Straubel Paper Company
Straubel Paper Company
Straubel Paper Company
Straubel Paper Company
Straubel Paper Company
Straubel Paper Company

What do specifications mean?

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BASIS WEIGHT...ln all cases with our product, basis weight is the weight in pounds of 3000 square feet, or 333.33 square yards, of material. Basis weight varies some. For example, 4-ply scrim, we say, weighs 40 pounds, or 40 pounds for 3000 square feet. Generally it weighs more. From three truckload lots selected at random the yield averages were 41.0#, 41.5# and 42.0#. In each of these cases the average is made up of the basis weights from 40 rolls of material.

All rolls do not have the same basis weight. We measure the variation from the average in terms of a statistical term called standard deviation. The average plus or minus a standard deviation will give the variability from the average of the basis weights of the rolls in the lot. The average +/- one standard deviation will include 75% of the roll basis weights. The average +/- two standard deviation will include about 95% of the roll basis weights. The average +/- three standard deviations will include about 99% of the roll basis weights. The three lots we selected at random had standard deviations as follows:
  Avg. Standard Deviation
LOT #1 41.2 0.59
LOT #2 42.14 0.89
LOT #3 42.61 1.19

So it could be said of Lot # 1 that 75% of the material will have a basis weight between 41.20 +.59, or 41.79# and 41.20 - .59, or 41.61#. 95% of the material will have a basis weight between 41.20 + 1.18, or 43.28# and 41.20 - 1.18, or 40.02#. 99% of the material will have a basis weight between 41.20 + 1.77, or 42.97# and 41.20 - 1.77, or 39.43#.

Sample size makes a difference in the basis weight found. The smaller the sample size, the greater the variability of basis weight found. For our purposes we use 12-inch square samples. We take three samples across the roll and average them. To give an indication of the variability of results as compared to sample size, we took a 12-inch square of 4-ply scrim and determined the basis weight to be 43.68#. We then cut this into nine 4-inch x 4-inch samples and determined the basis weight as below:

#1 46.38 #4 44.00 #7 44.60
#2 41.62 #5 42.82 #8 44.60
#3 42.82 #6 44.60 #9 44.60

Basis weight found is also a function of the moisture content of the paper. TAPPI procedure, T -402 OM-88 calls for samples of paper to be conditioned in an atmosphere at 50% (+/- 2%) relative humidity and 73.4 degrees F (+/- 1.8 degrees) temperature. The equilibrium moisture content of cellulose (paper) under these conditons is between 6-8%. Since 4-ply scrim is about 97.5% paper, the difference in moisture could make a difference The scrim coming off our laminator is about 5 1/2% moisture and it probably does not change much until the final user receves it.

In all probability, if a sample was conditioned as per this procedure, the basis weight would be a little over 1% higher, or 42# would actually be 42.42#. Normal practice in our lab is not to precondition the sample since, if we err, it is to the low side.

CROSS DIRECTION WET TENSIL...This is a determination of the strength of the material cross direction, or across the web when wet. The values, which we use and report, are based upon a 1-inch wide strip. The procedure is to first condition the sample in an oven at 105 degrees C (221 degrees F) for four minutes required by General Service Administration procedures, or 11 minutes according to TAPPI. This is to make sure that the wet strength resin in the paper is cured. At room temperature this takes from three to four weeks, according to testing in our laboratory. Since it is usually a month or more between the time the paper is made and the product arrives at the end user, this is no problem. This gives some indication of how well the product will perform when wet. It measures the wet strength in the paper, the strength of the nylon or rayon reinforcing threads and how well the two are bonded together. Because nylon stretches far more easily than paper, the bonding between paper and nylon is a significant factor.

We take nine samples across a 40-inch web. Here again, there is some variability in the tests. A typical example is below:
Average wet tensil of 34.72 oz. / nine individual tests:

#1 40.96 oz. #4 28.48 oz. #7 33.76 oz.
#2 32.96 oz #5 30.08 oz. #8 40.96 oz.
#3 32.80 oz. #6 32.00 oz. #9 40.80 oz.

On this group the standard deviation is 4.87 so 75% of the material would be between 29.85 and 39.59 oz. etc. As one might assume, the TAPPI procedure in which the sample is conditioned in an oven for 11 minutes yields slightly higher results. Below are the results of a series of tests we ran:

4-Ply Bio 42.20 oz. 44.48 oz.
3-Ply 25.76 oz. 26.08 oz.
2-Ply 25.76 oz. 41.44 oz.

We use the G.S.A. procedure in our testing.

CROSS DIRECTION DRY TENSIL...This is a determination of the strength of the material across the web when dry. The test is conducted on a dry 1-inch wide sample, however no pretreatment is required. According to TAPPI the sheet should be preconditioned to a constant moisture, but for practical purposes in the range of moisture, in which we operate, the variation caused by moisture content is small and our results are usually well above what we claim.

ABSORBTION RATE.. .This is a measure of how fast the material will absorb water. A sample of material is placed on a piece of metal with a hole about 1 5/8-inch diameter in the center. 0.1 mil of water is dropped on the sample over the hole and the time it takes for the shiny appearance of the water to disappear is measured. The specification for the G.S.A. is 8 seconds maximum. The bulk of our tests result at about 1 second.

TOTAL ABSORBTION - WATER AND OIL...This is a measure of the amount of these liquids that material will absorb and hold. The test is run by cutting 4-inch square samples of material, which are weighed and then soaked in distilled water at room temperature for three minutes. The sample is then hung by one of its corners and allowed to drain for one minute. Then it is reweighed and the result is measured as the weight of the water retained in the sample compared to the original weight of the sample in percent. If the weight of the water retained is 5 times the weight of the original sample, the result is 500%.

The test for oil is run much the same way except the sample is immersed in oil for three minutes and allowed to drain for 20 minutes.

The test is not a good indication of how much water the material will hold in practice because the sample is not touched between the time it is hung to drain and it is weighed. It does give an indication of differences between materials.

We take three samples across the web and average the results of the tests, which are usually closely grouped, as shown in the examples below:

559% 586% 601%
589% 594% 596%
557% 574% 621%
avg. 568% avg. 585% avg. 606%

We do the same for oil, as shown by typical results:

281% 280% 269%
274% 273% 257%
259% 273% 239%
avg. 271% avg. 275% avg. 255%

As an indication of how much water a 4-ply towel will hold, a 12-inch x 12-inch towel will weight about 6 1/3 grams, (there are 28 grams approximately to an ounce) so a towel could hold 31.65 grams, or slightly over an ounce, or 1/6 of a coffee cup. In actual conditions, the material will hold about 3 1/2 times its weight.

BULK...We measure bulk, or thickness in three ways:

One sheet with a micrometer, which gives us a thickness in thousandths of an inch.

We also cut 100 sheets 4-inch square and measure the height unrestrained and then with a known weight on the stack.This gives us an indication of how many sheets or thicknesses can be packed in a case of a certain size.

SCRIM YIELD...Nylon reinforced scrim gets its texture or pucker because the nylon machine direction threads are stretched slightly during the laminating process. When the material is wound in a roll the nylon threads are stretched so that they are as long as the paper and the material appears flat, without any texture. When the material is cut into sheets, the nylon, which is elastic, will pull on the paper and cause a shrinkage of the length cut. This shrinkage is be between 2% and 3%

Do you get what you paid for? We monitor the roll length off the rewinder in the following way:

On all shipments for the General Services Administration, we certify the properties. So the basis weight of each finished roll is determined. We use the average basis weight of the rolls divided into the total weight of all the rolls to determine the amount of area. We compare this to the area we claim to ship. We vary about 2% +/-.

Straubel Paper Company
Straubel Paper Company