JP7627159B2 - Papermaking felt - Google Patents

Description

The present invention relates to a papermaking felt used in the press part of a papermaking machine.

Papermaking felts are used in the press part of a papermaking machine when wet paper is pressed between a pair of press rolls to squeeze out water from the wet paper and smooth its surface by passing the wet paper between the press rolls together with the wet paper.
The most widely used papermaking felts are woven fabrics made by crossing warp and weft threads, non-woven fabrics made by pulling threads together without weaving, or polymer films or sheets that have been made breathable by perforating or foaming, either alone or in combination to form a base fabric, with batt fibers laminated on both sides of this base fabric.
In addition, in order to improve the quality of paper produced and to further improve productivity by increasing the papermaking speed, papermaking felts are required to have better properties such as water drainage, surface smoothness, anti-hair removal, anti-staining, etc. In order to meet these requirements, papermaking felts that have been subjected to resin processing have been widely used in recent years.
Resin processing is carried out, for example, by impregnating the papermaking felt with one or more resins (mainly polyurethane resins) dispersed in water or the like. Resin processing has the advantage of improving various properties of the papermaking felt, such as water squeezing ability, initial compatibility, and compression resistance.
However, resin processing increases the bending rigidity of the papermaking felt, making the papermaking felt hard, which has the disadvantage of making it difficult to insert the papermaking felt into a papermaking machine (hereinafter referred to as "insertion ability" for short).
For this reason, for example, Patent Document 1 discloses a method of performing a surface treatment on papermaking felt after resin processing by applying a softening agent.

JP 2017-150101 A

By subjecting the papermaking felt to a surface treatment that applies a softener, the flexibility of the felt is improved, i.e., the felt becomes softer, which improves the ease of insertion into a papermaking machine. As the amount of softener applied increases, the felt becomes even softer, which further improves the ease of insertion into a papermaking machine.
However, as the amount of softener applied to papermaking felt increases, the durability of the resin applied in the resin treatment decreases and the resin becomes more likely to fall off from the papermaking felt, resulting in the problem that it becomes difficult to obtain the benefits of the resin treatment.

The present invention was made in consideration of the above problems, and aims to provide a papermaking felt that can be easily inserted into a papermaking machine while optimally enjoying the benefits of resin processing.

The inventors of the present invention have conducted repeated tests to satisfy the requirements for improving ease of insertion into a papermaking machine and durability of the resin, and have found that by adding a softener so that the weight ratio with respect to the resin (polyurethane resin) falls within a specified range, the bending rigidity of the papermaking felt is reduced, improving ease of insertion, and the advantages of resin processing can be advantageously enjoyed.
The present invention is as follows.
1. A papermaking felt coated with a polyurethane resin and to which a softening agent is added,
A papermaking felt characterized in that the weight ratio of said softener to said polyurethane resin (weight of softener/weight of polyurethane resin) is in the range of 0.024 to 0.090.
2. The papermaking felt according to claim 1, wherein the softening agent contains a surfactant.
3. The papermaking felt according to claim 2, wherein the surfactant is a nonionic surfactant.
4. A base fabric layer and a surface batt layer disposed on the papermaking surface side of the base fabric layer,
4. The papermaking felt according to claim 1, wherein the surface batt layer comprises a surface layer portion containing fibers to which the polyurethane resin is bonded, and the softener is applied to the surface layer portion.

The papermaking felt of the present invention allows the user to enjoy the benefits of resin processing while improving ease of insertion into a papermaking machine.

The present invention will be further described in the following detailed description by way of non-limiting examples of exemplary embodiments according to the invention and with reference to the several drawings mentioned, in which like reference numerals refer to like parts throughout the several views of the drawings.
FIG. 2 is a schematic diagram showing another example of the cross-sectional structure of the papermaking felt of the present invention. FIG. 2 is an explanatory diagram showing a measuring device for measuring a weft bending stiffness value. 1 is a graph showing the relationship between the weight ratio of a softener to a polyurethane resin, and the resin remaining rate and the weft bending change rate of the papermaking felt obtained in the examples.

The matters set forth herein are illustrative and are intended to provide an illustrative description of the embodiments of the present invention, with the objective of providing what is believed to be the most effective and easily understood explanation of the principles and conceptual features of the present invention. In this respect, it is not intended to provide structural details of the present invention beyond the extent necessary for a fundamental understanding of the present invention, and the description, taken together with the drawings, will make clear to those skilled in the art how some forms of the present invention may be embodied in practice.

[1] Papermaking felt The present invention relates to a papermaking felt to which a polyurethane resin is applied and a softener is added, and the weight ratio of the softener to the polyurethane resin (weight of softener/weight of polyurethane resin) is in the range of 0.02 to 0.09.
In the papermaking felt of the present invention, the weight ratio of the softener to the polyurethane resin can further be set in the range of 0.03 to 0.09.

The papermaking felt of the present invention may have, for example, the configuration shown in FIG.
That is, as shown in FIG. 1, the papermaking felt 1 comprises a base fabric layer 11, a front batt layer 13 arranged on the papermaking surface side of the base fabric layer 11 (the upper surface side in FIG. 1), and a back batt layer 15 arranged on the running surface side of the base fabric layer 11 (the lower surface side in FIG. 1).
The surface batt layer 13 comprises fibers bonded with polyurethane resin 19. In this surface batt layer 13, the side facing the base fabric layer 11 on the inside is an inner layer portion 13A, and the side facing the papermaking surface on the outside is a surface layer portion 13B. A softener (not shown) is provided in a dispersed state mainly inside the surface layer portion 13B.
The papermaking felt 1 is formed as an integrated whole by intertwining each layer, such as the base fabric layer 11, the front batt layer 13, and the back batt layer 15, in the lamination direction.

The papermaking felt 1 may be configured, for example, without the back batt layer 15 .
The surface batt layer 13 of the papermaking felt 1 may have a multi-layer structure, for example, having two layers, an inner layer 13A and a surface layer 13B.
When the surface batt layer 13 has a multi-layer structure, an additional batt layer can be provided between the inner layer portion 13A and the surface layer portion 13B.

(1) Fabric Layer The fabric layer may be derived from a fabric used in papermaking felt, and typically made of thread.
Examples of the thread material include polyamide resins such as nylon 6, nylon 66, nylon 610, and nylon 612; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; and synthetic resins such as polyolefin resins such as polyethylene and polypropylene, as well as cotton, wool, and silk.
Among these examples, polyamide resin is particularly preferred as the material for the yarn constituting the base fabric layer, from the viewpoint of being able to produce a papermaking felt having excellent abrasion resistance, compression recovery, impact resistance, and the like.

The yarn may be in the form of a monofilament, a multifilament, a spun yarn, or a processed yarn such as a textured yarn, a bulky yarn, or a stretch yarn that has been subjected to a crimping process or a bulking process, or further may be a twisted yarn obtained by twisting these yarns together.
The cross-sectional shape of the thread may be circular, approximately elliptical, polygonal, approximately star-shaped, approximately rectangular, or the like.
The yarn may be a hollow yarn.

The diameter of the thread is not particularly limited. When the thread is in the form of a monofilament, the diameter is preferably 0.10 mm to 0.60 mm, more preferably 0.20 mm to 0.50 mm.
When the yarn is in the form of a multifilament, the fineness of the monofilaments constituting the multifilament is usually 3 dtex to 1,000 dtex, preferably 5 dtex to 600 dtex.
When the yarn is in the form of a multifilament, the number of filaments in the multifilament is usually 2 to 300, and preferably 2 to 100.

The fabric layer may be made of one type of yarn or two or more types of yarn.
The yarns constituting the base fabric layer may have an appropriate material, shape, diameter, etc. according to the strength, porosity, breathability, pressure uniformity, and other properties of the papermaking felt.

The structure of the base fabric layer is not particularly limited, and may be either a single-layer structure or a multi-layer structure.
In the case of a multi-layer structure, the fabric may be a multi-woven base fabric consisting of at least two layers formed by weaving two or more warp threads and two or more weft threads, or a fabric formed by stacking multiple different types of base fabrics.
The fabric layer may have a structure in which the yarns are arranged in the warp direction, the weft direction or an oblique direction.
The base fabric layer may be a polymer film or sheet that has been subjected to a perforation process, foaming process, or the like.

The thickness of the base fabric layer is not particularly limited, but is preferably 0.2 mm to 3.5 mm, and more preferably 0.4 mm to 2.0 mm.
The basis weight of the base fabric layer is not particularly limited, but is preferably 150 g/m ² to 1500 g/m ² , and more preferably 250 g/m ² to 1200 g/m ² .
The thickness and basis weight of the fabric layer are appropriately set depending on the strength, porosity, air permeability, and fabric mark prevention properties of the papermaking felt.
The thickness and basis weight of the base fabric layer are the thickness and basis weight of the single layer in the case of a single-layer structure, and the sum of the thicknesses and basis weights of the individual layers in the case of a multi-layer structure.

(2) Surface batt layer The surface batt layer is a layer composed of fibers (hereinafter also referred to as "surface batt fibers"), which is arranged on the papermaking surface side of the base fabric layer and has the function of transporting the wet paper while maintaining the surface smoothness during papermaking.
The structure of the surface batt layer is not particularly limited, and may be either a single-layer structure or a multi-layer structure.

Examples of materials for the surface batt fiber include polyamide resins such as nylon 6, nylon 66, nylon 610, and nylon 612; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; and synthetic resins such as polyolefin resins such as polyethylene and polypropylene, as well as cotton, wool, and silk.
Among these, polyamide resin is preferred as the material for the surface batt fiber from the viewpoints of abrasion resistance, compression recovery, impact resistance, hydrophilicity, hydrolysis resistance, chemical resistance, and the like.

The fineness of the face batt fiber is usually from 0.1 dtex to 100 dtex.
When the surface batt layer has a multi-layer structure, the fineness of the surface batt fibers may be the same or different in, for example, the inner layer 13A and the surface layer 13B shown in FIG.
Typically, the fineness of the surface batt fibers contained in the inner layer portion 13A can be 3 dtex to 150 dtex, and the fineness of the surface batt fibers contained in the surface layer portion 13B can be 0.1 dtex to 100 dtex.

The surface batt layer has a basis weight of preferably 100 g/m ² to 1,500 g/m ² , more preferably 300 g/m 2 to 1,200 g/m 2 , and even more preferably 400 g/m ² to 1,000 g/m ² as a whole, whether it has a single-layer ^structure or a multi-layer ^structure .
The fineness of the surface batt fibers and the basis weight of the surface batt layer are appropriately set depending on the strength, porosity, and air permeability of the papermaking felt, as well as the surface properties of the surface batt layer.

(3) Back Batt Layer The papermaking felt of the present invention may further include a back batt layer 15 on the running surface side of the base fabric layer 11 opposite the front batt layer 13 (see FIG. 1).
The back batt layer is a layer composed of fibers (hereinafter also referred to as "back batt fibers"), and has the effect of protecting the base fabric layer from abrasion, thereby improving the durability of the papermaking felt.

The material for the back batt fibers is not particularly limited, and like the front batt fibers, can be polyamide resins such as nylon 6, nylon 66, nylon 610, nylon 612, etc.; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, etc.; polyolefin resins such as polyethylene, polypropylene, etc.; synthetic resins, cotton, wool, silk, etc.
The fineness of the backing batt fiber is usually from 3 dtex to 150 dtex.
The back batt layer usually has a basis weight of 50 g/m ² to 500 g/m ² .

(4) Polyurethane Resin The papermaking felt of the present invention is coated with a polyurethane resin.
This polyurethane resin is applied to the papermaking felt to control the air permeability (water squeezing) in the cross-sectional direction of the papermaking felt within an appropriate range and to impart an appropriate hardness to the surface layer, thereby improving the water squeezing ability, initial conformability, compression resistance, etc. In other words, by applying a polyurethane resin to the fibers and carrying out a resin treatment, the papermaking felt can enjoy the benefits of improved water squeezing ability, initial conformability, compression resistance, etc.
As a specific example, as shown in FIG. 1, a papermaking felt 1 includes fibers 17 bound with polyurethane resin 19 in an inner layer portion 13A and a surface layer portion 13B of a surface batt layer 13.

The polyurethane resin may be bonded to the fibers in either a manner in which the polyurethane resin adheres to the fibers or a manner in which the polyurethane resin bonds the fibers together.
In addition, the polyurethane resin can be used to bond fibers together in either of two ways: the polyurethane resin bonds together fibers extending in perpendicular or intersecting directions at their intersections, or the polyurethane resin that has penetrated between multiple fibers bonds the fibers together.

The fibers bound with the polyurethane resin are not necessarily limited to the form contained in the inner layer portion 13A and the surface layer portion 13B of the surface batt layer 13 as exemplified in FIG.
In other words, if the papermaking felt 1 is configured to be coated with polyurethane resin, the fibers bonded with the polyurethane resin can be contained only in the surface layer portion 13B of the surface batt layer 13, or can be contained in both the surface batt layer 13 and the base fabric layer 11.

The polyurethane resin is synthesized by using polyol (hydroxyl group) and isocyanate-based compound (isocyanate group) as main raw materials. The types of polyol and isocyanate-based compound used as the main raw materials are not particularly limited.
Examples of the polyol include polyester polyols, polyether polyols, polycarbonate polyols, polyolefin polyols, etc., and any of these may be used. Examples of the isocyanate compound include aromatic isocyanate compounds, aliphatic isocyanate compounds, and alicyclic isocyanate compounds, and any of these may be used.
The polyurethane resin may be a resin synthesized only from the above-mentioned main raw materials, or a resin synthesized from a mixture of the main raw materials and secondary raw materials such as catalysts and crosslinking agents, and additives such as colorants and stabilizers.

Papermaking felt is obtained by subjecting a base fabric layer, a surface batt layer, and other components, which have been integrated together by interlacing or the like, to a resin treatment in which a polyurethane resin is applied to the base fabric.
Hereinafter, in the papermaking felt, the felt formed from an integrated body including a base fabric layer, a surface batt layer, etc., and which has not been subjected to resin processing or softening processing, in other words, the felt which has not been coated with polyurethane resin and has not been given a softener, will be referred to as "felt raw material."
In addition, felt that is made by only resin-processing a raw felt roll and not softening it is called "resin-processed felt".

The type of polyurethane resin used in the resin processing is not particularly limited, and any of foams such as soft polyurethane foam and hard polyurethane foam, and non-foams such as thermoplastic elastomers, thermosetting elastomers, and paints can be used.
The state of the polyurethane resin used for resin processing is not particularly limited, but is usually liquid. The method for obtaining the liquid polyurethane resin is not particularly limited, and any known method can be applied, but in particular, water-based polyurethane emulsions and water-based polyurethane dispersions obtained by dispersing polyurethane resin in water have the advantage that they can be easily resin-processed onto raw felt rolls.

(5) Softening Agent The papermaking felt of the present invention is obtained by adding a softening agent to the resin-processed felt.
The softening agent is added for the purpose of improving the flexibility of the papermaking felt, thereby making it easier to insert the papermaking felt into a papermaking machine.

Specifically, in the papermaking felt 1 shown in FIG. 1, the softener is applied to the surface layer 13B including fibers to which the polyurethane resin 19 is bonded, although this is not specifically shown.
This surface layer portion 13B enjoys the benefits of being coated with polyurethane resin 19, and is given appropriate flexibility by the addition of a softener.

The softener may be applied in any of the following forms: the softener is adsorbed or attached only to the fibers; the softener is adsorbed or attached to the fibers and the resin of the fibers to which the polyurethane resin is bonded; or the softener penetrates into the gaps between the fibers.
In addition, the softener is not necessarily limited to being applied only to the surface layer of the surface batt layer. As long as the softener is applied to the papermaking felt, the softener may be applied to the surface layer and inner layer of the surface batt layer, or to the surface batt layer and base fabric layer.

The softening agent used may generally contain a surfactant.
That is, the surfactant has a hydrophilic group and a lipophilic group, and by adsorbing the hydrophilic group to the fiber with the lipophilic group facing outward, the lipophilic group acts like a lubricant, reducing the frictional resistance between the fibers and improving slippage, thereby improving the flexibility of the papermaking felt.
The surfactant is not particularly limited, and one or more surfactants selected from ionic surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants, and nonionic surfactants can be used.
Among these surfactants, nonionic surfactants have hydrophilic groups (hydroxyl groups or ether bonds) that do not dissociate into ions in an aqueous solution, and since they do not ionize, they are less susceptible to the effects of water hardness and electrolytes, and can be used in combination with ionic surfactants, and therefore are preferred as surfactants to be contained in fabric softeners.

The softener may be a softener consisting of only a surfactant (preferably a nonionic surfactant), or may be a softener consisting of a surfactant (preferably a nonionic surfactant) to which an additive has been added.
The additives are not particularly limited, and additives used in known softeners, such as antistatic agents and colorants, can be used.

The additive may be a resin of the same type as the fiber material used in the felt roll. It is preferable that the resin of the same type is further provided with a hydrophilic group. For example, when the fiber material used in the felt roll is a polyamide resin, the additive may be a polyamide resin provided with a hydrophilic group.
When a resin of the same type is used as an additive, the resin of the same type has a high affinity with the fibers used in the raw felt roll, and therefore can form a coating on the surface of the fibers.
Furthermore, when the same resin is endowed with a hydrophilic group, it can act as an intermediary for adsorbing a surfactant onto the surface of the fibers used in the felt material.
For this reason, when a resin of the same type as the fiber used in the raw felt roll, especially a resin of the same type to which a hydrophilic group has been added, is used as an additive, the flexibility of the papermaking felt can be improved, and the hydrophilicity is increased, making it easier for water to penetrate the fibers, making it easier to remove dirt, and improving the dirt resistance of the papermaking felt.

(6) Composition and physical properties [weight ratio]
In the papermaking felt, the weight ratio of the softener to the polyurethane resin is in the range of 0.024 to 0.090. In this case, the papermaking felt can improve the ease of insertion into a papermaking machine and the durability of the polyurethane resin.
The weight ratio is preferably in the range of 0.035 to 0.080, and more preferably in the range of 0.050 to 0.070.
The weight ratio is a value obtained by the formula weight ratio = Ws/Wp, where the amount of polyurethane resin applied to the papermaking felt (basis weight) is the weight of polyurethane resin Wp (g/ ^m2 ) and the amount of softener applied to the papermaking felt (basis weight) is the weight of softener Ws (g/ ^m2 ).

[Resin coating amount]
The coating weight (Wp) of the polyurethane resin (hereinafter abbreviated as "resin coating weight (Wp)") is not particularly limited, and is appropriately set depending on the performance required for the papermaking felt, such as water drainage, initial compatibility, compression resistance, etc.
The resin coating weight (Wp) is obtained by measuring the weight per unit area (g/m ² ) of the polyurethane resin coated on the papermaking felt.
Specifically, the resin coating weight (Wp) can be preferably set to 10 g/m ² to 100 g/m ² , and more preferably 20 g/m ² to 90 g/m ² .

[Softener application amount]
The amount of softener applied (Ws) (hereinafter abbreviated as "amount of softener applied (Ws)") is not particularly limited, and is appropriately set depending on performance such as the ease of insertion of the papermaking felt into a papermaking machine, the durability of the polyurethane resin, etc.
The amount of softener applied (Ws) is obtained by measuring the basis weight (g/m ² ) of the solid content of the softener applied to the papermaking felt.
Specifically, the amount of softener applied (Ws) can be preferably 2 g/m ² to 10 g/m ² , more preferably 2.5 g/m ² to 8.5 g/m ² , and even more preferably 3 g/m ² to 6.5 g/m ² .

[Resin Residual Rate]
The performance of a papermaking felt against resin release can be expressed in terms of the resin remaining rate (%).
That is, during papermaking, the surface (surface batt layer) of the papermaking felt is directly subjected to external mechanical forces such as repeated compression, showering, suction, etc. When the papermaking felt is subjected to external mechanical forces, the resin (polyurethane resin in this application) applied to the papermaking felt deteriorates over time and peels off from the fibers, causing the resin to be detached, and it may become impossible to enjoy the benefits of the resin processing.
In other words, when used in a papermaking felt, if the resin is prone to detachment during use in a papermaking machine, it is difficult to fully enjoy the benefits of the resin processing, whereas if the resin is not prone to detachment, it is possible to adequately enjoy the benefits of the resin processing.

The resin residual rate (%) is a value indicating the performance of the papermaking felt against the detachment of the resin, in other words, the durability of the resin with respect to detachment from the papermaking felt. Specifically, the resin residual rate (%) in this application is a value obtained by carrying out a durability test described later on the papermaking felt and measuring the amount of the polyurethane resin remaining in the papermaking felt.
Specifically, the resin residual rate (%) is calculated from the above-mentioned resin coating amount (Wp) and the amount of resin that has fallen off ( _WL1 ; g/ ^m2 ) using the formula: [(Wp- _WL1 )/Wp] x 100 (resin residual rate (%) = [(Wp- _WL1 )/Wp] x 100).
The amount of resin loss (W _L1 ; g/m ² ) is calculated by measuring the weight (basis weight; g/m ² ) of the papermaking felt before the durability test and the weight (basis weight; g/m ² ) after the durability test, and calculating the weight change before and after the durability test (W _L1 = weight after durability test - weight before durability test).

The resin residual rate (%) is not particularly limited, and is appropriately set so as to optimally obtain the benefits of the resin processing in accordance with the ease of insertion into a papermaking machine required of the papermaking felt.
Specifically, the lower limit of the resin residual rate (%) is preferably 80% or more, more preferably 82% or more, and even more preferably 84% or more. Usually, the upper limit of the resin residual rate (%) is 100%.

[Weft bending change rate]
The ease of insertion of a papermaking felt into a papermaking machine can be expressed by the weft bending change rate (%).
That is, the papermaking felt to which a softener has been added changes so that its bending stiffness (g/cm) decreases as its flexibility improves, and when the change in the bending stiffness (g/cm) is large, the flexibility improves significantly and the threading ability increases, whereas when the change in the bending stiffness (g/cm) is small, the flexibility does not improve and the threading ability decreases.
Therefore, the rate of change between the bending stiffness (g/cm) of the papermaking felt before the application of the softener and the bending stiffness (g/cm) of the papermaking felt after the application of the softener, that is, the bending change rate (%), can be used to express the insertion ability as follows: when the bending change rate (%) is high, the insertion ability is high, and when the bending change rate (%) is low, the insertion ability is low.
The above-mentioned bending stiffness value (g/cm) is determined by measuring the bending stiffness value (g/cm) in the weft direction of the papermaking felt, i.e., the weft bending stiffness value (g/cm) using a measuring device (see FIG. 2).

Here, the measurement of the weft bending stiffness value (g/cm) will be described in detail.
2, the measuring device for weft bending stiffness has a load meter 21 for measuring bending stiffness and a base 22 for placing the measurement target 1 (paper felt or raw felt roll). The load meter 21 measures the load applied from the paper felt 1 placed below, and specifically, a "handheld digital force gauge DFG-50R (product name)" manufactured by Nidec-Shimpo Corporation is used.

The papermaking felt 1 for which the weft bending stiffness value is measured has the warp direction (MD direction in the figure) as the warp direction or flow direction, and the direction perpendicular to the warp direction as the weft direction (CMD direction in the figure).The surface on which the surface batt layer is provided is the front surface, and the papermaking felt 1 is folded in half in the weft direction so that the front surface is on the inside.
During measurement, the distance between the load meter 21 and the base 22 is set to 3 cm, and the papermaking felt 1 is placed between them in a state where it is folded in half in the weft direction. The load meter 21 is then lowered until the distance between the load meter 21 and the base 22 is 1 cm, and the load meter 21 is pressed against the papermaking felt 1. The load measured by the load meter 21 at this time is taken as the weft bending stiffness value (g/cm) of the papermaking felt 1.

The weft bending change rate (%) is calculated by the formula: weft bending change rate (%) = ( _F1 / _F0 ) x 100, where _F0 (g/cm) is the measured weft bending rigidity value of the raw felt and _F1 (g/cm) is the measured weft bending rigidity value of the resin-processed felt or papermaking felt.
The weft bending change rate (%) is not particularly limited, and is appropriately set so as to improve the ease of insertion into a papermaking machine within a range in which the advantages of the resin treatment applied to the papermaking felt can be enjoyed.
Generally, the upper limit of the weft bending change rate (%) can be set to preferably 115% or less, more preferably 110% or less, and further preferably 105% or less.
If the weft bending change rate (%) is less than 100%, the weft bending rigidity value will be lower than that of a raw felt material that has not been resin-treated, making it difficult to obtain the benefits of the resin treatment.

[2] Manufacturing method of papermaking felt The manufacturing method of papermaking felt includes a resin processing step in which polyurethane resin is applied to a raw felt roll to obtain a resin-processed felt, and a softening step in which a softener is applied to the resin-processed felt to obtain a papermaking felt.
Each step will be described below.

(1) Resin Processing Step The resin processing step is a step in which polyurethane resin is applied to a raw felt roll to obtain a resin-processed felt.
Specifically, the resin processing is carried out by applying or impregnating a dispersion obtained by dispersing polyurethane resin in water (hereinafter referred to as "aqueous dispersion") onto or onto a felt roll, drying it, heating it, and bonding the polyurethane resin to the fibers of the felt roll.

The felt raw material comprises a base fabric layer and a first fiber layer which serves as a front batt layer, and may, if necessary, comprise a second fiber layer which serves as a back batt layer on the opposite side of the first fiber layer.
The felt raw material is preferably an integrated product in which the base fabric layer, the first fiber layer, etc. are entangled by needling or the like.

The explanation of "(1) Fabric layer" in "(1) Papermaking felt" above applies to the fabric layer.
The first fiber layer may be either a single-layer type or a multi-layer type, and the explanation of "(2) Surface batt layer" in "(1) Papermaking felt" above applies. In addition, the fineness of the fibers constituting the outermost layer of the first fiber layer in the case of a single-layer type and the fineness of the fibers constituting the outermost layer in the case of a multi-layer type are both preferably 0.1 to 100 dtex, more preferably 0.3 to 70 dtex, even more preferably 1 to 50 dtex, and particularly preferably 2 to 30 dtex, because this improves the retention of polyurethane resin particles after the aqueous dispersion is applied.
When the raw felt roll has a second fiber layer, the explanation of “(3) Back batt layer” in “(1) Papermaking felt” above is applied to the second fiber layer.

The form of the aqueous dispersion may be an emulsion or the like, but is preferably a dispersion in which the polyurethane resin is dispersed in water, since this makes it easier to control the thickness of the binder portion (surface layer portion 13B) containing the polyurethane resin.
The aqueous dispersion may consist of only the polyurethane resin, or may further contain additives.

In the resin finishing step, the method for applying the aqueous dispersion to the surface of the raw felt roll is not particularly limited, and spray coating, roll coating, etc. can be applied.
The amount of the aqueous dispersion to be applied is appropriately selected depending on the solid content and viscosity of the aqueous dispersion, and is not particularly limited.

In the resin processing step, the felt roll coated with the aqueous dispersion is dried by heat treatment to remove water, which is the main medium of the aqueous dispersion, and the polyurethane resin contained in the aqueous dispersion is adhered to the fibers of the first fiber layer.
The heating temperature in the heat treatment can be preferably 100°C to 170°C, and more preferably 120°C to 150°C.

(2) Softening Treatment Step The softening treatment step is a step in which a softener is applied to the resin-processed felt to obtain papermaking felt.
Specifically, the softening treatment process is carried out by applying or impregnating the resin-processed felt with a softener solution (hereinafter referred to as the "treatment liquid") obtained by diluting the original softener liquid with water, and then drying the resin-processed felt to impart the softener to the resin-processed felt.

In the softening treatment step, the softener can be used as it is, but from the viewpoint of ease of application or impregnation to the resin-processed felt, it is preferable to use a treatment liquid obtained by diluting the undiluted softener with water.
The treatment liquid may consist of only a softener and water, or may further contain additives.
The concentration of the softener contained in the treatment liquid is not particularly limited, and can be appropriately set depending on the viscosity of the softener, etc.

In the softening treatment step, the method for applying or impregnating the resin-processed felt with the treatment liquid is not particularly limited, and spray coating, roll coating, etc. can be applied.
The amount of the treatment liquid to be applied or impregnated can be appropriately selected depending on the concentration and weight ratio of the softener.

In the softening treatment step, the resin-processed felt coated or impregnated with the treatment liquid is dried, and the softening agent contained in the treatment liquid is absorbed into the fibers to produce papermaking felt.
The method for drying the resin-processed felt is not particularly limited as long as it can remove water, which is the main medium of the treatment liquid. In this drying, the drying temperature, pressure, etc. are not particularly limited.

The present invention will now be described in detail with reference to examples.
[Manufacturing of felt rolls]
A twisted monofilament yarn (nylon 6, fiber diameter; 0.2 mm) and a single monofilament yarn (nylon 6, fiber diameter; 0.25 mm) were woven in a single weave to obtain a woven fabric (basis weight: 273 g/m ² ) which was used as the first base fabric layer.
A single monofilament yarn (nylon 6.10, fiber diameter: 0.4 mm) and a single monofilament yarn (nylon 6, fiber diameter: 0.4 mm) were woven in a double weave to obtain a fabric (basis weight: 583 g/m ² ) which was used as the second base fabric layer.
The above-mentioned first fabric layer and second fabric layer were laminated in the thickness direction, with the first fabric layer side serving as the papermaking surface and the second fabric layer side serving as the running surface to obtain a fabric (fabric layer).

On the papermaking surface side of the above-mentioned base fabric (base fabric layer), staple fiber (nylon 66, average fineness: 51 dtex) was arranged in an amount of 570 g/ ^m2 on the inner layer side, and staple fiber (nylon 66, average fineness: 31 dtex) was arranged in an amount of 234 g/ ^m2 on the surface layer side to form a first fiber layer.
Furthermore, staple fibers (nylon 66, average fineness: 51 dtex) were arranged in a basis weight of 190 g/m ² on the running surface side of the above-mentioned base fabric (base fabric layer) to form a second fiber layer.

The above-mentioned base fabric (base fabric layer), first fiber layer, and second fiber layer were entangled and integrated by needle punching, and further pressed to produce a felt roll in which the base fabric layer, front batt layer, and back batt layer were integrated.
The obtained raw felt sheet was subjected to a bending stiffness test, and the weft bending stiffness value was 1362.3 g/cm (see the "raw felt sheet" section in Table 1).

[Resin processing process]
The aqueous polyurethane dispersion solution was adjusted so that the solid content concentration was 8% by mass, to obtain an aqueous dispersion.
The above-mentioned raw felt roll was set in a finishing machine, and the aqueous dispersion was sprayed onto the papermaking side (surface batt layer side) of the raw felt roll so that the spray amount (basis weight) was 1000 g/m ^2. The raw felt roll was then dried at 130° C., and subsequently heated by blowing hot air at 150° C. to melt the polyurethane resin, and a resin-processed felt in which the polyurethane resin was bound to the fibers of the surface layer of the surface batt layer was obtained.
This resin-processed felt had a resin coating weight (Wp) of the polyurethane resin of 80 g/ ^m2 (see the "Experimental Example 0" in Table 1).

[Softening process]
A nonionic surfactant ("Innobesol NY-30" (trade name) manufactured by Lion Specialty Chemicals) was used as a stock solution, which was diluted with water so that the stock solution concentration became 5% by mass, to obtain a treatment solution.
The above-mentioned resin-treated felt (Experimental Example 0) was set in a finishing machine, and the treatment liquid was sprayed onto the paper-making surface side (surface batt layer side) of the resin-treated felt (Experimental Example 0) in a predetermined amount.
The amount of the treatment liquid sprayed was appropriately changed and adjusted in each experimental example so that the amount of softener applied (basis weight) was the value of Experimental Examples 1 to 8 shown in Table 1.
Thereafter, the resin-processed felt sprayed with the treatment liquid was dried at 130° C. to obtain papermaking felts (Experimental Examples 1 to 8) coated with polyurethane resin and imparted with a softener.
For the obtained papermaking felts (Experimental Examples 1 to 8), the resin coating weight (Wp) was 80 g/ ^m2 , and the softener application amount (Ws) was the value shown in Table 1.
For the papermaking felts of Experimental Examples 1 to 8, the weight ratio of the softener to the polyurethane resin (softener applied amount (Ws)/resin applied amount (Wp)) was calculated from the resin applied amount (Wp) and the softener applied amount (Ws), and is shown in Table 1.

[Durability test]
The resin-processed felt (Experimental Example 0) and the paper-making felt (Experimental Examples 1 to 8) were each cut to a length of 0.34 m and a width of 0.14 m, and sewn together into an endless belt shape with a total length of 5 m after connection, to obtain test samples of Experimental Examples 0 and 1 to 8. These test samples were attached to a press roll tester, and durability tests were conducted on the durability of the polyurethane resin.

The press roll tester is configured to press (compress) the test sample between a top roll and a bottom roll once per revolution during the durability test.
The press roll tester is structured so that a test sample is run through a plurality of rolls attached to the tester so that the surface of the test sample is bent both outward and inward.
Furthermore, the press roll tester has a structure including a high-pressure needle-type sliding shower and a suction box.

The durability test was carried out by running the test sample at a running speed of 150 m/min and a press linear pressure of 45 kN/m until the test sample was pressed 46,500 times.
The durability test was performed by sliding a high-pressure needle shower over the papermaking side of the test sample (the papermaking side of the papermaking felt) to spray water onto the papermaking side, and running the test sample while sucking up the water from the papermaking side of the test sample with a suction box.

The weight (basis weight; g/ ^m2 ) of the test sample before the durability test and the weight (basis weight; g/ ^m2 ) after the durability test were measured, and the weight difference before and after the durability test was calculated as the amount of resin loss ( _WL1 ; g/ ^m2 ).
The amount of resin remaining in the test sample after the durability test ( _Wp1 ; g/ ^m2 ) was determined from this amount of resin removed ( _WL1 ; g/ ^m2 ) and the above-mentioned amount of resin applied (Wp; g/ ^m2 ), and the resin remaining rate (%) was calculated from the ratio of the amount of resin remaining ( _Wp1 ; g/ ^m2 ) to the amount of resin applied (Wp; g/ ^m2 ) [( _Wp1 /Wp) x 100].
For the test samples of Experimental Examples 0 and 1 to 8, the amount of resin that fell off (W _L1 ; g/m ² ) and the resin remaining rate (%) are shown in Table 1.

[Bending stiffness test]
Test samples measuring 10 cm lengthwise and 10 cm widthwise were cut out from three locations of each of the raw felt rolls, the resin-processed felt (Experimental Example 0), and the papermaking felt (Experimental Examples 1 to 8), to obtain three test samples each of the raw felt rolls, Experimental Example 0, and Experimental Examples 1 to 8.
The weft bending stiffness values (g/cm) of all three test samples, namely, the raw felt sheet, Experimental Example 0, and Experimental Examples 1 to 8, were measured using the measuring device shown in FIG. 2, and the average value was calculated. The average value was used as the weft bending stiffness values (g/cm) of the raw felt sheet, Experimental Example 0, and Experimental Examples 1 to 8.
Then, the weft bending change rate (%) was calculated based on the weft bending rigidity values (g/cm) of the raw felt fabric, Experimental Example 0, and Experimental Examples 1 to 8. This weft bending change rate (%) was calculated from the formula: Weft bending change rate (%) = (F1/F0) x 100, where the weft bending rigidity values (g/cm) of Experimental Examples 0 and ₁ to 8 are _F1 and the weft bending rigidity value (g/ _cm ) of the raw felt fabric is _F0 .
Table 1 shows the weft bending stiffness (g/cm) and the weft bending change rate (%) for the raw felt sheet and the test samples of Experimental Example 0 and Experimental Examples 1 to 8.

[Results and Discussion]
FIG. 3 is a graph showing the relationship between the weight ratio shown in Table 1, the resin remaining rate (%), and the weft bending change rate (%) for Experimental Example 0 (resin-processed felt) and Experimental Examples 1 to 8 (papermaking felts).
3 and Table 1, the weft bending rigidity value (g/cm) of Experimental Example 0, which was not applied with a softener, was higher than those of Experimental Examples 1 to 8, and its weft bending change rate (%) was 129.4%. And, for Experimental Examples 1 to 8, which were applied with a softener, the weft bending change rate (%) decreased as the weight ratio increased, that is, as the amount of softener applied (Ws) increased.
Meanwhile, regarding the resin residual rate (%), the resin residual rate of Experimental Example 0, which was not given a softener, was 81.8%, but the resin residual rate of Experimental Example 1, in which a softener was given so that the weight ratio was 0.019, was 88.4%, which was a greater increase than that of Experimental Example 0. In other words, Experimental Example 1 was able to enjoy the benefits of the resin processing to a greater extent than Experimental Example 0, which was not given a softener.
Furthermore, following Experimental Example 1, the resin residual rate (%) was also 88.0%, 87.8%, and 84.6% in Experimental Examples 2, 3, and 4, which were higher than 81.8% in Experimental Example 0. From the graph in Fig. 3, it can be seen that the resin residual rate (%) only decreased very slightly in Experimental Examples 1 to 3 even when the weight ratio was increased to 0.019, 0.040, and 0.060, and that a tendency for it to decrease significantly was seen from Experimental Example 4 onwards, where the weight ratio was set to 0.080 or more.
That is, the weft bending change rate (%) decreases accordingly with an increase in the amount of softener applied (Ws), and the application property can be improved. On the other hand, when the weight ratio of the amount of softener applied to the amount of resin applied is within a certain range, the resin remaining rate (%) increases more than that of the resin-processed felt to which no softener is applied, which shows that the merits of resin processing can be satisfactorily enjoyed.

The range of the weight ratio for improving the resin residual rate (%) will be considered.
For the papermaking felts of Experimental Examples 1 to 8, the resin residual rate (%) was set to the standard value of 81.8% for Experimental Example 0, and the weft bending change rate (%) was set to 110%, which is 10% higher than the original felt roll of 100%. The weft bending change rate (%) standard value of 110% is more than 10% lower than the 129.4% for Experimental Example 0 to which no softener was applied.
Then, those with a resin residual rate (%) of 81.8% or more, which is the standard value, and a weft bending change rate (%) of 110% or less, which is the standard value, were rated as "Good", as they were able to optimally enjoy the benefits of resin processing and had improved ease of insertion into the papermaking machine, and all other items were rated as "NG".
The results of the evaluation are shown in Table 1.

Experimental Examples 2 to 4 were rated “Good” and had a resin residual rate (%) exceeding the standard value of 81.8%, which enabled the benefits of resin processing to be enjoyed favorably. Furthermore, the weft bending change rate (%) was below the standard value of 110%, which enabled the papermaking machine to be easily loaded.
In the experimental example 1, the resin residual rate (%) was 88.4%, exceeding the standard value of 81.8%, and the merits of resin processing were obtained. However, the weft bending change rate (%) was 129.4%, exceeding the standard value of 110% for judging "Good", and there were some problems with the ease of loading into the papermaking machine.
In Experimental Examples 5 to 8, the resin remaining rate (%) was less than the reference value of 81.8%, and it was found that the resin was easily removed, and therefore no benefit was obtained from the resin processing.

Regarding the weight ratio, when the upper limit of the weft bending change rate (%) at which the threading ability is not affected is set to the above-mentioned reference value of 110%, the value of the weight ratio is 0.024 or more as shown in the graph of FIG.
Regarding the weight ratio, the resin residual rate (%) was set to a reference value of 81.8% for Experimental Example 0, and when the lower limit of the resin residual rate (%) was set to 81.8% or more from the viewpoint of improving the durability of the resin, the value of the weight ratio was 0.090 or less from the graph in FIG. 3.
Therefore, it was found that the weight ratio in the present invention is in the range of 0.024 to 0.090 from the viewpoints of improving ease of feeding into a papermaking machine and of optimally enjoying the benefits of resin processing.

The papermaking felt of the present invention is suitable for use as a papermaking press felt in the press part of a papermaking machine, and has excellent water-squeezing properties, making it suitable for use in the manufacturing process of various types of paper, including paper that requires a large amount of water to be squeezed out, such as paperboard.

1: Papermaking felt, 11: Base fabric layer, 13: Surface batt layer, 13A: Inner layer, 13B: Surface layer, 15: Back batt layer, 17: Surface batt fiber, 19: Polyurethane resin.

Claims (6)

This papermaking felt is characterized in that a softener is added to a resin-processed felt coated with a polyurethane resin in a weight ratio to the polyurethane resin (weight of softener per unit area/weight of polyurethane resin per unit area) in the range of 0.024 to 0.090. The papermaking felt according to claim 1, wherein the softening agent contains a surfactant. The papermaking felt according to claim 2, wherein the surfactant is a nonionic surfactant. A base fabric layer and a surface batt layer disposed on the papermaking surface side of the base fabric layer,
4. The papermaking felt according to claim 1, wherein the surface batt layer comprises a surface layer portion containing fibers to which the polyurethane resin is bonded, and the softener is applied to the surface layer portion. 5. The papermaking felt according to claim 1, wherein the resin residual rate, which indicates the resistance to resin detachment, is 81.8% or more and 100% or less, and the weft bending change rate, which indicates the ease of insertion into a papermaking machine, is 100% or more and 110% or less. 5. The papermaking felt according to claim 1, wherein the resin residual rate, which indicates the resistance to resin detachment, is 84% or more and 100% or less, and the weft bending change rate, which indicates the ease of insertion into a papermaking machine, is 100% or more and 105% or less.

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