US20160145811A1

US20160145811A1 - Method For Making Molded Fiber Bottles

Info

Publication number: US20160145811A1
Application number: US14/548,440
Authority: US
Inventors: Edward Peter Socci; Jie Yan; Daniel Lee Witham
Original assignee: Pepsico Inc
Current assignee: Pepsico Inc
Priority date: 2014-11-20
Filing date: 2014-11-20
Publication date: 2016-05-26
Also published as: WO2016081614A1

Abstract

A method for forming a molded fiber bottle by pressurizing a flexible plastic bag in a molded pulp bottle preform to press the bag against the inner wall of the molded pulp bottle preform and thereby assist dewatering of the preform and form an internal plastic liner in the molded pulp bottle preform such that the liner provides a barrier function for the bottle and the resulting bottle produced by the method.

Description

FIELD OF THE INVENTION

This invention relates to a method for making molded fiber articles and particularly a molded fiber bottle. The invention particularly relates to a method in which an internal plastic liner, which serves a barrier function, is introduced as part of the process for molding the article. The invention also relates to the bottle produced by the method.

BACKGROUND

It is known to form bottles and other containers by molding a fibrous pulp, such as a cellulosic pulp of the type commonly used to make paper products. Such bottles provide the potential for a significant reduction in the consumption of plastics used for making bottles. Since the pulp-molded bottles can be manufactured using recycled paper, pulp-molded bottles may be more environmentally friendly as well
The prior art has proposed making such pulp molded articles by a method including a papermaking step in which a pulp slurry is fed to the papermaking side of a papermaking mold having a plurality of holes and the liquid portion of the slurry is sucked through the holes to accumulate pulp fibers on the papermaking side to form a wet preform. The papermaking step is followed by dewatering and drying steps in which the wet preform, as molded in the papermaking step, is dewatered, and in which the dewatered and yet un-dried preform can be put into a drying mold and press-dried.
Kao Corporation has issued a series of patents describing various methods for making such pulp molded bottles in which a pulp slurry is applied to and dehydrated on the surface of a split mold. To assist the dehydration of the slurry, the mold is both heated and evacuated. Included in these patents are U.S. Pat. Nos. 6,454,906; 6,468,398; 6,521,085; 6,592,720; 6,605,187; 6,918,997 and 7,048,975 (among others), the full disclosures of which are incorporated herein by reference.
Producing molded pulp articles thus involves a dewatering step in which a wet fibrous preform, typically formed by applying a vacuum to a pervious split mold, is further dewatered to reduce the energy demand and shorten the time for subsequent drying. One approach for accomplishing the dewatering of a nascent formed bottle involves pressing the preform against the surface of the mold by expanding an elastic bladder, a flexible bag, or a plastic parison within the mold. In these latter cases, the expanded bag and the expanded parison are not removed and form a liner on the interior wall of the bottle. See U.S. Pat. Nos. 6,468,398 and 6,521,085, the full disclosures of which are incorporated herein by reference.
In a more recently developed process (described in PCT application PCT/US13/46458), the injected molded preform (often referred to as a parison) having a shape akin to a test tube and having a threaded opening or spout, is inserted into a nascent molded fiber bottle and blow molded. The expanding, thermoplastic parison presses against the wet molded pulp preform. One unanticipated problem encountered when using the blow-molding of an injected molded parison to simultaneously dewater the molded pulp bottle and form a barrier layer on the inside of the bottle, was difficulty in forming an adequate bond between the inner wall of the molded pulp bottle and the blow-molded plastic liner. In connection with the blow-molding step, the plastic liner tends to shrink at the temperature of the hot, molded fiber preform and exhibits a tendency to separate from the molded fiber preform. The shrinkage and separation contributes to distortion of the bottle integration between the plastic liner and fiber wall and may damage the bottle structure.
The problem was solved by forcing the expanded thermoplastic liner into contact with the pulp layer on cooling either by maintaining the pressure within the pulp molded article until the dewatered preform and expanded thermoplastic liner have cooled to a temperature below a glass transition temperature of the thermoplastic parison or by first releasing blow molding pressure and transferring the dewatered preform with the expanded thermoplastic liner to a second step of blow molding and then cold expanding the expanded thermoplastic liner with a pressurized fluid to allow the temperature of the dewatered preform with the expanded thermoplastic liner to cool to a temperature below a glass transition temperature of the thermoplastic parison.

BRIEF SUMMARY OF THE INVENTION

The present application is directed to an alternative method of making a molded article from fibers, such as cellulosic fibers and especially a molded bottle from a paper pulp.
As in the prior art, the present invention starts with the making of a molded article using a first papermaking step. In one approach a pulp fiber slurry is applied onto a surface of a suitable papermaking mold, the mold having suction paths, alternatively referred to as drainage channels, through which water in the pulp slurry is withdrawn, so that a pulp fiber layer is deposited adjacent to the surface of the mold as a wet preform; and thereafter the wet preform is dewatered. In an alternative approach, the method of making a molded article involves a first step in which a moist fibrous sheets (or a sheet, e.g., of wet paperboard) are arranged to create a cylinder-like shape, perhaps by arranging sheet(s) in a spiral fashion. Then, either the bottom of the cylinder can be formed by pushing/deforming the lower end of the cylinder inwardly to form a base for the container, or one or more separate sheets of paperboard can be placed/positioned at the base of the cylinder to create a base for the container. Paperboard with a water content of 50 to 70% by weight should be suitable for forming the moist paperboard form. The mold is closed around the moist paperboard form and a vacuum is applied to pull the paperboard against the inner wall of the mold.
As used throughout the application and in the claims the phrases “wet fibrous preform,” “pulp molded container” and the like are intended to embrace these alternative methods for initially forming the wet molded container either from a fibrous pulp or from wet paperboard sheet(s).
In either case, in accordance with the method of the present invention, the deposited pulp fiber layer or the paperboard is dewatered by some combination of heating the mold (to heat the wet preform) and by pressurizing a flexible plastic bag against the wet preform.
The flexible plastic bag is preferably fitted with a threaded finish (opening) and has a generally cylindrical shape and is formed of a thermoplastic resin, generally a polyolefin such as polyethylene or polypropylene though a variety of other thermoplastic materials can be used. Usually the major portion of the flexible plastic bag can be formed by film extrusion and then shaped by welding together various edges of the film. A threaded finish (opening), made for example by injection molding, can be welded to the opening of the flexible plastic bag. The flexible plastic bag also can be supplied in either a monolayer or multilayer structure.
The flexible plastic bag may further be made using a roll-fed-form-seal-press method which is sealed at the bottom and along the side.
Thus, the present invention pertains to a method of producing a pulp molded article, the method broadly comprising steps of: feeding a pulp slurry or applying a wet paper sheet (or sheets) to a surface of a papermaking mold having drainage channels to remove water contained in the pulp slurry or wet sheet; removing water by suction through the drainage channels to cause pulp of the pulp slurry or the wet paper sheet to deposit on the surface of the papermaking mold; and optionally heating and dewatering the wet pulp preform, wherein the dewatering of the wet pulp preform comprises pressurizing a flexible plastic bag so that the expanded bag presses the wet pulp preform against the surface of the papermaking mold to produce a dewatered preform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C provide a schematic illustration showing the various steps of the method of molding a bottle and blow molding an internal barrier layer fitted with a finish in accordance with the method of the present invention.

FIG. 2 is a partial perspective view with a cutaway portion of a bottle made in accordance with an aspect of the present invention.

FIG. 3 is a perspective view of one pressurizing nozzle assembly for use in connection with one aspect of the present invention.

FIG. 4A depicts an illustration of a roll-fed-form-seal-press apparatus to form plastic bags, and FIGS. 4B and 4C show application of the bag to a bottle formed with paper pulp.

FIG. 5 is a cutaway portion of the top of a bottle in accordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One shortcoming of the prior approach of blow-molding an injected molded parison to dewater the wet fibrous preform and form a barrier layer in the molded pulp container is that the quantity of plastic used in the method is dictated by limitations associated with making the thermoplastic parison. One of the major goals of developing a molded pulp (paper) bottle is to produce a final product that is more environmentally friendly than current plastic bottles. As a result, one of the subsidiary goals is to limit the plastic component to only that amount of plastic needed to satisfy the functional barrier requirements associated with the potential contents of the bottle. It is preferred that other structural requirements of the bottle be met by the molded pulp. Unfortunately, due to limitations in the blow-molding approach, more than the functionally minimum amount of plastic is unavoidably used in making the final product. Thus, an alternative approach to making a molded pulp bottle that uses less plastic content would be highly desirable.
With reference to FIGS. 1A, 1B and 1C, an approach for making a molded pulp preform in accordance with the present invention will be described. A fibrous pulp slurry, for example originating from a suitable slurry tank, is introduced via conduit 13, possibly under pressure, into a mold cavity (female mold) made by bringing together separate (two or more) segments of a split mold. For example, the pulp slurry can be injected using a pressure pump operating at an injection pressure of 0.01 to 5 MPa, usually at an injection pressure of 0.01 to 3 MPa.
As shown in FIG. 1A (first illustration (1-a)) three cavity splits, vertical splits 10 and 11 and base split 12, can be assembled to form the mold cavity. The mold cavity 15 is defined by the inner surface of the mold elements and forms a core of a prescribed shape in conformity with the desired contour of the molded article (bottle) to be produced. The mold is provided with numerous suction paths 14, i.e., drainage channels, extending outwardly from the mold cavity 15 to interconnect that cavity with the outside of the mold and through which water can be drained and suctioned from the mold cavity 15, thus depositing a layer of pulp fibers 16 on the inner wall of the mold (FIG. 1A (see illustration (1-c))).
Thus, as shown in FIG. 1A (1-a), a suitable papermaking mold 1 can be formed using a set of splits 10, 11 and 12, each having a large number of fluid flow passageways (drainage channels), 14 which interconnect the inside and the outside of the mold cavity 15, a manifold (not shown) which connects to these flow passageways 14 for discharging the liquid component of a pulp slurry charged into the mold cavity 15, and possibly a papermaking screen (not shown) for facilitating the trapping of the solid components of the pulp slurry and preventing the solids components from passing into the drainage channels.
The suction paths or drainage channels can comprise small passages of a dimension (diameter) of 1 mm to 50 μm, possibly drilled through the walls of the mold. Alternatively, such flow passages can be provided by forming the elements comprising the mold by sintering, such as described in U.S. Pat. No. 7,909,964, the disclosure of which is incorporated herein by reference. The sintered elements having a porous framework thus provide a very large number of liquid flow paths (drainage channels) that penetrate through the mold.
As noted, the inner surface of the mold forming the mold cavity also may be provided with a papermaking net or screen of a suitable design and construction to allow the free passage of water from the cavity while restricting the flow of pulp fibers through the net or screen and thus preventing the loss of pulp through, or the plugging of the drainage channels. Suitable papermaking nets and screens of natural fibers, synthetic fibers or of a metal mesh are known and are suitable for use in connection with the present invention.
A suitable pulp slurry for making a molded pulp bottle comprises a blend of water and conventional cellulose fibers, as can be obtained from the pulping of wood. Pulp fibers of a maximum length between 0.1 and 10 mm and a maximum thickness between 0.01 and 0.1 mm are typical. The pulp fibers can be prepared in a known manner and the slurry can be prepared by dispersing the pulp fibers in water. While water is the main liquid component of the slurry, the pulp slurry may also have other components added, including additives that improve moisture resistance and the plastic adhesion of the molded pulp. The pulp fiber concentration is usually between 0.1% and 6% by weight and normally is not much greater than about 3% by weight. A slurry concentration of about 0.5 to about 2% pulp by weight is typical, and a pulp consistency of 0.5 to 1% is most often used. The pulp slurry can also contain a variety of other paper-making adjuvants, as well as both inorganic and organic pigments. For example, conventional papermaking adjuvants can be added in conventional amounts, such as fiber dispersants, wet-proofing agents, talc, kaolinite, inorganic fibers such as glass fibers and carbon fibers, particulate or fibrous thermoplastic resins such as polyolefins, and polysaccharides. Suitable inorganic pigments include titanium oxide, zinc oxide, carbon black, chrome yellow pigments, red iron oxide, ultramarine, and chromium oxide; while suitable organic pigments include phthalocyanine pigments, azo pigments, and condensed polycyclic pigments, all used in conventional amounts.
Coincident with, or shortly after injecting a predetermined amount of the pulp slurry into the mold cavity, evacuation of the liquid content of the pulp slurry through the drainage channels by suction (vacuum) can be initiated. The mold cavity is evacuated by suction through the drainage channels to remove the bulk of the water content of the pulp slurry and deposit pulp fibers on the inner wall of the cavity to form a pulp layer 16 (see FIG. 1A (1-c)). The water content of the pulp slurry is lowered by discharging water from the papermaking mold, while pulp fiber is deposited on the inner wall of the mold, typically on a papermaking screen (not shown), to build up a hollow bottle-shaped molded fiber article within and on the surface defining the mold cavity 15. After a prescribed amount of the pulp slurry is fed into the cavity, feeding of the pulp slurry is stopped.
The pulp layer 16 is formed by depositing the pulp fibers from the pulp slurry on the inner surface of the mold cavity 15 by the action of the vacuum and possibly centrifugal force causing the pulp slurry to spread onto the inner surface of the mold cavity 15. The thickness and weight of the bottle are controlled by vacuum force and duration. The initial dewatering typically reduces the moisture content of the deposited pulp layer to 70-80%.
In an alternative embodiment, the pulp layer 16 can be formed by arranging one or more moist fibrous sheets (often multiple sheets), e.g., of wet paperboard to create a cylinder shape inside the mold cavity 15. The cylindrical shape can be formed, for example, by wrapping a moist sheet in a spiral fashion. A bottom for the cylinder can be formed either by pushing/deforming the lower edge of the cylinder radially, inwardly to form the base, or by using a separate sheet of paperboard, which can be pushed/placed or positioned at the bottom of the cylinder to create the base for the container. Paperboard with a water content of 50 to 70% by weight should be suitable for forming a pulp layer 16. The mold is closed around the moist paperboard form and a vacuum is applied to pull the paperboard against the inner wall of the mold, to dewater the paperboard and form pulp layer 16.
After a wet molded fiber article or molded pulp preform of a desired thickness has formed (generally 0.3 to 2.0 mm in thickness and usually 0.5 to 1.0 mm thick) and a suitable amount of water has been removed by suction alone, still further water removal must be accomplished. This additional water removal can be done within the same mold, or, since the initial removal of water renders the preform strong enough to be removed from the forming mold, it can advantageously be done in a separate drying mold. In any event, in accordance with the present invention, further water removal is performed by pressing a flexible plastic bag against the molded pulp article and against the inner wall of a mold cavity, preferably in combination with heating the mold (120° to 150° C.).
In order to accomplish this pressing, and as shown in FIG. 1B (1-d and 1-c), a thin, thermoplastic bag 17 is inserted into the mold cavity through the opening of the mold. The dimensions of the bag can be exactly the dimensions of the inner volume of the molded pulp preform, or can be slightly smaller or larger. In order to facilitate insertion of the bag into the molded pulp preform, the bag may be twisted or evacuated (as shown at 18).
While the bag can be inserted while continuing evacuation of the mold by suction of the cavity through the drainage channels, as a general rule vacuum evacuation may be discontinued. The thermoplastic bag 17 is then pressurized in the cavity causing the bag to expand against the molded pulp 17 a (see FIG. 1B (illustrations (1-e) and (1-f))) and press the pulp layer against the inner wall of the mold cavity. A nozzle (see FIG. 3) can be fitted over the spout 20 of the flexible plastic bag and then the pressure will be increased slowly at first (1-50 psi) to fully inflate the bag and fill up the entire inner volume of the molded preform; followed thereafter by a full expansion pressurization (20-40 bar) to complete the expansion and simultaneously pressurize the molded pulp preform through the plastic bag layer. This pressing transfers the inner configuration of the cavity to the outer wall of the molded pulp bottle and dewaters the pulp layer by mechanical pressing.
The water content of the wet molded fiber article before such pressing and generally before additional heating as well, is usually about 30 to 95% by weight, more often between about 50 to 85% by weight water, i.e., at the time the plastic bag 17 is inserted into the mold cavity 15. With pressing (and usually with further heating as well), the water content of the wet molded fiber article is reduced significantly, typically to a water content of less than 30%, usually, less than 15% by weight. Usually, the heating and coincident pressing from the pressurized plastic bag reduces the moisture content of the molded article (bottle) to about 5% to 10% by weight. If the water content following pressing exceeds 30% by weight, the molded article requires a much longer time to dry in any subsequent drying step, which can result in reduced production efficiency or difficulty in transferring the molded fiber article in subsequent processing steps.
Thus, in accordance with the present invention, the wet molded article is further dewatered from the inside of the mold cavity by inserting a flexible plastic bag and pressurizing the bag, usually while further evacuating the cavity by suction. With this processing, a resulting molded fiber article can be prepared which has essentially no joints or seams. As a result, the process is able to produce a molded fiber article with enhanced strength and a good appearance.
According to various embodiments of this invention, initial dewatering and drying can be accomplished either in a single mold used also for forming the nascent bottle, or in a separate dewatering and drying mold.
A wide variety of plastic materials can be used for preparing the flexible plastic bag and the present invention is not to be limited to any specific material. In addition, the flexible plastic bag can be supplied as monolayer or alternatively can be supplied in the form of multilayers of a thermoplastic resin to meet different barrier requirements.
Flexible plastic bags suitable for use in the present invention can be made by conventional techniques, such as by extruding a flexible thermoplastic film of an appropriate resin or plastic, in a desired shape. For example, one way of making a suitable flexible plastic bag is by extruding a suitable plastic using a conventional extruder through an annular extrusion gap to form a continuous tube and heat sealing or heat welding (fusion bonding) a thin plastic film to one opened end and heat sealing or heat welding (fusion bonding) a suitable spout to the other opened end. While the flexible plastic bag can have any suitable shape, it is preferred that the bag have an approximately cylindrical shape (e.g., the desired shape of the completed bottle), as shown in FIG. 1B (version (1-d)). Although not essential, depending upon the ultimate use of the bottle, it also is convenient if the flexible plastic bag is fitted with a threaded finish as the spout such as shown in FIG. 1B. The threaded finish or spout itself can be made by injection molding and then heat sealed or otherwise heat welded to an opening of the flexible plastic bag. The plastic bag may be made of polyethylene, including high density (HDPE), low density (LDPE), and linear low density (LLDPE), nylon, ethylene vinyl alcohol (EVOH), polypropylene (PP), ethylene vinyl acetate (EVA), polyester, and ionomers. Examples of coextruded multilayer film suitable for use in making plastic bags suitable for use in the current invention include layered combinations such as polyethylene-ethyl vinyl alcohol-polypropylene (PE-EVOH-PP); PP-Nylon; PE-Nylon; polypropylene-ethyl vinyl alcohol-polypropylene (PP-EVOH-PP); HDPE/EVOH/LDPE, nylon/LDPE, etc.
The thickness of the walls of a suitable flexible plastic bag is expected to be between 0.0005 and 0.005 inch (0.0013 and 0.013 cm), usually between 0.001 and 0.004 inch (0.0025 to 0.010 cm) and most often between 0.0015 and 0.003 inch (0.0038 and 0.0076 cm).
When performing the entire operation of bottle formation according to the present invention, from pulp layer formation though pressing in a single mold, at some point during or following initial formation of the wet molded pulp preform, the mold usually is heated and maintained at a prescribed temperature for further drying of the molded article. As understood by those skilled in the art, the mold can be heated in a variety of ways and the present invention is not limited to any particular technique. For example, the mold can be heated with a plate member equipped with a heating means, such as an electric heater, which is fitted to the backside of the mold, i.e., a side opposite to the mold cavity. In this case, the heat generated in the plate member is indirectly applied to the fiber preform by conduction through the mold itself. Other ways of heating the mold also will be appreciated by those skilled in the art. The heat capacity of the material used to prepare the mold can be designed to facilitate developing and maintaining preferably a uniform temperature at the inner surface of the mold. This arrangement may be particularly advantageous in continuous large-volume production of fiber preforms to avoid temperature fluctuations of the mold. A suitable temperature for the mold surface during the drying operation is within the range of 105° to 180° C. and often will be in the range of 175-180° C.
The threaded finish or spout 20 of the flexible plastic bag is held by a blowing nozzle assembly 38 (a perspective view of one possible design is shown in FIG. 3). The blowing nozzle assembly 38 is designed to direct the pressurized blow molding gas into the flexible bag and support and retain the preform before, during and after the pressure expansion, possibly even after the split mold (splits 10, 11 and 12) is opened. The blowing nozzle assembly 38 thus forms an air-tight seal with the threaded finish 20 of the flexible bag (in part for reasons discussed hereafter). One possible design of the nozzle assembly is shown in FIG. 3 showing the nozzle 40 and the segmented retaining clamp 41.
A pressurizing fluid 26, usually a compressed gas such as compressed air, then is fed through the nozzle assembly 38 and nozzle 40 into the flexible bag to expand it and force it against the inner wall of the molded preform. Thus, in one embodiment, the pressurized gas can be fed into the flexible bag at the same time the cavity of the mold is subjected to continued evacuation through the drainage channels of the mold. A typical expansion pressure may range between 2 to 4 MPa (20 to 40 bar). As a result of the pressure expansion of the plastic bag 17, the pulp layer 16 is pressed onto the inner wall of the mold cavity (and often a papermaking screen) by the expanding parison. Since the wet molded pulp precursor is pressed from its inside against the inner wall of the mold cavity, the inner profile of the cavity is transferred to the surface (outer surface) of the pulp layer with good precision. The resulting molded article can have no seams or joints. The combination of mechanical pressure and heating contributes to a significant and rapid reduction in the water content of the molded pulp bottle. For example, the water content of the molded pulp bottle may be reduced from in excess of 70% by weight before the blow molding step to less than 5% by weight during and after the blow molding step.
In the broad practice of this invention, the pressurizing fluid which can be used to expand the plastic bag includes gases and liquids, usually compressed air (such as heated air). The pressure of the pressurizing fluid is generally in the range to 0.5 to 6 MPa (5 to 60 bar), particularly in the range from 2 to 4 MPa (20-40 bar). Using pressures lower than 0.5 MPa may lead to reduced drying efficiency and can result in poor surface properties of the molded article. Using pressures exceeding 6 MPa may necessitate a scaling up the apparatus without offering further advantages in terms of drying efficiency or surface properties of the molded article. The expanded bag presses the molded article against the cavity-forming surface. As a result, the water of the molded article is squeezed from the pulp layer and the water is removed through the drainage channels. Simultaneously with the progress of drying, the structure of the cavity-forming surfaces is transferred onto the outer surface of the molded fiber article. Since the molded fiber article is pressed to the cavity-forming surface, it dries efficiently even when using cavity configurations of a complicated shape. Moreover, the structure of the cavity-forming surface is transferred to the outer surface of the molded article with high precision.
As shown in FIG. 1B (1-d), the plastic bag is generally provided with a finish or spout having screw threads 21. The bag is inserted into the cavity of the mold and retained in place with the cooperation of the blowing nozzle assembly 38.
With the use of a plastic bag, instead of the thermoplastic parison of the prior art, the resulting liner has a relatively thin thickness. In accordance with the present invention, the expanded liner has a thickness between about 5 and 100 μm, sufficient to impart the required barrier characteristics to the molded article (bottle) in terms of water resistance (moisture barrier) and gas resistance (e.g., oxygen transport) barrier properties. Usually, the liner has a thickness between 10 and 75 μm. Often the liner 17 a will have a thickness of at least 10 but no greater than 40 μm. Fabricating the plastic bag 17 such that the liner 17 a has the desired thickness is well within the skill of the ordinary worker, given the desired internal dimension of the molded fiber bottle and the desired thickness of the liner.
Generally, following the press (and optionally heat) drying of the molded article to a desired water content by the pressure expansion of the plastic bag, the pressurizing fluid is withdrawn/reduced immediately to prevent the bottle from bursting when the mold is opened to remove the molded bottle.
Thus, in one embodiment the present invention pertains to a method of producing a pulp molded article comprising the steps of assembling a plurality of splits to form a mold cavity, each split optionally having an optional papermaking screen and having suction passageways or drainage channels into a papermaking mold, filling the mold cavity of the papermaking mold with a pulp slurry (or alternatively with a wet paperboard), removing the liquid component of the pulp slurry (or reducing the moisture of the wet paperboard) through the drainage channels (suction passageways) to deposit pulp fiber on the inner side of the mold cavity (and the papermaking screen if present) and form a pulp layer on the inner wall of the mold as a wet molded article, and thereafter dewatering the wet molded article deposited on the inner side of the mold cavity (and the papermaking screen if present), which optionally may be heated, by pressure expanding a flexible plastic bag within the optionally hot and wet molded article.
Pulp molded articles obtained by this invention can take the shape of cylindrical bottles whose opening is smaller in diameter than the cross-section of the body. As shown in FIG. 2, a pulp molded article 30 thus obtained in accordance with this invention can be a bottle-shaped cylindrical hollow article comprising a threaded finish 20 that also provides the opening for the bottle. The bottle has a dried pulp layer 16 on the outside and an inner plastic liner 17 a integral with the threaded finish. The pulp molded article 30 has a smooth surface on both the outer and inner surfaces. Such a pulp bottle is useful as a container for a variety of liquid and powdered contents.
It generally is more efficient to conduct both the initial papermaking step and the dewatering of the nascent moist pulp bottle in a single papermaking mold. Nonetheless, in accordance with the broad practice of the present invention, the pulp preform may be removed from a papermaking mold after the initial papermaking step and heated and dewatered in a separately prepared heating and dewatering mold of a similar design. The separate mold could be heated to a predetermined temperature, typically 100 to 200° C. In this alternative embodiment, following the insertion of the plastic liner and the coincident dewatering, the pulp molded bottle can then be delivered if needed to a further drying step.
While the present invention has been described with respect to a method of producing a molded fiber article using either a pulp slurry (and including the step of papermaking) or a moist paperboard in which two or more split mold pieces are joined to make a papermaking mold, the present invention is also applicable to other production methods. For example, the present invention can also be used with a method comprising immersing a papermaking mold in a container filled with pulp slurry in order to feed the pulp slurry by static pressure into the cavity of the papermaking mold. It is also applicable to a production method in which a papermaking mold having fluid passageways like a split mold piece is placed with its papermaking surface up, and an outer frame surrounding at least the papermaking surface is set up on the papermaking mold with liquid tightness to form a pool, in which a prescribed amount of a pulp slurry is poured and sucked through the passageways to build a molded article on the papermaking surface.
Often, the surface of the papermaking mold onto which the pulp slurry is deposited is fitted with a papermaking net or screen. The papermaking net or screen includes nets or screens made of natural fibers, synthetic fibers, such as fibers of thermoplastic resins, thermosetting resins, or semisynthetic resins or metal fibers, such as stainless steel fibers and copper fibers, which can be used either individually or as a combination of two or more elements. In order to improve slip properties and durability, the fiber used to fabricate the papermaking net or screen is preferably subjected to a surface treatment. The papermaking net or screen preferably has an average opening area ratio of 20% to 90%, particularly 30% to 60%, to avoid intimate contact with the inner side of the split mold and thereby maintain satisfactory suction efficiency. The papermaking net or screen preferably has an average maximum opening width of 0.05 mm to 1 mm, particularly 0.2 mm to 0.5 mm, to securely perform papermaking while preventing the pulp fibers from passing through the screen or clogging the screen.
In another embodiment of the invention, as shown in FIG. 4, pre-formed plastic bags are replaced with flexible bags formed with a roll-fed-form-seal-press apparatus. More particularly, roll(s) of plastic film(s) 50 are fed and sealed to form the plastic inner liner of the paper bottle in a manner similar to conventional form-fill-seal method of making flexible bags. Wide films 52 are slit first to multiple narrower lines and each line of film is rolled over a forming tube 54 to create a plastic tube and sealed by the side. A sealer 56 seals the bottom of the tube to form a flexible bag 60 having sealed bottom 62. The film 52 can be mono-layer polymers or multi-layers depending on the required barrier properties.
What is different from conventional form-fill-seal methods is that after the bag is formed, the forming tube has an external dimension that is the same as the internal dimension of the paper shell formed in the earlier process and a length of the bottle length. After a long thin plastic is formed by sealing the side and bottom, the bag is inserted into the wet paper shell which has been loaded into a mold cavity. The forming tube also has a dual function as the blowing nozzle to blow the plastic bag into the paper shell, press the bag against the shell, and also dry the paper shell.
After the newly formed bag 60 is fed into the wet paper shell 66, a low pressure compression air (1-50 psi) is blown into the bag 60 to fully inflate and stretch the bag inside the paper shell to fill up the entire volume of the shell, then a high blow pressure compression air (20-40 bar) is used to apply the pressure to the paper shell through the plastic bag layer. The low and high pressure air is depicted generally by 68.
Because both the paper shell 66 and plastic bag 60 are supported by the metal blowing mold 64, the pressure will be mostly endured by the mold. Thus though the blowing pressure is fairly high, the seam of the plastic bag won't burst open due to pressure. The pressure with the help of the hot mold (250 F-300 F) will press and dry the paper shell and all the design detail in the mold will be transferred into the outer surface of the paper shell to achieve a final bottle, while the plastic bag will stay inside as the barrier layers.
Flexible bags formed by roll-fed-form-seal-press eliminate the need of pre-making or purchasing flexible bags which can be expensive. The process is significantly simplified over the process using premade bags. By incorporating the bag making process into the bottle forming process, the steps of picking up the pre-made bag, erecting the bag, and feeding the bag into the paper shell can be reduced to one step of feeding the bag into paper shell by inserting the bag forming tube into the shell. The bag formed over the tube is smaller than the inner volume of the paper shell. After the bag is fed into the paper shell, the low pressure will fully inflate the bag and even stretch the bag a little bit to create a wrinkle free internal layer of the paper bottle.
A separate finish may be added into the integrated bottle afterward depending on the usage and necessity. The paper shell has been pressed and dried in the hot mold, and the paper shell becomes very rigid and strong in the neck area. A finish 50 as shown in FIG. 5 can be inserted on top of the bottle neck. The finish is typically a bottle closing system. Depending on the size and usage of the bottle, the bottle closing system can be an induction seal tab or a re-closable finish with a closer (cap). A circle groove 52 can in be inserted on to the top of the paper bottle at the bottom of the finish.
This embodiment maintains the benefit of using minimum amount of the plastic to achieve the same pressing and drying efficacy and perform the function of the leave-in barrier layer.
In a further embodiment, the present invention is:

1. A method of producing a pulp molded article with an internal liner, the method comprising (1) forming a wet pulp layer on a surface of a mold cavity; (2) heating the wet pulp layer, (3) dewatering the wet pulp layer by pressurizing a flexible thermoplastic bag to press the wet pulp layer against the surface of the mold cavity and to form an expanded plastic liner and a dewatered preform.
2. The method of embodiment 1 wherein the expanded thermoplastic bag is forced into contact with the pulp layer by maintaining a gauge pressure of at least 50 mm Hg within the pulp molded article.
3. The method of embodiment 1 or 2 wherein the gauge pressure is in the range of 250 to 1550 mm Hg.
4. The method of embodiment 1 through 3 wherein the step of: forming a pulp layer on the surface of the mold cavity comprises (1) feeding a pulp slurry to a surface of a mold having drainage channels for removing water contained in the pulp slurry; and (2) removing water by suction through the drainage channels to cause pulp of the pulp slurry to deposit on the surface of the mold cavity.
5. The method of embodiment 1 through 3 wherein the step of forming a pulp layer on the surface of the mold cavity comprises arranging a wet paperboard on the surface of the mold cavity.
6. A product made by the method of embodiments 1 through 5.

While the present invention has been described with reference to specific embodiments in which a bottle is prepared, it should be understood that the invention is not deemed to be limited thereto. For example, a split mold comprised of two or more splits can be used in place of a split mold comprising three splits. The papermaking mold having a cavity can be replaced with other papermaking molds, such as a combination of a male and a female mold. The shape of the pulp molded article includes not only bottle-shaped containers as hereinabove illustrated, but also includes a wide variety of other shapes, such as cartons having a rectangular parallelopipedonal shape whose opening and body may have substantially the same cross section.

Claims

1. A method of producing a pulp molded article having a plastic liner, the method comprising (1) forming a wet pulp layer on a surface of a mold cavity; (2) heating the wet pulp layer, (3) dewatering the wet pulp layer by pressurizing a flexible plastic bag and forcing the bag to press the wet pulp layer against the surface of the mold cavity and form the plastic liner on the pulp layer, wherein the flexible plastic bag is of the same dimension with the inner volume of the molded pulp.

2. The method of claim 1 wherein the flexible plastic bag is forced into contact with the pulp layer by maintaining a gauge pressure of at least 50 mm Hg within the flexible plastic bag.

3. The method of claim 2 wherein the gauge pressure is in the range of 250 mm Hg to 1550 mm Hg.

4. The method of claim 2 wherein the pressure within the flexible plastic bag is created by a pressurized gas at a pressure in the range of 2 MPa to 4 MPa.

5. The method of claim 1 wherein the forming step (1) comprises (4) feeding a pulp slurry to a surface of a mold having drainage channels for removing water contained in the pulp slurry; and (5) removing water by suction through the drainage channels to cause pulp of the pulp slurry to deposit on the surface of the mold cavity.

6. The method of claim 1 wherein the forming step (1) comprises arranging a wet paperboard on the surface of the mold cavity.

7. The method of claim 1 further comprising attaching a finish to the pulp molded article.

8. The method of claim 7 wherein the finish is an induction seal tab or a re-closable finish with a cap.

9. A product made by the method of claim 1.

10. A product made by the method of claim 2.

11. A product made by the method of claim 3.

12. A product made by the method of claim 4.

13. A product made by the method of claim 5.

14. A product made by the method of claim 6.

15. A product made by the method of claim 7.

16. A product made by the method of claim 8.

17. A method of producing a pulp molded article having a plastic liner, the method comprising (1) forming a wet pulp layer on a surface of a mold cavity; (2) heating the wet pulp layer; (3) dewatering the wet pulp layer by pressurizing a flexible plastic bag and forcing the bag to press the wet pulp layer against the surface of the mold cavity and form the plastic liner on the pulp layer, wherein the flexible plastic bag is prepared by a roll-fed-form-seal-press process.