Method for die cutting cellulose foam material

Abstract

The present invention relates to a method for cutting cellulose foam material, comprising: providing a die cutting tool a body having a serrated edge with more than one cutting tooth wherein the cutting tooth has a tooth length and a tooth width between the top of each tooth, providing a cellulose foam material having a thickness, positioning the cellulose foam material adjacent to the die cutting tool and applying a force to the die cutting tool thereby cutting the cellulose foam material wherein the teeth length of the cutting tooth is at least half the size of the thickness of the material and the compression of the material during cutting is less than 10% of the total thickness of the material. The invention also relates to a die cutting tool for cutting cellulose foam materials.

Description

[0001] METHOD FOR DIE CUTTING CELLULOSE FOAM MATERIAL

[0002] FIELD OF INVENTION

[0003] The present disclosure relates to a method for cutting cellulose foam materials and a die cutting tool that allow for efficient cutting with reduced compression of the cellulose foam material.

[0004] BACKGROUND

[0005] Cellulose foam materials have gained significant attention in various industries due to their unique properties, including low density, high porosity, and biodegradability. These materials are typically produced by creating a foam structure from cellulose fibers, often derived from wood or other plant sources. The resulting foam can be used in applications such as packaging, insulation, and absorbent products.

[0006] Die cutting is a common manufacturing process used to shape and cut various materials, including foams. Traditional die cutting tools often employ straight blades or serrated blades with relatively short teeth lengths. These conventional die cutting tools are designed to work effectively with a wide range of materials.

[0007] However, when conventional die cutting tools are applied to cellulose foam materials, they often encounter significant challenges. The unique structure of cellulose foams, which typically consists of a densified outer layer and a more porous core, can lead to material deformation. The low-density nature of cellulose foams makes them particularly susceptible to compression during the cutting process, which can result in a permanent reduction in thickness and alteration of the foam's desirable properties.

[0008] Furthermore, the fibers of the cellulose foam may become entangled or compressed before they are completely severed, which also leads to an undesired compression of the material. There is therefore a need for a new method and a tool for die cutting of cellulose materials in an improved way that overcomes at least some of the mentioned problems.

[0009] SUMMARY

[0010] It is an object of the present disclosure to provide an improved method for die cutting cellulose foam materials.

[0011] It is another object of the present disclosure to provide a method for die cutting cellulose foam material with reduced compression of the material.

[0012] It is an object of the present disclosure to provide a method that makes it possible to create clean cuts in cellulose foam materials.

[0013] It is another object of the present disclosure to provide a method that makes it possible to decrease the force used during cutting.

[0014] It is a further object of the present disclosure to provide a die-cutting tool suitable for die cutting cellulose foam materials.

[0015] According to a first aspect illustrated herein, a method for cutting cellulose foam material is provided. The method comprises: providing a die cutting tool comprising a body having a serrated edge with more than one cutting tooth wherein the cutting tooth has a tooth length and a tooth width between the top of each tooth, providing a cellulose foam material having a thickness, positioning the cellulose foam material adjacent to the die cutting tool and applying a force to the die cutting tool thereby cutting the cellulose foam material, wherein the teeth length of the cutting tooth is at least half the size of the thickness of the material and the compression of the material during cutting is less than 10% of the total thickness of the material. It has been found that it is possible to die cut a cellulose foam material in an improved way that will reduce or even eliminate the compression of the material during cutting. The compression of the material is measured where the material has been cut by the die cutting tool, i.e. the thickness of the material in the cutting edge is measured and the compression is calculated based on the thickness of the material before cutting. The compression of the material during cutting is preferably less than 7%, preferably less than 5% of the total thickness of the material.

[0016] It is a common problem that a material being cut by a die cutting tool is compressed during cutting. It is especially important when cutting a porous material such as a cellulose foam material that the material is not compressed during cutting. A compressed cellulose foam material often stays compressed also after cutting, therefore the properties of the material has changed and often in a negative way. This preservation of the structure of the cellulose foam material is important for applications where the foam's properties, such as insulation or cushioning, depend on its internal structure

[0017] The method according to the invention has also been found to produce clean and precise cuts. The longer teeth and reduced compression allow for a controlled cutting action, resulting in smooth cutting edges and shaping of the cellulose foam material.

[0018] Furthermore, the design of the die cutting tool and its interaction with the foam material could lead to reduced wear on the cutting edges. By distributing the cutting force over fewer, longer teeth, each tooth experiences less stress during the cutting process, potentially extending the lifespan of the die cutting tool. The improved cutting quality and reduced compression has also been found to result in less waste material during the cutting process. Foam materials that maintain their structure and properties are less likely to be rejected due to deformation or damage, potentially improving overall material efficiency in manufacturing applications.

[0019] The force applied during cutting may be below 6kN per die meter, preferably below 3kN per die meter, even more preferred below 2kN per die meter and most preferred below 1 ,5kN per die meter. The force may be between 0.2-6kN per die meter, preferably between 0.3-3kN per die meter, even more preferred between 0.5-2kN per die meter and most preferred between 0.5-1 ,5kN per die meter. The force applied is the maximum force applied for the die cutting tool to cut through the cellulose foam material. The force per die meter is the force applied calculated on the total length or circumference of the blade of the die cutting tool. It has been found that it is possible to decrease the needed force applied to the die cutting tool during cutting. The decreased force applied further reduces the risk of compressing the material too much.

[0020] The teeth length of the die cutting tool is at least half the size of the thickness of the material, preferably at least two-thirds, even more preferred at least the same length as the thickness of the material. The die cutting tool preferably has a tooth length of at least 2 cm, preferably between 2-10 cm, even more preferred between 3-8 cm and most preferred between 4-7 cm. The preferred length of the teeth of the die cutting tool is thus very long. These tooth length ranges allow for effective cutting of cellulose foam materials of various thicknesses while reducing the compression of the material. The thickness of the cellulose foam may be in the range of from 1 to 20 cm, or from 1 to 10 cm, or from 1 to 6 cm, or from 2 to 6 cm. When a force is applied to the die cutting tool, the longer teeth penetrate the cellulose foam material more easily. This initial penetration requires less force, reducing the likelihood of compressing the cellulose foam material. As the teeth continue through the foam, they maintain a more consistent cutting action due to their length.

[0021] The tooth width is a measurement of the distance between each tooth. The tooth width of the die cutting tool may be between 1-8 cm, preferably between 2-5 cm. Optimizing the tooth width helps distribute the cutting force evenly and contributes to achieving clean cuts with minimal compression. The tooth width (also known as tooth spacing) may be uniform or variable, meaning that the distance between the top of each tooth may vary. It is however preferred that the tooth width is uniform, meaning that the distance between each tooth is the same. The tooth width between the teeth of the die cutting tool is wider than in traditional designs. This configuration reduces the total surface area in contact with the cellulose foam material during the cutting process. As a result, the material experiences less overall compression, which helps preserve its internal structure and original properties. The shape of the tooth of the cutting tool is preferably in the form of a triangle. The angle at the top of each tooth is preferably between 20-50°. The preferred angle depends for example on the cellulose foam material being cut. The triangle shaped tooth with the mentioned angle has been found to efficiently cut the cellulose foam material.

[0022] The ratio between the tooth length (13) and the tooth width (d) is preferably more than 1 , preferably more than 1.2. It is preferred to have the mentioned ratio since it has been found to give an optimal cutting performance for cellulose foam materials.

[0023] The cellulose foam material may have a solid content in the range of 80 to 100 wt%, preferably between 90-100 wt% prior to the cutting step. The method may include a drying step to increase the solid content of the foam to the mentioned solid content. The cellulose foam material is thus a solid cellulose foam. This feature ensures that the method is effective for cutting cellulose foam materials with high solid content, which are typically more challenging to cut cleanly.

[0024] During drying a densified layer is formed on the outer surface of the wet cellulose foam and remain on the outer surface of the dried cellulose foam. The densified layer comprises cellulose fibers that are packed more tightly and partly oriented differently compared to the bulk. The densified layers have improved mechanical stability and strength as compared to the core of the cellulose foam. The core of the cellulose foam comprises a homogenous open-cell fiber network. The core is highly porous, and even though the densified layer has a denser structure than the core, it is still porous. The densified layer provides the cellulose foam with increased stability and mechanical strength. It is preferred that the at least one densified outer layer constitutes between 1 -10%, preferably between 2-6% and even more preferred between 2-5% of the total thickness of the material. The cellulose foam material may comprise at least one densified outer layer and a more porous core. The cellulose foam material may comprise at least one densified outer layer, it may be preferred that both surfaces, i.e. both the top and bottom surface of the cellulose foam material is densified and form densified layers. The density of the densified outer layer / s is preferably between 80-150 kg / m3. The cellulose foam material preferably comprises a more porous core. The core of the foam material preferably constitutes between 90-99%, preferably between 94-98% and even more preferred between 95-98% of the total thickness of the material. The density of the core of the material is preferably between 20-80 kg / m3. It has been found that the method is particularly effective for cutting cellulose foam materials with a non-uniform density structure, being able to maintain the integrity of both the densified outer layer and the porous core during cutting.

[0025] The cellulose foam material my comprise cellulose fibers in a range of 71 to 95 wt%, based on the total dry weight of the cellulose foam material. The cellulose foam material thus comprises a lot of cellulose fibers which contributes to the unique properties of the cellulose foam material.

[0026] The cellulose foam material preferably has a density between 10 to 80 kg / m3, or from 10 to 60 kg / m3or from 20 to 50 kg / m3. The cellulose foam material has thus a quite low density making it a porous material which has higher risk for compression during die cutting. The mentioned density is preferably on a solid cellulose foam material.

[0027] According to a second aspect illustrated herein, a die cutting tool is provided. The die cutting tool comprises a body having a serrated edge with more than one cutting tooth wherein the cutting tooth has a tooth length of at least 2 cm and a tooth width between the top of each tooth between 1-8 cm. The die cutting tool of the present invention is particularly suited for cutting cellulose foam materials that have a relatively soft core but a harder outer surface. Traditional die cutting methods often result in excessive compression of these materials before cutting, which can lead to undesirable deformation of the foam structure. The die cutting tool according to the present invention addresses this issue by providing a unique tooth configuration that allows for more effective cutting with reduced compression. BRIEF DESCRIPTION OF FIGURES

[0028] Embodiments of the present invention will be described, by way of example, with reference to the following figures, in which:

[0029] FIG. 1 shows a side view of a conventional die cutting tool.

[0030] FIG. 2 shows a side view of an die cutting tool according to the present invention. FIG. 3 shows a side view of a die cutting tool positioned adjacent to a foam material. FIG. 4 shows a die cutting tool cutting the foam material.

[0031] Common reference numerals are used throughout the figures to indicate similar features.

[0032] DETAILED DESCRIPTION

[0033] The present invention relates to a method and a tool for cutting cellulose foam materials. Specifically, the invention provides a die cutting tool designed to effectively cut cellulose foam materials while minimizing compression of the foam during the cutting process.

[0034] The term “foam”, as used herein, refers to a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets. Three requirements must be met in order for foam to form. Mechanical work is needed to increase the surface area. This can occur by agitation, dispersing a large volume of gas into a liquid, or injecting a gas into a liquid. The second requirement is that a foam forming agent, typically an amphiphilic substance, a surfactant or surface-active component, must be present to decrease surface tension. Finally, the foam must form more quickly than it breaks down.

[0035] The term “cellulose foam”, as used herein, refers to a foam comprising cellulose, and other components such as thickeners, surfactants and additives. The main component of the cellulose foam is cellulose, such that cellulose constitutes at least and the foam can thus also be defined to be a fibrous foam or a cellulose fiber foam.

[0036] The cellulose foam may be wet or solid.

[0037] The term “solid cellulose foam”, as used herein, refers to a dry porous cellulose material that has been formed from a wet cellulose foam, i.e. a foam formed material. During the drying process, a closed wet cellulose foam is transformed into an open solid cellulose foam. The network of cellulose fibers is prevented from collapsing during drying. The solid cellulose foam will as a result have a shape that to a large extent corresponds to that of the wet cellulose foam. The solid content of the solid cellulose foam is at least 80 wt%, even more preferred at least 85 wt% and even more preferred at least 95 wt% as calculated based on the total weight of the solid cellulose foam. The shape and density of the solid cellulose foam is retained also in a non-confined state. The solid cellulose foam has an open cell structure, allowing air to occupy the pores within the foam. The solid cellulose foam can also be described as a porous material or a low-density material.

[0038] The cellulose foam used in the present invention may comprise cellulose fibers in a range of from 71 to 95 wt%, such as from 75 to 95 wt%, based on the total dry weight of the cellulose foam. Cellulose fibers suitable for use in the present invention can originate from wood, such as softwood or hardwood, from leaves or from fiber crops (including cotton, flax and hemp). The cellulose fibers suitable for use in the present invention can also originate from regenerated cellulose such as rayon and Lyocell. The cellulose fibers suitable for use in the present invention may include lignin or hemicellulose or both, or the cellulose fibers may be free from lignin and hemicellulose. Preferably, the cellulose fibers originate from wood, more preferably the cellulose fibers are pulp fibers obtained by pulping processes which liberates the fibers from the wood matrix. Pulp fibers can be liberated by mechanical pulping, obtaining mechanical pulp such as thermomechanical pulp (TMP) or chemical thermomechanical pulp (CTMP), or by chemical pulping such as Kraft pulp or pulps obtained by the sulphite process, soda process or organosolv pulping process. More preferably, the cellulose fibers are pulp fibers liberated by chemical pulping processes. The different characteristic of each cellulose fiber will affect the properties of the final cellulose foam. A cellulose fiber is significantly longer than it is wide. Cellulose fibers can have a mean width of 0.01 to 0.05 mm. The fiber length of softwood can be from 2.5 to 4.5 mm, while hardwood can have a fiber length from 0.7 to 1 .6 mm, and Eucalyptus from 0.7 to 1 .5 mm. However, the fiber length can vary considerably with different growing place etc. The cellulose fibers in the cellulose foam disclosed herein can have a length from 0.1 mm to 65 mm, or from 0.1 mm to 10 mm, or from 0.5 mm to 65 mm, or from 0.5 mm to 10 mm, or from 0.5 mm to 7mm. The fiber lengths may provide different mechanical characteristics to the foam. Due to the length of fibers, they can entangle with each other and impart fiber to fiber interbonds that bring strength to the foam. The aspect ratio, i.e. the ratio of the fiber length to the fiber width, of the cellulose fibers in the cellulose foam according to the present invention can be at least 10, at least 25, at least 50, at least 75, or at least 100, which provides for preservation and stabilization of the foam structure during the drying procedure, making it possible to dry the wet cellulose foam with retained shape. The aspect ratio can be up to 6500, or preferably up to 2000.

[0039] Preferably, the cellulose fibers are selected from wood pulp, such as softwood Kraft bleached pulp, hardwood pulp, chemical-thermomechanical pulp, and from dissolving pulp, or a combination of one or more of these. More preferably the cellulose pulp fibers are from softwood pulp, chemical-thermomechanical pulp, or dissolving pulp. Most preferably the cellulose pulp fibers are from softwood pulp, such as softwood Kraft bleached pulp.

[0040] FIG. 1 describes a die cutting tool (1) according to prior art. The die cutting tool (1) comprises a body having more than one tooth (2). The teeth (2) have a teeth length (11) and the body has a length (I2).

[0041] The die cutting tool (1) of the present invention, as shown in FIG. 2, has a body having more than one tooth (2) with a significantly longer teeth length (I3) compared to conventional designs as described in FIG. 1. The tooth width (d) between the top of the teeth (2) allows for more effective cutting with reduced compression of the foam material (3). The body of the die cutting tool (1) has a length (I2). The length (12) of the body of the die cutting tool (1) is preferably at least the same length as the thickness (t) of the cellulose foam material. This is to ensure that the die cutting tool can cut through the entire thickness (t) of the cellulose foam material.

[0042] The method for cutting the cellulose foam material (3) using the die cutting tool (1) involves several steps. FIG. 3 and FIG. 4 illustrate the positioning and operation of the die cutting tool (1 ) relative to the cellulose foam material (3).

[0043] The method includes positioning the foam material (3) adjacent to the die cutting tool (1), as shown in FIG. 3. The teeth length (I3) of the die cutting tool (1) is at least half the size of the thickness (t) of the cellulose foam material (3).

[0044] After positioning, the method involves applying a force to the die cutting tool (1). FIG. 4 illustrates a direction (p) indicating the direction in which the force is applied to the die cutting tool (1). The direction (p) is typically perpendicular to the thickness (t) of the foam material (3). As the die cutting tool (1) is pressed into the foam material (3), the teeth (2) penetrate the material.

[0045] The cellulose foam material may be supported by a support material during cutting. In order for the die cutting tool to cut through the entire thickness of the cellulose foam material at least part of the teeth are pressed though the entire thickness of the cellulose foam material. Normally, the entire length of the teeth are pressed through the cellulose foam material. Consequently, the die cutting tool is pressed beyond the thickness of the cellulose foam material and through the support material. To avoid cutting of the support material, the support material must either have a cut-out in the same form as the die cutting tool or be flexible so that it flexes away from the diecutting tool when it pressed through. The support material may also be in form of a brush mattress comprising stiff brushes that flexes when the die cutting tool is pressed through the support material. For the die cutting tool to be able to cut through the entire thickness of the cellulose foam material the length of the body of the die cutting tool is preferably at least the same length as the thickness of the cellulose foam material.

[0046] The die cutting tool may be in any suitable form or shape. The die cutting tool can be in the form of a straight blade, a round blade or in any other form. The blade of the die cutting tool can be made from any suitable material, such as steel or aluminum. The die cutting blade can also be coated to prolong the lifetime of the blade.

[0047] EXAMPLE

[0048] A cellulose foam material was cut using two different die cutting tools. The cellulose foam material had a thickness of about 53mm and a density of 30kg / m3. The cellulose foam material had a densified surface which had a thickness of about 2.5mm and the density of the densified surface was 100kg / m3. The same cellulose foam material was used in both tests.

[0049] Test 1 : Cellulose foam material was cut using a die cutting tool with a teeth length of 2mm to be used as a comparative example. The die cutting tool had a blade length and a blade width of 100mm and a blade height of 70mm. The tooth width was 2.2mm.

[0050] Test 2: Cellulose foam material was cut with a die cutting tool with a teeth length of 51 mm. The die cutting tool had a blade length and a blade with of 116mm and a blade height of 110mm. The tooth width was 38.1 mm.

[0051] The results from the tests are shown in Table 1 . The compression was measured as the thickness difference of the material before cutting and after. The compression was measured at the cutting edge of the material. The mentioned force was the force applied before the blade of the die cutting tool cut through the material. Table 1. It can clearly be seen from Table 1 that the method according to the invention clearly reduced the compression of the material.

[0052] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS1. A method for cutting cellulose foam material (3), comprising:- providing a die cutting tool (1) comprising a body having a serrated edge with more than one cutting tooth (2) wherein the cutting tooth (2) has a tooth length (I3) and a tooth width (d) between the top of each tooth (2),- providing a cellulose foam material (3) having a thickness (t),- positioning the cellulose foam material (3) adjacent to the die cutting tool (1) and applying a force to the die cutting tool (1) thereby cutting the cellulose foam material (3) wherein the teeth length (I3) of the cutting tooth is at least half the size of the thickness (t) of the material and the compression of the material during cutting is less than 10% of the total thickness of the material.

2. The method according to claim 1 wherein the compression of the material during cutting is less than 7%, preferably less than 5% of the total thickness of the material.

3. The method according to any of the preceding claims wherein the force applied is below 6kN per blade meter, preferably between 0.3-6kN per blade meter.

4. The method of any preceding claim, wherein the die cutting tool (1 ) has a tooth length (I3) of at least 2 cm, preferably between 2-10 cm.

5. The method of any preceding claim, wherein the tooth width (d) is between 1-8 cm, preferably between 2-5 cm.

6. The method according to any of the preceding claims wherein the ratio between the tooth length (I3) and the tooth width (d) is more than 1 .

7. The method of any preceding claim, wherein the cellulose foam material (3) has a solid content in the range of 80 to 100 wt%, preferably between 90-100 wt% prior to the cutting step.

8. The method according to any of the preceding claims, wherein the cellulose foam material (3) comprises at least one densified outer layer and a more porous core.

9. The method according to claim 8 wherein the at least one densified outer layer constitutes between 1 -5% of the total thickness of the material.

10. The method according to any of the preceding claims, wherein the cellulose foam material (3) comprises cellulose fibers in a range of 71 to 95 wt%, based on the total dry weight of the cellulose foam material (3).11 . The method according to any of the preceding claims, wherein the cellulose foam material (3) has a density between 10 to 80 kg / m3.

12. A die cutting tool (1) comprising a body having a serrated edge with more than one cutting tooth (2) wherein the cutting tooth (2) has a tooth length (I3) of at least 2 cm and a tooth width (d) between the top of each tooth (2) that is between 1-8 cm.

13. The die cutting (1) tool according to claim 12 wherein in the ratio between the tooth length (I3) and the tooth width (d) is more than 1 .

Images