EP3898425B1

EP3898425B1 - Improved filling of propellant gas into polyurethane spray cans

Info

Publication number: EP3898425B1
Application number: EP19831741.4A
Authority: EP
Inventors: Ben PAUWELS; Bart Vervoort; Veerle Dirckx; Peter Geboes; Peter BRUGGEMAN; Jo VAN GORP; Wim DE BACKER
Original assignee: Soudal NV
Current assignee: Soudal NV
Priority date: 2018-12-20
Filing date: 2019-12-20
Publication date: 2023-06-21
Anticipated expiration: 2039-12-20
Also published as: WO2020128026A1; EP3898425A1; BE1026617B1; PL3898425T3; SI3898425T1

Description

SCOPE OF THE INVENTION

The present invention relates to the pressurized filling of spray cans or pressure containers. More in particular, the invention relates to injecting propellant gasses into spray cans in which a composition for forming a polyurethane (PU) foam is packaged.

BACKGROUND OF THE INVENTION

Polyurethane foam has many applications, especially in the construction industry. It is frequently used as a mounting material and as an insulation material, and often also for filling up and/or sealing holes and cracks. It is easily applicable from a pressurized spray can, easily adheres to most surfaces, and in many cases is even paintable. Shortly after application, a solid foam is formed that is easy to cut, so that excess volume may easily be removed.
Most spray cans containing PU foam contain a so-called "single component" PU foam (1k PU foam), but the family also comprises the so-called 2k and 1.5k versions.
In order to eventually obtain a foaming product, three components are required: the polyol mixture, the isocyanate, and the propellant gas. The polyol mixture and the isocyanate are the necessary ingredients for obtaining a polyurethane plastic. These two components are liquid under ambient conditions. The propellant gas ensures that the polyurethane foams and is driven out of the spray can. It does not take part in the reaction but does contribute to influencing the physical properties of the liquid in the spray can, such as its viscosity.
In the case of 1k PU, all of these components are already present, fully mixed, in one and the same spray can. The 2k PU systems comprise 2 pressurized containers, one containing the polyol mixture and the other containing the isocyanate, and, using pressure from propellant gas in each of the containers, these components are first combined and mixed before the mixture is expelled immediately afterwards. In the case of 1.5k systems, a smaller container is arranged inside the spray can, which contains a reagent, usually a fast-reacting polyol. Before using the spray can. the small container first needs to be opened or "activated" by the user, for instance by moving a rotary knob at the bottom of the spray can, releasing the contents of the smaller container. By shaking the whole, the contents of the small container may be mixed with the contents in the spray can around the small container, and the contents of the small container is allowed to react with the latter. Such an activating system is for instance described in WO 2016/120336 A1 .
Also WO 93/08099 A1 and DE 69218221 T2 disclose such a 1.5k version of a spray can for dispensing a two component system under pressure, the outer container being provided with an opening, a valve mounted in this opening, and the inner container being attached to the stamp of he valve underneath the outlet aperture in the valve, in such a manner that the spray can may be pressurized easily without requiring hereto further means in addition to the outlet valve.
In the case of 1k PU foam spray cans, the polyol mixture and the isocyanate react in the spray can immediately after filling, thereby forming the pre-polymer. The ratio in which these components are mixed, usually with an excess of isocyanate component, and the nature of the components themselves, are responsible for the eventual properties of the final product. After being sprayed from the spray can, the pre-polymer will foam, and the foamed pre-polymer will react with moisture from the ambient air and possibly also from the substrate with which it is put into contact. This final reaction with moisture is what causes the fresh foam to set and to foam even further due to the formation of CO₂. In the case of 2k and 1.5k PU foam, the final setting is much less, or even barely, dependent on a reaction met moisture from the environment.
1 k PU foam, especially, is nowadays used by both professionals and do-it-yourselvers (DIYers) alike, and has become a toolbox staple, in addition to silicone sealant and contact adhesive. The packaging, and in particular the development of the valve, have played a major role in this breakthrough and the acceptance of 1k PU foam as a "practical and effortless" product.
For intensive applications, directed mainly toward professionals, it is popular to use a dosing gun or spray-gun, or another device that handles well and usually also allows precise dosage and application, so that even narrow seams can easily be filled without too much waste. Cans or containers for such use are therefore provided with a specially adapted gun coupling piece or ring, which is placed around the valve onto the spray can, and is intended to enable a coupling with the spray-gun or other device, which is usually intended for applying the contents of the can where needed. The spray-gun may then be screwed onto the ring or onto the gun coupling piece, which is placed onto the can, threadedly or by means of a snap fit system, causing simultaneously the valve to be pressed into its open position, thus immediately readying the spray-gun for use. A handy and very easy-to-use "Click & Fix" system of a gun coupling piece and matching spray-gun is described in WO 98/43894 and WO 2011/151296 A2 . A threaded system is for instance described in US 5,271,537 and in EP 2576080 .
Containers with polyurethane foam intended for the do-it-yourself (DIY) market are usually not provided with a ring for screwing or snap-fitting a spray-gun onto them. The valve is usually freely accessible, and may itself be internally or externally threaded, allowing an applicator tube, sold separately or supplied together with the container, to be twisted or screwed onto it, or attached to it in any other suitable way, which is provided with a lever which when pressed tilts the valve and thus allows the valve to be manually opened, and, when released, to be closed again. For this application, the valve should therefore be freely accessible, and it is common for the container for the DIY market segment to be provided with a protective cap which is removably attached to the container, and which thus protects the valve until the time of use. A suitable protective cap is for instance described in EP 2371738 A1 .
Many products are packaged in spray cans or pressure containers from which they may be released under the pressure of a propellant gas, such as hairspray, insecticide, shaving cream, paint, deodorant, perfume, penetrating oil or lubricating oil.
Within this field, the compositions for obtaining PU foam occupy a special category. The PU foam compositions are characterized by a very high viscosity, much higher than the viscosity of virtually all other consumer products packaged in in a pressure container or spray can form, including lubricating oils.
Although spray cans containing PU foam are sometimes called "aerosol containers", the special properties of PU foam forming compositions confine them into a separate category within that large family. The development of a suitable valve has been important for the commercial breakthrough of PU foam. The valves on pressure containers containing PU foam are special because they have a very wide passage, to allow a sufficiently rapid discharge of the viscous contents from the spray can.
Most other products packaged in pressure containers are much more liquid, and those cans are therefore fitted with valves having a much narrower passage. Moreover, those valves are usually equipped with a "dip-tube" that directs liquid from the bottom of the spray can towards the valve, under pressure from the propellant gas in gaseous phase above it, so that the spray can may, or often even has to be used in an upright position.
An additional feature of pressure containers with 1k or 1.5k PU foam is that they usually, with a few exceptions such as "Multi Position" or MP Foam, have to be used in an inverted position. This is because the high viscosity of the PU foam forming compositions is not very suited for a pressure container having the classical narrow dip-tube, a.o. due to the more arduous trajectory through which the composition needs to pass before being able to exit the pressure container through the valve.
The filled spray can is pressurized, and its contents is still very reactive due to the excess of isocyanate groups, even after the pre-polymer forming reaction of the polyol with the isocyanate, a.o. due to the excess quantity of the latter. This reactivity of the contents in the spray can also distinguishes PU foam spray cans from many other spray cans, especially because it brings an extra risk to the user. These spray cans should therefore be handled in a safe way, to avoid the user coming into direct contact with the still reactive composition. Furthermore, it is advisable to not let the still reactive composition end up in places where it may cause problems due to its fast setting properties.
The pressure containers or spray cans themselves are usually made of metal, and are usually cylindrical in shape. The bottom is usually formed by a plate, arranged by means of a flange onto the cylinder, and is usually inwardly concave, to be better able to resist the internal pressures while maintaining the ability for the container to be placed upright onto a flat surface. The top is usually provided with a container head, which is also arranged onto the cylinder by means of a flange, and which is usually convex, for the same reasons of a higher resistance to pressure. A filling opening is provided, usually in a central position in the cylinder head.
During the packaging, the empty container is usually filled through this central filling opening in the head, and this opening is subsequently closed off by securing or "crimping" the valve onto the edge or rim of the filling opening. Many of the components may be filled into the container under atmospheric pressure, and the components intended to provide the higher pressure may then subsequently be introduced into the container after this has been closed off with the valve. This method is called "filling under pressure". The pressure in the can is then further increased after closing the container and injecting the propellant gasses, because an exothermic chemical reaction takes place between the components, in particular after the shaking of the container. The propellant gasses could also be introduced at the time of filling of the container, for instance as a sufficiently cold liquid, which may subsequently evaporate after the container is closed. This latter method is however phasing out, because it usually leads to higher emissions of propellant gasses, with adverse economic and ecological consequences.
The valve for spray cans containing PU foam is characterized, as described above, by a much wider passage than the one on spray cans having a less viscous content, to allow a sufficiently rapid discharge. This wider passage also brings advantages when introducing the propellant gas.
Spray cans containing PU foam are usually much larger than those containing the less viscous compositions listed hereinabove. A spray can containing PU foam often has a content of 1000 ml, while spray cans for other applications are often much smaller, at most 400 ml and often no more than 200 or as little as 150 ml. Usually, the pressure in the spray can containing PU foam is also significantly higher than in the other spray cans, mainly because of the higher viscosity of the composition in the can. The amount of propellant gas to be introduced is therefore significantly higher in spray cans containing PU foam than in most other spray cans containing a less viscous contents. The wider passage through the stem of the valve for PU foam offers the advantage that it allows this larger amount of propellant gas to still be introduced quickly, even only through the valve stem, so that the filling step of propellant gas does not, or only rarely, limit the throughput speed of the filling machine.
For valves having narrow valve openings, on pressure containers with a much more fluid contents, other solutions sometimes have had to be developed to allow more propellant gas to be injected quickly into the spray can. For instance, the documents GB 1269801 , US 6283171 B1 , WO 2005/007516 and US H2205 H describe methods in which propellant gas is not only introduced under pressure through the hollow valve stem, but in which the majority of the propellant gas arrives into the spray can through an opening around the valve stem, which at rest is closed off by a seal but which upon pressing the valve stem also opens. For this method of introducing the propellant gas, however, pressurized propellant gas needs to be provided in the space above the entire valve. The propellant gas in this space above the entire valve is subsequently lost to the atmosphere when the spray can is removed from under the filling station. With PU foam, the passage in the hollow valve stem alone is sufficiently large to allow a rapid entry of propellant gas. Thus, it suffices to inject the propellant gas through the valve stem. The valve for a spray can containing PU foam may thus be kept simpler, without such special arrangements. Moreover, the loss of propellant gas to the atmosphere during filling may be much lower.
The valve on a spray can containing PU foam is thus characterized by a valve bowl or valve cup of which the bottom (i.e. the "valve plate") is raised at its circumference and ends in an outwardly curling collar with which the valve cup is crimped onto the edge of the filling opening, which is usually located centrally in the head which was flanged onto the cylindrical spray can. In this valve collar, a plastic seal is usually provided to form a seal between the valve collar and the edge of the filling opening. In the bottom of the valve cup, the valve stem is resiliently mounted, protruding centrally above the valve plate, which forms the bottom of the valve cup. This resilient mounting may for instance be implemented by means of a central rubber seal, known as a "grommet" or "valve rubber", or by means of a steel spring, also known as a "valve spring".
By compressing the valve stem relative to the valve collar, towards the valve plate, the valve may be opened. Many types of valves may also at least partly be opened by pushing the tip of the valve stem laterally away from its central position relative to the valve cup. These valves are highly suited for spray cans intended for the DIY market segment as described above.
The inventors have found that the most elastic parts of the valve are the valve rubber or the valve spring, possibly followed by the valve plate.
We have found that the valve plate may deform, for instance during the assembly of the spray can and even still afterwards. Thus, in a newly filled spray can, the valve may be pushed outwardly when the pressure builds within the spray can, especially when the exothermal reaction also temporarily increases the temperature. The valve plate may also deform inwardly. This could for instance occur when the valve stem is compressed to open the valve for allowing the injection of propellant gas. If during this process forces are exerted which the valve plate is unable to withstand without deforming, the valve plate will yield and deform.
These deformations may cause the valve stem to move away from its initial position. As a result of this, the valve stem position may be different from the expected position and no be longer optimal, in case of gun foam, when the coupling with the dosing gun is to be established. This repositioning of the valve may thus affect the opening of the valve when the coupling is made between the spray can and the spray-gun, such that, when making the coupling, the valve does not always reach the desired degree of opening, or may even not be opened at all, or, conversely, the valve may open too soon and cause an accidental spillage of the substance.
The containers from the present invention may, under pressure, contain substances that are still highly reactive and only fully react once the substance has been applied to its ultimate location, such as in a crevice or onto a substrate. Any contact of the contents of the container with the skin, or even more importantly with the eyes, should therefore be avoided.
This deviation of the position of the valve stem relative to its expected position is clearly undesirable, and possibly even dangerous for the user. The risk for its occurrance should therefore be kept as small as possible, especially, though not only, in the case of so-called gun foam, i.e. in spray cans intended to be used with a dosing gun.
In pressure containers for handheld operation, this issue of deformation is somewhat less critical, though not entirely inexistent. The valve stem may for instance end up too close to the valve collar, as a result of which the tube can no longer be screwed sufficiently far onto the valve stem, or as a result of which the lateral freedom of movement of the arrangement of applicator tube and valve stem, possibly provided with a lever, is too much constricted by the valve collar to ensure a proper operation. Moreover, deformation during filling may cause the valve to be damaged to such an extent that it no longer functions, and the can is rendered entirely useless.
Also the valve rubber or the valve spring may become damaged during the production of the spray can. If these are subjected to excessive forces, their resilience may have been decreased, so that the valve no longer closes quickly. The valve has then lost its reaction speed or "snappiness". In this way, after the injection of propellant gas, content may still escape from the spray can and soil the spray can and/or the environment. When it is closed too slowly, a large part of the propellant gas may escape before the valve is fully closed, which may even render the spray can entirely unusable. This issue arises both with gun foam and with spray cans for handheld operation.
Another thing that may occur is, when the valve stem is subjected to excessive force, that the valve plate may break down and/or the valve rubber may be pushed through the valve plate, causing the spray can to leak or at least be rendered useless. If this occurs in the filling station, such an incident necessitates the station to be shut down and thoroughly cleaned, leading to a substantial loss of production.
There is therefore still a need for reducing the risk for damaging the valve of PU foam spray cans during the assembly of the spray can and the packaging of het PU foam. At least equally important, and in fact even more important, is to reduce the risk for the valve to have lost its reaction speed at the end of the filling with propellant gas, and the valve would close too slowly, allowing propellant gas or other contents to escape from the spray can before it leaves the production line.
The present invention aims to avoid or at least alleviate the problems described above and/or to provide improvements in general.

SUMMARY OF THE INVENTION

According to the invention, a method is provided as defined in each of the appended claims.
The invention provides a method for the production of a pressure container containing a composition for forming polyurethane foam, comprising the steps of

closing the container, after introducing the components of the composition that are liquid under ambient conditions, by securing into an opening in the container head a valve having a hollow valve stem centrally arranged in a round valve cup that extends laterally into a peripheral valve collar, and whereby the valve is secured to the container by crimping the valve collar in the opening in the container head, and
pressurizing the closed container by injecting at least one propellant gas through the valve stem, whereby the valve is opened by compressing the valve stem relative to the valve collar, in the direction of the valve cup,

The reference point on the force-compression distance curve is the point in the curve where, with progressive compression or pressing down of the valve stem relative to the valve collar, with an already opened valve, a clearly discernable change occurs for the first time in the evolution of the force as a function of the compression distance.
We have found that limiting as prescribed the distance over which the valve stem is compressed or pressed down during the injection of the propellant gas, offers the advantage that the force exerted on the valve remains limited, such that the valve maintains its full reaction speed or "snappiness" and closes immediately when the force is removed after each injection of propellant gas, so as to avoid an escape of major quantities of propellant gas or, even worse, of liquid, from the spray can while the spray can completes the rest of its course through the filling station for propellant gasses. An undesired escape of propellant gas in or while leaving the filling station may create a safety hazard, and bring economic and often also ecological disadvantages. Liquid escaping from the pressure container in this location in the production process would be even less acceptable, because it causes soiling of the spray can, the filling station and/or of the conveyor belt for spray cans. This usually leads to degradation of part of the production volume to waste, with associated disposal problems due to the still reactive contents, and to additional maintenance measures requiring the filling station and conveyor belt to be shut down and cleaned, with associated production losses.
The applicants have found that the present invention also reduces the risk of damage to the valve spring or the valve rubber or any other part of the valve, as well as reducing the risk of the valve plate to break down or deform, and consequently also reducing the risk for deviations of the position of the valve stem.
In valves for PU foam, the valve stem is resiliently attached to the valve plate. This may be arranged by means of a rubber gasket, the so-called "grommet" or valve rubber, or by means of a metal spring. In each of these cases, the result is that the force that needs to be exerted to further press the valve stem down increases with the distance over which the valve stem has already been compressed or pressed down relative to the valve collar. This force must be absorbed by the valve and is transferred via the valve collar to the pressure container onto which the valve was mounted.
The applicants have found that with a low compression distance, the valve rubber is compressed in height and expands in width. The force required to further compress the valve stem only slightly increases, or may even remain approximately constant over some distance, and this first deformation upon opening the valve was further found to be very quickly reversible. The applicants have found that with a deformation of the valve rubber of this nature, the valve retains its high reaction speed and quickly closes again when the force exerted on the valve stem is removed. The applicants have found that this is the case as long as the valve stem is compressed or pressed down no further than up to the reference point.
With a greater compression distance, however, i.e. beyond the reference point, the valve rubber will react differently. Further compression or pressing down beyond the reference point may for instance lead to the valve rubber bulging out, in a kind of lateral bulging. The transition from the previous reaction regime to the next one is even often characterized by a "kink" in the curve, probably because the valve rubber then briefly and quickly changes shape and snaps into a new position. During this "snapping", the valve rubber momentarily yields to the force, and the curve shows a valley or "dip", for instance as indicated by the arrow and the letter C in Figure 2. We have observed that beyond this marking point in the curve, the curve takes on a noticeably different slope. The applicants have found that after such deformations, the valve rubber may still recover its original shape, but that this recovery happens much slower, and the valve therefore has lost reaction speed or "snappiness". The valve rubber may possibly still recover its original shape, such that the valve stem again raises sufficiently to close the valve, but the time required for achieving that result has increased substantially due to that additional deformation of the valve rubber. The valve has, to a considerable degree, become "slower". The applicants have found that it is advisable to compress or press down the valve stem not further than up to or just before the "kink" or "dip" in the curve, beyond which the slope of the curve noticeably changes. The applicants have found that the desired effect of the present invention is achieved if the valve stem is not compressed any further, and thus the prescribed distance to the reference point is respected.
The applicants have found that a valve with a valve spring also exhibits a similar susceptibility. The applicants have found that in the case of a valve having a valve spring, during a part of the course with opened valve, the force increases approximately linearly with the compression distance. Without wishing to be bound by this theory, the applicants believe that this slope reflects the spring constant of the valve spring. The applicants have found that during this course, the valve retains its high reaction speed, and that the valve stem may very quickly regain its original position when the force is removed. During this course, the valve thus retains its original and desired "snappiness".
The applicants have found that also valves having a valve spring will react differently at greater compression distances. The force required for further compression or pressing down of the valve stem will in that case increase more rapidly as a function of the compression distance than at a lower compression distance. The transition from the previous regime to the next one may however be more gradual and therefore less apparent, without a clear "marking point" such as the "dip" in the curve described above. In the most clear case, the curve may exhibit a "tipping point", but sometimes this may only signify a gradual bending in the curve. Without wishing to be bound by this theory, the applicants believe that at the higher compression distances, other parts than the valve spring will react. We believe that certain parts start deforming plastically, because we have observed that with even higher compression distances, the valve often visibly breaks down physically and suffers permanent damage. The applicants have found that with valves having a valve spring, it is advisable to compress the valve stem no further than up to the point in the curve where the slope of the curve noticeably changes.
The curve of some valves, such as those having a valve spring, do not exhibit the "dip" as seen in the case of a valve having the valve rubber. Sometimes, a fairly noticeable "kink" is visible, but in other cases the transition is more gradual. The applicants have therefore found that the reference point in those cases is preferably determined by extrapolating the previously discussed linear part of the curve to greater compression distances, and taking the reference point where the force has increased 10% relative to this extrapolation.
The applicants have found that the desired effect of the present invention is achieved and preserved if the prescribed distance to the reference point is respected.
The applicants have found that the present invention further offers the advantage that the risk for damage to the valve stem during the filling of propellant gas is also greatly decreased. Consequently, later coupling of the valve stem to a dosing gun or to an applicator tube will incur fewer or no problems.
On the other hand, the applicants have found that, despite the prescribed limit to the compression distance, a sufficient valve opening may be obtained to obtain a quick filling of propellant gas, and thus a sufficiently high production rate may be achieved using the filling station for propellant gas. This is possible mainly thanks to the wider passage provided through the valve stem of valves that are mainly intended and developed for the pressure containers containing PU foam.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1a shows a resting position of a conventional valve with a valve rubber for gun foam.
Figure 1b shows an open state of a conventional valve with a valve rubber for gun foam.
Figure 2 shows a force-compression distance curve, for three conventional valves as shown in Figure 1, registered during tests on a test bench.
Figure 3 shows a force-compression distance curve registered during a test on a test bench for a valve having a valve spring.

DETAILED DESCRIPTION

The present invention will hereafter be described in particular embodiments and with possible reference to certain drawings, but the invention is not limited thereto, but is limited only by the claims. The possible drawings are only schematic and are non-limiting. In the drawings, some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions, including relative dimensions, therefore do not necessarily correspond to the way the invention is implemented in practice.
Furthermore, the terms first, second, third and the like, in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. These terms are interchangeable under appropriate circumstances and the embodiments of the invention can appear in other sequences than those described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for indicating relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention may appear in other sequences than those described or illustrated herein.
The term "comprising", used in the claims, should not be interpreted as restricting to the means listed in context therewith. It does not exclude the presence of other elements or steps. It should be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to an object consisting solely of components A and B. It means that with respect to the present invention, A and B are the only relevant components of the device. Correspondingly, the terms "comprising" or "including" also encompass the more limited terms "consisting essentially of" and "consisting of".
Unless stated otherwise, all ranges indicated in this document also include the extremes, and all values for ingredients and components of compositions are expressed in weight percentages or weight % of every ingredient of the composition.
The expressions "weight percent", "weight %", "percent weight", and variations thereof, denote the concentrations of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100, unless stated otherwise. The same applies to "ppm" or "ppm weight" or "weight ppm", only then by a factor of 1 million (1000000). In this document, "percent", "%", "%wt", are intended as synonyms of "weight percent".
It should also be understood that, as used in the present patent document and the appended claims, the singular "a" and "an" and "the" also refer to the plural, unless the context clearly indicates otherwise. Thus, for instance, reference to a composition comprising "a substance" also includes a composition having two or more substances therein. It should also be understood that the term "or" is usually employed in its sense of "and/or", unless the context clearly indicates otherwise.
Moreover, any substance may be discussed mutually interchangeably in the present document by reference to its chemical formula, chemical name, abbreviation, etc....
In the context of the present invention, the terms spray can and pressure container are used interchangeably and are considered synonyms of each other. With the term "container" or "can" may in the context of the present invention not necessarily always be meant a spray can or a pressure container, but these terms should indeed include spray cans and pressure containers.
At room temperature, the pressure in a filled and ready-to-use pressure container or container containing 1k PU foam is typically about 5 bar gauge. The containers are usually capable of not deforming permanently up to a pressure of 18 bar gauge, and are designed not to burst up to a pressure of below 21.6 bar gauge. The valve is usually designed to withstand a pressure of at least 22 bar gauge. Other containers exist which are merely capable of remaining intact up to a pressure of 12 or 15 bar gauge.
The container valve or "valve" usually consists of a valve bowl or "valve cup", i.e., a round metal cup, which is secured or "crimped" along its perimeter onto the central filling opening of the container or spray can, usually complemented by means of a rubber seal, usually an O-ring, to prevent leakage of pressure container content via this crimped valve collar.
In the conventional valve, the valve cup supports a central rubber seal, known as "grommet" or "valve rubber", through which a hollow and usually plastic stem of a valve is inserted. The stem is usually fairly stiff and has a central duct that, just before the stem at its lower end terminates in a blind flange, transitions laterally into one or more, usually four, lateral openings. In a resting state, the rubber gasket pulls the blind flange against the bottom of the gasket, thereby sealing the openings. The valve is designed to be opened by pushing the stem down relative to the gasket or cup, possibly only laterally, whereby the gasket is usually elastically deformed and whereby at least one of the lateral openings in the stem of the valve becomes available for passing the container contents.
Because the rubber of the gasket of the conventional valve, in particular when powdered carbon is used as filler in the rubber, allows the diffusion of water, which may then react with the still available isocyanate groups in the pre-polymer in the container to form a tacky solid substance, the conventional valve has the disadvantage that the blind flange of the valve may over time adhere to the rubber, especially if the container is for some time in a horizontal position. This may already occur when the container is left lying on its side for a period of only 3 to 6 weeks. Due to this adherence, it may become impossible to open the can and extrude the substance. Another disadvantage is that the rubber of the valve seal also allows the diffusion of propellant gasses to outside the container, so that the container may after a while have lost most or all of its pressure. For these reasons, other types of valves were developed that are not allowed to comprise a rubber gasket as described for the conventional valve. Such container valves may also be referred to as "feststof" valves, and suitable variants thereof are for instance described in WO 2009/004097 , US 5,014,887 , WO 03/062092 , or US 5215225 , US 5549226 and US 6058960 . These valves have no rubber seal, or only a rubber seal at the outside of the valve, that does not contact the contents of the container. These "feststof" valves may therefore be characterized in that the materials of the valve parts that come into contact with the contents of the spray can are virtually impermeable to water and/or propellant gasses, usually materials that are more solid than rubber (hence the name "feststof"). The valves may for instance be provided with one or even more than one metal spring, being a coiled spring or a leaf spring or a combination thereof. The spring or springs may be arranged and adjusted in such a way that the valve may be opened more easily than a conventional valve, and therefore offers further improved ergonomics to the user, as well as an improved capacity for aiming and dosing. The springs may also lead to a quicker closure of the valve when compared to the conventional valve. A valve with an internal coiled spring is for instance described in WO 2015/032963 A1 and in US 5,014,887 . Valves with external coiled springs may be found as part of the family of the valves MIKAVent PU-RF, available from Mikropakk. Valves with a leaf spring may be found in US 6058960 , WO 03/062092 and WO 2009/004097 .
Just like conventional valves, these "feststof" valves usually also have a valve cup and a stem. The valve cup of such valves may still be susceptible to deformation. These valves are usually provided with at least one surface for sealing at the outside of the stem of the valve, suitable for forming a seal when contacted with a gun adapter, a dosing gun, or a handheld applicator. These sealing surfaces may consist of strips for improving the sealing action, and these strips may be provided in suitable locations at the outside of the valve. Examples of such strips are described in US 5014887 , US 6058960 and in WO 2009/004097 .
For safety reasons, containers that are ready for the market are therefore always provided with a protective cap, which is to shield the container valve, and more specifically the valve stem, against damage, tearing or contact, and against shifting relative to the valve plate, and thus for safety reasons and to protect against accidental spilling. The containers for handheld use are typically provided without a gun coupling piece, i.e. with the valve fully accessible. For that reason, such containers are conventionally provided with a separate protective cap that is usually snapped onto the flange around the container head. Containers for professional use, i.e., for use combined with, for instance, a gun, are provided with a gun coupling piece, which is usually snapped onto the flange around the valve plate. Access to the valve stem through this first coupling piece is then typically blocked by means of a separate protective cover, which may for instance snap onto the upper edge of the gun coupling piece, which may suitably be adapted for snapping the cover back on, such as by providing a small collar.
The applicants have found that, when a valve in a test bench is subjected to a test whereby the valve stem is compressed or pressed down relative to the valve collar, the force to be exerted over the greater part of the entire course to further and further compress the valve stem, at least remains constant and usually increases as it is further compressed. The applicants have found that the curve showing the force as a function of the compression distance, here called "force-compression distance curve", is characterized in that for a large part of the curve, the increase of the force is mainly determined by the constant or increasing resistance of the most elastic part of the valve, for instance the valve spring or the valve rubber in its original shape. The applicants have found that during this part of the curve, the valve opens and, as the valve stem is further compressed, continues to open, and that when the force on the valve stem is removed, the valve stem immediately returns to its original position and the valve is closed.
The applicants have found that the force-compression distance curve for many types of valves, such as for valves having a valve rubber, upon further compression of the valve stem shows a clear tipping point whereby the force required to compress the valve stem further changes strongly when compared to during the course at the shorter compression distance, but with an already opened valve. Usually, the curve at that transition even exhibits a noticeable "dip" or valley, as explained above. The applicants argue that the reference point for a certain type of valve is this first tipping point with opened valve, and that this tipping point may readily be determined for any type of valve by subjecting a valve of a same embodiment to a suitable testing method on a test bench. Without wishing to be bound by this theory, the applicants believe that the strong change in the force-compression distance curve at that tipping point may be caused by the valve rubber having snapped into another shape, and that other shape reacting differently to the compression force than the shape of the valve rubber at the shorter compression distance. The applicants have found that for each embodiment of this type of valves for PU foam, the first tipping point with opened valve may be determined by means of such a test as the reference point.
The applicants have found that the force-compression distance curve in other types of valves, such as the valve having a valve spring, over a significant portion of the curve exhibits a slowly and linearly increasing force as a function of the compression distance. Without wishing to be bound by this theory, the applicants believe that this linearly increasing relationship with a valve having a valve spring reflects the spring constant of the valve spring. The applicants have found that at higher compression distances, the curve increases more rapidly, at a higher slope, as discussed above. Usually, the curve at that transition also shows a noticeable kink or "tipping point", which then represents the reference point according to the present invention.
The applicants have found, with some embodiments of valves, that this transition in the curve from the first, linear portion to the next, steeper portion may be less sharp and/or defined. Under such circumstances, the applicants prefer to determine the reference point in an alternative way, as follows.
The applicants have found that for the linear portion of the course, a linear mathematical relationship, having a correlation higher than 0.97, may readily be determined. The applicants have found that for valves having this type of force-compression distance curve, it is suitable to take as a reference point the point on the curve where the force is 10% higher than what the linear mathematical relationship yields for that compression distance, i.e. when the linear relationship is extrapolated to a greater compression distance. This method is described and explained in detail in the discussion of Figure 3 as part of the example.
The applicants have found that the reference point for one specific embodiment of valves for PU foam may be determined with sufficient precision. The applicants have found that it is sufficient to subject a few specimens of a selected valve to the compression test in the test bench, whereby the average of the compression distances at the reference point for the different specimens may then serve as the reference point for that same embodiment of valves.
In an embodiment of the method according to the present invention, the valve stem is compressed or pressed down relative to the valve collar over a distance of no more than 80% of the compression distance corresponding to the reference point, preferably at most 75%, more preferably at most 70%, even more preferably at most 65%, preferably at most 60%, more preferably at most 55%, even more preferably at most 50% of the compression distance corresponding to the reference point. The inventors have found that by complying with this condition, the risk for the valve having lost its high reaction speed, even only partially, after injecting the propellant gas into the spray can, is strongly reduced. We have also found that the risk of deformation of the valve and/or the valve stem and/or of a deviation of the valve position away from the expected position, is further reduced. The inventors have also found that within the prescribed range, sufficient opening of the valve remains obtainable for enabling at each injection the injection of the required amount of propellant gas into the spray can without problems.
In another embodiment of the method according to the present invention, the valve stem is compressed or pressed down at least 0.7 mm from the resting position with the valve closed, preferably at least 0.8 mm, more preferably at least 0.9 mm, even more preferably at least 1.0 mm, preferably at least 1.1 mm, more preferably at least 1.2 mm, even more preferably at least 1.3 mm, still more preferably at least 1.4 mm. This offers the advantage that a further opening of the valve is obtained, so that the amount of propellant gas to be filled during a given injection may be filled into the pressure container more quickly, and thus a higher production rate through the filling station may be achieved.
In an embodiment of the method according to the present invention, the valve stem is compressed or pressed down at most 3.2 mm, preferably at most 3.1 mm, more preferably at most 3.0 mm, even more preferably at most 2.9 mm, preferably at most 2.8 mm, more preferably at most 2.7 mm, even more preferably at most 2.6 mm, still more preferably at most 2.5 mm, preferably at most 2.4 mm, more preferably at most 2.3 mm, even more preferably at most 2.2 mm, preferably at most 2.1 mm, more preferably at most 2.0 mm, even more preferably at most 1.9 mm, still more preferably at most 1.8 mm, preferably at most 1.7 mm, more preferably at most 1.6 mm, and even more preferably at most 1.5 mm, during the injection of propellant gas. The applicants have found that for most valves, this range is sufficient for obtaining sufficient valve opening, especially if the filling head is set to the highest prescribed limit, while still keeping sufficiently low the risk for issues or problems with the valve after injecting propellant gas.
In an embodiment of the method according to the present invention two or more propellant gasses are injected, preferably at least three propellant gasses. The applicants have found that the filling of the pressure container may be carried out more quickly if two or more injections of propellant gas are performed in the filling station for propellant gas. The desired effect is even higher if those 2 or more injections are carried out, even if these are injections of one and the same propellant gas, by different filling heads.
In an embodiment of the method according to the present invention whereby the propellant gasses are injected sequentially in multiple steps in the same pressure container, at least one previously injected propellant gas differs from at least one propellant gas that is injected later. The applicants have found that a better operation of the pressure container may be achieved by using different propellant gasses.
In an embodiment of the method according to the present invention, the previously injected propellant gas has a higher boiling point than the propellant gas that is injected later. A higher boiling point usually goes htogether with a lower vapour pressure at the same temperature, especially at the temperature in the spray can. This offers the advantage during the injection of the propellant gas that is injected later, that the back pressure in the spray can is lower, and the injection may therefore be carried out more quickly and more easily.
In an embodiment of the method according to the present invention, the previously injected propellant gas has a higher solubility in the pressure container content than the propellant gas that is injected later. This, too, offers the advantage that during the injection of the propellant gas that is injected later, the back pressure in the pressure container is lower, and the injection may therefore be carried out more quickly and more easily.
In an embodiment of the method according to the present invention, the valve stem is provided at its side with a shoulder, and the filling head of the filling station for compressing or pressing down the valve stem contacts the shoulder, and preferably the force exerted by the filling head on the valve stem to open the valve is at least partly exerted on the shoulder of the valve stem. This offers the advantage that a larger contact area may be available for transferring the force required for opening the valve from the filling head onto the valve stem. As a consequence, the point load on the valve stem is lower, and the risk further decreases for deformation of the valve stem itself.
In an embodiment of the method according to the present invention, a gasket is provided between the valve stem and the filling head of the filling station, preferably a plastic gasket, more preferably a gasket made of rubber or polytetrafluorethylene (PTFE), and preferably the gasket is provided in the filling head of the filling station. The applicants prefer a gasket made from a resilient plastic. This may be a rubber or a polyolefin, but is preferably polytetrafluorethylene (PTFE). Preferably the gasket is provided in the filling head of the filling station, such that it does not need to be provided as part of each valve. The applicants prefer, if possible, to have the gasket to seal against the side wall of the valve stem, such that the force to be transferred from the filling head to the valve stem for opening the valve, does not need to be transferred via this gasket. The applicants have found that this embodiment is suitable in the case of a valve stem having a shoulder. For other valves, especially those having a larger upper surface of the valve stem, such as several embodiments of the valves having a valve spring, the applicants prefer to have the filling head sealing against the top of the valve stem, which is preferably manufactured in an elastic material, such as rubber.
In an embodiment of the method according to the present invention, the method comprises, after the injection of propellant gas, the step of shaking the spray can. The applicants prefer, in the case of multiple propellant gasses, to inject all of the propellant gasses before shaking the spray can. The shaking is intended to improve the mixing of the contents of the can, such that the chemical reaction between the isocyanate molecules and the other reagent, which is reactive with it, proceeds smoothly, and also to ensure that the propellant gasses are partially dissolved in the liquid in the pressure container and form a homogenous entity.
In an embodiment of the method according to the present invention, the valve is a valve for gun foam. This offers the advantage that, by means of a suitable tool, the pressure container may be suitable for use with a dosing gun, but also, with adequate selection of the tool, for handheld use, i.e. with an applicator for handheld operation, as described below.
In an embodiment of the method according to the present invention with a valve for gun foam, the method comprises, after the injection of propellant gas, the step of attaching an applicator for handheld operation suitable for a spray can with gun foam. An applicator for handheld operation is suitable for a spray can with a valve for gun foam is for instance described in WO 2012/052449 A2 and US 10106309 B2 . This offers the advantage for the manufacturer of the spray cans that in the production line of PU spray cans, only a single supply line, and/or only a single type of filling station for propellant gas needs to be provided, whereby a valve for gun foam may be arranged onto each spray can, but whereby a part of this production may be equipped for handheld use, i.e. aiming more at DlYers or the more occasional users. If all spray cans are produced on the same line, this offers the advantage that the production line no longer needs to be converted and adjusted as often or as drastically, even at all, when transitioning from the one can embodiment to the other.
In an embodiment of the method according to the present invention with a valve for gun foam, the method further comprises, after the injection of propellant gas, the step of attaching a gun coupling piece onto the valve collar, preferably a gun coupling piece provided with a protective cover. This prepares the spray can for use as gun foam, i.e. using a dosing gun. The protective cover offers the advantage that the valve of the spray can is protected during handling between the production line and the site where it is to be used, until right before being coupled with a dosing gun. A suitable gun coupling piece with a protective cover capable of being broken off is for instance described in WO 2009/004097 A1 . A suitable gun coupling piece where the protective cover is not only removable, but may also be reattached after a first use, is described in WO 2011/151295 A1 . The latter offers the advantage that the valve may also be protected between an earlier use and a later reuse of the same spray can.
In an embodiment of the method according to the present invention whereby a gun coupling piece is attached onto the valve collar, the gun coupling piece is also suitable for attaching an applicator for handheld operation. A gun coupling piece provided with a protective cover suitable for attaching an applicator for handheld operation is for instance described in WO 2011/151295 A1 . The gun coupling piece from WO 2011/151295 A1 thus offers the additional advantage that the logistical supply chain only needs to handle a single form of spray can in order to supply both the professional user, who prefers to work with a dosing gun, and DlYers, who prefer handheld operation.
In an embodiment of the method according to the present invention, the valve is a valve for handheld operation. This offers the advantage that, by means of a suitable tool, the spray can is suitable for use with handheld operation, such as after attaching onto the valve an applicator tube or an applicator for handheld operation with a lever, as already described above.
In an embodiment of the method according to the present invention provided with a valve for handheld operation, the method further comprises, after the injection of propellant gas, the step of arranging a protective cap onto the spray can head, preferably a protective cap containing an accessory item, preferably the accessory item comprising at least one plastic glove, more preferably at least one pair of plastic gloves. A suitable protective cap is for instance described in EP 2371738 A1 . This protective cap aims to protect the valve on the spray can during handling between the production line and the site where it is to be used by the user.

EXAMPLES

The present invention will be elucidated in more detail below with reference to the appended drawings.
Figure 1a shows a conventional valve 10 for gun foam, in resting position. The valve comprises a valve cup or valve bowl 1 consisting of a valve plate 3 which extends upwardly, and then laterally into a valve collar 2. By attaching this valve collar onto the edge of the opening in the spray can head (not shown), the valve may be secured in the opening and the spray can may be closed, the mounting being sealed using the gasket 6 provided inside the valve collar. The valve rubber or "grommet" 5 is centrally affixed to the valve plate 3, and keeps the valve stem 4 in its central position relative to the valve collar. The valve is closed as a result of the blind flange 7 at the bottom of the valve stem being pushed upward by the valve rubber against the bottom of the valve rubber. The valve stem is further provided with a laterally extending shoulder 8, which at its bottom provides an engagement surface for the upward force of the valve rubber onto the valve stem. The shoulder also, at its top, provides an optional additional engagement surface for the filling head (not shown), which may open the valve by pressing the valve stem downward.
In Figure 1a, the valve is shown in resting position, i.e. with the valve closed. The top of the valve extends a distance A over the top of the valve collar.
Figure 1b shows an open state of the same valve as shown in Figure 1a. When propellant gas is filled through the filling head (not shown), the valve stem is pressed downward, to a distance B above the top of the valve collar, such that the blind flange 7 at the bottom of the valve stem is released from the valve rubber 5, allowing the contents of the spray can (not shown) underneath the valve access to the lateral openings in the valve stem, and allowing it to leave the spray can through the central passage in the valve stem. In Figure 1b, the valve stem is compressed relative to the valve collar over a compression distance (A - B).
Figure 2 shows a force-compression distance curve, for a conventional valve as shown in Figure 1, registered during a test on a test bench. For this test, the valve 10 was placed with the valve collar 8 onto a vertical length of pipe in which the valve cup fitted snugly, so that the valve was resting with its valve collar on the end of the pipe. During the pressure test, a downward force was exerted, by means of a suitable accessory, on the top of the valve stem 4, and the force F was registered in Newton (N), as a function of the compression distance d in millimeter (mm) from the resting position shown in Figure 1a in the direction of the open position shown in Figure 1b, that was required to push the valve stem further and further downward, in the direction of the valve plate 3. The evolution of this force, as a function of the compression distance, yielded the force-compression distance curve in Figure 2.
This test was performed three times, each time using another specimen of the specific type of valve, distinguished from each other using the numbers 4.1, 4.2 and 4.3. The 3 curves in Figure 2 exhibit a very similar course for the portion of the curve that is of interest for this invention, i.e. until the force starts increasing more rapidly and a risk for the loss of reaction speed of the valve is expected. At a compression distance of 3.8 mm, all of the curves exhibit a noticeable kink C with opened valve. After this kink in the curve, the curve exhibits a steeper slope, presumably because the valve rubber has then taken on another shape that resists the force onto the valve stem in a different way than at a lower compression distance. This kink C constitutes the reference point for this embodiment of valves having a valve rubber.
The filling heads of the filling station for filling propellant gas into spray cans with this type of valve from Figure 2 were set to a compression distance of 1.5 mm, i.e. 39% of the compression distance corresponding to the reference point with opened valve on the force-compression distance curve determined for this embodiment of valve on a test bench. Over 2 years of operations, at a production rate of 7 million spray cans per year, no spray cans were observed with insufficient propellant gas filling or loss of propellant gas and/or liquid during and immediately after the filling of propellant gas. Moreover, no deviations were observed that could be due to a deformation of the valve or the valve stem during the filling of propellant gas.
Figure 3 shows a similar result for a specimen of a valve having a valve spring, registered during a similar test on the same test bench. This curve also shows a noticeable kink at 2.8 mm compression distance, where the curve suddenly starts rising more sharply. This point could therefore be taken as a reference point for this type of valves.
For the purpose of illustration, we will discuss below, and indicate on this curve, how a suitable reference point could be determined if the slope transition of the curve would be not as clear. Over the range D, shown in bold, from 1.4 mm to 2.4 mm, the curve shows a very linear relationship between the force F in Newton required for pushing further open the valve, and the compression distance d in millimeter. This linear relationship between the force expressed in Newton (N) and the compression distance expressed in millimeter (mm) may be expressed mathematically with high precision (R² = 0.9973) using the following formula: $y = 24.342 x + 39.043$
Figure 3 shows in a thin, continuous line the force corresponding to this mathematical relationship for each compression distance d over the entire range of the figure. Figure 3 further shows, in a dotted line, the force that would be 10% higher than the force that is calculated using the mathematical formula above. At point C, this dotted line intersects with the registered curve for the valve. Point C thus indicates, at a compression distance of 2.9 mm, the reference point for this valve if there were no noticeable and sharp tipping point.
Additionally, two other specimens of the same embodiment of the valve having a valve spring from Figure 3 were tested. These tests resulted in reference points, after extrapolation and the described calculation, of respectively 2.8 and 3.0 mm. For this embodiment of valves with a valve spring, this calculated reference point thus becomes (2.8+2.9+3.0)/3 = 2.9 mm.
The applicants note that in Figure 3, the tipping point at 2.8 mm and the calculated reference point at 2.9 mm are very close together. The applicants argue that the precaution prescribed according to the present invention, i.e. to stay a prescribed percentage away from the reference point, is sufficient as a safety margin to still obtain the desired effect, regardless of which of the two described methods was used to determine the reference point for valves such as this of Figure 3.
The filling heads of the filling station for filling propellant gas into spray cans with this type of valve were set to a compression distance of 1.2 mm, i.e. 52% of the compression distance corresponding to the reference point with opened valve on the force-compression distance curve determined for this embodiment of valve on a test bench. Over 2 years of operations, at a production rate of 7 million spray cans per year, no spray cans were observed with insufficient propellant gas filling or loss of propellant gas and/or liquid during and immediately after the filling of propellant gas. Moreover, no deviations were observed that could be due to a deformation of the valve or the valve stem during the filling of propellant gas.
With the present invention having been fully described, it will be clear to the person skilled in the art that the invention may be carried out using a wide range of parameters within what is claimed, without thereby departing from the scope of the invention, as defined by the claims.

Claims

A method for the production of a pressure container or spray can containing a composition for forming polyurethane foam, comprising the steps of
• closing the container, after introducing the components of the composition that are liquid under ambient conditions, by securing into an opening in the container head a valve (10) having a hollow valve stem (4) centrally arranged in a round valve cup (1) that extends laterally into a peripheral valve collar (2), and whereby the valve is secured to the container by crimping the valve collar in the opening in the container head, and

• pressurizing the closed container by injecting at least one propellant gas through the valve stem, whereby the valve is opened by compressing the valve stem (4) relative to the valve collar (2), in the direction of the valve cup (1),
characterized in that, during the injection, the valve stem (4) is compressed relative to the valve collar (2), from the resting position with the valve closed, over a distance of at most 85% of the compression distance corresponding to a reference point on the force-compression distance curve registered on a test bench for a valve of the same embodiment.
The method according to claim 1 whereby the valve stem (4) is compressed relative to the valve collar (2) over a distance of no more than 80% of the compression distance corresponding to the reference point.
The method according to claim 1 or 2 whereby the valve stem (4) is compressed at most 2.0 mm, and preferably at most 1.5 mm, during the injection of propellant gas.
The method according to any one of the preceding claims whereby two or more propellant gasses are injected, preferably at least three propellant gasses.
The method according to the preceding claim whereby the propellant gasses are injected sequentially into the same spray can and whereby at least one previously injected propellant gas differs from at least one propellant gas that is injected later.
The method according to the preceding claim whereby the previously injected propellant gas has a higher boiling point than the propellant gas that is injected later.
The method according to any of claims 5 and 6 whereby the previously injected propellant gas has a higher solubility in the spray can content than the propellant gas that is injected later.
The method according to any one of the preceding claims whereby the valve stem (4) at its side is provided with a shoulder (8) and whereby a filling head of a filling station for compressing the valve stem contacts the shoulder (8), and the force exerted by the filling head on the valve stem to open the valve is at least partly exerted on the shoulder (8) of the valve stem.
The method according to any one of the preceding claims whereby a gasket is provided between the valve stem (4) and the filling head of the filling station, and preferably said gasket is disposed in the filling head of the filling station.
The method according to any one of the preceding claims whereby the valve is a valve for gun foam.
The method according to the preceding claim further comprising, after the injection of propellant gas, the step of attaching an applicator for handheld operation suitable for a spray can with gun foam.
The method according to claim 10 further comprising, after the injection of propellant gas, the step of attaching a gun coupling piece onto the valve collar, preferably a gun coupling piece provided with a protective cover.
The method according to the preceding claim whereby the gun coupling piece is suitable for attaching an applicator for handheld operation.
The method according to any one of claims 1-9 whereby the valve is a valve for handheld operation.
The method according to the preceding claim further comprising, after the injection of propellant gas, the step of arranging a protective cap onto the spray can head, preferably the accessory item being a protective cap containing an accessory item, preferably at least one plastic glove, more preferably at least one pair of plastic gloves.