Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/18—Drying webs by hot air
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders

Definitions

• the present invention relates generally to open or porous fibrous web materials. More particularly, it is concerned with new and improved saturating and coating base materials having improved appearance and performance characteristics and with a new and improved method for their manufacture.
• Casings are made by multiple saturation or coating operations and generally are produced by slicing the long base web materials into longitudinal strips that are then formed into long cylinders and coated with viscose.
• some cylinders are formed from edge portions of the base web while others are formed from the center or intermediate portions thereof. Consequently, unless the base web possesses a substantially uniform or nonvarying transverse elongation profile across the width of the web, tubes or cylinders made from the center portions will vary substantially from those taken from the edge portions. As a result of this variation it has frequently been the practice to use only the center portion of the base web, discarding the edge portions and thereby increasing the ultimate cost of the product.
• Another object of the present invention is to provide a coating base of the type described that provides uniform acceptance of the treating material, and does not exhibit puckers or cockles, does not promote streaking upon saturation or coating with aqueous or nonaqueous s turants or coatings and exhibits an improved transverse elongation profile, that is, greater uniformity of elongation as measured at transversely spaced locations across the water-laid web.
• a further object of the present invention is to provide a new and improved method of producing open web materials of the type described by the use of processing conditions that obviate the development of stress areas in the web and the resultant irregularities heretofore evidenced upon saturation or coating.
• a still further object of the present invention is to provide a new and improved method for producing continuous webs of the type described utilizing a wet papermaking process that assures complete drying of the web material in an uninterrupted restrained condition thereby imparting to the web material improved appearance and performance characteristics. Included in this object is the provision for a method of drying porous tissue web material of low densimeter value to a water content of about 8 percent by weight and less by means of a single through drying unit capable of restrainably holding the web material during its entire drying cycle.
• the end product such as a stencil tissue
• a fibrous base stock material of light weight, porous, substantially lintless and highly absorbent character.
• the stock is preferably fabricated of extremely long, nonhydrated, natural fibers from a highly dilute aqueous suspension or dispersion of such fibers and is formed into a lightweight web on a papermaking machine such as the inclined wire type apparatus described in Osborne U.S. Pat. No. 2,045,095.
• the base tissue having the requisite characteristics, is dried and then coated by a suitable method such as, for example, roller coating, fountain coating, spray coating or the like, with a composition that is displaceable when acted upon by a typewriter, stylus or the like to form openings or passages in the coating through which ink may be transmitted.
• a suitable method such as, for example, roller coating, fountain coating, spray coating or the like, with a composition that is displaceable when acted upon by a typewriter, stylus or the like to form openings or passages in the coating through which ink may be transmitted.
• the base tissue web must not only exhibit excellent flexibility and strength but should provide a stencil sheet having ease and cleanliness of stencilization coupled with resistance to fiber rupture by the typewriter key or stylus and resistance to reaction with the particular ink employed.
• Typical of the stencil base tissue produced heretofore are the papers described in Osborne US. Pat. No. 2,045,- 096.
• the particular web material will vary in physical characteristics and in composition depending on its ultimate intended use.
• only those fibrous web mate rials having a densimeter value of less than 1 sec/100 ml. as measured by TAPPI test method T 460 os-68 will be considered.
• the fibers are relatively cylindrical, are slightly tapered and have little tendency to curl or twist when suspended in a highly dilute fiber dispersion.
• These low fluidity fibers have a fiber diameter of less than about 30 microns and a length to diameter ratio between about 300 and 400.
• the maximum fiber diameter is about 30 microns and may be as low as 5 to 7 microns.
• the preferred fiber length is about 5 mm. for a fiber having a diameter of about 18 microns.
• the preferred fiber content for stencil base webs is 100% abaca fibers
• these fibers can be admixed with various proportions of other natural or man-made fibers, the fiber selection depending only on the desired end use.
• natural fibers including but not limited to jute, caroa, sisal or various wood pulps such as bleached or unbleached kraft may be used, as may synthetics such as rayon, nylon, polyester or vinyl copolymers and the like.
• the fiber content of other coating base materials includes not only those fibers mentioned hereinbefore but also other suitable natural or synthetic fibers either alone or in admixture.
• the teachings of the present invention can be beneficially employed with fibrous webs containing up to percent synthetic fibers such as rayon.
• the materials produced from the aforementioned fibers are generally of high permeability, it is the open fibrous structure and particularly the low densimeter value of the web materials that is of principal importance for optimum utilization of the beneficial properties of the present invention.
• Typical examples of the properties of various base Webs for stencil, casing, tape and cushioning media are set forth below.
• the fibers employed in making the web material are dispersed in conventional fashion in a highly dilute aqueeous solution.
• the extremely large proportion of water in the dispersion facilitates free and rapid flow through the moving inclined screen of the papermaking machine leaving the fibers deposited on the screen in the form of an extremely wet, fibrous paper web, that is, a web having a water content substantially higher than about 65 percent by weight.
• the fibers might be dry laid to form webs that are subsequently treated in a wet back fashion to obtain the desired web strength when dried. In such instances the amount of water in the web is generally below that amount normally present in Water laid webs as formed prior to being dried.
• the wet web when the wet web was dried on standard steam-heated dryer cans to reduce the water content to about five percent by weight and less, the dried web frequently possessed randomly distributed surface defects that usually went undetected until the subsequent coating operation used in forming the stencil sheets. These defects have been termed cockles and puckers.
• the cockles generally take the form of uniform closely spaced undulations or ripples disposed along the machine direction of the web.
• the ripples are of varying length but usually average about /2 inch in length and occur in randomly distributed groups, primarily near the edges of the web material, but at times covering the entire cross dimension of the web.
• the puckers can be generally categorized as large cockles randomly spaced throughout the sheets, yet they still are diflicult to detect as the material comes directly from the dryer section of the conventional papermaking machine. As can be appreciated, these defects or imperfections in the web material have constituted an almost constant customer complaint over the years.
• the uninterrupted drying involves subjecting the wet web to a percolating or through drying technique whereby air is passed through the web as it is continuously held against a foraminous support.
• the process utilized for accomplishing this restrained and uninterrupted drying condition preferably is applied to the wet web material as it comes from the wet end of the papermaking machine before the water content of the web has been reduced to a level below about 65 percent by weight.
• utilization of this technique on webs rewet to a moisture content of about 50 percent by weight has also proved beneficial.
• the restrained conditions be maintained in a continuous and uninterrupted manner as the web is dried from a moisture level above which fiber shrinkage is initiated to a moisture content at or below which the web has become stabilized.
• this range falls'between about 50 percent and about 8 percent by weight moisture.
• partial drying of the web that is drying to a level below about 50 percent but substantially higher than about 10 percent by weight, by means of a thorough drying system followed by conventional drying to completion has also been found inadequate to produce the desired effect of the present invention.
• partial drying is, in effect, merely a first drying step of an interrupted drying operation.
• the material produced in accordance with the present invention is its ability to lie perfectly flat when placed on a table and to exhibit exceptional dimensional stability when exposed to different and changing temperatures and humidity conditions. Further it has been found that low densimeter webs dried in the uninterrupted restrained manner of the present invention accept the saturating or coating solutions in a uniform manner, as contrasted to the slower saturation rate exhibited by conventionally dried papers. As mentioned, the papers of the present invention also are particularly desirable in multi-coating operations since streaking and other mechanical defects are obviated due to the absence of the cockles and puckers.
• the specific operating conditions for the through drying operation will vary substantially depending upon the particular end product being made and upon the use thereof. However, as mentioned it is essential that the fibrous web material be thoroughly and completely dried under restraint to a moisture content of about 8 percent by weight and less in a continuous and uninterrupted fashion in order to achieve the new and beneficial results of the present invention. Accordingly, the temperature and flow rate of the drying air, the speed of the web through the drying unit and similar operating conditions cannot be delineated or limited to specific values, although heating to a temperature of 200 to 450 F. is preferred in commercial operation.
• the restrained condition of the web during the drying process is readily achieved by providing for the flow of gas against the web thereby forcing it into intimate engagement with the foraminous carrier of the dryer unit. This restrained condition can be enhanced not only by applying air pressure to the outer surface of the web material but also by simultaneously creating a vacuum condition on the opposite side of the foraminous surface to positively assure the restrained condition of the fibrous web during the entire drying operation.
• the dried web material can be immediately coated or saturated with an appropriate treating material or it can be wound on reels and stored for future coating operations.
• the moisture content of the webs may vary during storage depending on ambient storage conditions and the type and amount of fibers used to make the web.
• the dried fibrous material is fed through guide rolls to a coating station provided with, for example, a reverse coating roll and a coating bar to remove all of the excess coating solution from the treated web.
• the web material is then fed through a tunnel oven where it is dried by a stream of hot air which also is designed to support the sheet during its pass through the oven,
• the behavior of the base stock material is observed both prior to its entrance into the coater and subsequent to its emergence from the tunnel dryer.
• the material treated in accordance with the present invention exhibits a dramatic difference over the base material dried on conventional dryer cans or drums in that it exhibits no puckers or cockles and saturates in an extremly uniform manner as constrasted with the multi-puckered, can dried material that yields nonuniform impregnation.
• the material produced in accordance with the present invention is flat and devoid of surface defects while the cockles and puckers in the can dried material are pronounced and deemed objectionable from an appearance point of view.
• EXAMPLES 1-3 Fibrous web materials, having a basis weight of about 11 grams per sq. meter and suited for use as stencil base stock, were made from a 100 percent manila hemp fiber dispersion.
• One sample designated A was dried on conventional can dryers while the samples labelled Examples 1, 2 and 3 were dried in accordance with the present invention. All samples had an average densimeter value of 0.06 sec/100 ml.
• a significant quality increase was realized in accordance with the present invention by the elimination of objectionable surface defects such as cockles and puckers. Test data on these samples are set forth below:
• Example A and Example 3 materials were coated in a stencil coater under identical conditions and tested for stencil characteristics. These tests including cut out resistance and number of copies to failure were essentially equal for both samples but the Example 3 material advantageously exhibited no stretch after 3500 copies while the Sample A material exhibited 2.1 percent stretch after 3000 copies and 2.8 percent stretch after 3500 copies.
• Fibrous web materials having a basis weight of about 25 grams per sq. meter and suited for use as base stock for casing manufacture, were prepared from 100 percent manila hemp fiber dispersion. It was observed that each time the through dryer was used the web exhibited no cockles or puckers even when a previously dried material was treated with a viscose solution to a moisture content above 50 percent and again through dried. However, the elmination of surface defects like cockles and puckers was not realized it can dryers were used in the final drying stage after saturation to a moisture content above 50 percent even though the Web may have been through dried during an earlier operation. The densimeter value for all web material treated was 0.08.
• Fibrous web material was made from a fiber dispersion of wood pulp and about 40 percent abaca fibers. After drying in accordance with the present invention, the webs were free of surface defects. Test data on this material is set forth below.
• Fibrous sheet materials were made from a fiber dispersion of abaca fibers and about percent rayon fibers. The sheet material was dried on through dryers in accordance with the present invention. Typical test data on this material are set forth below:
• a method of producing low densimeter, coating base material substantially free of puckers and cockles and exhibiting improved dimensional stability comprising the steps of (a) providing a wet fibrous web having a moisture level greater than about 50% by weight, said fibrous Web when dry being capable of exhibiting a densimeter value less than 1 sec./ ml. as measured by TAPPI test method T 460 os-68;
• wet fibrous web is formed from an aqueous dispersion of fibers and is placed in contact with said support while having a moisture content of at least about 65 percent by weight.

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• 1972
  • 1972-05-22 US US00255528A patent/US3822182A/en not_active Expired - Lifetime
• 1973
  • 1973-03-27 CA CA167,141*7A patent/CA974104A/en not_active Expired
  • 1973-05-16 FR FR7319247A patent/FR2185722B1/fr not_active Expired
  • 1973-05-17 SE SE7306957A patent/SE389142B/xx unknown
  • 1973-05-21 DE DE2325649A patent/DE2325649C3/de not_active Expired
  • 1973-05-21 JP JP48055753A patent/JPS4941610A/ja active Pending
  • 1973-05-22 GB GB2425773A patent/GB1374965A/en not_active Expired

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