57% reduction)

Example 2:

Figure-3: 2 Sigma CD Spread= 3.7%

Figure-4: 2 Sigma CD Spread= 2.7% after 35 minutes in APC (27% reduction)

Figure-5: 2 Sigma CD Spread= 0.9% after 65 minutes in APC (76% reduction)

Independent verification using an Oakland offline Lab profiler with resolution of 5000+ points across the web showed a reduction in 2 Sigma CD Spread of 61%, after 45 minutes in APC.

Recent Results with Air Ring

Profile/Polar Plot Before:

Profile/Polar Plot After

Profile/APC Before

Profile/APC After

Economic Benefits The economic benefits to the multi-layer blown film manufacturer with the auto die or a manual die fitted with an air ring and the system with FSIR and APC described in this paper ensue from the following:

A) Reduction in CD variations: Typically in the range of 50-70%

B) Faster product change-overs Product change-over times typically reduced by about 67%.

C) Scrap reduction Scrap reduction at the Windup in the range of 50 %

Additional scrap reduction at downstream operations

Conclusions The new on-line gauging system for multi-layer blown film lines described in this paper combines the power of the FSIR sensor technology in multi-layer polymer discrimination with the technique of precisely map the double-layer lay-flat film using proprietary mapping algorithm to both viscosity heaters in the annular die and now the individual nozzles in the air ring. It offers the rapidly growing multi-layer barrier blown film market a tool to produce consistently uniform product to meet the stringent performance requirements of the high value barrier films for food and medical packaging applications while keeping costs under control. The economic savings to the barrier blown film manufacturers have proven top be quite significant.

Acknowledgements The author is grateful to Chuck Blanchette of Thermo Fisher Scientific, for providing results documentation of this blown film application.

Latest Developments in On-Line Measurement and Control of Multilayer Blown Films

Full Spectrum InfraRed (FSIR) and Air Ring

Presented byName: Doug WrightTitle: Director – Marketing and Business DevelopmentCompany: Thermo Fisher Scientific

Agenda

Problem statement

Review the original paper

Latest developments

Future Investigations

Questions

2008 PLACE Conference September 14-17, 2008

Portsmouth, VA

New Blown Film Measurement and Control

Presented by: Name Marty Lauginiger Title Regional Sales Manager Company Thermo Fisher Scientific

4

Problem Statement

For Multilayer Barrier FilmsWith the oscillating frame, difficult to map the measurement data back to the individual die Understanding and compensating for the natural twist angle between the die and the “frost” lineDon’t know how much of each polymer is being usedDon’t understand the material distribution Total measurement on the bubble is too slow for effective controlOn the bubble solutions contact the bubbleGetting a line under process control takes too long, creating excessive scrap and reduces overall production time

5

Typical Blown Film Line

Diagram Courtesy of Alpha Marathn

6

System Configuration

7

Why This Solution Unique?

FSIR provides material discrimination of key layers

Scans the collapsed tube (double layflat) and distinguishes between top and bottom

• Splitting the tube is not necessary

APC uses PI (Proportional-Integral) control on an annular die• Actuator are Viscosity Heaters

Rotational speed of the collapsing frame is measured using a high resolution quadrature encoder

• Accuracy is maintained via a reference input every rotation, at the home position

8

The Solution - Sensor

Full Spectrum Infrared (FSIR)

• Simultaneous software based analysis of a complete near infrared spectral range

• Discriminate between multiple components• Report individual layer thickness as well as overall thickness

Non nuclear

Invented the technology

• >20 years of providing FSIR technology to our customers to better understand therefore control their process

9

The Physics Behind IR Measurement - General

Absorption is stronger at certain wavelengths compared to others

Each material has unique absorption pattern

EVOH

weaker

STRONGER

10

FSIR Material Spectra

Absorbance spectra increases with increased weight

PE Surlyn PE and Surlyn

11

The Solution - Controls

21Plus! Operating SystemData Mapping:

• Film measured as a collapsed tube

• Speed:• Bubble rotational speed measured at the collapsing frame• Haul Off Speed is measured at the winder or other convenient location

• Distance from the rotational point to the measurement point is entered

• Monitored by the digital tachometer

• Rotational data is saved along with corresponding measurement point position during each scan of the collapsed tube

Dynamic Twist Angle algorithm determines twist angle under the frost line for superior mapping and reduces start-up time

Photo Courtesy: Macro Engineering

Photo Courtesy: Gloucester Engineering

12

Data Mapping Technique

Start with the collapsed bubble in a “layflat” position with the first data setData set rotates, due to tower/top nip oscillation, creating the second data setThe process continues, creating a set of simultaneous equations from which to refine the die mapping therefore improving material controlStarts resolving within 1 minute or 4 scans of the web

A CB D E

J HI G F

J BA C D

I GH F E

1ST Iteration

2ST Iteration

V XW Y Z

V XW Y Z

=A+J =C+H=B+I =D+G =E+F

=J+I =B+G=A+H =C+F =D+E

Bubble

Collapsed Bubble in “Layflat” Condition

13

The Solution

14

Results

Case Study: Poorly Centered Die

Before: 12% After: 4.7%

** Results based on an Oakland offline lab profiler with resolution of 5000+ points across the web

15

Results – Auto Die

Before: 3.0% (2σ)

After 45 Min: 1.3% (2σ)

5 Mil (127 μm) Barrier Film

>50% reduction in CD spread in ~45 minutes

16

Results – Auto Die

After 35 Min: 2.7% (2σ)

After 65 Min: 0.9% (2σ)

Start: 3.7% (2σ)

17

Air Ring

Situation: Upgrade of an auto Air Ring on an existing manual annular die

End Product: 3 different, 5 layer medical flexible package films with annual resin consumption of ~2,000 tons

Applied the same mapping measurement and control algorithms as with the viscosity heaters in the annual die

18

Customer Results – Air Ring

>75% reduction in CD spread in ~25 minutes

19

Customer Results – Air Ring

20

The Value – Air Ring or Viscosity Heaters

50-70% reduction in CD variations

60% reduction in time for product change-overs and restarts

50% scrap reduction at winder• Additional scrap reduction in downstream operations

21

Summary

New revolutionary solution for high performance, multilayer blown film lines

Proprietary mapping algorithm controlling critical barrier layer films

• Includes dynamic twist angle compensation

Much faster measurement feedback and control as compared to conventional designs

• ~45 minutes for viscosity heater• ~25 minutes for air nozzle

Typical CD reduction of > 50%

Does not require splitting the bubble onto two winders• Measures and distinguishes top and bottom plies of layflat

Have systems running at both end user and OEM sites

Offers significant annual resin, scrap, and time savings

22

Future Investigations

Does this new technique provide better uniformity over the traditional total thickness measurement combined with gravimetric resin monitoring?

23

Acknowledge

Macro Engineering – Ontario, Canada

Amcor Flexibles Healthcare – Mundelein, IL

Latest Developments in On-Line Measurement and Control of Multilayer Blown Films Full Spectrum InfraRed (FSIR) and Air Ring

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PRESENTED BY

Doug WrightTitle: Director – Marketing and Business DevelopmentCompany: Thermo Fisher Scientificdouglas.wright@thermofisher.com