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Thursday, February 27, 2014

How do we establish a master color/brightness standard?

Most mills today produce a variety of grades e.g. shades, weights and sizes. Also, companies want to be able to produce the same grade at any of their mills based on demand. They want the flexibility to move production of a certain grade to any of their mills based on customer needs, production efficiencies and utilization rates.  One thing that is necessary in order to make this work is to have a master color/brightness standard which all mills can produce to.

The master standard should always be established from one "originating" mill and one "originating" machine at that mill.  If at all possible, this machine should be the machine that produces the largest percentage of this grade for the market.  Once the master standard has been established, a large sample should be sent to all the mills for establishing their master file, master sample and reference sample (this will be covered in a future post).


Black bag and master samples
The master samples should be kept in a light-proof container, typically a sealed, heavy duty, black, plastic bag.  The master samples should be kept in a freezer to insure a longer shelf life.  The master samples should be checked on the originating mill's spectrophotometer at least once every few months to insure the master sample has not changed or degraded over time.  The master sample must be opened to atmosphere and allowed to acclimatize to lab conditions for 24 hours before being measured. When the first signs of degradation are detected in the measurements, a new master sample has to be established.  Acceptable limits are to be established for this degradation measurement.

When replacement of the master standard becomes necessary, the new master standard should come from the same mill and the same machine.  This master standard must be a good non-metameric match (reference Metamerism posts).  If major changes occur to the machine e.g. a top wire former is added, a new master standard may need to be established as soon as the changes on the machine have been stabilized.

Also, if any major changes in the mix of species (HW, SW, recycled) is made, a new master standard must be established.  Finally, if any change is made to the dye being used (supplier, type, mix) a new master standard will most likely need to be established.

For more information on practical aspects of paper color matching, contact me at toddp@technidyne.com.

Tuesday, February 25, 2014

Video Blogs

What type of information would you like to see in a video blog?

I am planning some video blogs. We have already posted a number of videos on YouTube for instructions on calibrating your Technidyne equipment. However, there may be other topics that lend themselves to video.

Please let me know by commenting or contacting me at toddp@techindyne.com.

Wednesday, February 19, 2014

Need Something New?

There is a lot of research and development going on here at Technidyne. We have at least 4 new products that will be released in 2014. We are putting some new technology in existing products, adding a new look to familiar tests and introducing new, advanced technology for our customers around the world. We will also have an announcement in the next few weeks that will expand our presence on the internet.

The best way to find out about these things is to follow this blog, see updates on our websiteTechnidyne on Facebook and see us at trade shows around the world.  Some of the upcoming trade shows are:
Please check out our ever-changing Technidyne Website.

Saturday, February 15, 2014

How to Increase the Dry-Strength Properties of Paper - Part 4

The primary tools by which papermakers can increase the dry-strength properties of paper are selection or purchase of a suitable quality and type of fibers, increased refining, the use of dry-strength additives, and changing the conditions of wet-pressing (if possible, given the equipment).

The size press is a very important tool for increasing paper strength, partly because of the fact that the practical addition levels are typically much higher, compared to wet-end addition. Also, it is possible to apply relatively inexpensive starch products. "Unmodified" corn starch, which is probably the major size-press additive used in the U.S., needs to be reduced in molecular mass by treatment with enzymes or oxidizing agent just before use in order to reduce the viscosity. Though the degradation decreases the strength of the resulting starch film, this is a necessary compromise that papermakers make in order to run the equipment effectively.An instrument like the Emtec PDA & EST can help you measure your surface sizing.

Sometimes poor performance of size-press starch can be traced to an undesired process of crystal formation, known as retrogradation. Retrogradation is most prominent in the linear component of most starch products, the amylose. Retrogradation is much less of a problem in the case of wet-end starches, since the molecules usually are substituted with cationic groups. Hydroxyethylated starch products for the size press are noted for high strength efficiency, as well as high resistance to retrogradation, and their performance often justifies their higher cost.

See the page related to hold out at the size press for a discussion of how to achieve a balance between internal bonding (if the starch penetrates into the paper) versus surface strength (if the starch is held out effectively).

Conditions needed to maximize tensile strength of paper will not necessarily maximize either the compression strength or stiffness. Such differences can be expected, due to the fact that the latter properties demand less flexibility of the overall product. By contrast, tensile strength can benefit from some ability of the paper to stretch and deform so that the load can be borne more evenly among fibers in the paper.

This information comes from NC State University with the following disclaimer.

PLEASE NOTE: The information in this Guide is provided as a public service by Dr. Martin A. Hubbe of the Department of Wood and Paper Science at North Carolina State University (m_hubbe@ncsu.edu). Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives.

Thursday, February 13, 2014

ISO TC 6 (Paper, board and pulps) Meeting in The Netherlands

The ISO Technical Committee (TC) 6 for Paper, board and pulps is meeting April 7-11 in Delft, The Netherlands.  Some of the Working Groups (WG) that will be meeting include:


WG 3 - Optical Properties
WG 4 - Chemical Properties
WG 10 - Automated Testing
WG 12 - Accelerated Aging
WG 25 - Surface Roughness
WG 26 - Microbiological
WG 27 - Tissue Test Methods
WG 37 - Air Permeance
WG 39 - Printability Testing
WG 41 - Contact Angle
WG 42 - Internal Bond Strength

and AHG1 (Ad-hoc Group) - Nanocellulose

Technidyne has participated in ISO, TAPPI PAPTAC, and many other technical committees for 40 years. If you have questions, always feel free to use us as your technical resource.

Wednesday, February 12, 2014

Video: Calibrating your PROFILE/Plus Opacity Module

We have been working on some new videos to add to our Technidyne YouTube Channel.  One of the latest videos is the calibration of the PROFILE/Plus TAPPI Opacity which 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.

Sunday, February 9, 2014

How to Increase the Dry-Strength Properties of Paper - Part 3

The primary tools by which papermakers can increase the dry-strength properties of paper are selection or purchase of a suitable quality and type of fibers, increased refining, the use of dry-strength additives, and changing the conditions of wet-pressing (if possible, given the equipment).

There has been some debate as to whether dry-strength chemicals increase the relative bonded area within paper or whether they increase the strength of bonding per unit of bonded area. The answer can depend on some definitions. Usually relative bonded area is defined based on optical tests, comparing the light scattering coefficient of a paper sample with a corresponding sheet that was formed from an organic solvent, such as butanol. The latter sample will have almost zero strength, due to the non-swollen condition of the fibers during the formation process, the inability of hydrogen bonds to form, and the inability of cellulosic macromolecules on the adjacent surfaces to intermingle. But the optical tests cannot sense effects of distances that are less than about a quarter of a wavelength of light, e.g. about 50 nm, which is much larger than the range of a typical chemical bond (except possibly polymeric bridges in the expanded form). That means that the optically bonded area generally is expected to be much higher than the actual area of contact on a molecular level. 
Experiments have shown that dry-strength chemicals such as cationic starch tend to increase the strength per unit of optically bonded area to a greater extent than they increase the optically bonded area [Howard, Jowsay 1989].

Once the pulp has been refined to an optimum extent (most important variable), moderate improvements in strength can be achieved by adding chemicals (secondary effect). The most popular dry-strength additive for the wet end in the U.S. is cationic starch. Cationic versions of corn, potato, and tapioca starches usually are formed by alkaline treatment of slurries of starch grains with an epoxide chemical that contains a quaternary ammonium group. In the case of wet-end products, there is no intentional degradation of the starch molecular mass, and most wet-end starches need to be cooked before use. Batch conditions often involve about 20 minutes of stirring below the boiling point of water. Alternatively, starch can be solubilized in a jet cooker.

The optimum addition point for cationic starch is usually complicated by local situations, including the availability of inlet taps and the need to use many of those addition points for other additives. A general principle is that adsorption of dry-strength agent onto long fibers is expected to yield a greater positive effect on paper strength than an equal amount added to the fines fraction. That means that there is sometimes an advantage of mixing cationic starch with the thick stock before it is diluted with fines-rich white water at the fan pump.

Strength benefits of cationic starch and similar additives (including cationic guar gum) tend to show diminishing returns with increasing dosage. The practical upper limit of starch addition usually is related to the available surface area of the wetted solids in the furnish, and to some extent also on the amount of negatively charged carboxylate groups of those surfaces. Common practical maximum addition levels of cationic starch, depending on the nature of the furnish and the need for strength, often lie between 1% and 1.5% (20 to 30 lb/ton). Evidence that the adsorption capacity of the fiber surface for cationic starch has been exceeded often comes in the form of increased foaming. This is because starch that is in solution, rather than on fiber surfaces, can act as a stabilizer for foam bubbles.

In cases where the dry-strength effects of cationic starch alone are not sufficient, one has options of (a) using a microparticle additive that may make it possible to increase the amount of starch that can be retained and also promote faster dewatering so that the sheet can enter the wet-press section with less water and become consolidated more effectively, or (b) using synthetic dry-strength additives. Anionic and amphoteric acrylamide polymers have been shown to have a superior dry-strengthening ability in some tests. Anionic acrylamide products and carboxymethyl cellulose (CMC) can be added in sequence with a suitable high-charge cationic polymer in order to achieve efficient retention on the fiber surfaces.

Conditions needed to maximize tensile strength of paper will not necessarily maximize either the compression strength or stiffness. Such differences can be expected, due to the fact that the latter properties demand less flexibility of the overall product. By contrast, tensile strength can benefit from some ability of the paper to stretch and deform so that the load can be borne more evenly among fibers in the paper.

This information comes from NC State University with the following disclaimer.

PLEASE NOTE: The information in this Guide is provided as a public service by Dr. Martin A. Hubbe of the Department of Wood and Paper Science at North Carolina State University (m_hubbe@ncsu.edu). Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives.

Thursday, February 6, 2014

Video: Calibrating Your Micro S-5

We have been working on some new videos to add to our Technidyne YouTube Channel.  One of the latest videos is the calibration of the Brightimeter Micro S-5 which 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.

Tuesday, February 4, 2014

Video: Calibrating your Color Touch PC

We have been working on some new videos to add to our Technidyne YouTube Channel.  One of the latest videos is the calibration of the Color Touch PC which 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.

Sunday, February 2, 2014

How to Increase the Dry-Strength Properties of Paper - Part 2

The primary tools by which papermakers can increase the dry-strength properties of paper are selection or purchase of a suitable quality and type of fibers, increased refining, the use of dry-strength additives, and changing the conditions of wet-pressing (if possible, given the equipment).

Refining (sometimes called "beating") can be defined as the repeated passage of wood pulp through zones of compression and shearing. Refiners usually consist of pairs of surfaces with raised metal bars that rotate relate to each other. Important variables include the energy input per unit mass of fiber (after subtracting out the energy required in the case of water alone), the rate of rotation, and the total length of bar edges encountered by fibers during one pass. The effects of refining are most often evaluated by freeness tests. This practice is somewhat unfortunate, since the reduction in rate of dewatering of the pulp is an undesired side-effect of refining, not the main goal. It has been shown that fines in the furnish, often produced during the refining process, tend to dominate the observed changes in freeness as pulp is refined. In theory it would be better to evaluate the extent of refining by measuring the strength of test sheets and by measuring the water content remaining in plugs of fiber that have been centrifuged under standard conditions (water retention value). Kraft fibers in particular are known to become more water-swollen during refining, and there is often a high correlation between water retention value and inter-fiber bond strength.

One of the first considerations in improving paper strength ought to be whether the refining conditions are at their optimum. Often there are opportunities to switch to refiner plates with a finer bar pattern, offering a lower energy input per number of bars encountered by a typical fiber (a measure of the intensity of the refining action). A finer pattern often is less energy-efficient in terms of freeness reduction, but there can be a substantially reduced tendency for fiber shortening. Rather, one achieves more of the desired effects of making the fibers more flexible and partially delaminating the outer layers, creating some fibrillation of the surfaces. It is expected that kraft fibers refined at low intensity ought to develop higher strength (especially tensile strength) compared to the same fibers refined to the same freeness at higher intensity. Some rules-of-thumb regarding optimum refining levels are given by Baker [1995].

Before turning to chemical factors, it is worth noting that wet-pressing can have a major impact on paper strength. This factor is sometimes overlooked due to the fact that papermakers generally keep wet-press nips near to their maximum practical pressure, short of crushing the sheet. A sheet that comes into a wet-press nip too wet, relative to the applied pressure may be crushed, meaning that the fiber structure created during formation is disrupted, often resulting in breaks.

Conditions needed to maximize tensile strength of paper will not necessarily maximize either the compression strength or stiffness. Such differences can be expected, due to the fact that the latter properties demand less flexibility of the overall product. By contrast, tensile strength can benefit from some ability of the paper to stretch and deform so that the load can be borne more evenly among fibers in the paper.

This information comes from NC State University with the following disclaimer.

PLEASE NOTE: The information in this Guide is provided as a public service by Dr. Martin A. Hubbe of the Department of Wood and Paper Science at North Carolina State University (m_hubbe@ncsu.edu). Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives.