WO2007132394A2

WO2007132394A2 - Method for forming a coating of agglomerated stone on a sheet consisting of light conglomerate material

Info

Publication number: WO2007132394A2
Application number: PCT/IB2007/051686
Authority: WO
Inventors: Luca Toncelli
Original assignee: Luca Toncelli
Priority date: 2006-05-12
Filing date: 2007-05-04
Publication date: 2007-11-22
Also published as: ITTV20060077A1; WO2007132394A3

Abstract

Method for forming a coating of agglomerated stone on a light sheet obtained through compaction by means of vacuum vibrocompression and subsequent hardening of a mix consisting of granules of expanded aggregate, an organic binder and an expanded filler. The method envisages firstly the distribution of a thin layer of very fluid bonding resin on at least one side of the sheet. While the sheet undergoes vibration, small granules of aggregate are sprinkled over the resin layer so as to penetrate into the resin. After hardening of the resin, the coating thus obtained is smoothed or brushed.

Description

"Method for forming a coating of agglomerated stone on a sheet consisting of light conglomerate material"

The present invention relates to a method for forming a thin coating of agglomerated stone on the surface of an article in the form of a sheet made using a light stone-like conglomerate material.

The process for manufacturing these sheets envisages a first step for preparing a mix consisting of an aggregate in the form of light expanded granules, an organic binder consisting of structural resin to which an expanded filler is then added. The various materials are thoroughly mixed together in order to obtain a homogeneous mix.

The following step envisages distribution of the mix thus prepared inside a forming support or mould where it undergoes vacuum vibrocompression. Finally, the mix thus compacted undergoes a hardening step by means of catalysis of the organic binder.

The technology mentioned above forms the subject of the international patent application WO-A-2005 111126 in the name of the same Applicant.

The end result is an article in the form of a sheet which, in addition to other advantageous technical properties, has the positive feature of being very light and therefore easy to process, transport and also arrange in position.

However, this type of article has limitations in that, since the expanded granules are hollow, the surface is porous and therefore, apart from not being particularly attractive from an aesthetic point of view, it is prone to considerable water absorption, albeit on the surface. These negative properties limit the use of these articles to applications which are not visible and exclude their use as components which also have a decorative function, in particular for external environments where the components are exposed to adverse weather conditions. The main object of the present invention is therefore to minimise the superficial absorption of water by these sheet-like articles which are intrinsically porous and provide these articles with a high-quality external appearance, so that they may also be used in external environments without undergoing deterioration with the passing of time.

Another object of the invention is to obtain sheet-like articles which are able to withstand sunlight in particular the ultraviolet component thereof, without the other superior physical and mechanical properties being affected.

A further object of the invention is to obtain articles which can be easily processed, transported and fitted, thereby reducing all the costs associated with the various processing, transportation and fitting costs. These objects are achieved by means of a method for forming a coating of agglomerated stone on sheet-like articles, in particular on a light prefabricated sheet obtained through compaction by means of vacuum vibrocompression and subsequent hardening of a mix consisting of an aggregate in the form of expanded granules, such as for example granules of clay or expanded glass, an organic binder and an expanded filler. The method comprises: a first step where a thin layer (a few millimetres thick) of a very fluid bonding resin which is resistant to ultraviolet rays is distributed on one of the sides of the hardened sheet arranged horizontally; a second step where, while the sheet is undergoing vibration, small granules of aggregate are distributed by means of sprinkling on said layer of resin so as to sink into the resin layer; a third step involving hardening by means of catalysis of the resin containing the granules so as to obtain the coating on said side of the sheet, and a final step involving smoothing or brushing of the coating.

The sheet-like article therefore remains extremely light, with the advantages already mentioned, and advantageously offers, owing to the UV-ray resistant layer of resin containing the granules of aggregate, in addition to a superior surface appearance, the possibility that it may be used also for external use without its aesthetic properties deteriorating over time. In other words, with the method according to the present invention it is possible to provide a permanent coating layer on at least one side of said sheet-like material.

These and other advantages of the present invention will be understood more clearly from the following detailed description provided purely by way of a non-limiting example. The method according to the invention is applied to an article consisting of a composite sheet of expanded conglomerate material which is obtained, for example in accordance with the already mentioned international patent application WO-A-2005 111126 in the name of the same Applicant and which therefore has a thickness approximately of between 10 and 60 mm. In order to obtain the coating on the sheet it would seem logical to spread on its surface a pre-mixed composition of resin, granules and filler. Said application, however, is not industrially feasible since such a mixture would be in practice difficult to distribute in a uniform thin layer and moreover would be prone to separation and the undesirable presence of air bubbles. The method according to the invention therefore comprises the operations below, performed on a sheet hardened beforehand.

A layer of bonding resin with a thickness of between 1 mm and 3 mm, and preferably equal to 1.5 mm, is distributed over one of the two sides of the sheet, if necessary pre-heated to about 4O⁰C. In order to prevent the inclusion of air bubbles inside it, the resin is not supplemented with any filler and has a very low viscosity, in particular between 50 cps and 150 cps, or between 50 and 150 mPa*s. For this purpose, deaerating agents or agents for preventing the formation of air bubbles are also added to the resin.

The resin used must be resistant to ultraviolet rays so that its external appearance is not altered when it is exposed to sunlight; it therefore consists preferably of an aliphatic resin, in particular an acrylic resin, which as is well known has the property that it is unaffected by ultraviolet rays.

Moreover, the resin is suitably formulated so as not to be too rigid and have, after hardening, a tensile stretch value of not less than 35%. It is in fact necessary to avoid bowing of the hardened sheet, and therefore the finished product, owing to the shrinkage which the resin undergoes during the catalysis reaction. A mechanical action, for example brushing, following distribution of the resin on the surface of the sheet, facilitates filling of the surface pores and/or cavities of the hardened sheet, which are induced by the presence of expanded granules in the mix.

In order to improve the adhesion of the resin layer to the surface of the hardened sheet, it is possible to envisage the application of a thin layer (0.1 to 0.2 mm) of adhesion primer prior to distribution of the bonding resin. Said primer consists preferably of an acrylic resin or in any case a resin which is chemically compatible with the bonding resin and is preferably applied by means of brushing, in order to achieve filling of the surface pores and/cavities of the hardened sheet.

Then, the base sheet, coated with the layer of resin in addition to any primer, is subjected to vibration preferably for a duration of roughly between 1 minute and 3 minutes and at a frequency ranging between a minimum value of 100 Hz and a maximum value of 200 Hz. At the same time, granules of aggregate are distributed by means of sprinkling on the bonding resin so as to cause them to penetrate into the resin layer.

In order to avoid separation during falling and during the vibrating action, the dimensions of the granules are kept within a very narrow band (so-called grading range). For example, granules with dimensions ranging between 0.1 and 0.3 mm or between 0.3 and 0.6 mm or between 0.6 and 1.2 mm are used. It is of great importance that sprinkling of the granules be performed slowly and uniformly over the entire surface of the sheet; varied sprinkling would in fact result in the formation of undulations and movement of the resin, so that the coating layer would not have a uniform thickness over the whole surface of the sheet.

The percentage volume of the granules of aggregate with respect to the total coating layer (resin + granules) is between 35% and 65%, and preferably equal to 50%, so that at the end of vibration the coating layer has a thickness of between 2 and 6 mm and preferably equal to 3 mm. In order to withstand the corrosive action caused by air and its polluting substances, - A -

the granules of aggregate are preferably of the silica or alumina-containing type; they therefore preferably consist of natural stone materials such as granite, quartz, siliceous sands or quartziferous agglomerated materials or ceramic materials.

The vibration which the sheet undergoes essentially has two functions: on the one hand it prevents the air, entrained by the falling granules, from remaining trapped in the coating resin, this adversely affecting the integrity of the finished product; and, on the other hand, it causes the granules of aggregate to settle, compacting them more closely together so as to achieve greater filling of the space available on the surface of the hardened sheet; this therefore results in the advantage that the quantity of resin present in the coating layer is kept to a minimum.

In view of the use of acrylic resins, in order to eliminate the possible air bubbles, it is not recommended to use a vacuum during or after sprinkling of the granules of aggregate, since part of the resin in the coating would evaporate.

Finally, during the next step in the method according to the invention, hardening of the resin layer is performed, said layer thus encapsulating in a permanent manner and bonding the granules of aggregate which have been sprinkled during the previous step. Hardening occurs by means of catalysis and may be performed in hot or cold conditions, or at room temperature. In the specific case of acrylic resin it is preferred to perform cold catalysis, i.e. without the application of external heat, the kinetics of which may be better controlled, in order to reduce the degree of shrinkage of the resin which, as mentioned above, could cause bowing of the coated sheet, and prevent evaporation of the volatile reactive monomers with consequent negative effects which may be encountered in the finished product. Obviously, the catalysis activators and regulators must be of the type which do not yellow under the action of the ultraviolet rays. The sheet thus coated undergoes, finally, the various operations of calibrating and smoothing or brushing as well as division into panels of the desired size.

As a result of the coating obtained with the process described above, an article which is aesthetically of superior quality and particularly an article resistant to atmospheric agents and in particular the ultraviolet component of sunlight is obtained. The coating moreover improves substantially the abrasion resistance of the article and, although it has a relatively small thickness, it also helps increase, albeit slightly, the mechanical strength of the article.

It should be noted that, despite the slight difference between the linear thermal expansion coefficient of the base sheet and the coating layer, significant fluctuations in temperature which occur in external environments are not a cause for concern. Both because of the limited thickness of the coating layer compared to the thickness of the hardened layer and the elasticity of the resin used, any difference in the thermal expansion between the base layer and the coating layer in fact produce deformations of a negligible nature.

It is obvious that functionally and conceptually equivalent modifications are possible and may be envisaged while remaining within the scope of the following claims.

For example, the sheet which is coated could be different from that described above, while retaining the characteristic of lightness.

Claims

1. Method for forming a coating of agglomerated stone on at least one side of an article in the form of a light prefabricated sheet obtained in a manner known per se through compaction by mean of vacuum vibrocompression and subsequent hardening by means of catalysis of a mix which is composed of granules of expanded aggregate, preferably chosen from glass or expanded clays, an organic binder and an expanded filler, preferably chosen from hollow microspheres of silicates, expanded igneous rock and expanded granules of thermoplastic material, characterized in that it comprises the steps of:

- placing the sheet so that it is arranged horizontally, - distributing a thin layer of bonding resin on the upper surface of the sheet,

- sprinkling small granules of aggregate and simultaneous vibration of the sheet so as to cause them to penetrate into the layer of resin, eliminating air bubbles and causing settling of said granules closer together,

- hardening, by means of catalysis, the resin layer which incorporates said granules, so as to form a permanent coating layer for the article,

- finishing said permanent coating layer.

2. Method according to Claim 1, characterized in that said bonding resin has a dynamic viscosity not greater than 150 cPs.

3. Method according to Claim 1 or 2, characterized in that said bonding resin and the catalysis activators and regulators are of the type resistant to ultraviolet rays.

4. Method according to Claim 1, characterized in that said bonding resin resistant to ultraviolet rays is an acrylic resin and in that the step for hardening said resin takes place without the application of external heat.

5. Method according to Claim 1, characterized in that the dimensions of said granules of aggregate are within a variation band or grading range not greater than 0.6 mm and preferably not greater than 0.3 mm.

6. Method according to any one of the preceding claims, characterized in that the granules of aggregate which form part of said permanent coating layer consist of natural stone materials or agglomerates or ceramic materials.

7. Method according to Claim 5, characterized in that said natural stone materials are chosen from among marble, granite, quartz and siliceous sands.

8. Method according to Claim 1, characterized in that the vibration of the sheet together with sprinkling of granules of aggregate is performed at a frequency of between 100 Hz and 200 Hz and has a duration of between 1 minute and 3 minutes.

9. Method according to Claim 1, characterized in that said layer of bonding resin has a thickness of between 1 mm and 3 mm and the granules have a size smaller than 2 mm.

10. Method according to Claim 1, characterized in that the percentage volume of the granules of aggregate with respect to the total coating layer, consisting of said bonding resin and said granules, is between 35% and 65% and preferably equal to 50%.

11. Method according to any one of the preceding claims, characterized in that it comprises a preliminary step in which an adhesion primer, which consists of a second resin chemically compatible with said bonding resin, is distributed over said at least one side of said hardened sheet.

12. Method according to Claim 11, characterized in that the adhesion primer consists of an acrylic resin.

13. Method according to any one of the preceding claims, characterized in that the layer to which the coating is applied is heated beforehand to about 4O⁰C.

14. Article in the form of a light prefabricated sheet with a coating of agglomerated stone on at least one side, characterized in that it may be obtained according to the method of any one of the preceding claims.