WO2016050693A1

WO2016050693A1 - De laval nozzle to apply an adhesive to the surface of a work piece

Info

Publication number: WO2016050693A1
Application number: PCT/EP2015/072266
Authority: WO
Inventors: Thomas DEVANNES; Christian Belanger; Francois Crouzet; Xabier MORRAL
Original assignee: Zephyros Inc.
Priority date: 2014-10-03
Filing date: 2015-09-28
Publication date: 2016-04-07
Also published as: WO2016050697A2; GB201417502D0; WO2016050691A1; WO2016050697A3

Abstract

The present invention relates to a nozzle for the deposition of an adhesive material onto a surface of a work piece.

Description

De Laval nozzle to apply an adhesive to the surface of a work piece

Adhesives, particularly heat activated adhesive materials are, for example, used in the automotive industry to bond parts together. It is proposed in United States Patent Application Publication 2014/0027039 that adhesives may be deposited on surfaces such as metal surfaces by spraying a powder of the adhesive material on the surface of a work piece with a spray-nozzle. However, spray nozzles have disadvantages like, for example, overspray.

It is objective of the present invention to provide an alternative apparatus to apply an adhesive powder coating to a work piece.

The problem is attained with an apparatus for applying an adhesive powder coating to a surface of a work piece, wherein the apparatus comprises a De Laval-nozzle.

The present invention suggests a De laval-nozzle for the provision of an adhesive layer on the surface of a work piece, for example a metal substrate. A gas flow is supplied to the inlet of the De Laval-nozzle, flows through the De Laval-nozzle and leaves it at its exit. A powdered adhesive is also supplied to the De Laval-nozzle, which mixes with the gas stream and exits the De Laval-nozzle together with the gas flow. The gas/particle mixture is directed to the surface of a work piece, where the powdered adhesive adheres to the surface of the work piece

The De Laval-nozzle comprises an entry region for a gas flow, an adhesive powder entry and an exit region for the gas/powder mixture. Furthermore, the De Laval-nozzle comprises a converging part and a diverging part and a nozzle throat in between. A detailed description of the De Laval-nozzle can be, for example found in wikipedia.org/wiki/De_Laval_nozzle. This publication is herewith incorporated by reference and hence part of the disclosure of the present patent application.

The gas flow is used to propel the powdered adhesive from the exit region onto the surface of the work piece. Preferably, the gas used is inert to the powder material. For many applications air and/or nitrogen is suitable. Typical gas pressures are in the range of 0,3 to 3,0 MPa at the inlet of the De Laval-nozzle. Preferably, the De Laval-nozzle forms a supersonic gas/powder flow in the diverging part of the nozzle. Preferably, the De Laval-nozzle has an overall length of 100-200 mm and the diverging part is preferably 70-90 % of the overall length.

According to a preferred embodiment of the present invention, the diameter of the entry region is preferably 8-10 mm and the diameter of the exit region is preferably 40-70 % of the diameter of the entry region.

Preferably, the diameter of the nozzle throat is 2-3 mm. The nozzle throat is the passage between the converging- and the diverging part of the De Laval-nozzle.

Preferably, the distance between the throat and the adhesive powder entry is 1 -10 mm. The adhesive powder entry can be upstream and/or downstream from the throat relative to the flow-direction of the gas.

Preferably, the length of the throat is between 0 and 10 mm, preferably 0 - 3 mm.

According to a preferred embodiment, the adhesive powder entry is provided at an angle of 1 - 90°, preferably 90°, relative to the center-axis of the nozzle or in line with the axis of the nozzle. A preferred range for the angle is 10 -80°, even more preferred 20 - 70°.

The De Laval nozzle can be made from any suitable material. However, it is preferably made from steel, preferably hardened steel, and/or tungsten carbide alloy and/or ceramic material..

Preferably, the De Laval nozzle and/or the work piece is/are connected to a movement device, so that the De Laval-nozzle and the substrate may move relative to each other.

Preferably, the movement can be programmed to deliver the adhesive coating precisely in any desired pattern on the surface of the substrate.

The exit of the De Laval-nozzle is preferably located close to the surface of the work piece, more preferably at a distance of from 20 to 60 mm from the surface of the substrate.

The apparatus shall be set up so that the particles of the adhesive powder are at the temperature at which they will adhere to the surface of the substrate when they reach and/or when they have reached the surface of the work piece. Deformation of the particle due to impact of the particles on the surface of the work piece will increase their temperature. Preferably, the temperature of the particles is 25 - 80 °C at the entry and/or the exit of the De Laval-nozzle. A more preferred upper limit is 60 °C and an even more preferred upper limit is 40 °C. A more preferred lower limit is 30 °C and an even more preferred lower limit is 35 °C.

Preferably, the De Laval-nozzle comprises multiple adhesive powder entries. Through each entry, a component or a mixture of at least two components of the powdered adhesive can be supplied. Through the entries powder can be supplied simultaneously and/or in sequence.

Preferably, the apparatus comprises a mixing device for at least two components of the adhesive powder. The mixing device is preferably upstream from the De Laval-nozzle.

According to a preferred embodiment of the present invention, the apparatus comprises a heating/cooling-device for the gas flow. A preferred gas temperature of the gas flow is in the range of 200°C to 600°C prior to the entry of the De Laval-nozzle. Preferred temperature ranges are 200 - 500 °C or 200 - 400 °C or 200 - 300 °C or 300 - 600 °C or 400 - 600 °C or 500 - 600 °C.

Preferably, the apparatus comprises a metering device for the adhesive powder. Preferably, the metering is adjusted relative to the gas flow. According to a preferred embodiment, the gas flow through the De Laval-nozzle is measured and the addition of the adhesive powder to the gas flow is adjusted accordingly.

Preferably, the apparatus comprises a control device for the gas flow and/or the gas pressure.

Preferably, the apparatus comprises a sensor for the quality of the coating. Preferably the parameters of the nozzle are controlled according to the signal of the sensor. The sensor can be, for example, a camera, a radiation type sensor, for example a X-ray sensor or an infrared-sensor. Potential quality parameters are the density of the coating, the dimensions of the coating, the position of the coating on the work piece, the stickiness of the adhesive layer.

Preferably, the apparatus comprises means to temper the work piece. According to a preferred embodiment, the work piece is heated, preferably uniformly heated. A preferred temperature range for the work piece is 40 - 80 °C.

The powered adhesive preferably has a particle size in the range of 50 to 300 microns preferably 100 to 200 microns. The volume median diameter Dv(50) of the particles is preferably in a range of 1 10 - 150 microns. The particle size is for example measured with a Malverne Mastersizer 3000 or 3000 E. The powders are preferably prepared by comminuting preferably by grinding pellets of the appropriate adhesive formulation preferably under a cold and/or inert atmosphere such as a stream of liquid nitrogen or gaseous nitrogen. Once prepared the powders are preferably stored and transported in a sealed container. In a preferred embodiment the powder are prepared at a temperature no higher than -20°C.

The adhesive applied by the De Laval-nozzle to the surface of the work piece is preferably a heat activatable adhesive and the temperature at which the adhesive is activated will depend upon the nature of the adhesive and the nature of the activation and when the activation is to take place. For example, it may be desirable that the adhesive adheres to the surface of the substrate but remains at a temperature at which it remains activatable by subsequent heating (such as by thermal cross linking and/or thermal expansion). Prior to its activation, the adhesive powder preferably only comprises a stickiness that is sufficient to maintain the adhesive power on the work piece.

In order to form a desirable adhesive that exists first in powder form, can then fuse to form a film layer, and later be activated to cure, the adhesive (e.g., the precursor layer) may include an epoxy based material. The epoxy may be any dimeric, oligomeric or polymeric epoxy materials containing at least one epoxy functional group. Moreover, the term epoxy can be used to denote one epoxy or a combination of multiple epoxies. The polymer-based materials may be epoxy-containing materials having one or more oxirane rings polymerizable by a ring opening reaction. A precursor layer may include up to 80% or more of an epoxy. The precursor layer may include between 2% and 70% by weight epoxy, between 4% and 30% by weight epoxy, or even between 7% and 18% by weight epoxy. The adhesive may be substantially free of an epoxy material (other than any epoxy supplied in the form of an epoxy/elastomer adduct). The epoxy may be aliphatic, cycloaliphatic, aromatic or the like. The epoxy may be supplied as a solid (e.g., as pellets, chunks, pieces or the like) or a liquid. The epoxy may include an ethylene copolymer or terpolymer that may possess an alpha- olefin. Preferably, an epoxy is added to the precursor layer to increase the adhesion, flow properties or both of the precursor layer. The epoxy may include a phenolic resin, which may be a novolac type (e.g., an epoxy phenol novolac, an epoxy cresol novolac, combinations thereof, or the like) or other type resin. Other preferred epoxy containing material includes a bisphenol-A epichlorohydrin ether polymer, or a bisphenol-A epoxy resin which may be modified with butadiene or another polymeric additive. Moreover, various mixtures of several different epoxies may be employed as well. Examples of suitable epoxies are sold under the trade name DER^® (e.g., DER 331 , DER 661 , DER 662), commercially available from the Dow Chemical Company, Midland, Michigan.

The epoxy may be combined with a thermoplastic component, which may include styrenics, acrylonitriles, acrylates, acetates, polyamides, polyethylenes, phenoxy resins or the like. The thermoplastic component may be present in an amount of at least 5% by weight of the precursor layer. The thermoplastic component may be present in an amount of at least 20% by weight of the precursor layer. The thermoplastic component may be present in an amount of at least 60% by weight of the precursor layer. The thermoplastic component may be present in an amount of less than 80% by weight of the precursor layer. The thermoplastic component may be present in an amount of less than 30% by weight of the precursor layer.

While it is contemplated that various polymer/elastomer adducts may be employed according to the present invention, one preferred adduct is an epoxy/elastomer adduct. The precursor layer may thus include an elastomer-containing adduct. The epoxy/elastomer hybrid or adduct may be included in an amount of up to 80% by weight of the precursor layer. The elastomer-containing adduct may be approximately at least 5%, more typically at least 7% and even more typically at least 10% by weight of the precursor layer. The adduct may be up to 60% or more, but more preferably is 10% to 30% by weight of the precursor layer. Of course, the elastomer-containing adduct may be a combination of two or more particular adducts and the adducts may be solid adducts or liquid adducts at a temperature of 23°C or may also be combinations thereof. The adduct may be composed of substantially entirely (i.e., at least 70%, 80%, 90% or more) of one or more adducts that are solid at a temperature of 23°C.

The adduct itself generally includes 1 :8 to 3:1 parts of epoxy or other polymer to elastomer, and more preferably 1 :5 to 1 :6 parts of epoxy to elastomer. More typically, the adduct includes at least 5%, more typically at least 12% and even more typically at least 18% elastomer and also typically includes not greater than 50%, even more typically no greater than 40% and still more typically no greater than 35% elastomer, although higher or lower percentages are possible. The elastomer compound may be a thermosetting elastomer. Exemplary elastomers include, without limitation, natural rubber, styrene-butadiene rubber, polyisoprene, polyisobutylene, polybutadiene, isoprene-butadiene copolymer, neoprene, nitrile rubber (e.g., a butyl nitrile, such as carboxy-terminated butyl nitrile), butyl rubber, polysulfide elastomer, acrylic elastomer, acrylonitrile elastomers, silicone rubber, polysiloxanes, polyester rubber, diisocyanate-linked condensation elastomer, EPDM (ethylene-propylene diene rubbers), chlorosulphonated polyethylene, fluorinated hydrocarbons and the like. An example of a preferred epoxy/elastomer adduct is sold under the trade name HYPOX commercially available from CVC Chemical.

The inventive apparatus may be used to provide structural adhesives. The apparatus is preferably used in the automotive industry, aerospace industry, building industry and/or furniture industry.

The present invention can be used to deposit powder of an adhesive on larger surface areas of the work piece than has hitherto been possible by extrusion deposition and by pumpable liquid adhesives or by other spray-technologies. It has been found useful in the provision of substantially uniform films of thickness ranging from 50 to 2000 μηη, preferably, 300 - 600 μηη on three dimensional structures including those of complex shape. The thickness and location of the adhesive film on the work piece can be varied by the use of masks and/or by a certain movement of the De Laval-nozzle. The adhesive may be applied without contact between the De Laval-nozzle and the surface of the work piece.

During and/or after impact on the work piece, each particle deforms and forms a layer on the work piece. Preferably, the particle melts at least partially on the surface of the work piece.

The invention is illustrated by the accompanying Figures.

Fig. 1 shows the De Laval-nozzle.

Fig. 2 shows the use of the De Laval-nozzle.

Figure 1 shows the inventive De Laval-nozzle 8 for the application of an adhesive powder to the surface of a work piece. The De Laval-nozzle 8 has a gas entry region 2 through which a gas flow is forced into the De Laval-nozzle 8. The gas passes the De Laval-nozzle 8 and is mixed with the adhesive powder, which is provided through at least one adhesive powder entry inlet 7. This inlet can be either collinear with the center axis of the De Laval-nozzle 8 and/or provided at an angle a, here 90°. The gas/powder mixture 6 leaves the De Laval- nozzle 8 at an exit region 5 and hits a work piece (not depicted) where the powder forms an adhesive film. The De Laval-nozzle 8 comprises a converging part 3 and a diverging part 4. In between is the nozzle throat 9. The De Laval-nozzle 8 has an overall length of Li which is preferably 100-200 mm and the length L2 of the diverging part is preferably 70-90 % of the overall length Li. The diameter Di of the entry region 2 is preferably 8-10 mm and the diameter D3 of the exit region 5 is preferably 40-70 % of the diameter of the entry region 2.The diameter D2 of the nozzle throat is preferably 2-3 mm. The distance L₄ between the throat and the adhesive powder entry 7 is preferably 1 -10 mm. The length of the throat L₅ is preferably between 0 and 10 mm, more preferably, between 0 and 3 mm.

Figure 2 shows the utilization of the De Laval-nozzle 8 to apply an adhesive coating (1 1 ) to a work piece 12. A gas flow 1 is provided at the entry of the De Laval-nozzle 8. The temperature of the gas may be adjusted by a heating/cooling-device 10. The gas flow and/or its pressure can preferably also be adjusted. In the De Laval-nozzle, the gas flow 1 is mixed with a adhesive powder material 7. This adhesive powder material can be a mixture of two or more components 13, 14. The components 13, 14 can be fed into the De Laval-nozzle directly through individual inlets and/or, as depicted, can be premixed in a mixer. Preferably, a metering-device is provided, which doses the adhesive powder material into the gas flow. The metering device may be controlled depending on the magnitude of the gas flow and/or based on the desired local thickness of the adhesive layer on the work piece and/or based on the magnitude of the relative movement between the De Laval-nozzle and the work-piece and/or based on the signal of a sensor, which determines at least one property of the adhesive layer on the work piece. The gas/powder-mixture, leaving the De Laval-nozzle can be additionally tempered. This can be done with a torch or the like which is preferably also controllable. The gas/powder stream hits the work piece and the particles are deposited on the surface of the work piece where they form a layer. The work piece can be heated or cooled as needed to assure that the particles stick to the surface of the work piece. The distance between the outlet of the De Laval-nozzle and the surface work piece is preferably 20 - 60 mm. This relatively small distance and the relatively small diameter of the exit of the De Laval-nozzle allows a very exact deposition of the adhesive powder material on the surface of the work piece. Certain pattern of the adhesive layer can be established and the local thickness and/or the local composition of the adhesive layer can influenced. Preferably, there is a relative movement between the De Laval-nozzle and the work piece.

Example 1 :

An adhesive formulation comprising the following ingredients was comminuted to an average particle size of about 100 μιτι (as measure used a Beckman Coulter LS 13320 laser scattering particle size analyzer):

Lotadei^ AX-8900¹ 15.50 wt.-%

Evatane^® 2805²/Escorene^® UL 7760³ 16.16 wt.-%

Polymer backbone

Elvax^® 420⁴ 10.00 wt.-%

Norsolene^® S105⁵ 12.20 wt.-% Wax and oil 6.7 wt.-%

Peroxide curing agent 1 .4 wt.-%

Curing agent 2.50 wt.-%

Blowing agent 1 .60 wt.-%

Pigment 0.01 wt.-%

Thixotropic agent 1 .00 wt.-%

Calcium carbonate filler 32.93 wt.-%

¹ Lotader^® AX-8900 is a random terpolymer of ethylene, acrylic ester and glycidyl methacrylate;

² Evatane^® 2805 is a random copolymer of Ethylene and Vinyl Acetate

³ Escorene^® UL 7760 is a high viscosity, 26.7% VA copolyme

⁴ Elvax^® 420 0 is an ethylene-vinyl acetate copolymer

⁵ Norsolene^® S105 is a light colored, low odor aromatic resin

The powder was sprayed onto a steel panel employing an apparatus as illustrated in Figure 2. Nitrogen was used as the propelling gas and the pressure in the gas chamber was 0,344 MPa and the temperature of the gas prior to the venturi was 580 °C. The tube (4) for delivery of the powder was at a temperature in the range 80-90 °C. The speed of ejection of the mixture of the powdered heat activatable adhesive and the gas from the nozzle was 300 mm/sec and the distance from the nozzle to the surface of the substrate was 30 mm. The substrate was a steel sheet held at room temperature and the nozzle was moved relative to the substrate to provide a coating of the powdered heat activatable adhesive over the desired bonding area.

A uniform coating 0.25 mm thick was provided on the desired bonding area and it could be subsequently activated to produce an automotive adhesive.

Example 2:

A series of powdered heat activatable adhesives was prepared only differing in the relative content of two different types of epoxy based material contained therein. The overall content of epoxy based material was kept constant (26 wt.-%), like all other ingredients, their content and the other overall properties of the powder material:

Sample Sample Sample

1 2 3

Solid epoxy resin: - type 1 (EEW 450-530 g/eq) - - -

- type II (EEW 590-630 g/eq) 18.00 - -

- type III (EEW 730-820 g/eq) - 18.00 -

- type IV (EEW 860-930 g/eq) - - 18.00

Liquid epoxy resin (EEW 200 g/eq) 8.00 8.00 8.00

MBS based core shell impact modifier 13.40 13.40 13.40

Polyvinylbutyral 4.85 4.85 4.85

Phenoxy resin derived from Bisphenol A 16.95 16.95 16.95

Epoxy terminated CTBN adduct 20.00 20.00 20.00

Micronized Polyamide 6/12 (particle size 20 8.00 8.00 8.00

Talc 1 .01 1 .01 1 .01

Calcium oxide 5.00 5.00 5.00

Thixotropic agent (Organo clay) 0.76 0.76 0.76

Pigment 0.05 0.05 0.05

Disubstituted urea 0.35 0.35 0.35

Dicyandiamide 3.00 3.00 3.00

Chemical blowing agent ADCA 0.63 0.63 0.63

TOTAL 100.00 100.00 100.00

List of reference signs:

1 gas flow

2 nozzle entry region

3 converging part

4 diverging part

5 nozzle exit region

6 gas/powder mixture-flow

7 adhesive powder entry inlet

8 laval-nozzle

9 nozzle throat

Di diameter of the entry region

D₂ diameter of the nozzle throat

D₃ diameter of the exit-region

Li overall length of the nozzle

L₂ length of the diverging part

Ls length of the converging part

L₄ distance (L₄) between the throat and the adhesive powder entry (7)

L₅ axial length of the throat

a angel of the adhesive powder entry 7 relative to the axis of the nozzle

Claims

Claims:

1 . Apparatus for applying an adhesive powder coating to a surface of a work piece, characterized in, that the apparatus comprises a De Laval-nozzle (8).

2. Apparatus according to claim 1 , characterized in, that the De Laval-nozzle (8)

comprises an entry region (5) for a gas flow (1 ), an adhesive powder entry (7) and an exit region (5) for the gas/powder mixture (6).

3. Apparatus according to claim 1 or 2, characterized in, that the De Laval-nozzle (8) comprises a converging part (3) and a diverging part (4) and a nozzle throat (9).

4. Apparatus according claim 3, characterized in that, the De Laval-nozzle (8) has an overall length (Li) of 100-200 mm and that the diverging part is preferably 70-90 % of the overall length (Li).

5. Apparatus according to one of claims 2 -4, characterized in, that the diameter (D1 ) of the entry region (2) is preferably 8-10 mm and the diameter (D3) of the exit region (5) is preferably 40-70 % of the diameter of the entry region (2).

6. Apparatus according to one of claims 3 - 5, characterized in, that the diameter (D2) of the nozzle throat is 2-3 mm.

7. Apparatus according to one of claims 2 -6, characterized in, that the distance (L₄) between the throat and the adhesive powder entry (7) is 1 -10 mm.

8. Apparatus according to one of claims 2 - 7, characterized in, that the adhesive

powder entry (7) is provided at an angle (a) of 1 - 90° relative to the center-axis of the nozzle (8) or in line with the axis of the nozzle

9. Apparatus according to one of the preceding claims, characterized in, that the De Laval nozzle is made from full core hardened steel or tungsten carbide alloy or a ceramic material.

10. Apparatus according to one of the preceding claims, characterized in, that the nozzle and/or the work piece is connected to a movement device. 10 Apparatus according to one of the preceding claims, characterized in, that it comprises multiple adhesive powder entries (7).

1 1 . Apparatus according to one of the preceding claims, characterized in, that it comprises a mixing device for at least two components of the adhesive powder.

12. Apparatus according to one of the preceding claims, characterized in, that it comprises a heating/cooling-device for the gas flow.

13. Apparatus according to one of the preceding claims, characterized in, that it comprises a metering device for the adhesive powder.

14. Apparatus according to one of the preceding claims, characterized in, that it comprises control devices for the gas flow and pressure.

15. Apparatus according to one of the preceding claims, characterized in, that it comprises a sensor for the quality of the coating.

16. Apparatus according to one of the preceding claims, characterized in, that it comprises means to temper the work piece.