PAPERMAKING FELT AND METHOD FOR MANUFACTURING PAPERMAKING FELT

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority from Japanese Patent Application No. 2024-042689, filed on Mar. 18, 2024, the entire contents of which are incorporated herein by reference.

BACKGROUND

Technical Field

The present invention relates to a papermaking felt and a method for producing a papermaking felt.

Background Art

A papermaking machine that removes water from a raw paper material is generally provided with a wire part, a press part and a dryer part. These wire part, press part and dryer part are arranged in this order along the wet paper web transfer direction.

A wet paper web is transferred and moisture thereof is removed while the wet paper web is being successively passed through papermaking devices provided in the wire part, the press part, and the dryer part, and the wet paper web is finally dried in the dryer part. In those parts, the papermaking devices corresponding to a function of dehydrating the wet paper web (wire part), a function of squeezing water (press part), and a function of drying the wet paper web (dryer part) are used.

The press part generally comprises one or more press devices arranged in series along the wet paper web transfer direction. In each press device, either an endless papermaking felt is placed, or ended papermaking felts are connected on the papermaking machine to form an endless papermaking felt which is placed in the press device. And, each press device has a roll press mechanism consisting of a pair of rolls opposing to each other, or a shoe press mechanism having an endless shoe press belt placed between a roll and a concave-shaped shoe opposing to the roll. The felt carrying a wet paper web moves along the wet paper web transfer direction, passing through either the roll press mechanism or the shoe press mechanism, where the water is squeezed out of the wet paper web by pressing the felt carrying the wet paper web such that the papermaking felt continuously absorbs water or the water passes through the felt to be drained to the outside.

However, in the press device, in the part from the center to the outlet of the pressurized part, the pressure applied to the wet paper web and the papermaking felt is released rapidly, so that the volume of the papermaking felt and the wet paper web expands rapidly in this part. As a result, a negative pressure is generated on the papermaking felt and the wet paper web. Furthermore, a capillary phenomenon is also applied because the wet paper web is made of fine fibers, resulting in so-called rewetting phenomenon, in which the water that was absorbed by the papermaking felt is transferred back to the wet paper web.

Here, the water amount (water content) of the wet paper web at the outlet of the press part is directly related to the energy consumption for drying in the dryer part at the later stage. For example, if the water content of the wet paper web increases even a little, the energy required for drying will increase considerably (for example, if the water content of the wet paper web increases by 1%, the energy increase will be about 4%). Therefore, it is preferable to reduce the water content of the wet paper web as much as possible in the press part.

JP 2007-100277 A proposes a papermaking transfer felt for shoe-press, characterized in that it comprises a base layer, a first batt layer formed on the surface of the wet paper web side of the base layer, a second batt layer formed on the surface of the roll side or shoe side of the base layer, and a wet paper web contact fiber layer comprising a hydrophilic fiber and formed on the surface of the wet paper web side of the first batt layer so as to be in direct contact with the wet paper web, wherein the hydrophilic fiber is fibrillated by being pressed by the roll and the shoe.

Moreover, JP 2004-143627 A proposes a press felt for papermaking comprising a base body and batt layers provided with a wet paper web side layer and a press side layer, characterized in that a hydrophilic nonwoven fabric is placed within the wet paper web side layer of the batt layers.

SUMMARY

Technical Problem

As mentioned above, the water amount (water content) of the wet paper web at the outlet of the press part is directly related to the energy consumption for drying in the dryer part at the later stage. Therefore, it is preferable that the water amount of the wet paper web at the outlet of the press part can be further reduced by further preventing the rewetting phenomenon.

Accordingly, an object of the present disclosure is to provide a papermaking felt which can suppress the rewetting phenomenon in the wet paper web and sufficiently reduce the moisture content of wet paper web after being pressed, and a method for manufacturing the same.

Solution to Problem

The present inventors have made a diligent investigation in order to achieve the above-described object and have focused on a configuration in which a batt layer and a nonwoven fabric are arranged on a base fabric. Then, the present inventors have found that there is a correlation between the rewetting phenomenon and the needle penetration resistance during needle punch treatment of the nonwoven fabric, and as a result of further diligent investigation, reached the present invention.

A gist of the present invention is as follows:

• • (1) A papermaking felt comprising a wet paper web carrying surface for carrying the wet paper web, comprising:
    • a substrate;
    • a batt layer which is placed on the wet paper web carrying surface side of the substrate and which comprises a short fiber; and
    • a nonwoven fabric which is placed adjacent to the batt layer on the wet paper web carrying surface side of the substrate;
    • wherein the nonwoven fabric has a penetration resistance of 2.0 N/(100 g/m²×number of needles) or less per one needle when the basis weight of the fabric is 100 g/m².
  • (2) The papermaking felt according to (1), wherein the nonwoven fabric comprises a continuous yarn.
  • (3) The papermaking felt according to (1), wherein the nonwoven fabric comprises a hydrophilic fiber having an official moisture regain equal to or more than 10.0%.
  • (4) The papermaking felt according to (3), wherein the hydrophilic fiber comprises one or more types selected from the group consisting of cupra, rayon, lyocell, silk, hemp and wool.
  • (5) A papermaking felt according to (1), wherein the fiber constituting the aforementioned nonwoven fabric has a fiber diameter equal to or more than 5.0 μm and equal to or less than 30 μm.
  • (6) The papermaking felt according to (1), wherein the nonwoven fabric is a spun-bond nonwoven fabric.
  • (7) The papermaking felt according to (1), wherein the batt layer is in contact with the nonwoven fabric and is placed on the substrate side of the nonwoven fabric.
  • (8) The papermaking felt according to (1), further comprising a second batt layer which is placed on the wet paper web carrying surface side of the substrate and which comprises a second short fiber;
    • wherein the batt layer and the second batt layer are arranged across the nonwoven fabrics.
  • (9) The papermaking felt according to (1), wherein the difference between the official moisture regain of the fiber constituting the nonwoven fabric and the official moisture regain of the short fiber is equal to or more than 2.0% and equal to or less than 12%.
  • (10) The papermaking felt according to (8), wherein the difference between the official moisture regain of the fiber constituting the nonwoven fabric and the official moisture regain of the second short fiber is equal to or more than 2.0% and equal to or less than 12%.
  • (11) The papermaking felt according to (1), wherein the fineness of the short fiber is equal to or more than 2.0 dtex and equal to or less than 70 dtex.
  • (12) The papermaking felt according to (8), wherein the fineness of the second short fiber is equal to or more than 2.0 dtex and equal to or less than 70 dtex.
  • (13) A method for manufacturing a papermaking felt, comprising a step of laminating a nonwoven fabric and a short fiber on one side of the substrate and performing a needle punch treatment to form the nonwoven fabric and a batt layer consisting of the short fiber on the one side of the substrate,
    • wherein the nonwoven fabric has a penetration resistance of 2.0 N/(100 g/m²×number of needles) or less per one needle when the basis weight of the fabric is 100 g/m².

Advantageous Effects of Invention

With above configuration, it is possible to provide a papermaking felt which can suppress the rewetting phenomenon in a wet paper web and sufficiently reduce the moisture content of the wet paper web after being pressed, and a method for manufacturing the same.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a cross machine direction showing a papermaking felt according to one embodiment of the present invention.

FIG. 2 is a schematic diagram to illustrate a method for measuring the needle penetration resistance of a nonwoven fabric.

FIG. 3 is a schematic diagram to illustrate the behavior of the papermaking felt and the wet paper web before and after pressing in one embodiment of the present invention.

FIG. 4 is a cross-sectional view in a machine direction showing a papermaking felt according to one modified example of the present invention.

FIG. 5 is a schematic diagram to illustrate a method for testing water-squeezing property.

DESCRIPTION OF EMBODIMENTS

Hereinbelow, referring to the drawings, preferred embodiments of a papermaking felt and a method for manufacturing a papermaking felt according to the present invention will be described in detail.

1. Papermaking Felt

First, a papermaking felt according to a preferred embodiment of the present invention will be described.

FIG. 1 is a cross-sectional view in a cross machine direction showing an example of a papermaking felt according to a preferred embodiment of the present invention. Note that, in the drawings, each member has been emphasized in size as appropriate for ease of illustration and thus does not indicate the actual proportion and size of each member. Herein, the aforementioned cross machine direction may be referred to as “CMD”, and the machine direction may be referred to as “MD”.

The papermaking felt 1 shown in FIG. 1 is used for carrying and transferring a wet paper web and squeezing water from wet paper web in the press part of a papermaking machine. The papermaking felt 1 forms an endless band-shaped body. That is, the papermaking felt 1 is an annular belt. In addition, the papermaking felt 1 is normally placed such that its circumferential direction runs along a machine direction (MD) of the papermaking machine. Moreover, in the papermaking felt 1, the side of one surface is usually a wet paper web carrying surface 41 side which will be in contact with the wet paper web, and the side of the other surface is a roll contact surface 51 side which will support the papermaking felt 1.

The papermaking felt 1 comprises a substrate 10; a first batt layer 20 and a nonwoven fabric 30 and a second batt layer 40 which are placed on the wet paper web carrying surface 41 side the substrate 10; and a third batt layer 50 placed on the roll contact surface side. In addition, the first batt layer 20 and the nonwoven fabric 30 and the second batt layer 40 are arranged in this order from the substrate 10 toward the wet paper web carrying surface 41. Moreover, these layers of the papermaking felt 1 are all joined to each other by needle punch treatment.

The substrate 10 is a reinforcing fibrous substrate that ensures physical strength (such as tensile strength) of the papermaking felt 1.

The substrate 10 is not particularly limited, and, for example, a woven fabric consisting of warp yarns and weft yarns woven by a weaving machine, etc., may generally be used. An unwoven grid-like web material in which warp rows and weft rows are superimposed on each other can also used. Alternatively, the woven fabric, grid-like material, etc. may be used in combination of two or more.

As materials of the substrate 10, polyester (polyethylene terephthalate, polybutylene terephthalate, etc.), aliphatic polyamide (polyamide 6, polyamide 11, polyamide 12, polyamide 612, etc.), aromatic polyamide (aramid), polyvinylidene fluoride, polypropylene, polyether ether ketone, polytetrafluoroethylene, polyethylene, sheep wool, cotton, metal, etc., may be used either alone or in combination of two or more.

The fineness of the fiber constituting the substrate 10 is not particularly limited, and can be, for example, equal to or more than 300 and equal to or less than 10,000 dtex, preferably, equal to or more than 500 and equal to or less than 6,000 dtex.

Moreover, the fineness of the fiber that constitutes the substrate 10 may vary depending on the part in which the fiber is used. For instance, the warp yarns and weft yarns of the substrate 10 may have different fineness.

The thickness of the above-mentioned substrate 10 is not particularly limited, and can be, for example, equal to or more than 0.2 mm and equal to or less than 3.5 mm, preferably equal to or more than 0.5 mm and equal to or less than 3.0 mm. The weight of 1 m² of the substrate 10 is not particularly limited, and can be, for example, equal to or more than 150 g/m² and equal to or less than 1,200 g/m², and preferably equal to or more than 300 g/m² and equal to or less than 1,000 g/m².

The first batt layer 20 is a short fiber layer provided adjacent to the substrate 10 on the wet paper web carrying surface 41 side of the substrate 10. On the wet paper web carrying surface 41 side of the first batt layer 20, a nonwoven fabric 30 is disposed adjacently.

The material of the short fiber which constitutes the first batt layer 20 is not particularly limited, and a polyester (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), an aliphatic polyamide (polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 612, etc.), an aromatic polyamide (aramid), polyvinylidene fluoride, polypropylene, polyether ether ketone, polytetrafluoroethylene, polyethylene, sheep wool, cotton, metals, etc., can be used either alone or in combination of two or more types. Among those mentioned above, polyamide is preferred as the material for the short fiber from the viewpoints of abrasion resistance, compression recoverability, impact resistance, hydrophilicity, hydrolysis resistance, chemical resistance, etc.

The fineness of the short fiber constituting the first batt layer 20 is not particularly limited, but is, for example, equal to or more than 0.1 dtex and equal to or less than 200 dtex.

Moreover, the fineness of the first short fiber constituting the first batt layer 20 is not particularly limited, though it is, for example, equal to or more than 0.1 dtex and equal to or lower than 200 dtex, preferably equal to or more than 2.0 dtex and equal to or lower than 70 dtex, more preferably equal to or more than 6.0 dtex and equal to or lower than 70 dtex. By this configuration, the first batt layer 20 can have a sufficient strength while sufficiently absorbing moisture from the wet paper web through the capillary phenomenon caused by fine short fibers.

The weight of 1 m² of the first batt layer 20 is not particularly limited, and can be, for example, equal to or more than 50 g/m² and equal to or less than 800 g/m², preferably equal to or more than 50 g/m² and equal to or less than 700 g/m², and more preferably equal to or more than 50 g/m² and equal to or less than 600 g/m². By this configuration, a moderate space for absorbing water under pressure can be maintained.

The nonwoven fabric 30 is a layer provided adjacent the first batt layer 20 on the wet paper carrying surface 41 side of the first batt layer 20. On the wet paper web carrying surface 41 side of the nonwoven fabric 30, a second batt layer 40 is disposed adjacently.

The nonwoven fabric 30 functions as a barrier layer to suppress the migration of moisture from the first batt layer 20 side to the wet paper carrying surface side when a negative pressure is generated on the papermaking felt 1 and the wet paper web immediately after pressing, and thereby suppresses the rewetting phenomenon in the wet paper web after pressing.

Here, the present inventors focused on this function of the nonwoven fabric 30 as the barrier layer to suppress the rewetting phenomenon and investigated the conditions for improving the function. As a result, the present inventors have found that there is a significant correlation between the needle penetration resistance of the unwoven fabric 30 and the rewetting phenomenon, and reached the present invention. Specifically, the present inventors have found that the rewetting phenomenon can suitably be suppressed and the moisture content of wet paper web after pressing can sufficiently be reduced when the unwoven fabric 30 have a penetration resistance of 2.0 N/(100 g/m²×number of needles) or less per one needle when the basis weight of the fabric is 100 g/m².

Although the principle of such correlation between the penetration resistance against the needle and the suppressive effect on the rewetting phenomenon is not clear, the present inventors considers as follows. That is, when manufacturing papermaking felt 1, it is necessary to perform a needle punch treatment to join the layers one another. In this case, a large penetration resistance of the nonwoven fabric 30 against the needle means that many fibers in the nonwoven fabric 30 collide with the needle and become entangled with fibers in adjacent layers, e.g., the first batt layer 20 and the second batt layer 40.

When many fibers in the nonwoven fabric 30 become entangled with fibers of adjacent layers, the fibers in the nonwoven fabric 30 are dispersed in the thickness direction, thereby reducing the substantial density of the nonwoven fabric 30 after the needle punch treatment. It is therefore considered that if the substantial density of the nonwoven fabric 30 is reduced, its function as the barrier layer as described above will be reduced. Accordingly, it is considered that the substantial decrease in the density of the nonwoven fabric 30 will be suppressed by using the nonwoven fabric 30 having a relatively small penetration resistance against the needle, and as a result, the nonwoven fabric 30 will sufficiently function as the barrier layer.

The penetration resistance of the nonwoven fabric 30 for the basis weight of 100 g/m² per one needle may be within the range mentioned above, and it is preferably equal to or less than 1.8 N/(100 g/m²×number of needles), further preferably equal to or less than 1.5 N/(100 g/m²×number of needles), and particularly preferably equal to or less than 1.2 N/(100 g/m²×number of needles). Thus, the nonwoven fabric 30 can fully exert its function, and can further suppress the rewetting phenomenon in the wet paper web after pressing.

The lower limit of the penetration resistance of the nonwoven fabric 30 for the basis weight of 100 g/m² per one needle is not particularly limited, though the penetration resistance is, for example, equal to or more than 0.10 N/(100 g/m²×number of needles), preferably equal to or more than 0.30 N/(100 g/m²×number of needles), and further preferably equal to or more than 0.50 N/(100 g/m²×number of needles). This configuration enables the contact between the first batt layer 20 and the nonwoven fabric 30 created by needle punching during manufacturing to be maintained, makes the layering of the second batt layer 40 easy, can sufficiently increase the density of the nonwoven fabric 30 itself before the needle punch treatment, and can further suppress the rewetting phenomenon in the wet paper web after pressing.

In addition, the penetration resistance of the above-described nonwoven fabric 30 for the basis weight of 100 g/m² per one needle can be measured as described below. FIG. 2 is a schematic diagram to illustrate a method for measuring the needle penetration resistance of a nonwoven fabric.

The penetration resistance of a nonwoven fabric against a needle can be measured using a tensile testing machine. First, the jigs 101A and 101B of the tensile testing machine shown in FIG. 2 are arranged in a vertical direction facing each other. To the upper jig 101A, a holder 105 having a plurality of needles 103 is attached. The number of needles 103 is not particularly limited, though it can be, for example, equal to or more than 10 and equal to or less than 100 needles. In addition, although the needle implanting density is not particularly limited, though it can be, for example, equal to or more than 0.030 needles/cm² and equal to or less than 0.20 needles/cm².

The lower jig 101B is a pedestal with a space in the center, on which a nonwoven fabric 30 sandwiched between two fixing plates 109 is arranged. Here, a plurality of nonwoven fabrics 30 are arranged in layers as necessary such that their total basis weight becomes approximately 100 g/m². Note that the total basis weight of the layered nonwoven fabrics 30 need not strictly be 100 g/m², and may be adjusted appropriately for example, between 70 g/m² and 150 g/m².

In addition, the fixing plate 109 is provided with a through hole 1091 corresponding to the position of the needle 103, and the fixing plate 109 is arranged in a relative position such that the through hole 1091 and the needle 103 do not interfere with each other during measurement.

In this way, while the nonwoven fabric 30 being fixed, the needle 103 is moved to the nonwoven fabric 30 side using the tensile testing machine to penetrate the first barb of the needle 103 into the nonwoven fabric 30. The maximum value of the resistance force loaded on the needle 103 at this time can be set as the penetration resistance. Moreover, the moving speed of the needle 103 can be, for example, equal to or more than 50 mm/min and equal to or less than 400 mm/min.

The penetration resistance obtained as above is converted so as to be per 100 g/m² of the basis weight of the nonwoven fabric 30 and per one needle 103 to obtain the penetration resistance per 100 g/m² of the basis weight of the unwoven fabric 30 per one needle as described above. Specifically, it is expressed as in the following Equation (1).

R = R T ÷ W NWF × 100 ÷ N NDL ( Equation ⁢ 1 )

In the equation, R is the penetration resistance of the nonwoven fabric 30 for the basis weight of 100 g/m² per one needle [N/(100 g/m²×number of needles)], R_T is the maximum resistance force [N] of the nonwoven fabric 30 at the time of penetration of the needle 103, W_NWF is the total basis weight (g/m²) of the nonwoven fabric 30, and N_NDL is the number of the needles 103.

The penetration resistance of the nonwoven fabric 30 as mentioned above can be changed as appropriate by changing the material and fineness of the fibers constituting the nonwoven fabric, the density of the nonwoven fabric, the form of the nonwoven fabric, the manufacturing method, etc.

The material of the fiber constituting the nonwoven fabric 30 is not particularly limited, and in addition to the materials listed as the material of the short fiber of the first batt layer 20, includes hydrophilic fibers such as cellulose-based fibers such as rayon, polynosic, lyocell, cupra, cellulose nanofibers, cotton and linen, and silk and wool, which can be used alone or in combination of two or more.

Among those mentioned above, the fiber constituting the nonwoven fabric 30 preferably includes a hydrophilic fiber. When the nonwoven fabric 30 comprises a hydrophilic fiber, the nonwoven fabric 30 can easily retain moisture, and as a result can more suitably suppress the rewetting phenomenon after pressing.

The hydrophilic fiber can be a fiber that has an official moisture regain of, for example, equal to or more than 4.0%, preferably equal to or more than 5.0%. For example, an official moisture regain is 4.5% for nylon, 11.0% for rayon, 11.0% for polynodic, 13.0% for lyocell, 11.0% for cupra, 8.5% for cotton, 12.0% for hemp, 12.0% for silk, and 13.0% for wool.

The official moisture regain of the hydrophilic fiber is more preferably equal to or more than 8.0%, and particularly preferably equal to or more than 10.0%. By this configuration, the nonwoven fabric 30 can more easily retain moisture, and as a result can further suppress the rewetting phenomenon after pressing.

Moreover, the difference between the official moisture regain of the fiber constituting the nonwoven fabric 30 and that of the short fiber constituting the first batt layer 20 is not particularly limited, though it is, for example, equal to or more than 2.0% and equal to or less than 12%, and preferably equal to or more than 4.0% and equal to or less than 10%. Thus, because there is a moderate difference in official moisture regain between the fiber constituting the nonwoven fabric 30 and the short fiber constituting the first batt layer 20, the moisture transferred to the first batt layer 20 side via the nonwoven fabric 30 during pressing is suitably discharged to the substrate 10 and out of the papermaking felt 1.

Moreover, the difference between the official moisture regain of the fiber constituting the nonwoven fabric 30 and that of the short fiber constituting the second batt layer 40 is not particularly limited, though it is, for example, equal to or more than 2.0% and equal to or less than 12%, and preferably equal to or more than 4.0% and equal to or less than 10%. Thus, because there is a moderate difference in official moisture regain between the fiber constituting the nonwoven fabric 30 and the short fiber constituting the second batt layer 40, the nonwoven fabric 30 can easily retain moisture when a negative pressure is generated on the papermaking felt 1 and the wet paper web immediately after pressing, thereby more certainly suppress the rewetting phenomenon.

Among those mentioned above, the fiber constituting the nonwoven fabric 30 preferably comprises one or more fibers selected from nylon, cupra, rayon, lyocell, silk, hemp and wool, and more preferably one or more fibers selected from cupra, rayon, lyocell, silk, hemp and wool. Nylon has a moderate hydrophilicity as well as an excellent strength. Other preferred fibers also have a moderate strength and furthermore have an excellent hydrophilicity.

Moreover, the fiber constituting the nonwoven fabric 30 can be a short fiber yarn (200 mm or less), a long fiber yarn (more than 200 mm and 15,000 mm or less), or a continuous yarn. Among those mentioned above, the fiber constituting the nonwoven fabric 30 preferably comprises a long fiber yarn and/or a continuous yarn, and more preferably a continuous yarn. When the fiber constituting the nonwoven fabric 30 is relatively long and its penetration resistance is small, there would be less movement of the fibers from the nonwoven fabric 30, and the density of the nonwoven fabric 30 can be maintained high. Moreover, the “continuous yarn” as used herein refers to a yarn which is continuously manufactured in the manufacturing process and ideally does not have an end portion, and is a so-called filament whose end portion is formed for a reason relating processes such as, for example, cutting of the nonwoven fabric 30.

In addition, the fiber diameter of the fiber constituting the nonwoven fabric 30, especially the fiber diameter of the continuous yarn, is not particularly limited, though it is, for example, equal to or more than 5.0 μm and equal to or less than 30 μm, preferably equal to or more than 10 μm and equal to or less than 25 μm. When the fiber constituting the nonwoven fabric 30 has a fineness that is equal to or higher than the above-described lower limit value, the nonwoven fabric 30 can have a sufficient strength while ensuring a moderate water permeability during pressing. When the fiber constituting the nonwoven fabric 30 has a fineness that is equal to or less than the above-described upper limit value, the nonwoven fabric 30 can have a sufficient water retention capacity through the capillary phenomenon, thus the moisture can smoothly migrate from the second batt layer 40 to the nonwoven fabric 30 during pressing and at the same time the migration of moisture from the nonwoven fabric 30 to the second batt layer 40 immediately after pressing can be suppressed.

In addition, the nonwoven fabric 30 can be manufactured by, for example, a dry method, a wet method, a spun-bond method, a melt-blowing method, or the like. Among those mentioned above, it is preferable that the nonwoven fabric 30 is a spun-bond nonwoven fabric manufactured by the spun-bond method. In the spun-bond method, it is possible to manufacture the nonwoven fabric 30 with continuous yarns.

Moreover, the nonwoven fabric 30 may be processed by a processing method such as a thermal bonding method, a chemical bonding method, a needle punching method, or a hydroentanglement method (spunlace). By being processed in these ways, the penetration resistance of the nonwoven fabric 30 can be adjusted.

The weight of 1 m² (basis weight) of the nonwoven fabric 30 is not particularly limited, and can be, for example, equal to or more than 10 g/m² and equal to or less than 100 g/m², preferably equal to or more than 15 g/m² and equal to or less than 60 g/m², and more preferably equal to or more than 20 g/m² and equal to or less than 50 g/m². By this configuration, the nonwoven fabric 30 can ensure an appropriate air permeability while sufficiently functioning as a barrier layer to suppress the rewetting phenomenon. It is also noted that, in order to adjust the basis weight of the nonwoven fabric 30, a plurality of nonwoven fabrics may be prepared so as to be a target basis weight, for example, which are layered to make a single-layer nonwoven fabric 30.

The second batt layer 40 is a layer constituted with short fibers, provided adjacent to the nonwoven fabric 30 on the wet paper web carrying surface 41 side of the nonwoven fabric 30. The second batt layer 40 is arranged with the first batt layer 20 across the nonwoven fabric 30. In addition, the second batt layer 40 is located on the outermost layer of the papermaking felt 1, forming the wet paper web carrying surface 41 for carrying the wet paper web.

The material for the short fiber constituting the second batt layer 40 (the second short fiber) is not particularly limited, and includes the materials that constitute the first batt layer 20, which can be used alone or in combination of two or more types. Polyamide is preferred as the material for the short fiber from the viewpoints of abrasion resistance, compression recoverability, impact resistance, hydrophilicity, hydrolysis resistance, chemical resistance, etc.

The fineness of the second short fiber constituting the second batt layer 40 is not particularly limited, and it is, for example, equal to or more than 0.1 dtex and equal to or less than 200 dtex, preferably equal to or more than 2.0 dtex and equal to or less than 70 dtex, and more preferably equal to or more than 2.0 dtex and equal to or less than 30 dtex.

By this configuration, the second batt layer 40 can have a sufficient strength while providing the wet paper web carrying surface 41 with a sufficient smoothness and at the same time sufficiently absorbing the moisture from the wet paper web through the capillary phenomenon caused by the fine second short fibers.

The weight of 1 m² of the second batt layer 40 is not particularly limited, and can be, for example, equal to or more than 50 g/m² and equal to or less than 800 g/m², preferably equal to or more than 50 g/m² and equal to or less than 700 g/m², and more preferably equal to or more than 50 g/m² and equal to or less than 600 g/m². By this configuration, a moderate space for absorbing water under pressure can be maintained.

The total basis weight of the first batt layer 20 and the second batt layer 40 can be equal to or more than 100 g/m² and equal to or less than 1,600 g/m², preferably equal to or more than 100 g/m² and equal to or less than 1,400 g/m², and more preferably 100 g/m² and equal to or less than 1,200 g/m². The total basis weight of the first batt layer 20 and the second batt layer 40 is appropriately set according to the intended characteristics such as the strength, porosity and air permeability of the papermaking felt 1.

A third batt layer 50 is a layer constituted with short fibers, provided adjacent to the substrate 10 on the roll contact surface 51 side of the substrate 10. Moreover, the third batt layer 50 is located on the outermost layer of the papermaking felt 1, forming the roll contract surface 51 that comes in contact with the roll. Note that, without being limited to the illustrated embodiments, the papermaking felt 1 can also be constructed without a third batt layer 50.

The material for the short fiber constituting the third batt layer 50 (the third short fiber) is not particularly limited, and includes the materials that constitute the first batt layer 20, which can be used alone or in combination of two or more types. Polyamide is preferred as the material for the short fiber from the viewpoints of abrasion resistance, compression recoverability, impact resistance, hydrophilicity, hydrolysis resistance, chemical resistance, etc.

The fineness of the third short fiber constituting the third batt layer 50 is not particularly limited, and it is, for example, equal to or more than 3.0 dtex and equal to or less than 150 dtex, preferably equal to or more than 6.0 dtex and equal to or less than 100 dtex, and more preferably equal to or more than 10 dtex and equal to or less than 70 dtex. By this configuration, the third batt layer 50 can have a sufficient strength and abrasion resistance.

The weight of 1 m² of the third batt layer 50 is not particularly limited, and can be, for example, equal to or more than 50 g/m² and equal to or less than 200 g/m². By this configuration, a moderate space for absorbing water under pressure can be maintained.

The weight of 1 m² of the papermaking felt 1 is not particularly limited, and is, for example, in entirety, equal to or more than 250 g/m² and equal to or less than 3,000 g/m², and preferably equal to or more than 400 g/m² and equal to or less than 2,000 g/m². Moreover, the thickness of the papermaking felt 1 is not particularly limited, and is, for example, equal to or more than 1.0 mm and equal to or less than 6.0 mm, and preferably equal to or more than 2.0 mm and equal to or less than 4.0 mm.

Hereinabove, the configuration of the papermaking felt 1 has been described. As above, the papermaking felt 1 of the present embodiment can suppress the rewetting phenomenon in the wet paper web and sufficiently reduce the water content of wet paper web after being pressed. Specifically, with reference to FIG. 3, it can be explained as follows. FIG. 3 is a schematic diagram to illustrate the behavior of the papermaking felt and the wet paper web before and after pressing according to the present embodiment. Note that, although a single-felt press roll mechanism has been exemplified as a press device in the figure, a similar explanation can be made for a single-felt or double-felt shoe press mechanism, or for a double-felt press roll mechanism.

As shown in FIG. 3, in the press part, the papermaking felt 1 carries the wet paper web W on its wet paper web carrying surface 41 and runs along the machine direction MD and passes through the press mechanism comprising press rolls 200A and 200B. At this time, in a region 201, the wet paper web W and the papermaking felt 1 are yet to enter the press mechanism and are not under pressure in the thickness direction.

Next, in the press region 203, which is the region where the wet paper web W and the papermaking felt 1 entered the press mechanism, the wet paper web W and the papermaking felt 1 are subjected to the pressure in the thickness direction by the press rolls 200A and 200B and are compressed in the direction of the black arrow in the figure. Here, a part of the moisture contained in the wet paper web W is transferred from the wet paper web carrying surface 41 to the papermaking felt 1 due to the compression of the wet paper web W in its thickness direction, and most of it is discharged from the papermaking felt 1, by the press roll 200B when 200B is a suction roll, or as a splash SP from the roll contact surface 51 side on the region 205 side when 200B is a plain roll. Alternatively, it is discharged from the roll contact surface 51 side on the region 201 side. On the other hand, the portion of the moisture that has been transferred to the papermaking felt 1 but not discharged remains in the papermaking felt 1.

Next, in the press region 205, which is the region where the wet paper web W and the papermaking felt 1 have come out of the press mechanism, the wet paper web W and the papermaking felt 1 are released from the pressure by the press rolls 200A and 200B and thereby expand rapidly. As a result, a negative pressure is generated in the wet paper web W and the papermaking felt 1, and they begin to absorb ambient air and moisture.

Here, focusing on the relationship between the wet paper web W and the papermaking felt 1, when a negative pressure is generated in the wet paper web W, the wet paper web W begins to absorb air and moisture from the papermaking felt 1 (rewetting phenomenon). However, in the papermaking felt 1 according to the present embodiment, the nonwoven fabric 30 is placed between the first batt layer 20 and the second batt layer 40. The nonwoven fabric 30 has a sufficiently low penetration resistance against needles so that the fibers are not dispersed in the thickness direction and the density of the nonwoven fabric 30 itself is high. As a result, the transfer of moisture M on the roll contact surface 51 side from the nonwoven fabric 30 of the papermaking felt 1 to the wet paper web carrying surface 41 side is suppressed by the nonwoven fabric 30, and only a portion of the moisture, m, is transferred to the second batt layer 40. In this way, the migration of the moisture M is suppressed by the nonwoven fabric 30 and the rewetting phenomenon in wet paper web W is suppressed.

In particular, because the nonwoven fabric 30 comprises a hydrophilic fiber, it has a greater capability to hold the moisture M, and further suppress the migration of the moisture M to the second batt layer 40 side.

Moreover, in the present embodiment, the second batt layer 40 is arranged on the wet paper web carrying surface 41 side of the nonwoven fabric 30. This can render the second batt layer 40 functions such as providing the wet paper web carrying surface 41 with smoothness and adhesion to the wet paper web W, while allowing the nonwoven fabric 30 to have a configuration that is specialized in suppressing the migration of the moisture M. As a result, each function of the papermaking felt 1 is fully exerted, and the effect of suppressing the rewetting phenomenon in the papermaking felt 1 is further enhanced.

Also, in the present embodiment, the nonwoven fabric 30 is arranged between the first batt layer 20 and the second batt layer 40 on the wet paper web carrying surface 41 side of the substrate 10, that is, between the batt layers on the wet paper web carrying surface 41 side of the substrate 10. By this configuration, the volume of a portion of the papermaking felt 1 that is on the roll contact surface 51 side of the nonwoven fabric 30 can be relatively large, and the nonwoven fabric 30 can function as a barrier layer against more moisture present in that portion. As a result, the effect of suppressing the rewetting phenomenon in the papermaking felt 1 is further enhanced.

As above, the papermaking felt 1 can suppress the rewetting phenomenon in the wet paper web and sufficiently reduce the water content of wet paper web after being pressed.

3. Modified Examples

Next, some modified examples of the papermaking felt according to the aforementioned embodiments are to be explained. Hereinbelow, differences from the aforementioned embodiments are mainly explained, and the description about similar matters is omitted. Characteristics of the modified examples described below and embodiments mentioned above may each be applied alone, though two or more may be applied in combination as long as it is technically acceptable.

3.1. The First Modified Example

FIG. 4 is a cross-sectional view in a machine direction showing a papermaking felt according to one modified example of the present invention. The papermaking felt 1A shown in FIG. 4 has a substrate 10, a first batt layer 20A, a nonwoven fabric 30A, and a third batt layer 50, and the second batt layer 40 is omitted. Furthermore, the nonwoven fabric 30A is arranged between the first batt layer 20A and the substrate 10. Such papermaking felt 1A can also suitably suppress the rewetting phenomenon.

3.2 Second Modified Example

In the embodiments described above, the papermaking felt 1 has been described as having an endless form, though the present invention is not limited thereto. The papermaking felt according to the present invention may be an ended band-shaped felt. In this case, at the both machine direction ends of the papermaking felt, seam loops are provided. Then, the seam loops at both ends are engaged with each other, and a pintle wire is inserted into the seam loops to form an annular (endless) papermaking felt, which is then installed inn the papermaking machine.

4. Method for Manufacturing Papermaking Felt

At last, methods for manufacturing a papermaking felt according to preferred embodiments of the present invention will be described. The method for manufacturing a papermaking felt according to the present invention comprises a step of laminating a nonwoven fabric and a short fiber on one side of the substrate and performing a needle punch treatment to form the nonwoven fabric and a batt layer consisting of the short fiber on the one side of the substrate, wherein the penetration resistance of the nonwoven fabric for the basis weight of 100 g/m² per one needle is 2.0 N/(100 g/m²×number of needles) or less. Hereinbelow, the method of manufacturing the papermaking felt 1 described in FIG. 1 is explained as one example.

First, the substrate 10 is prepared. Next, a card of short fiber that will become the first batt layer 20, the nonwoven fabric 30, a card of second short fibers which will become the second batt layer 40, and a card of short fibers which will become the third batt layer 50 are prepared. Next, these cards and the nonwoven fabric 30 are laminated together with the substrate 10. In this case, the cards, the substrate 10 and the nonwoven fabric 30 are laminated such that each layer of the papermaking felt 1 is formed in the order of the third batt layer 50, the substrate 10, the first batt layer 20, the nonwoven fabric 30, and the second batt layer 40. In addition, in this case, the number of cards and nonwoven fabrics 30 may be adjusted so as to provide the necessary basis weight.

Next, the needle punch treatment is carried out such that the cards, the nonwoven fabric 30 and the substrate 10 are entangled and integrated to give a precursor of paper felt 1. It should be noted that, in the present embodiment, it was explained that all of the cards, nonwoven fabric 30 and substrate 10 are laminated at once and collectively processed by needle punch treatment, but it is also possible that the cards are laminated one by one per layer onto the substrate 10 and subjected to needle punch treatment, and this process is repeated so that all layers are laminated and integrated.

Here, the nonwoven fabric 30 has a relatively small penetration resistance as mentioned above. Therefore, the dispersion of fibers of the nonwoven fabric 30 in the thickness direction in the needle punch treatment is suppressed, and the density of the nonwoven fabric 30 is maintained in a relatively high state. As a result, in the papermaking felt 1, too, the nonwoven fabric 30 can suitably suppress the rewetting phenomenon in the wet paper web.

Finally, the precursor of the papermaking felt 1 is subjected to chemical treatment, heat set, press working, etc. as necessary, to give the papermaking felt 1.

As above, the present invention has been described in detail based on preferred embodiments, though the present invention is not limited thereto, and each component can be substituted with any one that is capable of performing an equal function, or an optional component can be added.

Examples

Hereinbelow, the present invention will more specifically be described with examples, though the present invention is not to be limited to these examples.

<1. Manufacture of Papermaking Felt>

First, as the substrate, a woven fabric having the following configuration was prepared:

• • Warp yarns: A twist yarn comprising two fibers twisted together, each fiber consisting of two 330 dtex nylon monofilaments twisted together.
  • Weft yarns: A twist yarn comprising three fibers twisted together, each fiber consisting of two 330 dtex nylon monofilaments twisted together.
  • Weave pattern: 31 twill weave (four twill (3/1)), 44 warp yarns/5 cm, 40 weft yarns/5 cm.
  • Weight of 1 m²: 400 g/m².

Next, cards of short fibers corresponding to each of the following layers and nonwoven fabrics were prepared.

• • First batt layer: Nylon 6 staple fibers; fineness: 22 dtex; weight of 1 m²: 400 g/m²; official moisture regain: 4.5%.
  • Second batt layer: Nylon 6 staple fibers; fineness: 22 dtex; weight of 1 m²: 100 g/m²; official moisture regain: 4.5%.
  • Third batt layer: Nylon 6 staple fibers; fineness: 22 dtex; weight of 1 m²: 100 g/m²; official moisture regain: 4.5%.

In Examples 1 to 4, a nonwoven fabric of cupra (official moisture regain: 11%; weight of 1 m²: 20 g/m²; fiber diameter: 20 μm; a spun-bond nonwoven fabric processed by a water jet (hydroentanglement method)) was used, and the number of sheets was adjusted according to the required weight of 1 m².

In Examples 4 to 8, a nonwoven fabric of rayon (official moisture regain: 11%; weight of 1 m²: 20 g/m²; fiber diameter: 20 μm; a spun-bond nonwoven fabric) was used, and the number of sheets was adjusted according to the required weight of 1 m².

In Examples 9 to 12, a nonwoven fabric of lyocell (official moisture regain: 13%; weight of 1 m²: 20 g/m²; fiber diameter: 16 μm; a spunlace nonwoven fabric) was used, and the number of sheets was adjusted according to the required weight of 1 m².

In Examples 13 to 15, a nonwoven fabric of nylon (official moisture regain: 4.5%; weight of 1 m²: 20 g/m²; fiber diameter: 18 μm; a spun-bond nonwoven fabric) was used, and the number of sheets was adjusted according to the required weight of 1 m².

Next, the cards of the third batt layer, the substrate, the first batt layer, and the second batt layer were laminated in this order, and needle punch treatment was performed on them to produce papermaking felts of Examples 1 to 15 and comparative examples. Note that the needle punching density was 4000 times/inch² (3000 times/inch² on the front surface and 1000 times/inch² on the back surface).

<2. Evaluation>

(1) Penetration Resistance of Nonwoven Fabric

The needle penetration resistance was measured for each of the nonwoven fabrics used in Examples 1 to 15. The penetration resistance was measured by performing a compression test using the tensile testing machine shown in FIG. 2. Specifically, several nonwoven fabrics 30 sandwiched by fixing plates 109 were fixed to a jig 101B. Here, the number of the nonwoven fabrics 30 to be laminated was adjusted such that their weight of 1 m² becomes about 100 g/m².

In this way, while the nonwoven fabric 30 being fixed, needles 103 were moved to the nonwoven fabric 30 side using the tensile testing machine to penetrate the first barb of the needles into the nonwoven fabric 30. The maximum value of the resistance force loaded on the needles 103 at this time was set as the penetration resistance. In addition, the number of needles was 54, the area in which needles are implanted was 602 cm², the density of needles implanted was 0.090 cm/cm², and the moving speed of the needles 103 was 200 mm/min. Also, needles used had a needle count of 32nd, a point diameter of 0.08 mm, a point-to-first barb distance of 6.35 mm, a barb depth of 0.09 mm, a kick-up of 0.01 mm, and a barb length of 0.5 mm.

The penetration resistance obtained as above was converted so as to be per 100 g/m² of the basis weight of the nonwoven fabric 30 and per one needle 103 to obtain the penetration resistance per 100 g/m² of the basis weight of the unwoven fabric 30 per one needle. Specifically, it was calculated based on the following Equation (1):

R = R T ÷ W NWF × 100 ÷ N NDL ( Equation ⁢ 1 )

In the equation, R is the penetration resistance of the nonwoven fabric 30 for the basis weight of 100 g/m² per one needle [N/(100 g/m²×number of needles)], R_T is the maximum resistance force [N] of the nonwoven fabric 30 at the time of penetration of the needle 103, W_NWF is the total basis weight (g/m²) of the nonwoven fabric 30, and N_NDL is the number of the needles 103.

(2) Water-Squeezing Properties

Papermaking felts according to Examples 1 to 15 and Comparative Example were evaluated for their water-squeezing property by the method shown below. FIG. 5 is a schematic diagram to illustrate the method for testing water-squeezing property.

As shown in FIG. 5, first, on a metal pedestal 301, a papermaking felt F according to any one of Examples 1 to 15 and Comparative Example that was cut out to have a diameter of 7 cm was placed, and the moisture content of the papermaking felt F was adjusted to 30%. Here, the moisture content is the mass of water divided by the sum of the mass of papermaking felt and the water.

Next, three sheets of toilet paper were stacked as a model of wet paper web, which was moistened with water to adjust the moisture content to 80%. The moisture content is the mass of water divided by the sum of the mass of the toilet paper and the water. This was cut out to have a diameter of 6 cm to form a wet paper web W and placed on the papermaking felt F. At this point, the dry weight of the wet paper web W was 0.136 g and the moisture content of the wet paper web W was 0.544 g.

Next, a metal top plate 302 (6 kg) was allowed to fall freely from 20 cm above the wet paper web W to press it. The pressing pressure at this time had been adjusted to be 50 kg/cm². Note that the top plate 302 which has been made to fall freely rebounds and moves upwards upon hitting the wet paper web W. Therefore, the test was conducted by fixing the top plate 302 at the time when the top plate 302 moves upward after the first pressing so that the second press is not performed.

The water content of the wet paper web W after pressing was calculated from the mass of wet paper web W after pressing, the water amount in wet paper web W (the dry weight of the wet paper web W being subtracting from the weight of the wet paper web W) and the dry weight of the wet paper web W, and the dryness ΔK (%) was calculated as a value obtained by subtracting the water content of the wet paper web W after pressing from 100. In this evaluation, the dryness ΔK (%) represents the degree of the moisture content reduced by pressing. Generally, it is known that a 1% reduction in the moisture content of wet paper web in the press part can reduce the energy required for drying in the dryer part in the later stage by about 4%. The obtained dryness ΔK (%), and the estimated reducible energy for drying from the Comparative Example calculated based thereon are shown in Table 1.

	TABLE 1
	Configuration of nonwoven fabric	Evaluation of water-

Penetration resistance

squeezing property

		Fiber			Weight of	per 100 g/m2 per 1 needle		Estimated energy
		diameter		Manufacturing	1 m2	[N/(100 g/m2 × number		reduction
	Type	(μm)	Form of fibers	method	(g/m2)	of needles)]	ΔK(%)	for drying (%)

Example 1	Cupra	20	Continuous yarns	Spun-bond	20	0.96	40.9	12.0
Example 2	Cupra	20	Continuous yarns	Spun-bond	40	0.96	42.8	19.6
Example 3	Cupra	20	Continuous yarns	Spun-bond	60	0.96	43.6	22.8
Example 4	Cupra	20	Continuous yarns	Spun-bond	80	0.96	44.3	25.6
Example 5	Rayon	20	Continuous yarns	Spun-bond	20	1.74	39.2	5.2
Example 6	Rayon	20	Continuous yarns	Spun-bond	40	1.74	40.2	9.2
Example 7	Rayon	20	Continuous yarns	Spun-bond	60	1.74	40.8	11.6
Example 8	Rayon	20	Continuous yarns	Spun-bond	80	1.74	41.2	13.2
Example 9	Lyocell	16	Short fibers	Spunlace	20	1.78	39.1	4.8
Example 10	Lyocell	16	Short fibers	Spunlace	40	1.78	40.2	9.2
Example 11	Lyocell	16	Short fibers	Spunlace	60	1.78	40.9	12.0
Example 12	Lyocell	16	Short fibers	Spunlace	80	1.78	41.4	14.0
Example 13	Nylon	18	Continuous yarns	Spun-bond	20	1.71	38.5	2.4
Example 14	Nylon	18	Continuous yarns	Spun-bond	40	1.71	39.5	6.4
Example 15	Nylon	18	Continuous yarns	Spun-bond	60	1.71	40.3	9.6
Comparative	—	—	—	—	—	—	37.9	—
Example

As shown in Table 1, it was shown that the papermaking felts according to Examples 1 to 15 had greatly better water-squeezing property during pressing as compared to the papermaking felt according to Comparative Example, and that the rewetting phenomenon was suitably suppressed when using the papermaking felt according to Examples 1 to 15. In addition, it was suggested that it was possible to greatly reduce the energy for drying in the dryer part after the press part by using the papermaking felts according to Examples 1 to 15.

Moreover, comparing Examples 13 to 15 and Examples 5 to 8, although the penetration resistance of the nonwoven fabrics used therefor was about the same, the papermaking felts of Examples 5 to 8 were greatly better in water-squeezing property when being compared for a similar level of basis weight. It is considered that this is because the official moisture regain of the fibers constituting the nonwoven fabric is greatly larger for the rayon fibers of Examples 5 to 8, so that the nonwoven fabric in the papermaking felt retains moisture and suppresses the rewetting phenomenon.

Note that it was observed that there is a tendency that the dryness is improved when the basis weight of the nonwoven fabric is increased. On the other hand, if the weight of 1 m² of the nonwoven fabric is set too large, the wet paper web may break depending on the type of or the basis weight of the wet paper web. Therefore, in the actual papermaking machine, it is necessary to select a nonwoven fabric with an appropriate basis weight.

REFERENCE SIGNS LIST

• • 1, 1A, 1B: Papermaking felt
  • 10: Substrate
  • 20, 20A, 20B: The first batt layer
  • 30, 30A, 30B: Nonwoven fabric
  • 40: Second batt layer
  • 41: Wet paper web carrying surface
  • 50: Third batt layer
  • 51: Roll contact surface