JP2010007224A - High caliper paper and papermaking belt for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a papermaking belt for producing a high caliper web of papermaking fibers and the paper produced thereby. <P>SOLUTION: The papermaking belt comprises a reinforcing structure having a continuous network region and a plurality of discrete deflection conduits disposed thereon. The deflection conduits are sized, shaped, and arranged to maximize fiber deflection along the periphery of the conduits. The conduits are generally elliptical in shape having a mean width sized relative to the mean fiber length. The conduits are arranged to maximize perimeter and corresponding fiber deflection per unit area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates to a papermaking belt for use in a papermaking machine for making a low density, soft and absorbent paper product and to a paper product made with the belt. In particular, the present invention relates to a papermaking belt made of a patterned resin component and a reinforced structure, and a large thickness and low density paper product made by the belt.

Background of the Invention Cellulose fiber webs such as paper are well known in the art. This fibrous web is commonly used today for paper towels, toilet tissue, cosmetic tissue, napkins and the like. Based on the enormous demand for such paper products, there has been a demand for improving paper products and their manufacturing methods.

  Cellulosic fiber webs need to exhibit several properties in order to meet consumer demands. For this purpose, it must have sufficient tensile strength to prevent tearing or cutting of the paper tissue when a relatively small tensile force is applied during normal use. This cellulosic fibrous web must be absorbable so that it can absorb liquid quickly and retain well within the fiber structure.

  Tensile strength is the ability of a cellulose fiber web to retain physical integrity during use. Tensile strength can be viewed as a function of the basis weight of the cellulose fiber web.

  Absorptivity is a property of the cellulose fiber web that sucks and holds the contacted liquid. Absorbency is affected by the density of the cellulose fiber web. When the web is too dense, the gaps between the fibers are too small and the absorption rate is not large enough to meet the intended application. If this gap becomes too large, the capillary attraction of the contacted fluid will be reduced and the surface tension will be limited, preventing the fluid from being retained by the cellulose fiber web.

  The web should also be soft to the touch and not feel rough during use. Softness is the ability to give a particularly desirable feeling to the user's skin as a tactile sensation provided in cellulose fibers. Softness is proportional to the ability of the cellulose fiber web to resist deformation in the direction perpendicular to the plane of the fiber web.

  Thickness is the thickness of a cellulosic fiber web measured under some mechanical pressure and can be viewed as a function of basis weight and web structure. Strength, absorbency and softness are affected by the thickness of the cellulose fiber web.

  The process of producing a paper product generally involves preparing an aqueous slurry having cellulosic fibers and subsequently removing moisture from the slurry simultaneously while rearranging the fibers to form an initial web. Accompanied by. In this dehydration process, various types of devices that assist dehydration are used. A typical manufacturing process uses a long wire machine that feeds paper slurry to the surface side of an endless belt that moves. The endless belt performs initial dewatering and performs fiber rearrangement.

  After forming the initial web, the paper web is subjected to a drying process on another fabric called a dry fabric in the form of an endless belt. This drying process includes mechanical squeezing of the papermaking web, vacuum suction, through-air drying and other types of methods. During this drying process, the initial web assumes a specific pattern or shape that results from the alignment and deflection of cellulose fibers.

  U.S. Pat. No. 4,529,480 issued Jul. 16, 1985, issued to Trokhan, proposes a papermaking belt comprising a perforated woven member surrounded by a cured photosensitive resin composition. . This resin component comprises a plurality of discrete, discontinuous passages known as deflection passages. The papermaking belt used in this process is called a deflecting member because when the pressure difference is generated in the fluid, the papermaking fibers are biased in the passage and rearranged there. The use of papermaking belts in the papermaking process has the potential to produce papers with certain properties that are desirable in terms of strength, absorbency and softness.

  Paper made using the method disclosed in U.S. Pat. No. 4,529,480 is described in U.S. Pat. No. 4,687,859 to Trokhan, incorporated herein by reference. ing. This paper is characterized by having two physically distinct areas distributed on both sides of the page. One region is a region of continuous tissue having a relatively high density and a large intrinsic strength. The other region is a region composed of a plurality of domes completely surrounded by the continuous tissue. The dome in the latter region is relatively low density and has a relatively low inherent strength compared to the continuous tissue region.

  This dome is formed when the fiber fills the deflection path of the papermaking belt during the papermaking process. When the paper web is pressed during the drying process by this deflecting passage, it is possible to prevent the fibers in the passage from becoming dense. As a result, the dome will increase in thickness, have a lower density and inherent strength compared to the densely populated area of the web. Thus, the thickness of the paper web is limited by the inherent strength of the dome.

  As soon as the paper has been dried, the paper fiber rearrangement and deflection is complete. However, depending on the type of finished product, the paper undergoes additional processes such as calendaring, softening, and special processing. These processes tend to close the paper dome area and reduce the thickness. Therefore, in a paper product having two regions which are physically distinguished, it is required to form a cellulose fiber structure having resistance to mechanical pressure inside the dome.

  When a cellulose fiber web is formed, the fibers are primarily oriented in the XY plane of the web, resulting in negligible structural stiffness in the Z direction. As soon as the fibers oriented in the XY plane are compacted by mechanical pressure, these fibers are simultaneously pressed and the paper web decreases in thickness while the density increases.

  The orientation of the fibers in the Z direction can increase the structural rigidity of the web in the Z direction. Therefore, it is possible to maximize the thickness by maximizing the orientation of the fibers in the Z direction.

  The deflection passage provides a means for deflecting the fibers along the periphery of the passage, thereby causing the orientation of the fibers in the Z direction. The deflection of the entire fiber depends on the size and shape of the deflection path which is related to the fiber length.

  Large deflection passages do not prevent fibers smaller than the passage openings from accumulating at the bottom of the passages, and as a result limit the subsequent deflection of fibers that fall into the deflection passages. Conversely, small passages minimize fiber deflection because large fibers bridge the passage openings and plug them.

  The shape of the deflection passage also affects the fiber deflection. For example, a deflection path comprised of sharp corners or a peripheral portion forming a small radius is more likely to cause fiber cross-linking that minimizes fiber deflection. See U.S. Pat. No. 5,679,222 issued Oct. 21, 1997 to Rusk et al. For examples of various channel shapes that affect fiber cross-linking.

  Accordingly, the present invention provides a papermaking belt comprising a continuous tissue region and a plurality of discontinuous deflection passages that are sized and shaped to maximize fiber deflection and fiber orientation consistent with the Z direction.

  Furthermore, the present invention provides a paper web comprising a tissue region that is essentially continuous, essentially and macroscopically a single plane, and a plurality of discontinuous domes distributed throughout the tissue region. The dome is sized and shaped to produce the optimum thickness.

SUMMARY OF THE INVENTION The present invention is directed to a papermaking belt having a patterned composition for making a low density / large thickness paper web and a paper web made by the belt. The papermaking belt includes a reinforced structure having a patterned component. This patterned structure comprises a continuous tissue region and a plurality of discontinuous deflection channels. The deflection passages are separated from each other by successive tissue regions.

This deflection passage is generally oval in shape and is sized to the average web fiber length L such that the average width W of the deflection passage is in the relationship of L < W < 3L . . The deflection path has an aspect ratio ranging from at least about 1.0 to about 2.0, with a ratio of the minimum radius to the average width ranging from at least about 0.29 to about 0.5.

  The deflection channels are arranged in a hexagonal shape to maximize the density of channels per unit area while at the same time minimizing the area of successive tissue regions. The continuous tissue region comprises a knuckle region having a width that ranges from at least about 0.0007 inches to about 0.020 inches.

  The paper produced on this papermaking belt is essentially and macroscopically distributed over a single planar tissue region and continuous tissue regions, and is separated from each other by the tissue regions. Provide a dome. The dome has the same shape and arrangement as the generally oval deflection passage described above.

Detailed Description of the Invention
Definitions As used herein, the following terms have the meanings set forth below.
The flow direction indicated by MD is a direction parallel to the direction in which the papermaking web flows through the papermaking machine.
The width direction indicated by CD is a direction perpendicular to the flow direction in the XY plane.
The region center is a point in the deflection path that coincides with the center of the thin and uniform dispersion aggregate whose boundary is defined by the periphery of the deflection path.
The main axis is the longest axis that crosses the center of the area of the deflection path and connects two points on the periphery of the deflection path.
The auxiliary axis is the shortest axis or width that crosses the center of the area of the deflection path and connects two points on the periphery of the deflection path.
The aspect ratio is the ratio of the main shaft length to the auxiliary shaft length.
The average width of the deflection path is the average length of a straight line that passes through the center of the area of the deflection path and connects two points on the periphery of the deflection path.
The radius of curvature is the instantaneous radius of curvature existing at one point on the curve.
To be surrounded by a curve is to accompany the curve.
To be surrounded by a straight line is to accompany the straight line.
The height in the Z direction refers to the portion of the resin component that extends from the surface of the reinforced structure facing the papermaking side.
The average fiber length is a weighted average fiber length.

  The description includes detailed descriptions of (1) the papermaking belt according to the present invention and (2) the finished paper product according to the present invention.

(1) Papermaking belt In a typical papermaking machine schematically shown in FIG. 1, the papermaking belt of the present invention employs a papermaking belt in the form of an endless belt. The papermaking belt 10 has a surface 11 in contact with paper and a back surface 12 opposite to the paper contact surface 11. The papermaking belt 10 conveys the papermaking web (or “fiber web”) in a variety of steps related to the formation (initial web 27 and intermediate web 29). The process of forming the initial web is described in U.S. Pat. No. 3,301,746 issued to Sanford and Sison, issued January 31, 1974, and Morgan, both of which are hereby incorporated by reference. And in rich literature such as U.S. Pat. No. 3,994,771 issued Nov. 30, 1976 to Rich. The papermaking belt 10 moves around the return rolls 19a and 19b, the pressure nip roll 20, the return rolls 19c, 19d and 19e, and the emulsion distribution roll 21 in the direction indicated by the direction arrow B. The loop in which the papermaking belt 10 moves includes means for applying a fluid pressure difference to the initial web 27, such as a vacuum pickup shoe (PUS) 24 a and a multi-slot vacuum box 24. In FIG. 1, the papermaking belt 10 also moves around a pre-dryer such as a blow-through dryer 26 and further passes between the nip formed by the pressure nip roll 20 and through the Yankee drying drum 28.

  A preferred embodiment of the papermaking belt 10 according to the present invention is in the form of an endless belt 10, which may be, for example, a stationary plate used in the manufacture of handsheets or a rotating drum used in other types of continuous processes. Including many forms other than endless belts. Regardless of the physical form employed by the papermaking belt 10 to carry out the claimed invention, in general, the invention has certain physical characteristics as detailed below. The papermaking belt 10 of the present invention can be manufactured according to US Pat. No. 5,334,289 to Trokhan et al., Incorporated herein by reference.

  As shown in FIG. 2, the papermaking belt 10 according to the present invention comprises two main components: a component 30 and a reinforcing structure 32. This constituent 30 is preferably made of a cured photosensitive polymer resin. The component 30 and the papermaking belt 10 have a first surface 11 that forms the paper contact surface 11 of the papermaking belt 10 and a second surface 12 that faces the direction of the papermaking machine that uses the papermaking belt 10.

  As used herein, the X, Y, and Z directions relevant to the papermaking belt 10 of the present invention (or the paper web 27 placed on the belt) are directions in a Cartesian coordinate system. The papermaking belt 10 according to the present invention is macroscopically a single plane. The plane of the papermaking belt 10 defines its XY direction. The Z direction of the papermaking belt 10 is perpendicular to the XY direction and the plane of the papermaking belt 10. Similarly, the paper web 27 according to the present invention can be considered macroscopically as a single plane and is in the XY plane. The Z direction of the paper web 27 is perpendicular to the XY plane and the plane of the web 27.

  Preferably, the structure 30 includes a knuckle area 36 that defines a predetermined pattern boundary and indents the appropriate pattern on the paper web 27 of the present invention. A particularly preferred pattern for composition 30 is an essentially continuous texture. Given the preferred pattern of essentially continuous texture for the construction 30, the discontinuous deflection passage 34 extends from the first surface 11 to the second surface 12 of the papermaking belt 10. This essentially continuous tissue surrounds and delimits the deflection passageway 34.

  This composition 30 forms an indentation on the papermaking web 27 that has the same pattern as that of the composition 30 conveyed thereon. In any case, the indentation occurs when the papermaking belt 10 and the papermaking web 27 pass between two rigid surfaces that maintain a sufficient gap to imprint it. This generally occurs at the nip between the two rolls and often occurs when the papermaking belt 10 moves the paper to the Yankee drying drum 28. The formation of the indentation occurs by pressing the component 30 against the papermaking web 27 at the position of the pressure roll 20.

  The first surface 11 of the papermaking belt 10 is in contact with the paper web 27 conveyed there. During conveyance of the papermaking, the first surface of the papermaking belt 10 forms a pattern on the papermaking web 27 that is identical to the pattern applied to the component 30.

  The second surface 12 of the papermaking belt 10 is a paper machine contact surface of the papermaking belt 10. This second surface is made of a back tissue having a passage different from the deflection passage 34. This passage imparts irregularity to the back surface structure of the second surface of the papermaking belt 10. This passage takes into account air leakage that does not necessarily flow in the Z direction through the deflection passage 34 of the papermaking belt 10 in the XY plane of the papermaking belt 10. US Pat. No. 5,098,522 issued on Mar. 24, 1992 to Smarkoski et al., 1994 granted to Smarkoski et al. Manufactured in accordance with US Pat. No. 5,364,504 issued Nov. 15, 1997 and US Pat. No. 5,260,171 issued Nov. 9, 1993 to Smarkoski et al. . The disclosures of these patent specifications are incorporated herein by reference.

  The second main component of the papermaking belt 10 according to the present invention is a reinforced structure 32. Similar to the component 30, the reinforced structure 32 has a first surface or paper facing surface 13 and a second surface or paper machine facing surface 12 opposite the paper facing surface. The reinforcing structure 32 is mainly disposed between the back-to-back surfaces of the papermaking belt 10 and has a surface flush with the back surface of the papermaking belt 10. The reinforcing structure 32 provides support for the structure 30. This reinforcing element is typically made by weaving, as is well known in the art. The portion of the reinforced structure 32 that overlaps with the deflection passage 34 prevents the fibers used in papermaking from passing completely through the deflection passage 34, thereby reducing the occurrence of pinholes. If it is not desired to use a woven fabric for the reinforced structure 32, the non-woven element, screen, net or plate having a plurality of holes provides adequate strength and support for the structure 30 of the present invention. You may make it give.

  As shown in FIG. 3, the structure 30 is coupled to a reinforced structure 32. The component 30 extends outward from the paper facing surface 13 of the reinforced structure 32. The reinforced structure 32 gives strength to the structure 30 so that the vacuum dewatering equipment used in the paper manufacturing process can properly remove moisture from the initial web 27 and discharge the removed moisture from the papermaking belt 10. A suitable opening area projecting into

  The papermaking belt 10 according to the present invention is manufactured according to any of the following patent specifications, the disclosure of which is hereby incorporated by reference. No. 4,514,345 issued Apr. 30, 1985 to Johnson et al., U.S. Pat. No. 4,528,239 issued Jul. 9, 1985 to Trokhan. US Pat. No. 5,098,522 issued March 24, 1992, US Pat. No. 5,260,171 issued November 9, 1993, issued to Smarkoski et al. US Pat. No. 5,275,700 issued Jan. 4, 1994 to Trokhan, US Pat. No. 5,328,565 issued Jul. 12, 1994 to Rusk et al. US Pat. No. 5,334,289 issued August 2, 1994 to Trokhan et al., US Pat. No. 5,431,786 issued July 11, 1995 to Rusk et al. Issue U.S. Pat. No. 5,496,624 issued March 5, 1996, issued to Steruges Jr. et al., U.S. Pat. No. 5,500, issued March 19, 1996, issued to Trokhan et al. No. 277, U.S. Pat. No. 5,514,523 issued May 7, 1996 to Trokhan et al., U.S. Pat. No. 5, issued September 10, 1996 to Trokhan et al. No. 554,467, U.S. Pat. No. 5,566,724 issued to Trokhan et al., Issued on Oct. 22, 1996, U.S. Pat. No. 5,624,790, U.S. Pat. No. 5,628,876 issued May 13, 1997, granted to Ayers et al., Oct. 2, 1997, granted to Rusk et al. U.S. Pat. No. 5,679,222 issued on the 1st and U.S. Pat. No. 5,714,041 issued Feb. 3, 1998 to Ayers et al.

  The ability to produce a paper web having a certain density can be viewed as a function of the web thickness. Thickness is the apparent thickness of a cellulose fiber web measured under a certain mechanical pressure. Thickness can be viewed as a function of web basis weight and web structure. The basis weight weighs 0.4536 kg (1.00002 lb) per 278.7 square meters of paper. The web structure is related to the orientation and density of the fibers constituting the papermaking web 27.

  The fibers that make up the paper web 27 are typically oriented in the XY plane, with minimal structural support in the Z direction. Therefore, when the paper web 27 is pressed by the patterned structure 30, the paper web 27 is dense, resulting in a dense, patterned high density region. In contrast, the portion of the paper web 27 that overlaps the deflection passage 34 does not become dense, resulting in a thicker, lower density region.

  A low density region called a dome imparts an apparent thickness to the paper web 27. Since the fibers that make up a typical dome are primarily oriented in the XY plane of the paper web 27, the support in the Z direction by these fibers is negligible. Therefore, the dome is significantly easier to deform and becomes thinner during subsequent papermaking operations. Therefore, the thickness of the paper web 27 is generally limited by the force against the mechanical pressure on the dome.

  However, the deflection channel 34 provides a means for deflecting the fibers along the periphery 38 in the Z direction. Fiber deflection results in fiber orientation, including a Z-direction component. Such fiber orientation not only increases the apparent thickness of the papermaking web, but also increases the structural stiffness in the Z direction by a certain amount that allows the paper web 27 to maintain its thickness throughout the paper manufacturing process. Therefore, in the case of the present invention, the deflection passage 34 is configured in size and shape so as to maximize the deflection of the fibers along the peripheral portion 38.

  The removal of moisture from the initial web 27 begins when the fibers 50 are deflected and enter the deflection passageway 34. This removal of moisture reduces the fluidity of the fiber which helps to fix the fiber in place after the fiber is biased and rearranged. The deviation of the fibers entering the deflection passage 34 is caused by the pressure difference of the fluid acting on the initial web 27. One preferred method of creating a pressure differential is to expose the initial web 27 to a vacuum through the deflection passage 34. FIG. 1 shows that a vacuum pickup shoe 24a is used as a preferred method.

  Without being bound by theory, the rearrangement of the fibers of the initial web 27 associated with the deflection path 34 is generally dependent on many factors, including fiber length, and one of two models is determined. Think to take. As schematically shown in FIG. 4, both ends of the long fiber 50 are constrained to the upper surface of the knuckle 36 in a state where the intermediate region of the fiber 50 is bent without being sufficiently biased into the deflection passage 34. Therefore, a “bridge” of the deflection passage 34 occurs. As an alternative, as shown in FIG. 5, if the fiber 50 (mainly a fiber having a short length) is deflected, a small amount of the fiber 50 is formed in the deflecting passage 34. The fibers that are accumulated and subsequently descend into the deflection passage 34 are kept from deflecting to a minimum.

  Fiber orientation can be viewed as a function of resistance to paper web bending. The bending stiffness of the web depends on two factors; (1) the bending stiffness of the individual fibers and (2) the bond strength between the fibers. However, the web is in a wet state at the location of the vacuum pick-up shoe 24a, and the fibers are not satisfactorily bonded by the large amount of moisture contained in the web. Therefore, the main factor is the bending stiffness of the individual fibers. The greater the bending stiffness of this fiber, the smaller the fiber deflection.

  Even though the deflection of the fiber depends on the inherent bending stiffness of the fiber 50, the magnitude of the deflection depends primarily on whether or not the fiber 50 is long enough to bridge the width of the deflection path 34. Figures 6 and 7 show two possible backgrounds in fiber deflection. In FIG. 6, the fiber 50 is fixed at point A and is in a cantilevered state above the opening of the deflection passage 34. When a uniform load such as a vacuum acts on the fiber 50, a high bending moment is generated at the point A and a deflection determined by the following equation is generated at the point B.

f _B = FL ³ / 8EI (1)
Where f _B : deflection amount at point B
F: Force uniformly distributed over the fiber length
L: Fiber length from the support point
E: Longitudinal elastic modulus
I: Moment of inertia In FIG. 7, the fiber segment 50 is longer than the width of the deflection path, resulting in two fixed points A, B. If the fiber segment 50 is subjected to the same vacuum pressure, the supporting force at the points A and B generates an eccentric bending moment, and a deflection of the fiber determined by the following equation occurs at the point C.

f _C = FL ³ / 384EI (2)
Here, f _C is the amount of deflection of the fiber at point C.

Assuming the parameters F, L, E and I are the same for the fibers shown in FIGS. 6 and 7, it is clear that the fiber deflection f _B is 48 times greater than the fiber deflection f _C. .

f _B = 48 f _C (3)
Thus, fiber deflection can be enhanced by sizing the deflection passage 34 to minimize the occurrence of fiber cross-linking. However, the deflection path also suppresses a group of small fibers in the stock that can accumulate within the deflection path 34 for their size, and thus a large amount of fibers biased inside the deflection path 34. Limited by.

Paper stocks usually include both hardwoods and conifers. An example of a hardwood fiber is a Eucalyptus tree (EUC) material, while an example of a softwood fiber is a Northern Softwood Craft (NSK) material. An example of the stock consists of 30% softwood and 70% hardwood by weight. Since the average fiber length of conifers is about three times the average fiber length of hardwoods, adjusting the size of the deflection path to the average fiber length of the conifer is significantly affected by the accumulation of hardwood fibers with smaller deflection paths. This limits the deflection of longer fibers. Therefore, it is preferable that the width W of the deflection passage is matched with the average fiber length L of the stock.

W ≧ L (4)
In the case of the present invention, the average fiber length is a length obtained by comparative consideration of the average fiber length determined by the following equation.

Where L _i : average fiber length of class i
n _i : Number of fibers measured in class i In the case of the present invention, the length weighted average fiber length is about 0.043 inches.

  As shown in FIGS. 9 and 10, the deflection passage 34 can adopt a variety of different shapes having either a variable or constant width. A passage shape having a variable width defines the conditions of the main shaft 40, the auxiliary shaft 42 and the average width 46. The main axis 40 is defined as the longest axis or maximum width across the deflection path area center, the auxiliary axis 42 is defined as the shortest axis across the deflection path area center, and the average width 46 is defined as the average width across the deflection path area center.

  The average width 46 is determined by first measuring the length of a line that passes through the center of the region in the CD direction and connects two points on the periphery of the deflection path. Measure the length of a similar line oriented with an increment of angle Δθ relative to CD (such as 15 degrees or an angle smaller than the range of 0 ° to 165 ° representing CD) and average width Find the average to determine.

Since fiber bridging is most likely to occur along the auxiliary axis 42, it is preferable to size the minimum width of the deflection passage 34 relative to the average fiber length L as follows.

W _min ≧ L (6)
Thus, for the present invention, the preferred minimum passage width is at least about 0.043 inches.

Small fiber accumulation occurs along both the major and minor axes 40, 42 of the deflection path, thus minimizing fiber accumulation for both axes 40, 42 and maximizing fiber deflection. It is difficult to set an upper limit. However, in the present invention, when the average width 46 of the combined size of the deflection path 34 to be between the average fiber length L and the average fiber length 3 times the value of L, resulting in the largest It has been found that thickness can be obtained.

L < W <3 L
Thus, for the present invention, it is preferred that the deflection path be sized so that the average path width ranges from about 0.043 inches to about 0.129 inches.

The paper web 27 has a substantially two-dimensional fiber structure. An ideal fiber structure consists of disjointed distributions in which the fiber orientation is not biased in a specific direction. For such ideal fibers, the average fiber length L is the same in all directions.

However, the fiber texture is typically arranged as a paper web with fiber orientation biased in a particular direction. In the case of such a biased structure, the average fiber length changes in accordance with the orientation angle in the XY plane of the paper web 27. Such average fiber length L theta can be expressed as follows.

Here, θ: orientation angle in the XY plane with respect to CD
Lθ _i : Length of the component fiber having the orientation angle θ in the XY plane
L θ : Average fiber length when the orientation angle is θ in the XY plane
n: Number of fibers measured at an orientation angle θ in the XY plane In the case of the present invention, the fibers 50 constituting the two-dimensional fiber structure can be mainly oriented in the flow direction MD. Therefore, the average fiber length in the flow direction is larger than the average fiber length in the width direction CD.

The following result can be obtained from the above equation (4).

W _MD > W _CD (9)
Therefore, as shown in FIG. 11, it is preferable to orient the main shaft 40 with respect to the deflection passage 34 so as to move parallel to the flow direction of the papermaking belt. However, since the fiber orientation is typically biased in the flow direction MD, those skilled in the art will be able to incline the main axis 40 with respect to the MD at 22.5 ° ± 22.5 ° as shown in FIG. It can be understood that it may be directed at an angle so as to maintain.

The shape of the deflection path defines the condition of the aspect ratio _RA , which is defined as the ratio between the main shaft 40 and the auxiliary shaft 42. In order to obtain the maximum deflection of the fiber, the aspect ratio is defined as follows from the above equations (8) and (9).

However, it is not practical to measure the average fiber length in a specific direction of the papermaking web in the XY plane in the web state before the fibers are just deflected in the deflection passage 34. Therefore, it is necessary to take into account the inherent physical properties of the paper web as a function of fiber length in order to determine the preferred aspect ratio for the channel shape that results in maximum fiber deflection.

  The physical properties of the paper web 27 are mainly affected by the fiber orientation in the XY plane of the paper web 27. For example, in the paper web 27 having a fiber orientation biased in the flow direction MD, MD is stronger than CD in tensile strength, CD is larger than MD in elongation, and MD is larger than CD in bending stiffness.

  In addition to fiber orientation, the tensile strength of the paper web is proportional to the length of the fiber oriented in a particular direction in the XY plane. Accordingly, the web tensile strength in the flow direction MD and the width direction CD is proportional to the average fiber length of the MD and CD.

_TMD , _CD (tensile strength) Ｌ _LMD , _CD (11)
Therefore, the following result can be obtained from the equation (8).

T _MD > T _CD (12)
Furthermore, the aspect ratio R _A that defines the passage shape by substituting T _MD / T _CD into L _MD / L _CD in the equation (10) can be expressed as follows.

  The tensile strength of the paper web 27 in the flow direction MD and the width direction CD was measured using a Swing-Albert Intellect II standard tensile tester manufactured by Swing-Albert Co., Philadelphia, PA. It was measured. A preferred channel shape that results in maximum fiber deflection and generation of a thickness consistent with the Z direction has an aspect ratio of 1 to about 2. A more preferred passage shape has an aspect ratio in the range of about 1.3 to 1.7. The most preferred channel shape has an aspect ratio in the range of 1.4 to 1.6.

  The shape of the deflection passage 34 is not only important to minimize fiber bridging that occurs across the passage width, but is also important to minimize fiber bridging along the periphery 38 with the passage walls. is there. Special designated points for bridging the fibers are provided with passage walls that form a radiused or sharp corner with no gaps. Examples of channel shapes that are undesirable for such purposes are shown in FIGS. 8a and 8b.

  As shown in FIGS. 9 and 10, one of the preferred channel shapes for the present invention generally includes, but is not limited to, a circle, an ellipse and a polygon consisting of 6 or more faces. It consists of an oval. FIG. 9 shows an oval deflection passage having a straight line perimeter consisting of individual side wall segments 44. For such channel shapes, fiber cross-linking along the periphery can be minimized by providing a depression angle 39 between two adjacent side wall segments of at least about 120 °.

  FIG. 10 shows an oval deflection passage having a peripheral portion made of a curve recessed toward the center of the deflection passage. The perimeter composed of this curve has a minimum radius 48. Similarly, fiber bridging along the perimeter can be minimized by limiting the minimum radius 48 to average passage width ratio to at least 0.29 and no more than 0.50.

  As shown in FIG. 13, ideally, the paper web 27 on the upper surface of the knuckle 36 has zero elongation, whereas the paper web 27 above the deflection passage 34 is sufficiently biased into the passage, Yields an average elongation of ε.

Where ε is the average elongation
OB: Height in the Z direction
W: Passage width The critical elongation amount is determined based on the value when the papermaking web 27 is broken. If the elongation amount is larger than the limit elongation amount of the papermaking web 27, the fiber structure breaks and pinholes are generated in the web. The critical elongation of the papermaking web 27 depends on the properties of the fiber structure such as fiber length and fiber orientation. Since the webs are in a wet state at the location of the vacuum pick-up shoe and the bonding between the surfaces cannot be maintained well, the bonding between the surfaces hardly plays a role in increasing the limit elongation.

  The total distance when the papermaking web 27 is biased toward the deflection passage 34 depends on the height 60 in the Z direction. Since the limit elongation of the papermaking web increases and decreases in direct proportion to the OB60, the conclusion is reached that the OB60 is limited by the limit elongation of the papermaking web 27. Therefore, a reasonable range for OB from equation (15) can be expressed as:

This critical elongation ε _critical is a complex function of handling that involves fiber length, fiber orientation and basis weight. Qualitatively, this critical elongation increases as the fiber length and / or basis weight increases. For the present invention, the preferred Z-direction height for maximum web deflection ranges from at least about 0.127 mm (0.005 inches) to about 0.991 mm (0.039 inches).

  The total amount of deflection that the paper web undergoes in the deflection path is also determined primarily by the angle forming the knuckle / path interface of the patterned component. This paper web deflection angle 62 is defined as the web angle at the knuckle / passage interface point relative to the Z direction. FIG. 14 shows how the paper web is deflected. The fibers 50 that accumulate at the knuckle / passage interface are oriented to have a Z-direction component that allows the fibers to provide a support structure that can withstand external pressing forces. Fibers oriented parallel to the Z direction at the knuckle / passage interface can provide maximum support. However, since the papermaking web 27 does not bend indefinitely, it cannot completely follow the contour of the deflection passage 34. Moreover, due to manufacturing constraints, the side walls of the deflection passage are inclined, resulting in a resin angle 64 at the knuckle / passage interface. Furthermore, since the deflection angle 62 does not become smaller than the resin angle 64, the resin angle 64 limits the deflection of the web. In the present invention, the resin angle 64 is preferably inclined in the range of 5 to 10 degrees. This web deflection angle typically ranges from about 20 degrees to about 50 degrees.

  When external force is applied to the paper through various processes, reaction force is generated according to the supporting force from the fiber at the knuckle / passage interface. The larger the number of fibers in this region, the higher the supporting force and the greater the thickness. can do. The number of fibers 50 in this transition zone can be optimized by maximizing the total perimeter length 38 of the knuckle / passage interface. This is equivalent to maximizing the number of deflection passages 34 per unit area or minimizing the percentage of knuckles 36. Theoretically, the deflection passage 34 can increase in number to an extreme value. However, as shown in FIGS. 11 and 12, the knuckle 36 separated from the deflection passage 34 is required to have a minimum width 52 for securely fixing the resin to the second element 32. For the present invention, the preferred minimum knuckle width 52 ranges from at least about 0.007 inches to about 0.020 inches.

  Furthermore, the number of deflection passages 34 per unit area can be maximized by arranging them efficiently and packing them without waste. A preferable arrangement of the deflection passage 34 is to form a hexagonal shape as shown in FIGS.

(2) Papermaking The paper 80 of the present invention comprises two main areas. The first region includes an indentation formation region 82 in which an indentation is formed on the component 30 of the papermaking belt 10. This indentation zone 82 preferably consists essentially of continuous tissue. A continuous structure 82 constituting the first region of the paper 80 is formed on the essentially continuous structure 30 of the papermaking belt 10 and geometrically at a predetermined location during paper manufacture. It is generally consistent with it and placed very close to it.

  The second region of the paper 80 is comprised of a plurality of domes 84 distributed throughout the tissue region 82. The dome 84 is geometrically coincident with the deflection path 34 of the papermaking belt 10 at a predetermined position during paper manufacture. The fibers in the dome 84 are deflected in the Z direction along the deflection path 34 between the paper facing surface of the component 30 and the paper facing surface of the reinforcing structure 32 during the paper manufacturing process. As a result, the dome 84 protrudes outward from the continuous tissue region 82 of the paper 80. The domes 84 are preferably discontinuous and separated from each other by a continuous tissue region 82.

  Without being bound by theory, the dome 84 and the essentially continuous tissue region 82 of the paper 80 are generally considered to have equivalent basis weights. The density of the dome 80 is biased into the deflection passageway 34 and is reduced compared to the density of the essentially continuous tissue region 82. Further, the essentially continuous fiber region 82 (or other pattern, as selected) may be post-processed, for example, against a Yankee drying drum to form an indentation. Such indentation can further increase the density of the essentially continuous fiber region 82 compared to the density of the dome 84. The paper 80 thus obtained is embossed in a later step, as is well known in the art.

  Paper 80 according to the present invention is disclosed in U.S. Pat. No. 4,529,480 issued Jul. 16, 1985 to Trokhan, the disclosure of which is hereby incorporated by reference. U.S. Pat. No. 4,637,859 issued on May 20th, U.S. Pat. No. 5,364,504 issued on Nov. 15, 1994, granted to Smarkoski et al. US Pat. No. 5,529,664 issued June 25, 1996, and US Pat. No. 5,679,222 issued October 21, 1997 to Rusk et al. Can do.

  The shape of the dome 84 in the XY plane includes, but is not limited to, a circle, an ellipse, and a polygon composed of 6 or more planes. Preferably, the dome 84 is generally oval with a peripheral portion 86 that is enclosed by either a curve or a straight line. The curved perimeter 86 comprises a minimum radius ranging from a ratio of the minimum radius to the average width of the dome ranging from at least about 0.29 to about 0.50. The peripheral portion 86 surrounded by a straight line is configured by determining the number of side wall segments so that the included angle between two adjacent side wall segments is at least about 120 degrees.

  Providing paper 80 with a large thickness requires maximizing the number of fibers in the Z direction per unit area of the web. When the fibers are oriented in the Z direction, most of them are oriented along the periphery 86 of the dome 84 where fiber orientation occurs. Therefore, the fiber orientation in the Z direction and the thickness corresponding to the Z direction in the paper web depend mainly on the number of domes per unit area.

  As shown in FIG. 15, the number of domes 84 per unit area is maximized by keeping the distance between adjacent domes to a minimum, which is achieved by arranging the domes efficiently and arranging them without waste. For the present invention, the preferred minimum distance 88 between the domes 84 is at least about 0.007 inches and no greater than 0.020 inches. This preferred arrangement of the dome 84 is a hexagonal arrangement.

  The number of domes 84 per unit area of the paper 80 depends on the size and shape of the deflection path described above. For the present invention, the preferred average width of the dome 84 is at least about 0.043 inches and less than about 0.129 inches. A preferred oval for the dome is an oval having an aspect ratio in the range of 1.0 to about 2.0. A more preferred oval has an aspect ratio in the range of about 1.3 to 1.7. The most preferred oval has an aspect ratio in the range of 1.4 to 1.6.

The thickness of the paper web, typically a pressure of 6.4516cm ² (1 square inch) per 95g by using a circular presser foot having a diameter of 5.08 cm (2 inches), the 3-second rest time of Measured after placing. This thickness can be measured using a Swing-Albert thickness tester (Model 89-100) manufactured by Swing-Albert Co., Philadelphia, PA. This thickness was measured under the specified temperature and humidity conditions of the American Paper and Pulp Technology Association (TAPPI) test method.

  For the present invention, the thickness was measured on a two-ply paper web. The thickness of the two-ply paper web is preferably between 0.508 mm (20 mils) and 1.016 mm (40 mils). A more preferred two-ply paper web thickness is between 0.965 mm (38 mils) and 1.168 mm (46 mils). The most preferred bilayer papermaking web thickness is between 0.635 mm (25 mils) and 0.762 mm (30 mils).

  While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the invention. The appended claims are intended to cover all such changes and modifications that are within the scope of this invention.

FIG. 1 is a schematic side view showing an embodiment of a paper machine using a paper making belt according to the present invention. FIG. 2 is a plan view showing a part of a papermaking belt according to the present invention, which represents a resin structure having a paper side opening of a deflection passage formed in an oval shape and coupled with a reinforcing structure. FIG. 3 is a longitudinal sectional view showing a part of the papermaking belt taken along line 3-3 in FIG. FIG. 4 is a longitudinal sectional view showing a part of the papermaking belt shown in FIG. FIG. 5 is a longitudinal sectional view showing a part of the papermaking belt shown in FIG. 3, showing fibers gathering at the bottom of the deflection passage. 6 is a longitudinal cross-sectional view showing a portion of the papermaking belt shown in FIG. 3, showing the fiber deflecting in a cantilevered manner above the opening of the deflection passage to show fiber deflection. FIG. 7 is a longitudinal cross-sectional view of a portion of the papermaking belt shown in FIG. 3, showing the fibers cross-linked in the deflection path to show fiber deflection. FIG. 8a is a plan view showing the shape of a passage having a radiusless or acute corner with no gaps that are prone to fiber cross-linking. FIG. 8b is a plan view showing a channel shape with a clear radius or acute corner that is prone to fiber cross-linking. FIG. 9 is a schematic plan view showing an oval passage having a perimeter surrounded by a straight line. FIG. 10 is a schematic plan view showing an oval passage having a perimeter surrounded by a curve. FIG. 11 is a schematic plan view showing deflection passages arranged in a hexagonal shape with a main shaft oriented parallel to the flow direction of the papermaking belt. FIG. 12 is a schematic plan view showing deflection passages arranged in a hexagonal shape with a main shaft oriented obliquely with respect to the flow direction of the papermaking belt. FIG. 13 is a longitudinal sectional view showing a part of the papermaking belt shown in FIG. 3 showing the deflection of the fiber into the deflection passage and showing the relationship between the passage width, the Z-direction height of the passage and the amount of web extension. . FIG. 14 is a longitudinal cross-sectional view of a portion of the papermaking belt shown in FIG. 3 showing the deflection of the fibers into the deflection path and showing the relationship between the web deflection angle and the angle forming the knuckle / passage opening interface. It is. FIG. 15 is a schematic plan view showing a papermaking web having domes arranged in a hexagonal shape. FIG. 16 is a longitudinal sectional view showing a part of the papermaking web along the line 16-16 in FIG.

Claims (1)

A papermaking belt having a paper web contact surface for conveying a web having papermaking fibers having an average fiber length L and a paper machine contact surface opposite to the paper web contact surface, wherein the papermaking belt comprises:
A reinforcing structure having a patterned structure consisting of a continuous tissue region and a plurality of discontinuous deflection passages, wherein the deflection passages are separated from each other by the continuous tissue region, but consists sidewall segments form a generally oval, having a peripheral portion surrounded by a straight line, the average width W in the relation of L <W <3 L, at least 1.0 2. A papermaking belt comprising an aspect ratio over a range up to 0 and an included angle between adjacent side wall segments of at least 120 degrees.

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