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SWOP, SNAP, GRACOL Paper Grades Question

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  • SWOP, SNAP, GRACOL Paper Grades Question

    How can i tell what grade a paper is? The specific paper is Carolina C1S 24pt, but i would like to know for future reference.
    Ernie

  • #2
    Re: SWOP, SNAP, GRACOL Paper Grades Question

    Paper grade for coated paper is usually based predominately on brightness...90 and above usually being considered a "grade 1" sheet. Quicl google shows Carolina C1s at a brightness of 94 (?), which would put it at grade #1. Other important attributes being basis weight (or more intuitively grammage), finish/gloss, opacity, whiteness, hue and fluorescence

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    • #3
      Re: SWOP, SNAP, GRACOL Paper Grades Question

      If brightness is the main qualification why is #3 SWOP specified LPI 150 and #4 133? I guess my question is what about the papers limits LPI?

      Edited by: Ernie on Apr 28, 2008 2:08 PM
      Ernie

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      • #4
        Re: SWOP, SNAP, GRACOL Paper Grades Question

        >If brightness is the main qualification why is #3 SWOP specified LPI 150 and #4 133? I guess my question is what about the papers limits LPI?

        Quite likely because of typical fiber contents of these grades and the processes they are used with (Web offset versus sheetfed for grade 1). A Grade 5 is typically groundwood for example, rather than "groundwood-free" or cotton fiber as in grade 1-3. The grading "system" isn't very intuitive, and "standards" for paper classification are loose...some manufacturers define their own. Idealliance has established a print predictability paper task force to define paper attributes more important to the end result...might interest you.

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        • #5
          Re: SWOP, SNAP, GRACOL Paper Grades Question

          I have always considered Carolina a board stock, but it appears they are trying to compete with No.1 and No.2 coated cover. It appears to be heavily brightened. I ran into a job on press with Carolina and I was surprised how bright/blue it was. In the past it was much yellower.


          The linescreens are really recommendations. We regularly print uncoated papers at 175, and have printed 200LS and 20 micron stochastic (with some serious cutback curves).

          We also have done paper promotions on #4 paper @ 200LS and 20 micron on a commercial web press.


          Bret

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          • #6
            Re: SWOP, SNAP, GRACOL Paper Grades Question

            Okay, thanks. Thats what i assumed that it has something to do with the manufacturing process that limits LPI. Thanks for all your help.
            Ernie

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            • #7
              Re: SWOP, SNAP, GRACOL Paper Grades Question

              Ernie:
              I think the most important requirement for higher LPI is surface smoothness of the paper, and the ability to faithfully accept small dots or spots from the blanket. Carolina is pretty smooth. Uncoated papers can be smooth and print 200 or more LPI. The amount of ink density per unit ink film thickness increases with paper smoothness. There is still a connection to sheet brightness for paper grade, but this is all optical brightening and has little to do with sheet smoothness.
              John Lind
              Cranberry Township, PA
              724-776-4718

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              • #8
                Re: SWOP, SNAP, GRACOL Paper Grades Question

                >There is still a connection to sheet brightness for paper grade, but this is all optical brightening and has little to do with sheet smoothness.

                Hi John,

                Good point. Is there specification for the degree of smoothness that could be alluded to by paper manufacturers, or is it kind of a un-tracked metric?

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                • #9
                  Re: SWOP, SNAP, GRACOL Paper Grades Question

                  Michael:
                  Very important metric, but only tracked at the mill. Costs a lot of money to measure smoothness. Done in a lab like GATF or a vendor. Two methods: Sheffield smoothness, an air leak method, best suited for uncoated paper; and the better method, Parker Print Surf, PPS for acronym junkies, is air leak with a "blanket like" surface, best for coated paper. The closest you might get in something like the Paper Grade Finder is Gloss, which is an indirect measure of smoothness. Well, so is air leak. When you print on plastic, the wise printer measures surface roughness, R(a) with a a surface profilometer. These toys can cost $10,000 to $20,000. Still, a very important metric. Blanket suppliers use R(a) too.
                  John Lind
                  Cranberry Township, PA
                  724-776-4718

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