Coating processes – Spraying – Heated coating material
Reexamination Certificate
1999-07-16
2001-02-27
Beck, Shrive (Department: 1762)
Coating processes
Spraying
Heated coating material
C427S421100, C427S424000, C427S314000, C427S207100, C427S372200
Reexamination Certificate
active
06194035
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a process and a machine for surface sizing flexible parts having a porous surface, such as fabric parts, foam parts etc, with a water-based adhesive.
At the present time, flexible parts made of fabric and/or foam are sized either with adhesives of the hot melt type or with adhesives in a volatile organic solvent of which the composition may be easily chosen in order to prevent any penetration of the adhesive into the thickness of the parts.
Indeed, when it is desired to size a flexible part having a porous surface, it is important to prevent, or in any case to minimize, penetration of the adhesive into the thickness of the part in order to prevent, on the one hand, a boarding effect (i.e. a hardening of the superficial thickness of the surface affecting its flexibility qualities) and, on the other hand, a waste of adhesive (only the adhesive deposited on the surface providing subsequent adhesion). Such is, for example and in particular, the case when seat covers and seat cushions are sized for their relative assembly by gluing.
Now, the volatile organic solvents used (acetone, toluene, methanol etc) are toxic and harmful to the environment and human health.
In addition, adhesives are known without a volatile organic solvent such as so-called “water-based adhesives”. These water-based adhesives are adhesive compositions formed of a base of one or more synthetic or natural adhesives (polyurethanes, elastomers, thermoplastic polymers, acrylics, synthetic resins etc) dispersed in water. Nevertheless, these water-based adhesives have a much longer drying time and are difficult to transfer on account of their tendency to adhere to the walls of pipes, to precipitate and to form plugs. They are however fluid and tend inevitably to penetrate into the pores of the surfaces to which they are applied.
It should be noted that, in these water-based adhesives, unlike solvent-based adhesives, most of the dry solids which are proportionally much higher in quantity (of the order of 50%), are not dissolved but are in suspension, water only having the function of liquefying the composition and acting as a vehicle for the adhesive bases. As a consequence, the techniques used for sizing with solvent-based adhesives cannot be transposed to water-based adhesives.
So-called “two-component” water-based adhesives are also known, namely those associated with a second composition sprayed simultaneously and intended to accelerate the polymerization of the adhesive. However, this technique then requires the use of two costly application devices (two atomizing nozzles), which accordingly increases the risk of blockage as well as investment and running costs. This solution is therefore not compatible with continuous industrial production. Moreover, the said second composition based on ammonia or salts has a strong odor, is an irritant and attacks the skin and respiratory tracts.
In all cases, water inevitably penetrates into the pores, producing residual moisture which is harmful and undesirable in the part.
SUMMARY OF THE INVENTION
The object of the invention is therefore to overcome these drawbacks by providing a process and a machine enabling flexible parts with a porous surface, such as fabric parts, foam parts etc, to be surface sized with a water-based adhesive, by means of which the adhesive (and in particular the water which it contains) does not penetrate, or scarcely penetrates, the superficial thickness of the part, so that any boarding effect and any water retention are prevented, and this without the necessity for simultaneously applying a composition other than the adhesive itself.
The object of the invention is also to provide a process and a machine which can be used with various compositions and types of adhesive (with various adhesive bases, which can be reactivated or which are contact adhesives, etc) while preventing any precipitation, blocking or clogging phenomena in the equipment by the water-based adhesive.
The object of the invention is nevertheless also to provide a process and a machine more particularly and advantageously applicable to sizing with a water-based polyurethane and/or elastomer which can be heat-reactivated.
To this end, the invention concerns a process for surface sizing flexible parts having a porous surface such as fabric, foam etc with a water-based adhesive, wherein:
the surface to be sized of each part is preheated to a temperature above 50° C.,
the water-based adhesive is sprayed by atomization under low pressure onto the preheated surface.
Advantageously and according to the invention, the surface is preheated to the highest possible temperature that will not cause damage to the part, in particular by blowing hot air at a temperature of between 50° C. and 100° C.
According to the invention, as an adhesive agent for the water-based adhesive, it is possible to use in a general manner within the scope of the invention, one or more agents from among polyurethanes, synthetic or natural elastomers, acrylic thermoplastic polymers, resins etc, as long as the water-based adhesive is compatible with the material constituting the parts to be assembled and with the desired properties.
Advantageously and according to the invention, the water-based adhesive is warmed to a temperature of between 20° C. and 45° C. before spraying it by atomization. This temperature is also chosen in order to prevent any precipitation or blocking phenomena.
Similarly, advantageously and according to the invention, gas microbubbles are dispersed in the water-based adhesive, in particular by adding an effervescent agent compatible with the water-based adhesive, before it is sprayed by atomization.
The water-based adhesive is sprayed under low pressure, i.e. with a pressure just sufficient to enable it to be sprayed by atomization.
Advantageously and according to the invention, the water-based adhesive is sprayed by atomization under a relative pressure of between 0.2×10
5
Pa and 1×10
5
Pa.
Advantageously and according to the invention, the water-based adhesive is sprayed by atomization using contact with an air jet compressed to a low pressure, in particular between 0.2×10
5
Pa and 1×10
5
Pa (relative pressure)
Additionally, advantageously and according to the invention, the water-based adhesive is sprayed in a direction forming a non-zero angle &agr; with the direction normal to the surface. The angle &agr; is preferably between 30° and 60°, in particular of the order of 45°. In addition, advantageously and according to the invention, the water-based adhesive is sprayed with an atomizing nozzle which is held at a distance of between 5 cm and 50 cm, in particular of the order of 20 cm, from the surface.
Advantageously and according to the invention, the water-based adhesive is dried by radiant heating and/or by air extraction immediately after the water-based adhesive is sprayed.
The invention also concerns a machine for implementing a process according to the invention. The invention thus concerns a machine for surface sizing flexible parts with a porous surface such as fabric, foam etc, with a water-based adhesive, wherein it comprises:
at least one unit for spraying the water-based adhesive by atomization under low pressure,
and, upstream from each spray unit, at least one unit for preheating, in particular by hot air, the surface of the parts to a temperature above 50° C.
Advantageously and according to the invention, the spray unit includes means for spraying the adhesive by atomization under a relative pressure of between 0.2×10
5
Pa and 1×10
5
Pa, including in particular an atomizing gun connected to a pipe supplying adhesive under low pressure and to a pipe supplying air under low pressure.
In addition, advantageously and according to the invention, the machine includes means for holding a nozzle for spraying the adhesive directed at a non-zero angle &agr; with respect to the direction normal to the surface of the part. Advantageously and according to the invention, the angle &agr; is between 30°
Guilhem Christian
Guilhem Jacques
Barr Michael
Beck Shrive
Young & Thompson
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