Large Lightweight Molded Material and Method for its Manufacture

TECHNICAL FIELD

Generally, embodiments herein relate to large lightweight molded materials, and to the method of making such molded materials.

More specifically, different embodiments of the application relate inter alia to different 3-D shaped lightweight material made by using spacer lined materials.

BACKGROUND

Pulp molding is known in the art for producing small packages such as egg cartons, disposable food dishes, box inserts and other protective packing materials etc.

RELATED ART

US 6 245 199 describes a method of pulp molding trays where the starting material is a suspension containing cellulose fibers. The male mold half is dipped in a bath of the suspension, and the mold halves are then pressed together under heat and pressure.

SE 529 897 C2 describes the pulp molding of a tray where a dewatering receptacle is used to shape a tray of pulp which is then transferred to a compression tool where the tray is subjected to pressure and heat. It involves a transfer step and is not readily usable for large containers.

EP 0466653 describes a coffin made of molded pulp without any reinforcing spacer lining. WO06016072 describes a large container, in this case a coffin made up of panels consisting of honeycomb layers with paper sheet faces.

However, none of the related art discloses or hints at how to achieve the solutions provided by embodiments herein.

OBJECT OF THE INVENTION

Embodiments herein intends to solve a complex of difficult-to-reconcile interrelated problems still present in the designs of the prior art:

It has been very difficult to use existing pulp molding methods to produce very large three dimensional objects. This is due partially to the problem of thermal expansion and contraction of the two metal mold halves used in the compression of the pulp in the press. If the dimensions of the mold halves change, due to unavoidably becoming cooler and hotter during the compression process, the strength of the container will be compromised and the surface will not be smooth and even. This is not a problem if the surface quality and the strength of the finished object is of no great importance, such as for packaging materials or disposable dishes, but where the strength and surface finish of the finished molded product is of great importance then this is a problem. In general it is difficult to achieve uniformity of strength and surface in pulp molded products, particularly in such products which are thin.

It is now possible to make a large volume lightweight shell of molded pulp with improved strength and smoothness using the mold halves and apparatus described and claimed in our co-pending patent application No. 1550864-1, entitled Pulp Molding Apparatus and Molds for Use Therein. Providing a large pulp molded 3-D shaped material, which is lightweight, very strong, with smooth and even outer surface and above all is easy and inexpensive to manufacture has hitherto proved very difficult.

SUMMARY

This entire complex of problems listed above finds its solution in embodiments herein as defined in the appended main patent claims.

In a first aspect, a large lightweight three dimensional molded material comprising an outer shell of molded pulp and a reinforcing spacer conforming to and adhering to the interior of the shell and an inner shell made of molded pulp or a flexible paper based material adhering to the spacer liner is provided.

In embodiments, the spacer may be a honeycomb sheet of hexagonal cells.

In embodiments, the reinforcing spacer and the inner shell may be made of a Re-board© with a single cover paper sheet.

In embodiments, the Re-board© spacer may have only a single interior cover sheet.

In embodiments, the reinforcing spacer liner may comprise hollow cells separated by walls substantially perpendicular to the shell.

In embodiments, the reinforcing spacer may comprise a honeycomb structure made of paper.

In embodiments, the reinforcing spacer may be made of a spacer structure made of molded pulp. In embodiments, the parts made of molded pulp may have been made with functional additives such as fire-retardants, hydrophobization additives, dry strength additives and/or a wet strength additives.

In embodiments, a material cover may also comprise an outer shell of molded pulp and a reinforcing spacer liner.

In embodiments, the material may have a length of at least 1 m.

In another aspect, a method of producing a molded 3-D shaped material is provided. The method comprises a. Pressing a water based pulp slurry between a first male mold half covered with elastomeric material and a second female mold half, and drying the material at elevated temperature under pressure, to form the molded pulp shell, b. providing a core spacer structure and gluing the reinforcing spacer structure to the interior of the molded pulp shell. c. provide an inner shell made of molded pulp or another flexible paper based material and gluing it to the core spacer structure.

In embodiments, the pressing may be effected in a frame in which one of the mold halves is mounted in means for translational movement towards the other mold half, by means for compressing and holding the pair of mold halves fitted against each other and a bath of pulp slurry, and the means for translational movement may be adapted for

immersing a first mold half in the bath of pulp slurry and moving the first mold half into fitting compression against the second mold half.

In yet another aspect, a large lightweight three dimensional object is provided. The object comprises a curved outer shell of molded pulp and a reinforcing flexible spacer conforming to and adhering to the interior of the shell and an inner shell made of molded pulp or a flexible paper based material adhering to the spacer liner.

In embodiments, the reinforcing flexible spacer may be a honeycomb sheet of hexagonal cells.

In embodiments, the reinforcing flexible spacer may be a corrugated core structure.

In embodiments, the reinforcing flexible spacer and the inner shell may be made of a Re-board® fluted paperboard with a single cover paper sheet.

In embodiments, the Re-board® flexible spacer may have only a single interior cover sheet.

In embodiments, the reinforcing spacer liner may comprise hollow cells separated by walls substantially perpendicular to the shell.

In embodiments, the reinforcing flexible spacer may comprise a

honeycomb structure made of paper.

In embodiments, the reinforcing flexible spacer may be made of a spacer structure made of molded pulp.

In embodiments, the parts made of molded pulp may have been made with functional additives such as fire-retardants, hydrophobization additives, dry strength additives and/or a wet strength additives.

In embodiments, the object may have a length of at least 1 m.

In another aspect, a method of producing a molded 3-D shaped object is provided. The method comprises a. Pressing a water based pulp slurry between a first male metal mold half spray coated or cast with elastomeric material and a second female metal mold half, and drying the pulp slurry at elevated temperature under pressure, to form the curved molded pulp shell, b. providing a core spacer structure and gluing the reinforcing spacer structure to the interior of the molded curved pulp shell. c. providing an inner shell made of molded pulp or another flexible paper based material and gluing it to the core spacer structure.

In embodiments, steps b and c are carried out by gluing one-faced

Reboard® to the interior of the curved molded pulp shell.

In embodiments, a single sheet of one-faced Reboard® may be glued to the entire interior of the curved molded pulp shell.

In embodiments, the pressing may be effected in a frame in which one of the mold halves is mounted in means for translational movement towards the other mold half, by means for compressing and holding the pair of mold halves fitted against each other and a bath of pulp slurry, and the means for translational movement may be adapted for

immersing a first mold half in the bath of pulp slurry and moving the first mold half into fitting compression against the second mold half.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments herein will now be described in more detail with reference to the appended drawings, wherein:

Fig. l shows a cross sectional view of a container made of a light-weight material according to embodiments herein.

Fig. 2 shows a perspective view of the light-weight container shown in Fig. i. Fig. 3 shows schematically the pair of mold halves used in a method which can be used to manufacture the shell for a material according to embodiments herein.

Figs. 4a-f show a frame which can be used with such mold halves to manufacture a shell for a material according to embodiments herein.

DETAILED DESCRIPTION

The large lightweight 3-D shaped pulp molded material, for example an object, according to embodiments herein is shown in the form of a container in cross section in Fig. 1 and in perspective in Fig. 2. The lightweight exemplary container in the material according to

embodiments herein is built up as a sandwich construction by three different parts comprising:

An outer shell 17 made of 3-D shaped molded pulp. This is the surface of the material and will by, for example, using the novel method for producing large molded pulp objects described in our co-pending Patent Application No. 1550864-1, entitled Pulp Molding Apparatus and Molds for Use Therein i) , have a smooth and even surface and make possible complex 3- D shaped designs.

ii) A core 18 composed of a flexible spacer structure that may but is not limited to a core of ReBoard™, a paper honeycomb structure, a molded core structure (as described in e.g. International Patent Application No. WO2010138066 Ai), or the corrugated core structure made by fluting used in corrugated boards. iii) An inner shell 19 made of molded pulp or a flexible paper based material such as a linerboard or paperboard.

By using a sandwich construction as described above, complex 3D- shaped designs may be utilized in the material while at the same time obtain a high strength material.

In one of the embodiments herein, a shell 17 is made of molded pulp and is lined in the embodiment shown with ReBoard^™ ⁾ with only a single linerboard, on its exposed interior surface. The ReBoard™then

composes both the core structure (ii) above) and the inner shell (iii) above). As one of the linerboards has been removed from a normal reboard material, the ReBoard™ 18 can be bent, without breaking, to conform to the inside of the molded pulp shell 17 before being glued to the shell, which will then replace the missing linerboard of the

reinforcing ReBoard™ spacer structure.

It is of course also possible to use other core materials used as spacer materials to line the molded pulp shell 17 that are able to conform to the interior curvature of the molded pulp shell. A honeycomb structure, having walls extending perpendicular to the surface of the shell 17 is also one possible spacer material, as well as the corrugated core used in corrugated board, or pulp molded spacer material as described above, thereafter covered with another inner shell made of molded pulp of a paper-based material in order to create a strong lightweight material.

In order to improve the properties further of the material, various functional additives may be used when producing the molded parts of the material. Additives that may be used in order to increase the

functionality of the material may be fire retardants, hydrophobization additives, dry strength additives and wet strength additives. This may be added in the pulp slurry used to make the molded material or object or may be added as a surface treatment by e.g. spraying or coating.

The molded 3-D shaped material is characterized by having an even and smooth surface and good mechanical properties. The density of the molded materials needs to be at least 100 kg / ms in order to obtain proper stiffness but may be even higher depending on the pressure used during the molding process.

The molded material or object maybe made of pulp from various fibers such as virgin wood fibers (e.g. chemothermo-mechanical pulp, chemical pulp or mechanical pulp), recycled wood fibers, textile fibers made of viscose, cotton or other cellulosic fibers, but may also be made of pulp comprising fibers mixed with thermoplastic fibers such as polylactic acid (as described in e.g. patent no EP2171154 Ai) in order to create

composite materials.

An apparatus is shown in Fig. 4 which can be used to make the molded pulp shell to form the container according to embodiments herein, and is described in our co-pending patent application No. 1550864-1, entitled Pulp Molding Apparatus and Molds for Use Therein.

It comprises a frame 1, holding a stationary platform holding a female mold half 3 and below it a movable platform 12 holding a male mold half 5-

Six synchronously motor driven nuts on six long screw rods 4 move the male mold half 5 from the slurry bath 16 (99.5 % water and 0.5% pulp fibers at 25-30 degrees C) to engagement in the female mold half 3, which is heated.

Fig. 3 shows in longitudinal cutaway view a pair of mold halves 3, 5 used for manufacturing shells 17 for the reinforced containers of embodiments herein. The male mold half 5 is made of hollow aluminum and is coated with an elastomer 6 which is ca 30 mm thick. This elastomer is

preferably sprayed onto the aluminum mold half. It is also possible to cast the elastomer onto the aluminum mold half. A typical elastomer should be hydrophobic but not be subject to hydrolysis. An advantageous hardness, particularly for a sprayed on elastomer is 70 A-Shore, to provide optimal elastic properties. 5 mm diameter through-holes spaced 15 mm from each other cover the elastomer layer and connect to

through-holes 8 in the aluminum body of the male mold half 5. Within the male mold half there is generated a vacuum of 0.5-0.9 bar. On top of the elastomer layer there is a wire mesh. In this case it is a 100 mesh (i.e. 100 threads per inch) and is approximately 1 mm thick. The wire mesh can also be laid in multiple layers which will further contribute to distributing the vacuum forces more evenly. The female mold-half 3 is made of aluminum and has in this example a weight of 700 kg. It is heated to ca. 200 degrees C, for example by means of heating rods embedded in the material of the female mold-half 3. This is the most energy effective method of heating the female mold-half. Its inner surface will create the outer surface of the product. The two mold halves, or parts of the mold halves such as an insert, can be made of porous aluminum to increase strength over sintered material and to increase heat

conductivity. The male mold-half 5 after being dipped in the slurry bath 6 (see Fig. 4a) dewaters the slurry through vacuum to approximately 20% dryness (80% water) and the male mold-half 5 is then pressed into the female mold-half 3 down to a gap of ca. 1 mm between the two mold halves. It can vary for this particular product between ca. 0.8 and ca. 1.2 mm without detrimental effects. The material is then dried under pressure at an elevated temperature (>ioo degrees, preferably 150 degrees). Due to absorbing coolness from the male mold-half 3 (temp of ca. 25 ⁰ C), the hot aluminum female mold-half 5 (initially ca. 200 ⁰ C) will in turn drop ca. 13 degrees C during the compression process. This temperature change causes the female mold-half to shrink over its length approximately 7-8 mm with corresponding contractions in its width (2.5 mm) and height (1.5 mm). This is compensated for by the elastomer layer 6. The temperatures in both the female and male mold-halves will vary up and down during the compression process thus repeatedly changing slightly the dimensions on the molds. In conventional pulp molding processes, these dimensional variations would cause stresses and unevenness in the finished product, possibly even ruptures. In this particular exemplary product, without an elastomer layer, the

temperature of the female mold-half must be rather precise, i.e. in this example between ca. 195 ⁰ and 204 ⁰ C. This precision is difficult to achieve and maintain in an industrial process of this type. These problems have been experienced even in the manufacture of relatively small pulp molded products, and require precise adjustment of the temperature to avoid them. Most pulp molded products, such as egg cartons, are several millimeters thick and are thus more porous and it makes no difference whether such products have a rough surface. A product with a rough surface cannot be used in many applications. For a large product, the problems of dimensional heat expansion/contraction will be greatly increased. These problems have hitherto made it impossible to

manufacture large pulp molded products with reasonable reject rates and with a smooth surface.

Embodiments herein was developed in order to produce shells for large containers with very few rejects and no necessity of precisely monitoring and continually adjusting the temperatures of the two mold-halves. Since the elastomer is used to absorb much of the dimensional variation of the male and female mold-halves, they can be made much lighter and thinner than otherwise since they will not require a large mass to prevent temperature variations. For instance in this example the female mold- half weighs ca. 750 kg. If it had to maintain a more constant temperature it might have to have a mass of several tons, requiring more energy to heat such a large mass and maintain the heat.

For example, a casket has in general curved sides, something which is expensive to produce in plywood or with wood planks. According to embodiments herein it is possible to produce shells of ca. 1-2 mm in thickness, which provides the maximum stiffness. Thicknesses greater or less than this thickness (1-2 mm) provide less stiffness.

These problems are solved by coating the surface of the male mold-half with an elastomeric material, onto which the wire mesh or meshes is/are then applied. This elastomeric material continually compensates for the varying dimensions of the two mold-halves during the

compression/heating process.

It is also advantageous for molding the shell to mount the stationary mold half (in this case the female mold half) to be slightly horizontally moveable (+- 25 mm) to make sure that any heating expansion will not prevent a correct horizontal alignment between the male and female mold halves during the pressing operation.

It is also advantageous to equip the pulp molding apparatus with mechanical jacks, combined with a more incremental final stage for the compression step. This final stage can also be accomplished with the aid of hydraulic pistons.

As can be seen in Fig. 3, the male mold half 5 is provided with channels 14 and large holes 8 beneath the elastomer layer 6 in order to prevent any reduction of the vacuum which holds the pulp slurry and dewaters it on the surface of the wire mesh.

Other embodiments herein further describes a method to produce the 3- D shaped molded lightweight material described above. The steps to produce the material comprises: i) Provide a 3-D shaped molded material 17, or object, with the apparatus described above with or without addition of functional additives used as outer shell in the sandwich material ii) Provide a spacer material 18 used as core in the sandwich

material, and glue said core spacer material to the 3-D shaped molded material or object

iii) Provide an inner shell 19 made of a 3-D shaped molded material or object or a flexible paper based material which will adhere to the spacer material.

The manner of providing the three dimensional molded material or object will now be described with reference to the figures and in

particular to Figs. 4a-4f. One apparatus for achieving this for comprises a frame 1, holding a stationary platform 2 on which is mounted a female mold half 3 and below it a movable platform 12 holding a male mold half 5. Figs. 4a, 4b and 4f show the apparatus in its mold-separated position and Figs. 4c, 4d and 4e show the apparatus its mold-compressed positon for forming the molded pulp shell. The same reference numerals for the same components are used throughout all of the drawings. The apparatus is shown in Fig. 4a in perspective view in the mold-separated position with the male mold half 5 submerged in a slurry bath 16. The liquid slurry itself is not shown in the figure. This same mold-separated position is shown in vertical section in Fig. 4b. The male mold half 5 is submerged in a pulp slurry bath 16 (99.5 % water and 0.5% pulp fibers at 25-30 degrees C) and a suction system 17 is connected to the hollow interior cavity 15 of the male mold, whereby a coating of pulp slurry is sucked onto the surface of the male mold half 5.

Six synchronously motor driven nuts on six long screw rods 4 move the male mold half 5 from the slurry bath 16 into pressure engagement with the female mold half 3, which is heated, in the compression position of the molds shown in Figs. 4c, 4d and 4e.

The large molded material or object of embodiments herein maybe of any size. The method of embodiments herein is in particular of use when the material has a size larger than what can be made with conventional molding technology. The 3-D molded material or object of embodiments herein may for example have a length of 1 m or longer or in another example a diameter of 1 m or bigger.