WO1997010060A1

WO1997010060A1 - A method for flocking

Info

Publication number: WO1997010060A1
Application number: PCT/SE1996/001140
Authority: WO
Inventors: Lars Ruud; Raymond Meyer
Original assignee: Laray Ab
Priority date: 1995-09-13
Filing date: 1996-09-13
Publication date: 1997-03-20
Also published as: AU7004396A; SE9503195L; SE9503195D0

Abstract

Method for flocking of surfaces with fiber particles held to the surface by a solid layer, where the fibre particles are charged with static electricity during the application of the particles to the layer in a state of the same when the particles can be bound. The layer is obtained by giving pulver particles of a polymer a static charge, and sprayed onto the object which is to be flocked. Subsequently the particles are applied by spraying, after having been given a static charge of different potential or polarity in respect to that which the pulver particles have been given. Finally the object is heated, so that the polymer melts and forms said layer, and solidifies after cooling, thereby keeping the fiber particles in place.

Description

TITLE: nethod for flocking

TECHNICAL FIELD: The present invention relates to a method for flocking of surfaces with fiber particles.

PRIOR ART:

Flocking as a method for coating surfaces is well known, see for example US, A, 4 246 294. The method involves coating the surface which is to be flocked with a layer of glue. While the glue is still open and adhesive it is sprayed with fiber particles with a typical length of a tenth of a millimeter up to a few millimeters. During the spraying the particles are electrostatically charged. The charging field is concentrated to the ends of the fiber particles, which causes one end to stick to the glue, while the other end extends straight out from the glue-coated surface. A velvet-like surface is thus obtained. Using this method, packaging, decorating articles etc. can be given such a surface in a considerably easier and less costly way than through wrappng with a textile material. Apart from this decorative effect, which can be obtained through flocking, certain practical advantages can be can be obtained, such as a certain degree of heat isolation and shock-proofing among others.

During the process, the glueing is the most problematic part. In a rational, industrial process, the open period of the glue during application and spraying of the fiber must be sufficiently long to carry out these steps of the process, while it at the same time is important for the glue to assume its hardened form as quickly as possible, so that the product can be handled without the risk of damaging the coating, for example by pressing the pile which is formed by the fibre, into glue which hasn't yet hardened. Furthermore, glueing is always a complex process, with difficulties in keeping tools and machines free from hardened glue. From an environmental point of view most glues are also unsuitable, since solvent evaporates during use. Finally, it can be added that it is difficult to apply a smooth layer of glue on uneven surfaces, which will result in an increase in the amount of material necessary, and which can also jeopardize the result.

SUMMARY OF THE INVENTION:

All of these disadvantages are eliminated by the invention. This is achieved by a process where the earlier used so called wet glue is replaced by a pulverous meltable polymer glue. The pulver is activated to melt efter it has been applied, and only after the application of the fibre particles as well. A completely dry process is thus used from the beginning, and there are no evaporating, volatile substances involved. This makes the process extremely rational.

The glue pulver can be applied in an absolutely even layer regardless of the shape of the processed surface.

The process will be described in more detail below, which will show the advantages of the process clearly.

PREFERED EMBODIMENT:

The process according to the invention is, in a prefered embodiment, carried out in the following steps:

1. Preparation of the pulverous glue, the main component of which should be a meltable polymer. It should be chosen among those which in solid form at room temperature can be manufactured as a pulver, which when heated forms an adhesive layer, which when cooled solidifies. The polymer can be a thermoplast such as polyamide or a thermoset plastic such as polyester. The melting temperature should not be too high, preferably below 250° C, and it is possible to go below 100° C.

Certain additives can be added, such as agents for increasing the levelling during heating. Colour pigments can also be added, if a coloured coating below the flocking is desired. The size of the pulver grains are preferably in the area of 10 μm.

2. Preparation of spraying equipment for the pulver. This should be arranged to spray the pulver using an air flow, and to, before the spraying charge the pulver with static electricity. This can be done in two ways, either by inserting into the spraying equipment one or more electrodes connected to a voltage source with a voltage in the range of 40 000 - 60 000 V, or by arranging flow channels in the spraying equipment in which the pulver is carried by the air flow, while in friction with the walls of the channel. These walls are made of a material which charges the pulver by friction. One such material can be tetrafluorethyelene. The spraying equipment can thus discharge a pulverous cloud carried by an air flow, in which the grains have a preferably positive charge with a high potential. Design of the equipment for charging by friction is in many cases to be prefered.

3. Preparation of the fibre particles. These can have a length from approximately a tenth of a millimeter, up to several millimeters, up to the order of 10 mm. The thickness can be one, or a few tenths of a millimeter. The material prefered is artificial fibre, for example amidfibre (Nylon ®) . The material must not melt or be significantly deformed at the temperature necessary for the glue used in the process. The material must be of a kind which is suitable for static charging.

4. Preparation of the spraying equipment for the fibre particles. These are also sprayed using an air flow, and are to be charged. Charging using a high voltage electrode is usually to be prefered, although friction charging cannot be excluded. The particles must be given a difference in potential relative to the pulver. This can be obtained by giving the fibres a charge which has a polarity opposite to that of the pulver, thus in this case a negative charge. A difference in potential can also be obtained by charging the pulver and the fibre with different strengths in potential. The pulver which is applied first must be given the higher potential. It is desirable that there is no external field extending from the electrode in the spraying equipment. It is therefore desirable to shield the electrode, or to divert external fields by using grounded elements.

5. Preparation of the object which is to be flocked. Its surface must be conducting. If the object is made of metal, this is already the case. Objects of other materials, such as wood, paper or cardboard can be given a conducting surface by varnishing them with an electrically conducting varnish, or by exposing them to moisture which condenses against the surface. The surface should be grounded, so that a difference in potential is created with respect to the charged pulver particles, respectively to the fibre particles. In this way the particles are attracted by the object. An increased attraction can be obtained by exposing the object to an electrostatic field, opposite to that of the particles. If the glue pulver is charged positively the field should thus be negative. In case of different polarity in the pulver and the fibre, the strength of the charge should be adjusted, so that after the pulver particles have been applied, there is no significant negative remaining field, which might influence the attraction of the fibre particles. In case of equal polarity the pulver particles must be charged to a higher potential than the fibre particles, as their application after the pulver might otherwise influence the adhesion of the pulver.

6. Exposing the object which has been arranged in the described way to a flow of pulver particles which have been prepared as described in (1), and of spraying in the way which has been described in (4 and 5). In this way the object receives in surfaces which are exposed to the flow of particles an even coating of the pulver. It should be noted that since the particles relative to each other are similarly charged they will spread from each other in the air flow, and form a cloud, which due to the difference in potential between pulver particles and object will adhere in an even layer to the surfaces of the object, and which also has the ability to spread around the object, so that all surfaces which are not shielded will be coated.

7. In immediate proximity to the coating with pulver, the fibre particles are now applied (see 3) in the way which has been explained in (4 and 5) above. The field from these charged fibre particles extends from their ends. Due to the reverse polarity relative to the pulver, and due to the difference in potential with respect to the object, the fibre particles will be arranged with one end towards the surface of the object, down in the layer of pulver, while the other end extends outrwards, so that the elongated fibre particles will extend straight out from the surface and form a pile. 8. Immediately after the spraying of the fibre particles, the object is placed in a heating zone, and heated, so that the surface reaches a temperature of preferably 200-250°. This causes the pulver particles to melt and form a continous layer, which adheres to the surface of the object, and holds the fiber particles at their one end. The heating will cause a hardening of the polymer which the pulver is made of, if the pulver consists of a thermoset plastic. If the pulver is made of a thermoplast, this will assume a solid form by cooling after the heating.

The main principle of the process is thus to apply the glue as a polymer pulver with a certain electrostatic charge, after which the fibre particles ar charged with a different potential, and are applied to the pulver covered surface, subsequent to which the pulver through heating is transfered to a rigid layer which adheres to the surface of the object and keeps the fibre particles in place. It is important in order for the process to work that the electrostatic charge is adjusted in a correct manner. Said preferably used polarity with positive charge for the pulver and negative charge for the fibre particles is the suitable polarity for certain materials. As an exception the reverse charge might however be necessary. As has been mentioned, it is possible to use same polarity with differing potentials. It has been mentioned that the object must have an electrically conducting surface, which can be obtained through the application of a conducting layer, if the material of the object is not conducting. Within the scope of the process it is however possible to charge even articles without a conducting surface in a strong electrostatic field immmediately before the pulver is applied.

It is important that the process is carried out relatively quickly within the steps (6) and (7). The charge given the pulver must be kept at a certain level, and since it has a tendency to dissipate to the ambient air, the spraying of the pulver particles must follow shortly after the charged pulver has been applied. The heating must also be done within a relatively short time, while the pulver and the flocking particles are held in place by their charge.

Claims

PATENT CLAIMS:

1. A method for flocking of surfaces with fiber particles adhered to the surface by a solid layer, where the fibre particles are charged with static electricity during the application of the particles to the layer in a state of the same when the particles can be bound, c h a r a c t e r i z e d by the steps of:

1. Preparation of a glue in the form of pulver particles of a polymer such as a thermoplast or a thermoset plastic.

2. Preparation of a spraying equipment for the pulver, which is arranged to spray the pulver using an air flow, and before the spraying charge t h e pulver particles with static electricity.

3. Preparation of the fibre particles of a material which is suitable for static charging.

4. Preparation of spraying equipment for the fibre particles, which is arranged to spray the particles and to charge them with static electricity with a difference in potential relative to that which the pulver particles have been charged with.

5. Preparation of the object to be flocked, in sih a manner that its surface is conducting and in contact with ground, alternately, a non-conducting surface, exposing the object to a high voltage electrical field of a polarity which is opposite to that which the pulver particles have been charged with.

6. Exposing the, in the described manner prepared object, to a flow of pulver particles which have been prepared in the manner described in (1) and sprayed in the manner described in (2 and 5) .

7. In connection to the coating with pulver applying the fibre particles in the manner described in (4 and 5).

8. Immediately after the spraying with fibre particles, the object is placed in a heating zone and heated so that the surface reaches a temperature of preferably 100-250°C, so that the pulver particles melt and form a continous layer, which adheres to the surface of the object and holds the fibre particles at their one end.

9. Letting the object reach a lower temperature, e that the layer formed by the melting of the pulver particles becomes solid, thus holding the fibre particles in place.

2. Method for flocking according to patent claim 1, c h a r a c t e r i z e d in that said difference in potential is obtained by giving the fibre particles a static charge with a polarity opposity to that with which the pulver particles have been charged.

3. Method for flocking according to patent claim 2, c h a r a c t e r i z e d in that the pulver is given a positive elctrical charge, and the fibre particles a negative static charge, and are applied within a short time span after the charged pulver has been applied and still maintains most of its electric charge. 4. Method for flocking according to patent claim 1, c h a r a c t e r i z e d in that said difference in potential is obtained by charging the pulver particles to a potential higher than that of the fibre particles.

5. Method for flocking according to any of claims 1-4, c h a r a c t e r i z e d in that the polymer in the pulver particles at least mainly consists of a thermoset plastic, and in that said heating is carried out in such a manner that the plastic sets.