EP0245250B1 - Veredlungsverfahren für papier mit wärmeverformung der trägerschichten - Google Patents

Veredlungsverfahren für papier mit wärmeverformung der trägerschichten Download PDF

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Publication number
EP0245250B1
EP0245250B1 EP85905975A EP85905975A EP0245250B1 EP 0245250 B1 EP0245250 B1 EP 0245250B1 EP 85905975 A EP85905975 A EP 85905975A EP 85905975 A EP85905975 A EP 85905975A EP 0245250 B1 EP0245250 B1 EP 0245250B1
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Prior art keywords
web
nip
drum
process according
temperature
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French (fr)
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EP0245250A1 (de
EP0245250A4 (de
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Jay Henry Vreeland
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Warren SD Co
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Scott Paper Co
Warren SD Co
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Priority to AT85905975T priority Critical patent/ATE53085T1/de
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
    • D21G9/00—Other accessories for paper-making machines
    • D21G9/009—Apparatus for glaze-coating paper webs

Definitions

  • This invention relates generally to the manufacture of paper and in particular to a novel method of finishing printing paper in a manner which improves its properties.
  • High quality printing paper must have a number of physical properties. Two of the most important are a flat and smooth surface to facilitate printing in a press and gloss to produce a more attractive surface, particularly after printing. These properties can be obtained by a variety of techniques, such as coating the paper with pigments and binder and finishing it in one or more pressing operations.
  • Supercalendars commonly consist of a large number of rolls.(9 to 14), alternating steel and resilient, in order to obtain the desired smoothness and gloss.
  • rolls.(9 to 14) alternating steel and resilient, in order to obtain the desired smoothness and gloss.
  • cushion rolls two resilient rolls running together midway in the stack to perform the necessary reversing of the side toward the steel rolls. This action is only partly successful at providing two smooth sides since the first side finished towards the steel is later deformed by the exposure to the resilient rolls.
  • finishing is machine calendering wherein the paper web is passed between two normally unheated steel rolls pressed together at high pressures. This process produces smoothness, but little gloss because of the absence of shear in the nip.
  • gloss calendering which uses heated finishing rolls to produce high gloss finishes on coated paper or board without the high pressure of supercalendering.
  • the nip pressures for commercial machines are typically between about 87.5 to 175 KN/M (500 to 1000 pounds per lineal inch) of nip loading. This typically results in nip pressures of 6,890 KN/M 2 to 13,780 KN/M 2 (1000 to 2000 p.s.i.).
  • the lower pressure causes less densification of the paper, and therefore, better opacity, while the high temperature softens the coating and permits better gloss enchancement.
  • the finishing effect is limited to the coating and the uppermost surface of the web.
  • the surface of the sheet is not as smooth and flat as that produced in supercalendering and has generally been applied-to coated board rather than high quality papers.
  • gloss calendered sheets do not print as satisfactorily in a printing press as do supercalendered - sheets.
  • the one parameter which has been found to be the most critical in gloss calendering and supercalendering has been the moisture content of the paper. High moisture improves the smoothing and glossing effects of both the coating and the paper substrate. Many developments in supercalendering and gloss calendering involve techniques for increasing the moisture in the web or at least in some portions of it before finishing.
  • moisture is an undesirable control parameter. Small variations in moisture cause large variations in the finished properties of the paper. Also, it is undesirable to have more than about 3.5% to about 4.5% moisture in the finished sheet to avoid uneven reel building and sheet curl from later drying. This amount of moisture is a stable amount, and the sheet will not dry significantly below this level under ambient conditions.
  • desired high moisture content e.g. 7% to 9%
  • Nonuniformity of moisture in the sheet can be even a bigger problem than too much moisture.
  • nonuniformity it is meant that the moisture content at once place on the sheet is higher or lower than at other locations across the width of the sheet.
  • the nonuniformity can also exist in the machine direction and the thickness of the sheet. Nonuniformity is most severe when calendering takes place immediately after coating, which is to say when the calender is in line with the coater. If coating is done in a separate operation from calendering, the moisture content of the coated paper has time to equalize throughout the web before calendering.
  • the above cited patent No. 3,124,504 is primarily concerned with very moist webs (up to 35% or 50% moisture) and includes the concept of drying the web while finishing it. Very high temperatures are employed for drying, but temperatures above the boiling point of water are said to be needed only if the web is wetter than 5% to 8% of the bone dry weight.
  • the web moisture content is also noted as being an important element in the process disclosed in above cited patent Nos. 3,442,685 and 3,451,331.
  • the patents teach that it is best for the paper to have about 7% moisture content, and moisture can be added before the supercalender to improve the finishing effects. The addition of moisture before finishing is also described in above cited patent No. 3,124,481 to manufacture glazed uncoated paper.
  • 2,214,641 also moistens the surface of the web before finishing.
  • gloss calendering is undertaken immediately after coating before too much of the moisture is lost from the coating.
  • finishing is carried out at a web moisture content of 9% to 10% of the bone dry weight.
  • U.S. Patent No. 3,268,354 takes special steps to dry the surface of the coating, but to maintain a wet interface between the coating and the fibrous web before gloss calendering.
  • the web in this disclosure has a moisture content of at least 15% at the interface.
  • the present invention is a new process which permits the manufacture of paper with supercalender smoothness and gloss without the above noted disadvantages of supercalendering.
  • the invention is a process for producing gloss and smoothness on the surface of a paper web, comprising the steps of:
  • the invention which can be described as substrata thermal molding, is based upon molding the critical substrate of the web into a flat strata permitting the surface of the fibrous web and any coating to be flattened, smoothed and glossed to the degree obtainable by supercalendering.
  • This strata is the foundation for the surface, and molding below this level is not critical to obtaining supercalender flatness.
  • the molding of the entire thickness of the sheet as in supercalendering is unnecessary, provides little advantage, and results in the previously noted disadvantages.
  • the present invention does not require a web as moist as those generally subjected to supercalendering and gloss calendering.
  • the present invention performs satisfactorily on a web having a moisture content less than 7% of the bone dry weight of the fibers and even less than 6% or 5%.
  • the invention works satisfactorily at even lower moisture contents, even as low as 3%. Consequently, finished products can be easily produced at desirable moisture levels without having to dry them in the finishing process.
  • the ability to finish the web at lower moisture contents permits drying down the web immediately before finishing at a low level where moisture content is substantially uniform throughout the web, preferably with no variation greater than 0.5% from the average.
  • the invention is particularly valuable where coating and finishing are done continuously in line with each other. It is even more valuable when coating and finishing are done continuously in line with the papermaking machine.
  • the finishing apparatus includes a second resilient backing roll pressed against the drum preferably within the same pressure range as the first to form a second nip.
  • the web is advanced through the second nip after the first nip within a short period of time, less than 4 seconds; toprovide a great advantage, uniquely valuable to this invention and explained as follows.
  • the key to the invention is to heat a critical substrata of the web to its Tg. Obviously, this requires a drum surface temperature hotter than the Tg. At the-same time, the Tg increases with reduction in moisture. Thus, conflicting goals exist in selecting the drum temperature.
  • the heating time required which is limited to dwell time in the nip, will be too long and cause too much loss in web moisture, as well as a tendency to raise the temperature of the entire web to the same temperature. If the temperature is too high, the web must be sped through the nip too fast to provide the dwell time needed as well as perhaps being beyond commercially feasible machine speeds.
  • the critical portion of the web can be brought to the critical temperature using a lower drum temperature or faster process speed than needed with only a single nip.
  • the additional pressing time provided by two nips will result in surface improvements also.
  • the web will be passed through the nip or nips without contacting the heated drum except in the nips for the reasons stated above.
  • it is desirable and not too disadvantageous to have some additional drum contact In those cases, it will be preferable to limit the contact to less than 20% of the drum circumference.
  • Parker Print-Surf - a quantitative measurement commonly used in the papermaking field for the printing roughness and porosity of paper made by sensing the leakage of air at low pressure between the surface of the sample and the measuring sensing head. The lower the value, the smoother the paper.
  • Parker Print-Surf can be measured with several different pressures of the dam against the paper being measured. In the present specification and claims, all were measured with a pressure of 10 Kg/cm2.
  • Supercalendered coated woodfree paper will typically have a Parker Print-Surf of less than 1.4 and less than 1.0 for very high quality.
  • Gloss calendered coated woodfree paper will typically have a Parker Print-Surf of between 1.2 and 2.0.
  • the present invention can be carried out on an apparatus like that illustrated in Fig. 1.
  • a paper web 1 is advanced through the first nip formed by smooth surface finishing drum 2 and resilient backing roll 3, around guide rolls 4, and through a second nip formed by drum 2 and a second resilient backing roll 5 pressed against drum 2. Thereafter, if desired for finishing the other side of the web, the web 1 is advanced to a second smooth surface finishing drum with a pair of nips formed by resilient backing rolls similar to the first unit (not illustrated for simplicity). The finished web is then wound onto reel 6. Variations in the process can be carried out by omitting or bypassing the second nip on each drum and/or finishing on one side only, in which case the second drum is bypassed or omitted.
  • the web 1 supplied to the finishing apparatus can come directly from a papermaking machine 7 and/or coater 8, if the paper is to be coated.
  • the web 1 can be supplied from a roll of previously manufactured paper which may or may not have already been coated.
  • the papermaking machine and coater are illustrated only as blocks since they can be provided by any conventional apparatus well known in the art.
  • the finishing apparatus employed in the invention can be provided by any of the many disclosed in the previously described prior art relating to gloss calendering if they are designed or can be adapted to operate at the temperature, pressure and speed conditions of the invention. Accordingly, little description of the apparatus will be given herein except to emphasize the importance of choosing a finishing drum which can be heated to the temperatures required by the invention and has a smooth metal surface and choosing a resilient backing roll which is yieldable but will have sufficient hardness at operating temperatures to provide a nip force between 35 and 700 KN/M (200 and 4000 pounds per lineal inch) of nip, which could require pressures as high as 6000 KN/M 2 (8,700 p.s.i.) at the extreme end of the range.
  • the actual pressure to which the paper web is subjected in the nip will depend upon the force applied and the width of the nip.
  • Resilient backing rolls flatten somewhat at the nip and will preferably have a nip width of from 1.27 to 2.54 cm (0.05 inch to 1.00 inch) for the present invention.
  • Nip widths shorter than 1.27 cm and longer than 2.54 cm could be usable with the invention. Howver, widths shorter than about 635 cm will likely require undesirably slow machine speeds and nip widths wider than 2.54 cm will likely require backing rolls of undesirably large diameter and/or softness. It is preferable for the backing roll surface to have a P. & J.
  • An uncoated and uncalendered bodystock of a mixture of Northern hardwood and softwood fibers produced in a Kraft pulping process was unwound from a roll and passed through an apparatus similar to that illustrated in Fig. 1.
  • the web had been mineral filled and sized to have 10% ash content by weight, and the web weighed 93.3 g/m 2 (63 pounds per ream of 3300 ft 2 ).
  • the finishing apparatus was operated with only one nip at a force of 175 KN/M (1000 pounds per lineal inch) and a nip width of .47 cm (.185 in).
  • the temperature of the web was about 26.7°C (80°F) just before entering the nip.
  • the moisture content of the web was measured to be 4.8% of the bone dry weight of the fibers.
  • the web was passed through the finishing apparatus of 1.02 m/s (200 feet/min), resulting in a dwell time in the nip of 4.5 milliseconds.
  • the temperature of the drum was adjusted throughout the test from a surface temperature of 82.2°C (180°F) to 171.1°C (340°F), and samples of the finished product were taken at various intervals. The samples were tested for 75° Hunter gloss values and Parker Print-Surf values, which were plotted against drum surface temperature in Fig. 2.
  • a bodystock like that of Example 1 was coated on one side with a conventional pigment binder coating having a weight of 14.8 g/m 2 (10 pounds per ream of 3300 ft 2 ), dried and passed through the same apparatus and same procedure as Example 1, except the finishing drum surface temperature was adjusted from 25.6°C (78°F) to 190.6°C (375°F).
  • the coater was in line with the finishing apparatus.
  • the moisture content of the coated web was about 3.9% of the bone dry weight of fibers.
  • the temperature of the web was about 48.9°C (120°F) just before entering the nip. Samples were taken for different temperature intervals and tested for 75° Hunter gloss values and Parker Print-Surf values, which were plotted against drum surface temperature in Fig. 3.
  • a bodystock like that of Examples 1 and 2 was coated on both sides with coatings of the same type and amount as in Example 2 and passed through a finishing-apparatus in line with the coater and similar to that employed for Examples 1 and 2, but with two finishing drums.
  • Each of the drums had two resilient backing rolls forming a pair of nips.
  • One side of the paper was finished against one drum and the other side against the other drum.
  • the nip pressure for the first drum was varied during the test from 263 KN/M (1500 pounds per lineal inch) to 333 KN/M (1900 pounds per lineal inch).
  • the nip pressure on the second drum was held at 333 KN/M (1900 pounds per lineal inch) and its drum surface temperature at 162.8°C (325°F) throughout the test.
  • the moisture content of the web was about 4.7% just prior to the first drum and about 0.5% less at the second drum. (The decrease was due to evaporation of moisture from the heated web surface between drums.)
  • the web was passed through the nips at 8.89 m/s (1750 feet per minute).
  • the nip widths were about 2.21 cm (.87 in), resulting in a nip dwell time of about 1.5 milliseconds.
  • the temperature of the web was about 71.1°C (160°F) just before entering the first nip. Samples of the product produced were taken at the following conditions for the first side and first finishing drum.
  • An uncoated and uncalendered bodystock of a mixture of Southern hardwood and softwood fibers produced in a kraft pulping process was prepared for this example.
  • the web was mineral filled and sized to have an ash content of about 10% by weight.
  • the web weighed about 79.9 g/m 2 (54 pounds per ream of 3300 ft.2
  • the web was coated on one side with a conventional pigment binder coating having a weight of 12 g/m 2 (8.1 pounds per ream of 3300 ft. 2 ), dried and passed through an apparatus similar to that illustrated in Figure 1.
  • the apparatus was operated with both finishing nips.
  • the coater was in line with the finishing apparatus. After coating, the web was dried and it entered the finishing apparatus at a moisture content of about 4.0% of the bone dry weight of the fibers and with a web temperature of about 60°C (140°F) just before entering the first nip.
  • the web was passed through the finishing apparatus at a speed of 2.73 m/s (500 feet/min.), resulting in nip dwell times of 3.21, 3.59, 3.91, and 5.0 milliseconds for the aforementioned pressures. At each of these pressures, the temperature of the drum surface was allowed to drop from a starting surface temperature of 177°C (350°F) to a temperature of 110°C (230°F) at the finish while taking on-machine measurements for 75° Hunter gloss values.
  • the curve is shown in two portions, the left covering temperature ranges up to about 110°C (230°F) and the right from about 104.4°C (220°F) up.
  • the left covering temperature ranges up to about 110°C (230°F) and the right from about 104.4°C (220°F) up.
  • gloss and Parker Print-Surf increase at a steady rate with increasing temperature up to about 104.4°C (220°F). This is believed to be the effects from molding and coalescing the surface of the web and is what one would expect from the prior art.
  • Fig. 2 On the right side of Fig. 2 is illustrated the unexpected results of the invention. That is, at a specific temperature, about 110°C (230°F) in this case, there is a sudden rapid improvement in Parker Print-Surf for increasing temperatures. There is also a similar increase in gloss, and this is believed to be due to the interrelationship of flatness to gloss. This additional increment of gloss and flatness was unexpected, but once discovered is believed to be due to the portion of the web beneath the surface, or the subsurface strata, being heated to its glass transition temperature and suddenly softening and becoming moldable to allow the surface to be flattened to a greater degree than before. The advantages provided by the thermal moldability of the subsurface strata continue only up to about 148.8°C (300°F), after which there is no improvement in gloss or flatness for the next 16.7°C (30°F).
  • Fig. 3 displays a similar phenomenon to Fig. 2.
  • the Parker Print-Surf and gloss increase at a steady rate with increasing temperature up to about 93.3°C (200°F), after which there appears to be no further increase with increasing temperature.
  • This flattening of the curve is believed to be due to the behaviour of coating being thermally molded and is believed to be what one would expect from the prior art.
  • gloss calendering which is more temperature controlled than supercalendering, was thought to have limited ability to improve Parker Print-Surf values.
  • On the right of Fig. 3 is illustrated the results of the invention. At about 126.7°C (260°F) there is a rapid improvement in gloss and flatness for the next 36.8°C (65°F). This result is totally unexpected.
  • the same phenomenon which facilitates flattening of the critical substrata in the present invention causes the entire thickness of the web in supercalendering to be molded at a temperature above its Tg. The reason is that the high moisture content of paper employed in supercalendering, can result in a Tg low enough to be reached throughout the web by the temperature conditions of supercalendering, even when unheated.
  • the first drum temperature in a two drum apparatus will be set for the moisture content at the second nip. If there are two drums, the second drum temperature will preferably be higher than the first to accommodate the lower moisture content of the web resulting from heating at the first drum. Since satisfaction of any needed drum surface temperature for any one nip will provide some of the advantages of the invention, this invention includes a process wherein one or more of the nip conditions do not satisfy the temperature requirements.
  • Fig. 5 illustrates Tg values for cellulose fibers at various moisture levels.
  • the curve was derived from the experimental work of N. L. Salmen & E. L. Beck (The Influence of Water on the Glass Transition Temperature of Cellulose, TAPPI Journal, Dec. 1977, Vol. 60, No. 12) and (Glass Transitions of Wood Components Hold Implications for Molding and Pumping Processes, TAPPI Journal, July 1982, Vol. 65, No. 7, pp. 107-110). The curve was adjusted for the dynamic conditions in a finishing nip.
  • the Tg values have been increased over those derived by Salmen & Beck by about 12°C., since the yieldability of any polymer-like material will become less for any given temperature if the force is applied over a shorter time span. The result is that the Tg of the material appears to be higher at dynamic conditions than for static conditions. To make this adjustment, the Williams-Landel-Ferry equation was employed. The very large increase in Tg for small reductions in moisture content in the range of the invention, 3% to 7%, should be noted.
  • the web dwells in the nip very briefly, due to short nip widths and fast operating speeds. For example consider nips widths of .635 to 2.54 cm (1" to 1") and machine speeds of 2.54 to 25.4 M/S (500 to 5000 feet per minute).
  • the web dwell time in the nip will be from 0.3 to 12 milliseconds. At these short dwell times, the heat from the drum does not penetrate very far into the web.
  • Fig. 6 illustrates the temperature gradient into a web at 1.5 milliseconds of dwell time (corresponding to a nip width of 1.32 cm and a machine speed of 8.9 M/S).
  • the drum surface temperature is 138°C
  • the web temperature prior to entering the nip is 71°C
  • the backing roll surface temperature is 71°C.
  • the gradient in the web was determined by the formula: where:
  • Fig. 7 illustrates the temperature gradient into the thickness of the web for various nip dwell times.
  • the drum surface temperature is 137.8°C (280°F) and the paper temperature just prior to reaching the nip is 71°C.
  • the approximate location of the critical substrata is believed to be about .0076 mm (0.3 mils) deep and is illustrated by the cross-hatched portion. It can be seen that the temperature of the critical substrata will depend upon dwell time and surface temperature. Whether or not the critical substrata temperature is as high as its Tg will depend in part upon its moisture content. Thus, for the conditions illustrated in Fig. 7, the critical temperature will be reached for moisture contents from 5% to 7.5%, depending upon the dwell time chosen.
  • Fig. 8 further illustrates the effects of dwell time, moisture content and surface temperature of the drum in raising the critical substrata to its Tg.
  • the curves illustrated in Fig. 8 assume the same .0076 mm (0.3 mils) of depth for the critical substrata as in Fig. 7 and a web temperature of 71°C just prior to entering the nip. This temperature is not uncommon where finishing takes place immediately after coating and drying. It is expected that the webs may be at other temperatures from ambient to about 93.3°C (200°F), in which case the curves would vary somewhat.
  • the drum surface temperature needed for a web entering the nip can be determined by the formula: where:
  • Tg the dynamic glass transition temperature of the web at the moisture conditions existing in the nip, in °C.
  • the Tg can be determined from the curve in Fig. 5.
  • a formula which very closely approximates that curve is the following: where: .
  • the following is a guide for determining the drum surface temperature Ts, in °C required for the present invention for various moisture contents, initial web temperatures and dwell times.
  • Ts drum surface temperature
  • Example 2 where moisture content was about 3.9%, nip dwell time was 4.5 milliseconds, and initial web temperature was about 48.9°C (120°F), the Ts value is about 161.7°C (323°F). Looking at Fig. 3, this value, illustrated by the line identified as Ts. can be seen to be at the top of the temperature range where the unexpected rise in gloss and flatness occur also. The advantages of the invention actually begin about 40°C (70°F) lower. This is considered good correlation with the results for Fig. 2.
  • Example 3 produced too little data to produce the full curves of the other examples, but the temperature settings in that test were chosen in accordance with the above formula with the intent to show the inflection of gloss and flatness near the unexpected rise.
  • Moisture content of 4.7%, nip dwell times of 1.5 milliseconds, and initial web temperature of 71.1°C (160°F) result in a calculated Ts value of about 153.9°C (309°F).
  • Fig. 4 shows by the line identified as Ts where this point is located on the gloss and flatness curves. This part of the curve appears to correspond to the end of the unexpected rise, this being consistent with the results from Examples 1 and 2 and the formula.
  • the location of the critical substrata is one already identified. Another is the exact value of the nip dwell time.
  • the formula assumes that heating of the web occurs through the entire nip, but the greatest molding pressure only occurs in the center of the nip. Thus, the temperature reached upon exiting the nip is not as meaningful as that reached at some point between the center and the end. Determining what portion of the nip that should be used in the formula is difficult and not necessary. Also, the meaning of reaching the Tg of the fibers needs further explanation.
  • the softening of polymeric materials is a second order transition and occurs over a range of temperature rather than sharply as in a first order transition, such as in the melting of ice.
  • the breadth of the range is also a function of the molecular weight distribution with a wider distribution giving a wider range. The same softening may occur prior to reaching the temperature where the maximum effects are noted. None of these components need to be known precisely to develop a useful formula, because the formula need only be compared to the test results in the examples and a correction made to determine the starting and ending point of the unexpected rise in gloss and flatness. It is not known nor important to know which component or components have been estimated incorrectly, if any. The empirically determined adjustment corrects them and provides a formula suitable for determining the invention for all conditions contemplated by the invention. The good correlation between the examples is evidence of this.
  • Fig. 4 also includes in dotted lines the results of samples 3 and 7 of Example 3. They are located, as expected, slightly higher due to increased pressure effect of 2 nips, but in a nonimproving relationship to each other with increase in temperature. This is believed to be for the reason stated earlier, that two nips in rapid succession are equivalent to higher drum temperature: Thus, if the solid curves were extended into higher temperatures in the manner predicted by Fig. 2, they-would be flat. The single point represents the higher pressure of sample 2.
  • Fig. 9 illustrates the unexpected large benefits of the invention when the process is carried out at nip pressures above 13,780 KN/M 2 (2000 psi).
  • the calculated Ts is shown for each nip pressure at approximately 142°C-147°C, with each being different because of the different dwell times (due to larger nip widths with increasing pressure).
  • Each curve starts approximately 20°C below its Ts, and shows the much more rapid gloss improvement which occurs at nip pressures above 13,780 KN/M 2 (2000 psi) with increasing temperature over the critical temperature range (Ts-20 to Ts).
  • gloss only improves about 2 points when the nip pressure is under 13,780 KN/M 2 (2000 psi), while it improves about 5 points when the nip pressure is over 13,780 KN/M 2 (2000 psi). Moreover, the improvement at the higher pressures is at the higher gloss range where a point of improvement is harder to obtain.
  • the drum surface should be heated to no less than 20°C below the Ts to provide the pressure benefits of the invention. It is even more preferable that the drum be heated to no less than the calculated Ts to obtain all the temperature benefits of the invention. There is no well defined critical upper limit, but for economy and other obvious reasons it is preferable that the Ts not be exceeded by more than about 25°C, particularly for coated paper.
  • the present invention provides control parameters which provide the ideal controls described above and also supercalender quality. These advantages cannot be obtained with supercalendering because its range for control parameters cause pressure to be the feast effective control and moisture the most.
  • the temperature effects of the invention are believed applicable for almost any pressure applied in the nip. That is, it is expected that the effects of increasing pressure will follow their known curve, except of course, the results will be significantly better.
  • the pressures will preferably be over 13,780 KN/M 2 (2000 pounds per square inch). It is at these pressures that supercalender and better quality can be obtained, and it is at these pressures where the temperature effects of the invention are greatly increased.
  • nip pressure determination can be complex. Accurate nip loads (unit force per unit roll length) are easy to determine by merely dividing the easily measured force applied to the total resilient press roll by the easily measured nip length. However, the nip width is more difficult to measure.
  • a widely accepted formula which is believed to provide a satisfactory approximation of nip width for many common installations is the Hertzian equation set forth by Narayan V. Deshpande, in Calculation of Nip Width, Penetration and Pressure for Contact Between Cylinders With Elastomeric Covering, TAPPI October 1978, Vol. 61, No. 10, pp. 115-118.
  • the Young modulus will depend upon the hardness of the resilient roll cover. For example, roll covers having a P. & J. hardness of 4-5 at operating temperature will have a modulus of about 517,000 KN/M 2 (75,000 psi). The modulus changes significantly with temperature changes in the roll cover.
  • the principles of the invention are believed to be applicable to any type of web papermaking fibers, whether coated to uncoated, groundwood or woodfree.
  • the invention is valuable for woodfree papers (which will be defined herein as having at least 80% of its papermaking fibers provided by chemical pulp), and groundwood papers (which will be defined herein as having at least 50% of its papermaking fiber provided by groundwood pulp) and those in between, which will comprise from 50% to 80% chemical pulp fibers and from 20% to 50% groundwood fibers. Any of these may be coated.
  • Coatings for woodfree sheets preferably will be in an amount of at least 7.5 g/m 2 and those for the other sheets preferably will be in an amount of at least 4.5 g/m 2 .
  • the invention is believed to be applicable to all conventional basis weights, including the heavy weight board products.
  • the invention is capable of producing, at least with the coated woodfree sheets, gloss higher than 50 and even 70, and Parker Print-Surfs better than 1.4 and even better than 1.0.
  • N. L. Salmen has described lignin as having a static Tg at 115°C (239°F) or dynamic Tg of 127°C (260°F) for moisture content of 2.5% and above. (See previously cited Salmen and Beck references and also Thermal Softening of the Components of Paper and its Effects on Mechanical Properties, N. L. Salmen, C.P.P.A. 65th Annual Meeting, Feb., 1979, pp. B11-B17.) This value is equivalent to the Tg for Cellulose at a moisture content of 4.7%.
  • a typical groundwood web would have about 30% lignin, causing a similar but perhaps smaller rise in gloss and smoothness when its Tg was reached as with cellulose. A second and probably larger rise would occur when the Tg of the cellulose was reached, which could be at a higher or lower temperature than the Tg of the lignin, depending upon moisture content. Therefore, the invention is also subjecting a groundwood web (at least 50% groundwood) to a drum surface temperature which is at least as high as that calculated by the formula using a moisture content of 4.7%.

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  • Paper (AREA)
  • Excavating Of Shafts Or Tunnels (AREA)
  • Printing Plates And Materials Therefor (AREA)
  • Developing Agents For Electrophotography (AREA)
  • Laminated Bodies (AREA)

Claims (23)

1. Verfahren zur Erzeugung von Glanz und Glätte auf der Oberfläche einer Papierbahn, das folgende Schritte umfaßt:
A. Schaffung einer Veredelungsvorrichtung, die eine glatte Veredelungstrommel aus Metall und eine elastische Gegenwalze umfaßt, die mit einem Anpreßdruck von bis zu 700 KN/M (4000 Pfund je linearem Zoll) gegen die Trommel gepreßt wird, um einem Walzenspalt mit einem Druck gegen das Papier von zumindest 13.780 KN/M2 (2000 Pfund je Quadratzoll) zu bilden.
B. Transport einer Bahn von Papierfasern mit einem Feuchtigkeitsgehalt von 3% bis 7% des völlig trockenen Fasergewichts durch den Walzenspalt bei einer Geschwindigkeit, die die Papierbahn in dem Walzenspalt 0,3 Millisekunden bis 12 Millisekunden verweilen läßt; und
C. Gleichzeitig mit Schritt B, Beheizen der Trommel auf eine Oberflächentemperatur von einem Wert, der nicht weniger als 20°C unter dem Ts-Wert liegt, der durch folgende Formel berechnet wird:
Figure imgb0015
wobei:
Ts = Oberflächentemperatur der beheizten Trommel in °C
Ti = die Anfangstemperatur in °C der Papierbahn unmittelbar vor Eintritt in den Walzenspalt
t = Verweildauer, in Millisekunden, der Papierbahn im Walzenspalt
e = die Basis des natürlichen Logarithmus
m = Feuchtigkeitsgehalt der Fasern in der Papierbahn in Gewichtsprozent des völlig trockenen Fasergewichts.
2. Verfahren nach Anspruch 1, wobei der Feuchtigkeitsgehalt der Papierbahn in Schritt B weniger als 6% des völlig trockenen Fasergewichts beträgt.
3. Verfahren nach Anspruch 1, wobei der Feuchtigkeitsgehalt der Papierbahn in Schritt B weniger als 5% des völlig trockenen Fasergewichts beträgt.
4. Verfahren nach Anspruch 1, wobei der Feuchtigkeitsgehalt der Papierbahn im wesentlichen in der gesamten Papierbahn gleichmäßig ist.
5.-Verfahren nach Anspruch 1, wobei der Veredelungsvorrichtung eine zweiten Walzenspalt umfaßt, der durch eine glatte Veredelungstrommel aus Metall und eine elastische Gegenwalze gebildet wird und durch den die Papierbahn innerhalb von 4 Sekunden läuft, bevor oder nachdem sie den ersten Walzenspalt durchlaufen hat, und wobei in beiden Walzenspalten dieselbe Seite der Papierbahn gegen die Trommel zeigt.
6. Verfahren nach Anspruch 1, wobei der Veredelungsvorrichtung einen zusätzlichen Walzenspalt umfaßt, der durch eine zweite glatte Veredelungstrommel aus Metall une eine elastische Gegenwalze gebildet wird und durch den die Papierbahn mit der Seite der Papierbahn gegen die Trommel läuft, die jener Seite gegenüberliegt, die im ersten Walzenspalt gegen die Trommel zeigt, und wobei die Temperatur der Trommeloberfläche im zusätzlichen Walzenspalt auf dieselbe Art und Weise berechnet wird, wie für den ersten Walzenspalt, und wobei Einstellungen zur Verringerung des Feuchtigkeitsgehalts zwischen der ersten und zweiten Trommel vorgenommen werden.°
7. Verfahren nach Anspruch 1, wobei die Beschichtung der Papierbahn in einem fortlaufenden Arbeitsgang mit den Veredelungsschritten erfolgt.
8. Verfahren nach Anspruch 1, wobei die Bildung der Papierbahn auf einer Papiermaschine in einem fortlaufenden Arbeitsgang mit den Veredelungsschritten erfolgt.
9. Verfahren nach Anspruch 7, wobei die Bildung der Papierbahn auf einer Papiermaschine in einem fortlaufenden Arbeitsgang mit den Beschichtungs- und Veredelungsschritten erfolgt.
10. Verfahren nach Anspruch 1, wobei zumindest 80% der Papierfasern aus chemischem Holzstoff bestehen.
11. Verfahren nach Anspruch 1, wobei zumindest 50% der Papierfasern aus Holzschliff bestehen.
12. Verfahren nach Anspruch 1, wobei 50% bis 80% der Papierfasern aus chemischem Holzstoff und 20% bis 50% der Papierfasern aus Holzschliff bestehen.
13. Verfahren nach Anspruch 11, wobei vor Schritt B die Papierbahn zumindest auf einer Seite mit einer Beschichtungszusammensetzung beschichtet wird, die Papierbeschichtungspigmente und Bindemittel in einer Menge von zumindest 4,5 g/m2 (3 Pfund je Ries von 3300 Quadratfuß) enthält, und wobei zumindest eine Seite mit einer beschichteten Zusammensetzung gegen die Trommel zeigt, wenn die Papierbahn durch den Walzenspalt läuft.
14. Verfahren nach Anspruch 10, wobei vor Schritt B die Papierbahn zumindest auf einer Seite mit einer Beschichtungszusammensetzung beschichtet wird, die Papierbeschichtungspigmente und Bindemittel in einer Menge von zumindest 7,5 g/m2 (5 Pfund je Ries von 3300 Quadratfuß) enthält, und wobei zumindest eine Seite mit einer beschichteten Zusammensetzung gegen die Trommel zeigt, wenn die Papierbahn durch den Walzenspalt läuft.
15. Verfahren nach Anspruch 6, wobei die Schritte, die an einer Seite der Papierbahn durchgeführt werden, die Glanz- und Glätteeigenschaften nicht beträchtlich beeinträchtigen, die der anderen Seite durch die Schritte verliehen wurden, die auf dieser anderen Seite durchgeführt wurden.
16. Verfahren nach Anspruch 14, wobei die hergestellte Papierbahn einen 75° Glanz von zumindest 50 und einen Parker Print-Surf Wert von nicht mehr als 1,4 auf zumindest einer Seite mit einer Beschichtungszusammensetzung aufweist.
17. Verfahren nach Anspruch 16, wobei die hergestellte Papierbahn einen 75° Glanz von zumindest 70 und einen Parker Print-Surf Wert von nicht mehr als 1,0 auf zumindest einer Seite mit einer Beschichtungszusammensetzung aufweist.
18. Verfahren nach Anspruch 1, wobei die Trommeloberfläche auf eine Temperatur erwärmt wird, die nicht unter dem Wert liegt, der durch die Formel, die in Anspruch 1 angeführt ist, errechnet wird.
19. Verfahren nach Anspruch 1, wobei die Trommeloberfläche auf eine Temperatur erwärmt wird, die nicht mehr als 25°C über dem Ts-Wert liegt, der durch die Formel, die in Anspruch 1 angeführt ist, errechnet wird.
20. Verfahren nach Anspruch 1, wobei die Trommeloberfläche auf eine Temperatur erwärmt wird, die nicht weniger als 17°C über dem Ts-Wert liegt, der durch die Formel, die in Anspruch 1 angeführt ist, errechnet wird.
21. Verfahren nach Anspruch 11, wobei die Trommeloberfläche auf eine Temperatur erwärmt wird, die nicht geringer ist als jene, die durch die Formel, die in Anspruch 1 angeführt ist, errechnet wird, bei einem Feuchtigkeitsgehalt von 4,7%.
22. Verfahren nach Anspruch 1, wobei die Papierbahn in Schritt B die Trommel nicht berührt, außer im Walzenspalt oder in den Walzenspalten.
23. Verfahren nach Anspruch 1, wobei in Schritt B die Berührung der Papierbahn mit der Trommel nicht mehr als 20% des Trommelumfangs beträgt.
EP85905975A 1985-11-06 1985-11-06 Veredlungsverfahren für papier mit wärmeverformung der trägerschichten Expired - Lifetime EP0245250B1 (de)

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DE4112537A1 (de) * 1991-04-17 1992-10-22 Escher Wyss Gmbh Verfahren und vorrichtung zur glaetteerzeugung
EP0598737A1 (de) † 1990-11-30 1994-06-01 Warren S D Co Verfahren und vorrichtung zum kalandern von papier mit von innen beheizter walze.
DE4321061A1 (de) * 1993-06-24 1995-01-05 Escher Wyss Gmbh Verfahren und Vorrichtung zur Beeinflussung von Dicke und Glanz und/oder Glätte bei der Behandlung von Faserstoffbahnen

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CA1319286C (en) * 1989-04-20 1993-06-22 Robert James Harry Mason Application of superheated steam
DE4126233C1 (de) * 1991-08-08 1992-09-17 Sulzer-Escher Wyss Gmbh, 7980 Ravensburg, De
FI105935B (fi) † 1996-12-03 2000-10-31 Valmet Corp Menetelmä paperin kuivaamiseksi sekä paperikoneen kuivapää
US6076281A (en) * 1997-03-03 2000-06-20 Valmet Corporation Web finishing section in a paper machine
FI102093B1 (fi) * 1997-03-03 1998-10-15 Valmet Corp Rainan viimeistelyosa paperikoneessa
US5943787A (en) * 1997-03-03 1999-08-31 Valmet Corporation Web finishing section in a paper machine
FI111401B (fi) 2000-01-28 2003-07-15 M Real Oyj Menetelmä kalanteroidun paperiradan valmistamiseksi sekä kalanteroitu paperituote
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FI107554B (fi) * 2000-02-25 2001-08-31 Metso Paper Inc Menetelmä paperi- tai kartonkirainan valmistuksessa ja paperi- tai kartonkikone
US6547929B2 (en) 2000-04-12 2003-04-15 Rohm And Haas Company Paper having improved print quality and method of making the same
FI120596B (fi) * 2003-03-07 2009-12-15 Metso Paper Inc Menetelmä paperin tai kartongin muokkaamiseksi
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EP0598737A1 (de) † 1990-11-30 1994-06-01 Warren S D Co Verfahren und vorrichtung zum kalandern von papier mit von innen beheizter walze.
EP0598737B2 (de) † 1990-11-30 2001-12-05 S.D. Warren Company Verfahren und vorrichtung zum kalandern von papier mit von innen beheizter walze
DE4112537A1 (de) * 1991-04-17 1992-10-22 Escher Wyss Gmbh Verfahren und vorrichtung zur glaetteerzeugung
US5387782A (en) * 1991-04-17 1995-02-07 Sulzer-Escher Wyss Gmbh Apparatus for smoothing paper webs
DE4321061A1 (de) * 1993-06-24 1995-01-05 Escher Wyss Gmbh Verfahren und Vorrichtung zur Beeinflussung von Dicke und Glanz und/oder Glätte bei der Behandlung von Faserstoffbahnen

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EP0245250A1 (de) 1987-11-19
FI872939A0 (fi) 1987-07-03
ATE53085T1 (de) 1990-06-15
WO1987002722A1 (en) 1987-05-07
JPS63500188A (ja) 1988-01-21
FI88733B (fi) 1993-03-15
JPS6356360B2 (de) 1988-11-08
FI872939A (fi) 1987-07-03
DE3577894D1 (de) 1990-06-28
EP0245250A4 (de) 1988-11-23

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