WO2013192260A1 - Method for making molded fiber bottles - Google Patents

Abstract

A method for forming a molded fiber bottle by expanding a thermoplastic parison in a molded pulp bottle to form an internal plastic liner in the molded pulp bottle wherein the liner provides a barrier function for the bottle and the resulting bottle produced by the method.

Description

METHOD FOR MAKING MOLDED FIBER BOTTLES

CROSS REFERENCE TO RELATED APPLICATIONS

[001] This application claims priority to U.S. Provisional Application No. 61/661,521, filed June 19, 2012, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

[002] 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

[003] The blow molding of plastic bottles is a well-developed technology. Broadly, a bottle can be considered to be any container or hollow article which has an opening whose cross-sectional area is smaller than that of its body. In the blow-molding process, an initial parison, alternatively referred to as a plastic preform, generally is prepared by injection molding. The injection molded parison has a shape akin to a test tube, but typically has a threaded opening designed to be sealed with a threaded cap. This threaded opening remains intact through the blow-molding process and serves as the closure/opening of the ultimate blow-molded bottle. After its formation, the injection molded parison is transferred to a blow molding station where usually a high pressure gas is used to expand its volume into a mold having the desired shape of a bottle. As noted, the technology of blow-molding is well-developed.

[004] More recently, efforts have been made to form bottles from 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 and since they potentially 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.

[005] 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. Patents 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.

[006] 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 a flexible film, or a plastic parison within the mold. See U.S. 6,521,085), the full disclosures of which is incorporated herein by reference.

BRIEF SUMMARY OF THE INVENTION

[007] The present application is directed to a method of making a molded article from fibers, such as cellulosic fibers and especially a molded bottle from a paper pulp.

[008] In one embodiment, the method of making a molded article involves a first papermaking step in which 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. Dewatering can be accomplished by some combination of heating the wet preform in a mold and by pressing the wet preform against the surface of the possibly heated mold, wherein, in accordance with the present invention, the pressing is accomplished by expanding a thermoplastic parison against the wet preform by blow molding.

[009] In an alternative embodiment, the method of making a molded article involves a first step in which a moist fibrous sheet (or sheets, e.g., of wet paperboard) is arranged to create a cylinder-like shape, perhaps by arranging the sheet in a spiral fashion. Then, either the bottom of the cylinder can be pushed/de formed 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 is the case with a deposited pulp fiber layer, the paperboard is dewatered by some combination of heating the mold (to heat the wet preform) and by pressing the wet preform against the surface of the possibly heated mold, wherein, the pressing is accomplished by expanding a thermoplastic parison against the wet preform by blow molding.

[010] Thus, as used throughout the application and in the claims the phrase "pulp molded" is intended to embrace both methods of forming a wet preform from a fibrous pulp or wet paperboard sheets, and includes both a method of dewatering a pulp fiber slurry and a method of dewatering a wet (moist) paper sheet (wet paperboard).

[011] As understood by those skilled in the art, a thermoplastic parison (or plastic preform) is formed of a thermoplastic resin, generally polyethylene terephthalate (PET) though a variety of other thermoplastic materials can be used. Usually the parison (or plastic preform) is formed using injection molding techniques, though other forming methods such as extrusion blow molding also can be used. In addition, the thermoplastic parison (or plastic preform) can be supplied in either a monolayer or multilayer structure.

[012] Applicants have unexpectedly discovered that 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 cause damage to the bottle structure. The plastic liner shrinkage and separation between the molded pulp container and the plastic liner are unacceptable. In order to overcome this problem, applicants propose two alternative solutions that form a part of the present invention.

[013] In a first embodiment, applicants have determined that such separation can be prevented by maintaining a positive, above atmospheric pressure, within the expanded (blow molded) parison at the end of the blow molding step while the molded article continues to cool, rather than allowing the pressure to fall immediately to substantially atmospheric pressure as would have been the expected/conventional practice according to the prior art.

[014] In a second embodiment, applicants have determined that such separation also can be reduced or even eliminated by conducting a second expansion step of the previously blow molded parison, i.e., the previously expanded parison, following an initial period where the pressure within the bottle has been reduced, such as by allowing the pressure to fall to substantially atmospheric pressure

[015] Thus, the present invention pertains to a method of producing a pulp molded article, the method 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 expanding a thermoplastic parison by blow molding to form an expanded plastic liner and to press the wet pulp preform against the surface of the papermaking mold to produce a dewatered preform and wherein following the expanding of the parison by blow molding either (1) maintaining an above-atmospheric pressure of at least 1-60 psi (50- 3100 mm Hg) gauge pressure, or usually within the range of 5-30 psi (260-1550 mm Hg) gauge pressure within the pulp molded article until the dewatered preform and expanded liner have cooled to a temperature below a glass transition temperature of the thermoplastic parison, e.g., until the liner has cooled to a temperature of at least 15-30° C below a glass transition temperature of the thermoplastic parison, or (2) releasing the blow-molding pressure and transferring the de -pressurized and dewatered preform with the expanded liner to a second blowing station in order to cold expand the liner by introducing a pressurized fluid into the pulp molded article in a cold mold. Using a cold mold in this second blowing station, instead of hot as in the first station (which was employed in order to dry the paper preform), allows the plastic liner to expand sufficiently to avoid the separation/distortion problem and cool down below its glass transition temperature, hence, minimizing the shrinking issues.

BRIEF DESCRIPTION OF THE DRAWINGS

[016] Figures 1A, IB 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 closure in accordance with the method of the present invention.

[017] Figure 2 is another schematic showing an alternative embodiment for securing a suitable internal barrier layer fitted with a closure in accordance with the method of the present invention

[018] Figure 3 is a schematic of another bottle design to be employed in connection with the alternative embodiment described in connection with Figure 2.

[019] Figure 4 is a partial perspective view with a cutaway portion of a bottle made in accordance with the present invention.

[020] Figure 5 is a perspective view of one blowing nozzle assembly for use in connection with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[021] With reference to Figures 1A, IB and 1C, a first embodiment of the invention will be described. In practicing this embodiment of the present invention, a fibrous pulp slurry, for example originating from a suitable slurry tank, is introduced via conduit 13 into a mold cavity (female mold) made by bringing together separate (two or more) segments of a split mold. As shown in Figure 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 (Figure 1A (see illustration (1-c))).

[022] Thus, as shown in Figure 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.

[023] The suction paths or drainage channels can comprise small passages of a dimension (diameter) of 1 mm to 50 μιη, 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. Patent 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.

[024] 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 a metal mesh are known and are suitable for use in connection with the present invention.

[025] 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 length between 0.1 and 10 mm and a 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. 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 polyolefms, 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.

[026] Again, one embodiment of the method for producing a molded fiber article according to the present invention is described with reference to the schematic drawings of Figures 1A, IB and 1C. As shown in these figures, separate (two or more) splits are assembled to form a mold cavity 15. A pulp slurry is injected into the cavity (see Figure 1A (1-b)), possibly under pressure, through a suitable conduit 13 usually positioned at the open top of the papermaking mold. 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.

[027] Coincident with, or 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 Figure 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. [028] 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.

[029] 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.

[030] After a wet molded fiber article 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 it can be done in a separate drying mold. In any event, in accordance with the present invention, further water removal is performed by pressing the molded pulp article against the inner wall of a mold cavity, preferably in combination with heating the mold.

[031] In order to accomplish this pressing, and as shown in Figure IB (1-d), a thermoplastic parison 17 is inserted into the mold cavity through the opening of the mold, generally while continuing evacuation of the mold by suction of the cavity through the drainage channels. The thermoplastic parison 17 is then inflated in the cavity by blow molding causing the expanded parison 17a (see Figure IB (illustration (1-e))) to press the pulp layer against the inner wall of the mold cavity. 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. [032] 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 thermoplastic parison or thermoplastic preform 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 through the blow molding step 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.

[033] Thus, in accordance with the present invention, the wet molded article is further dewatered from the inside of the mold cavity by inserting and blow molding a thermoplastic parison in the cavity, 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.

[034] 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.

[035] In the conventional process of blow-molding, a plastic parison, or preform, typically made from polyethylene terephthalate (PET) is prepared by injection molding. In the process of the present invention still other techniques and other plastic materials also can be used for preparing the plastic parison or preform and the present invention is not to be limited to any specific material.

[036] In addition, the parison (or plastic preform) can be supplied as monolayer of the thermoplastic resin or the preform can be supplied in the form of multilayers of the thermoplastic resin to meet different barrier requirements. While it is common to make such preforms by injection molding, the formation of a suitable preform can be made by other techniques. Besides injection molding a thin monolayer or multilayer plastic preform, another method such as extrusion blow molding also can be used as well. Based on the desired barrier requirements, different material combinations also can be chosen to co-extrude a thin multilayer plastic preform, such as a combination of polypropylene-ethyl vinyl alcohol-polypropylene (PP-EVOH - PP); polyethylene- ethyl vinyl alcohol-polypropylene (PE - EVOH-PP); PP-Nylon; PE-Nylon; etc. The thin plastic preform will be placed in the modified blow molding machine to be re- inflated and form the thin plastic liner as described in more detail hereafter.

[037] Thus, in one embodiment, the parison is made by injecting a molten mass of the plastic into a cooled mold of a shape desired for the parison. Typically, the mold is designed such that the parison 17 resembles a test tube having a threaded bottle neck 19 at its open end. In the typical blow-molding process of the prior art, following formation, the hot parison is placed within a cool, bottle blow mold which clamps the parison by its neck upon closing off the blow mold. The parison, whose initial length is shorter than that of the finished bottle, may be stretched axially to its approximate final length using a pushrod or by a telescoping extension of the blow mold, thereby effecting axial or longitudinal orientation; while radial orientation/expansion is achieved by introducing a compressed gas, usually air, inside the axially stretching or stretched parison to expand it outward and into contact with the cooled surface of the bottle blow mold. After cooling sufficiently for subsequent handling, the blow mold is opened, which reduces the pressure and the biaxially oriented bottle is ejected from the molding machine. These and other known techniques for forming the parison using a thermoplastic resin and for blow molding the thermoplastic resin parison can adapted, in accordance with the present invention, for blow molding the inner plastic liner of a molded pulp bottle.

[038] 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.

[039] As shown in Figure IB (1-d), a thermoplastic parison 17 of a suitable temperature for blow molding is inserted into the inside of the molded fiber article, usually while the inside of the mold continues to be evacuated by suction through the drainage channels and the mold is heated. The parison 17 is held by a blowing nozzle assembly 22 (a perspective view of one possible design is shown in Figure 5). The blowing nozzle assembly 22 is designed to direct the pressurized blow molding gas into the parison and support and retain the preform both before, during and after the blow molding operation, even after the split mold (splits 10, 11 and 12) is opened. The blowing nozzle assembly 22 thus forms an air-tight seal with the threaded neck 19 of the parison (in part for reasons discussed hereafter). One possible design of the nozzle assembly is shown in Figure 5 showing the nozzle 40 and the segmented retaining clamp 41.

[040] A pressurizing fluid 20, usually a compressed gas such as compressed air, then is fed through the nozzle assembly and nozzle 40 into the parison to expand it rapidly by blow molding. Thus, in one embodiment, the blow molding fluid, e.g., pressurized gas, can be fed into the parison at the same time the cavity of the mold is subjected to continued evacuation through the drainage channels of the mold. A typical blowing pressure may range between 2 to 4 MPa (20 to 40 bar). As a result of the blow molding operation, the pulp layer 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.

[041] Again, the well-known techniques of blow molding are directly applicable to this step of the method. The expanding parison presses the still wet molded fiber article against the inner surface of the mold defining the mold cavity. In the broad practice of this invention, the pressurizing fluid which can be used to expand the parison includes gases and liquids, usually compressed air (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 blow molded parison 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.

[042] As shown in Fig IB (1-d), the parison 17 is generally designed with screw threads 19 at its opening and is inserted into the cavity of the mold and retained in place with the cooperation of the blowing nozzle assembly 22. The screw threads serve as the closure of the molded bottle. Usually, the thermoplastic parison 17 to be inserted into the mold for blow molding has previously been heated (thermally conditioned), or may be obtained in a heated state directly from its injection molding operation, so that it may be readily inflated by blowing an optionally heated fluid into the mold (blow molding). While polyethylene terephthalate (PET) is often the material of choice for the parison 17, other thermoplastic resins that can be used include, without limitation, polypropylene (PP), polyethylene naphthalate (PEN) and others. Those skilled in the art appreciate suitable temperatures for blow-molding these materials. For example a suitable temperature for blow molding PP may be between 120 to 140° C, while a suitable temperature for blow molding PET may be a temperature between 100 to 130° C.

[043] With the understanding that the mold can be heated to facilitate dewatering/drying of the molded fiber article and in order to maintain the integrity of the threaded opening of the resulting plastic liner during and following the blow molding operation, it often is important that the portion of the mold 18 in the area of the opening be appropriately insulated to avoid causing plastic deformation of the threaded closure during the bottle formation process. This result can be accomplished by providing an insulation layer 18, e.g., a material with a very low thermal conductivity such as silica, in the vicinity of the mold opening where the parison is positioned for blow molding. In addition, an air (or other coolant) channel (not shown) can be added in the vicinity of the area where the threaded closure 19 is supported by the mold to allow the threaded closure portion of the parison to be cooled during the blow molding operation. In addition, a coolant stream of gas (such as refrigerated air), 23 can be blown onto the nozzle assembly to cool the neck of the bottle. Other configurations for accomplishing this cooling will be apparent to those skilled in the art and the present invention is not limited to any specific design.

[044] The thermoplastic parison 17 is designed so that the resulting blow molded inner liner has a relatively thin thickness, particularly as contrasted with typical blow molded plastic bottles. In accordance with the present invention, the blow molded liner has a thickness between about 5 and 400 μιη, 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 blow molded liner has a thickness between 10 and 100 μιη. Often the expanded parison 17a will have a thickness of at least 10 but no greater than 50 μιη. Designing the parison 17 such that the blow molded liner 17a has the desired thin thickness is well within the skill of the ordinary worker in the blow molding art, given the desired internal dimension of the molded fiber bottle and the desired thickness of the liner. As noted above, the parison can have either a monolayer or multilayer structure, depending on a variety of considerations including desired barrier properties.

[045] Generally, following the press (and optionally heat) drying of the molded article to a desired water content by the blow-molding of the parison in the mold, the pressurizing fluid is withdrawn/reduced immediately to prevent the bottle from bursting when the mold is opened to remove the molded bottle. Applicants have unexpectedly found that when using the expansion of a thin parison to accomplish press dewatering, once the pressure is reduced at the elevated temperature of the mold, an undesired separation tends to occur between the inner wall of the molded article and the outer surface of the expanded, blow-molded parison, i.e., the interface between the plastic liner and the molded pulp experiences a separation at the elevated molding temperatures encountered in the pulp molding/dewatering process.

[046] In accordance with one embodiment of the present invention, schematically illustrated in Figure 1C (see illustration 1-fl), in order to reduce the tendency of the hot expanded, blow-molded parison to shrink and separate from the pressed fiber article, while the pulp molded bottle is cooled, a residual level of positive gas pressure 21 is maintained within the molded article once the blow-molding has ended and the split molds 10, 11 and 12 are separated to release the molded article 30. This is accomplished through the cooperation between the blowing nozzle assembly 22 and the threaded closure 19 of the bottle forming an air-tight seal and holding the bottle when the split mold opens.

[047] As noted above, in a typical blow molding operation, once the blow molding of the bottle has been completed, the pressure within the expanded bottle is immediately released to substantially ambient pressure. Contrary to this conventional processing, in this embodiment of the invention, an elevated pressure is maintained within the molded fiber bottle until the bottle has sufficiently cooled to avoid separation between the blown liner and the molded pulp. Generally, maintaining an above-atmospheric pressure of at least 1-60 psi (50-3100 mm Hg) gauge pressure, or usually within the range of 5-30 psi (260-1550 mm Hg) gauge pressure within the molded article until the molded fiber bottle has sufficiently cooled should be sufficient. The internal gauge pressure of the molded bottle usually should not need to be greater than about 2000 mm Hg. Designing the process to maintain an even higher residual pressure simply increases operating and equipment costs without any additional benefit. The pressure is maintained in the mold cavity until the temperature of the bottle has cooled to below the glass transition temperature, and typically at least 15-30° C below the glass transition temperature, of the thermoplastic used as the liner material. With this level of positive pressure within the molded bottle, the plastic liner is forced to hold its shape as the bottle is cooled. In addition, the adhesion initially established between the molded pulp bottle and the expanded plastic liner and the stiffness of the dried paper bottle also helps to hold the bottle shape.

[048] Alternatively, another embodiment designed to counter the tendency of the expanded blow-molded parison to shrink and separate from the pressed fiber article at the elevated blowing temperature is schematically illustrated in Figure 2. In accordance with this embodiment, a two stage blow-molding is conducted.

[049] After an initial stage of blow-molding (such as detailed in Figures 1A and IB) the thermoplastic parison to form the inner plastic liner in the heated, molded article (as schematically illustrated and described in connection with Figure IB) and the blowing pressure has been released, the de -pressurized and dewatered molded preform with the expanded liner is transferred to a second cold blowing station in order to cold expand the liner by introducing a pressurized fluid into the pulp molded article in a cold mold. Using a cold mold in this second blowing station, instead of being hot as in the first station (which was employed in order to dry the paper preform), allows the plastic liner to expand sufficiently to avoid the separation/distortion problem and cool the liner down below its glass transition temperature, hence, minimizing the shrinking issues. Thus, the plastic inner liner is subjected to a second step of cold expansion (see Figure 2). The hot mold, comprising splits 10, 11 and 12, is opened and the molded bottle 30 is transferred to the second cold blow-molding station 40. This blow molding station may have the same basic configuration as the original hot blow mold, but that is not necessary. As common to typical blow-molding processing, the bottle would generally be transferred by its neck (threaded closure) to the second blow mold. This can be accomplished, for example, by using a blowing nozzle assembly such as that schematically represented in Figures IB and 1C and in Figure 5.

[050] In the second blow-molding station, a second pressurizing fluid, such as a pressuring gas 20, is introduced into the molded article to cause a further re-expansion of the so- formed liner. Typically, the temperature of the mold at this second, blow-molding station ranges from 4° to 30° C. The shrunken plastic liner is re-blown at the lower temperature into the full shape of the bottle cavity and to cause the liner to adhere to the molded pulp. Again 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 exceeding 6 MPa may necessitate a scaling up the apparatus without offering further advantages in terms of the properties of the molded article. Following the cold expansion, the pressure is released, usually to ambient pressure, and the final molded article is removed from the mold.

[051] Controlling this cold blowing step to ensure that sufficient expansion of the liner occurs to result in an acceptable bond between the liner and the molded pulp bottle can be difficult to achieve. Over expansion in this step can cause the molded pulp bottle to rupture. Under expansion can result in an inacceptable bond between the liner and the pulp bottle. Depending upon the nature of the plastic used to form the liner, obtaining the proper degree of expansion also can be further complicated by the plastic's inherent elasticity. When the blowing pressure is released, the plastic may further shrink because of that elasticity, regardless of the blowing condition. Figure 3 illustrates one approach for ensuring that the re -inflated plastic liner assumes a snug fit within the paper bottle while minimizing other possible complications.

[052] Briefly, in the Figure 3 embodiment, the second blowing mold (3b) is given a slightly larger diameter than the first blow mold (3b) (i.e., dl<d2). In particular, the second blow mold (3b) may have about a 1-3 mm larger diameter than the first blowing mold (3a). Thus, in the second blowing mold, the plastic liner can be blown a little oversized, such that when its shrinks, it will tightly fit in the paper bottle.

[053] In order to minimize the possibility of rupturing the molded pulp bottle when the plastic liner is re-blown in this fashion, the conditions under which the molded pulp bottle is prepared in the first mold is adjusted in two respects. Normally, when a molded pulp bottle is dried to a fairly low moisture content (<10 % by weight water), it tends to lose much of its elasticity. So, in this alternative embodiment, the molded pulp bottle is made at a slightly higher level of moisture, typically about 20 % by weight water. In addition, the design of the first mold also can be altered to allow for a small amount of expansion of the pulp body in the second blowing mold. In particular, the wall of the mold can be altered so that a ridge (50 and 51) or what essentially forms a crease in the outer wall of the molded pulp bottle. Thus, even though the first mold has a slightly smaller diameter than the second mold, the formation of what is essentially a crease (50 and 51) in the wall of the molded pulp bottle gives the molded pulp bottle an effective circumference that approximates the circumference of the second mold.

[054] As a consequence of this design, when the molded pulp bottle produced in the first blowing mold (paper bottle with plastic liner) is re-blown in the second mold, the combination of the slightly higher moisture level and the crease in the wall of the molded pulp bottle allows the molded pulp bottle to expand enough to accommodate the expansion of the plastic liner. Thus, any rupturing of the paper bottle is avoided and the plastic liner can be re-inflated to tightly fit in the paper.

[055] Obviously, the size and number of such creases can be adjusted depending on the differences in the size of the first and second blowing molds. With reference to Figure 3, in particular, one such design is shown. As shown in Figures 3a(l) and 3a(2) (rotated 90° relative to each other), the blowing mold has an overall diameter of "a." equal to "dl". The mold however, is provided with two protuberances or ridges 50 and 51 diametrically opposed and extending longitudinally along the wall of the mold. As shown in the cross-section of Figure 3a(l), the tips of the oppositely arranged protuberances are spaced a distance of "b" apart. As a result the height of each protuberance is (a-b)/2. Because of these protuberances, when the pulp bottle is molded, a bottle is formed having two longitudinally extending creases. The presence of these creases provides the so-formed bottle with an effective circumference slightly larger than 2 a. Thus, when this bottle is introduced into the second blowing mold, 3b(l) and 3b(2), having a slightly larger diameter "d2" than the first blowing mold (i.e., d2 >dl), slight expansion of the molded pulp bottle is accommodated by the combination of its slightly higher moisture content and the presence of the longitudinal creases. Accordingly, through this design, the risk of rupturing the molded pulp bottle on the re-expansion of the inner plastic liner is minimized.

[056] 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 blow molding a thermoplastic parison within the optionally hot and wet molded article.

[057] 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 Figure 4, a pulp molded article 30 thus obtained in accordance with this invention can be a bottle-shaped cylindrical hollow article comprising a threaded closure 19 that also provides the opening for the bottle. The bottle has a dried pulp layer 16 on the outside and an inner plastic liner 17a integral with the threaded closure. 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.

[058] 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.

[059] In another embodiment, conventional blow molding equipment can be modified or retrofitted to accommodate the process of pulp molding. For example, a conventional blow mold can be modified by drilling a suitable number of fine holes, e.g., drainage channels, having a diameter of from 50 μιη to 1 mm, into the separate elements of the blow mold. The density of such drainage channels may lie between about 10 to 2500 holes per square centimeter of mold area. Alternatively, the blow mold itself could be fabricated from a sintered metal to provide a mold design inherently having an equivalent structure of drainage channels. The design will be further modified to functionally integrate the drainage channels to a vacuum pump and a water collection vessel, so that pulp dewatering can be accomplished from the cavity of the blow mold. The blow mold also could be modified such that it also can be heated. The modified design should accommodate heating of the mold to a temperature of up to about 200° C, and often in the range of 105° to 180° C.

[060] 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.

[061] 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 a further embodiment, the present invention is: 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 expanding a thermoplastic parison by blow molding to press the wet pulp layer against the surface of the mold cavity and to form an expanded thermoplastic liner and a dewatered preform and (4) forcing the expanded thermoplastic liner into contact with the pulp layer on cooling. The method of embodiment 1 wherein the expanded thermoplastic liner is forced into contact with the pulp layer by maintaining a gauge pressure of at least 50 mm Hg within the pulp molded article following the expanding of the thermoplastic parison by blow molding and 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. The method of embodiment 1 or 2 wherein the gauge pressure is in the range of 250 to 1550 mm Hg. The method of embodiment 1, 2 or 3 wherein the pressure is maintained until the dewatered preform and expanded thermoplastic liner have cooled to a temperature at least 15° C and preferably at least 30° C below the glass transition temperature. The method of embodiment 1 wherein the expanded thermoplastic liner is forced into contact with the pulp layer by 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. The method of embodiment 5 wherein the dewatered preform with the expanded thermoplastic liner cools to a temperature at least 15° C and preferably at least 30° C below the glass transition temperature. The method of embodiment 5 or 6 wherein the pressurized fluid is a gas at a pressure in the range of 2 to 4 MPa. The method of embodiment 1 through 7 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. The method of embodiment 1 through 7 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. The method of embodiment 5 wherein the mold cavity on which the wet pulp layer is formed has a smaller diameter than a mold cavity in which the expanded thermoplastic liner is cold expanded. The method of embodiment 10 wherein the mold cavity on which the wet pulp layer is formed has substantially the same circumference as the mold cavity in which the expanded liner is cold expanded. A product made by the method of embodiments 1 through 11. 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

What is claimed 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 expanding a thermoplastic parison by blow molding to press the wet pulp layer against the surface of the mold cavity and to form an expanded thermoplastic liner and a dewatered preform and (4) forcing the expanded thermoplastic liner into contact with the pulp layer on cooling.

2. The method of claim 1 wherein the expanded thermoplastic liner is forced into contact with the pulp layer by maintaining a gauge pressure of at least 50 mm Hg within the pulp molded article following the expanding of the thermoplastic parison by blow molding and 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.

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

4. The method of claim 2 wherein the pressure is maintained until the dewatered preform and expanded thermoplastic liner have cooled to a temperature at least 15° C below the glass transition temperature.

5. The method of claim 1 wherein the expanded thermoplastic liner is forced into contact with the pulp layer by 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.

6. The method of claim 5 wherein the dewatered preform with the expanded thermoplastic liner cools to a temperature at least 15° C below the glass transition temperature.

7. The method of claim 5 wherein the pressurized fluid is a gas at a pressure in the range of 2 to 4 MPa.

8. The method of claim 1 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.

9. The method of claim 1 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.

10. The method of claim 5 wherein the mold cavity on which the wet pulp layer is formed has a smaller diameter than a mold cavity in which the expanded thermoplastic liner is cold expanded.

11. The method of claim 10 wherein the mold cavity on which the wet pulp layer is formed has substantially the same circumference as the mold cavity in which the expanded liner is cold expanded.

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

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

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

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

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

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

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

19. A product made by the method of claim 11