CA1059066A - Process for coating hollow metal articles - Google Patents

Process for coating hollow metal articles

Info

Publication number
CA1059066A
CA1059066A CA268,119A CA268119A CA1059066A CA 1059066 A CA1059066 A CA 1059066A CA 268119 A CA268119 A CA 268119A CA 1059066 A CA1059066 A CA 1059066A
Authority
CA
Canada
Prior art keywords
coating
primer
article
surfacer
cure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA268,119A
Other languages
French (fr)
Inventor
William F. J. Dabbs
Roy L. Baylis
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rover Co Ltd
Imperial Chemical Industries Ltd
Original Assignee
Rover Co Ltd
Imperial Chemical Industries Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rover Co Ltd, Imperial Chemical Industries Ltd filed Critical Rover Co Ltd
Application granted granted Critical
Publication of CA1059066A publication Critical patent/CA1059066A/en
Expired legal-status Critical Current

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B05SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05DPROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50Multilayers
    • B05D7/56Three layers or more
    • B05D7/58No clear coat specified
    • B05D7/587No clear coat specified some layers being coated "wet-on-wet", the others not
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B05SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05DPROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00Processes for applying liquids or other fluent materials
    • B05D1/007Processes for applying liquids or other fluent materials using an electrostatic field
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B05SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05DPROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00Processes for applying liquids or other fluent materials
    • B05D1/02Processes for applying liquids or other fluent materials performed by spraying

Landscapes

  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)

Abstract

ABSTRACT
A process for coating hollow metal articles. Water-borne primer/
surfacer is sprayed onto selected external surfaces and the article is dried without fully curing the primer/surfacer coating. The remaining surfaces are then electrophoretically coated with primer and the article is baked to at least partially cure both the sprayed and the electrophoretically deposited primer coatings. A top coat is then applied and the article is stoved to fully cure the top coat and to cure any previously non-fully cured coating.

COATING PROCESS

BRITISH LEYLAND UK LIMITED, Leyland House, 174 Marylebone Road, London NWI 5AA; and IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House,Millbank, London SW1P 3JF, England

Description

` ` 1059~66 COATING PROC~SS

l~lis invention relates to a coating process for hollow metal articles that is particularly useful in the coating of vehicle bodies.
It has heretofore been proposed to coat hollow metal articles with an electrically insulating coating on the outer sùrfaces of the article and then with an electrophoretic coating on the inner surfaces; the advantages of such a coating method being that the insulating coating ensures a cosmetically acceptable coating having the necessary corrosion protection on the visible outer surfaces and limits the consumption of electrophoretic coating material, whilst the electrophoretic coating provides the normally necessary corrosion protection within internal sections that are otherwise difficult to coat.
Whilst such a method of coating has advantages with regard to the coated article, the process has disadvantages in production because the need to apply two separate coatings necessitates the use of additional space-consuming plant to separately apply and stove each of the coatings.
Moreover the need for separate stoving stations inherently means that considerable energy is eonsumed in the several stoving operations, and this disadvantage is accentuated by the pre~sent general need to provide plant for treating the fumes generated during each stoving operation.
Thus the plant necessary for the production application of such a process would be both space consuming and expensive in installation and energy consuming in operation.

lOS9~66 According to one aspect of this invention a process for coating a hollow metal article includes a) preparation of the surface of the article to be coated;
b) spraying a water-borne primer/surfacer onto preselected areas of the outer surface of the article;
c) drying the article without curing, or without fully curing, the primer/surfacer coating material d) electrophoretically coating the remaining surfaces of the article with a primer;
e) baking the article such as to at least partially cure both the electrophoretically deposited primer coating and the primer/surfacer coating;
f) applying atop coat on at least those surfaces of the article that will be visually apparent; and g) stoving the article such as to cure the top coat and fully cure any previously non-fully cured coating.
Thus the process of invention provides the advantage that as the primer/surfacer only requires partial curing before the electrophoretic coating step, the drying may be effected at a relatively low temperature, with a consequential potential saving in energy consumption as compared with a full bake, and the fumes generated at this stage do not normally require incineration or other treatment thereby providing a further potential saving in energy consumption.

. ~

- 3 _ 1~59~66 Prel`erabl)r, tllerefore~ the process includes baking the article to part cure the primer/surfacer coating at a low temperature such as to avoid a need for incineration of the fumes generated during baking.
Furthermore it has been found that certain primer/surfacers can be applied satisfac-torily to a surface that is not completely dry. Hence~ according to another aspect of the invention a process for coating articles includes the steps of a) surface preparation terminating in a water rinse, b) applying a primer/surfacer onto the sur~ace of the article in a "damp dry" state.
In the art and in this specification the expression "damp dr~" means that the surface is free of surface water without being in a completely dry state such as is achieved by baking. Such a damp dry state may be produced after a water rinse by high pressure air blowing of the surface or by a low pressure warm air blow.
Thus, the conventional heated bake step which usually preceeds the application of paint following a water rinse is eliminated with a consequential potential saving in tho space requirements and the cost of produotion plant 7 and a consequentia]
potential saving in energy conswllption.
It should be appreciated that the above aspect of the invention may be combined such as to provide a process for coating hollow metal articles which includes a) surface preparation te~minating with a water rinse;
b) spraying a water borne primer/surfacer onto preselected outer surfaces of the article in a damp dry state by spray means;

_ L~ _ 1059~66 c) drying the article without curing, or without fully curing, the primer/surfacer coating material;
d) electrophoretically coating the remaining surfaces of the article with a primer;
e) baking the article such as to at least partially cure both -the electrophoretically deposited primer coating and the primer/surfacer coating;
f) applying a top coat on at least those surfaces of ~;
the article that will be visually apparent 9 and g) stoving the article such as to cure the top coat and fully cure any previously non-fully cured coating.
In the art it has, in the past, been found impracticable to apply a primer/surfacer to an article of complicated shape, such as a vehicle body, by fully automatic means that include spray guns that have to track the surface of the article.
For example in the case of vehicle bodies it has been found t~
that when automatic spray guns are used it is still necessary for certain areas of the automatically sprayed coating to be "reinforced" by further manual controlled spraying.
However, this invention can eliminate such a need for manual applied reinforcemont and allow the fully automatic application of primer/surfacer. This is because, by using a primer/surfacer that is compatible with the electrophoretically deposited primer coating in terms of the required appearance and paint performance of the finished article, the electrophoretically deposited primer coating will serve to "reinforce" areas -that were inadequately covered with automatically sprayed primer/surfacer.

l~S9~66 Moreover, if malfunctions in the automatic spraying installation should cause defects, such as for example "runs"
and "sags" in the sprayed primer/sur*acer coating~ the defects can normally be removed by wiping witll an appropriate solvent and suitable wiper after partial curing of the sprayed primer/surfacer because even areas that are overwiped such a~ to leave bare substrate or only a very thin coating of primer/surfacer will subsequently be coated with electrophoretically applied primer.
Furthermore~ in the prior art when automatic spraying of surfacer has followed electrophoretic priming~ it has been found that a subsequent top coat may not adhere satisfactorily in the marginal re~ions of the area covered by the sprayed surfacer because, in these regions, the surfacer tends to remain as discrete droplets.- Consequently it has in some such cases been necessary for the droplets of surfacer to be rubbed off in these marginal regions to ensure satis~aclory adhesion and appearance of a subsequent top coat. In the present invention it has been found that the electrophoretic primer coats around~ and in some cases over, the droplets of sprayed primer/surfacer and the top coat normally adheres satisfactorily without any need ~or the above described manual preparation.
The initial surface preparation may include the normal cleaning and chemical conversion coating, such as a zinc or iron phosphate in the case of ferrous substrates, and preferably, particularly in the case of vehicle bodies, includes a spray-dip-spray sequence in which each zone of the chemical processing - 6- 1059~66 plant contains botll a spray and a dip stage which rnay for convenience be accommodated in the same part of a process tunnel. In the case of ~ehicle boclias, the dip level should usually be arranged to ensure that all maior structural box members of the vehicle body that are susceptible to corrosion are immersed thus giving a more controlled chemical conditioning of the box members than can be accommodated by spray only.
Secondary sprays should also usually be arranged at the exit of eacll 20ne to ensure removal of any residues and scum which may be left on the external surfaces as the vehicle eaves the dip tank.
In the prior art the surface preparation of mixed-metal vehicle bodies before coating by electrodeposition has been critical and special procedures or phosphating solutions have been necessary in order to ensure a consistent finished appearance. For example such bodies may typically have a main structure which is formed from steel and have non-stressed parts, such as doors and boot lids, which are formed from aluminium. In the prior art such aluminium parts have been suitably prepared before the parts were fixed to the main body and the subsequent surface perparatiorl solutions have been chosen to be effective on the steel parts but ineffective on the alwninium parts, alternatively special phosphates have been used which effectively pretreat both the steel and aluminium parts.
In practising this invention, the visually significant parts of such mixed-metal bodies are coated with sprayed primer/surfacer before electrophoretic painting, and thus the need for different pretreatment for the different metals or 1059~66 a subsequent top coat may not adhere satisfactorily in the marginal regions of the area covered by the sprayed surfacer because, in these regions, the surfacer tends to remain as discrete droplets. Consequently it has in some such cases been necessary for the droplets of surfacer to be rubbed off in these marginal regions to ensure satisfactory adhesion and appearance of a subsequent top coat. In the present invention it has been found that the electrophoretic primer coats around, and in some cases over, the droplets of sprayed primer/surfacer and the top coat normally adheres satisfactorily without any need for the above described manual preparation.
The initial surface preparation may include the normal cleaning and chemical conversion coating, such as a zinc or iron phosphate in the case of ferrous substrates, and preferably, par-ticularly in the case of vehicle bodies, includes a spray-dip-spray sequence in which each zone of the chemical processing plant contains both a spray and a dip stage which may for convenience be accommodated in the same part of a process tunnel. In the case of vehicle bodies, the dip level should usually be arranged to ensure that all major structural box members of the vehicle body that are susceptible to corrosion are immersed thus giving a more controlled chemical conditioning of the box members than can be accommodated by spray only. Secondary sprays should also usually be arranged at the exit of each zone to ensure removal of any residues and scum which may be left on the external surfaces as the vehicle leaves the dip tank.

- 8 _ lOS9~66 to ensure any subsequent solvent wipe operation will not result in tacky sealer being spread over the surface of the ~` article.
The final top coating may comprise a conventional liquid paint or a powd3r coating which is conveniently applied electrostatically in kno~n manner.
The final stoving may comprise a conventional stoving operation at a tempera-ture and for a time suitable for the top coat that has been ussd.
In the case of vehicle bodies the electrophoretic stoving plant should normally be provided with full incineration ~ facilities to reduce the fumes caused by stoving degradation s products given off from the primer/surfacer and the electrophorctic primer during any flash-off. Usually the heat generated during incineration may be recovered and used, for example, in the pretreatment process, or the primer/surfacer drying zone or the stoving of the top coat.
Thu~s the process provides yet another potential saving in ~j energy consumption.
The invention will now be illustrated by the following ; examples.

A mild steel door for an automotive vehicle was cleaned and pretreated with a proprietory zinc phosphate solution, rinsed with demineralised water and had excess water removed by air jets. A water-borne epoxy primer/surfacer was sprayed onto the outer panel of the door at a film thickness of approximately 37-40 micrometers.
After 10 mimltes flash-off at ambient temperatures and drying at 110 C for 10 minutes such that the pr~mer/surfacer i 1059~66 was not fuliy cured, the door was to-tally lmmersed in an epoxy electroprimer and electroprimed. Over the whole of' the primer/sur~acer-electroprimer inter~ace there was a film thickness o~ at least 25 micrometers. The primed cloor was then stoved for 20 minutes a-t 160C (eff`ective metal temperature) such that -the sprayed primer/surfacer and the electroprimer is f`ully cured. Then the door was sprayed with a pigrnented alkyd/melamine automotive enamel to give a total ~ilm thlckness o~ 55-70 micrometers and stoved for 20 minutes at 150 C (ef~f~ective metal temperature). The door was considered to have an acceptable visual appearance and an acceptable performance as assessed by conventional accelerated testing methods.

The coating process of` Example 1 was repeated using an aluminium door that was pretreated in a proprietory oxychromate bath. Once again the coated door was acceptable.

A mild steel door was coated as in Example 1 except that -the top coat was a pigmented acry]ic powder that was stoved f`or 15 minutes at 180 C (ef~f'octive metal temperature).
Again the coated door was acceptable.

Claims (5)

C L A I M S
The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:-
1. A process for coating hollow metal articles having inner and outer surfaces which includes the steps of a) preparation of the surfaces off the article to be coated;
b) spraying water-borne primer/surfacer coating material onto the outer surfaces that will be visually significant;
c) drying the article without fully curing the primer/
surfacer coating material;
d) electrophoretically coating the remaining surfaces of the article with a primer;
e) baking the article such as to at least partially cure the electrophoretically deposited primer coating and the primer/surfacer coating;
f) applying a top coat on at least those surfaces of the article that will be visually apparent; and g) stoving the article such as to fully cure all the coatings.
2. A process for coating hollow metal articles as claimed in Claim 1 in which after the electrophoretic coating step the article is baked to fully cure both the electrophoretically deposited primer coating and the sprayed primer coating.
3. A process for coating hollow metal articles as claimed in Claim 2 which includes terminating the surface preparation in a water rinse and applying primer/surfacer to the surface of the article in a damp dry state.
4. A process for coating hollow metal articles as claimed in Claims 1, 2 or 3 which includes removing any "runs"
or "sags" on the sprayed primer surfacer coating by wiping with an appropriate solvent and suitable wiper after partial curing of the sprayed primer/surfacer.
5. A process for coating hollow metal articles having inner and outer surfaces which includes the steps of a) preparation of the surface of the article to be coated terminating with a water rinse;
b) spraying a water-borne primer/surfacer coating material onto preselected outer surfaces of the article whilst the surfaces are in a damp dry state;
c) drying the article without curing, or without fully curing, the primer/surfacer coating material;
d) electrophoretically coating the remaining surfaces of the article with a primer;
e) baking the article such as to at least partially cure the electrophoretically deposited primer coating and the primer/surfacer coating;
f) applying a top coat on at least those surfaces of the article that will be visually apparent; and g) stoving the article such as to cure the top coat and fully cure any previously non-fully cured coatings.
CA268,119A 1975-12-18 1976-12-17 Process for coating hollow metal articles Expired CA1059066A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB5193375 1975-12-18
GB4784176 1976-11-17

Publications (1)

Publication Number Publication Date
CA1059066A true CA1059066A (en) 1979-07-24

Family

ID=26266149

Family Applications (1)

Application Number Title Priority Date Filing Date
CA268,119A Expired CA1059066A (en) 1975-12-18 1976-12-17 Process for coating hollow metal articles

Country Status (9)

Country Link
JP (1) JPS5290540A (en)
AU (1) AU508886B2 (en)
CA (1) CA1059066A (en)
DE (1) DE2657138A1 (en)
ES (1) ES454356A1 (en)
FR (1) FR2352072A1 (en)
IT (1) IT1065396B (en)
PL (1) PL106433B1 (en)
SE (1) SE7614211L (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3314776A1 (en) * 1983-04-23 1984-10-25 Herberts Gmbh, 5600 Wuppertal Process for preparing multicoloured decorative coatings

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2328342A1 (en) * 1973-06-20 1974-12-19 British Leyland Austin Morris PROCEDURE FOR PULLING OBJECTS

Also Published As

Publication number Publication date
AU2062476A (en) 1978-06-22
DE2657138A1 (en) 1977-06-23
FR2352072B1 (en) 1980-10-24
IT1065396B (en) 1985-02-25
AU508886B2 (en) 1980-04-03
JPS5290540A (en) 1977-07-29
FR2352072A1 (en) 1977-12-16
SE7614211L (en) 1977-06-19
PL106433B1 (en) 1979-12-31
ES454356A1 (en) 1977-12-16

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