NL2010773C2 - A method of applying adhesive. - Google Patents

Abstract

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. 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.

Description

A method of applying adhesive 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.

EP-A2-1396288 relates to achieving automated spray nozzle cleaning and is considered background prior art.

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 usual 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 interchanged. 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 relates 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 directed 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 area 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 (combined) droplet. If larger areas would be considered a multitude 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 pm. 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 smaller than 250 pm. 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 pm (about 2.5 gr/m2-250 gr/m2) , prefera- bly with a thickness of 100-1000 pm (about 10 gr/m2-100 gr/m2) , such as with a thickness of 250-500 pm (about 25 gr/m2-50 gr/m2) . 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.

In an example, the first- and second- components are 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-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 systems 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 (copolymer) dispersion, ethylene-vinylacetate dispersion, natural rubber dispersion, styrene-butadiene-styrene copolymer dispersion, nitrile-butadiene rubber, polyvinyl butyral dispersion, andstyrene-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 multivalent metal such as zinc, aluminium or calcium; or an acid solution, such as selected from citric acid, formic acid, acetic 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 adhesive 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 therebetween .

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.

An amount of adhesive used (one sided) is 200 gram/m2. 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 (final) 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 component, 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.

More detailed examples are given below:

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 contact 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.

Claims (11)

A method of applying a layer of a multicomponent adhesive to a surface, the method comprising spraying a first and a second component of the multicomponent adhesive simultaneously without air such that a first spray comprising the first component and a second spray comprising the second component coming into contact at or above the surface. The method of claim 1, wherein the first and second mists are directed to meet in a focal point, focal line, or focal area. The method according to claim 2, wherein the focal point, focal area or focal line is from -2.5 cm (bottom) to 2.5 above the surface, preferably 0.1 cm to 2.0 cm from the surface, more preferably from 0.25 cm to 1.5 cm from the surface. Method according to one or more of the preceding claims, wherein the first and second components are sprayed at a pressure of 150-2000 Pa (1.5-20 Bar), preferably of 200-1000 Pa (2-10 Bar), more preferably from 400-600 Pa (4-6 Bar). The method of any one of the preceding claims, wherein the viscosity of the first and second components is in the range of 0.2 mPa.s to 10 Pa.s at 25 ° C. Method according to one or more of the preceding claims, wherein the first and second components are sprayed through a nozzle with an opening size in the range of 0.05 mm to 5 mm, preferably 0.3 mm to 0.6 mm. A method according to any one of the preceding claims, wherein pressure spraying is provided by one or more selected from: displacement pumps, such as double diaphragm pumps or piston pumps; pressure systems such as pressure tanks; and, gravity feed systems. A method according to any one of the preceding claims, wherein a first and second current are provided through a first and second slit, such as a rectangular slit, a circular slit, a polygonal slit, an annular aperture, and a polygonal aperture. A method according to any one of the preceding claims, wherein the first component is selected from a polychlorinated pre-dispersion, polyurethane dispersion, poly-acrylate dispersion, vinyl acetate-ethylene dispersion, ethylene-vinyl acetate dispersion, natural rubber dispersion, styrene-butadiene-styrene copolymer dispersion and styrene-butadiene. redispersion, and wherein the second component is a coagulant, for example selected from a salt of a polyvalent metal, such as zinc, aluminum or calcium; or an acid solution such as selected from citric acid, formic acid, acetic acid, lactic acid and mineral acid with a pH of less than 5, preferably below 4.5, most preferably less than 4. Use of a method according to one or more of the preceding claims in flexible foam bonding such as in foam confection, mattress and furniture production. An adhesive layer, such as is obtainable by a method according to any of claims 1-9, wherein the layer comprises first and second components of a multi-component homogeneously mixed adhesive, preferably such that regions of pure first and pure second component are present. with a concentration gradient from pure first component to pure second component between them.