EP4689286A1 - Highly refined fibre forming process - Google Patents

Abstract

The present invention relates to a forming process. In particular it relates to a double-layer forming process improved with the purpose of obtaining in the final product an oil-proof barrier without using chemical additives.

Description

HIGHLY REFINED FIBRE FORMING PROCESS

DESCRIPTION

The present invention relates to a forming process. In particular, the invention relates to a double-layer forming process improved with the purpose of obtaining in the final product an oil-proof barrier without using chemical additives.

Background

Currently, the double-layer thermoforming is used for the production of two-layer products, typically in the food industry, with the purpose of minimizing the content of quality raw material and chemical products and concentrating them exclusively in the layer in contact with the food products, thus falling within the limits provided by the International institutions to release the compostability certifications and obviously by meeting the food prerequisites.

The resulting products are made of possibly different materials, but still made of cellulose pulp.

It is known in the art that the films made of cellulose having a high refining degree (microfibri Hated cellulose) lead to oil-proofing of the produced objects.

However, despite the observed barrier properties are very good, currently the application of the microfibrillated cellulose in the thermoforming field finds a great obstacle consisting in the difficulty in obtaining adequate and homogeneous layer thicknesses. In fact, the microfibrillated cellulose is formed by very thin particles which clog early and unevenly the water draft porous septum, which indeed prevents from reaching the wished thicknesses (and, therewith, the weight) and uniformity.

The problem of forming the high refining fibre, in principle, is generated by the fact that the obstruction of the forming porous septum is caused before succeeding in forming a layer with convenient thickness for great part of applications (indicatively > 0.3 mm).

For this reason, the microfibrillated cellulose is not (currently) used for this kind of applications. Therefore, in order to be able to use the cellulose refined at very high levels in the processes of thermoforming 3D objects it is necessary to find alternative solutions.

Within the present description: under the term of ‘high refining’ one means a fibre treated (mechanically or chemically) so as to reach a high fibrillation (higher than 70°SR) and this is used in the production process with a consistency ranging between 0.7% and 3%, preferably 1%; under the term ‘low refining’ one means a fibre with low fibrillation degree (lower than 70°SR), the consistency of this fibre typically is comprised between 0.2% and 0.6%,

Under the term consistency one means the percentage of the fibre mass with respect to the total mass of water plus fibre.

Technical problem solved by the invention

The object of the present invention is then to solve at least partially one or more of the problems left unsolved by the known art, in order to be able to produce - through thermoforming - a double-layer product wherein at least one of the two layers is made of cellulose with high refining degree, then oil-proof, as defined in claim 1.

This is obtained through a process as defined in claim 2.

The present invention further relates to a plant for producing - through thermoforming - a double-layer product wherein a layer is made of cellulose with a high refining degree, then oil- and greaseproof, as defined in claim 8.

Additional features of the present invention are defined in the corresponding depending claims.

The evolutive step with respect to the already known technology, then, was that of detecting the use of the double layer as a first solution to the problem. On the contrary, the subsequent step was to understand how to obtain the adequate weight, that is by working with the high-consistency fibre to guarantee the adequate amount of fibre to form the layer. It is known that by applying high consistencies (>0.7%) one incurs in the agglomeration of fibres in the bath which is commonly designated as flocculation. The fact of working with higher consistencies, then in flocculation regime, brought advantages related to the layer weight, but it made difficult to distribute adequately the fibre. The crucial step to solve this problem was to apply transversal and vertical motions during the process of forming the high refining layer. Apart from the transversal motion on the horizontal plane, which already gives very good results, in combination or individually even the vibration in the vertical direction can be applied to solve the problems due to the flocs’ distribution.

The internal layer made of high refining fibre of the deep objects (depth higher than 2 cm) may require even the application of a cold pre-pressing (deepsqueezing) step in order to guarantee a pre-compression and a good distribution of the fibre even on the vertical sides of the formed object.

Additional advantages, together with the features and the use modes of the present invention, will result evident from the following detailed description of preferred embodiments thereof, shown by way of example and not for limitative purposes.

Brief description of figures

The drawings shown in the enclosed figures will be referred to hereinafter in this description, wherein:

• figure 1 is a schematic view of a first plant portion for implementing a process according to the invention;

• figure 2 shows an alternative mode relatively to the step of forming the high refining layer;

• figure 3 is a schematic view of a second plant portion for implementing a process according to the invention;

• figure 4 shows an alternative mode relatively to the step of forming the low refining layer;

• figure 5 is a schematic view showing the coupling of two layers of cellulose;

• figure 6 describes the possible step of cold pre-compression (deepsqueezing); • figure 7 is a schematic view showing the thermoforming of a product;

• figure 8 shows, by way of example, a finished resulting product.

Detailed description of preferred embodiments

The present invention will be described hereinafter by making reference to the above-mentioned figures.

According to the present invention, a thermoforming process, for the production of double-layer products wherein one of said layers is a layer of high refining fibre, comprises the following steps:

• providing a high refining fibre;

• forming, through a first forming counter-mould 1 , a first layer 6 of high refining fibre.

Preferably, the process further provides:

• to provide a low refining fibre;

• to form, through a second forming counter-mould 11 , a second layer 16 of low refining fibre.

Subsequently, the two layers 6 and 16 could be coupled, by approaching said first and second forming counter-moulds 1, 11 , to form a union 21 of the two layers 6, 16. Such union 21 could be then thermoformed according to the known technology in order to obtain the finished product.

In case of production of deep objects even the application of a cold pre-pressing (deep-squeezing) step could advantageously be provided, which allows a first compaction of the thickness of the two coupled layers.

In particular, figure 1 shows, schematically and by way of example, a first portion of a plant for implementing the production process.

Such first plant portion is assigned to form the first layer 6 of high refining fibre. In particular, in a first tank 3 the high refining fibre is inserted. A first forming counter-mould 1 , which preferably has a porous functional septum 2 for example a forming net, and having the profile of the product to be implemented - is soaked into the tank 3 containing the high refining fibre, so that the net-like face 2 is soaked into the cellulose pulp 4.

The first forming counter-mould 1 has a hollow or concave shape and it comprises a sleeve 5 for the connection with the water draft system.

According to the invention, a suction can be applied through the sleeve 5 (arrow F1 in figure 1). For example, through a pump a vacuum up to about 33 mbar is generated.

In this way the cellulose pulp is sucked, the fibres thereof deposit onto the net 2 by forming said first layer 6.

By way of example, figure 1 illustrates an embodiment wherein the suction takes place from top, that is according to a direction opposite to that of the force of gravity Fg.

The fibre pulp 4 at a consistency ranging between 0.7 and 3% results to be very flocculous and indeed this allows to succeed in sucking the fibre amount suitable to the formation of the wished layer before the occlusion of the porous septum occurs. In case of the not flocculated pulp, the forming suction pores would be locked by the fibrils before it is possible reaching the fibre amount sufficient to form the layer.

Upon starting the vacuum through the sleeve 5, the flocs of the diluted pulp present in the tank are sucked through the net by locking the cellulose fibres on the same to form a wet layer, while allowing the drainage and removal of the dilution water which will be extracted with the vacuum flow.

Preferably, the first forming counter-mould 1 is left soaked into the tank 3, with the applied vacuum, for a predefined suction time T1. The suction time is set depending upon the wished weight for the final product, typically, but not exclusively, between 100 and 800 g/m². The time T1 can vary even based upon the type of used fibre and upon the bath consistency. Preferably, for the shown weights, T1 is comprised between 0.1 and 10 seconds. Once the suction time T1 has elapsed, the first forming counter-mould 1 is extracted from the bath. Preferably the suction through the sleeve 5 remains active even during this step, and even when the first forming counter-mould 1 is outside the tank 3, no more soaked in the cellulose pulp. In this way, a first dehydration of the preformed product is implemented. This dehydration step can last for a predefined dehydration time T2, set so as to obtain, in the end, a dry degree ranging between 15% and 35% by weight of solid content. Time T2 can vary even depending upon the cycle time. Preferably, a minimum dehydration time of 2 seconds and a maximum dehydration time of 20 seconds is taken into consideration.

Advantageously, the first forming counter-mould 1 , during soaking in the tank while sucking the refined pulp, can be made to vibrate in the vertical direction (that is the direction z in figure 1) with at least a vibrator 24, preferably having a nominal frequency of 100-600 Hz. Preferably two vibrators 24 can be provided, placed parallelly, each one having the nominal frequency of 100-600 Hz. In case, the first forming counter-mould 1 can even be made to swing horizontally and alternatively, for example by ±5-150 mm in the x-y plane, according to a directrix y-y as indicated by the arrows F25 in Figure 1 and/or according to the directrix x-x, so as to guarantee a good distribution of the fibre composing the various flocs on the forming net 2.

It is to be noted that the process takes place in flocculation regime. A layer is generated and by definition the flocs generate a not homogeneous layer. The application of a vibration and/or of an alternative motion of the mould allows to uniform these flocs.

According to an alternative mode, the layer forming can take place even with a forming counter-mould T positioned differently inside the tank 3, as illustrated in figure 2.

For sake of clarity, the elements and modes which are equal to what described in relation to the preceding embodiment are identified through equal numbers and, of such alternative embodiment, only the aspects which differ therefrom will be described.

In particular, figure 2 illustrates the step of forming the layer 6 (with high refining fibre).

As in the preceding embodiment, the forming step preferably takes place through a porous septum 2 crossed by the diluted pulp which allows the formation of the layer 6. Such step is carried out by sucking through a sleeve 5’ (arrow FT in figure 2). For example, through a pump a vacuum up to about 33 mbar is generated.

According to this alternative mode, the forming takes place by sucking from bottom, that is according to a direction in agreement with the force of gravity Fg.

With reference to figure 3, in a second tank 13 low refining fibre is inserted.

According to modes analogous to what already described in relation to the forming of the first layer 6, a second forming counter-mould 11 , which preferably has a porous functional septum 12 for example a forming net, having the profile of the product to be implemented - is then soaked in the tank 13 containing the low refining fibre, so that the net-like face 12 is soaked in the cellulose pulp 14.

The second forming counter-mould 11 preferably has a hollow shape and it comprises a sleeve 15 for the connection with the external environment.

According to the invention, a suction can be applied through the sleeve 15 (arrow F2 in figure 2). For example, through a pump a vacuum up to about 33 mbar is generated.

In this way, through the sleeve 15 and the net-like face 12, the cellulose pulp is sucked, the fibres thereof deposit onto the net 12 thus by forming the second layer 16.

By way of example, figure 3 illustrates an embodiment wherein the suction takes place from top, that is according to a direction opposite to that of the force of gravity Fg. With reference to figure 4, according to a mode alternative to the just described one, the forming of the layer 16 (with fibre having low refining degree) can take place even with a forming counter-mould 11’ positioned differently inside the tank 13, as indeed illustrated in figure 4.

For sake of clarity, the elements and modes which are equal to those described in relation to the preceding embodiment are identified through equal numbers and, of such alternative embodiment, only the aspects which differ therefrom will be described.

In particular, figure 4 illustrates the step of forming the layer 16 (with low refining fibre).

As in the preceding embodiment, the forming step preferably takes place through a porous septum 12 crossed by the diluted pulp which allows the formation of the layer 16. Such step is carried out by sucking through a sleeve 15’ (arrow F2’ in figure 2). For example, through a pump a vacuum up to about 33 mbar is generated.

According to this embodiment, the forming takes place by sucking from bottom, that is according to a direction parallel to the force of gravity Fg.

Generally, the forming from top allows to obtain thinner and more uniform thicknesses and better definition of the edges. However, the de-watering (removal of water portion by simple suction once the product has re-emerged from the bath) results to be more difficult due to the contrast between draft and force of gravity and therefore the product will result to have less dry content and then to be softer, with consequent less manoeuvrability for the transfers of the same.

On the contrary, the forming from bottom allows to obtain greater thicknesses and a better de-watering since the suction takes place in the direction of the force of gravity.

It is to be meant that the different forming modes (from top and bottom) can be used for forming only one of the layers or both of them without this involving variations in the subsequent steps of the process which will be described hereinafter, except for the systems for conveying the layers to bring them to the station in which the overlapping and thermoforming take place, systems which can be implemented according to different methods already applied in known art.

Then, the invention has not be considered to be limited to one of the described modes (from top and/or bottom), but rather comprising even other forming modes. The method for transferring the layers to the coupling/thermoforming station can neither be considered a variant subject of original inventive activity.

The preferred combination of the above-described forming modes, for implementing the double-layer products, with the high refining fibre in the internal layer and the low refining fibre in the external layer, is the one in which the internal layer is formed from top and the external layer is formed from bottom.

Once the layers are formed with the above-described methods, they are typically, but not exclusively, transferred to the overlapping and thermoforming station.

Once even the second layer 16 has formed, in order to obtain a finished product, the two layers 6 and 16 are coupled. The coupling procedure is schematized by way of example in figure 5, which represents the detachment of the first layer 6 from the counter-mould 1 and its overlapping to the second layer 16 - already transferred onto the definition mould 51 - to form a union 21.

The illustrated and described example shows the coupling of a first layer 6 formed from top with a second layer 16 formed from bottom directly. Said arrangement revealed to be the preferred one upon experimentation, although even the other coupling combinations between layers formed from top or from bottom can be applied alternatively.

More conveniently, the overlapping can be performed directly even at level of one of the two forming stations (for example in the above-described preferred combination the overlapping could take place directly on the forming mould 11’), with the result that the coupled layers then will have to be transported to the subsequent thermoforming station.

Moreover, especially in case of implementing hollow objects with depth higher than 2 cm and draft angles lower than 10-20°, a cold pressing (deep-squeezing) procedure may become necessary, adapted to induce a pre-compacting of the thickness of the coupled layers (figure 6). Said pre-compacting, which can be performed with methods already applied in known art (mechanical or pneumatic/hydraulic compression by inserting expandable membranes (100) reproducing in negative the objects to be implemented), typically, but not exclusively, is performed at the overlapping and coupling station in the abovedescribed variants of the latter.

At this point the process proceeds with thermoforming, illustrated by way of example in figure 7.

The techniques for transferring the layers and/or the coupled layers of cold pre-compression (deep-squeezing) of the coupled layers where conveniently applicable and of thermoforming (in one or more stages) are widely described and experimented in known art, thereto it is herein referred.

Figure 8 shows, by way of example, a product 200, for example a dish, implemented by having an internal layer 6 made of high refining fibre.

Advantageously, the product 200 can be implemented according to what described.

The present invention has been sofar described with reference to preferred embodiments thereof. It is to be meant that each one of the technical solutions implemented in the preferred embodiments, herein described by way of example, can advantageously be combined, differently from what described, with the other ones, to create additional embodiments belonging to the same inventive core and, however, all within the protective scope of the herebelow reported claims.

Claims

1. A thermoformed product (200) with double layer of cellulose fibres, wherein a first layer (6) of said double-layer is a layer of high refining fibre.

2. A process for forming layers of cellulose fibre for the subsequent production of a double-layer thermoformed product wherein a first layer (6) of said double-layer is a layer of high refining fibre.

3. The forming process according to claim 2, comprising the following steps:

• providing a high refining cellulose fibre (4) with consistencies higher than 0.7% so as to work in flocculation regime to form said first layer (6) of high refining fibre;

• distributing the flocs on a first forming counter-mould (1,1’) by applying a vibration to said first forming counter-mould (1 ;T);

• forming, by means of said first forming counter-mould (1 ; T), said first layer (6) of high refining fibre.

4. The forming process according to claim 2 or 3, comprising the following steps:

• providing a low refining cellulose fibre (14);

• forming, through a second forming counter-mould (11 ; 11’), a second layer (16) of low refining fibre.

5. The process according to one of the preceding claims, wherein said step of forming said first layer (6) of high refining cellulose fibre provides to apply an alternative motion in the x-y plane according to a directrix y-y or x-x.

6. The process according to one of claims 4 or 5, further comprising the steps of: coupling said first and second layer (6, 16) to form a union (21) of the two layers (6, 16); • thermoforming said union (21) of said first and second layers (6, 16) coupled to form said product.

7. The process according to the preceding claim, further comprising a step of cold pre-compressing (deep-squeezing) said union (21) of said first and second coupled layers (6, 16), preceding said step of thermoforming said union (21).

8. A plant for forming layers of cellulose fibre for the subsequent production of a double-layer thermoformed product wherein a layer (6) of said doublelayer is a layer of high refining fibre, comprising:

• a first forming stage comprising a first tank (3) suitable to contain a high refining cellulose pulp (4), a first forming counter-mould (1 ; T) to form a first layer (6) of high refining fibre and at least a vibrator (24) configured to put into vibration said first forming counter-mould (1 ; 1’).

9. The plant according to the preceding claim, wherein said vibrator vibrates at a nominal frequency ranging between about 100 Hz and about 600 Hz.

10. The plant according to claim 8 or 9, further comprising a second forming stage comprising a second tank (13) suitable to contain a low refining cellulose pulp (14) and a second forming counter-mould (11 ; 1 T) to form a second layer (16) of low refining fibre.

11. The plant according to one of claims 8 to 10, wherein said first forming stage comprises horizontal translation means so as to make said first forming counter-mould (1 ; T) to translate alternatively according to opposite directions on x-y plane.

12. The plant according to the preceding claim, wherein said translation has a width between about 5 and 150 mm in each direction y-y or x-x.

13. The plant according to one of claims 8 to 12, further comprising a cold precompressing (deep-squeezing) counter-mould (101) to perform a step of squeezing the coupled layers (6, 16).

14. The plant according to one of claims 8 to 13, further comprising:

• a thermoforming counter-mould (41) for thermoforming the two coupled and overlapped (21) layers (6, 16);

• means for moving moulds and/or counter-moulds.