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The present invention relates to museum display cases; in the following, the term display cases will sometimes be used for the sake of brevity, it being understood that reference is always made to museum display cases.
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Museum display cases have to fulfil many requirements in order to guarantee both the correct protection and preservation of the objects exhibited therein and the best visibility of these objects for the public. Normally, these display cases comprise glass (or in any case transparent) walls assembled together and/or to a frame. Normally, one or more of the walls can be opened to allow access to the interior of the display case.
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In many cases a museum display case has to guarantee a total separation between the exterior exhibition environment and the interior exhibition environment; this is the situation when the display case has to accommodate objects that would be damaged by external environmental conditions. In this case, the museum display case is expected to be airtight and to be equipped with a system to control the internal climatic and air quality conditions, in order to have in the interior exhibition environment a predefined controlled atmosphere that is suitable for the objects exhibited. To this end, the various parts of the display case are assembled by bonding with suitable adhesives and sealing gaskets are provided at the openable walls. The interior environment is thus separated from the exterior environment and can be adequately controlled, with more or less complex air conditioning and filtering systems.
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However, the material of the adhesives, the material of the gaskets and the material of other parts used for the construction of the structure of the display case (e.g. painted parts) are often liable to emit volatile substances harmful to preservation, such as VOCs (volatile organic compounds). In fact, many materials, especially plastics or synthetics, retain more or less large quantities of solvents and volatile chemicals used for production and tend to release them over time; moreover, certain materials gradually transform over time and tend to release volatile substances. If the display case is airtight, the volatile substances emitted towards the interior thereof remain trapped inside the display case and normal filtering systems struggle to remove them. These volatile substances that are present inside the display case can cause unexpected deteriorations of the objects exhibited, despite the presence of accurate systems for the control of the internal atmosphere.
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For the sake of best preservation, it is therefore appropriate to select the construction materials of the display case also on the basis of the emission power thereof, regardless of the performance of the filtering apparatus. However, making an airtight display case without using materials liable to emit harmful volatile substances has proved to be substantially impossible. Above all, all materials that are sufficiently elastic to ensure the tightness of the openable parts, as well as all adhesive materials required to bond glass and metal materials together, and all paints used on glass or metal parts, have been shown to be liable to emit volatile substances.
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An attempt has been made to expose the display case to air for a reasonably long degassing time, so as to allow the natural evacuation of volatile substances before using the display case. However, the results were not satisfactory, as these materials continue to emit volatile substances even after degassing, however long it may be.
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EP 4230089A1 by the same Applicant describes a method for solving this problem by submitting the parts of the display case that are likely to emit harmful volatiles to heating beforehand.
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The present invention addresses the problem of further improving the removal of volatile substances from museum display cases.
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In accordance with the invention, this problem is solved by a method for improving the behaviour of a museum display case in relation to objects exhibited therein according to claim 1, as well as by a museum display case according to claim 8.
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More in particular, according to the invention, a method for improving the behaviour of a museum display case in relation to objects displayed therein, wherein the display case comprises an inner display space, comprises submitting at least the inner display space to a heat treatment, and is characterised in that the heat treatment comprises heating steps at a heating temperature for a heating period alternating with rest steps for a rest period.
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Such a heat treatment allows accelerating the release of volatile substances from the materials liable to emit them that have been used for manufacturing the display case. After such heat treatment, these materials no longer emit volatile substances in significant quantities; consequently, the display case can be used to exhibit relatively delicate objects. It has been verified that alternating heating steps with resting steps achieves the desired removal of volatiles more efficiently. In particular, when comparing such a method with a method involving only heating, without resting steps, it was noted that the same degree of removal could be achieved with much less energy consumption, in only a slightly longer overall time. This is deemed to be due to the fact that the removal of volatile substances, accelerated by the heating, continues to remain accelerated for some time even after the heating has stopped.
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Preferably, the heating temperature is at least 35° C, more preferably about 50° C.
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Preferably, the heating period is at least 24 hours, more preferably about 48 hours.
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Preferably, the rest period is at least 24 hours, more preferably about 48 hours.
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Preferably, all the heating steps and all the rest steps have approximately the same duration.
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Preferably, the heat treatment comprises at least three heating steps alternating with two rest steps.
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In one embodiment, the heat treatment is performed by placing the assembled display case in a treatment chamber. This method ensures uniform treatment of all parts of the display case, but it requires a treatment chamber that is adequately larger than the display case, and is therefore rather expensive.
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Preferably, according to an alternative embodiment method, the heat treatment is performed by placing heating members in the display case. Thereby, the treatment is easier to implement and still allows the volatile substances to be removed from the parts facing the interior of the display case, and it is precisely in these parts that it is important to remove volatile substances: in fact, the emission of volatile substances outside the display case is not a problem, because these substances do not reach the objects exhibited.
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Preferably, during the heat treatment, an air exchange step is periodically performed in the inner display case, for a duration of at least 5 minutes every hour. This allows all the volatile substances emitted during heat treatment to be carried outside the display case.
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Further features and advantages of the invention will best be seen from the following description of a display case according to the invention, shown in the attached figure 1.
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In the drawing, a museum display case 10 is schematically shown, which comprises a base 20, surmounted by a box 30. In the box 30, there is the display space of the display case 10, intended to accommodate the objects to be exhibited, while in the base 20 there is a technical space for housing the systems for the control of the atmosphere inside the box 30 (for example, a simple container with hygroscopic material or a more complex air conditioning and/or filtering system).
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The box 30 comprises a frame 31, typically made of steel, aluminium or another metal material. The box 30 then comprises glass walls mounted on the frame 31, in particular fixed glass walls 32 and at least one openable glass wall 33. The fixed glass walls 32 are welded to each other, to the frame 31 and to the base 20 by bonding, using an adhesive substance (not highlighted in the figure). The openable glass wall 33 is mounted on the frame 31 by means of an openable system, for example a hinge system (not visible in the figure). It should be noted that the frame 31 may be eliminated, either completely or in part, leaving the fixed glass walls 32 - suitably sized and welded together - with the function of load-bearing structure of the box 30; in this case, the openable glass wall 33 is mounted on one or more of the fixed glass walls 32.
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The display case 10 further comprises sealing gaskets 36, both between the openable glass wall 33 and the fixed glass walls 32, and between the openable glass wall 33 and the base 20.
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In the display case 10, the material of the sealing gaskets 36 is liable to emit volatile substances, in particular VOCs, which are potentially harmful to the objects to be displayed in the display case 10. This material is for example a silicone rubber, another elastic material or plastoferrite; the latter material combines excellent elasticity with the possibility of being magnetized, so that the openable glass wall 33 can be closed by magnetic attraction.
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The adhesive substance with which the fixed glass walls 32 are welded and sealed is also a material liable to emit potentially harmful volatile substances.
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The display case 10 may further comprise other parts (e.g. accessories of various kinds, not shown in the figure, such as partitions, support shelves, lighting fixtures, etc.) made of materials liable to emit volatile substances such as VOCs or other, or painted with paints that can emit such substances.
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The display case 10 is assembled in a normal way, assembling the various parts as required. Once the assembly has been completed so as to obtain the structure of the display case, without however any hygroscopic material used for moisture control being housed in the base 20 of the display case 10, the display case 10 is subjected to a heat treatment to remove volatile substances from the materials liable to emit them.
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The heat treatment involves submitting the display case 10 to alternating heating and rest steps. Each heating step involves bringing the display case 10 to a heating temperature for a heating period, while each rest step involves keeping the display case 10 unheated for a rest period.
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The heating temperature is preferably at least 35°C, more preferably about 50°C.
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The heating period is preferably at least 24 hours, more preferably about 48 hours.
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The rest period is preferably at least 24 hours, more preferably about 48 hours.
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Preferably, the duration of the heating and rest steps is about the same.
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Preferably, the heat treatment involves submitting the display case 10 to at least three heating steps alternating with two rest steps. The heating and rest steps can also be greater in number, always alternating with each other, with the first and last heat treatment steps always being heating steps.
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In order to carry out the heat treatment, in particular the heating step, the display case 10 can be placed in a heating chamber, where it is heated to the specified heating temperature.
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Alternatively and preferably, to perform the heat treatment, in particular the heating step, heating members are placed inside the display case 10, so as to heat the display case 10 from the inside. This mode is preferred because the removal of volatile substances is especially important for all the materials facing the interior of the display case 10, because precisely the volatile substances emitted by these materials - if not removed beforehand - would then be emitted inside the display case 10, creating potentially hazardous situations for the objects exhibited. The heating members may act by convection, heating the air inside the display case 10, and/or by radiation; if the heating members act by radiation (or both by convection and radiation), they are placed so as to direct the radiation towards those parts of the display case 10 in which the materials most liable to emit VOCs or other volatile substances are located, which are potentially harmful for the objects to be exhibited in the display case 10.
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Furthermore, this method allows the display case 10 to be treated even at the installation site and is therefore preferred when the display case 10 (e.g. due to its large size) has to be assembled at the installation site.
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During the heat treatment, regardless of the method with which this is performed, an air exchange is periodically performed in the interior exhibition space of the display case 10, for a duration of at least 5 minutes every hour. This air exchange step is therefore carried out during both the heating and rest steps, and allows all the volatile substances emitted during heat treatment to be removed from the interior of the display case 10.
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Once the heat treatment has been completed, any hygroscopic material may be housed in the base 20 of the display case 10, in a manner known per se.
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The display case 10 treated in this way can therefore be used safely, because the materials used therein, even if liable to emit volatile substances, have exhausted their emission ability, or rather they have reduced it in such a way that any residual emission is minimal, such that it is not dangerous for the objects exhibited in the display case 10.
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Depending on the intended use of the display case 10, i.e. depending on the ability of the objects exhibited to be damaged by VOCs or other volatile substances, it may be necessary to use higher or lower temperatures and treatment times to ensure that at the end of the heat treatment the display case 10 is completely safe, i.e. that the objects exhibited cannot be damaged.