Field of the invention

[0001] The invention relates to a method of processing a porous article.

Background

[0002] Most natural stones are porous. The pores allow water, air pollutants, or the like compounds, to penetrate into the stone structure. The resulting chemical reactions, if any, and/or physical phenomena, such as changes in states of water, may deteriorate the durability of stone. In addition, compounds penetrating into the stone may produce undesirable changes in the appearance of the stone.

[0003] There are known methods intended_forLprocessing stones, which methods are to prevent or at least reduce occurrence of the above- mentioned problems. Typically, in the methods polymer coatings are applied on the surface of the stone, which coatings are to block pores on the surface of the stone.

[0004] However, the known methods have some drawbacks, for instance, the fact that the coatings provide a thin surface layer on the stone which is easily damaged by the effect of UV radiation, for instance, and which, after damaging, no longer protects the stone.

Brief description

[0005] A solution may be presented for a method for processing a porous article, the basic idea of the method comprising: treating the article with a hydrophobicity enhancing component that is arranged in a treatment mixture in fluent state, dispensing the treatment mixture on the surface of the article, arranging a wall that is at least substantially impermeable to the treatment mixture on the article surface comprising the treatment mixture in such a way that the treatment mixture is between the article and said wall, and allowing the hydrophobicity enhancing component to absorb into the article from the space between the wall and the article.

[0006] An advantage with the method is that a porous article may be treated hydrophobic in an affordable manner not only on the surface but also in a subsurface layer: the stone may be made hydrophobic even throughout. [0007] According to an embodiment, the article comprises porous mineral material.

[0008] According to an embodiment, the mineral material is natural stone, such as marble.

[0009] According to an embodiment, recesses are provided in the surface of the article and the treatment mixture is dispensed in said recesses.

[0010] According to an embodiment, the recesses comprise grooves.

[0011] According to an embodiment, the recesses comprise pits.

[0012] According to an embodiment, the volume of recesses is dimensioned such that said volume corresponds to an estimated pore volume in the article.

[0013] According to an embodiment, a wall is provided by using a plastic film.

[0014] According to an embodiment, the plastic film is a shrink film.

[0015] According to an embodiment, the processing is carried out when the temperature of the article is within a temperature range of 50 to 120 °C.

[0016] According to an embodiment, the surface of the article comprises a layer of particles comprising a photocatalytic compound, e.g. titanium dioxide ΤΊΟ2, and a hydrophobicity enhancing component is allowed to absorb into the article through said layer.

[0017] Inventive embodiments are also disclosed in the specification and drawings of this patent application. The inventive content of the patent application may also be defined in other ways than those defined in the following claims. The inventive content may also be formed of several separate inventions, especially if the invention is examined in the light of expressed or implicit sub-tasks or in view of obtained benefits or benefit groups. In such a case, some of the definitions contained in the following claims may be unnecessary in view of the separate inventive ideas. Features of the different embodiments of the invention may within the scope of the basic inventive idea be applied to other embodiments.

Brief description of the figures

[0018] Some embodiments will now be described in greater detail, with reference to the attached drawings, in which Figure 1 shows schematically a partly cross-sectional side view of a step in a method,

Figure 2 shows schematically a partly cross-sectional side view of a step in a second method,

Figure 3 shows schematically a partly cross-sectional side view of a step in a third method,

Figure 4 shows schematically a partly cross-sectional side view of a step in a fourth method,

Figure 5 shows a detail in the partly cross-sectional side view of the method step of Figure 4, and

Figure 6 shows schematically a partly cross-sectional side view of a step in a fifth method.

[0019] For the sake of clarity, the embodiments are shown in the figures in a simplified manner. Like reference numerals refer to like parts in the figures.

Detailed description

[0020] Figure 1 shows schematically a partly cross-sectional side view of a step in a method. An article 1 is a plate-like object made of natural stone. It should be noted that, naturally, the article 1 may be of some other shape or completely different in essence, e.g. a powdery product comprising natural stone or some other mineral material.

[0021] Typically, natural stone comprises pores, and therefore water and impurities may penetrate into the stone. Examples of impurities include dissolved acids, dirt of organic origin and other pollutants, such as sulphur, sulphur oxides and nitric oxides. Impurities migrate into the article 1 mainly along with water. Some natural stores are particularly susceptible to damage by the effect of water and impurities. Marble may be given as an example. It should be noted, however, that, apart from marble, the natural stone included in the article 1 may be e.g. chalk, sandstone, granite, gneiss, limestone, etc.

[0022] The article 1 may comprise concrete, cement, gypsum, burnt or unburnt bricks, or any other mineral-rich and pore-containing material. Further, the article 1 may be powdery or granulated, mineral-rich material, such as gypsum.

[0023] An idea of the present method is to treat the article 1 so that water and impurities dissolved or undissolved therein, will be prevented, at least to some extent, from penetrating into the article 1. The method may ena- ble hydrophobization of the article, i.e. modifying the article more water repellent at least on the surface. According to an embodiment, the article is processed more water repellent to some extent deeper than the surface. According to another embodiment, the article is processed to be water repellent all over, i.e. throughout.

[0024] In the solution of Figure 1 , the article 1 is arranged in a closed space 3 provided by a wall 2. In the closed space 3 there is also arranged a treatment mixture 4. The treatment mixture 4 contains a component that enhances hydrophobicity of the article 1 . The treatment mixture 4 is dispensed directly on the surface of the article 1 , in this case on the upwardly orienting surface of the article 1. Dispensing may be so abundant that a substantial amount of the treatment mixture 4 also runs on the side of the downwardly orienting surface of the article.

-[0025]— he-article-1-and the treatment mixture 4 < are kept in the closed space 3 for a time required by the treatment, i.e. the processing time. The duration of the processing time is determined by, inter alia, material properties of the article 1 , physical and chemical properties of the treatment mixture 4, desired depth of hydrophobic treatment, and conditions prevailing during the processing, i.e. atmospheric pressure and temperature.

[0026] In an embodiment the treatment mixture 4 comprises a hydrophobicity enhancing component alone. In a second embodiment the hydrophobicity enhancing component is mixed into a carrier, whereby the treatment mixture 4 comprises both the hydrophobicity enhancing component and the carrier. The hydrophobicity enhancing component may be dissolved in the carrier or be insoluble therein. The mixture ratio of components may be selected in a manner that is best suited for the purpose. The treatment mixture 4 is in a fluent form. Typically, it is in a liquid form, but it may at least partly vaporize in the course of the process due to a rise in the temperature and/or a decrease of pressure.

[0027] The hydrophobicity enhancing component may be, for instance, an organic compound having a carbon chain of 2 carbon atoms or more. These compounds are efficient hydrophobic agents. The molecular chain of said organic compound may comprise hydrocarbon, fluorocarbon or a mixture of hydrocarbon and fluorocarbon groups. The organic compound may comprise a phosphate group (RO-PO3 ^2" ) or a phosphonate group (R-PO3 ^2" ), a phosphonic acid group (RR'P0 ₂ H), where R and R' are organic groups, such as -CH3, containing at least one carbon atom, or a corresponding salt. The organic compound may comprise polyphosphate or polyphosphonate or, generally, a polymer containing phosphate or phosphonate groups, for instance, a fluoropolymer, such as polytetrafluoroethylene.

[0028] The hydrophobicity enhancing component may also be a silicone compound.

[0029] The carrier may include a solvent, such as petrol, thinner, turpentine, 1-methoxy-2-propanol, methanol, ethanol, propanol, acetone, buta- nol, ethylene glycol, tetrahydrofurane, dimethyl sulphoxide, cyclohexane, etc., or a combination thereof.

[0030] In an embodiment of the method, the treatment mixture includes pigments or colorants which may change the appearance of the article 1.

[0031 ] The wall 2 m ay be elastic in essence and made for instance; of plastic film of thermoplastic or thermoset polymer material. Alternatively, the wall 2 may be substantially rigid, for instance, made of plastic board, or the like. Further, some of the walls 2 may be elastic and some substantially rigid.

[0032] The closed space 3 is closed at least to the extent that the treatment mixture 4 or at least a component thereof cannot evaporate, flow out or otherwise exit the closed space 3. Thanks to this, the surface of the article 1 will stay uniformly moist, and the component ratio in the mixture 4 does not change during the treatment process - apart from differences, if any, due to migration of said components into the article 1. According to an idea, air may be removed from the closed space 3 partly, or substantially completely, prior to closing the space.

[0033] The hydrophobicity enhancing component penetrates into the pores of the article 1 at least partly by the effect of capillarity. The components and their proportions in the treatment mixture 4 are selected such that e.g. its viscosity, surface tension in relation to the surface of the article 1 , possible dry solids content, etc., are optimal. Because the composition of the treatment mixture 4 does not change at least substantially in the course of the process, thanks to the closed space 3, the processing time of the article 1 may be adjusted freely to have a necessary duration. Thus, the hydrophobicity enhancing component may be ensured to have sufficient time to penetrate into the article 1 to a desired depth. The duration of the treatment may be from 10 minutes to 10 hours, or even more. [0034] The treatment may be carried out once, or it may be repeated twice or more times. Repeated treatment refers to the fact that more treatment mixture 4 is added to the process after the earlier introduced treatment mixture 4 is partly or completely absorbed into the article 1. The added treatment mixture 4 may have the same composition as the earlier treatment mixture 4, or it may differ therefrom.

[0035] The article 1 may be left for treatment, which does not require any active processing by the operator or treatment means, after the article 1 and the treatment mixture 4 have been enclosed inside the walls 2. Thus, the method may be implemented extremely cost-effectively.

[0036] The penetration depth or saturation depth or treatment depth of the hydrophobicity enhancing component may be selected according to need, for instance, on the basis of the use or the environment of use of the article 1.

[0037] In an embodiment, the article 1 , for instance a plate-like product as shown in Figure 1 , is treated on one surface, i.e. side, alone, in other words, the treatment mixture is absorbed into the article through the surface on this one side alone. In a second embodiment, the article 1 , for instance a plate-like product as shown in Figure 1 , is treated on two sides, in other words, the treatment mixture is absorbed into the article 1 , for instance through surfaces on two opposite sides of the article. In a third embodiment, the article 1 , for instance a plate-like product as shown in Figure 1 , is treated through more than two of its sides.

[0038] In all the above-mentioned embodiments, the article may be treated throughout, in other words, in such a way that at least substantially the whole volume of the article 1 is treated to be hydrophobic. It is also possible to proceed in such a way that the surface of the article 1 is treated just to a given depth, and consequently the article 1 may have untreated portions.

[0039] It may be preferable to treat the article 1 throughout, because, as known, the atmospheric humidity condenses at the so-called dew point. When the article 1 is placed, for instance, in such a way that one of its surfaces is at a higher temperature than another surface, the dew point may be found inside the article 1. Moreover, the location of the dew point may change as the thermal conditions change. If water vapour condenses to water inside the pores of the article 1 , said water in the pores of the article 1 freezes as the temperature goes below zero. Freezing water may break the article 1. When the pores of the article 1 are treated to be hydrophobic at least substantially throughout the whole volume of the article, only very little water may condense in the pores, whereby said problem is avoided, or at least its importance to the life cycle of the article 1 may be reduced.

[0040] Figure 2 shows schematically a partly cross-sectional side view of a step in a second method. On the surface of the article 1 there is arranged a treatment mixture 4 that is enclosed against the article 1 by a wall 2. The article 1 and the wall 2 provide between them a closed space which the treatment mixture 4 fills at least substantially. The wall 2 prevents or reduces evaporation of the treatment mixture 4.

[0041] It should be noted that in Figure 2 the wall 2 is placed at a distance from the article 1 and the treatment mixture 4, in other words, the wall has not yet been arranged into place to provide the closed space.

[0042]^Fhe edges of the wall 2 may be attached directly to rthe article 1 , or alternatively, to a suitable support structure, which in turn is arranged tightly against the article 1.

[0043] The wall 2 may be made of elastic material, for instance, plastic film. In an embodiment the wall 2 is of shrink film, i.e. plastic film that can be tightened against the treatment mixture by means of heat.

[0044] On the surface of the article 1 there is arranged a layer 15 that comprises particles containing a photocata lytic compound. The treatment mixture is allowed to absorb into the article 1 through the layer 15.

[0045] The photocatalytic compound may be, for instance, titanium dioxide T1O2, silver Ag, cerium oxide CeO2, magnesium tantalum oxide MgTa ₂ O ₆ , zinc sulphide ZnS, zinc oxide ZnO, tin oxide SnO ₂ , either in pure form or alloyed, precursors of said compounds or various combinations thereof.

[0046] The photocatalytic compound is of material, in which UV light and/or visible light may activate photocatalytic reactions degrading organic compounds. The particles containing the photocatalytic compound may be in the order of nano size, in other words, 1 to 100 nm, or micrometre size, in other words, 0.1 to 100 μητι.

[0047] Figure 3 shows schematically a partly cross-sectional side view of a step in a third method. The article 1 is arranged in a closed space 3 defined by the wall 2. In this respect the solution resembles that shown in Figure 1. [0048] Here the treatment mixture is arranged in an absorption element 5. The absorption element 5 may be an elastic and porous, spongy or cushion-like element that is made of natural or synthetic material, such as cotton, cellulose or foamed plastic.

[0049] The absorption element 5 is placed in contact with the surface of the article 1 , and it may be attached to the article 1 , for instance, with glue, adhesive tape or with mechanical attachment means such as clamps.

[0050] The absorption element 5 is saturated with the treatment mixture 4 either before the absorption element 5 is arranged in contact with the article 1 or after said arrangement. The treatment mixture 4 migrates from the absorption element 5 onto the surface of the article 1 and further into its pores.

[0051] Around the article 1 and the absorption element 5 there are arranged walls 2 which prevent or reduce evaporation of the treatment mixture 4 or at least a component thereof.

[0052] Figure 3 shows an option of heating 6 the article 1 , the treatment mixture 4 and the absorption element 5 during the process.

[0053] The hydrophobization of the article 1 may be carried out at room temperature, i.e. when the temperature of the article 1 is about 20 to 25 °C or even lower than that. An advantage is that consumption of thermal energy is low. Alternatively, the treatment may be carried out at an elevated temperature, whereby the temperature of the article 1 may be 50 to 120 °C, for instance. The elevated temperature may speed up the absorption of the treatment mixture 4 into the article 1. Thus, the processing of thick articles 1 , in particular, can be expedited. The elevated temperature does not increase the evaporation of the treatment mixture 4 from the process, because the treatment mixture 4 is in the closed space 3. Naturally, the elevated temperature may also be utilized in those embodiments of the method, where no absorption element 5 is used.

[0054] In an embodiment of the method, the wall 2 comprises shrink film that is made to shrink by heating. The shrinking shrink film presses the absorption element 5, which enhances migration of the treatment mixture 4 soaked therein into the article 1. The shrink film may be arranged, like any other implementation of the wall 2, to cover only one surface, such as a rear surface 10, of the article, or several surfaces, or to envelope the whole article 1.

[0055] Figure 4 shows schematically a partly cross-sectional side view of a step in a fourth method, and Figure 5 shows a detail of Figure 4. [0056] The article 1 may be, for instance, a lining plate which is used for wall lining in buildings and which is made of marble, for instance. The article has a rear surface 10, which is arranged to face the framework of the wall to be lined, and a front surface 11 , which provides part of the visible surface of the lining.

[0057] The rear surface 10 is provided with recesses 7, which in this embodiment are grooves extending from one edge of the rear surface to the opposite edge. The grooves are arranged mutually parallel in such a way that two adjacent grooves are at a first distance 8 from one another. The cross section of the grooves is here square-shaped, but this is not necessary. The cross section may also be rectangular, etc.

[0058] All recesses 7 may be equally deep - like in the present embodiment - but, alternatively, some recesses 7 may be deeper than others. Other dimensions-— such as width— of the recesses 7 may be mutually the same or they may be different.

[0059] The width and depth of a groove may be, for instance, 1 to 10mm, e.g. 5mm, if the thickness 9 of the article 1 is in the order of 40 to 50mm. In that case, the first distance 8 may be, for instance, 5 to 20mm, e.g. 13 to 16mm. The recesses 7 are preferably designed such that they do not substantially deteriorate the strength properties of the article 1.

[0060] The recess 7 may be a groove that extends from edge to edge in the surface of the article. In that case, the groove ends may be closed by the wall 2 or another element. The recess 7 may also be a groove that is closed at one end or both ends and that does not extend from edge to edge in the article. The recess 7 may be a pit, for instance a blind hole whose depth is selected not to extend through the article. The cross section of the blind hole may be round. A recess 7 of this kind may be made by drilling, for instance. The recess may be a blind hole having a polyhedral, such as triangular, square etc., cross section.

[0061] Figure 5 shows how the treatment mixture 4 is dispensed in the recess 7. In practice, it is possible to proceed in such a manner that the treatment mixture 4 is poured onto a horizontally placed article 1 , and by the effect of gravity the treatment mixture finds its way into the recesses 7, i.e. in this case into the grooves. The treatment mixture may also be dispensed into an absorption element 5 described in connection with Figure 3. [0062] The article 1 is preferably placed in such a way that the bottom of the grooves is in a substantially horizontal position. Thus, the treatment mixture 4 does not tend to flow out of the grooves.

[0063] The recesses 7 serve as storage and absorption spaces for the treatment mixture 4 so that the amount of the treatment mixture 4 and the contact surface between the article and the treatment mixture 4 will be increased, and the dwell time of the treatment mixture 4 on the surface of the article 1 may be prolonged. The recesses 7 facilitate the control of the treatment mixture 4 on the surface of the article 1. In addition, the treatment time of the article may be shortened in comparison to the article not comprising recesses. Yet another advantage is that the recesses 7 may be designed such that their volume is sufficient to receive a required amount of treatment mixture 4 for the processing of the article . The number and size of the recesses 7 may be optimized according to the properties and the desired treatment 61 Vrie articleT Said properties include, i.a. material and dimensions of the article, thickness of the layer to be hydrophobicized etc.

[0064] When the purpose of the treatment is to hydrophobicize the pores in the whole volume of the article, i.e. to impregnate the article 1 substantially throughout, there is determined an average degree of porosity in the manufacturing material of the article 1 , i.e. the ratio of pore volume to total volume. For instance, a typical degree of porosity in the marble is 1 to 3% (vol.). On the basis of the degree of porosity is determined the volume of pores contained in the article 1 concerned. Recesses are produced in the article 1 in such a way that their volume is at least equal to the volume of pores calculated above in the article . In an embodiment, the volume of recesses is exactly the same as the calculated volume of pores in the article. In that case, the amount of treatment mixture 4 required for the treatment will be dispensed by filling up the recesses 7. To give an example: if the pore volume in the article 1 is determined to be 625 cm ³ , the article whose length is 1000 mm may be provided with groove-shaped recesses which are 5 mm in width and depth and 1000 mm in length. When these recesses are produced at the intervals of 40 mm, the total volume of the recesses will be 625 cm ³ .

[0065] The rear surface 10 of the article and the recesses provided therein may be covered with a tight wall 2, such as a plastic film or the like. The wall may comprise a shrinking portion, for instance of shrink film, or it may be unshrinkable. [0066] The wall 2 may be attached to the article 1 with attachment means, e.g. a double-faced adhesive tape 12, whereby a closed space is formed on the rear side of the article. The closed space may be mainly provided by the volume of the recesses 7. In that case the wall 2 may be in contact with the portions of the rear surface 10 between the recesses 7. This is not necessary, however, but the wall may be at least partly off from the rear surface 10.

[0067] Figure 6 shows schematically a partly cross-sectional side view of a step in a fifth method. In this embodiment, the article 1 is placed in a horizontal position with the rear surface 0 facing down and the front surface 11 facing up. Naturally, the recesses 7 provided in the rear surface 10 thus open downward.

[0068] The article 1 is arranged in a closed space 3 which is provided by- a wall 2-The wall comprises two parts ¾ ^~ 2brwhich are tightly attached to one another, for instance, by using adhesive tape, glue, heat sealing or an openable connection element, such as a zipper or Velcro tapes, or the like. The wall parts 2a, 2b may be manufactured of mutually different materials, which feature is highlighted by different dashed lines in Figure 6. It should be noted that, for ease of illustration, the first wall part 2a is shown only in part in the figure.

[0069] In the closed space 3 is fed a necessary amount of treatment mixture 4 either before closing it or after closing it by using a specific dispensing channel. The treatment mixture may be fed onto the upward facing surface of the article 1 , whereby it runs over the edges of the article 1 on the other side thereof. In the embodiment of Figure 6 the procedure takes place in this manner: the treatment mixture 4 running below the article fills the recesses 7 and diffuses 13 not only through said recesses but also from other surfaces of the article into the pores of the article 1. The treatment mixture 4 may be dispensed so abundantly that the article 1 will be covered all over with it.

[0070] In some cases, features disclosed in this application may be used as such, regardless of other features. On the other hand, when necessary, features disclosed in this application may be combined in order to provide various combinations.

[0071] The drawings and the relating description are only intended to illustrate the idea of the invention. It is apparent to a person skilled in the art that the invention is not restricted to the embodiments described above, in which the invention is described by way of example, and many modifications and different embodiments of the invention are possible within the scope of the inventive idea defined in the following claims.