Patent Publication Number: US-2004040680-A1

Title: Papermaking process and paper made therefrom

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This is a divisional application of U.S. application Ser. No. 09/496,981, filed on Feb. 2, 2000 which is incorporated herein by reference in its entirety for all purposes. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Technical Field  
       [0003] The present invention relates to processes for making paper, and more particularly to processes using agricultural crop material or recycled paper products, and to paper products made from the process.  
       [0004] 2. Description of Related Art  
       [0005] In conventional papermaking processes, virgin wood fibers are commonly used for making various types of paper and paper board products. The treatment of virgin wood fibers prior to paper formation may include debarking of logs, wood chipping or mechanical defibration, chemical cooking, various washing and chemical bleaching steps and refining or other further mechanical conditioning of the fibers. Screening, cleaning, thickening and diluting-steps may be repeated numerous times through out the relatively complex process. The treatment of virgin wood fibers is energy intensive, is dependent on many chemical processes, and is expensive. Many of the cooking and bleaching processes used for pulp delignification are sulfur or chlorine based, producing significant environmental hazards from the chemical processes themselves and from the by-product handling and disposal. Alternatives to chlorine based bleaching are often very expensive. Conventional papermaking processes also use large volumes of water for transporting and treating the fiber. While many mills are converting to closed loop systems, process requirements remain complex and expensive.  
       [0006] In some areas of the world, trees are not readily available, and the logs for papermaking are imported. In economically emerging countries, capital investment may not be available for complex and expensive conventional papermaking processes. The necessary infrastructure, including long range transportation, chemical supply and available energy for practicing conventional papermaking processes, often, are not present.  
       [0007] While trees are a renewable resource, in many parts of the world, including North America, tree growth is relatively slow, and even fast growing species may require ten or more years from crop planting to harvest. As a result, large tracts of land are dedicated to tree growth and paper fiber supply. In heavily populated areas, or in climates not conducive to tree growth, it is necessary to transport logs or wood fiber for papermaking, or the finished paper for use. Transportation over long distances can increase costs significantly.  
       [0008] Secondary fiber utilization has become more common in recent years; however, new problems have been encountered as paper products are recycled repetitively. When paper products made of recycled fiber are recycled again, fiber quality is reduced as fiber length shortens in each subsequent recycling generation. Conventional paper forming processes require fiber bonding in the paper sheet. Reduced fiber lengths, and diminished fiber quality resulting from multiple recycling generations reduces bonding and thereby paper strength. As a result, it is common and often necessary to add virgin wood fibers to the recycled pulp, to increase sheet strength.  
       [0009] As an alternative to wood fibers, other cellulosic materials have been used for papermaking. These alternative materials have included agricultural based materials such as corn stalk, kenaf, sugar cane, banana and pineapple leaves. Many of the agricultural crop based fiber sources can be harvested in one growing season, and can be grown in regions not suitable for tree growth. An additional advantage occurs in that lignin content is lower in grassy plants than in wood fibers, and bleaching or washing requirements are less, even when a white sheet is desired. For example, the inner core of industrial hemp, called hurd, is naturally white, and little or no bleaching is required if herd is used to form writing papers.  
       [0010] The pulping and pulp treating processes for alternative fiber papermaking differ from those used for wood fiber papermaking. However, the papermaking process itself, once the pulp is prepared, is substantially similar to that used for wood fiber papermaking. In the conventional process, a very dilute slurry of papermaking fibers is discharged from a headbox onto a forming wire. Water is drained from the slurry on the wire, referred to as a web. The web passes through a plurality of stages for the removal of water, including pressing the web between nipped rollers and drying the web by passing the web through an area of heated air and/or heated rollers. Throughout a substantial extent of the process just described, the web must be fully supported, as the wet strength of the web is insufficient to support the web by itself. The need to support the web on felts or fabrics complicates the structure and operation of conventional paper machines.  
       [0011] The mechanical treatment of virgin wood during chipping, chip screening, rechipping or chip slicing and refining, as well as the treatment of recycled fibers produces undesirable short wood fibers called pins or fines. While a small amount of pins or fines can be used in conventional papermaking processes, the use of too many short fiber components weakens the sheet. If a process generates more fines or pins than can be used, the excess is wasted. It would be advantageous to have a papermaking process that can make use of fines and pins.  
       [0012] It would be advantageous to reduce energy, water and chemical consumption in the papermaking process, while decreasing the dependence on wood fibers by utilizing fast growing agricultural crop fibers for papermaking. It would be further advantageous to have a simplified papermaking process that can be used on a small scale.  
       [0013] A feature of the present invention is a papermaking process with reduced energy, water and chemical requirements as compared to conventional papermaking processes.  
       [0014] Another feature of the present invention is a papermaking process which can utilize agricultural crop based materials, with lessened reliance on virgin wood fibers.  
       [0015] A further feature of the present invention is a papermaking process which can utilize lower quality papermaking materials than needed for conventional papermaking processes, and which can make a higher quality paper from recycled paper products.  
       [0016] Yet another feature of the present invention is a simplified papermaking process which can be used without significant capitol investment and is suitable and economical for use in small output volume operations.  
       [0017] Still another feature of the present invention is providing a process for making paper products which eliminates the need for conventional pulping.  
       BRIEF SUMMARY OF THE INVENTION  
       [0018] The present invention comprises a process from making paper in which a biodegradable plastic is used to provide strength in a paper web. In one aspect of the invention, a biodegradable plastic substrate is provided, and a surface material of papermaking fibers is deposited on the substrate. In one form of the process, the substrate is wetted, and the surface material is powdered. The powdered material is applied to the wetted surface of the substrate, which is thereafter pressed and dried.  
       [0019] In another form of the process, the powdered surface material is mixed with vegetable mucilage or slime, to create a paste which is then applied to the substrate. Drying may occur with or without the application of heat.  
       [0020] In yet another form of the process, recycled paper products are repulped, deinked if necessary and fiberized. A slurry of the recycled pulp is applied to the biodegradable plastic substrate, which is dried.  
       [0021] Another aspect of the invention is the use of biodegradable plastic fibers as an additive to paper pulp slurry, to increase strength. Discrete filaments may be added to the papermaking slurry. Hollow fibers may be filled with powdered or fine papermaking fibers.  
       [0022] Yet another aspect of the present invention is a paper product comprising a biodegradable plastic substrate with at least one surface coated with papermaking materials selected from agricultural crop based grassy plants and recycled paper products.  
       [0023] Further features and advantageous of the present invention will become apparent from the following detailed description and the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0024]FIG. 1 is a process diagram of the papermaking process according to the present invention;  
     [0025]FIG. 2 is a more detailed process diagram of a first embodiment of the present invention of a process for papermaking;  
     [0026]FIG. 3 is a process diagram of a second embodiment of the present invention for a papermaking process;  
     [0027]FIG. 4 is a process diagram of the present invention for a papermaking process as utilized for recycled fiber;  
     [0028]FIG. 5 is an enlarged cross sectional view of paper made according to the present invention; and  
     [0029]FIG. 6 is a process diagram of yet another papermaking process in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0030] Referring now more specifically to the drawings, and to FIG. 1 in particular, numeral  10  designates the papermaking process of the present invention, and more particularly the preferred life cycle of paper made according to the present invention.  
     [0031] Papermaking process  10  is useful in the formation of a paper product  12 , shown in FIG. 5. Paper product  12  has a substrate  14  and top and bottom layers  16  and  18  respectively. The nature and content of substrate  14 , top layer  16  and bottom layer  18  will be described and explained in greater detail hereinafter.  
     [0032] With reference again to FIG. 1, papermaking process  10  includes a surface material preparation subprocess  20  and a substrate preparation subprocess  22 . The prepared surface material and substrate are combined in a paper formation subprocess  24 . The formed paper product continues through a converting and use subprocess  26 . Thereafter, the paper product may be, and preferably is, recycled in a recycling subprocess  28 , and returned in one of several ways, to be described hereinafter, to the surface material preparation subprocess  20 .  
     [0033] Substrate material  14  used in the present invention is a biodegradable plastic. Some biodegradable plastics contain aliphatic polyester resin skeletons. Others have polyvinyl alcohol molecular skeletons, while still others utilize molecular skeletons based on polysaccharides. Some characteristics of an appropriate biodegradable plastic for the present invention include strength, chemical resistance and water resistance, in addition to biodegradability when disposed of in nature. Preferred characteristics of the biodegradable plastic substrate may differ depending on the ultimate use of the paper product being formed. For example, if heavy weight material is to be formed, for possible use in containers, grocery bags, or the like, the desired strength characteristic may be different than if the product being formed is a light weight paper product to be used more for its appearance or surface characteristics than for strength.  
     [0034] One suitable biodegradable plastic for use in the present invention is marketed by Shimadzu Corporation of Japan under the product name Lacty. Another suitable biodegradeable plastic is marketed by Kanebo, Ltd. Of Japan under the product name Lactron. Each is a plant starch based product having characteristics similar to petroleum based plastics, except that each is biodegradable in nature, unlike petroleum based plastics. The physical structure of substrate  14  may take several forms. A scrim or felt of randomly oriented fibers has been found to work well for some applications. In other applications, individual biodegradeable plastic fibers, hollow fibers, and fibers oriented as a strand or twine can be used. Alternatively, a fine mesh or screen with discrete openings may also be used. Much of the tear, tensile and burst strength of the resultant paper product results from the similar strength properties of substrate  14 . Therefore, selection of the particular structure for substrate  14  should take into consideration these and other characteristics preferred in the resultant product.  
     [0035] Top layer  16  and bottom layer  18  are formed of the prepared surface material, which may include different types of agricultural fibers and/or recycled fibers. The terms top and bottom are used herein only as a way of differentiating between the layers, as shown in FIG. 5, separated by the substrate  14 . It should be understood that the two layers may be the same, and used interchangeably. Alternatively, the components of the layers may differ, being selected for particular desirable characteristics of one compared to the other. The desirable characteristics may include color, texture, moisture resistance or the like. Virgin or recycled wood fibers may be used for top layer  16  and bottom layer  18 . However, one of the advantages of the present invention is that lower quality, lesser used but more easily grown and obtained fibers may also be used. Additionally, by-products or remains from agricultural crops can be used. Such can include the remaining portions after crop processing for other purposes. For example, corn stalk, grain husks, sugar cane, banana and pineapple leaves may be used as surface material. Additionally, hemp, wheat and rice stalks, jute, bamboo, coconut fibers, papyrus or virtually any kind of grassy plant may be used to provide unique surface appearance and characteristics.  
     [0036] Referring now to FIG. 2, a more detailed moist process  40  is shown, which utilizes virgin agricultural fibers. Surface material preparation sub-process  20  of virgin fiber moist process  40  includes steps of crop growth  42 , which may occur in a cultivated agricultural setting or may be natural growth of the desired material, and a harvesting and drying step  44 . The method of harvesting may differ for different plant sources, depending upon the nature of the agricultural crop or material being used. Harvesting may include mechanized cutting and removal from cultivated fields, or harvesting may include a simple gathering step of naturally growing vegetation. Harvesting may occur as part of a processing procedure for an agricultural crop grown principally for another purpose.  
     [0037] Drying may be performed in mechanized crop dryers. Direct fired, rotary drum dryers can be used advantageous, as can waste heat dryers using heat from other processes. However, in a low energy consumption process embodying the present invention, the harvested crop of material may be air dried in fields or collection areas. The complexity of the drying step may depend upon the nature of the material being used and the stage of dryness at which it is harvested. If by-product material is used, it may have been dried in previous processing. The harvested and dried material is conditioned in a mechanical treatment step  46 , which may include shredding and powdering of the dried material. Shredding and/or powdering may be accomplished with conventional apparatus including hammer mills, shredders, rolling mills, refiners, beaters and the like. Since paper made according the present invention does not rely on fiber to fiber bonding for strength, low quality material can be used, and fiber integrity is not critical. Even pins or fines from conventional papermaking pulp preparation processes can be used.  
     [0038] Preparation of the substrate, as shown in FIG. 2, includes a substrate presentation step  50  which, in a continuous process, may include unwinding substrate material from a supply roll of the material. In a batch process, presentation step  50  may include flattening a sheet of substrate material. A moistening step  52  readies the substrate for formation of the paper product. Moistening step  52  can be accomplished by passing an unrolling web of substrate material  14  through a shower or misting area wherein water or other liquid is deposited on the surface of substrate  14 . In a low volume or batch process, which can be essentially a hand performed process, moistening step  52  can be performed by use of a hand sprayer, sprinkler of the like.  
     [0039] Paper formation subprocess  24 , in accordance with virgin fiber moist process  40  shown in FIG. 2, includes a deposit step  54  in which the prepared surface material is placed on the moistened substrate, and a subsequent pressing and drying step  56 . Deposit step  54  can be performed by blowing or spraying the dried powdered material onto the moistened substrate or, in a smaller process, may be performed by hand spreading the powdered material on the substrate. Deposit step  54  may be performed on both sides of the substrate simultaneously, prior to rolling and drying step  56 , or a first side may be prepared, rolled and dried, with the second side completed thereafter. Rolling and drying step  56  may include pressing the substrate and deposited material between nipped rollers, or may include simply air drying the formed sheet without an initial or simultaneous pressing. Heat  58  may be used to assist in the process. When heat is used, the temperature may be selected to slightly melt the biodegrable plastic substrate, causing the surface materials to adhere readily to the substrate. If nipped rollers are used, one or both may be heated, internally or externally. The roller surface characteristics should be such as to allow ready release of the sheet from the rollers, without sticking.  
     [0040] In the process shown on FIG. 2, if a heating step  58  is included with rolling and drying step  56 , to partially melt the biodegradable plastic, the formed product can be created with a relatively hard surface. Such may be useful in forming tree plugs for nursery seedlings and the like. Slight melting of substrate  14  enhances bonding of top layer  16  and bottom layer  18  to substrate  14 , and may improve moisture resistance.  
     [0041] From paper formation subprocess  24 , the material proceeds to the converting and use subprocess  26 . It should be understood that converting and use subprocess  26  may directly follow paper formation subprocess  24 , or the paper product formed may be rewound or otherwise accumulated and stored for later converting and use. Depending on the material having been made, converting and use subprocess  26  may include sheeting to individual sheets, bonding in tablets, formation into bags, boxes and the like. Conventional slitters, sheeters, perforators, folders and the like may be used.  
     [0042] Recycling subprocess  28  follows converting and use subprocess  26 . It should be recognized that while it is preferred that the used or discarded materials be recycled, and that the process of the present invention is particularly useful for subsequent recycling, recycling may not occur in all instances. In such situations, used product may be disposed of in landfills and will breakdown quickly, due to the biodegradability of the substrate as well as all other materials used. One suitable recycling subprocess is shown in FIG. 2, wherein the used product is acquired in a collecting step  60 . Depending upon the manner in which the product is collected, cleaning and separating may be necessary to remove particularly undesirable elements. For example, in a municipal waste collecting process, screening and separating may be used to remove recyclable metals, glass and other objects. Thereafter, the remaining material is processed in a composting step  62 . The composted material may then be returned to the crop growth step  42  of surface material subprocess  20 , wherein the composted material is used as a fertilizer or soil amendment for the growing crop.  
     [0043] Referring now to FIG. 3, a dry substrate process  70  is shown. Substrate preparation subprocess  24  is similar to that described previously for virgin fiber moist process  40 , except that it is not necessary to moisten the substrate. Surface material preparation subprocess  20  in dry substrate process  70  also is similar to that shown and explained for virgin fiber moist process  40 . In dry substrate process  70 , however, the powdered surface material is mixed with a mucilage or vegetable slime juice created in a vegetable slime juice preparation step  72 . Pulp from Okra fruits may be mixed with water to create the mucilage or vegetable slime juice. Other suitable vegetable slimes may be obtained from other plants including Jew&#39;s Mellow leaves, Fenugreek seeds and tubers of Tororo Aoi, which is a vegetable additive used to increase bonding and improve fiber distribution in traditional Japanese papermaking processes. These and other suitable vegetable components, when mixed with water, produce a viscose, stringy mucilage slime, which can act as an adhesive. The mucilages are polysaccharides, found in a number of plants, that form viscous, colloidal dispersions in water. Such mucilages are used in the preparation of certain ethnic dishes, and are valued for their slimy consistency. The suitable substances differ from starch based adhesives in that mucilages produced from Okra, Tororo Aoi, Jew&#39;s Mellow and Fenugreek remain flexible when dried, as contrasted with starched based adhesives which become brittle upon drying.  
     [0044] A paste is made from the powdered surface material by mixing the powdered material with vegetable slime juice in a paste creating step  74 . During an application step  76 , the paste is applied to the substrate. Application step  76  may include spraying or spreading the paste on the substrate, depending upon the consistency of the paste. The paste coated substrate is pressed to remove excess water, and is allowed to dry. Drying may occur naturally, or may be forced through the use of air movement, heated air or the like. The vegetable slime juice works much as an adhesive in adhering the surface material to the substrate. Therefore, pressing of the coated substrate will not require the application of heat to bond the surface material to the substrate. Heat can be used, if desired, to obtain the physical characteristics, including moisture resistance, that result from slightly melting the biodegradable plastic.  
     [0045] If paper products made in accordance with the dry mesh process  70  are not hardened by the application of heat, the paper made in accordance with dry mesh process  70  will remain soft and flexible. The dry mesh process may be particularly suited for the preparation of thinner papers such as stationary and office paper or artistic papers. A further advantage of the process using a vegetable slime adhesive is realized during recycling. Upon reliquification of the slime, the surface material is released readily from the substrate, allowing separate processing of each, and possible reuse of the substrate.  
     [0046] Following paper formation subprocess  24  in dry substrate process  70 , converting and use  26  and recycling  28  may occur as described previously for virgin fiber moist process  40 . Converting will be as appropriate for the material being made and the use to which it is applied. Recycling again may include steps of collecting  60  and composting  62 .  
     [0047] Referring now to FIG. 4, a recycled fiber process  80  is shown. In surface material preparation subprocess  20 , recycled fibers are gathered and undergo a plurality of steps, including pulping  82 , deinking  84  and cleaning  86 . Shredding  88  or powdering may be used to ready the fibers for application on the substrate. A final slurry preparation step  90  includes consistency adjustment by adding water or by thickening to achieve the desired consistency. The recycled fibers are then deposited on the substrate in a deposit step  92 . Pressing and drying step  56  follows, which normally will include the application of heat. Converting and use subprocess  26 , as needed, follows. Used or excess product is collected and recycled, being returned to the preparation step  82 . In this regard, the recycling subprocess  26  of process  80  differs from that shown for process  40 , in which recycling includes returning the recycled material to the soil as fertilizer or as a soil amendment. In recycled fiber process  80 , recycled fibers are returned for use in another paper product. Typically, recycled fiber process  80  will be used for recycling conventional papermaking fibers such as wood fibers, and recycling subprocess  28  will include the accumulation of suitable surface material from a number of sources. Because of the gluing effect created by heating the biodegradable substrate, low quality recycled fibers may be used. The problem associated with repeatedly recycling fibers, which reduces fiber length and fiber to fiber bonding strength, is overcome, since fiber to fiber bonding is not critical for the generation of strength in the completed paper product.  
     [0048] Biodegradable plastic can also be used advantageously as an additive in a more conventional papermaking process, and need not be used only as a substrate as described previously herein. In FIG. 6, a biodegradable plastic fiber additive process  110  is shown, in which biodegradable plastic fibers are added to a papermaking slurry or pulp prior to web formation. As mentioned previously, during recycling of paper products formed using the dry substrate process, wherein vegetable slime juice is used to adhere surface material to the substrate, the substrate is separated readily from the surface material. The biodegradable plastic substrate may then be fiberized and added to papermaking pulp in fiber additive process  110 . Addition of the biodegradable plastic fibers adds strength to the resultant paper sheet, and can reduce the need for virgin fiber in paper products made using primarily recycled wood fiber.  
     [0049] While the biodegradable plastic fiber additive process  110  shown in FIG. 6 may take several forms, as shown in FIG. 6 process  110  includes several sources of material for the formation of the paper product. An agricultural crop growth and harvesting step  112  supplies material to a conventional crop pulping step  114 . Alternatively, or I additionally, papermaking fibers may be provided from a repulping recycled fiber process I step  116 , supplying fiber to a deinking and screening step  118 . A recovery step  120  may provide material to a composting step  122  for fertilization or soil enhancement of the crop growth and harvesting step  112 . Additionally, recovery step  120  may provide material to a recovered material separation step  124  which, depending upon the material having been recovered, may forward material to the repulping recycled fiber step  116  or may provide material directly to a combining organic material step  126 . Recovered material separation step  124  may also provide biodegradable plastic material to a fiberizing step  128 , wherein discrete fibers or filaments are created. Additionally, virgin plastic fiber may be provided in a step  130  to the fiberizing biodegradable plastic step  128 . Fiberized biodegradable plastic is combined with the organic fibers in a mixed fibers step  132 . Thereafter, the mixed fibers are provided to formation, pressing, drying, converting and use step  134 . While the formation, pressing, drying, converting and use step  134  may be conventional, it may also incorporate some of the processes described previously herein, and may utilize a vegetable slime preparation step  136 , with deposit of the fibers on a substrate  14 .  
     [0050] The various processes disclosed herein can be modified to achieve a variety of desired physical characteristics for the resulting product. As mentioned previously, the application of heat during pressing or drying increases water resistance of the resulting material, by melting the surface of substrate  14  or of individual fibers in the fiber additive process shown in FIG. 6. Combining a number of the previously described methods can produce a variety of products, depending on the varying functions of the material. Layering of the sheets, including a felt or scrim of recycled fiber, agricultural material residue powder and thin biodegradable plastic substrate may be suitable for diapers, feminine napkins and other hygienic products. Subsequent breakdown in landfills or the like is improved when compared with conventional products, since all materials are biodegradable in nature.  
     [0051] Through proper selection of materials, artistic papers having unique surface characteristics and appearance may be created. Further, waterproof wall papers may also be formed. In yet a further modified use of the materials, hollow biodegradable plastic filaments may be filled with recycled papers fibers or crop material, and woven conventionally into fabric. Surface coatings as described previously herein may then be applied.  
     [0052] In yet another modified application for using a paper product made in accordance with the present invention, strips or strands can be cut from the powder coated substrate, and subsequently woven or knitted into fabrics having elasticity and conformability. Fabric made in such a manner may have particular suitability for wall coverings with distinctive textures and patterns, and for packaging materials with shock absorbability.  
     [0053] Processes according to the present invention are not complex when compared to conventional processes for making paper. The biodegradable plastic substrate provides wet strength in the web being formed and in the end product, making handling easier.  
     [0054] Processes according the present invention readily make use of low quality fiber and easily renewable fiber sources such as agricultural products. Additionally, processes according to the present invention may utilize papermaking materials which otherwise would be wasted, such as left over leaf and stalk components from other agricultural processes and fines and pins from conventional papermaking. The present processes may also utilize naturally white materials, thereby reducing or eliminating the need for chemical bleaching of the papermaking material to achieve a white surface. Chemical pulping of the papermaking material is eliminated.  
     [0055] Processes according to the present invention are amenable to use in low tech configurations including manufacture by hand. Thus, art and specialty papers may be made in small batches at reasonable expense. Further, the processes are adaptable to use in emerging countries with readily available materials and can be used locally, at small volume locations where infrastructure necessary for conventional papermaking processes, such as utilities, roads for transporting materials and the like are not readily available.  
     [0056] While the present invention has been described in detail herein, including several embodiments thereof, it should be understood that additional modifications and changes thereto may be made without departing from the scope of the present invention, as defined in the claims to follow.