FIELD OF THE INVENTION

The present invention is in the field of airless spraying of multi component adhesives.

In an embodiment, the invention relates to flexible foam bonding, such as in foam converting, mattress and furniture production.

BACKGROUND OF THE INVENTION

Most adhesives are applied using either air-spray equipment or air-assisted spray equipment. Such systems are not suitable for the present invention; for instance, since the spray and spray droplets they generate do not have the required characteristics, such as in terms of spray velocity, spray dispersion, droplet size, focus, and applicability. Also such systems form a hazard for the environment and form a risk for the health of people using such systems. In practice a direct environment of the system becomes polluted with adhesive .

The present invention relates to using airless-spray equipment. Airless spraying involves using pressure to force a fluid to be sprayed through a small orifice. When the fluid enters the atmosphere, it breaks up into small droplets forming a spray. Airless spray equipment is often operated at lower pressures than air-spray- or air assisted- spray equipment .

Methods of applying a layer of adhesive onto a surface wherein the method comprises spraying the adhesive airlessly are known in the prior art.

EP-A2-1396288 recites a method of airless spraying of a primary product and a secondary product comprising:

providing a sprayer tip; providing a primary product chamber having an outlet, the primary product chamber being in selective fluid communication with the sprayer tip; providing a secondary product chamber having an inlet and outlet, the secondary product chamber outlet being in selective fluid communication with the sprayer tip; providing a primary product to the primary product chamber; opening the primary product chamber outlet and thereby dispensing the primary product, the primary product chamber outlet being opened while the secondary product chamber outlet is closed; closing the primary product outlet; providing a secondary product to the secondary product chamber outlet; opening the second product chamber outlet and thereby dispensing the secondary product, the secondary product chamber outlet being opened after the primary product chamber outlet is closed; and closing the secondary product chamber outlet.

The following documents are considered background prior art.

EP-A2-1396288 relates to achieving automated spray nozzle cleaning.

Document US 6,319,559 Bl recites a method and system for air assisted spraying of an adhesive agent to a covering material in the process of bonding the covering material to a foam cushion member to produce a bonded unit forming a seat.

As a base material of the adhesive agent, only a primary component material and secondary curing agent are used, without any organic solvent added in the primary component material. Heat of a predetermined temperature is continuously applied to the primary component material by heating elements so as to retain its lowered viscosity through a whole fluid passage from a storage point to a spray gun, so that the heated primary component material in a fluid state may be injected from the spray gun, while being mixed with the curing agent in the air at the same time, thereby applying a properly atomized state of the mixture, as an adhesive agent, to the covering material .

Document DE 20 2005 018206 Ul recites a two- component spray gun with a double nipple handle and a lever in the cylindrical housing that has two inlet openings with hoses for materials. Guide sleeves with compression springs inside the gun housing regulates the material flow with tappet .

Document WO2011/144754 A2 recites a method for providing organic, semi-organic, mineral, inorganic and hybrid thin layers and thin layers containing nanoparticles , by simultaneous or alternate spraying of solutions of reactive partners (that is polymer/polymer interacting by hydrogen bonding, polyelectrolyte/small oligo-ion, inorganic com- pounds, etc.) on the surface of a solid substrate.

Document O1993/008929 recites a multiple nozzle coating apparatus and method which simultaneously propels a plurality of coating compositions in substantially overlap- ping coating patterns.

It is an object of the invention to provide an adhesive layer having improved characteristics and to provide an alternative to methods of applying adhesives of the prior art, which overcome one or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

In a first aspect, the present invention relates to a method of applying a layer of a multicomponent adhesive on a surface, wherein the method comprises spraying airlessly a first- and a second- component of the multicomponent adhesive simultaneously such that a first spray comprising the first component and a second spray comprising the second component come into contact at- or above- the surface.

The term multicomponent adhesive is used in its usu- al sense as would be understood by a person skilled in the field of adhesives. The multicomponent adhesive coagulates upon mixing of (at least) the first- and the second- components thereof in appropriate ratios and under appropriate conditions (temperature, humidity etc.). Coagulating may also occur under sub-optimal conditions; in such a case coagulating is relatively slower.

When applying a layer amongst others the first and second spray leave a spraying equipment or the like, travel over a certain distance, and arrive at a surface, on which the sprays or combined sprays are to be applied. At the end of the travel distance, close to the surface or at the surface, the two spray come into contact. Such is considered a rather atypical way of contacting or (partial) mixing.

By applying a layer of a multicomponent adhesive on a surface according to the invention, it has been found that the resulting layer comprises substantially inhomogeneously mixed droplets, droplets of the first spray and droplets of the second spray. Inhomogeneously mixed droplets are droplets having a domain comprising the first component (but no second component) , a domain comprising the second component (but no first component) , and a region therebetween having a concentration gradient from first component to second component (and vice versa) .

Advantageously, the first- and second- components of the multicomponent adhesive can be applied simultaneously on a single surface without significant mixing occurring. Furthermore by spraying airlessly, overspray is reduced compared to when spraying using air- or air-assisted spraying methods.

It is noted that the first and second spray taken separately have virtually no adhesive properties. Only upon contacting the two sprays, and optionally minimal (albeit partial) mixing thereof, adhesive properties are provided. The present multicomponent adhesives only become active once the components making up the multicomponent adhesive have combined in the correct proportions. Upon activation the mixture begins to coagulate. Advantageously, an inhomogeneous layer such as results from the method of the invention becomes readily activated, i.e. uniformly mixed, upon bringing the surface comprising the layer of the multicomponent adhesive, and a further surface, to which it is to be bonded, together .

In the description the terms "first spray" and "second spray" (or similar expressions) can in principle be in- terchanged. When giving further details the first spray may relate to an "adhesive" composition, such as a chloroprene dispersion, and the second spray may relate to an activator, such as citric acid.

In an example the "adhesive" spray is provided in an amount ratio of 10:1 to 3:1, preferably 8:1 to 4:1, such as 5:1, relative to an amount of "activator" spray (i.e. adhesive : activator ) . Such can be established by varying boundary conditions, such as size of a nozzle opening, pressure, pulse frequency, opening and closing time lengths, etc., thereby taking into account the respective viscosities.

It is noted that spraying airlessly relates to spraying using airless spray equipment. Basic principles of airless spray equipment and the characteristics thereof are familiar to a person skilled in the art. In further aspects the present invention also re ^¬ lates to use of the method of the invention in flexible foam bonding and to an adhesive layer.

Thereby the present invention provides a solution to one or more of the above mentioned problems.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present invention relates to a method according to claim 1.

In an example, the first and second sprays are di ^¬ rected to meet at a focal point, focal line or focal area (e.g. depending on the shape of the first and second sprays) . A focal point relates to a relative small two-dimensional ar- ea having a diameter or length and width, with dimension smaller than about 3 mm. Similarly, a focal line relates to a relative narrow but long two-dimensional area having a length and width, with a width smaller than about 3 mm and a length of 1 cm - 100 cm. The width may be in the order of a size of a (combined) droplet. Similarly, a focal area relates to a relative broad and long two-dimensional area having a length and width, with a width of about 1-30 cm and a length of 1 cm - 100 cm. The width may in the order of a size of a (com ^¬ bined) droplet. If larger areas would be considered a multi- tude of sprays and/or spraying systems may be considered. A thickness of these focal point, line or area is in principle in the order of a thickness of a droplet, i.e. 10-250 μπι. Due to limitations of e.g. a spraying system, the thickness may be somewhat larger, i.e. an order of magnitude larger, such as 100-2500 pm. It is preferred to have a thickness of small ^¬ er than 250 μπι. Such assures a high degree of contact between the first- and second- sprays and hence between droplets thereof .

The present adhesive layer may be provided with a thickness of 25-2500 μτ (about 2.5 gr/m ² -250 gr/m ² ) , prefera ^¬ bly with a thickness of 100-1000 m (about 10 gr/m ² -100 gr/m ² ) , such as with a thickness of 250-500 μτα (about 25 gr/m ² -50 gr/m ² ) . A layer may comprise a "stack" of one or more droplets. The adhesive component droplets typically have a particle size distribution with an average particle size (based on volume) of 10-250 pm, and a standard deviation (1σ) of 0.1-0.5 times the average particle size. For some application it is referred to have a larger standard deviation, especially when a more inhomogeneous layer is intended.

In an example, the focal point, focal line, or focal area is located from -2.5 cm (below) to 2.5 cm above the surface, preferably 0.1 cm to 2.0 cm from (above or below) the surface, more preferably from 0.25 cm to 1.5 cm from (above and below) the surface. Distances within these ranges have been found to give optimum droplet formation and minimal mixing of the first and second components. It is noted that the focal region (point, line or area) is located from 1-50 cm from a spray system, preferably 2-30 cm, more preferably 5-15 cm. It has been found that at those distances the most reproducible and controllable results are obtained.

The first- and second- components are preferably sprayed at a pressure of 150-2000 Pa (1.5 to 20 Bar), preferably 200-1000 Pa (2-10 Bar), more preferably 400-600 Pa (4-6 Bar) . Pressures in this range have been found to be optimal for spraying adhesive using airless-spray equipment. As the pressures are relatively low, even compared to airless spraying pressures of prior art (in other fields of technology) , relative simple and cheap equipment for spraying may be used. Also reliable and reproducible results are obtained.

In an example the first- and second- components are sprayed through a nozzle having an orifice size (diameter) in the range of 0.05 mm to 5 mm, preferably 0.1 mm to 2.0 mm, more preferably 0.3 mm to 0.6 mm. These orifice sizes provide in combination with applied pressure and type of adhesives the best results.

In an example, the (dynamic) viscosities of the first- and second- components (being regarded as Newtonian fluids) are in the range of 0.2 mPa^s to 10 Pa -s at 25°C, preferably from 0.5 mPa -s to 1 Pa ^r s, more preferably from 1 mPa -s to 0.1 Pa-s. At the applied pressure and in combination with the applied orifices inventors have found that these viscosity ranges provide the best results. In particular at the spray pressures and viscosities of the previous examples, orifice sizes within the above mentioned ranges give optimal droplet sizes and optimal adhesive function .

In an example, pressure for spraying is provided by one or more selected from: positive displacement pumps, such as double diaphragm pumps or piston pumps; pressurised sys ^¬ tems such as pressure tanks; and, gravity feed feeding systems .

In an example, a first and second stream are provided through a first and second slit, such as a rectangular slit, an circular slit, a polygonal slit, an annular opening, an polygonal opening.

In an example, the first component is selected from a waterborne adhesive containing at least one dispersion chosen from a polychloroprene dispersion, polyurethane dispersion, polyacrylate dispersion, vinylacetate-ethylene (copoly ^¬ mer) dispersion, ethylene-vinylacetate dispersion, natural rubber dispersion, styrene-butadiene-styrene copolymer dis- persion, nitrile-butadiene rubber, polyvinyl butyral dispersion, and styrene-butadiene rubber dispersion, and wherein the second component is a coagulant, for example selected from solutions of polyvalent ions, such as sodium citrate, sodium polyphosphate or sodium borate, a salt of a multiva- lent metal such as zinc, aluminium or calcium; or an acid so ^¬ lution, such as selected from citric acid, formic acid, ace ^¬ tic acid, lactic acid and mineral acid having a pH below 5, preferably below 4.5, most preferably below 4.

In a second aspect, the invention relates to use of a method according to the present invention in flexible foam bonding such as in foam converting, mattress and furniture production .

In a third aspect, the invention relates to an adhe ^¬ sive layer, such as obtainable by a method according to any of claims 1-9, wherein the layer comprises first- and second- components of a multicomponent adhesive inhomogeneously mixed, preferably such that domains of pure first- and pure second- component are present with a concentration gradient from pure first component to pure second component there- between .

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

EXAMPLES

Airless versus air .

Inventors have compared various adhesives sprayed with air and sprayed without air (airless) . Results hereof are that airless spraying does not give environmental issues or health issues, and a good adhesive function is provided, especially when an adhesive layer comprises first- and second- components of a multicomponent adhesive inhomogeneously mixed .

Such is detailed by the table below.

Initial tack

N/cm ²

Air spraying standard air pressure (2.0 bar)

Air spraying, low air pressure (0.75 bar)

I Airless spraying 1.04

An amount of adhesive used (one sided) is 200 gram/m ² . Foam parts are pressed to 50% of volume for 10 seconds. The initial tack is measured 1 minute after pressing foam. The above confirms that initial tack of airless spraying is comparable to spraying with air. It has further been found that initial tack with airless spraying is significant better when spraying a less mixed spray airless.

A disadvantage with air spraying is that an area to be covered with adhesive is not well controlled; also sputtering and splashing is observed.

The initial tack is considered to be a good measure of (fi ^¬ nal) tack obtained (or obtainable).

Focal distance Inventors have compared various focal distances. A distance of more than 5 cm from the surface did not provide sufficient adhesive function for various applications. At a distance of 2.5 cm, or likewise at the surface (distance is 0 cm) the adhesive function is considered to be sufficient. Optimal results were obtained at a distance of 0.25-1.5 cm from the surface.

Layer wise spraying

As an alternative the present multicomponent is applied as a stack of two (or more) layers, a first layer comprising a first component, a second layer comprising a second compo ^¬ nent, etc. It has been found that adhesive function of such a stack of layers is present, especially when a limited number of relatively thick layers are applied, but the function is considered to be sub-optimal. On the contrary, for comparable thicknesses, the present method and layers obtained thereby provide a significant better adhesive function.

Size distribution

The surface comprising the present adhesive is inspected in detail. In an example on the surface island like structures can be observed, the islands having a diameter in the order of the size of the droplets in the present spray.

Also a concentration gradient is made visible.

Adhesives

Below are some examples of adhesives used. All percentages are wt . %, based on the total weight.

Formulation A Formulation B

adhesive adhesive

Chloroprene dispersion 80 - 100 %

Polyurethane dispersion 80 - 100% defoaming agent 0 - 0.001% 0 - 0.001% anti-oxidant 0 - 1%

water 0 - 10%

tackifier dispersion 0 - 20% 0 - 20%

Total 100% 100%

Formulation C Formulation D activator activator

Citric acid (monohydrate ) 7.5- 12.5%

Zinc sulfate (hexahydrate ) 15 - 30% water 87.5-92.5% 70-85%

Total 100% 100%

More detailed examples are given below:

Formulation A Formulation B adhesive adhesive

Chloroprene dispersion 89%

Polyurethane dispersion 89% defoaming agent 0.001% 0.001% anti-oxidant 1%

water 4.999%

tackifier dispersion 5% 10.999%

Total 100% 100%

Formulation C Formulation D activator activator

Citric acid (mono hydrate) 10%

Zinc sulfate (hexa hydrate) 25%

water 90% 75%

Total 100% 100%

Typically a chloroprene dispersion comprises about 55 wt . % solids . SUMMARY OF FIGURES

Fig. la,b are simplified representations of a multi- component adhesive being applied.

Fig. 2 shows possible forms of the inhomogeneously mixed droplet .

Fig. 3a, b show results of spraying with air.

Fig. 4 shows results of airless spraying.

DETAILED DESCRIPTION OF FIGURES

Fig. la is a simplified representation of a multi- component adhesive being applied onto a surface according to the method of the invention. A first- and a second- component of a multicomponent adhesive are sprayed simultaneously such that a first spray 1 comprising the first component and a second spray 2 comprising the second component come into con- tact at a focal point p above the surface 3. Upon meeting, inhomogeneously mixed droplets of the first- and second- component are formed.

Likewise in fig. lb a focal point of contact is below surface 3.

Fig. 2 shows possible forms of the inhomogeneously mixed droplet. The first component is shown in white, the second component in black.

Advantageously, the first- and second- components of the multicomponent adhesive can be applied simultaneously on a single surface without significant mixing occurring. The first- and second- component only become uniformly mixed, and therefore activated, upon bringing the surface comprising the layer of the multicomponent adhesive, and a further surface, to which it is to be bonded, together.

Fig. 3a, b show results of spraying with air. In fig.

3a a standard pressure of about 200 Pa (2.0 Bar) is used. In fig. 3b a lower pressure of about 75 Pa (0.75 Bar) is used. AS a result in fig. 3a a more homogeneous spray pattern is obtained, whereas in fig. 3b a more coarse spray pattern is obtained. In both cases overspray is present (not

shown/visible) .

Fig. 4 shows results of airless spraying. As a result a relatively coarse spray pattern is obtained.

It should be appreciated that for commercial appli- cation it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.