WO2016050691A1

WO2016050691A1 - Method to apply an adhesive coating to the surface of a work piece with a de laval-nozzle

Info

Publication number: WO2016050691A1
Application number: PCT/EP2015/072264
Authority: WO
Inventors: Christian Belanger; Morgan CHENE
Original assignee: Zephyros Inc.
Priority date: 2014-10-03
Filing date: 2015-09-28
Publication date: 2016-04-07
Also published as: GB201417502D0; WO2016050693A1; WO2016050697A2; WO2016050697A3

Abstract

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

Description

Method to apply an adhesive coating to the surface of a work piece with a De Laval- nozzle

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 method to apply an adhesive powder coating to a work piece.

The problem is attained with method to apply an adhesive coating to a work piece wherein a gas flow is mixed with an adhesive powder material and sprayed on the surface of a work piece by an acceleration device to form the adhesive coating, wherein the adhesive powder material is accelerated with to 50 - 1000 m/s.

The present invention suggests a method utilizing an acceleration device for the provision of an adhesive layer on the surface of a work piece, for example a metal substrate. The adhesive powder material is accelerated to 50 -1000 m/s. Due to this acceleration, the adhesive powder material has enough kinetic energy to deform and/or melt at least partially, when it hits the surface of the work piece and hence forming a preferably continuous layer on the work piece. During their time of flight and even after hitting the work piece, the temperature of the adhesive powder material is kept so low, that the adhesive is not activated, i.e. does not comprise sticky-properties which are high enough to glue two parts together.

Preferably, the adhesive powder material is accelerated to >50 - 400 m/s, more preferably, >50 - 300 m/s.

Preferably, the acceleration device is a De Laval nozzle.

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 material from the exit region onto the surface of the work piece. Preferably, the gas used is inert to the powder adhesive material. For many applications air and/or nitrogen and/or helium or a mixture thereof is suitable. Preferably, the De Laval-nozzle forms a supersonic gas/powder flow in the diverging part of the nozzle.

The inventive method shall be set up so that the particles of the adhesive powder material are at the temperature at which they will adhere to the surface of the work piece 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 exit of the acceleration device. 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.

This temperature can be achieved by heating the adhesive powder material and/or the gas flow carrying the adhesive powder material and/or by providing a certain kinetic energy to the particles.

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 acceleration device. 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 pressure of the gas at the convergent part is 0.3 - 3 MPa.

The powered adhesive preferably has a particle size in the range of 20 - 1000 micros, more preferably 50 to 300 microns and even more 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.

According to a preferred embodiment, the work piece is at room temperature or heated at 40°- 120°C depending of the expected green state adhesion. The work piece can be heated by the gas flow of the apparatus without powder adhesive material.

Preferably, the adhesive powder material flow rate in g/sec varies during the coating of one work piece. More preferably, the adhesive powder material flow rate depends on the relative movement speed between the work piece and the De Laval nozzle. During application of the adhesive powder, the work piece and/or the De Laval-nozzle can be moved.

Preferably, the powder material flow rate density changes during one application. This allows to alter the amount of adhesive powder material applied to the work piece in a certain time period. Hence, the coating-thickness on the work piece can be varied.

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.

Preferably, the ratio of the components changes during one application. This allows to deposit an adhesive layer on the work piece, whose composition changes locally. This allows to provide different bonding forces locally.

Preferably, the acceleration device 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 a mixing device for at least two components of the adhesive powder is utilized. The mixing device is preferably upstream from the acceleration device.

Preferably, a metering device for the adhesive powder material is used to dose the adhesive powder material into the acceleration device. Preferably, the metering is adjusted relative to the gas flow. According to a preferred embodiment, the gas flow through the acceleration device is measured and the addition of powered adhesive to the gas flow is adjusted accordingly.

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

Preferably, the apparatus comprises a sensor for the quality of the coating. Preferably the parameters of the acceleration device are controlled according to the signal of the sensor. The sensor can be, for example, a camera. The sensor can be also be utilized to control the relative movement between the acceleration device and the work piece.

The adhesive powder material applied by the inventive method to the surface of the work piece is preferably a heat activated adhesive powder material and the temperature at which the adhesive powder material is activated will depend upon the nature of the adhesive powder material and the nature of the activation and when the activation is to take place. For example, it may be desirable that the adhesive powder material 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). It may be desirable that a heating during and/or after ejection from the acceleration device raises the temperature of the adhesive powder material to a temperature at which it will adhere to the surface of the substrate and will not be heat activated.

The inventive method may be used to provide structural adhesives. The method 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 acceleration device, here a De Laval-nozzle.

Fig. 2 shows the use of the acceleration device, here a De Laval-nozzle.

Figure 1 shows a 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):

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 De Laval-nozzle

9 nozzle throat

10 tempering device for the gas

1 1 adhesive coating

12 work piece

13 first component

14 second component

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 : 90°

Claims

Claims:

1 . Method to apply an adhesive coating (1 1 ) to a work piece (12) wherein a gas flow (1 ) is mixed with an adhesive powder material (13, 14) and sprayed on the surface of a work piece (12) by an acceleration device (8) to form the adhesive coating (1 1 ), characterized in, that the adhesive powder material is accelerated with to 50 - 1000 m/s.

2. Method according to claim 1 , characterized in, that the adhesive powder material is accelerated to >50 - 400 m/s, preferably, >50 - 300 m/s.

3. Method according to one of the preceding claims, characterized in, that the

acceleration device is a De Laval nozzle (8).

4. Method according to one of the preceding claims, characterized in, that the

temperature of the adhesive powder material is lower than the activation temperature of the adhesive powder material (13, 14) and/or that the temperature of the adhesive powder material is between 25 - 80°C, prior and/or after its acceleration, respectively.

5. Method according to one of the preceding claims, characterized in that the carrier gas is air or Nitrogen or Helium or a mixture of these.

6. Method according to one of the preceding claims, characterized in, that the

temperature of the gas is 200°C - 600°C at the inlet of the acceleration device.

7. Method according to one of the preceding claims, characterized in, that the pressure of the gas at the convergent part is 0.3 - 3 MPa at the inlet of the acceleration device.

8. Method according to one of the preceding claims, characterized in that the particle size of the adhesive powder material is between 20 - 1000 μηη.

9. Method according to one of the preceding claims, characterized in that the volume median particle size (Dv50) of the adhesive powder material is 1 10 - 150 μηη

10. Method according to one of the preceding claims, characterized in, that the work

piece is at room temperature or heated at 40°- 120°C, preferably depending of the expected green state adhesion.

1 1 . Method according to one of the preceding claims, characterized in that the adhesive powder material flow rate in g/sec depends of the substrate motion speed relatively to the actuator handling the De Laval nozzle.

12. Method according to one of the preceding claims, characterized in, that the powder flow rate density changes during one application.

13. Method according to one of the preceding claims, characterized in that the powder comprises at least two components.

14. Method according to claim 13, characterized in, that the ratio of the components changes during one application.