METHOD AND APPARATUS FOR PRODUCING SOLID FOAM, PRODUCT AND USE

Abstract

The application relates to a method and apparatus for producing a solid foam continuously. A homogeneous suspension is formed from a raw material in which the suspension comprises a solidifying agent, and a foam mixture which comprises bubbles is formed by mixing air bubbles into the suspension. The foam mixture is injected via at least one nozzle to form a foam pattern and the foam pattern is laid on a moving surface and the foam mixture of the foam pattern is solidified in order to form a solid foam such that the bubbles of the foam mixture shrink in off-length directions to form the shaped bubbles. Further, the application relates to the product and the use of the method.

Claims

1. A method for producing a solid foam continuously, wherein the method comprises forming a homogeneous suspension from a raw material in which the suspension comprises a solidifying agent, forming a foam mixture which comprises bubbles by mixing air bubbles into the suspension, and injecting the foam mixture via at least one nozzle to form a foam pattern and laying the foam pattern on a moving surface and solidifying the foam mixture of the foam pattern in order to form a solid foam such that the bubbles of the foam mixture shrink in off-length directions to form the shaped bubbles.

2. The method according to claim 1, wherein a chemical which lowers surface tension, increases viscosity and/or facilitates a solidification is added to the suspension.

3. The method according to claim 2, wherein the chemical is methylcellulose, derivate of the methylcellulose, carboxymethyl cellulose, hydroxypropyl cellulose, ethyl cellulose, or their combination.

4. The method according to claim 2, wherein the chemical is a photopolymer.

5. The method according to claim 1, wherein a solid fibre material is added to the raw material and/or the suspension, and the solid fibre material is selected from the group consisting of carbon fibers, carbon nanotubes, graphene, carbon mesh, laponite, hemp, expanded polystyrene, polystyrene, polymer, polymer sticks, yarn and their combinations.

6. The method according to any one of claim 1, wherein the raw material is a bio-based material selected from the group consisting of biomass, bio-based residue material, wood, wood-based material, forest-based material, cellulose, treated bio-based material, untreated bio-based material, or their combinations.

7. The method according to claim 1, wherein the foam mixture is solidified by heat, photocatalytes, crosslinking, freezing or their combinations.

8. The method according to claim 1, wherein the foam mixture is solidified at temperature of 1-90° C.

9. The method according to claim 1, wherein the pattern is a stripe, plate, predetermined structure, complex structure or their combination.

10. The method according to claim 1, wherein a product is formed from one or more foam patterns.

11. An apparatus for producing a solid foam continuously, wherein the apparatus comprises at least one mixer for forming a homogeneous suspension from a raw material in which the suspension comprises a solidifying agent, at least one foamer for forming a foam mixture which comprises bubbles by mixing air bubbles into the suspension, and at least one nozzle for injecting the foam mixture to form a foam pattern, a moving surface on which the foam pattern is laid and at least one solidifying device for solidifying the foam mixture of the foam pattern to form a solid foam such that the bubbles of the foam mixture shrink in off-length directions to form the shaped bubbles.

12. The apparatus according to claim 11, wherein the apparatus comprises at least one extruder comprising at least one nozzle.

13. The apparatus according to claim 11, wherein the solidifying device comprises at least one heater for solidifying the foam mixture by heat so that radiant heat, conductive heat and/or convective heat is used.

14. The apparatus according to claim 11, wherein the apparatus comprises at least one rheomodifier for changing rheological properties.

15. The apparatus according to claim 11, wherein the apparatus comprises at least one transporter for transporting the foam mixture or the solid foam to a storage area.

16. A solid foam product obtained by the method according to claim 1, wherein the solid foam comprises a foam mixture formed from a suspension comprising a solidifying agent and bubbles, and the foam mixture has been injected to form a foam pattern and the foam mixture of the foam pattern has been solidified to the solid foam and the bubbles in the solid foam has been shrunk in off-length directions to form the shaped bubbles.

17. The product according to claim 16, wherein the product comprises at least two foam patterns arranged one on top of the other to form a layered structure, and the each foam pattern is arranged in a desired direction on top of one another in the structure.

18. A use of the method according to claim 1, wherein the method is used in a continuous process, a roll-to-roll process, a packaging industry, a construction industry or their combinations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which are included to provide further understanding of the invention and constitute a part of this specification, illustrate some embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

[0041] FIG. 1 illustrates the measured elongation of the bubbles which shows that the dimension in the direction of elongation (y-axis) is eight times the elongation in cross direction (z-axis) for 8 different samples,

[0042] FIG. 2 illustrates the elongation in the bubble walls which causes the fiber structure in the walls to orient creating high strength in the orientation direction,

[0043] FIG. 3 illustrates a structure, in which the orientation dependent structure has been created by the process with significantly larger compression strength along the bubbles and fibers (left) than in cross direction (right),

[0044] FIG. 4 illustrates that modifying the process changes the way in which the bubbles interact with each other causing dramatic differences in the stress-strain response, and Figs a) and b) illustrate four different groups of material with different orientation and manufacturing process,

[0045] FIG. 5 illustrates comparison of FoamWood's strength per density to other materials which shows that while the cross strength (square) is lower than the average foam, the strength in the bubble elongation direction is very good (circle) for a biobased material,

[0046] FIG. 6 illustrates a single extrusion process comprising a schematic a) and a photograph b) illustrations, and in the process the drying of the rods under tension in temperature above the viscous transition of the methylcellulose jams/arrests the bubble and thus the fiber structure to oriented state,

[0047] FIG. 7 illustrates examples of bulk products, rod, plate and a block, and

[0048] FIG. 8 illustrates a schematic illustration of many parallel extrudes with one (or more) foam generators generate plate like objects in a continuous process.

DETAILED DESCRIPTION

[0049] The detailed description provided below in connection with the appended drawings is intended as a description of examples and is not intended to represent the only forms in which the example may be constructed or utilized. However, the same or equivalent functions and structures may be accomplished by different examples.

[0050] FIG. 1 illustrates a measurement of the anisotropic bubbles in 8 different samples. The dimension in the elongation direction (y-axis) is 8 times the dimension in the cross direction (z-axis). The elongation leads to oriented fibre structures in the bubble walls illustrated in the high magnification image in FIG. 2. The small-scale structure in the bubble walls can be inherited to the large-scale structures, as shown in FIG. 3. FIG. 4 shows that the practical gain is revealed in the accompanying compression tests as the stress-strain (load-displacement) curves are clearly different depending on the orientation. For instance, at the strain of 0.1, the difference in the load carrying capacity is nearly 100-fold along the elongated axis of the bubbles compared to the cross direction. FIG. 5 shows how the strength/density of FoamWood compares to other materials.

[0051] In the process, a homogeneous suspension containing solid fiber ingredients is prepared and mixed with a sufficient amount of methyl cellulose (MC). The suspension is then pumped into a capillary, where a junction is used to mix the air bubbles in the suspension to form the foam. The foam is laid on a moving surface, e.g. a wire surface, a solid surface and/or an even surface, using a set of capillary nozzles producing a set of foam stripes on the moving surface. These stripes of foam pass under an infrared heater, which elevates the temperature increasing the rate of evaporation, and causing the MC effect as explained below.

[0052] The MC acts as 1) a surface-active agent lowering the surface energy of the suspension allowing it to be foamed and 2) a rheology modifier in the suspension increasing the viscosity of the suspension increasing the bubble shape relaxation times. Furthermore, the MC rheological behaviour is peculiar in a sense that the MC particles tend to swell as a function of the temperature. This leads to a situation, where the foam effectively arrests as the temperature of the foam is increased during drying causing the structure to solidify and arrest.

[0053] Drying of liquid foams always leads to its shrinkage due to reduction in the amount of material (water) in the structure. When the foam is laid in stripes on the wire the shrinkage can be utilized to cause additional stress towards the bubbles in the off-length direction because in the length direction shrinkage is not possible. This in turn adds on to the anisotropy of the bubbles.

[0054] FIG. 6 shows the schematic illustration of the device in a small-scale production. The foam is driven onto the hot moving plate from the foamer, via controlled air pressure. The linear moving plate moves as the foam is extruded, creating a solid rod-shaped object which is dried by the radiant heater. The process can be repeated until desired amounts of rods are deposited onto the moving plate one next to each other. The rods are dried using the radiant heater. Further, once the layer of the rods is fully dried another layer can be created on top of the existing layer.

[0055] The process produces rod and plate like objects that can be laminated to a block shown in FIG. 7. The FIG. 8 shows a large-scale machine capable of producing continuously the foam using multiple extruders.

[0056] A foamer is a device for creating foams with user specific bubble radius and polydispersity; average bubble radii from 10 um to 100 mm with polydispersity 0.01 percent to 100 percent or the bubble radii. The polydispersity is the standard deviation of the radii of the bubbles. The foam production is continuous as the raw materials are continuously injected with pressure, e.g. by air, liquid or screw pump or similar method. The output is continuously injected to an extruder with a screw pump or similar device. The output can be other device for e.g. quality control or storage unit. The foamer can be rheomodified heated, cooled or shaken with ultrasonics or sonic to affect flow of raw materials or foam.

[0057] The extruder is a device which dispersers the bubbles onto the moving surface and/or transporter and which injects foam from the foamer. The dispersion creates internal shear that elongates the bubbles and creates a pattern for creating internal structures to foam. The patterns can be flat, rodlike, ridged, zikzak, on-off, dotted, dashed, wavy or combination or similar. Number of extruders can be one or more in parallel operation. Number of extruders or set of parallel extruders can operate in series. For example, the extruders can operate with following cases: independently with pattern different from others, in sync with same pattern with others, zero or more number of extruders operate independently with same or different pattern, and/or zero or more extruders operate in sync. The sync means both temporal and spatial sync e.g. different phase (staring time) of dotted pattern or different pattern or different starting location of the pattern. The extruder can comprise a rheomodified shake with ultrasonics or sonic to affect the flow of raw materials or foam. Zero to multiple extruders can move to make the pattern. Zero to multiple extruders can be stationary to make the pattern.

[0058] The solidifier, such as the solidifying device, is a device which the changes the rheological properties of the foam from its liquid-like stage to solid-like stage. A solid-like stage can be a gel or solid or highly viscous stage with viscosity over 100 Pa.Math.s (Pascal-second). The solidifying method can be heat (0-5000 degree celsius), cold (−273 to 0 degrees celcius), light including lasers, leds, heat, gas discharge, ultrasonic, sonic, magnetic, charged (remove charge screening by e.g. salt), chemical and/or pressure or similar. The solidifying method depends on the material and is a material dependent parameter. For example, methylcellulose is solidified with heat. The methylcellulose solidifies in high temperatures from 30 degrees Celsius to 80 degrees Celsius depending on the degree of substitution. Heat can be infrared (radiant heat), conductive or convective via carrier gas. Water is solidified in low temperatures below 0 degrees. Alcohol solidifies in low temperatures below −4 degrees. Photopolymers solidify in UV light. Shear thickening materials, e.g. cornstarch, solidify in sonic and ultrasonic vibration. Shear thinning materials solidify when sonic or ultrasonic vibration is stopped. Iron powder solidifies in magnetic field. Sand or granular matter solidifies under pressure or loading. Charged particles solidify when the charge screening is removed, e.g. charged stabilised cellulose when salt is added. Chemical solidification can be made by crosslinking e.g. mixing two components similar to epoxy resin.

[0059] A transporter is a device or operator, e.g. human or robot, that can transport the foam from the extruder to storage area. An example of the transporter is a conveyer belt, moving plate or similar.

[0060] A rheomodifier, such as a rheomodifying device, is a device that changes the rheological (load-displacement) properties of the materials and/or foam during the manufacturing. The modification uses the same methods as the solidifier but during the process starting from the injection of materials to the storaging of the foam. A solidifier can act as a rheomodifier.

[0061] The method and apparatus are suitable in different embodiments for using in different industrial processes. The method and apparatus are suitable in different embodiments for producing effectively different foam products from different raw materials.

[0062] The invention is not limited merely to the embodiments and examples referred to above; instead many variations are possible within the scope of the inventive idea defined by the claims.