CA1269920A - Sole plate for an ironing device - Google Patents

Abstract

Abstract of the Disclosure Sole Plate for an Ironing Device The invention is directed to a sole plate (1) for an ironing device, comprising a base body (12) of high thermal conductivity which is preferably an aluminum casting and has on its fabric contacting surface (27) a porous coating of a mechanically resistant compound (20), preferably metallic or ceramic materials. The mechanically resistant layer (20) of metallic or ceramic materials is coated with an organic bonding agent (26) having particularly good sliding, antiadhesive and sealing properties.

Description

12~:~9~0 Sole Plate for an Ironing Device This invention relates to a sole plate for an ironing device which is made of a metal of high thermal conductivity, preferably aluminum, and has on its fabric contacting surface a porous coating of a mechanically resistant compound, preferably metallic or ceramic materials.
A sole plate of the type referred to above is described in applicant's U.S. Patent No. 4,665,637, issued May 19, 1987. In order to reduce the weight of the ironing device lo making it easier to handle and to improve the thermal conductivity of the sole plate, a sole plate made of aluminum is used. In view of the reduced weight of the aluminum sole plate as compared to conventional materials such as iron or steel, the sliding ability of the fabric contacting surface over the article being ironed is improved.
Since aluminum is known to be less strong than iron or steel, ironing over hard objects as, for example, zippers or buttons tends to scratch the fabric contacting surface, causing burrs protruding from the face of the sole plate similar to a metal cutting operation. When ironing particularly delicate textile fabrics such as silk, these burrs tend to pull threads from the fabric, thereby damaging it. However, such a fabric becomes damaged already when a burr merely roughens the silk luster on the fabric surface.
To avoid these disadvantages, in the above-identified patent the fabric contacting surface was coated with a mechanically resistant layer produced by flame or plasma spraying techniques and preferably made of metallic or ceramic materials. The mechanically resistant layer applied by spraying in this patent has the rn/~

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~ 2 - 05213 ~j disadvantage of being porous and of absorbing in particular water, humidity, air and other foreign substances which may penetrate to the aluminum sole plate. This produces corrosion on the aluminum surface on the side close to the , fabric contacting surface, tending to cause warpage or blistering and even detachment of the mechanically resistant layer. In consequence, the fabric contacting surface of the sole plate is damaged, damaging in turn the textile fabric being ironed in addition to requiring increased forces to move the ironing device across the article being ironed.
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~~ In prolonged-use,~'such sole plates ~nown from the prior art are subject to a great deal of contamination by ad-hering fabric finishing'agents,'stàrch'and textile particles burning into the surface when'the ironing'temperature is too high for these textiles. The result is a dull sole surface impairing the sliding ability across the article being ironed. ~Removing the burnt-in finishing agents by cleaning agents is practically impossible. The only ~ay to restore the sliding ability of the sole plate is to grind off the coating and apply a new coating to the sole plate.

From German published patent application DE-A1-1,952,846, it is further known to coat the metallic fabric contacting surface with a layer of temperature-resistant plastic material as, for example, PTFE, which resists contamination and has a particularly good sliding ability. Sole plates of this type the fabric contacting surfaces of which are made of plastic material are easily scratched and have an insufficient thermal stability, particularly when in con-tinuous use or overheated. Particularly the pla~tic ma-terial becomes locally worn down completely by the pressing action. The scratch resistance is materially reduced . . .

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in particular in sole plates made of aluminum because the hardness of the aluminum base is insufficient. It has been found that ironing over hard objects as, for example, metal zippers or buttons produces deep scores extending into the aluminum surface, causing detachment of the plastic coating whereby the bare metal may become exposed.
Burrs ~re formed at the ends of the scratches which pro-trude from the sole plate and damage the article being ironed. Burrs by the plastic material form already when the plastic material has not yet been worn down to the metal surface.

Accordingly, it is an object of the present invention to provide a sole plate for an ironing device which is highly resistant to scratches while having a good sliding ability, which resists wear, corrosion and the effect of temperature, which is easy to clean and which can be manu-factured simply and inexpensively.

According to the present invention, this object is achieved by coating the mechanically resistant layer of ceramic or metallic material with an antiadhesive and sealing organic bonding agent having particularly good sliding abilities. The mechanically resistant coating applied to the metallic fabric contacting surface of the sole plate using, for example, a flame or plasma spraying or some other economical deposition technique, is inter-spersed with pores and fine channels inevitable with such techniques. The bonding agent applied will seal the pores and fine channels of the mechanically resistant layer such that the steam escaping from the still moist article being ironed cannot penetrate the mechanically resistant layer, whereby damage to the sole plate due to corrosion is avoided.

lXt~ o l _ 4 _ 05213 i ; The arrangemen~ of the invention is highly advantageous in particular with steam irons, since the steam discharged from the steam outlet ports cannot damage the sole plate by corrosion. The sole plate of the invention is also capable of resisting the action of major mechanical forces as they may occur sometimes during the pressing action.
The antiadhesive and sealing coating of the mechanically resistant layer makes it nearly impossible for foreign substances to deposit on the fabric contacting surface.
However, should the sole plate have become contaminated once by burnt-in particles of fabric or plastic, the sur-face can be cleaned ~aaily and without major effort by means of a hard sponge, steel wool or even a special clean-ing~agent~ etc.,-without the surface-showing-any appreciable signs of wear or scratches.
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^- In an improvement of the invention, these advantages are particularly enhanced in a manner essential to the invention by coating the mechanically resistant layer with the bonding agent such that the mechanically resistant layer forming the surface texture is substantially main-tained on the surface of the bonded coating. As a result, the fabric contacting surface has a specific desired rough-ness contributing to the invention as an essential element thereof. It is to be noted that the application of an ex-cessively thick bonded coating to the mechanically resistant layer, while increasing the sliding ability of the sole plate, reduces its scratch resistance, since burrs may form easily in the bonded coating which is relatively soft as compared to the mechanically resistant layer, the burrs causing raised spots on the surface of the bonded coating as already explained with reference to the prior art.
Although the resistivity of these raised burrs is not too high, it is nevertheless sufficient to damage especially delicate textile fabrics.

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Practice has shown that a particularly resistant sole plate results if the surface texture of ~he mechanically resistant layer has a roughness average rating Rt in the range of 10 to 20 micrometers. According to the invention, it is decisive in this sole plate that the micrograph of the roughness of the surface texture on the mechar.ically resistant layer is such that the elevations are smoothed and that the valleys are provided with a microstructure.
By this improvement of *he sole plate of the invention, the elevations which exist on the sole plate surface after the mechanically resistant layer has been sprayed on and which are recognizable as peaks under the micro-scope are truncated. As a result, the surface does not have the effect of a very fine abrasive paper but is capable of sliaing with sufficient ease, causing no appreciable wear on the article being ironed. The rough-ness height is thus reduced. This smoothing operation performed on the surface of the mechanically resistant layer also serves to help the bonding agent to form an easily sealing protective film on the surface of the mechanically resistant layer and to accomplish a still better adhesion of the bonding agent through the micro-structure of the valleys.

With a thickness of the mechanically resistant layer of below 1~0 micrometers, preferably between 50 and 70 micrometers, the effect of temperature produces in the mechanically resistant layer only minor mechanical stresses which are taken up by the elastic properties of the layer.
The stresses are predominantly due to thermal stresses in the (aluminum) sole plate. If the layer was too thick.
stress cracks ~oulc occur causing the layer to detach it-self or to disintegrate into small pieces. This would make the ironing device useless. However, a minimum layer thick-ness is necessary to ensure a sufficient bearir.g strength or resistance to mechanical impacts on the relatively soft surface of the aluminum sole plate.

12~9~20 To substantially maintain the surface roughness of the mechanically resistant layer, the thickness of the bonded coating is advantageously below 10 micrometers. Bonding agents suitable for that purpose are, in particular, resinous binders enriched by PTFE, PFA or silicone. These materials have particularly good sliding properties also in combina-tion with resinous binder, are highly temperature-resistant and, by virtue of the roughness rating of the invention, have good a & esion to the sole plate substrate. When diluted, the bonding agent creeps particularly readily, thereby sealing the pores and fine channels in the deeper regions of the mechanically resistant layer.

To avoid that the fabric contacting surface of the sole plate stains the article being ironed at elevated ~empe`ratures,~ ensuring at the~same time à good appearance of the sole plate as used to be the case previously with . .
prior known uncoated sole plates made of cast iron or steel, the bonding agent of the invention is colorless and transparent. This enables the color of the mechanically resistant layer to shine through.

A preferred dark-gray to black color is obtained by the mechanically resistant layer being composed of a mixture of A12O3 and TiO2, with the mixture ratio being of the order of 2:1. Using these compounds in other suitable mixture ratios, any color gradation from white to gray to black is possible. As a result of the pre-determined fine roughness of the fabric contacting surface of the sole plate, a dull-bright surface is obtained showing excellent resistance to foreign substances and good sliding ability. While the mechanical consistencv of this colorless bonding agent is more sensitive than and not as stable as colored bonding agents, practice has '"`'`- 12~j~920 ` ~ 7 - O 2 .
nevertheless shown that the bonding agent of the invention produces excellent results, without the risk of the article being ironed becoming stained by coloring pigments.
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According to the invention, the bonding agent is ad-vantageously heat-treated by infrared radiation for the purpose of curing the sole plate. By contrast with the conventional hot-air oven drying technique, this is the first time that the bonded coating can be cured in a much shorter period of time, so that on the one hand the manu-facture of the sole plate of the invention is not significant-ly more expensive than the manufacture of known sole plates coated with organic bonding agents, while on the other hand the shorter curing period of the bonding agent largely prevents the expansion of gases in the cavities (pores, shrinkholes) produced in the casting of the aluminum sole plate. In the recirculated air-drying process, it has shown that gas volumes escape from the sole plate aluminum casting because of the substantially longer heat treatment required for curing the bonding agent, causing local warpage of the aluminum sole and/or the bonded coating. These characteristics would also apply in the presence of an additional mechanically resistant layer, unless the bonded coating was treated with infrared radiation. An infrared radiation apparatus builds to substantially smaller dimensions as compared to a conventional drying apparatus, thereby affording price advantages in the manufacture of the sole plate of the invention.

The manufacturing process of the sole plate of the in-vention involves a surface treatment of the mechanically resistant layer prior to the application of the bonding agent. In this process, a mechanica~ surface treatment has proved to be particularly economical, permitting the ~2699;~V

desired roughness height to be maintained accurately.
In"~the process,"the surface of the~mechanicall'y resistant' '' layer is treated such that predominantly only the peaks of the elevations on the surface texture are removed.
Advantageously, this operation is performed by a brush tool smoothing the surface of the mechanically resistant layer within a minimum of time. It is to be understood that other known smoothing methods are also possible, provided the required surface texture is-maintained.

Following smoothing of the surface of the mechanically resistant'layer and, according to a'further invention, its 'sub'sequent cleaning by-àn'inert gas'as, fox exampl'ë,`~CO2 gasj to ob~ain--a grease-free surface,- only such an'amount ;
of bonding agent is applied that the roughness height on the surface of the bonded coating substantially corresponds to the roughness height of the surface of the mechanically resistant layer. This can be accomplished particularly easi-ly by spraying the bonding agent on the surface of the mechanically resistant layer. Spraying permits an extremely fine jet in which the droplets produced, on account of their good creeping ability, are able to penetrate directly into the pores and the fine channels of the mechanically resistant layer, the bonding agent thus coating the surface texture with a nearly homogeneous film. For this purpose, the highly brushable bonding agent which, for example, consists of PTFE, PF~ or silicone and resinous binder with a thinner is diluted in a specific ratio. Already shortly after the bonding agent is sprayed, the highly volatile thinner will evaporate, leaving PTFE, PFA or silicone constituents enclosed in the remaining resinous binder.

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Subsequently, the bonding agent is cured by exposure to infrared radiation, this operation being performed also if the aluminum sole plate is coated with just a coating of bonding agent. For this purpose, quartz lamps are preferably used heating the sole plate rapidly and intensively at acceptable energy cost. The infrared radiation impinging evenly on the sole plate cures the bonding agent within an extremely short period of time.
Such an infrared apparatus also affords the advantage of building to substantially m.ore compact dimensions which is reflected in a correspondingly lower purchase price.

A single embodiment of a surface layer structure of a sole plate of the invention will be described in more de-tail in the following with reference to the accompanying drawing.

In the drawing, there is shown a longitudinal sectional view of the surface of a sole plate 1 of an ironing device, illustrating from top to bottom the individual surfaces of each of the sections 2 to 9 after the respective surface treatment operation. Starting from surface 10, each of the sections 2 to 9 is shown as extending only to a depth of the aluminum base body 12 of the sole plate 1 illustrated by the break line 11, since the sectional views are shown on a greatly enlarged scale.

In section 2, part of the base body 12 is shown as cast.
The base body 12 was made of aluminum using a generally known casting process.

The vertical break lines 13, 14 shown in the sections 2 and 3 of the drawing indicate that part of the layer thickness of the base body 12 has been omitted in this area.

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- This was necessary to be able to illustrate also the surface 10 of the sections 2 and 3 of the drawing. In ; the cross sectional view of the aluminum base body 12, inclusions, shrinkholes or other pores 15 necessarily forming in the casting of aluminum will be recognized.

Following casting of the base body 12, the surface 10 is blasted for cleaning and deburring purposes. The result is approximately the texture of the surface 17 shown in section 3.

Subsequently, the surface 17 is ground until the surface ` 18 produced thereby has a roughness height Rt in the range from 4 to 0.6-micrometers. Grinding is necessary because the base body 12 will warp following casting as-a result of the drop in temperature, producing a very uneven surface 10. Following grinding, oxygen and other impurities ; are removed from the surface 18 by corundum blasting or a similar process. The result is the surface 19 shown in section 5.

The surface 19 is then further treated by applying to it an adhesive vehicle such as nickel aluminum (NiAl) by flame or plasma spraying. The NiAl particles 16 are applied to the surface 19 such as to form not a coherent layer, the reason being on the one hand to improve the adhesion of the coating subsequently applied and, on the other hand, to avoid thermal stress between the aluminum sole plate 12 and the mechanically resistant layer 20.

In the next operation, a ceramic or metallic layer 20 of a mechanically resistant material is applied to the particles 16 and to the partially still uncoated surface 19 by flame or plasma spraying. The surface 21 thus obtained has a roughness height Rt of 30 micrometers, - ~ 9~o - ll - 05213 approximately. In this process, the material of the mechanically resistant layer 20 will fill the voids 22 formed between the particles 16, coating at the same time the surface 19. The material of the mechanically resistant layer 20 will also spread behind the pxojections 24 engaging the voids 22, thereby establishing a partic-ularly intimate and tight bond between the mechanically resistant layer 20 and the base body 12. The NiAl particles 16 are good adhesive vehicles, establishing a particularly durable bond between the aluminum base body 12 and the mechanically resistant layer 20 while at the same time compensating for stresses and strains.

Since the surface 21 of the mechanically resistant layer 20 has particularly sharp-edged peaks 23 resulting from the production method, these are worn down to a pre-determined height in a subsequent mechanical surface treatment as, for example, polishing or brushing. The surface 29 thereby obtained is shown in section 8. In this surface treatment process, thero~ghness height Rt is reduced from 30 micrometers to 15 micrometers, approxi-mately. This smoothing operation has no or only a minor effect on the deeper regions of the valleys 25.

The last but one operation involves spraying of the organic bonding agent 26 as shown in section 9. The organic bonding agent is a combination of PTFE, PFA or silicone with a resinous binder and a thinner. The bonding agent is sprayed on to form such a thin coating that the resulting roughness height of the bonded coating remains almost unchanged relative to the roughness height indicated in section 8. The mechanically resistant layer 20 incorporates a large number of inclusions or pores 28 and fine channels 30 which would allow liquid matter and 9~0 impurities to penetrate unless prevented by the bonded coating 26. The channels 30 are formed as a result of the pancake structure of the mechanically resistant layer 20 produced by the flame or plasma spraying pro-cess. Section 9 does not, however, show the embedding of the bording agent 26 in the deeper subsurface regions of the mechanically resistant layer 20.

In the final operation, the fabric contacting surface 27 of the sole plate 1 is exposed to infrared radiation to dry and cure the bonding agent 26. Infrared radiation heats the sole plate 1 rapidly, curing the bonded coating 26 within a minimum of time without the risk of the heat causing an expansior. in the aluminum base body 12 which would adversely affect the sole plate 1.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A sole plate for an ironing device which has a base portion of a metal of high thermal conductivity, a coating of a mechanically resistant compound on the ironing side of said base portion to provide a surface texture that has peaks and valleys and a roughness average rating of between five and ten micrometers, and an antiadhesive and sealing organic bonding agent coating the surface of said mechanically resistant layer with only a thin film such that the valleys and the regions at the highest peaks of said mechanically resistant layer are coated with only a thin film of said bonding agent, so that the roughness average rating of said mechanically resistant layer is substantially maintained at the surface of said bonding agent, said bonding agent having good sliding abilities and the mean thickness of said thin film being below ten micrometers, preferably between 0.01 and 2 micrometers.

2. A sole plate as claimed in claim 1, characterized in that the surface texture (29) of the mechanically resistant layer (20) has a roughness average rating R1 in the range of 10 to 20 micrometers.

3. A sole plate as claimed in claim 1, characterized in that the micrograph of the roughness of the surface texture on the mechanically resistant layer is such that the elevations (23) are smoothed and that the valleys (25) are provided with a microstructure.

4. A sole plate as claimed in claim 1, claim 2 or claim 3, characterized in that the thickness of the mechanically resistant layer (20) is below 100 micrometers, preferably between 50 and 70 micrometers.

5. A sole plate as claimed in claim 1, claim 2 or claim 3, characterized in that the thickness of the bonded coating (26) is below 10 micrometers.

6. A sole plate as claimed in claim 1, characterized in that the bonding agent (26) is a resinous binder enriched by PTFE (polytetrafluorethylene), FPA (perfluoroalkyloxide polymers) or silicone.

7. A sole plate as claimed in claim 6, characterized in that the bonding agent (26) is colorless and transparent.

8. A sole plate as claimed in claim 7, characterized in that the mechanically resistant layer (20) is composed of a mixture of alumina (Al2O3) and titania (TiO2).

9. A sole plate as claimed in claim 8, characterized in that the mixture ratio of Al203 to TiO2 is approximately 2:1.

10. A sole plate as claimed in claim 1 wherein said base portion is of cast aluminum; and said bonding agent is heat treated by infrared radiation for curing purposes.

11. A method of coating the sole plate provided with a mechanically resistant layer as claimed in claim 1, characterized in that the mechanically resistant layer (20) is surface-treated prior to the application of the bonding agent (26).

12. A method as claimed in claim 11, characterized in that the surface treatment is a mechanical operation.

13. A method as claimed in claim 11, characterized in that the surface (21) of the mechanically resistant layer (20) is treated such that predominantly only the peaks (23) of the elevations on the surface texture are removed.

14. A method as claimed in claim 11, claim 12 or claim 13, characterized in that the surface is treated by brushing.

15. A method as claimed in claim 13, characterized in that only such an amount of bonding agent (26) is applied to the surface (29) of the mechanically resistant layer (20) that the roughness height on the surface (27) of the bonded coating (26) substantially corresponds to the roughness height of the surface (29) of the mechanically resistant layer (20).

16. A method as claimed in claim 15, characterized in that the bonding agent (26) is sprayed on the surface (29) of the mechanically resistant layer (20).

17. A method as claimed in claim 15 or claim 16, characterized in that the bonding agent (26) is applied to a high degree of dilution.

18. A method as claimed in claim 11, characterized in that the bonding agent (26) is cured by infrared radiation.

19. A method as claimed in claim 18, characterized in that a quartz lamp apparatus is used for producing the infrared radiation.