Coatings Technology Handbook Episode 1 Part 4 ppt

Proper viewing conditions require controlled lighting in a viewing booth where the different types of light, such as simulated daylight, tungsten, and fluorescent light sources, can be u

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9-4 Coatings Technology Handbook, Third Edition

Colborn, Robert, Modern Science and Technology Princeton, NJ: Van Nostrand, 1965

Foreman, Jon, “Dynamic mechanical analysis of polymers,” American Laboratory, January 1997, p 21 Hassel, Robert L., “Evaluation of polymer flammability by thermal analysis,” American Laboratory, January

1997

Hassel, Robert L., Using Temperature to Control Quality, Second Quarter 1991 P1 Quality Hitchcock,

1991

Hassel, Robert L., “Thermomechanical analysis instrumentation for characterization of materials,”

Kelsey, Mark, et al., “Complete thermogravimetric analysis,” American Laboratory, January 1997, p 17 Neag, C Michael, Coatings Characterizations by Thermal Analyses ASTM Manual 17 West Consho-hocken, PA: American Society for Testing and Materials, 1995

Park, Chang-Hwan, et al., “Syntheses and characterizations of two component polyurethane flame retar-dant coatings using 2,4dichlor modified polyester,” J Coat Technol., December 1997, p 21 Reading, Micheal, et al., “Thermal analysis for the 21st century,” American Laboratory, January 1998, p 13 Riesen, Rudolf, “Maximum resolution in TGA by rate adjustment,” American Laboratory, January 1998,

p 18

TA Instruments Company, Thermal Analysis Application briefs available from TA Instruments Company, New Castle, Delaware: TA-8A, Thermal Solutions — Long Term Stability Testing of Printing Inks

by DSC; TA-73, A Review of DSC Kinetics Methods; TA-75, Decomposition Kinetics Using TGA; TA-121, Oxidation Stability of Polyethylene Terephthalate; TA-123, Determination of Polymer Crystallinity by DSC; TA-125, Estimation of Polymer Lifetime by TGA Decomposition Kinetics; TA-134, Kinetics of Drying by TGA; and TA-135, Use of TGA to Distinguish Flame-Retardant Polymers from Standard Polymers

DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM

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10

Color Measurement for the Coatings Industry

Color is the most important appearance of coatings for their formulation, application, or inspection Color is also the most subjective parameter to characterize visually, and characterization is often attempted under uncontrolled conditions that result in poor color judgement Proper viewing conditions require controlled lighting in a viewing booth where the different types of light, such as simulated daylight, tungsten, and fluorescent light sources, can be used for evaluation Visual evaluation always requires a physical standard for comparison because the “color memory” of the brain is quite poor without one, but very good when two samples are compared beside each other Even when proper viewing conditions are used, it is often difficult to determine the direction and intensity of color difference between two samples This process requires a trained colorist to make the evaluation

A more accurate and consistent approach to evaluate color difference is the use of a color measurement instrument The two types of instruments that can be used for this purpose are colorimeters and spectrophotometers A colorimeter uses optical filters to simulate the color response of the eye, and a spectrophotometer breaks the visible spectrum into intervals that mathematically simulate the color response of the eye The advantage of using spectrophotometers to determine color difference is in their accuracy, stability, and ability to simulate various light sources Spectrophotometer cost and complexity

of operation are greatly reduced on new versions of the instruments

There are three different technologies that are used in modern industrial spectrophotometers: inter-ference filters, gratings, and light-emitting diodes (LEDs) Interinter-ference filters require a filter for each wavelength measured and usually have 16 or 31 filters depending on the resolution required Grating-based instruments have diode arrays of 20 to 256 elements to provide higher resolution for applications that require it The advantage of interference filters is in their simplicity of operation and mechanical ruggedness However, they are difficult to make consistent and deteriorate over time High-performance instruments usually have gratings that give more resolution and better consistency, but they are usually more expensive and complex to build and calibrate A new market entrant for spectrophotometers is based on LEDs of different illumination colors Up to nine separate color LEDs are now available to cover most of the visible spectrum The instruments operate by illuminating one LED at a time while measuring the reflected light The advantage is that they can be made very small and cost less to manufacture The disadvantages are reduced accuracy and stability, but the technology is improving with the advent of newer LEDs with better methods for compensation

There are several different measurement geometries: sphere, 45/0, and multiangle A sphere instrument illuminates a sample from all directions and views the sample at near normal or perpendicular The 45/

0 illuminates the sample at 45 degrees from all directions and views the sample normal It is also possible

to illuminate at 0 and view at 45 The multiangle approach illuminates at multiple angles and views at

a fixed angle It is also possible to illuminate at a fixed angle and view at multiple angles

Harold Van Aken

GretagMacbeth

Bibliography 10-2

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The Use of X-ray Fluorescence for Coat Weight Determinations

11.1 Introduction 11-1 11.2 Technique 11-1 11.3 Method 11-2 11.4 Accuracy 11-3 11.5 Repeatability and Reproducibility 11-3 11.6 Conclusion 11-5

11.1 Introduction

The technique of elemental analysis by x-ray fluorescence (XRF) has been applied to the quality control

of coating weights at the plant level Measurements by nonlaboratory personnel provide precise and rapid analytical data on the amount and uniformity of the applied coating XRF has proved to be an effective means of determining silicone coating weights on paper and film, titanium dioxide loading in paper, and silver on film

11.2 Technique

XRF is a rapid, nondestructive, and comparative technique for the quantitative determination of elements

in a variety of matrices XRF units come in a variety of packages; however, the type of unit most prevalent

in the coating industry is described in this chapter

The XRF benchtop analyzer makes use of a low level radioisotope placed in close proximity to the sample The primary x-rays emitted from the excitation source strike the sample, and fluorescence of secondary x-rays occurs These secondary x-rays have specific energies that are characteristic of the elements in the sample and are independent of chemical or physical state These x-rays are detected in

a gas-filled counter that outputs a series of pulses, the amplitudes of which are proportional to the energy

of the incident radiation The number of pulses from silicon x-rays, for example is proportional to the silicone coat weight of the sample Because the technique is nondestructive, the sample is reusable for further analysis at any time

To ensure optimum excitation, alternate radioisotopes may be necessary for different applications For silicone coatings and titanium dioxide in paper, an iron-55 (Fe-55) source is used Fe-55 x-rays are soft (low energy) and do not penetrate far into a sample For silver on film, a more energetic

americanum-241 source has been used

Wayne E Mozer

Oxford Analytical, Inc.

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FIGURE 11.2 Differences in sensitivities in products from different suppliers of silicone.

FIGURE 11.3 Differences in paper backings.

200

150

100

50

Concentration g/m 2

Vendor A

Vendor B

Vendor C

200

150

100

50

Concentration g/m 2

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Sunlight, Ultraviolet,

and Accelerated

Weathering

12.1 Introduction 12-1 12.2 Sunlight 12-1

Variability of Sunlight

12.3 Accelerated Light Sources Compared to Sunlight 12-2

The Importance of Short-Wavelength Cutoff

12.4 Arc-Type Light Sources 12-4

12.5 Fluorescent UV Lamps 12-7

12.6 Conclusions 12-9 Acknowledgments 12-9 References 12-10

12.1 Introduction

Sunlight is an important cause of damage to coatings Short-wavelength ultraviolet (UV) light has long been recognized as being responsible for most of this damage.1

Accelerated weathering testers use a wide variety of light sources to simulate sunlight and the damage that it causes Comparative spectroradiometric measurements of sunlight and laboratory testers of various types show a wide variety of UV spectra These measurements highlight the advantages and disadvantages

of the commonly used accelerated light sources: enclosed carbon arc, sunshine carbon arc, xenon arc, and fluorescent UV The measurements suggest recommendations for the use of different light sources for different applications

12.2 Sunlight

The electromagnetic energy from sunlight is normally divided into ultraviolet light, visible light, and Infrared energy (not shown) consists of wavelengths longer than the visible red wavelengths and starts above 760 nanometers (nm) Visible light is defined as radiation between 400 and 760 nm Ultraviolet light consists of radiation below 400 nm The International Commission of illumination (CIE) further

Patrick Brennan

Q-Panel Lab Products

Carol Fedor

Q-Panel Lab Products

G 155)

infrared energy Figure 12.1 shows the spectral energy distribution (SED) of noon midsummer sunlight

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Sunlight, Ultraviolet, and Accelerated Weathering 12-3

of cycles, or the reproducibility of results For simulations of direct sunlight, artificial light sources should

be compared to what we call the “solar maximum” condition: global, noon sunlight, on the summer solstice, at normal incidence The solar maximum is the most severe condition met in outdoor service, and, as such, it controls which materials will fail It is misleading to compare light sources against “average optimum sunlight,” which is simply an average of the much less damaging March 21 and September 21 equinox readings In this chapter, graphs labeled “sunlight” refer to the solar maximum: noon, global, midsummer sunlight Despite the inherent variability of solar UV, our measurements show surprisingly little variation in the solar maximum at different locations Figure 12.3 shows measurements of the solar maximum at three widely varied locations

FIGURE 12.2 Seasonal variation of sunlight UV.

FIGURE 12.3 Solar maximum at three locations.

400 380 360 340 320 300 280 260

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Wavelength (nm)

2 /nm)

December

June

March Equinox

400 380 360 340 320 300 280 260

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Wavelength (nm)

2 /nm)

Kitt Peak 6/86 Cleveland 6/86 Miami 6/87

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Another type of xenon arc filter that is intended to simulate sunlight through window glass is the Window Glass Filter It is typically used to test products with a primary service life that will be indoors Figure 12.8 shows the SPD of noon summer sunlight behind glass compared to a xenon arc with a Window Glass Filter

12.4.3.2 Xenon Arc Moisture

The xenon arc uses a system of intermittent water spray to simulate the effects of rain and dew The water-spray cycle is especially useful for introducing thermal shock and mechanical erosion

12.4.3.3 Effect of Irradiance Setting

Modern xenon arc models, including the Q-Sun, have a light monitoring system to compensate for the inevitable light output decay due to lamp aging The operator presets a desired level of irradiance or brightness As the light output drops off, the system compensates by increasing the wattage to the xenon

2

how these two irradiance settings compare to noon summer sunlight

Several different sensors to measure and control irradiance are available (depending on the manufac-turer): 340 nm, 420 nm, TUV (total ultraviolet), or total irradiance The difference between these sensors

FIGURE 12.7 Xenon arc with Daylight Filter versus sunlight.

FIGURE 12.8 Xenon arc with Window Glass Filter versus sunlight through window glass.

400 380 360 340 320 300 280 260

1.2 1.0 0.8 0.6 0.4 0.2 0.0

Wavelength (nm)

2 /nm)

Sunlight

Xenon with Daylight Filter

400 380 360 340 320 300 280 260

1.2 1.0 0.8 0.6 0.4 0.2 0.0

Wavelength (nm)

2 /nm)

Sunlight through

Window Glass Filter

burner The most common irradiance settings are 0.35 or 0.55 W/m /nm at 340 nm Figure 12.9 shows

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13

Cure Monitoring: Microdielectric

Techniques

13.1 The Dielectric Response 13-1 13.2 Changes In Resistivity During Cure 13-2

13.3 Summary 13-5

Developments in the area of microelectronics now enable the fabrication of microdielectric sensors that can analyze drying, curing, and diffusion phenomena in coatings.1 Several types of microdielectric sensors have evolved in the past few years, the most sensitive being based on interdigitated electrodes and field effect transistors fabricated on a 3 × 5 mm silicon chip.2 The chip sensor is housed in a polyamide package

13.1 The Dielectric Response

The dielectric response arises from mobile dipoles and ions within the material under test As a coating cures, the mobilities of dipoles and ions are drastically reduced, sometimes by as much as seven orders

of magnitude Microdielectric sensors are sensitive enough to follow those changes and are therefore useful for cure monitoring, cure analysis, and process control.3

The dielectric response is typically expressed by the quantities of permittivity or dielectric constant (E′) and loss factor (E″):

(13.1)

(13.2)

where (E4 – Eu)/(1 + wt2) is the dipole term, se0ω is the conductivity term, and

E′ = dielectric constant

E″ = loss factors

s = bulk ionic conductivity

e0 = permittivity of free space (a constant)

+

1 ωτ2

+

e

0ω 1 ωτ2 ωτ

David R Day

Micromet Instruments, Inc.

Process Control through Dielectric Feedback • Process Control

References 13-5

through Dielectric–Thermal Feedback

and configured for ease of placement in various processing environments (Figure 13.1)

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1 Heat and hold at 250°F until a log resistivity of 7.0 is reached (allows for degassing while preventing premature cure)

2 Hold log resistivity (viscosity) at 7.0 until 350°F is reached (allows for controlled curing and prevents second viscosity minimum)

3 Hold at 350°F until the dielectric reaction rate is near zero (allows reaction to go to completion)

4 Cool and notify operator that cycle has been completed

FIGURE 13.4 Ionic resistivity data and T g during isothermal epoxy–amine cure.

FIGURE 13.5 Process control of epoxy graphite cure utilizing microdielectric feedback.

11.3

6.2

40 80 120 160 200

Time (min)

13

12

11

10

9

8

7

6

5

300

250

200

150

100

50

350 400 450

Time (min)

Hold at 250 ° F until Ionvisc = 7.0

Hold Ionvisc

at 7.0 until Temp = 350 ° F

Hold at 350 ° F until

1 & 10 Hz

1 K & 10 K Hz

Pressure Signal Issued

100 Hz Temperature ( ° F)

Fiberite F-934

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