WO2001032442A1

WO2001032442A1 - Control of paint skinning

Info

Publication number: WO2001032442A1
Application number: PCT/AU2000/001353
Authority: WO
Inventors: Aziz George Haddad; Don Malek
Original assignee: Viscount Plastics Vic Pty Ltd
Current assignee: Viscount Plastics Vic Pty Ltd
Priority date: 1999-11-03
Filing date: 2000-11-03
Publication date: 2001-05-10
Anticipated expiration: 2002-05-03
Also published as: NZ518484A; WO2001032442A8

Abstract

A container for water based paints, the container comprising: i) a container body moulded from plastics material; and ii) a container closure moulded from plastics material; wherein at least a part of the inner surface of either the container body or container closure has a coating applied thereto to control the contamination of the paint by reducing paint skin or thickened paint falling from the coating into the body of the paint. The coating may be applied during the container manufacturing process or during the process of packaging paint in the container.

Description

CONTROL OF PAINT SKINNING

INTRODUCTION

This invention relates to the control of the contamination of paint due to paint skinning. In particular the invention relates to a method of packaging paint to control contamination of paint in paint containers due to paint skinning. The invention also relates to a paint container for packaging paint which minimises contamination of paint due to paint skinning.

BACKGROUND

In paint containers a skin or thickening of the paint can occur on the underside of the container lid and on the sidewalls of the container, especially in the region above the top surface of the paint therein. Whilst not wishing to be bound by theory it is thought that this occurs due to the presence of a headspace in the paint container (i.e. a pocket of air in the top of the container). It is thought that in the headspace paint is splashed onto the container walls and lid during transit of the container followed by evaporation of the solvent leading to skin formation.

The skin formation is undesirable as the quality of the paint can be downgraded if the paint skin or thickened paint falls from the surface where it has formed into the main body of the paint. It has been found that paints in which this has happened are generally unsuitable for spray applications necessitating either filtration of the paint prior to use or vigorous agitation of the paint in an attempt to return the paint to a homogeneous state. It is generally found that neither of these techniques overcomes all problems caused by paint skinning and neither one is commercially acceptable to end users of the paint. It is therefore desirable to minimise the occurrence of paint skinning as well as to reduce the transfer of skin or thickened paint from the container walls or lid to the main body of the paint once the skin has formed.

In metal containers contamination of the paint by the skin is usually not a particularly significant problem as the paint skin tends to adhere to the container. Normally the metal is coated with a baked epoxy layer such as Epon. Where, however, plastic containers are used, the skin does not adhere very well to the plastic container and tends to fall into the body of the paint thereby causing a problem. It is of course not possible to utilise a baked Epon layer on plastic containers due to its method of application (high temperature baking) which tends to adversely affect the plastic. There have been a number of attempts in the paint industry to overcome this problem in order to enable plastic containers to be reliably used. This is because plastic containers offer significant advantages in other areas (such as cost) over the use of metal containers. Notwithstanding these attempts the problems have, however, not been satisfactorily resolved.

It would therefore be desirable to provide a method of packaging paint which at least partly overcomes the problem of paint skin being admixed with the paint in the container.

It would also be desirable to provide a container for packaging paint which also at least partially overcomes this problem.

Throughout the description of the specification the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps.

SUMMARY OF THE INVENTION

It has now been found that the problem of paint skinning can be reduced or ameliorated to some extent by the provision of a coating on the surface of the paint container that contacts the paint. It is preferable that the coating has at least a partial affinity for both the materials used in the construction of the paint container and the components of the paint itself.

In one aspect the present invention provides a container for water based paints, the container comprising: i) a container body moulded from plastics material; and ii) a container closure moulded from plastics material; wherein at least a part of the inner surface of either the container body or container closure has a coating applied thereto.

Preferably the container body is a pail and the container closure is a lid.

Even more preferably the coating is applied to at least a part of both the container body and the container closure. It is most preferable that the coating is applied to the entire inner surface of the container body and the container closure which may come into contact with the paint.

In a further aspect the present invention provides a method of packaging paint comprising the steps of: a) providing a paint container comprising: i) a container body moulded from plastics material; and ii) a container closure moulded from plastics material; b) applying a coating to at least part of the inner surface of at least one of the container body and the container closure; c) curing the coating; d) filling the container body to the required level with water based paint; and e) applying the container closure to the container body.

Preferably the container body is a pail and the container closure is a lid.

Even more preferably the coating is applied to at least a part of both the container body and the container closure. It is most preferable that the coating is applied to the entire inner surface of the container body and the container closure. Of course, as will be appreciated by a skilled addressee if only partial coating is done it is preferred that the parts of the container body and container closure that come into contact with the headspace are coated. This is because, as noted previously, the paint skinning is more often noted to occur in or around the areas of the paint container that contact the headspace.

In yet a further aspect the invention provides a method of producing a container for packaging paint comprising: a) providing a paint container comprising: i) a container body moulded from plastics material; ii) a container closure moulded from plastics material; b) applying a coating to at least a part of the inner surface of either the container closure or container body; and c) allowing the coating to cure.

As discussed above the coating used in the present invention preferably, upon curing, has an affinity for the plastics material used in container manufacture as well as some affinity for the components in the water based paint. Whilst not wishing to be bound by theory it is thought that the attraction of the cured coating to both the plastics material and the components in the paint allow the coating to act as an interface between the plastics material and any paint skin thus formed. It is though that the presence of the interface inhibits the paint skin from falling back into the paint.

DETAILED DESCRIPTION OF THE INVENTION (a) The Container

The containers of the present invention typically comprise a container body and a container closure. The container body is preferably a pail and the container closure is preferably a lid. Plastic pail-like containers are well known in the art. As will be appreciated by a person skilled in the art many plastic containers may be considered to be of a size and shape so as to be suitable for packaging of paint. In general, it is typically found that these containers are round however substantially square or rectangular containers are also envisaged for the containers of the present invention. In general, the containers of the invention can be any size with the preferred sizes ranging from as small as 250 ml up to greater than 50 litres. In general, the only limitation placed on the size of the container is a practical one as the containers are usually presented in such a way that a single container can be carried by a painter to a desired application point. Accordingly, therefore, whilst there is no size requirement or limitation placed on the containers of the present invention it is preferred that the containers are between 250 ml and 20 litres with 1 , 2, 4, 10, 12.5, 15 and 20 litre containers being preferred.

The container closure and the container lid can be related to each other in a number of ways. As will be appreciated by a skilled addressee there are a number of ways in which a container closure can be fitted to the container body to achieve the desired closure of the container. Thus, for example, the two portions can be related via a screw thread, via lugs, or via a snap fit. In essence, it is immaterial how the container body and the container closure are related to each other for the purposes of working the present invention.

The components of the container used in the present invention are typically moulded from plastics material. Whilst it is typical that both the container body and the container lid are moulded from the same plastics material this need not be the case. It is preferred that the container body and container lid are moulded from polyethylene, polypropylene, high density polypropylene or a mixture thereof.

(b) The Coating The coating used is a coating that preferably has at least a partial affinity for both the plastics material and the paint components. A number of coatings have this functionality.

The coating used in the invention preferably comprises an epoxy resin and is most preferably provided as a two part epoxy coating system in which the parts are admixed shortly before application of the coating. In such cases the epoxy resin is contained in the first part of said coating system. The epoxy resin is preferably a resin produced by polymerisation of monomers of epichlorohydrin and Bisphenol A. The epoxy resin may preferably represent between 50% and 90% (by weight) of the polymeric components in the first part of the coating system. It is preferably present at between 60-80%, more preferably 70-75%, most preferably 72% by weight of the polymeric components in the first part of the coating system.

The first part of the coating also preferably comprises a further polymeric material. The further polymeric material in the first part of the coating is preferably a vinyl resin based on polymerisation of monomers such as vinyl acetate and vinyl chloride. The vinyl resin preferably represents between 10 and 50%, more preferably 20-40%, even more preferably 25-35%, most preferably 28% of the polymeric components in the first part of the coating system.

The first part of the coating system also preferably comprises pigments and/or filler. The pigments are preferably selected from the group consisting of appropriate grades of barium sulphate, amorphous silica, clay, zinc phosphate, talc and colouring pigments such as titanium dioxide. Coating grades of these materials would be of a quality that would be well understood by a skilled practitioner. The pigments/fillers preferably represent between 10-50 wt.% of the solids, more preferably 20-40%, most preferably 30 wt.% of the total weight of solids in the first part of the coating.

In essence the coating used in the present invention may contain a number components additional to the ones referred to above. Whilst there is no express limit on the solids level of the first part of the coating it is noted that the solids level of the coating prior to application should be optimised to ensure optimal handling conditions. Thus, for example, if the coating is formulated with too low a solids content it will be far too fluid and will not provide consistency in coating of the container leading to wastage of product. In contrast, if the solids content is too high the coating will not be sufficiently viscous to provide easy material handling and application. It is preferred that the solids content of the first part of the coating is within the range of 30-60 wt.%, more preferably 45-55 wt.%, most preferably about 48 wt.%.

The first part of the coating is typically treated with a curing agent (the second part of the coating system) and allowed to partially cure prior to its application to the surfaces of the container body and/or container closure. The amount of second part of the coating used is typically equal to the amount of first part used although this is not required. (Indeed the relative amount of each material to be used will depend on the resin components and curing agent chosen). It is preferred that the second component contains a curing agent which comprises a cross-linking agent. A suitable cross-linking agent that may be used is a polyamide. In such cases the cross-linking of the first component of the coating occurs by combining it with the second component. The second component preferably contains an organic solvent as the liquid phase. The polyamide resin used in such cases is preferably the amine terminated reaction product of one or more polyamines with one or more polyfunctional carboxylic acids. The organic solvent or liquid phase used for the second component is preferably selected from the group consisting of aromatic hydrocarbons, aliphatic alcohols, ether esters and ether alcohols.

If a curing agent is used the first component of the coating is typically allowed to react with the second component containing the curing agent (i.e. allowed to partially cure) for a period of time prior to application of the coating onto the container body and/or container closure. The appropriate period of time the material is allowed to cure prior to application will vary depending on the curing agent chosen and the exact coating composition. Thus for example the time of application will be delayed until the coating has reached the desired consistency for application.

(c) Application

A number of ways are known that can be used for applying the coating to the surfaces of the container body and/or container closure as appropriate. Thus, for example, the coating may be applied by any conventional technique employed in the art. The coating may, for example, be painted or sprayed onto the surfaces of the body and closure of the container. Application by spraying is preferred as this is typically found to be most commercially acceptable and provides the most complete and consistent coverage of the coating onto the surfaces of the container body and container closure.

Once the coating has been applied it is allowed to cure completely. This can be done in a number of ways well known in the art. The coating may be cured, for example, by being allowed to air cure at ambient temperature until dry. Alternatively, various means can be employed to increase the rate of curing such as air flow drying, exposure to elevated temperatures and the like. Curing of the coating can also occur by exposure to UV radiation. The coating is typically applied so that when cured it preferably has a thickness of at least 5 micron. It is further preferable that the entire inner surface of the container body and container closure are covered with the coating.

Method of Packaging Paint

The method of production of the container for packaging paint can also, of course, be incorporated into a continuous method for packaging paint. Thus, whilst it is clearly to be seen that the containers discussed hereinbefore could be produced by a packaging manufacturer and then on-sold to a paint manufacturer (it is expected that this will be the case), the procedure for producing the containers can also be incorporated as part of a continuous method for packaging paint in a paint factory.

In a further aspect the present invention provides method of packaging paint comprising the steps of: a) providing a paint container comprising: i) a container body moulded from plastics material; and ii) a container closure moulded from plastics material; b) applying a coating to at least part of the inner surface of either the container body and the container closure; c) allowing the coating to cure; d) filling the container body to the required level with water based paint; e) applying the container closure to the container body.

In this method a suitable plastic container is treated in a continuous fashion with a coating as discussed hereinbefore to form the packaging container with coating applied to at least a portion of the inner surface of either the container body or container closure. The coating is allowed to cure prior to the container being filled to the appropriate level with paint and the container closure being placed thereon. This therefore means that a paint manufacturer can pretreat the plastic pails or containers in situ at the paint factory if desired. It is anticipated that such an approach is, unlikely, to be seen to be commercially desirable as the manual handling difficulties of the untreated containers is most likely to be more easily handled by a packaging manufacturer who can generate the treated pails or containers prior to despatch to the paint manufacturer for filling.

In the specification a reference to "paint" is to be understood to include various surface coating products including paint, varnish, stain, inks and other surface coating materials.

The invention will now be further described with reference to the following example.

EXAMPLE 1

A pail and lid were injection moulded from polypropylene and/or high density polypropylene. The pails had nominal capacities in the range 1 to 20 litres. The inner surfaces of the pail and lid were painted with a coating known as EP40* which had been admixed with an epoxy coating curing agent EP401^* in a 1 :1 ratio and allowed to partially cure for 30 minutes, (both EP40 and EP401 are available from AM Coatings Pty. Ltd. of Braeside, Victoria). The coating was permitted to air dry for at least 1 hour and had a thickness of at least 5 microns when dry. It is envisaged that in commercial production the coating would be sprayed onto the inner surfaces of the pail and lid and then cured using a dryer or the like. After drying of the coating, the container was filled with paint to its normal capacity and the lid closed on the container. The paint was a water based paint such as an acrylic paint of trade grade supplied by Dulux Australia. The container was then moved randomly so as to simulate movement which would normally occur during manufacture and distribution. After about one week the lid was removed and inspected. It was found that a relatively thin skin had formed on the underside of the lid and on the exposed surfaces inside the pail above the level of the paint. The skin, however, adhered to the underside of the lid and the said exposed surfaces and there was little or no evidence of the skin falling back into the main body of the paint.

^*EP40 is a product which contains an epoxy resin, based on polymerisation of monomers including epichlorhydrin and Bisphenol A, and a vinyl resin, based on polymerisation of monomers including vinyl acetate and vinyl chloride. The resins are dissolved in organic solvents selected from the group consisting of aliphatic ketones, aromatic hydrocarbons and aliphatic alcohols. The pigments in the product may include appropriate grades of barium sulphate, amorphous silica, clay, zinc phosphate, talc and colouring pigments including titanium dioxide. The product may also include additives present at less than 1 % of total formula weight.

^*EP401 is a product which consists of a solution of a polyamide resin in an organic solvent such as aromatic hydrocarbons, aliphatic alcohols, ether esters and ether alcohols. The polyamide resin is the amine-terminated reaction product of polyamines and polyfunctional carboxylic acids.

Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

Claims

CLAIMS:

1. A container for water based paints, the container comprising: i) a container body moulded from plastics material; and ii) a container closure moulded from plastics material; wherein at least a part of the inner surface of either the container body or container closure has a coating applied thereto.

2. A container according to claim 1 wherein said coating is applied to at least a part of both the inner surface of the container body and the inner surface of the container closure.

3. A container according to claim 2 wherein said coating is formed from a two part coating system wherein the two parts are admixed prior to application to the container components.

4. A container according to claim 3 wherein said first part of said coating system comprises an epoxy resin.

5. A container according to claim 4 wherein said epoxy resin is an epoxy resin based on polymerisation of monomer units of epichlorohydrin and bisphenol A.

6. A container according to claim 4 wherein said first part of said coating system further comprises an additional polymeric component.

7. A container according to claim 6 wherein said additional polymeric component is a vinyl resin produced by polymerisation of vinyl acetate and vinyl chloride.

8. A container according to claim 4 wherein said first part of said coating system contains between 60 and 80% epoxy resin by weight of the total amount of polymeric components in first part of the coating system.

9. A container according to claim 4 wherein said first part of said coating system contains about 72% epoxy resin by weight of the total amount of polymeric components in the first part of coating system.

10. A container according to claim 6 wherein said additional polymeric component comprises between 25-35% of the total weight of the polymeric components in the first part of the coating system.

11. A container according to claim 6 wherein said additional polymeric component comprises about 28% by weight of said polymeric components in said first part of said coating system.

12. A container according to claim 4 wherein said first part of said coating system further comprises an addition component selected from barium sulphate, amorphous silica, clay, zinc phosphate, talc and titanium dioxide.

13. A container according to claim 10 wherein said first part of said coating system contains talc.

14. A container according to claim 4 wherein said first part of said coating system has a solids content of between 45% and 55% by weight based on the total weight of the first part of the coating system.

15. A container according to claim 14 wherein said first part of said coating system has a solids content of about 48% based on the total weight of said coating system.

16. A container according to claim 3 wherein said first part of said coating system is partially cured by admixture with said second part of said coating prior to application of the coating.

17. A container according to claim 16 wherein said second part of said coating system comprises a crosslinking agent.

18. A container according to claim 1 wherein said cured coating has a thickness of at least 5 microns.

19. A container according to claim 1 wherein said plastics material is polyethylene, polypropylene, high density polypropylene or a mixture thereof.

20. A method of packaging paint comprising the steps of: a) providing a paint container comprising: i) a container body moulded from plastics material; and ii) a container closure moulded from plastics material; b) applying a coating to at least part of the inner surface of either the container body and the container closure; c) allowing the coating to cure; d) filling the container body to the required level with water based paint; e) applying the container closure to the container body.

21. A container according to claim 20 wherein said coating is applied to at least a part of both the inner surface of the container body and the inner surface of the container closure.

22. A container according to claim 21 wherein said coating is formed from a two part coating system wherein the two parts are admixed prior to application to the container components.

23. A container according to claim 22 wherein said first part of said coating system comprises an epoxy resin.

24. A container according to claim 23 wherein said epoxy resin is an epoxy resin based on polymerisation of monomer units of epichlorohydrin and bisphenol A.

25. A container according to claim 23 wherein said first part of said coating system further comprises an additional polymeric component.

26. A container according to claim 25 wherein said additional polymeric component is a vinyl resin produced by polymerisation of vinyl acetate and vinyl chloride.

27. A container according to claim 24 wherein said first part of said coating system contains between 60 and 80% epoxy resin by weight of the total amount of polymeric components in first part of the coating system.

28. A container according to claim 23 wherein said first part of said coating system contains about 72% epoxy resin by weight of the total amount of polymeric components in the first part of coating system.

29. A container according to claim 25 wherein said additional polymeric component comprises between 25-35% of the total weight of the polymeric components in the first part of the coating system.

30. A container according to claim 25 wherein said additional polymeric component comprises about 28% by weight of said polymeric components in said first part of said coating system.

31. A container according to claim 23 wherein said first part of said coating system further comprises an addition component selected from barium sulphate, amorphous silica, clay, zinc phosphate, talc and titanium dioxide.

32. A container according to claim 29 wherein said first part of said coating system contains talc.

33. A container according to claim 23 wherein said first part of said coating system has a solids content of between 45% and 55% by weight based on the total weight of the first part of the coating system.

34. A container according to claim 33 wherein said first part of said coating system has a solids content of about 48% based on the total weight of said coating system.

35. A container according to claim 22 wherein said first part of said coating system is partially cured by admixture with said second part of said coating prior to application of the coating.

36. A container according to claim 35 wherein said second part of said coating system comprises a crosslinking agent.

37. A container according to claim 20 wherein said cured coating has a thickness of at least 5 microns.

38. A container according to claim 20 wherein said plastics material is polyethylene, polypropylene, high density polypropylene or a mixture thereof.

AMENDED CLAIMS

[received by the International Bureau on 23 March 2001 (23.03.01); original claims 21-30 amended; remaining claims unchanged (3 pages)]

21. A method according to claim 20 wherein said coating is applied to at least a part of both the inner surface of the container body and the inner surface of the container closure.

22. A method according to claim 21 wherein said coating is formed from a two part coating system wherein the two parts are admixed prior to application to the container components.

23. A method according to claim 22 wherein said first part of said coating system comprises an epoxy resin.

24. A method according to claim 23 wherein said epoxy resin is an epoxy resin based on polymerisation of monomer units of epichlorohydrin and bispheπol A.

25. A method according to claim 23 wherein said first part of said coating system further comprises an additional polymeric component.

26. A method according to claim 25 wherein said additional polymeric component is a vinyl resin produced by polymerisation of vinyl acetate and vinyl chloride.

27. A method according to claim 24 wherein said first part of said coating system contains between 60 and 80% epoxy resin by weight of the total amount of polymeric components in first part of the coating system.

28. A method according to claim 23 wherein said first part of said coating system contains about 72% epoxy resin by weight of the total amount of polymeric components in the first part of coating system.

29. A method according to claim 25 wherein said additional polymeric component comprises between 25-35% of the total weight of the polymeric components in the first part of the coating system.

30. A method according to claim 25 wherein said additional polymeric component comprises about 28% by weight of said polymeric components in said first part of said coating system.

31. A method according to claim 23 wherein said first part of said coating system further comprises an addition component selected from barium sulphate, amorphous silica, clay, zinc phosphate, talc and titanium dioxide.

32. A method according to claim 29 wherein said first part of said coating system contains talc.

33. A method according to claim 23 wherein said first part of said coating system has a solids content of between 45% and 55% by weight based on the total weight of the first part of the coating system.

34. A method according to claim 33 wherein said first part of said coating system has a solids content of about 48% based on the total weight of said coating system.

35. A method according to claim 22 wherein said first part of said coating system is partially cured by admixture with said second part of said coating prior to application of the coating.

36. A method according to claim 35 wherein said second part of said coating system comprises a crosslinking agent.

37. A method according to claim 20 wherein said cured coating has a thickness of at least 5 microns.

38. A method according to claim 20 wherein said plastics material is polyethylene, polypropylene, high density polypropylene or a mixture thereof.