AU2011254082A1 - Internal anti-skinning coating of composition containers - Google Patents

Abstract

C:\NRPorbl\,DCC\KLL\404066S2.DOC-15/12fl01 I The invention provides a container for a water based coating composition, the container comprising at least one plastic component having an anti-skinning surface layer which makes 5 contact with the water based coating composition during normal use of the container, wherein the anti-skinning layer is formed from a single part coating system and has a surface tension of at least 38 dynes/cm.

Description

Australian Patents Act 1990 - Regulation 3.2 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title "Internal anti-skinning coating of composition containers" The following statement is a full description of this invention, including the best method of performing it known to me/us:- U:\N~rWbN UU\LL4U4U166_I.UU-31512/2U II INTERNAL ANTI-SKINNING COATING OF COMPOSITION CONTAINERS This application is a divisional application of Australian Application No. 2006326859, the specification of which as originally filed are incorporated herein in their entirety by reference. 5 Field of the Invention The present invention relates generally to containers for water based coating compositions. 10 Background of the Invention Containers for water based coating compositions (e.g. paints, varnishes, stains, inks, and the like) may be provided in a variety of shapes and sizes and typically comprise a container body and a closure means such as a lid. The containers may also comprise ancillary components such as a 15 wipe surface to facilitate removal of excess coating composition from a coating applicator, or a spout structure to facilitate pouring of the coating composition out of the container. Container components such as the container body, closure means, wipe surface and spout structure are commonly made from plastic or metal. 20 During use of the filled or partially filled containers, a skin originating from the coating composition can form on the surface of those parts of the container which make contact with the coating composition. This skin is unlikely to revert back to the liquid form of the coating composition and therefore will not reincorporate into the bulk coating composition upon stirring or shaking. Skin formation of the coating composition is believed to primarily result from 25 temperature differentials of the coating composition within different locations of the container and subsequent evaporation of water from the coating composition in regions within the container that are prone to skin formation. Detailed theories relating to skin formation may be found in US635063 and WO 00/27725. 30 Skin formation of the coating composition on container components is undesirable in that skin may fall from the surface of the component where it has formed into the bulk coating composition. Where this problem does occur, application of the coating composition to a surface, for example by brushing, can result in the transfer of the skin lumps to the -2 substrate being coated. The spray application of a bulk coating composition effected in this manner can also lead to blockage of the spray equipment. While it may be possible to remove skinned composition from the bulk composition through filtration, this can be time consuming and is generally unacceptable to the end users of the coating compositions. It 5 would therefore be desirable to avoid or minimise the transfer of skin from container surfaces to the bulk coating composition. For convenience, the problem of the transfer of skin from surfaces of the container into the bulk coating composition will hereinafter be referred to as "skinning". 10 Metal container components do not generally present a significant skinning problem as the coating composition tends to adhere very well to the metal components. Generally, the surface of such metal components is coated with a baked epoxy layer such as EPONTM. The baked epoxy layer is used to primarily inhibit rust of the metal components, but is also 15 believed to promote adhesion of the coating composition to the metal component. Containers for water based coating compositions may also comprise plastic components. Such containers can have one or more plastic components, for example a plastic container body, a plastic closure, and plastic structures that function as a wipe surface and/or spout. 20 The entire container may even be made from a plastic material. However, plastic components used in these containers are often prone to skinning as most water borne coating compositions have poor adhesion to plastic materials. Numerous attempts have been made to overcome the skinning problem associated with the 25 use of plastic components of containers for water based coating compositions. For example, WO 00/27725 contemplates promoting adhesion between the coating composition and plastic components by texturising the surface thereof to increase the surface area contact between the coating composition and the component. However, texturisation of some plastic components can be practically difficult to achieve and can be 30 expensive to implement.

-3 WO 01/32442 discloses a container for water based paints wherein the plastic components thereof are coated with a two part epoxy resin coating system. The coated plastic components are said to reduce the effects of skinning. However, the use of such two part coating systems are in themselves problematic in that upon the two parts being admixed 5 prior to application to the container components, the coating system must be used relatively quickly before it cures. Furthermore, the two parts must be mixed in correct ratios to effect cure. These limitations can add a further cost and complexity to the coating process. 10 Despite the problems associated with using plastic components in containers for water based coating compositions, the relative ease of their fabrication and cost benefits makes them particularly attractive compared with metal equivalents. It would therefore be desirable to provide containers for water based coating compositions 15 that comprise plastic components that 1) have little if no susceptibility to skinning, and 2) derive this property via a simple and cost effective means. Summary of the Invention 20 The present invention provides a container for a water based coating composition, the container comprising at least one plastic component having an anti-skinning surface layer which makes contact with the water based coating composition during normal use of the container, wherein the anti-skinning layer is formed from a single part coating system and has a surface tension of at least 38 dynes/cm. 25 The present invention further provides a plastic component for a container suitable for a water based coating composition, the plastic component having an anti-skinning surface layer which makes contact with the water based coating composition during normal use of the container, wherein the anti-skinning layer is formed from a single part coating system 30 and has a surface tension of at least 38 dynes/cm.

-4 The invention also provides a method of modifying a plastic component for a container suitable for a water based coating composition, said method comprising applying an anti skinning coating to a surface of the plastic component that makes contact with the water 5 based coating composition during normal use of the container, wherein the anti-skinning coating is a single part coating system and forms on said surface of the plastic component an anti-skinning layer having a surface tension of at least 38 dynes/cm. The invention further provides a plastic component for a container suitable for a water 10 based coating composition, wherein said component is modified in accordance with the method defined immediately above. It has now been found that plastic components with an anti-skinning surface layer that 1) is formed from a single part coating system, and 2) has a surface tension of at least 38 15 dynes/cm, have little if no susceptibility to skinning. As used herein, the term "anti skinning" is intended to be an expression of when the problem of the transfer of skin from surfaces of the container into the bulk coating composition is minimised if not avoided all together. The anti-skinning property of the plastic components can be obtained by relatively simple processing techniques in a cost effective manner. In particular, the use of 20 a single part coating system to provide for the anti-skinning surface layer simplifies and renders the production of the plastic components more cost effective. Without wishing to be limited by theory, it is believed that the surface tension of at least 38 dynes/cm of the anti-skinning surface layer promotes adhesion of the water based coating 25 composition to the plastic component. In particular, the anti-skinning surface layer is believed to function as a tie layer between the plastic component and the coating composition and prevent or minimise the problem of skinning. 30 -5 Detailed Description of the Invention As used herein, the expression "water based coating composition" is intended to embrace various water based surface coating products such as paints, varnishes, stains, inks and 5 other surface coating materials prone to the problem of skinning. Containers for water based coating compositions in accordance with the invention will generally comprise components such as a container body and a container closure. The container body is preferably a pail and the container closure is preferably a lid. Pail-like 10 containers are well known in the art and may have any shape suitable for containing water based coating compositions. Generally, the containers have a circular cross section, but containers having substantially square or rectangular cross sections are also known. The containers of the invention may also be of any size, with preferred sizes ranging from about 250ml up to greater than 50 litres. In practice, the only limitation placed on the size 15 of the containers is a practical one in that the containers will generally be of a size that is capable of being carried by a user to the desired point of application of the coating composition. Accordingly, while there is no particular size requirement or limitation on the containers of 20 the present invention, it is preferred they are of a size suitable to contain about 250ml to about 50 litres, more preferably about 1, about 2, about 4, about 10, about 12.5, about 15 and about 20 litres of coating composition. The container closure may also be provided in a variety of shapes and sizes and can engage 25 with the container body in any number of ways. The size and shape of the container closure will, at least to some extent, generally be dictated by the size and shape of the container body. Those skilled in the art will appreciate the various means by which a container closure can 30 engage a container body to provide the desired closure of the container. For example, the container closure and the container body may engage via a screw thread, via lugs, or via a -6 snap fit. While the function of the closure may be an important feature of a container to ensure that the coating composition is adequately contained, it will be appreciated that the shape and size of the container closure and how the container closure engages the container body is not particularly important for the purposes of working the present 5 invention. Containers in accordance with the invention may also comprise a structure that functions as a wipe surface to facilitate removal of excess coating composition from a coating applicator such as a brush. Such structures will generally have a relatively sharp edge that 10 extends at least partially over an aperture in the container body such that when the coating applicator is wiped on the relatively sharp edge excess coating composition falls back into the bulk coating composition for reuse. A container in accordance with the invention may also comprise a structure that functions 15 as a spout to facilitate pouring the water based coating composition out of the container. Such a structure will generally extend out from the container body and be shaped to concentrate the flow of the coating composition through or over the structure as the container is tipped. As used herein, the term "spout" is not intended to define any particular shape of the structure but rather the function of concentrating a flow of coating 20 composition to facilitate pouring of the coating composition out of the container. Accordingly, the spout may be of any shape or size provided that it provides for this function. The wipe surface and the spout may be in the form of separate components or may form 25 together a single component. In normal use, a container in accordance with the invention comprising a water based coating composition will generally be provided with a container closure to engage with the container body and achieve the desired closure of the container. However, structures that 30 function as a wipe surface and/or spout may or may not be provided with the container comprising the coating composition at the point of sale. For example, these structures may -7 be manufactured independent of the container body and closure and be offered for sale to a user as an ancillary container component. In this case, the structures will typically be adapted to securely engage some part of the container when in use. Such independently manufactured structures may also be fitted to a container body or closure to form part of 5 the overall container structure at the point of sale. Alternatively, structures that function as a wipe surface and/or spout may be formed integral with the container body and/or the container closure. 10 A container in accordance with the invention may be made from any suitable material (e.g. plastic and/or metal) provided that the container comprises at least one plastic component having an anti-skinning surface layer which makes contact with the water based coating composition during normal use of the container. By the expression "during normal use of the container" is meant normal use of the container comprising the coating composition. 15 Thus, this would include storage and transport of a container comprising the coating composition, shaking of the coating composition within the container, pouring the coating composition out of the container, and gaining access to the coating composition within the container using an applicator such as a brush or spray device. 20 Preferably, the at least one plastic component of the container is selected from a plastic container body, a plastic container closure, a plastic structure that functions as a wipe surface to facilitate removal of excess coating composition from a coating applicator, a plastic structure that functions as a spout to facilitate pouring of the water based coating composition out of the container, and combinations thereof. Under some circumstances, it 25 may be preferred that the container comprises a plastic or metal container body and a plastic container closure, with one or both plastic components having the required anti skinning surface layer. It may also be preferable that such a container further comprises a plastic structure that functions as a wipe surface and/or a plastic structure that functions as a spout, with one or both of these components also having the required anti-skinning 30 surface layer Preferred plastic materials from which the at least one plastic component may be made of include, but are not limited to, polyolefms such as polyethylene (e.g. high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE)) and polypropylene (PP), and polyesters such as polyethylene 5 terephthalate (PET). The at least one plastic component used in accordance with the invention may be fabricated using techniques well known in the art such injection moulding, blow moulding, rotational moulding, extrusion, thermoforming and the like. 10 In accordance with the present invention, the container comprises at least one plastic component having an anti-skinning surface layer. As used herein, the expression "anti skinning surface layer" is intended to denote a layer of material that is located on the surface of at least one plastic component of the container. This surface layer is believed to 15 function as a tie layer between the at least one plastic component and the coating composition to promote adhesion between the plastic component and the coating composition and thereby avoid or reduce the problem of skinning. In other words, the layer of material is believed to function as an "anti-skinning" surface layer by promoting adhesion of the coating composition to the plastic component. 20 Preferably, the anti-skinning surface layer is present on the at least one plastic component as a substantially continuous coating and with a substantially uniform thickness. Generally, the anti-skinning surface layer will have a thickness ranging from about 1 micron to about 50 microns, preferably from about 5 microns to about 25 microns. 25 In accordance with the invention, the anti-skinning surface layer is formed from a single part coating system. Those skilled in the art will appreciate that a "single part" coating system is distinct from a multi part (e.g. two part) coating system in that the former does not require the addition of a curing agent prior to the application of the coating whereas the 30 latter does. In multi part systems, where the addition of curing agent is required, those skilled in the art will also appreciate that once the curing agent has been added there is a -9 relatively short period of time available to apply the composition to the desired substrate before the composition cures into an unworkable mass. Furthermore, it will generally be critical that the correct proportions of each component are mixed to ensure the effective cure and functionality of the multi part coating system. Multi part coating compositions 5 therefore present a number of practical processing problems such as the correct weighing of each component, the inability to store unused coating composition for subsequent use, and difficulties with cleaning application equipment on or in which the coating composition has cured. 10 In contrast, single part coating systems used in accordance with the invention will generally cure primarily through solvent evaporation and therefore enable unused composition to be readily stored in a sealed container for future use. Furthermore, due to more generous curing times associated with single part coating systems, the cleaning of application equipment is generally much easier. 15 The anti-skinning layer formed from the single part coating system has a surface tension of at least 38 dynes/cm (mili N/m). Those skilled in the art will appreciate that surface tension can be readily measured using standard test ink sets available from companies such as 3DT LLC (USA). Such standard test ink sets contain ink having a range of known 20 surface tensions that may be sequentially applied to the surface of interest. The surface tension of the surface to be tested is said to correspond to that of the test ink which first, in sequential test order (i.e. low dyne to high dyne), enables a continuous line to be drawn on the test surface. 25 Preferably, the surface tension of the anti-skinning layer ranges from 38 to about 46 dynes/cm. Polyolefins such as polyethylene and polypropylene typically have a surface tension of about 30 dynes/cm. Accordingly, the effect of applying the anti-skinning layer onto such 30 plastic materials is to increase their effective surface tension. It is preferred that such an increase in surface tension is provided in an even and uniform fashion across the surface of -10 the at least one plastic component. As discussed above, the required surface tension provided by the anti-skinning layer is believed to promote adhesion between the coating composition and the at least one plastic component. 5 Prior to the application of the anti-skinning layer to the plastic component, it is preferred that the surface of plastic material to be coated is flame treated or exposed to carona discharge to further enhance the adhesion between the anti-skinning layer and the plastic. Those skilled in the art will be familiar with the various ways that can be used to apply the 10 single part coating system to the surface of plastic components. The coating may be conveniently applied using any conventional technique employed in the art. For example, the coating may be painted or sprayed onto the at least one plastic component. 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 system onto the 15 surfaces of the at least one plastic component. Once the single part coating system has been applied it is allowed to cure to form the anti skinning surface layer. The coating system may be simply left to cure at ambient temperature until dry, or various means can be employed to increase the rate of curing such 20 as air flow drying, exposure to elevated temperatures and the like. Depending upon the nature of the plastic component, the entire component or only parts thereof may be coated with the anti-skinning surface layer. For example, components such as a plastic spout or plastic wipe surface may have their entire surface covered with the 25 anti-skinning surface layer, whereas a plastic container body and a plastic container closure may only have their inner surfaces (i.e. the surfaces which the define the inner region of the sealed container) covered with the anti-skinning surface layer. Having said this, it will be appreciated that it may be more convenient in some cases to simply apply the anti skinning surface layer to the entire plastic component or container rather than only to the 30 part(s) of the component or container that make contact with the coating composition during normal use of the container.

- 11 Any single part coating system may be used in accordance with the invention provided that it can form an anti-skinning layer having the required surface tension. The single part coating system will also of course have an adequate binding affinity to the plastic 5 component in order to form the required anti-skinning surface layer. Examples of suitable single part coating systems include, but or not a limited to, those which comprise halogenated polymer. Without wishing to be limited by theory, it is believed that halogenated polymer in such coating systems provides for a desirable surface 10 tension of the resulting anti-skinning layer. Examples of suitable halogenated polymers include, but are not limited to, chlorinated polymers such as chlorinated rubber and co-polymers of vinyl chloride such as a vinyl chloride/vinyl acetate co-polymer, and combinations thereof. 15 Examples of suitable single part coating systems for use in accordance with the invention include, but are not limited to, Luxaprime UMP and Luxachlor T sold by Dulux Australia. The method in accordance with the invention of modifying a plastic component for a 20 container suitable for a water based coating composition may also form part of an overall method of manufacturing the component per se. Accordingly, the invention also provides a method of manufacturing a plastic component for a container suitable for a water based coating composition, said method comprising moulding the plastic component and applying an anti-skinning coating to a surface of the plastic component that makes contact 25 with the water based coating composition during normal use of the container, wherein the anti-skinning coating is a single part coating system and forms on said surface of the plastic component an anti-skinning layer having a surface tension of at least 38 dynes/cm. The method in accordance with the invention of modifying a plastic component for a 30 container suitable for a water based coating composition may also be integrated with a method of packaging a water based coating composition. Accordingly, the invention -12 further provides a method of packaging a water based coating composition, said method comprising the steps of: a) providing a container for a water based coating composition, the container 5 comprising at least one plastic component; b) applying an anti-skinning coating to a surface of the plastic component that makes contact with the water based coating composition during normal use of the container, wherein the anti-skinning coating is a single part coating system and forms on said surface of the plastic component an anti-skinning 10 layer having a surface tension of at least 38 dynes/cm. c) allowing the anti-skinning coating to cure; d) filling the container to the required level with water based coating composition; and e) sealing the water based coating composition in the container with a 15 container closure. In practice, it is expected that a manufacturer of containers for water based coating compositions is likely to modify the appropriate plastic components in accordance with the invention rather than this modification being performed at the site of a coating composition 20 manufacturer prior to the packaging of the coating composition. The invention will now be further described with reference to the following non-limiting examples. 25 Examples Containers consisting of the following componentry were evaluated: a metal container body in the form of a pail with a circular cross-section, a high density polythene closure and a polypropylene plastic collar adapted to securely engage the upper rim of the 30 container body, the collar consisting of an integrated plastic structure that functions as a wipe surface to facilitate the removal of excess coating composition from a coating - 13 applicator and a plastic structure that functions as a spout to facilitate pouring of the water based coating composition out of the container. All plastic components were fabricated via injection moulding. 5 The plastic components were flame treated prior to the application of the anti-skinning layer. Within I day of the flame treatment, single part coating systems respectively comprising 10 chlorinated rubber and vinylchloride co-polymer, were each spray applied onto the internal surfaces of separate plastic container closures, collars and integrated wipe surface and spout structures at a dry film thickness of 5-25 microns. The applied coating systems were allowed to cure overnight at ambient temperature. 15 The surface tension of the applied coatings were each assessed using Dyne pens and found to be 40 Dynes/cm. The effectiveness of the respective anti-skinning layers (i.e. formed from the two different coatings) were assessed by filling the assembled container detailed above (i.e. pail, collar 20 and closure) with an acrylic water based formulation that has been shown to exhibit significant skinning tendencies, sealing the container and then inverting the container subjecting the internal surfaces of the plastic componentry to the acrylic water based formulation. The assembled container containing the acrylic water based formulation was placed upright in an environmental chamber set at 40 degrees celsius for a period of 4 25 weeks. Comparative assembled containers that did not have the anti-skinning layer applied to the plastic components were also included in the test. This testing protocol was found to provide a realistic accelerated test regime that had excellent alignment with real time performance. 30 -14 Following the test period, the internal surfaces of the plastic componentry were visually assessed. The assembled containers that did not have the anti-skinning layer applied showed significant skin formation that was loosely adhered to the plastic componentry. In particular, the skin on the underside of the lid immediately became detached in one 5 uniform piece upon removal of the lid. Skin on other areas of the plastic was also easily detached with gentle agitation of the surface of the skin whereby the skin could be removed in continuous strips. In contrast, the assembled containers that did have the anti skinning layer applied revealed excellent adhesion of the skin to all regions of the internal plastic componentry. Only under severe agitation - not representative of the normal forces 10 the skin is subjected to during normal use - could the skin be removed, although not in the form of continuous strips as seen in assembled containers that did not have the anti skinning layer applied. Throughout this specification and the claims which follow, unless the context requires 15 otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), 20 or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. 25 Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within its spirit and scope. The invention also includes all the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and 30 any and all combinations of any two or more of said steps or features.

Claims (22)

1. A container for a water based coating composition, the container comprising at least one plastic component having an anti-skinning surface layer which makes contact 5 with the water based coating composition during normal use of the container, wherein the anti-skinning layer is formed from a single part coating system and has a surface tension of at least 38 dynes/cm.

2. The container according to claim 1 having a size suitable to contain about 250ml to 10 about 50 litres of the coating composition.

3. The container according to claim 1 or 2 having a container body in the form of a pail and a container closure in the form of a lid. 15

4. The container according to any one of claims I to 3 provided with a wipe surface structure.

5. The container according to any one of claims I to 4 provided with a spout. 20

6. The container according to any one of claims 3 to 5, within the at least one plastic component is selected from one or more of the pail, lid, wipe surface structure and spout.

7. A plastic component for a container suitable for a water based coating composition, the plastic component having an anti-skinning surface layer which makes contact with the 25 water based coating composition during normal use of the container, wherein the anti skinning layer is formed from a single part coating system and has a surface tension of at least 38 dynes/cm.

8. The plastic component according to claim 7 in the form of a pail, a lid, a wipe 30 surface structure, a spout, or a wipe surface structure and spout. -16

9. The container or plastic component according to any one of claims 1 to 8, wherein the plastic component is made from a polyolefin or a polyester.

10. The container or plastic component according to any one of claims 1 to 9, wherein 5 the anti-skinning surface layer has a thickness ranging from about 1 micron to about 50 microns,

11. The container or plastic component according to any one of claims I to 10, wherein the surface tension of the anti-skinning layer ranges from about 38 to about 46 dynes/cm. 10

12. The container or plastic component according to any one of claims 1 to 11, wherein the anti-skinning surface layer comprises a halogenated polymer.

13. The container or plastic component according to claim 12, wherein the halogenated 15 polymer is selected from chlorinated rubber, a co-polymer of vinyl chloride, and combinations thereof.

14. The container or plastic component according to any one of claims 1 to 13, wherein the water based coating composition is selected from paints, varnishes, stains, and inks. 20

15. A method of modifying a plastic component for a container suitable for a water based coating composition, said method comprising applying an anti-skinning coating to a surface of the plastic component that makes contact with the water based coating composition during normal use of the container, wherein the anti-skinning coating is a 25 single part coating system and forms on said surface of the plastic component an anti skinning layer having a surface tension of at least 38 dynes/cm.

16. A method of manufacturing a plastic component for a container suitable for a water based coating composition, said method comprising moulding the plastic component and 30 applying an anti-skinning coating to a surface of the plastic component that makes contact with the water based coating composition during normal use of the container, wherein the -17 anti-skinning coating is a single part coating system and forms on said surface of the plastic component an anti-skinning layer having a surface tension of at least 38 dynes/cm.

17. A method of packaging a water based coating composition, said method 5 comprising the steps of: a) providing a container for a water based coating composition, the container comprising at least one plastic component; b) applying an anti-skinning coating to a surface of the plastic component that 10 makes contact with the water based coating composition during normal use of the container, wherein the anti-skinning coating is a single part coating system and forms on said surface of the plastic component an anti-skinning layer having a surface tension of at least 38 dynes/cm. c) allowing the anti-skinning coating to cure; 15 d) filling the container to the required level with water based coating composition; and e) sealing the water based coating composition in the container with a container closure. 20

18. The method according to any one of claims 15 to 17, wherein the plastic component for the container is in the form of a pail, a lid, a wipe surface structure, a spout, and/or a wipe surface structure and spout.

19. The method according to any one of claims 15 to 18, wherein the plastic 25 component is made from a polyolefin or a polyester.

20. The method according to any one of claims 15 to 19, wherein the anti-skinning coating is applied by spraying to provide the anti-skinning layer having a thickness ranging from about 1 micron to about 50 microns. 30

21. The method according to any one of claims 15 to 20, wherein the anti-skinning - 18 coating comprises a halogenated polymer.

22. The method according to claim 21, wherein the halogenated polymer is selected from chlorinated rubber, copolymers of vinyl chloride and combinations thereof.