Patent Grant
8303775
The present invention relates to a papermaking press felt (also called “press fabric”) used in a papermaking machine. In greater detail, the present invention relates to a papermaking press felt (hereinafter also simply called “felt”) having good water squeezing capability of the wet paper web wherein, when a new papermaking press felt is installed in a papermaking machine, the period of time is shortened which is required for gradually increasing the papermaking speed from immediately after the start of the papermaking operation until the highest papermaking speed is reached (this period is called the initial warming-up period), and wherein the operation of the papermaking machine is stabilized.
Conventionally, papermaking machines in the papermaking process are generally equipped with a wire part, a press part and a dryer part to dewater wet paper webs. These parts are provided in the direction in which the wet paper web is transferred in the order of: wire part, press part and dryer part. The wet paper web is squeezed and dewatered and, at the same time, transferred while being passed from one papermaking equipment to the next provided in the wire part and press part, respectively, to be finally dried in the dryer part.
In these parts, papermaking equipment is used which corresponds to the functions of dewatering the wet paper web (wire part), squeezing water from the wet paper web (press part) and drying the wet paper web (dryer part). Moreover, the press part is generally equipped with one or more press devices arranged in series in the direction in which the wet paper web is transported.
Each press device comprises an endless felt (closed type) or an open-ended felt that has been formed into an endless felt by connecting it in the papermaking machine. Each press device also comprises a pair of rolls, which face each other (i.e. a roll press), or a roll and a shoe, which face each other (i.e. a shoe press); the wet paper web is placed on the felt, and, while it is moving together with the felt in the wet paper web conveyance direction, moisture is squeezed from the wet paper web by pressing the wet paper web together with the felt in the roll press or in the shoe press; the moisture pressed from the wet paper web is continuously absorbed by the felt or passes through the felt to be drained to the outside of the felt.
Hereinafter, one example of the press part of a papermaking machine will be described in detail with reference to
The above-mentioned transfer twinbar type papermaking machines use a plurality of papermaking felts (4 felts in
The above-mentioned felts are made from a reinforcing fiber base material 5 and batt layers 6, 7 as shown in
Of the above-mentioned felt function, particularly the function of squeezing water from the wet paper web is considered to be important. The wet paper web is pressure squeezed together with the felt by passing the pressure position of the roll press or the shoe press; and after the moisture of the wet paper web has been transferred to the felt, it is drained outside the felt by the suction force of a suction box or the pressure of a squeeze press; therefore, the water permeability for assuring a suitable void volume in the felt and the ability to maintain compressibility and recoverability are considered to be important properties.
The above-mentioned suitable void volume is the void volume of a felt when the highest papermaking speed has been reached after it has been gradually increased. In other words, from the viewpoint of productivity, it is important that the operating speed of a papermaking machine rapidly reaches the highest papermaking speed as soon as possible after starting to make paper with a new felt. The period until the highest papermaking speed is reached (the initial warming-up period) differs according to the operating conditions of the papermaking machine; however, in general one to two days, at most five days, are required. It is particularly important to shorten the initial warming-up period of the above-mentioned felts with wet paper conveyance methods such as the no-draw straight-through method, of which the Tandem-Nipco Flex Press and OptiPress papermaking machines are representative examples, because high operating speeds are used.
Strategies to make the felt thinner and increase the felt density by applying pressure after the felt has been made have been used to shorten the initial warming-up period of these felts. There are also cases in which the felt is brought into contact with a roll that has been heated by a heating medium in order to increase the pressing effect of the felt. Due to the operating and the effect of a high density felt it is possible to facilitate the transfer of the pressing force received by the felt in the press part to the wet paper web by reducing the void volume in the felt.
In JP, T, 2005-524002 (Patent document 1), a felt and a production method are disclosed in which the void volume of the felt surface is reduced and the density is increased by polishing the felt surface after the felt front side (wet paper web carrying side) has been treated with a polymer substance. A papermaking felt of this structure is compacted as a new felt from the beginning (with an increased density); therefore, when the felt is used in a papermaking machine, the initial warming-up period is shortened.
Nevertheless, even though a papermaking felt using a polymer of the polymer substances mentioned in Patent document 1, which are polyurethane, polycarbonate urethane, polyacrylate, acryl resin, epoxy resin, phenol resin or mixed polymers thereof, can be compacted due to the adhesive force and the coagulating force of the polymers, stiffness is given to the felt as a whole. When the stiffness of a felt increases, the compressibility and recoverability under the press of a papermaking machine is suppressed; therefore, there is a loss of the wet paper web water squeezing performance; moreover, when the papermaking felt is placed in a papermaking machine, due to the felt stiffness, it is difficult to place the felt which has to be manually inserted in the narrow spaces between the rolls inside the papermaking machine.
Furthermore, US, A1, No. 2009/0163104 (Patent document 2) discloses a press fabric (felt), wherein the felt surface is coated with a polymer dispersion liquid which, by drying, bridges the batt fiber spaces by covering them with a polymer film (membrane); moreover, by covering the surroundings of the batt fibers (the polymer layer thickness is 0.05 mm to 1.5 mm), the polymer membrane adjusts the void volume and the density of the felt surface layer without separating from the batt fibers. Examples of polymers include polyurethane elastomers, polyether-polyamide elastomers, engineering polyamides (polyamide 11, polyamide 12, polyamide 6.12, or the like). The blending amount of the polymers in relation to the felt weight is not disclosed by specific figures.
This felt is characterized in that the air-permeability is suitably adjusted and in that it can be subjected to washing by a high pressure water jet. Nevertheless, even though the initial warming-up period of the felt can be shortened, there is the disadvantage that, since the void volume is reduced and the overall thickness of the felt is thinner, the felt is flattened by the press pressure repeatedly received during use and rapidly arrives at the limit of the thickness that can be used, and the period during which the wet paper web can be sufficiently squeezed (felt life) is shortened.
Compared to conventional felts, wherein the void volume for transferring mechanical pressure and hydraulic pressure to the squeezed wet paper web is poor, the object of the present invention is to provide a felt, wherein a suitable void volume for the initial warming-up period can be ensured from the start of use, and wherein the initial warming-up period of the felt can be shortened to four days or less. Moreover, the present invention also provides a felt, wherein, if the thickness deformation resistance of the felt is reduced, pressure density tends to increase when pressure is applied by the press rolls or the like, recoverability after pressing is high, accumulation of dirt and excessive flattening are less likely to occur, and water permeability and compressibility can be maintained for a long time. To provide such a felt is also an object of the present invention.
Specifically, the present invention provides a papermaking press felt, wherein, by including a polymeric elastomer having suitable flexibility and good compressibility and recoverability, a suitable void volume can be assured in the felt, water permeability and compressibility can be maintained for a long time, the initial warming-up period of the papermaking press felt is shorter than that of a conventional felt, the felt life is long, and water squeezing capability is good.
The invention according to claim 1 provides a papermaking press felt comprising a reinforcing fiber base material and batt layers provided on both the wet paper web carrying side and the press roll side of said reinforcing fiber base material or a batt layer provided only on the wet paper web carrying side of said reinforcing fiber base material; wherein a polymeric elastomer is dispersedly attached to the batt layer inside the felt on the wet paper web carrying side of the felt; wherein, when said polymeric elastomer is in the form of a film and when measured at a room temperature of 20° C. and a relative humidity of 65%, the 100% modulus value of the film is 1 to 100 kg/cm2, the residual strain after 100% elongation is 30% or less, and the attached amount of polymeric elastomers is 0.5 to 20 wt. % of the papermaking press felt weight.
The invention according to claim 2 provides a papermaking felt according to claim 1; wherein the polymeric elastomer comprises one or more members selected from the group consisting of natural rubber, isoprene rubber, 1,4-butadiene rubber, 1,2-butadiene rubber, styrene-butadiene copolymer rubber, chloroprene rubber, nitrile rubber, butyl rubber, ethylene-propylene copolymer rubber, ethylene-propylene-butadiene copolymer rubber, ethylene-propylene-ethylidene norbornene copolymer rubber, chlorosulfonated polyethylene elastomer, acrylic rubber, epichlorohydrine rubber, polysulfide rubber, silicone rubber, fluoro rubber, polyurethane elastomer, polyolefin elastomer in which the above-mentioned rubbers or ethylene-vinyl acetate copolymers have been blended with polyethylene, polyamide elastomer, polyester elastomer, polystyrene elastomers selected from the group consisting of styrene-butadiene-styrene-copolymer elastomer, styrene-ethylene-butylene-styrene copolymer elastomer, acrylonitrile-butadiene-styrene copolymer elastomer or hydrogenated products thereof, and plasticized vinyl chloride resin.
With the papermaking press felt according to the present invention, a suitable void volume for the initial warming-up period can be ensured from the start of use, and the initial warming-up period can be shortened. Moreover, the present invention also provides a felt, wherein, if the thickness deformation resistance of the felt is reduced, pressure density tends to increase when pressure is applied by the press rolls or the like, recoverability after pressing is high, accumulation of dirt and excessive flattening are less likely to occur, and water permeability and compressibility can be maintained for a long time. By means of such a felt, it is possible to obtain a papermaking press felt having a good balance of the fundamental felt functions such as a maintenance of the water squeezing capability of the felt, or the like.
Hereinafter, the present invention will be described in detail with reference to the drawings.
The present invention is a press felt for use in the press part shown in
The reinforcing fiber base material 5 generally is a woven fabric woven from a CMD (Cross Machine Direction) yarn and a MD (Machine Direction) yarn by a loom or the like; however, a lattice material obtained by overlapping rows of CMD yarns and MD yarns without weaving may also be used.
Examples of materials for the reinforcing fiber base material, which is made from CMD and MD yarns, and for the batt include polyesters (polyethylene terephthalate, polybutylene terephthalate, or the like), engineering polyamides (polyamide 11, polyamide 12, polyamide 6.12, or the like), aromatic polyamides (aramide), polyvinylidene difluoride, polypropylene, polyether-polyester ketone, polytetrafluoroethylene, polyethylene, cotton, wool, metal, or the like.
Examples of materials for the polymeric elastomer include one or more members selected from the group consisting of natural rubber, isoprene rubber, 1,4-butadiene rubber, 1,2-butadiene rubber, styrene-butadiene copolymer rubber, chloroprene rubber, nitrile rubber, butyl rubber, ethylene-propylene copolymer rubber, ethylene-propylene-butadiene copolymer rubber, ethylene-propylene-ethylidene norbornene copolymer rubber, chlorosulfonated polyethylene elastomer, acrylic rubber, epichlorohydrine rubber, polysulfide rubber, silicone rubber, fluoro rubber, polyurethane elastomer, polyolefin elastomer in which the above-mentioned rubbers or ethylene-vinyl acetate copolymers have been blended with polyethylene, polyamide elastomer, polyester elastomer, polystyrene elastomers selected from the group consisting of styrene-butadiene-styrene-copolymer elastomer, styrene-ethylene-butylene-styrene copolymer elastomer, acrylonitrile-butadiene-styrene copolymer elastomer or hydrogenated products thereof, and plasticized vinyl chloride resin.
In both tests, a polymeric elastomer specimen 41 was a film of 10 mm width, 120 mm length (including 40 mm for the grip on each side), 40 mm grip distance, and 0.5 mm thickness. The tests were performed at a room temperature of 20° C. and a relative humidity of 65%.
The specimen 41 was set in grips 42, stretched to an elongation percentage of 110% at a stretching speed of 200 mm/min, and the stress (kg/cm2) at an elongation percentage of 100% was taken as the 100% modulus value.
Further, the specimen was stretched to an elongation percentage of 100%, the elongation was reversed at the same speed the moment after reaching the elongation percentage of 100%, and the percentage of elongation when the stress reached 0 kg/cm2 was taken as the residual strain after an elongation of 100%.
The polymeric elastomer may be foamed or partially cross-linked. It may further comprise (an) inorganic filler(s) and (a) thermal stabilizer(s). Examples of foaming agents include ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, sodium hydrogencarbonate, or the like and examples of inorganic fillers include titanium oxide, kaolin, clay, talc, diatomaceous earth, calcium carbonate, calcium silicate, magnesium silicate, fused silica, mica, or the like.
The polymeric elastomer is attached to the short fibers (staple fibers) constituting the batt by dispersing fragments with 5 μm to 2 mm thickness. It can also be envisioned to use the short fibers (staple fibers) as the center which becomes a core around which the polymeric elastomer is coated in the shape of a sheath with a thickness of 1 to 40 μm. When the polymeric elastomer is attached to the batt fibers in the shape of fragments and/or in the shape of a sheath formed around a core, the felt has good compressibility, recoverability and water squeezing capability; there is moreover the added advantage that, during the period of use of the felt, these characteristics can be maintained for a long time.
In view of felt compressibility, recoverability and water squeezing capability, the 100% modulus of the polymeric elastomer film is 1 to 100 kg/cm2, and preferably 70 kg/cm2 or less. Also in view of felt compressibility, recoverability and water squeezing capability, the residual strain after 100% elongation is 30% or less, and preferably 20% or less.
The amount of attached polymeric elastomer is 0.5 to 20 wt. % of the papermaking press felt weight. When the amount is less than 0.5 wt. % of the felt weight, it is not possible to maintain water permeability and compressibility of the felt for a long time, which results in a deterioration of the felt durability. If, on the other hand, the amount is more than 20 wt. % of the felt weight, felt stiffness is too great and the thickness deformation resistance cannot be reduced, the pressure density does not easily increase when pressure is applied by the press rolls or the like, and the recoverability after pressing can decline.
The location in which the polymeric elastomer is included in the papermaking felt is not particularly limited; however, preferably it is included in the region comprising the reinforcing fiber base material and the wet paper web carrying side batt layer (front batt layer). Specifically, it can be included in the wet paper web carrying side batt layer only, in the region extending from the wet paper web carrying side batt layer to the press roll side batt layer (rear batt layer), in the region from the wet paper web carrying side batt layer to the reinforcing fiber base material, or in the region from the press roll side batt layer to the reinforcing fiber base material.
The polymeric elastomer can be attached(bonded) to the short fibers (staple fibers) constituting the batt by coating/impregnating on the felt surface by means of coating, spraying, blade coating, or the like and, thereafter, drying a solvent dispersion liquid of the polymeric elastomer.
The papermaking press felt according to the present invention should include a void volume (air permeability: 2 to 50 cc/cm2 sec., 125 Pa) that enables the felt to transmit mechanical and hydraulic pressure to the squeezed wet paper web. In other words, the felt should maintain a fixed void volume from the initial warming-up period to the highest papermaking speed region, in which the operating speed has stabilized, and until the end of service is reached.
The degree of felt hardness (stiffness) of the papermaking press felt according to the present invention is preferably such that the felt is easily deformed when pressure is applied by the press roll, or the like, and the felt density is increased to its highest limit. To achieve this, the polymeric elastomer included in the felt has an elasticity expressed by the above-mentioned 100% modulus and the residual strain after 100% elongation.
Hereinafter, the present invention will be described with reference to the Examples and Comparative Examples. The present invention is, however, not limited to these Examples.
The basic configuration of the felts used in the Examples and Comparative Examples was as follows:
After making the felt by stacking and intertwiningly integrating the rear-side batt fibers and the front-side batt fibers with the reinforcing fiber base material by needling, the polymeric elastomer was spray coated from the front side of the felt, dried at 105° C., and, thereafter, cured at 140° C.
The polymeric elastomer resins shown in Table 1 were applied under the conditions given in the same Table.
1)Daiichi Kogyo Seiyaku Co., Ltd.
2)Bayer Japan Co., Ltd.
3)Nippon A & L Inc.
4)Shinetsu Chemical Co., Ltd.
5)Toho Chemical Industry Co., Ltd.
6)Nicca Chemical Co., Ltd.
7)ADEKA Corporation
The press tester shown in
When the press tester shown in
The squeezing test of the wet paper web was performed with the following press tester conditions and formulae:
The lower the moisture content of the wet paper web after pressing, the better is the water squeezing capability of the felt. In the papermaking sector it is understood that, even if the difference in moisture content of the wet paper web after squeezing is only 1%, there is a big impact on the amount of thermal energy required in the paper drying process after pressing.
The compression test of the felt was performed with the following press tester conditions and formulae:
In the press tester:
The results of these tests are shown in Table 2.
Table 2 shows that the smaller the value of the moisture content of the wet paper web after pressing, the better is the water squeezing capability, and the bigger the values of compression rate during pressing (corresponding to the compressibility of the felt) and the thickness maintaining rate before and after the pressing (corresponding to the recoverability of the felt after compression), the better is the ability to maintain elasticity.
Examples 1 to 8 show that the capability to squeeze water from a wet paper web as well as the felt compressibility and recoverability and the maintaining properties thereof are improved according to a kind of a polymeric elastomer included.
The papermaking felt obtained according to the present invention can improve the capability to squeeze water from a wet paper web throughout its period of use including the initial warming-up period until the highest papermaking speed is reached, at which stable production of a papermaking machine is possible; and, compared to felts like those in Comparative Example 2 in which a high modulus resin was used, a felt according to the present invention can be easily installed in a papermaking machine.
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