TREATING EARTHENWARE BODIES

Abstract: A method of treating earthenware bodies to enhance resistance to freezing and to assist the application of decals and the like thereto comprises treating the bodies with a liquid medium containing a water-repellant material such as silicone. In a subsequent drying step, the bulk of the liquid medium is removed while leaving the water-repellant material deposited in the pores of the earthenware body. In this way, subsequent entry of water and freezing and cracking is resisted. It has also been discovered that the treatment also enchances the ability of the earthenware surface to receive decals and the like without the need for glazing and an additional firing step.

Description: TREATING EARTHENWARE BODIES This invention relates to the treatment of ceramic and other earthenware bodies, and is particularly but not exclusively concerned with the treatment of fired clay bodies in the form of ceramic garden or patio pots. Other applications include hanging pots, wall hangers, house bricks and ceramic roof tiles, or any other ceramic, fired clay or earthenware article. One particular problem associated with ceramic pots and containers intended for use outdoors eg in gardens, patios and on walls, is the tendency towards damage due to the action of frost. It is a well-known fact that when water is absorbed into the walls of porous earthenware pots, freezing temperatures will cause that water to expand and the pots will often crack, laminate, effloresce or simply fracture. Attempts have been made in the past to obviate this problem by making surfaces of the pot water repellent or waterproof, eg by glazing. If the glaze is applied while there is still some moisture in the earthenware then freezing temperatures will nevertheless have the same detrimental effect on the ware. Further, it has been found that because of the environment in which garden or patio pots are used and located, damage is often suffered by the glaze, allowing ingress of water or moisture which is acted upon by the freezing temperature so that expensive and attractive pots are damaged and often destroyed. Some earthenware pots are decorated by decalco ania transfers or by hand painting, the decoration being then fired onto the surface. It is preferred that the surface area of the pot where the transfer or paint is to be applied is smooth and for this reason the surface is sometimes glazed before applying the transfer or other art work. This process involves an additional firing which adds to the cost of the decorated ware. It is an object of the invention to provide a method of treating ceramic or other earthen ware that does not suffer from some or all of the above disadvantages and which results in a pot which reduces the damage by reason of freezing temperatures acting on the ware, and/or to provide improvements generally. A further alternative object is to attempt to provide a method of treating earthenware and the like to enable it to be more receptive to decals or other decoration without the need for glazing the ware before decorating it. A further alternative object includes attempting to provide ceramic or other earthen ware which does not suffer from the known limitations and faults of ware produced by conventional processes. According to the present invention there is provided a process of impregnating a fired earthenware body and a product made by that process, as claimed in the accompanying claims. In one embodiment, a method of treating a fired earthenware body comprises treating the body with a liquid medium comprising a water-repellent constituent such as silicone, drying the body so as to leave the water-repellent constituent within the pores of the body, whereby resistance to-entry of water and subsequent freezing is improved. In the embodiment, the step of drying the body is preferably carried out at a raised temperature below 200°C, whereby the rate of drying is increased, but degregation of the silicone or other water- repellent material is minimised. In the embodiment, pressure may be applied to cause the water-repellent medium to more thoroughly permeate the porous structure of the earthenware. In another embodiment, an earthenware body is provided with enhanced ability to receive a decal or transfer or other decorative element by treatment with a liquid medium such as a silicone-containing liquid medium (in the form of a solution in a solvent, or a dispersion or emulsion in water, for example) . In this way, it has been found, surprisingly, that the necessity for the provision of a glazed surface for the satisfactory application of decals and the like is avoided. Surprisingly, after treatment with a silicone-containing liquid medium, and subsequent drying, decals can be applied. In a subsequent firing step, in which the temperature is raised above 200°C, the silicone material is removed, while the transfer remains and thus significant advantages are provided over previous techniques in this field. A process of treating ceramic ware according to the invention will now be described by way of example only with reference to the accompanying drawings in which :- Figure 1 is a section view through a drying or other treatment oven containing an earthenware pot r ^ 4 in part of the processing operation; Figure la is an enlarged section of part of the pot seen in Figure 1; Figure 2 is a section view of an impregnation tank containing a pot in a further part of the process; Figure 2a is an enlarged section view of part of the pot seen in Figure 2; Figure 3 is a view similar to Figure 2 in a further part of the process; Figure 3a is an enlarged section view of part of the pot seen in Figure 3; Figure 4 is a section of a drying apparatus; Figure 4a is an enlarged section view of part of the pot seen in Figure 4; Figures 5a, 5b, 5c, 5d and 5e are part sections through the wall of a pot during a process for decorating the fired clay pot. As seen in Figure 1 an earthenware pot P, having side walls W is located within a drying oven 2 and any moisture present within the pot is caused to evacuate. After cooling, the totally dried out pot is then placed within a tank 4 containing a silicone water solution S, which then impregnates the pot hydrostatically. To expedite the impregnation process a lid 6 is sealingly fitted over the top of the tank and compressed air is fed through a port 8 to pressurize the tank as seen in Figure 2. The tank remains in this condition for a pre-determined period of time according to the size and thickness of the pot or pots placed therein, when the earthenware is totally impregnated by the silicone solution S,. If desired, the silicone solution may include any other vehicle besides water, eg a solvent. In this specification, unless otherwise stated, references to a "silicone solution" in water are intended to refer to a solution or dispersion or emulsion of a silicone compound in water, for example an aqueous solution of potassium methyl siliconate. The tank is then depressurized and the solution is drained away via a drain cock 10 as seen in Figure 3. The silicon impregnated wall of the pot is shown in Figures 2a and 3a. The next step in the process is to remove the moisture from the silicone solution S s . To this end, the pot is placed within a kiln 14 and subjected to a temperature of between 100° centigrade and 150° centigrade. This drives the remaining moisture out of the pot in the form of water vapour. Alternatively removal of the moisture content may be effected by subjecting the ware to a vacuum, eg by sealing the ware in a tank and then connecting to a vacuum source or the body may be exposed, after impregnation to a carbon dioxide atmosphere. The earthenware pot is thus fully impregnated with water resistant silicone crystals S s as illustrated in Figure 5a, which is found to be effective in preventing any moisture being absorbed by the fired clay pot and therefore is immune from frost damage. It is frequently desired to decorate earthenware pots by the application of a decal transfer or by hand-painting or spraying. It is found to be beneficial for the transfer or other decorating medium to be applied over an area of the pot or other ware which has been impregnated by a silicone mixture after which the transfer is "fired on" to the ware in the usual manner. Such a preparatory process enables light-fast and waterproof colours to be applied resulting in vivid long-life decorations on the earthenware body. "Fired on" colour is also found to provide the effect of fine lines and detail, giving greater definition on waterproofed ceramic bodies than on porous fired clay bodies. In this process an earthenware pot is dried thoroughly in a drying oven after which the area of the pot to be decorated has applied thereto the silicone based water repellent solution, by painting by brush, by spraying, or by total immersion of the pot in the solution. The pot with its applied solution is next allowed to thoroughly dry after which the art work or decoration eg decal transfer, brush or spray painting, rubber gelatine or silicone stamping, screen printing, montage or thermoplastics technique is applied in the usual manner. The transfer or other decoration is then "fused on" to the pot by subjecting it to kiln firing at a temperature between 700°C and 800°C. During this firing, when the temperature has exceeded 200°C the silicone base burns away without disturbing the transfer, leaving a totally porous pot. Impregnation of the pot with a liquid silicone solution can then be applied as described earlier if so desired. The above decorating process is illustrated in Figures 5a, 5b, 5c, 5d and 5e. Figure 5a illustrates part section of the wall of an earthenware pot showing a small section of the pot being impregnated on the outer surface by a brushed on solution S s of silicon. Figure 5b illustrates the wall of the pot after it has been subjected to a drying operation whereby the outer surface of the wall comprises an internal "skin" of silicone crystals Sc. Figure 5c illustrates the application of a transfer T to the outer surface of the wall of the pot and Figure 5d illustrates the decorative element having been "fused on" into the wall of the pot. Figure 5e illustrates the final resultant wall of the pot after the silicone solution has been impregnated into the pot and the moisture content of the solution has been evacuated leaving the waterproofing silicone crystals Sc within the clay body. In a further process a backing of light coloured paint or a light coloured decal transfer, may be applied to the ware after the initial impregnation of silicone, in order that the colours of the transfer may be more outstanding. In sons circumstances it is beneficial to impregnate the mare with a silicone solution which contains a colouring medium and the ware would then be coloured where impregnation takes place. The ware need not be impregnated by coloured silicone solution over its entire area, only selected bands or other areas being so treated. One method of effecting this is to impregnate the area where colouring is not required with colourless silicone solution. The coloured silicone solution is then applied by brushing, spraying or immersion, the colourless solution acting as a mask to prevent colour passing on to the plain areas. Although the process of the invention has been described with reference to an earthenware pot, it should be understood that it can be used in the treatment of other fired clay products, eg house bricks, roof tiles, and un-glazed floor tiles.

Claims: CLAIMS : - 1 A process of impregnating a fired earthenware body comprising the steps of :- a) drying the earthenware body to render it devoid of any moisture, b) covering at least part of the body with a silicone solution or medium and causing the solution to impregnate , the body, c) drying the body to extract the moisture content of the silicone solution, whereby the earthenware body is at least partly impregnated with waterproof silicone crystals. 2 A process according to claim 1 wherein the body is immersed in a water/si icone solution or medium which is caused to impregnate the body. 3 A process according to claims 1 or 2 wherein the solution is caused to impregnate the body under super-atmospheric pressure. 4 A process according to claim 3 wherein the body is placed within a sealed tank containing water/silicone solution and the tank is pressurized to cause the solution to impregnate the body. 5 A process according to all or any of the above claims wherein drying of the body to expel the water content of the silicone solution is effected by exposing the surface of the body to warm air. 6 A process according to claim 5 wherein the body is treated within a drying kiln. 7 A process according to all or any of the above claims wherein the process is followed by the application of a surface decoration. 8 A process according to claim 7 wherein the body is then fired at a temperature of less than 200°C. 9 A process according to claim 7 wherein the body in then fired at a temperature in excess of 200°C. 10 A process according to claim 9 wherein the body is fired at a temperature of between 600°C and 1500°C. 11 A process according to claims 7-10 wherein the decoration is applied in the form of a decal transfer. 12 A process according to claims 7 - 10 wherein the decoration is painted on the ware by a brush or spray. 13 A process according to claims 7 - 10 wherein the decoration is applied by stamping or impressing by a pad. 14 A process according to claims 7 - 13 wherein an underbody of light coloured paint or a light coloured decal is applied to that area of the ware where the decoration media is to be applied. 15 A fired earthenware body treated by a process according to all or any of the above claims. 16 A method of treating a fired earthenware body to increase its resistance to the effect of freezing, characterised by the step of treating the body with a liquid medium containing a water-repellant material and subsequently drying the body to remove the liquid content of the medium while depositing the water-repellant material in the pores of the body. 17 A method according to claim 16 characterised by the said step of drying the body comprising heating the body to a temperature below that at which the water-repellant material is decomposed. 18 A method of applying a decoration such as a decal to a fired earthenware body comprising surface- treating the body to provide a surface for application of the decoration thereto, characterised by said step of surface treating comprising applying a liquid medium comprising a water-repellant material such as silicone, and drying the body to remove the liquid element of said medium while said water-repellant material remains on the surface of the body for subsequent application of said decoration thereto.

Inventors: MACMULLEN PAUL NEIL, MACMULLEN, PAUL, NEIL
Applicants: MACMULLEN PAUL NEIL, MACMULLEN, PAUL, NEIL
Application year: 1993
Main classification: C04B41
IPC codes: C04B41