Patent Publication Number: US-2021164167-A1

Title: Fiber assembly-forming method, fiber assembly-forming apparatus, and sheet

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-216462, filed Nov. 29, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a fiber assembly-forming method, a fiber assembly-forming apparatus, and a sheet. 
     2. Related Art 
     Dry fiber assembly-forming apparatuses using substantially no water for the purpose of size reduction and energy saving have been proposed. For example, JP-A-2012-144826 describes that, in a dry paper recycling apparatus, the paper strength is increased in such a manner that water containing a paper strength additive such as starch or polyvinyl alcohol (PVA) is sprayed from a water sprayer on deposits of deinked fibers deposited on a mesh belt. 
     However, in the manner described in JP-A-2012-144826, while the deposits of the fibers are being transported on the mesh belt, the fibers rise from the mesh belt in the form of paper dust to clog nozzles of the water sprayer in some cases. Therefore, it is difficult to uniformly spray the paper strength additive on the deposits and formed paper is variable in strength. 
     SUMMARY 
     According to an aspect of the present disclosure, a fiber assembly-forming method includes a step of providing a first feedstock containing fibers with a binding material bonding the fibers to each other, a step of forming disintegrated matter by disintegrating the first feedstock provided with the binding material, a step of depositing the disintegrated matter, and a step of heating the deposited disintegrated matter. 
     In the fiber assembly-forming method, in the step of providing the binding material, the binding material may be applied to a surface of the first feedstock. 
     In the fiber assembly-forming method, in the step of forming the disintegrated matter, the first feedstock provided with the binding material and a second feedstock unprovided with the binding material may be disintegrated. 
     According to an aspect of the present disclosure, a fiber assembly-forming method includes a step of preparing material containing fibers and a binding material bonding the fibers to each other, a step of forming disintegrated matter by disintegrating the material, a step of depositing the disintegrated matter, and a step of heating the deposited disintegrated matter. In the step of preparing the material, the material is prepared such that the binding material accounts for 6.0% by mass or more of the fibers. 
     In the fiber assembly-forming method, in the step of preparing the material, the material may contain a resinous substance made of the binding material. 
     In the fiber assembly-forming method, the binding material may be a thermoplastic resin or a thermosetting resin and the glass transition temperature of the binding material may be 45° C. or higher. 
     According to an aspect of the present disclosure, a fiber assembly-forming apparatus includes a provision section providing a first feedstock containing fibers with a binding material bonding the fibers to each other, a disintegration section disintegrating the first feedstock provided with the binding material to form disintegrated matter, a deposition section depositing the disintegrated matter, and a heating portion heating the deposited disintegrated matter. 
     In the fiber assembly-forming apparatus, the provision section may include a roller applying the binding material to the first feedstock. 
     In the fiber assembly-forming apparatus, the provision section may include a spray discharging the binding material to the first feedstock. 
     In the fiber assembly-forming apparatus, the disintegration section may disintegrate the first feedstock provided with the binding material and a second feedstock unprovided with the binding material. 
     In the fiber assembly-forming apparatus, the binding material may be a thermoplastic resin or a thermosetting resin and the glass transition temperature of the binding material may be 45° C. or higher. 
     According to an aspect of the present disclosure, a sheet contains fibers and resin. The resin may be contained so as to account for 6.0% by mass or more of the fibers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a fiber assembly-forming apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a flowchart illustrating a fiber assembly-forming method according to an embodiment of the present disclosure. 
         FIG. 3  is a flowchart illustrating the fiber assembly-forming method. 
         FIG. 4  is a flowchart illustrating the fiber assembly-forming method. 
         FIG. 5  is a flowchart illustrating a modification of the fiber assembly-forming method. 
         FIG. 6  is a flowchart illustrating the modification of the fiber assembly-forming method. 
         FIG. 7  is an illustration of a sheet used for evaluation. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Preferred embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. The embodiments below do not unfairly limit the scope of the present disclosure that is recited in the claims. All of components described below are not necessarily essential elements of the present disclosure. 
     1. Fiber Assembly-Forming Apparatus 
     1.1. Overall Configuration 
     A fiber assembly-forming apparatus  100  according to an embodiment of the present disclosure is described with reference to a drawing.  FIG. 1  is a schematic view of the fiber assembly-forming apparatus  100 . 
     As shown in  FIG. 1 , the fiber assembly-forming apparatus  100  includes, for example, a supply section  10 , a rough crushing section  12 , a disintegration section  20 , a screening section  40 , a first web-forming section  45 , a rotator  49 , a deposition section  60 , a second web-forming section  70 , a sheet-forming section  80 , a cutting section  90 , and a provision section  110 . 
     The supply section  10  supplies a feedstock to the rough crushing section  12 . The supply section  10  is, for example, an automatic input section for continuously inputting the feedstock to the rough crushing section  12 . The feedstock supplied by the supply section  10  contains, for example, fibers of waste paper, pulp sheets, or the like. 
     The provision section  110  provides the feedstock supplied from the supply section  10  with a binding material bonding the fibers to each other. Details of the provision section  110  are described below. 
     The rough crushing section  12  cuts the feedstock supplied by the supply section  10  into small pieces in gas such as air. The small pieces are, for example, several centimeters square pieces. In an illustrated example, the rough crushing section  12  includes rough crushing blades  14  and can cut the input feedstock with the rough crushing blades  14 . The rough crushing section  12  used is, for example, a shredder. The feedstock cut by the rough crushing section  12  is received in a hopper  1  and is then transferred to the disintegration section  20  through a pipe  2 . 
     The disintegration section  20  disintegrates the feedstock cut by the rough crushing section  12 . The term “disintegrate” as used herein means that a feedstock containing a plurality of bonded fibers is disentangled into the fibers one by one. The disintegration section  20  has the function of removing substances, such as resin particles, ink, toner, and a bleeding inhibitor, adhering to the feedstock from fibers. 
     One having passed through the disintegration section  20  is referred to as “disintegrated matter”. The “disintegrated matter” contains disentangled disintegrated fibers and also contains resin particles separated from fibers when the fibers are disintegrated, a colorant such as ink or toner, or an additive such as a bleeding inhibitor or a paper strength additive in some cases. Disentangled disintegrated matter is string-shaped. The disentangled disintegrated matter may be present in such a state that the disentangled disintegrated matter is not intertwined with other disentangled fibers, that is, such a state that the disentangled disintegrated matter is independent or in such a state that the disentangled disintegrated matter is intertwined with other disentangled fibers to form aggregates, that is, such a state that the disentangled disintegrated matter forms lumps. 
     The disintegration section  20  performs disintegration in a dry mode. Herein, performing treatment such as disintegration in gas, such as air, rather than liquid is referred to as a dry mode. The disintegration section  20  used is, for example, an impeller mill. The disintegration section  20  has the function of generating such an air flow that sucks the feedstock and discharges the disintegrated matter. This enables the disintegration section  20  to suck the feedstock from an inlet  22  by means of an air flow generated by the disintegration section  20  together with the air flow, to disintegrate the feedstock, and to transport the disintegrated matter to an outlet  24 . The disintegrated matter having passed through the disintegration section  20  is transferred to the screening section  40  through a pipe  3 . Incidentally, an air flow for transporting the disintegrated matter from the disintegration section  20  to the screening section  40  may be the air flow generated by the disintegration section  20  or an air flow generated by an air flow generator such as a blower. 
     The screening section  40  imports the disintegrated matter having passed through the disintegration section  20  from an inlet  42  and screens the disintegrated matter depending on the length of fibers. The screening section  40  includes a drum portion  41  and a housing portion  43  that houses the drum portion  41 . The drum portion  41  used is, for example, a sieve. The drum portion  41  includes a net and can separate fibers or particles smaller than the size of openings of the net, that is, first screened fractions passing through the net, and fibers, undisintegrated pieces, or lumps larger than the size of the openings of the net, that is, second screened fractions not passing through the net. For example, the first screened fractions are transferred to the deposition section  60  through a pipe  7 . The second screened fractions are returned to the disintegration section  20  from an outlet  44  through a pipe  8 . In particular, the drum portion  41  is a cylindrical sieve rotationally driven with a motor. The net of the drum portion  41  used is, for example, a metal gauze, an expanded metal obtained by expanding a slit metal plate, or a punching metal obtained by forming holes in a metal plate with a press or the like. 
     The first web-forming section  45  transports the first screened fractions having passed through the screening section  40  to the pipe  7 . The first web-forming section  45  includes a mesh belt  46 , tension rollers  47 , and a suction mechanism  48 . 
     The suction mechanism  48  can suck the first screened fractions which have passed through openings of the screening section  40  and which have been distributed in air onto the mesh belt  46 . The first screened fractions are deposited on the moving mesh belt  46  to form a web V. The basic configuration of the mesh belt  46 , the tension rollers  47 , and the suction mechanism  48  is substantially the same as that of a mesh belt  72 , tension rollers  74 , and suction mechanism  76  of the second web-forming section  70  as described below. 
     The web V passes through the screening section  40  and the first web-forming section  45  and is thereby formed in such a state that the web V contains a lot of air, is soft, and is bulgy. The web V deposited on the mesh belt  46  is input to the pipe  7  and is transported to the deposition section  60 . 
     The rotator  49  can cut the web V. In the illustrated example, the rotator  49  includes a base portion  49   a  and protruding portions  49   b  protruding from the base portion  49   a.  The protruding portions  49   b  have, for example, a plate shape. In the illustrated example, the number of the protruding portions  49   b  is four and the four protruding portions  49   b  are arranged at equal intervals. The base portion  49   a  rotates in a direction R and therefore the protruding portions  49   b  can rotate about the base portion  49   a . Cutting the web V by the rotator  49  enables, for example, the change in amount of the disintegrated matter supplied to the deposition section  60  per unit time to be reduced. 
     The rotator  49  is placed in the vicinity of the first web-forming section  45 . In the illustrated example, the rotator  49  is placed in the vicinity of a tension roller  47   a  located downstream in the path of the web V. The rotator  49  is placed at a position where the protruding portions  49   b  can come into contact with the web V and do not come into contact with the mesh belt  46 , on which the web V is deposited. This enables the mesh belt  46  to be inhibited from being worn by the protruding portions  49   b.  The shortest distance between each protruding portion  49   b  and the mesh belt  46  is, for example, 0.05 mm to 0.5 mm. This is the distance that the web V can be cut without damaging the mesh belt  46 . 
     The deposition section  60  imports the first screened fractions from an inlet  62 , disentangles the intertwined disintegrated matter, and sprays the disentangled disintegrated matter such that the disentangled disintegrated matter is dispersed in air. The deposition section  60  can uniformly deposit the first screened fractions on the second web-forming section  70 . 
     The deposition section  60  includes a drum portion  61  and a housing portion  63  that houses the drum portion  61 . The drum portion  61  used is, for example, a rotary cylindrical sieve. The drum portion  61  includes a net and sprays fibers or particles smaller than the size of openings of the net. The configuration of the drum portion  61  is the same as, for example, the configuration of the drum portion  41 . 
     Incidentally, the “sieve” of the drum portion  61  need not have the function of screening a specific target. That is, the “sieve” used as the drum portion  61  means one equipped with a net. The drum portion  61  may spray all of the disintegrated matter imported into the drum portion  61 . 
     The second web-forming section  70  deposits a passing object having passed through the deposition section  60  to form a web W. The second web-forming section  70  includes, for example, a mesh belt  72 , tension rollers  74 , and a suction mechanism  76 . 
     The mesh belt  72  allows the passing object having passed through an opening of the deposition section  60  to be deposited thereon while moving. The mesh belt  72  is tensioned by the tension rollers  74  and is configured such that the passing object is unlikely to pass through the mesh belt  72  and air passes through the mesh belt  72 . The mesh belt  72  moves because the tension rollers  74  rotate. The passing object having passed through the deposition section  60  is deposited on the mesh belt  72  that is continuously moving, whereby the web W is formed on the mesh belt  72 . 
     The suction mechanism  76  is placed under the mesh belt  72 . The suction mechanism  76  can generate an air flow directed downward. The disintegrated matter dispersed in air by the deposition section  60  can be sucked onto the mesh belt  72  by the suction mechanism  76 . This enables the discharge rate from the deposition section  60  to be increased. Furthermore, a down-flow can be formed in the fall path of the disintegrated matter by the suction mechanism  76 , thereby enabling the disintegrated matter and an additive to be prevented from being intertwined during falling. 
     As described above, passing through the deposition section  60  and the second web-forming section  70  allows the web W to be formed in such a state that the web W contains a lot of air, is soft, and is bulgy. The web W deposited on the mesh belt  72  is transported to the sheet-forming section  80 . 
     The sheet-forming section  80  pressurizes and heats the web W deposited on the mesh belt  72  to form a sheet S. In the sheet-forming section  80 , heat is applied to a mixture of the disintegrated matter and binding material mixed together in the web W, thereby enabling a plurality of fibers in the mixture to be bonded to each other with the binding material. 
     The sheet-forming section  80  includes a pressurizing portion  82  pressurizing the web W and a heating portion  84  heating the web W pressurized by the pressurizing portion  82 . The pressurizing portion  82  is composed of a pair of calender rollers  85  and applies a pressure to the web W. Pressurizing the web W reduces the thickness of the web W and increases the bulk density of the web W. The heating portion  84  used is, for example, a heating roller, a hot press molding machine, a hotplate, a hot air blower, an infrared heater, or a flash-fusing system. In the illustrated example, the heating portion  84  includes a pair of heating rollers  86 . Composing the heating portion  84  using the heating rollers  86 , rather than composing the heating portion  84  as a plate-like press machine, enables the sheet S to be formed in such a manner that the web W is continuously transported. The calender rollers  85  and the heating rollers  86  are arranged such that, for example, the axes of rotation thereof are parallel. The calender rollers  85  can apply a higher pressure to the web W than the pressure applied to the web W by the heating rollers  86 . The number of the calender rollers  85  and the heating rollers  86  is not particularly limited. 
     The cutting section  90  cuts the sheet S formed by the sheet-forming section  80 . In the illustrated example, the cutting section  90  includes a first cutting portion  92  cutting the sheet S in a direction crossing the transport direction of the sheet S and a second cutting portion  94  cutting the sheet S in a direction parallel to the transport direction thereof. The second cutting portion  94  cuts the sheet S having passed through, for example, the first cutting portion  92 . 
     The above allows the sheet S to be formed such that the sheet S is a single sheet with a predetermined size. The cut sheet S, which is such a single sheet, is discharged to a discharge section  96 . 
     1.2. Provision Section 
     The provision section  110  provides the feedstock, which contains the fibers, with the binding material, which bonds the fibers to each other. The feedstock, which contains the fibers, is, for example, waste paper. In the illustrated example, the provision section  110  provides the feedstock which is supplied from the supply section  10  and which is roughly uncrushed by the rough crushing section  12  with the binding material. The length of the fibers contained in the feedstock is, for example, 0.6 mm to 3.0 mm as length-weighted mean length. The length-weighted mean length of the fibers can be measured in accordance with ISO 16065-2:2007 using L&amp;W Fiber Tester CODE 912. 
     The provision section  110  may apply liquid containing the binding material to a surface of the feedstock. The provision section  110  may include a roller applying the binding material to the feedstock. Alternatively, the provision section  110  may include a spray discharging the binding material to the feedstock. Alternatively, the provision section  110  may be an ink jet head discharging the binding material to the feedstock. 
     The binding material, which is provided from the provision section  110 , may be dissolved or dispersed in liquid. The liquid is preferably emulsion in which the binding material is dispersed. The binding material is preferably nano-sized. When the liquid is the emulsion, the viscosity of the liquid can be reduced, the liquid can penetrate to the inside of a fiber assembly, and the bonding force can be further enhanced, which is preferable. When the binding material is nano-sized, for example, nozzle clogging, which occurs in sprays and ink jet heads, is likely to be avoided, which is preferable. 
     The binding material, which is provided from the provision section  110 , is, for example, a thermoplastic resin or a thermosetting resin. 
     Examples of the thermoplastic resin include an acrylonitrile-styrene (AS) resin, an acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, polyethylene, polyvinyl chloride, polystyrene, an acrylic resin, a polyester resin, polyethylene terephthalate, polyphenylene ether, polybutylene terephthalate, nylon, polyamide, polycarbonate, polyacetal, polyphenylene sulfide, and polyether ether ketone. These resins may be used alone or in combination and may be copolymerized or modified. Examples of a family of these resins include styrenic resins, acrylic resins, styrene-acrylic copolymers, olefinic resins, vinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. 
     Examples of the thermosetting resin include a phenol resin, an epoxy resin, a melamine resin, a urea resin, an unsaturated polyester resin, an alkyd resin, polyurethane, and a thermosetting polyimide resin. 
     The glass transition temperature of the thermoplastic resin and the thermosetting resin is preferably high from the viewpoint of high-temperature resistance and is in an appropriate range in consideration of reasons such as energy saving in terms of manufacture. The glass transition temperature is appropriately selected depending on, for example, the thickness or heat treatment temperature of the sheet S. The glass transition temperature is preferably 45° C. or higher, more preferably 50° C. or higher, and further more preferably 60° C. or higher. The glass transition temperature is preferably 130° C. or less and more preferably 100° C. or lower. When the glass transition temperature is 45° C. or higher, the softening of the binding material at high temperature is suppressed and the obtained sheet S has high paper strength. Furthermore, when the glass transition temperature is 60° C. or higher, it can be suppressed that the binding material is softened by the heat of the disintegration section  20  to adhere to the disintegration section  20  in the course of disintegrating the feedstock provided with the binding material in the disintegration section  20 . The binding material is preferably resin having a melting point higher than or equal to the temperature of the disintegration section  20 . The melting point of the binding material is preferably 220° C. or lower. 
     The provision section  110  provides the feedstock with the binding material such that the binding material accounts for 6.0% by mass or more of the fibers contained in the feedstock, preferably 9.0% by mass or more. When the binding material accounts for 6.0% by mass or more of the fibers, the paper strength of the sheet S can be enhanced. The sheet S contains the binding material such that the binding material accounts for, for example, 6.0% by mass or more of the fibers. 
     The provision section  110  may provide the feedstock with an additive such as a flame retardant, a perfume, an antistatic agent, or an ultraviolet absorber in addition to the binding material. If the additive is provided from the provision section  110  together with the binding material, a cartridge for providing the additive need not be used. Therefore, the downsizing of an apparatus is possible. The provision section  110  does not provide the feedstock with any colorant. 
     When the feedstock is undisintegrated by the disintegration section  20 , the provision section  110  may provide the feedstock roughly crushed by the rough crushing section  12  with the binding material. This is not shown. In this case, the provision section  110  is preferably a spray. In a case where the binding material is applied to the feedstock using a roller, the provision section  110  preferably provides the feedstock roughly uncrushed by the rough crushing section  12  with the binding material. 
     The provision section  110  may provide the binding material to the feedstock in the form of powder instead of the liquid containing the binding material. However, when the binding material is powder, the binding material is preferably fixed to the feedstock by heat for the purpose of suppressing the fall of the binding material from the feedstock. For example, the binding material may be charged into the disintegration section  20  such that the binding material is fixed to the feedstock by the heat of the disintegration section  20 . 
     1.3. Effects 
     The fiber assembly-forming apparatus  100  has, for example, effects below. 
     The fiber assembly-forming apparatus  100  includes, the provision section  110 , which provides the feedstock containing the fibers with the binding material bonding the fibers to each other; the disintegration section  20 , which disintegrates the feedstock provided with the binding material to form the disintegrated matter; the deposition section  60 , which deposits the disintegrated matter; and the heating portion  84 , which heat the deposited disintegrated matter. Therefore, in the fiber assembly-forming apparatus  100 , the binding material need not be provided to the disintegrated matter deposited by the deposition section  60  and therefore there is no possibility that the fibers rise from the mesh belt  46  in the form of paper dust to clog a nozzle of the provision section  110 . Thus, the sheet S (fiber assembly) can be formed so as to have little variation in paper strength. 
     Furthermore, in the fiber assembly-forming apparatus  100 , the disintegration section  20  has the function of mixing the feedstock and the binding material together. Therefore, even if the binding material is unevenly distributed at the point in time when the binding material is provided to the feedstock, the uneven distribution of the binding material can be reduced by the disintegration section  20  and the sheet S can be formed so as to have little variation in paper strength. Thus, if the nozzle of the provision section  110  is partly clogged, the binding material can be provided without regard to the unevenness of the binding material. Furthermore, since a mixing section mixing the feedstock and the binding material together is not necessary, the downsizing of an apparatus is possible. 
     In the fiber assembly-forming apparatus  100 , the provision section  110  may include a roller applying the binding material to the feedstock. Therefore, in the fiber assembly-forming apparatus  100 , the binding material can be uniformly applied to the feedstock. The roller can readily apply the binding material to the feedstock without consideration of the viscosity of the liquid containing the binding material as compared to sprays and ink jet heads. 
     In the fiber assembly-forming apparatus  100 , the binding material may be the thermoplastic resin or the thermosetting resin and the glass transition temperature of the binding material may be 45° C. or higher. Therefore, in the fiber assembly-forming apparatus  100 , the binding material can be readily melted by the heating portion  84 . 
     2. Fiber Assembly-Forming Method 
     Next, a fiber assembly-forming method according to an embodiment of the present disclosure is described with reference to a drawing.  FIG. 2  is a flowchart illustrating the fiber assembly-forming method. 
     The fiber assembly-forming method is performed using, for example, the above-mentioned fiber assembly-forming apparatus  100 . The fiber assembly-forming method may be performed using an apparatus other than the fiber assembly-forming apparatus  100 . 
     As shown in  FIG. 2 , the fiber assembly-forming method includes a binding material-providing step (Step S 11 ) of providing a feedstock containing fibers with a binding material bonding the fibers to each other, a disintegration step (Step S 12 ) of forming disintegrated matter by disintegrating the feedstock provided with the binding material, a deposition step (Step S 13 ) of depositing the disintegrated matter, and a heating step (Step S 14 ) of heating the deposited disintegrated matter. 
     The binding material-providing step (Step S 11 ) is performed using, for example, the provision section  110  of the fiber assembly-forming apparatus  100 . 
     The disintegration step (Step S 12 ) is performed using, for example, the disintegration section  20  of the fiber assembly-forming apparatus  100 . 
     The deposition step (Step S 13 ) is performed using, for example, the deposition section  60  of the fiber assembly-forming apparatus  100 . 
     The heating step (Step S 14 ) is performed using, for example, the heating portion  84  of the fiber assembly-forming apparatus  100 . 
     The fiber assembly-forming method may include, for example, a step such as a step of pressurizing the web W by the pressurizing portion  82  as described in above-mentioned “1. Fiber Assembly-Forming Apparatus” in addition to the above steps. 
     In the fiber assembly-forming method, the sheet S can be formed so as to have little variation in paper strength as described in above-mentioned “1. Fiber Assembly-Forming Apparatus”. 
     In an example shown in  FIG. 2 , in the disintegration step, the feedstock provided with the binding material in the binding material-providing step is disintegrated. As shown in  FIG. 3 , in the disintegration step, the feedstock (first feedstock) provided with the binding material in the binding material-providing step and the sheet S formed through the heating step may be disintegrated. In an example shown in  FIG. 3 , the sheet S is a feedstock (second feedstock) unprovided with the binding material. The disintegration section  20  may disintegrate the first feedstock and the second feedstock. The term “feedstock unprovided with the binding material” as used herein refers to material that is a sheet, formed through the heating step, unprovided with the binding material in the binding material-providing step. 
     As shown in  FIG. 4 , in the disintegration step, the feedstock provided with the binding material in the binding material-providing step and the sheet S, formed through the binding material-providing step, provided with the binding material in the binding material-providing step may be disintegrated. 
     3. Modification of Fiber Assembly-Forming Method 
     Next, a modification of the fiber assembly-forming method is described with reference to a drawing.  FIG. 5  is a flowchart illustrating the modification. Hereinafter, in the modification, what is different from the fiber assembly-forming method is described and what is common to the fiber assembly-forming method is not described. 
     As shown in  FIG. 2 , the fiber assembly-forming method includes the binding material-providing step (Step S 11 ). As shown in  FIG. 5 , the modification includes a material-preparing step (Step S 21 ) of preparing material containing fibers and a binding material boding the fibers to each other. 
     As shown in  FIG. 5 , the modification includes the material-preparing step (Step S 21 ), a disintegration step (Step S 22 ) of forming disintegrated matter by disintegrating the material, a deposition step (Step S 23 ) of depositing the disintegrated matter, and a heating step (Step S 24 ) of heating the deposited disintegrated matter. 
     In the material-preparing step (Step S 21 ), the material contains, for example, waste paper and a resinous substance made of the binding material. The resinous substance may be composed of a thermoplastic resin or a thermosetting resin or may be composed of the thermoplastic resin and the thermosetting resin. 
     The shape of the resinous substance is not particularly limited and is, for example, a sheet shape (single sheet shape), a strip shape formed by fragmenting a single sheet, a dice shape, or a spherical shape. The resinous substance is preferably a sheet-shaped resin sheet. When the resinous substance is such a resin sheet, the resinous substance can be supplied by attaching a sheet-feeding stacker for supplying the resinous substance to the supply section  10  of the fiber assembly-forming apparatus  100 . In the material-preparing step, the same number of resin sheets as that of sheets of waste paper may be prepared. In a case where the modification is performed using the fiber assembly-forming apparatus  100 , the provision section  110  need not be driven. Alternatively, the provision section  110  need not be used. 
     In the material-preparing step, the material is prepared such that the binding material accounts for 6.0% by mass or more of the fibers. In a case where, for example, waste paper and the resinous substance are prepared as material, supposing that the mass of fibers contained in the waste paper is 100, the sum of the mass of resin contained in the waste paper and the mass of the resinous substance is 6.0 or more. In the material-preparing step, the material is preferably prepared such that the binding material accounts for 9.0% by mass or more of the fibers. When the material is such that the binding material accounts for 6.0% by mass or more of the fibers, the sheet S can be formed so as to have high paper strength. 
     The disintegration step (Step S 22 ) is substantially the same as the above-mentioned disintegration step (Step S 12 ). The deposition step (Step S 23 ) is substantially the same as the above-mentioned deposition step (Step S 13 ). The heating step (Step S 24 ) is substantially the same as the above-mentioned heating step (Step S 14 ). 
     The modification has, for example, effects below. 
     In the modification, as well as the fiber assembly-forming method, the sheet S can be formed so as to variation in paper strength. 
     In the modification, no provision step is performed unlike the fiber assembly-forming method; hence, for example, the provision section  110  of the fiber assembly-forming apparatus  100  can be omitted. Therefore, the downsizing of the fiber assembly-forming apparatus  100  is possible. 
     In the modification, in the material-preparing step, the material may contain a resinous substance made of the binding material. Therefore, liquid containing the binding material need not be applied; hence, a drying step subsequent to the application of the liquid can be omitted. 
     Furthermore, a sheet-shaped resinous substance is easy in stock control and has good operation efficiency. Furthermore, the type of the resinous substance can be selected without being restricted by crushability, powder characteristics such as fluidity, dispersibility, dischargeability, storage stability, or compatibility. 
     Furthermore, a plurality of different functional agents can be provided to the fibers depending on purposes using a resinous substance made of resins with different glass transition temperatures or a resinous substance containing a flame retardant, an antistatic agent, an ultraviolet absorber, a perfume, and the like; hence, functional customization is easy. 
     In the modification, if the material can be prepared in the material-preparing step such that the binding material accounts for 6.0% by mass or more of the fibers, the sheet S, which is formed through the heating step, may be prepared as material in addition to the waste paper and the resinous substance as shown in  FIG. 6 . 
     In the modification, if the material can be prepared in the material-preparing step such that the binding material accounts for 6.0% by mass or more of the fibers, the waste paper and the sheet S may be prepared as material without preparing the resinous substance. 
     4. EXAMPLE AND COMPARATIVE EXAMPLE 
     4.1. Preparation of Samples 
     4.1.1. Example 1 
     Liquid was provided to recycled paper, G80 (a basis weight of 64 g/m 2 ), available from Mitsubishi Paper Mills, Ltd. using an ink jet printer, EW-M770T, available from Seiko Epson Corporation, whereby a feedstock was prepared. Components of the liquid were as described below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Components of liquid 
                 Mass percent 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Polyurethane 
                 15 
               
               
                   
                 PG 
                 10 
               
               
                   
                 E1010 
                 1 
               
               
                   
                 Water 
                 Balance 
               
               
                   
                 Total 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     Polyurethane used was SUPERFLEX 130 available from Dai-ichi Kogyo Seiyaku Co., Ltd. Polyurethane is a binding material bonding fibers to each other. In Table 1, “PG” is polypropylene glycol and “E1010” is Olfine E1010 available from Nissin Chemical Industry Co., Ltd. 
     Next, a sheet with a basis weight of 70 g/m 2  was prepared using a papermaking machine, PaperLab A8000, available from Seiko Epson Corporation and the feedstock coated with the liquid. The content of the binding material with respect to fibers in the sheet was 9.0% by mass. In PaperLab A8000, no binding material was provided to the feedstock. That is, in Example 1, after liquid containing the binding material was applied, disintegration was performed. 
     4.1.2. Comparative Example 1 
     A web was prepared using G80 as a feedstock without providing the binding material in PaperLab A8000. Next, the liquid shown in  FIG. 1  was applied to the web using EW-M770T. Thereafter, the web was pressurized with a pressurizing portion and was heated with a heating portion, whereby a sheet with a basis weight of 70 g/m 2  was prepared. That is, in Comparative Example 1, after disintegration was performed, liquid containing the binding material was applied. 
     4.2. Evaluation Method 
     4.2.1. First Evaluation 
     Printing with EW-M770T was performed in such a state that four nozzles were clogged. As shown in  FIG. 7 , in Comparative Example 1, dropouts N due to dot loss were observed on the prepared sheet. In Example 1, since disintegration was performed after printing, no dropout was observed on the prepared sheet. Each of the prepared sheets was cut to a rectangle with a width of 20 mm. In Comparative Example 1, the sheet was cut such that the dropouts N were contained. Referring to  FIG. 7 , the sheet cut in Comparative Example 1 is drawn with a dashed line. The sheets were measured for specific tensile strength in a longitudinal direction by a method specified in JIS P 8113:2006 using a tensile tester, AGS-X-500N, available from Shimadzu Corporation. 
     Evaluation standards for specific tensile strength were as described below. 
     A: A specific tensile strength of 20 Nm/g or more.
 
B: A specific tensile strength of less than 20 Nm/g.
 
     4.2.2. Second Evaluation 
     Printing with EW-M770T was repeatedly performed in such a state that four nozzles were clogged. Subsequently, the uneven application of the liquid was visually checked. 
     Evaluation standards for uneven application were as described below. 
     A: Uneven application incapable of being visually observed.
 
B: Uneven application capable of being visually observed.
 
     4.3. Evaluation Results 
     Evaluation results of specific tensile strength and uneven application were as shown in Table 2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
               
               
                   
                 Example 1 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 First evaluation 
                 A (29 Nm/g) 
                 B (19 Nm/g) 
               
               
                   
                 (specific tensile 
               
               
                   
                 strength) 
               
               
                   
                 Second evaluation 
                 A 
                 B 
               
               
                   
                 (uneven application) 
               
               
                   
                   
               
            
           
         
       
     
     In Example 1, since disintegration was performed after printing, the prepared sheet had no dropouts due to dot loss. Therefore, Example 1 showed a specific tensile strength higher than that in Comparative Example 1. Furthermore, in Example 1, since disintegration was performed after printing, the binding material was homogenized and no uneven application was observed, even though printing was repeatedly performed in such a state that the four nozzles were clogged. These evaluations showed that a sheet with little variation in paper strength could be formed by applying liquid containing the binding material before performing disintegration. 
     In the present disclosure, configurations may be partly omitted insofar as features and effects described in the present application are retained and embodiments and modifications may be combined. 
     The present disclosure is not limited to the above embodiments and various modifications can be made. The present disclosure includes, for example, substantially the same configurations as configurations described in the embodiments. Substantially the same configurations are, for example, configurations identical in function, method, and result or configurations identical in object and effect. The present disclosure includes configurations obtained by replacing nonessential portions of configurations described in the embodiments. Furthermore, the present disclosure includes configurations capable of providing the same advantageous effects as those of configurations described in the embodiments or capable of achieving the same object. Furthermore, the present disclosure includes configurations obtained by adding a known technique to configurations described in the embodiments.