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Monday, November 30, 2015

Effects of Moisture Content on Mechanical Properties

The moisture content of a sheet of paper is dependent on the relative humidity (RH) of its surrounding atmosphere because paper is hygroscopic (increase in RH causes and an increase in moisture content & decrease in RH causes a decrease in moisture content).  Besides swelling, the uptake of water molecules produces an increase in fiber flexibility, which is important for many mechanical properties of paper. Moisture pickup due to water vapor in the air has a weakening effect on fiber-to-fiber bonds and influences mechanical properties in this way.

Tensile Strength
Tensile strength increases slightly to a maximum at 30-35% RH and then decreases quite rapidly at higher relative humidity. This decrease has been attributed to a weakening of fiber-to-fiber bonding.

Tearing Resistance
Tearing resistance increases over the entire range of RH, however, at some point above 80% the curve will fall off rapidly due to the disruption of interfiber bonding.

Stiffness
Stiffness continuously decreases with increasing moisture content primarily as a result of increased fiber flexibility.

Bursting Strength
Bursting strength is thought to be primarily a function of tensile strength and stretch. From 20-35% RH, both tensile and stretch increase, producing an increasing burst; from 35-55% stretch continues to increase and tensile falls off at an increasing rate, but stretch continues to rise although at a decreasing rate. Finally, above 55% RH, the decrease in tensile strength is greater than the increase in stretch, and bursting strength decreases continuously.

Folding Endurance
Folding endurance is strongly influenced by moisture content, increasing noticeably up to 65-75% RH and then falling off beyond that. Folding endurance is a complex function of various factors and this response is not easily analyzed.

Considering the variation in these properties due to variations in moisture, it is important to understand what conditions measurements are made under.  If a sample is quickly moved from the machine to the lab for testing, the additional moisture from the machine can have a significant effect on the results. Conversely, paper will be most brittle when moisture-free. Using standard laboratory conditions and conditioning procedures will result in more consistent data that can be compared and used to make reasonable adjustments to achieve the desired results.

Reference: Scott, William & Stanley Tosset, "Properties of Paper: An Introduction", p. 91-93, 1989.

Monday, November 23, 2015

Difference Between Source & Illuminant

Source (or UV Level): A physical emitter of light.

Illuminant: Standardized, tabulated spectral distribution based on statistical

measurements or theoretical equations.

In any discussion of the measurement of the optical properties of paper, it is important to understand the difference between a light source (or UV Level) and an illuminant. The term light source refers to the actual light energy when striking the specimen during measurement or observation. For example, when paper is being viewed by a human being, the source of light striking the paper is generally either fluorescent light, incandescent light, daylight filtered through office windows or some combination of these.


On the other hand, the light striking the sample in a measuring instrument is generally provided by either a quartz tungsten halogen (QTH) lamp or xenon lamp, either of which may be filtered to alter their spectral energy distribution. These are physical sources of light and are therefore referred to as sources not illuminants. An illuminant is a light defined by a spectral power distribution, which may or may not be physically realizable. For example, illuminant D65 was arrived at by taking a large number of measurements of daylight throughout the world at various times of the year. The data was averaged to arrive at the D65 spectral distribution curve. There is no known lamp and filter combination that will produce an exact duplication of the D65 spectral curve, therefore, D65 is an illuminant (a table of spectral data describing the spectral distribution of light energy) but it is not a light source (a physical object that produces light). 


In most colorimeters, the source and the reflected light are filtered to Illuminant C. This is true of the Technidyne Brightimeter and Technibrite instruments where the light source is filtered quartz tungsten halogen (very similar in spectral distribution to Illuminant A), however, the standard observer to which all of the filter functions are adjusted is based on Illuminant C. Most spectrophotometers offer either source C or 65. This is done by using a xenon lamp which has lots of UV energy and then a cutoff filter is used during calibration to set the UV Level to C or D65, respectively.  The Technidyne Color Touch provides the user with a choice of three different sources, which differ by the amount of ultraviolet energy contained in each, D65 (high ultraviolet), C (moderate ultraviolet) and UV-EX (no ultraviolet). When this flexibility is available, and especially when dealing with the measurement of optically brightened papers, both the source (UV Level) and the illuminant must be individually specified.

Thursday, November 19, 2015

Technidyne Thanksgiving Lunch 2015

David opening his BINGO gift
Thanksgiving isn't until next week in the US, however, we celebrated yesterday at Technidyne. It was a fun time filled with great food, camaraderie, games and laughter.  Thanks to the Technidyne staff for making everyone enjoy working together.  Here are some photos of the fun.
James getting Star Wars gear

Matt seeing what his winnings are
All 4 BINGO winners: David, James, Matt & Cindy

Tuesday, November 17, 2015

Color Measurement: What is UV Level (or source)?

When making color measurements it is important to understand the terms Illuminant, Observer and UV-Level (or source). There will be three separate blogs addressing each of these points.

UV Level (or source)

When making measurements on a spectrophotometer, many times different UV Levels or sources may be selected.  The UV Level determines the amount of UV that will physically strike the sample when the measurement is made. This is generally calibrated to one of three levels, D65, C or UV-EX. In most cases a pulsed xenon lamp us used and there is a cutoff filter which is adjusted in the calibration procedure to mimic the amount of UV from the appropriate source.

UV Level D65
As seen in the chart (right), D65 has a lot of UV energy, similar to outdoor daylight.

UV Level C
C has a moderate amount of UV energy, similar to office lighting e.g. some energy from fixed lights in the office and additional UV energy from light coming in through the windows.
Note: UV Level C is nearly identical to what is referred to as QTH.

UV-EX
UV-EX is UV-excluded, therefore, there is no UV energy when using this UV Level.

Ideally, the UV Level should be selected which matches the Illuminant that is being used, e.g. D65 Illuminant & D65 UV Level. However, some people choose different combinations.  The UV Level is important when measuring things with fluorescence. The UV energy will excite the fluorescing agent and provide a boost in the visible spectrum.

Since a change in UV Level is a physical change in the amount of UV energy striking the sample, multiple measurement must be made to get the results of a single specimen under different UV Level conditions. This cannot simply be calculated. It is important to understand, though, that color values obtained under one UV Level will be different than those obtained under a different UV Level, The one exception is where the sample is totally non-fluorescent. In that case measurements under D65, C and UV-EX will all yield the same results.

In the Paper Industry, UV Level D65 and C are very common. Typically, D65 is used to make process changes on the machine as it expands the measurement scale and allows for more fine tuning of chemicals. However, C is more commonly used in final specification setting since it relates to more common UV conditions that someone may encounter.  Finally, there are still instances where specifications are based on D65 and UV-EX, primarily for specialty products.

Thursday, November 12, 2015

Video: TEST/Plus product line

We have been working on some new videos to add to our Technidyne YouTube Channel.  One of the latest videos is the TEST/Plus product line can be seen HERE. 

We are posting product videos, calibration videos and maintenance videos. 

If you have ideas of other videos that would be helpful to you, please let me know by sending me an email at toddp@technidyne.com.

Monday, November 9, 2015

Color Measurement: What is Observer?

When making color measurements it is important to understand the terms Illuminant, Observer and UV-Level (or source). There will be three separate blogs addressing each of these points.

Standard Observer

The color data obtained from spectrophotometric measurements has no relationship to human visual assessments of color.  The spectrophotometer measures the reflectance of different wavelengths of light which is a physical phenomena.  It is of no value to measure color unless the measurements relate to what we see.  In order to make use of spectrophotometric data in the setting of product specifications, acceptance tolerances, etc., it is necessary to first convert the spectrophotometric data to a color scale which relates to visually observed color.

Figure A
In 1931, the CIE (Commission Internationale de l'Eclairage) established the "Standard Observer" utilizing and experiment depicted in Figure A.  Monochromatic light of individual wavelengths is produced by the prism system shown and is projected onto a white screen. Three controllable colored light sources, red, green and blue are also projected onto the white screen superimposed upon each other. To begin the experiment, a single wavelength of 400 nanometers is projected onto the screen. The observer then adjusts the three colored light sources until the resultant color matches the individual 400-nanometer wavelength. The observer then records the relative output of the three colored light sources. To continue, a single wavelength light source of 410 nanometers is then projected onto the screen and the observer produces a matching color by again adjusting the three colored light sources. This procedure was repeated over and over until individual wavelengths throughout the visible spectrum of 400 to 700 nanometers were reproduced by the three primary light sources, red, green and blue. After this experiment was performed by many observers, average observer responses were plotted and are shown in Figure B.
Figure B


            Thus, the CIE Tristimulus functions X (red), Y (green) and Z (blue) were developed. These results obtained in 1931 were based on a cone angle of 2º viewing. Color measuring instruments which faithfully reproduce the standard average human eye response normally produce excellent agreement with human color assessments. Figure 3.2 shows the response curves of Technidyne colorimeter (dashed curves) superimposed on the average human eye response (solid curves). Effective wavelengths for the CIE functions based on illuminant C, 2º observer are: X (595nm), Y (557nm), and Z (455nm).

In 1964, CIE developed a new set of tristimulus functions for a 10º observer to correlate with the viewing of larger samples. The relationship between the 2º and 10º standard observers is illustrated in Figure B. At approximately arms length the 2º observer would view an area the size of a U.S. quarter and the 10º observer would view an area the size of a softball.

Remember that the so-called “Standard Observer” is actually an Average Observer. Every person has a different spectral response from every other person and that response is continually changing. The CIE standard observer has quantified a single, average, spectral response, which can be built into every color-measuring instrument. The instruments will, therefore, all agree with each other but an instrument will only agree with a human observer if the human has average spectral response.

Summary:


1931 Standard Observer (2º Standard Observer) - how the average person saw color as a result of the 1931 CIE experiment where samples were observed via an area of approximately 2º at arms length e.g. an area the size of a U.S. quarter


1964 Standard Observer (10º Standard Observer) - how the average person saw color as a result of the 1962 CIE experiment where samples were observed via an area of approximately 10º at arms length e.g. an area the size of a softball


Since a change in observer is just a calculation in a spectrophotometer, after the sample is measured, color values for different observers can be determined with just a click of a button. It is important to understand, though, that color values obtained under one observer will be different than those obtained under a different observer, This is because the size of the area being viewed does have an effect on how people see color. 

In general, if illuminant C is used the observer is normally 2º.  Likewise, if standard illuminant D65 is used the observer is normally 10º.

Thursday, November 5, 2015

Color Touch™ X Luncheon

Technidyne recently released the Color Touch™ X. Instruments have already shipped all over the world in just the first few months.
Back of the t-shirt for all Technidyne employees
Today was a celebration to recognize the time and effort put in to getting the Color Touch™ X to the market. Many hours of planning, development, software, hardware, prototyping, testing, debug, training, documentation and transitioning have led to this point.

Tom explains the marketing efforts of the Color Touch™ X

Many thanks to the customers, agents and employees that have helped launch the Color Touch™ X. It has many revolutionary developments and keeps Technidyne as the leader in optical testing equipment for the Pulp and Paper Industry.

Monday, November 2, 2015

Color Measurement: What is Illuminant?

When making color measurements it is important to understand the terms Illuminant, Observer and UV-Level (or source). There will be three separate blogs addressing each of these points.

Illuminant
An illuminant is a light defined by a spectral power distribution, which may or may not be physically realizable.  We may use a certain light to shine on the actual sample when we make a measurement. The illuminant is applied as a calculation to tell us how the sample would have looked if it were under that standard lighting condition (or illuminant).

For example, most spectrophotometers use a pulsed xenon lamp to shine on the sample when measurements are made. The instrument then uses this reflectance and applies a calculation based on the illuminant selected to give us data that represents how the sample would look under that particular lighting condition. 

Some common illuminants:

Standard illuminant A - incandescent lamp light; has a red-orange tint; color temperature 2855.6 K

Illuminant C - northern sky daylight; spectral energy distribution is very similar to typical daylight but with less ultraviolet energy (like on a cloudy day); often used to simulate indoor lighting; color temperature 6774 K

Standard illuminant D65 - daylight illuminant; color temperature 6504 K; there are also D50 , D55 and D75 illuminants

Standard illuminants F1 to F12  - fluorescent lamps of different types differ widely in spectral power distribution. The CIE has published distributions for 12 fluorescent illuminants; F2 represents a cool white fluorescent lamp; color temperature 4200 K

Since a change in illuminant is just a calculation in a spectrophotometer, after the sample is measured, color values for different illuminants can be determined with just a click of a button. It is important to understand, though, that color values obtained under one illuminant will be different than those obtained under a different illuminant, This is because the lighting does have an effect on how people see color. 

In the Paper Industry illuminant C and standard illuminant D65 are most commonly used. They will give similar, but different results.  In general color applications standard illuminant D65 is most common.