WO2017108706A1

WO2017108706A1 - A pressurized canister

Info

Publication number: WO2017108706A1
Application number: PCT/EP2016/081772
Authority: WO
Inventors: Aster De Schrijver; Ricardo JOÃO FERREIRA SIMÕES; Jorge RUI MACHADO FONTES DA SILVA
Original assignee: Greenseal Nv
Priority date: 2015-12-21
Filing date: 2016-12-19
Publication date: 2017-06-29

Abstract

The present invention is directed to a pressurized canister for dispensing a foam precursor in the form of a foam, said canister having a dispenser channel comprising a microcapsule rupturing section exposing microcapsules present in the foam precursor to friction, shear and/or compression thereby rupturing the microcapsules.

Description

A PRESSURIZED CANISTER

FIELD OF THE INVENTION The present invention relates to a pressurized canister for containing catalytically reactive monomers and/or oligomers and microcapsules containing active molecules.

BACKGROUND OF THE I NVENTION Pressurized fluids stored in containers (cans or vessels) are used in a wide field of applications. Sprayable foams are used for several industrial applications as well as by hobbyists. Typical existing sprayable foam formulations are one and two component PU foams (OCF = One Component Foams; TCF = Two Component Foams) in aerosol cans and/or pressure vessels. One well known example of sprayable foam is polyurethane foam. Spray polyurethane foams (SPF) are of particular applicative interest as SPF insulation may be rigid, lightweight, flexible, wind resistant, and effective in extreme temperatures and weather conditions.

In order to avoid eventual clogging of the dispenser channel upon dispensing two component foams (TCF), One Component Foams (OCF) have been developed.

To process OCF, microcapsules containing active molecules are contained in the foam precursor. Microcapsules are tiny particles or droplets composed of an active material, such as a catalyst or an initiator, enclosed in a coating or shell isolating the active material from the catalytically reactive monomers and/or oligomers in the canister.

Micro-encapsulation of initiators, catalysts and crosslinking agents avoids the need for mixing of the reactive components in the dispenser channel upon dispensing the foam, because the microencapsulated catalysts and the non-cured oligomers or polymers can be safely mixed in the canister and will only react when the microcapsules burst.

Several Technologies for capturing active molecules in microcapsules and inducing burst of these microcapsules upon dispensing are known in the state of the art. The shell can be ruptured by mechanical forces such as pressure drop upon dispensing. In other systems, the shell is broken by solvent action, enzyme attack, chemical reaction, hydrolysis, or slow disintegration. For example, US3839220 describes a system wherein active substances are stored in pressurized storage systems encapsulated in microcapsules having internal pressures sufficient to burst the microcapsules. The pressure inside the microcapsules is sufficiently higher than the ambient pressure outside the canister, causing bursting of the microcapsules upon their removal from the canister. A problem with the microcapsules proposed in this document however is that their organic wall is not leach proof for most active components, thus limiting the lifetime of the reactive content of the pressurized can and decreasing shelf life. EP2451569 solves the above problem by providing optimized leach-proof microcapsules only bursting upon a pressure drop of at most 5 bar, preferably 0.5 to 1 bar, upon dispensing out of the pressurized canister.

However, it is clear that in the above cited documents burst of the microcapsules is very much dependent on shell design and shell characteristics and on pressure differences between the inside and outside of the microcapsules.

Another problem is that in some cases, the precursor upon dispensing out of the pressurized canister acts as an isobaric chamber such that microcapsules within are not affected by the pressure drop.

It is therefore an object of the present invention to provide a pressurized canister making the release of active molecules less dependent on shell design and shell characteristics. Another object is to make the release of the microcapsule content more controlled with regards to the exact location of the release in the dispenser channel, thereby avoiding that reaction is early catalyzed.

It is further an object of the present invention, to enable the release of active molecules inside the dispenser channel from microcapsules which do need pressure differences over the shell of more than 5 bar.

In general, it is an object of the present invention to achieve more efficient release of active molecules and faster curing upon dispensing.

The present invention meets the above requirements by providing a pressurized canister for dispensing a foam precursor in the form of a foam, said canister having a nozzle comprising a microcapsule rupturing section exposing the microcapsules to friction, shear and/or compression thereby rupturing microcapsules present in the foam precursor.

SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

FIG 1 illustrated schematically a working principle of an embodiment in accordance with the present invention.

FIGS 2 to 6 illustrate different embodiments of a microcapsule rupturing section for use in a pressurized canister according to the present invention.

DETAI LED DESCRIPTION OF THE INVENTION

Since upon dispensing, microcapsules are forced to pass the microcapsule rupturing section thereby being exposed to such friction, shear and/or compression that the shell breaks or gets ruptured and active molecules are released, release may be made less dependent on shell design and shell characteristics. In other words, even if the shell is very stable, not easily to break and/or not ruptured by a modest pressure difference between the inside and the outside of the microcapsule, the mechanical system will apply sufficient local friction, shear and/or compression to rupture the shell.

Another benefit is that release of the microcapsule content may be more controlled with regards to the exact location of the release in the dispenser channel. The exact location in the nozzle where the friction, shear and/or compression are applied will define where chemical reaction is catalyzed, thereby avoiding early catalyzing. Making use of a microcapsule rupturing section for rupturing the microcapsules also enables controlling the release rate, e.g. the amount of ruptured microcapsules per unit time. By applying different designs and configurations different release rates may be achieved.

In the context of the present invention, microcapsules are hollow micro-particles composed of a solid shell surrounding a core-forming space available to entrapped active material, such as a catalyst or an initiator. The active material is thereby isolated from the catalytically reactive monomers and/or oligomers in the canister.

The pressurized canister in the context of the present invention may be any canister suitable for containing foam precursor under pressure of propellant gas, such that upon opening the canister's valve, the foam precursor is forced out via the dispenser channel. In the context of the present invention, the microcapsule rupturing section may be any section of the dispenser channel adapted to expose a microcapsule present in the foam precursor and passing through that section to sufficient friction, shear and/or compression for making it burst and releasing its active content. In an embodiment according to the present invention, a pressurized canister is provided, wherein the dispenser channel comprises a stem valve connected to a nozzle, wherein the microcapsule rupturing section is located after the stem valve within the nozzle. Since curing is initiated in the rupturing section within the nozzle, the nozzle may be replaced after use or before re-using the canister.

When the user wishes to dispense the product from the canister, the upstanding valve stem is tilted or may be vertically depressed, resulting in that the foam precursor is forced by the propellant pressure in the canister to flow through the valve stem side lateral openings and up through the stem central bore to exit the stem via the nozzle to the area where the foam is being applied. So a possibility may be to provide the microcapsule rupturing section between the end of the central bore and the nozzle.

The microcapsule rupturing section may comprise a static and/or dynamic mechanical system for rupturing the microcapsules. In the context of the present invention, a static mechanical system exposes the microcapsule shell to friction or compression without making use of moving parts, while in a dynamic mechanical system burst is induced by moving parts exposing the microcapsule shell to friction or compression. A combination of both may be possible, and may be more efficient.

In an embodiment in accordance with the present invention, a pressurized canister is provided wherein the static and/or dynamic mechanical system comprises obstructions located in the foam precursor's flow path through the dispenser channel. Such obstruction may be any type of geometrical form or object, moveable or non-moveable, or any type of mechanical system in the dispenser channel changing the flow path of the foam precursor and preventing normal transit of foam precursor compared to its flow path without the presence of the obstruction.

In an embodiment of the present invention, the obstruction may be constituted by an abrupt or gradual constriction in the flow path. Preferably, the constriction is constituted by an abrupt or gradually increased section diameter following an abrupt or gradually decreased section diameter in the flow path.

Without being bond by any theory, in FIG 1 is generally explained what the effect may be of a constriction in the foam precursor flow path. Considering that the foam precursor containing microcapsules is moving from point 1 to point 2, at a constant velocity through the dispenser channel, delivering foam at a constant pressure, when the foam precursor passes through a constriction in the dispenser channel (i.e. the microcapsule rupturing section) the velocity will increase (V2) and again decrease (V1 ) over the microcapsule rupturing section, making the pressure inversely proportionally decreasing (P2) and increasing (P1 ) again. The variation on the transversal section makes the microcapsules burst with the sudden pressure/velocity variation releasing the catalyst agent on the primary fluid.

In FIG 2a, three models are shown having a section diameter reduction (a) in several different configurations. The section diameter reduction may depend on the size and characteristics of the microcapsules, i.e. on the friction, shear and/or compression and/or shear to be induced on the microcapsules to rupture them. Preferably, a diameter reduction of minimum about 50% or, more preferably between about 50% to 70% may be sufficient. In addition, the minimum diameter of the reduction may preferably be not smaller than about twice the microcapsule diameter in order to avoid clogging within the nozzle. In a preferred embodiment as shown in FIG 2b, the section diameter reduction may also be obtained by providing a number of channels (b), preferably conical, through which the foam precursor has to pass. The number of channels may vary from a few channels up to more than 10, or even more forming a grid constituted by a plurality of channels. This model may have as additional effect, besides pressure variation onto the microcapsule shell, also increased friction induced on the shell, resulting in more efficient shell rupturing. Optionally, at the exit of the conical channels a grid may be provided to further increase the rupturing section's efficiency.

As further illustrated in FIG 3, the length of the channels (b) may be between 0.2 and 5mm, preferably between 0.5 and 2mm, and even more preferably about 1 mm, in order to avoid clogging. The intake diameter of the channels may depend on the stem size, for example between 4 and 15mm, and may further depend on the flow rate to be obtained. In addition, in case the channels are conical, the channel diameter may decrease, for example with an inclination between 8° and 12°, preferably 10°. It is understood that length and diameter of the channels may be proportional to the microcapsules diameter.

Another approach may be to induce a turbulent flow regime in the foam precursor flow in the dispenser channel. Therefore, in an embodiment in accordance with the present invention, a pressurized canister is provided wherein the static and/or dynamic mechanical system comprises means for generating turbulent flow in the flow path. Turbulent flow causes the microcapsules to collide with each other, and with the relatively rough inside surface of the dispenser channel, or more specifically the nozzle, which generates increased friction between the microcapsules and between the microcapsules and the surface. Another effect of turbulent flow regime may be generation of shear forces in the flow resulting from high velocities in the vortex area of the flow path, as illustrated in FIG 4. The collisions and shear forces, and combination of both, may cause efficient burst of the microcapsules.

Turbulent flow in the flow path may be induced by restriction, bends, or combinations thereof in the flow path, generating a vortex in the foam precursor flow.

FIG 5a and FIG 5b illustrate dispenser channels inducing turbulent flow in the foam precursor flow path. In FIG 5b the obstruction is constituted by a double bend (c) in the flow path. In FIG 5a the obstruction is constituted by a bullet (d) axially extending in the dispenser channel, e.g. a static turbine shape, which is well known for creating high pressure differentials on the exit. In a more specific embodiment similar to FIG 5a, Fig 6 illustrates a geometry intended for microcapsules with a diameter above 100 nm, preferably between 100 and 300 nm, wherein the bullet (d) has a length between 8 and 16 mm, preferably, about 12 mm, with the largest diameter between 5 and 12mm, preferably between 7 and 9mm. Preferably the bullet has an number of axially extending slits (e) around its periphery. This slits may have a width of about 1 mm. Without being bound by any theory, the slits have two functions, namely (i) providing physical support for holding the bullet in the center of the hollow section of the nozzle, allowing the fluid to flow around the bullet, and (ii) promoting further compression or shear by inducing a more turbulent flow regime through the formation of vortices.

In alternative embodiment in accordance with the present invention, the microcapsule rupturing section comprises an obstruction constituted by moving gears (f) in the flow path. These moving gears also expose the foam precursor and the microcapsules to friction, shear and/or compression and/or shear sufficient to rupture the microcapsules. Preferably, the gears may be two counter-rotating gears in the flow path as illustrated in FIG 7. The microcapsules will be squeezed or smashed by two gear wheels with a small gap in between. This can also be achieved through a worm-gear or two worm-gears rotating on parallel axes, within a cylindrical chamber, with increasing diameter, progressively compressing the fluid.

The foam precursor released under high pressure from the pressurized canister into the dispenser channel will cause the gears to rotate. This is accomplished by a hydrodynamic profile on the teeth of the spur-gear/worm-gear that fosters the movement of the passing precursor flow. If necessary the gears may be optionally motor driven in order to mechanically power their rotation. This embodiment may be specially suitable for hard shell microcapsules that need higher forces to break the shell. The teeth of the gears will cause compression or shear forces that will break the capsule and thus release the catalyst agent.

The microcapsules present in the foam precursor may be of any type and size of microcapsules used in the application of dispensing foams. Examples are organosilica capsules, such as 0,2 sol-gel microcapsules of aqueous glycerol in silica-based microspheres, or thermo-regulating microcapsules having shell material consisting of polystyrene or poly(methyl methacrylate). Preferably, microcapsules used in a canister in accordance with the present invention, are glycerol based. The microcapsule rupturing section in the dispenser channel may be adapted for rupturing microcapsules requiring a pressure difference for being ruptured over the shell of more than 1 bar, or more than 3bar, or even more than 5bar. For example, microcapsules between 100 and 300 micrometer may break with a pressure variation of 5 to 6 bar when exposed to atmospheric pressure right outside the nozzle.

In addition the microcapsule rupturing section may be adapted for exposing microcapsules of 0.01 to 1 mm, preferably between 100 and 500 micrometer, or between 100 and 300 micrometer to sufficient friction, shear and/or compression for rupturing said microcapsules.

The present invention allows dispensing foam by catalyzing a reaction selected from all sorts of polymerization reactions, comprising an active molecule-containing microcapsule, in which one or more reactants enter into said catalytic reaction and whereby said reaction comprises breaking the shell of the active-containing microcapsule and fast release of its content, allowing a product resulting from said catalytic reaction.

Preferably, a pressurized canister according to the present invention may be used in dispensing coatings, adhesives, sealants and/or foams. Various microencapsulated initiators, catalysts, and crosslinkers may be commercially used to polymerize different unsaturated oligomers and various isocyanate and novel non-isocyanate monomers to form polyurethane polymers, used as adhesives, sealants and foams.

Claims

1. A pressurized canister for dispensing a foam precursor in the form of a foam, said canister having a dispenser channel comprising a microcapsule rupturing section exposing microcapsules present in the foam precursor to friction, shear and/or compression thereby rupturing the microcapsules.

2. A pressurized canister according to claim 1 , wherein the dispenser channel comprises a stem valve connected to a nozzle, wherein the microcapsule rupturing section is located after the stem valve within the nozzle.

3. A pressurized canister according to claims 1 or 2, wherein the microcapsule rupturing section comprises a static and/or dynamic mechanical system for rupturing the microcapsules.

4. A pressurized canister according to claim 3, wherein the static and/or dynamic mechanical system comprises obstructions located in the foam precursor's flow path through the dispenser channel.

5. A pressurized canister according to claim 4, wherein the obstruction is constituted by an abrupt or gradual constriction in the flow path

6. A pressurized canister according to claim 5, wherein the microcapsule rupturing section is constituted by an abrupt or gradually increased section diameter following an abrupt or gradually decreased section diameter in the flow path.

7. A pressurized canister according to claim 5, wherein the obstruction is constituted by a number of conical channels through which the precursor has to pass.

8. A pressurized canister according to claim 4, wherein the obstruction additionally comprises a grid.

9. A pressurized canister according to claim 3, wherein the microcapsule rupturing section is constituted by means for generating turbulent flow in the flow path.

10. A pressurized canister according to claim 9, wherein the means for generating turbulent flow in the flow path comprises a combination of bends and restrictions in the flow path.

11 . A pressurized canister according to claim 9, wherein the obstruction is constituted by a bullet axially extending in the dispenser channel.

12. A pressurized canister according to any of the above claims, wherein the microcapsules require a pressure difference for being ruptured over the shell of more than 5 bar.

13. A pressurized canister according to any of the above claims, wherein the microcapsule rupturing section is adapted for exposing the shell locally to a pressure of at least 5 bar.

14. A pressurized canister according to any of the above claims, wherein the microcapsule rupturing section is adapted for exposing microcapsules of 10 micrometer to 1 mm to sufficient friction, shear and/or compression for rupturing said microcapsules.