Patent Application
20060113712
None
N/A
This invention relates to plastic containers such as pails for holding paint and other liquids on which a film or “skin” may form; and, more particularly, to a surface treatment for interior surfaces of the container to attract a skin formed on the surface of the liquid and to prevent the skin from detaching and breaking up into clumps in the liquid (paint) stored in the container.
Plastic containers are gaining in popularity. Among the reasons for this is that they do not rust, nor are they easily dented during use. Further, plastic containers are readily made in a wide variety of sizes and shapes. The majority of plastic containers are used to hold and store liquids, one type of which includes paints.
Paint is formulated to be applied wet to a surface and then dry once it has been applied. However, some paint tends to dry prior to its application, while still in an un-opened container. This drying is commonly referred to as “skinning”. Tests have shown that skin formation occurs under a variety of circumstances, sometimes even when paint is stored in a hermetically sealed glass jar. While skin formation occurs over time, it has been found to be accelerated by high temperatures; and in some paint formulations, particularly those having low VOCs (volatile organic compounds), the skin forms quicker than for paint formulations having higher VOCs.
If a skin forms in a container prior to opening, it is not necessarily bad. This is because if the “skin” has not fully formed, it can be dissolved or dispersed back into the paint by shaking or stirring the container and its contents. Skin becomes a problem when a fully formed skin does not adhere to the interior surfaces of its container, but instead settles into or on top of the paint stored in the container. This condition manifests itself in one of two ways: first, a sheet or thin layer of skin settles on the top of the liquid; or second, pieces of skin settle down into the paint.
Paint can shakers which mix a color concentrate into a base color (white) in a paint can will cause skin that has not sufficiently adhered to the inside surfaces of the container surfaces to fall into the paint. If an article or surface is now painted using paint from the can, clumps or chunks of paint may be carried by the brush or applicator onto these surfaces and result in a clumpy rather than smooth surface appearance. If a spraying attachment is attached to the paint can, any skin clumps can clog the spraying head of the attachment, requiring that the attachment then be taken part and cleaned.
When paint has been stored in metal cans, skin adhesion has not been a major problem. This is because the skin tends to adhere to metal or “tinplate” from which the paint can is made. For water borne paint formulations, the tinplate has an internal coating or “lining” which serves as a barrier to the metal substrate of the container and keeps the paint can from rusting. Depending on the paint formulation and the type of container lining, skin adhesion may be a problem. However, in general, the problem has been managed, and fillers of paint containers have accepted a slight occurrence of detached skin in the metal cans they fill as a matter of course.
Now, with plastic containers increasingly replacing metal ones, primarily to reduce dents and eliminate rusting, skinning has become a problem. This is due to quicker moisture permeation thru the plastic versus metal containers and because the plastic compounds used for forming paint pails and paint cans are chemically inert. Thus, there is no chemical attraction between the paint and the container and therefore no adhesion of skinned paint to inner surfaces of a plastic container. Fillers of paint cans have found that “floating” a small amount of ethylene glycol on top of the paint will delay the formation of skin; but, lack of adhesion still creates a significant problem and this float material is not an acceptable constituent of low V.O.C. paints.
To promote skin adhesion, covers used on the larger pails are typically flame treated. However, over a relatively brief period of time after flame treatment (a few weeks to possibly two months), the energy of the treated surface returns to its original state and any advantage in promoting adhesion is lost. Paradoxically, this undoing of the energy treatment benefits occurs about the time a skin usually starts to form. Accordingly, it is questionable as whether or not energy treatment alone serves a useful purpose.
The present invention, briefly stated, is directed to a method for promoting adherence of paint “skin” to a surface of a plastic paint container so the skin does not break up into clumps in the paint and be transferred by a paint brush or the like to a surface being painted. The container includes a can, a plug for covering an open mouth end of the can, and a ring secured adjacent the open mouth end of the can and providing means of attachment for the cover. The method first includes molding the can, plug, and ring so they have interior surfaces which are textured, non-smooth surfaces. Next, the interior surfaces of the can, plug, and ring are subjected to a flame treatment after these parts are removed from their molds. This is done to produce a surface energy change of these surfaces. Third, an adhesion promoting material is added to the interior surface of the can, ring, and plug after the energy treatment. This chemical change treatment acts as an adhesion promoting material, which is preferably a chlorinated polyolefin, and causes the paint to adhere to these surfaces. Also preferably, this material is applied within two days after the parts are flame treated so to benefit from the method of the invention as it is implemented. Alternatively, the same invention can be applied to a 2 piece plastic container having a body and cover such as a pail.
Other objects and features will be in part apparent and in part pointed out hereinafter.
The objects of the invention are achieved as set forth in the illustrative embodiments shown in the drawings which form a part of the specification.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what I presently believe is the best mode of carrying out the invention. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Referring to the drawings, a plastic container such as a paint can or the like is indicated generally 10 in
As discussed above, when the container is filled with paint, over time, a skin forms on the interior surfaces of the container within the vapor phase. A problem arises when this skin is allowed to detach from the interior surfaces. To prevent this problem, it is desirable for the skin, once formed, to cling to interior surfaces of the paint container. To achieve this adherence, the present invention is directed to three improvements each of which contributes to causing the paint skin to cling to the container and not break up in the paint.
The first improvement is to modify the molds in which the can, ring, and plug are formed so that rather than the resulting component being produced with a smooth paint contact surface, the surface rather has a textured finish. Referring to
Next, in addition to forming the inside surfaces of the can, ring, and plug as textured surfaces, the method includes treating the respective interior surfaces of these components to produce a an energy change in the surface to improve bonding of paint skin or the third step chemical treatment. This energy treatment can be performed in a number of ways to achieve the desired results. One such way is to direct a flame at each surface after the particular components are removed from their respective molds. Another way is to expose these surfaces to a corona discharge, again after the parts are removed from the molds. A third energy treatment procedure uses a gas plasma.
A third step, the chemical treatment, in the method is to coat the interior surfaces of the can, ring, and plug with a fluid material that further promotes paint skin adherence to the surfaces. This is accomplished by applying a solution to the surfaces after their energy treatment. The material used for this purpose is preferably a chlorinated polyolefin; although the material can be selected from a group of materials which includes liquid chlorinated polyolefin, halogenated, carboxyl modified, hydroxyl modified, or oxidized materials. While an application of one coat of the solution may be sufficient, those skilled in the art will understand that a plurality of coats can be applied, or that the surfaces of the can, for example, may receive multiple coats; while the inner surface of the plug may receive only a single coat.
Referring to
The cans are unloaded from their container and placed upon a conveyor C1. As the cans move along the conveyor, they pass through an energy treating installation FT where they are subjected to a flame treatment, a corona discharge, or a gas plasma environment which produces the desired energy change to the inner can surface. From the energy treatment station, the cans continue along the conveyor to a spray station SP. As the cans pass through this installation, a chlorinated polyolefin (or other preferred material) is sprayed into the interior of the can.
Simultaneously with the cans 12, rings 14 are unloaded from their container and placed on a conveyor C2. The rings are now similarly energy treated and sprayed as they pass along the conveyor. At the end of conveyor C2, the rings 14 are transferred to another conveyor C3. This conveyor moves the rings toward the end of conveyor C1 where the cans 12 are located. Now, an operator O takes a can 12 and ring 14, connects them together and places them in an assembly machine which could be a spin or sonic welder or gluing type unit SW. In this unit, the rings are permanently attached to the cans. The completed assembly is removed from the assembler unit and packaged for shipment to a filler who fills the cans with a paint.
At the same time the cans and rings are being treated and assembled together, the plugs 16 are deposited on a conveyor C4 and also energy treated and sprayed. After these treatments, they are also forwarded to the filler for closing the paint cans after they have been filled with paint. After the cans are filled, the plugs are put in place and the filled, closed containers can be inventoried, or set sent to a retail outlet for sale to the consumer. Regardless of whether the container sits on a shelf for a while, or is sold and the contents used relatively soon after filling, the method of the invention insures that if a skin does form on the interior surface of the container, the skin will adhere to these surfaces of the paint can, or the cover, and not break up into clumps.
In view of the above, it will be seen that the several objects and advantages of the present invention have been achieved and other advantageous results have been obtained.
