The present invention relates to a smoothing belt for use in a closed-draw-type papermaking machine. More specifically, the present invention is concerned with a smoothing belt for transferring a wet paper web, while one surface thereof is being held by the smoothing belt, and for smoothing the surface of the wet paper web.

Papermaking machines generally include a wire part, a press part and a drier part. The wire part, the press part and the drier part are arranged in the order named along the direction in which the wet paper web is transferred.

In the papermaking machines, the wet paper web is transferred by being delivered successively to papermaking transfer tools disposed respectively in the wire part, the press part and the drier part. The wet paper web is pressed to squeeze water out, and is finally dried in the drier part.

The press part includes a press apparatus comprising a plurality of press devices which are arranged in line along the direction in which the wet paper web is transferred.

Each of the press devices comprises a pair of paper transfer felts in the form of endless belts and a press. The press has parts disposed in vertically facing relation to each other with portions of the paper transfer felts being interposed therebetween. The press may comprise a pair of rolls (i.e., a roll press) or a roll and a shoe (i.e., a shoe press).

The wet paper web is transferred by the paper transfer felts which travel in the same direction at substantially the same speed. In each of the press devices, the roll and the roll (or the roll and the shoe) press therebetween the wet paper web and the paper transfer felts, and then squeeze water out of the wet paper web and cause the paper transfer felts to absorb the water.

The press apparatus disposed in the press part includes a smoothing press apparatus in its final stage. The smoothing press apparatus presses the wet paper web transferred by a smoothing belt and also presses the smoothing belt, thereby smoothing the surface of the wet paper web.

A closed-draw-type papermaking machine incorporating a smoothing press is proposed in International Publication WO 2004/101885. According to the proposed papermaking machine, wet paper web is transferred while one surface thereof is being held by an elastic member, and the wet paper web and the elastic member are pressed by a pair of press rolls to smooth the surface of the wet paper web.

The smoothing press of the papermaking machine disclosed in International Publication WO 2004/101885 employs the elastic member which holds one surface of the wet paper web and which is pressed, together with the wet paper web, by a pair of press rolls.

The elastic member comprises a paper feeding belt, which does not have air permeability, or a surface property improving felt which is permeable to air. A rubber belt is illustrated as an example of the paper feeding belt which does not have air permeability. A felt which is slightly permeable to air with a permeability of less than 10 cm³/(Sec·cm²) is illustrated as an example of the surface property improving felt.

From EP 1 688 536 A1 a paper transporting felt is known that includes a base layer, a first batt layer formed on a wet paper side surface of the base layer, a second batt layer formed on a press side surface of the base layer, a polymeric elastic material impregnated in the base layer, the first batt layer and the second batt layer and a wet paper contacting layer which is formed on a wet paper side surface of the first batt layer so as to come into direct contact with a wet paper, and includes a flexible resin material.

EP 1 674 612 A1 discloses a paper transporting felt that includes a base layer, a first batt layer formed on a wet paper side surface of the base layer, a second batt layer formed on a roll side surface or a shoe side surface of the base layer and a wet paper contacting layer formed on a wet paper side surface of the first batt layer so as to come into direct contact with a wet paper. The wet paper contacting material is formed of a flexible resin material.

WO 2003 091498 A1 pertains to a method of manufacturing a press felt that comprises a base structure, a batt fiber layer being attached to a first web-side surface of the base structure. The structure of the press felt is compacted by treating it with a polymer material at least on the side of the first felt surface.

In recent years, there have been growing demands for papermaking processes at higher speeds and smoother wet paper web surfaces. Papermaking machines according to the background art are not necessarily good enough to meet the above demands, and remain to be improved.

The present invention has been made in view of the above problems. It is an object of the present invention to provide a smoothing belt, for use in a closed-draw-type papermaking machine, which is capable of smoothing wet paper web surfaces and of producing paper at high speeds.

The above object is achieved by a smoothing belt according to claim 1. The smoothing belt according to the invention is adapted to be used in a smoothing press apparatus disposed in a press part of a closed-draw-type papermaking machine, comprising a first press roll having a smooth surface, a second press roll having a smooth surface and disposed in facing relation to the first press roll, the smoothing belt for smoothing a surface of a wet paper web being pressed, together with the wet paper web, by the first press roll and the second press roll, and a paper transfer felt for transferring the wet paper web and for delivering same to the smoothing belt.

The smoothing belt comprises a base body, a first batt layer disposed on a wet paper web side surface of the base body, a second batt layer disposed on a roll side surface of the base body, and a porous thin film layer, disposed on a wet paper web side surface of the first batt layer, for direct contact with the wet paper web. The porous thin film layer of the smoothing belt comprises a foamed resin layer. The foamed resin layer is formed by mixing a polyurethane resin, a plurality of types of surfactants having different hydrophilic degrees, and a powder of inorganic compound with a solvent, and forming a mixture, and impregnating the first batt layer from the wet paper web side surface with the mixture to form an impregnated layer, and holding the impregnated layer in contact with water. The foamed resin layer is applied in an amount ranging from 50 g/m² to 150 g/m², and the smoothing belt has an air permeability ranging from 1 cm³/cm²/sec. to 5 cm³/cm²/sec. The foamed resin layer has preferably a wet paper web side surface polished to open air bubbles therein and make itself smooth. The surfactants preferably comprise a plurality of types of surfactants selected from anionic surfactants including carboxylate, sulfuric ester salt, sulfonate, phosphoric ester salt, etc. and polyethylene glycol-based and multiple alcohol-based nonionic surfactants, and have hydrophilic degrees by way of HLB (Hydrophile Lyophile Balance) which are different by at least 1 or greater. The powder of inorganic compound preferably comprises a mixture of one or a plurality of materials selected from sodium bicarbonate, sodium carbonate, sodium chloride and sodium nitrate.

With the smoothing press apparatus according to the above, the wet paper web is transferred by the permeable paper transfer felt, and is delivered to the smoothing belt which has the foamed resin layer on the wet paper web side surface of the first batt layer. The smoothing belt and the wet paper web are pressed by the pair of press rolls to smooth the surface of the wet paper web.

A nip pressure is applied to the wet paper web when the wet paper web is held between the paper transfer felt and the smoothing belt. The wet paper web which is transferred generally has such a characteristic that it sticks to a smoother surface and a harder surface. Therefore, the wet paper web which is transferred by the paper transfer felt is reliably delivered to the smoothing belt which has a high hardness and a smooth surface. Since the wet paper web is pressed, together with the smoothing belt, by the pair of press rolls and is held in contact with the smooth surface of the smoothing belt, the surfaces of the wet paper web are smoothed.

The smoothing belt has the foamed resin layer on the wet paper web side surface of the first batt layer. Therefore, a bulky and smooth wet paper web surface can be obtained even in high-speed papermaking processes by the shock absorbing capability (cushioning capability) of the first batt layer and the denseness of the foamed resin layer. The foamed resin layer has uniform, dense, minute, and continuous open pores. Therefore, the foamed resin layer is effective to provide a capability for attracting the wet paper web through the minute pores and also to provide a surface smoothness.

As a result, since the wet paper web can reliably be received from the paper transfer felt, the wet paper web which is obtained is bulky and has a good surface smoothness. At the same time, the foamed resin layer is highly durable even in high-speed papermaking processes.

Details of the present invention will be further clarified by referring to best modes for carrying out the present invention with reference to the accompanying drawings.

• Fig. 1 is a schematic view of a closed-draw-type papermaking machine which incorporates a smoothing press apparatus and a smoothing belt according to the present invention;
• Fig. 2 is a vertical cross-sectional view of a paper transfer felt;
• Fig. 3 is a vertical cross-sectional view of the smoothing belt;
• Fig. 4 is a view showing a surface of a foamed resin layer according to the present invention;
• Fig. 5 is a cross-sectional view of the smoothing belt according to the present invention;

Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

Fig. 1 is a schematic view of a closed-draw-type papermaking machine which incorporates a smoothing press apparatus and a smoothing belt according to the present invention,
Fig. 2 is a vertical cross-sectional view of a paper transfer felt, and Fig. 3 is a vertical cross-sectional view of the smoothing belt.

As shown in Fig. 1, the closed-draw-type papermaking machine includes a press part 11 and a drier part 13 which are arranged in line in the order named along the direction in which a wet paper web W is transferred. The press part 11 has a smoothing press apparatus 100 disposed therein.

The smoothing press apparatus 100 comprises a smoothing press 17 which is disposed as a press in a final stage in the press part 11 downstream of final water-squeezing press rolls 15A, 15B of the press part 11.

The water-squeezing press rolls 15A, 15B are disposed in facing relation to each other across a transfer path for the wet paper web W. A transfer felt 19 and a paper transfer felt 21 hold the wet paper web W between the transfer felt 19 and a paper transfer felt 21 and transfer the wet paper web W. The water-squeezing press rolls 15A, 15B hold and press the transfer felt 19 and the paper transfer felt 21, together with the wet paper web W, thereby squeezing water out of the wet paper web W.

The smoothing press 17 serves to smooth the surfaces of the wet paper web W, from which water has been squeezed, and to transfer the wet paper web W to the drier part 13. The smoothing press 17 comprises a first press roll 23 and a second press roll 25 which are disposed in facing relation to each other across the transfer path for the wet paper web W. Both the first press roll 23 and the second press roll 25 have a high surface hardness and smooth surfaces.

The paper transfer felt 21 transfers the wet paper web W and delivers the wet paper web W to a smoothing belt 27. The smoothing belt 27 runs while holding one surface of the wet paper web W. The first press roll 23 and the second press roll 25 hold and press the smoothing belt 27 and the wet paper web W between the roll 23 and the roll 25 for thereby smoothing the surfaces (both surfaces) of the wet paper web W.

A pair of transfer rolls 29A, 29B is disposed between the water-squeezing press rolls 15A, 15B and the smoothing press 17. The transfer rolls 29A, 29B generate a nip pressure by pressing the wet paper web W, which is transferred by the paper transfer felt 21, while the wet paper web W is being held between the paper transfer felt 21 and the smoothing belt 27. The transfer rolls 29A, 29B deliver the wet paper web W to the smoothing belt 27.

As shown in Fig. 2, the paper transfer felt 21 includes batt layers 43, consisting of staple fibers 47, which are intertwiningly integrated with both surfaces of a base body 41 by needle punching. Specifically, the paper transfer felt 21 is made of a permeable felt including a first batt layer 43A disposed on a wet paper web side surface and a second batt layer 43B disposed on a roll side surface.

The smoothing belt 27 used in the smoothing press apparatus 100 according to the present embodiment will be described in detail below.

As shown in Fig. 3, the smoothing belt 27 includes batt layers 43, which consist of staple fibers 47, which are intertwiningly integrated with both surfaces of a base body 41 by needle punching. Specifically, the smoothing belt 27 comprises the base body 41, a first batt layer 43A disposed on a wet paper web side surface of the base body 41, and a second batt layer 43B disposed on a roll side surface of the base body 41. A porous thin film layer 45 is disposed on a wet paper web side surface of the first batt layer 43A for direct contact with the wet paper web W.

The base body 41 is made of a woven fabric of yarns in an MD (Machine Direction) direction (in other words, a direction in which the wet paper web W runs (flows)) and yarns in a CMD (Cross Machine Direction) direction (in other words, a widthwise direction).

The base body 41 may comprise both yarns superimposed, rather than woven, or a film or a knitted material, or a spirally wound narrow ribbon. If the base body 41 comprises the film or the knitted material, then the base body 41 is made of polyamide, polyester, aromatic polyamide, aromatic polyimide, high-polymer polyethylene, or the like.

The present invention employs a suitable method of forming the porous thin film layer 45. According to this method, a polyurethane resin and a plurality of types of surfactants, having different hydrophilic degrees (HLB: Hydrophile Lyophile Balance), and a powder of inorganic compound are mixed with a solvent, so that a mixture is formed. The first batt layer 43A is impregnated from the wet paper web side surface thereof with the mixture to form an impregnated layer, which is then held in contact with water to form a foamed resin layer.

Specifically, the first batt layer 43A is impregnated from the wet paper web side surface thereof with the mixture to form an impregnated layer, so that the mixture seeps in the first batt layer 43A. The mixture is also put on the first batt layer 43A, and the first batt layer 43A is then held in contact with water to extract the solvent and the powder of inorganic compound to convert the impregnated layer into a porous foamed resin layer.

The above method is generally called a wet-type film forming method. The foamed resin layer can be formed in and on the first batt layer 43A according to this method.

The resin of the foamed resin layer, which serves as the porous thin film layer 45 according to the present invention, comprises a polyurethane resin. Particularly suitable are polyurethanes such as polyester-based polyurethane which is of high mechanical strength, polyether-based polyurethane, polycarbonate-based polyurethane, etc.

The resin of the foamed resin layer according to the present invention should preferably comprise an aqueous resin or an emulsion resin having a solid content ranging from 20 weight % to 50 weight % and a viscosity ranging from 10 Pa s (10,000 cp) to 200 Pa s (200,000 cp) at 25°C.

The foamed resin layer according to the present invention can have closed pores opened and simultaneously increase the smoothness of the surface of the smoothing belt 27 when the wet paper web side surface of the formed resin layer is polished.

According to the present invention, the surfactants for forming the mixture comprise a plurality of types of surfactants selected from anionic surfactants including carboxylate, sulfuric ester salt, sulfonate, phosphoric ester salt, etc., and polyethylene glycol-based and multiple alcohol-based nonionic surfactants.

The plurality of types of surfactants have different HLB values where the hydrophilic degrees by way of HLBs (Hydrophile Lyophile Balances) are different by at least 1 or greater.

Hydrophilic surfactants with high HLB values have a property to promote the formation of a film according to the wet-type film forming method. Conversely, lyophilic (hydrophobic) surfactants with low HLB values have a property to suppress the formation of a film according to the wet-type film forming method.

As a result, pore diameters in a certain range are obtained by using together hydrophilic surfactants with high HLB values and lyophilic surfactants with low HLB values. Specifically, the diameters of the pores of the foamed resin layer are held to a range from 20 µm to 100 µm by using a plurality of types of surfactants.

The amount of the surfactant used according to the present invention should preferably be in a range from 1 weight % to 5 weight % with respect to the amount of the resin of the foamed resin layer. The reasons are that if the amount of the surfactant is 1 weight % smaller than the amount of the resin of the foamed resin layer, then its ability to form the foamed resin layer will become lowered, and if the amount of the surfactant is 5 weight % greater than the amount of the resin of the foamed resin layer, then the mixture will be foamed excessively and will poorly impregnate the wet paper web side surface of first batt layer 43A.

The powder of inorganic compound used according to the present invention should preferably be a mixture of one or a plurality of materials selected from sodium bicarbonate, sodium carbonate, sodium chloride and sodium nitrate. The mixture is easily dissolvable in water, hardly dissolvable in a solvent, and forms good pores according to the wet-type film forming method. In particular, sodium bicarbonate is preferable as the powder of inorganic compound.

According to the wet-type film forming method of the present invention, the first batt layer 43A is impregnated from the wet paper web side surface thereof with the mixture, and an impregnated layer and a stacked layer thereon are formed. Thereafter, the impregnated layer and the stacked layer thereon are brought into contact with water to extract the solvent and the powder of inorganic compound, thereby opening the pores.

Since the region including the impregnated layer and the stacked layer thereon is held in good contact with water, the minute and continuous pores are produced. As the impregnated layer in the first batt layer 43A is late in contacting water, part of the powder of inorganic compound may remain left therein. However, any powder of inorganic compound which may remain left will not impair the function of the smoothing belt 27.

The solvent used according to the present invention should preferably be of a material capable of uniformly dispersing the foamed resin layer, the plurality of surfactants of different HLBs, and the powder of inorganic compound, and the solvent should preferably be of the material capable of keeping the mixture dispersed stably.

According to the present invention, the solvent should preferably comprise dimethylformamide (DMF) which keeps the mixture dispersed stably and which is of excellent extractability by water (i.e., miscibility with water, dissolvability into water) and which is easy to handle.

If the applied amount of foamed resin layer is smaller than 50 g/m², then the smoothing belt 27 will have high air permeability and a low hardness, so that lowering the smoothness of the wet paper web side surface of the smoothing belt 27. As a result, it will be difficult to receive the wet paper web W from the paper transfer felt, and the wet paper web W will not have a good surface smoothness.

Conversely, if the applied amount of foamed resin layer is greater than 150 g/m², then the shock absorbing capability (cushioning capability) of the first batt layer 43A of the smoothing belt 27 will be lowered, so that failing to produce a bulky wet paper web surface in high-speed papermaking processes.

Therefore, the foamed resin layer according to the present invention is applied in an amount ranging from 50 g/m² to 150 g/m². The smoothing belt 27 has an air permeability ranging from 1 cm³/cm²/sec. to 5 cm³/cm²/sec.

A sequence for forming the foamed resin layer according to the
present invention will be described by way of example below. However, the present invention is not limited to the sequence described below.

For forming the foamed resin layer which is a porous thin film layer according to the present invention, 100 parts of an aqueous polyurethane resin (having an active ingredient concentration of 30 %), 120 parts of DMF as a solvent, 1 part of EMULGEN 105 (manufactured by KAO Corporation: HLB 9.7) and 1 part of EMULGEN 106 (manufactured by KAO Corporation: HLB 10.5) as nonionic surfactants (polyoxyethylene lauryl ether) are mixed together in the order named, and are stirred with 80 parts of a powder of sodium bicarbonate being added thereto, so that a mixture is produced.

Then, as shown in Fig. 3, the mixture is applied to impregnate the first batt layer 43A from its surface and to enter in the first batt layer 43A. Furthermore, the mixture is also stacked on the first batt layer 43A. The assembly is passed through a coagulating tank filled with water, so that the impregnated layer is converted into a foamed resin layer. The size of the coagulating tank and the time during which the assembly is kept in contact with water may be appropriately determined depending on the thickness of the impregnated layer.

After the foamed resin layer is dried, the wet paper web surface of the foamed resin layer is polished with a polishing paper, a grid brush, or the like. The denseness and smoothness of the wet paper web surface of the foamed resin layer are thus adjusted.

Fig. 4 shows the surface of the foamed resin layer of the smoothing belt 27 according to the first embodiment. Fig. 5 shows a cross section of the smoothing belt 27 including the foamed resin layer. The foamed resin layer has a pore diameter ranging from 50 µm to 100 µm, and is applied in an amount of 100 g/m², and has a thickness of 500 µm, and has an air permeability of 2.3 cm³/cm²/sec.

Identical reference characters denote identical parts throughout views.

The smoothing press apparatus according to the present invention is applicable to closed-draw-type papermaking machines which are capable of performing papermaking processes at high speeds.