Press Mold for Receiving a Fiber-Based Blank, and Method for Reducing the Water Content in a Fiber-Based Blank

The present invention relates to a press mold for receiving a fiber-based blank, in particular for receiving a container or a fiber-based closure element, and a method for reducing the water content in a fiber-based blank, in particular in a container or in a fiber-based closure element for a container according to the preamble of the independent claims.

A fiber-based blank in the form of a container was disclosed in WO 2012/139590 A1. To produce this container, so-called pulp is injected into an upside-down mold and pressed against a corresponding wall in this mold using a flexible balloon and compressed accordingly. The pulp is compressed and heated to a temperature of around 180° C. in order to dry the container. It is also known to produce closure elements for containers from pulp.

The pulp is a mixture of fibers and water, in particular natural fibers such as hemp fibers, cellulose fibers or flax fibers or a mixture thereof. Optionally, the pulp has additives that, for example, improve the curing of the compressed pulp or have an influence on the later appearance or generally change the properties of the pulp or the later container.

The aforementioned method is time-consuming and energy-intensive. It has therefore already been suggested to improve this. WO 2018/020219 A1 introduced a further method for drying wet, fiber-based blanks. In this case too, the blanks are containers. Here, the wet pulp is also pressed together with a flexible balloon inside the casting mold. The pre-processed container is then demolded together with the balloon inside it and placed on a conveyor belt. The balloon is removed from the cold-formed container. The container is then exposed to microwaves to dry it. The blank is very sensitive to the application of force before drying and must be handled very carefully. During the drying process, the container may become deformed, for example due to uneven drying or a non-uniform layer thickness, or it may be damaged by external influences.

It is the object of the invention to remedy at least one of the disadvantages of the prior art. In particular, a device and a method are to be provided which make it possible to dry wet fiber-based blanks, in particular containers, such as bottles, cups, bowls or dishes or wet fiber-based closure elements, with low energy expenditure, while ensuring that they remain dimensionally stable.

This object is achieved by the devices and methods defined in the independent claims. Further embodiments result from the dependent claims.

A device according to the invention is provided by a press mold for receiving a fiber-based blank. The fiber-based blank can in particular be a container or a fiber-based closure element for a container. The press mold is intended for use in a microwave chamber. In addition, the press mold is permeable to microwaves. In the closed state of the press mold, at least one gap is formed inside the press mold through which moisture can escape.

By providing a microwave-permeable press mold for the fiber-based blank, a wet fiber-based blank can remain within the mold during the drying process, i.e. during exposure to microwaves. The blank is thus protected against external influences and damage or deformation is prevented. By providing the wet fiber-based blank inside the microwave-permeable mold, it can also be ensured that said blank is accessible to the microwaves from all sides and drying can therefore be carried out from all sides. After this drying step, the wet fiber-based blank has a water content of approximately 5% to 12%.

In the present method, the wet fiber-based blanks are typically shaped as already known in the prior art. In other words, pulp is introduced into a porous casting mold or into a solid casting mold having water-draining channels, the inlets of which are covered with screens or the openings of which are small enough that the fibers of the pulp cannot penetrate, and the fibers of the pulp are applied to the inner wall of the casting mold so as to form a wall of a blank. Once the wall is sufficiently thick, the swelling of the pulp stops. The semi-finished product now present, i.e., the wet fiber-based blank, is removed from the casting mold and introduced into the microwave-permeable press mold and thus provided in the press mold. At this point, the wet fiber-based blank has a water content of approximately 75% or less, such that it can be transported between the processing stations in a dimensionally stable manner.

The wet fiber-based blank is removed from the casting mold using a suitable transfer device. Subsequently, the wet fiber-based blank is inserted into the opened press mold. After insertion, the press mold is closed. The press mold is preferably formed in two parts. In this case, removal and insertion may require blowing out and/or a suction by means of negative or positive pressure. It is also possible to use purely mechanical grippers for this transfer.

Typically, the press mold can have an inner wall that is designed with a higher surface quality compared to the inner wall of the casting mold.

Preferably, after the fiber-based blank has been provided in the press mold, an expandable tool is introduced into the fiber-based blank. By expanding the expandable tool, the water content of the fiber-based blank can be reduced in a first step by compressing a wall of the blank. At this point, the wet fiber-based blank has a water content of approximately 50%-60%.

The at least one gap on the press mold allows the displaced moisture, which in this case is substantially water, to escape from the press mold.

Accordingly, it is not necessary to make the press mold as such water-permeable. On the one hand, this makes it possible to produce the surfaces of the press mold with a higher quality, and on the other hand, any pores or channels in the press mold do not have to be laboriously cleaned after the press mold has been used.

The moisture can also be removed in a targeted manner through a gap, or the regions in which the moisture is removed can be selected in a targeted manner.

The gap also allows moisture to be removed in a later step, namely during exposure to microwaves. However, in this step the moisture is typically present as vapor.

A gap within the meaning of the present description is an opening with an elongated extension. In other words, the opening has a length whose dimension is several times greater than the width dimension, in particular more than twenty times. A gap is also arranged in each case in such a way that moisture can escape from the inside of the press mold, i.e. from a cavity, to the outside. In other words, the gap is an opening that provides a passage arranged radially with respect to a longitudinal axis of the press mold.

It can be provided that the at least one gap is formed in a region of the press mold that corresponds to a region on the fiber-based blank that is removed prior to use of a product made from the fiber-based blank. It may be provided that additional further gaps are arranged on the press mold.

Under certain circumstances, the gap may leave machining marks on the surface of the blank. If the gap is formed in a region that will later be cut off from the blank, this circumstance is irrelevant. Any changes to the surface are therefore not visible on the finished product, as these regions are cut off accordingly.

In particular, it can be provided that the at least one gap is formed in a region of the press mold which corresponds to a neck of the blank.

The neck of the blank can be selected to be correspondingly longer in relation to the finished product and the protruding region can be easily cut off.

As already explained, the press mold can be formed in two or more parts. Accordingly, it has one or more mold parting lines. It can be provided that the gap is formed on at least one of the mold parting lines. This is as an alternative or in addition to a gap in a region that is later cut off from the blank, as described above.

The formation of the gap at a mold parting line enables simple production of the gap, since the mold parting line is easily accessible with tools during production. In addition, a gap at the mold parting line can be cleaned easily and inexpensively.

If the mold parting line of the press mold extends in the same region as a corresponding mold parting line of a casting mold, corresponding defects that arise on the blank after casting can be captured at the same location in the press mold. This means that the blank is not subjected to unnecessary stress.

In particular, provision may be made to divide the gap between the two elements of the mold parting line. In other words, in the case of a two-part mold, half on each part of the mold. However, it would also be possible and conceivable to provide the gap in only one of two mold halves.

In other words, the press mold halves do not touch each other in the region of the cavity, i.e. on the inner wall of the cavity, but are spaced apart by the gap. In the radial direction outwards, this gap can widen and form a channel, which narrows again as the radial distance to the center of the press mold increases. The two press mold halves then rest on top of each other such that the channel is closed. When the press mold is completely closed, the mold parting line forms the gap in the direction towards the inside of the press mold.

Preferably, the at least one gap is formed circumferentially along the entire mold parting line.

This increases the opening cross-section through which the moisture can escape. In addition, by arranging the gap along the entire mold parting line, the entire blank is also substantially accessible from all sides. This is also advantageous because a visible marking will appear on the product in this region due to the casting process. By arranging the gap at the same location, an additional machining mark can be prevented.

It is conceivable that the press mold is formed in two parts in the region of a container body and additionally has a separate one-part shoulder region and/or a separate one-part floor region.

As already explained, the at least one gap can open into a moisture-discharging channel which is arranged within a wall of the press mold. In other words, the gap can spread out and expand/enlarge in the direction into the press mold such that a corresponding channel is formed. The moisture can be discharged within this moisture-discharging channel.

By providing a channel, it can be ensured that even larger amounts of moisture can be discharged without causing a build-up in the region of the gap. A corresponding channel also makes it possible to create a forced flow to discharge the moisture.

The at least one gap can have a width of 0.04 mm to 0.1 mm, in particular up to 0.4 mm. The preferred width is from 0.6 mm to 0.25 mm.

On the one hand, these values are large enough that a corresponding amount of moisture can be discharged, but on the other hand, small enough that no marks remain on the fiber-based blank.

The length of the gap is many times greater, preferably at least 20 times, preferably 100 times greater than its width. In particular, the length of the gap extends along the press mold over at least 25% of the inner contour, preferably in the axial direction, i.e. in the direction of the longitudinal axis of the press mold or of the fiber-based blank formed therein.

Provision may be made for additional openings or gaps to be provided in or on the press mold for discharging moisture. In particular, with certain geometries of the blank it may be necessary or advantageous to discharge moisture at other critical locations in addition to a gap at the mold parting line.

The moisture-discharging channel can be connected to a device for generating a negative pressure or an overpressure, so that a specific flow can be created in the moisture-discharging channel. This allows the moisture to be discharged more quickly and in a more targeted manner.

In addition, it may also be provided to temper and/or dry the flow in this channel. If an appropriate temperature, for example an elevated temperature, is provided in the channel, vapor can be prevented from condensing as moisture in the form of water in the channel.

Openings, holes or channels that have a direct connection to the outside can open into the moisture-discharging channel, such that the moisture can be discharged more quickly. In addition, corresponding channels also allow moisture to be discharged at specific locations along the moisture-discharging channel, so that moisture discharge can be accelerated in preferred regions.

The press mold may have a substantially uniform wall thickness. This ensures that the blank in the press mold is exposed substantially uniformly to microwaves and that these act correspondingly uniformly on the blank.

Bearing elements can also be provided on the press mold in order to support the press mold. Typically, a press mold as described here is relatively thin-walled and/or made of at least partially elastic materials. Deformation of the press mold can be prevented by using appropriate bearing elements.

The microwave-permeable press mold can be made of a material selected from the list of materials comprising PEI, PI, PE, POM, PEEK, wood, PTFE, ceramic, glass and PP.

A method according to the invention for reducing the water content in a

fiber-based blank, in particular in a fiber-based container or a fiber-based closure element for a container, comprises the steps of:

This enables moisture to be discharged from the blank in a targeted manner and the moisture content of the blank to be reduced accordingly, such that it has a residual moisture content of less than 15%, in particular between 6% and 12%.

The fiber-based blank is preferably provided in a microwave-permeable press mold.

The wet fiber-based blank is preferably exposed to microwaves after being provided in the press mold.

It can be provided that the expandable tool remains in the expanded state during exposure to microwaves.

Pressure on the wall of the wet fiber-based blank can be maintained. In addition, as the expandable tool remains inside the wet fiber-based blank, it is supported from the inside and unwanted deformation is prevented. This also improves the surface quality of the blank.

In particular, the blank is exposed to microwaves when the expandable tool is pressurized and expanded.

Exposure to microwaves can, in particular, convert the moisture in the fibers into a vaporous phase such that it can escape from the fibers. This vaporous or gaseous phase is preferably discharged through the at least one gap.