NL2012089C2

NL2012089C2 - Sub optimal elements.

Info

Publication number: NL2012089C2
Application number: NL2012089A
Authority: NL
Inventors: Stephen James Picken
Original assignee: Univ Delft Tech
Priority date: 2014-01-15
Filing date: 2014-01-15
Publication date: 2015-07-16

Description

Sub optimal elements

FIELD OF THE INVENTION

The present invention is in the field of a method for producing sub optimal quality elements, an element obtainable by said method, a product comprising said element, and use of said element.

BACKGROUND OF THE INVENTION

The present invention is in the field of forming copies of original elements in a cheap and reliable manner. Thereto a mold is made from concrete or cement, which mold is then used to make a copy. The term "cement" and "concrete" as used in the present application are considered to encompass similar type of materials, such as "cementitious" materials.

Various optical elements exist, such as for converging light, such as a lens, a mirror, and a Fresnel lens. For lenses amongst others convex and concave lenses exist. Convex lenses may relate to biconvex, plano-convex, positive meniscus and negative meniscus.

Mirrors may relate to parabolic mirrors, cylindrical mirrors, concave mirrors, convex mirrors, spherical mirrors and trough shaped mirrors. Mirrors are typically provided with a reflective coating on a suitable substrate.

Optical elements suffer (inherently) from various (optical) aberrations, which can typically only partly be overcome. Optical elements are rather expensive, especially when good quality is required. Often optical elements comprise compounded elements.

Concrete is a composite construction material composed primarily of aggregate, cement and water, with mortar being similar thereto, however using finer aggregates. There are many formulations that have varied properties. The aggregate is generally a coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementing materials such as fly ash, blast furnace slag cement, ground calcium carbonate, etc. serve as a part of binder for the aggregate. Typically further additives are present.

The present invention therefore relates to a simple method of obtaining copies with good, though not optimal, characteristics, which solve one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates to a method of producing an element, an element obtainable by said method, a product comprising said element, and use of said element, such as an optical element.

The objects of the invention relate to solid objects, typically having a rather complicated and/or (functional) demanding structure, in particular a 3-dimensional structure, such as optical components and architectural components, such as curved windows. As in an example the optical objects do not have optimal optical quality, e.g. a sharp focus of an object to be imaged is largely absent, it is rather difficult to form images with sufficient sharpness which can be observed by the human eye. For (advanced) optical application such lack of focus is considered a disadvantage; for the present invention, on the contrary, it is an advantage as some, but sufficient, concentration of (solar) light is typically enough for an intended application.

In a first step of the present method a mold of an original element is made. It is noted that the present method is particularly suited for making large (r) numbers of copies of otherwise rather complex and expensive originals, such as optical elements. Complexity of originals may relate to a shape, details, tolerance, functional quality, restrictions due to materials used, etc. Originals may be expensive due to its complexity and production cost, and due to materials used, such as precious metals. Production of originals may further included advanced and sophisticated post processing, such as extensive polishing and grinding, making the original even more expensive. Originals may also be expensive due to a size or scale thereof, such as a large mirror. Especially in case of large originals, the present method is capable of making a copy in parts. The parts of the copy can thereafter be assembled into a whole copy.

The present method may also relate to forming more than one molds, or forming in a sequence a mold of an original, a copy of the original, a mold of the copy, a copy of the copy, etc. As such an original can be reproduced many times, directly by a first mold, and/or by applying the above sequence a number of times. The present method thereby provides a powerful tool for reproduction.

In a present method step the original is coated by fluid concrete or fluid cement, such as Portland cement. The fluid can be obtained in a usual way, and then be applied directly to the original, or by first providing a casing or the like and then applying the fluid. The fluid can be applied as a sort paste, e.g. by using a spatula or the like, such as in a layer by layer mode, or by pouring. After coating the original element the fluid concrete or cement needs time to set, typically a few hours to a few days. After setting the original can be removed, typically quite easy. Sometimes a release layer may be applied first on the original, in order to support release of the original from the mold. A release layer may relate to a polymer, such as a fiber reinforced polymer, an expoxy, a foil, paper, and the like. It came as a surprise that the present mould follows a shape of the original with high accuracy and provides a smooth surface.

The mold is now in principle ready to make a copy of the original. Making a copy typically involves further steps. Sometimes however a mold represents a (true) copy of the original .

Therewith the present method can be applied with ease and at low costs, providing good, but typically not optimal, quality objects. Production costs can be reduced by an order of magnitude, possibly two orders of magnitude. It is noted that some of the examples relate to improvement of the quality with again relatively simple measures.

An advantage of the present optical elements, especially solar concentrators, is that the quality thereof, e.g. in terms of focus, is not that good. Instead of a small focal area a larger foal area is provided, which is very well suited for conversion of solar energy, such as in cooking, photo voltaic devices, and the like. In view of use of the present op tical elements a risk of burning, overheating, or even melting is reduced by the present method, whereas a conversion efficiency of the present copy remains practically the same as that of the original.

For various applications the mold forms part of the copy, such as a support thereof. It is a further advantage that the mold is made of a relative lightweight materials (having a specific density of about 2.5 -3 kg/dm3) , having good strength, good durability, which lightweight materials are readily available and relatively cheap. In comparison to materials typically used as a support, such as glass, steel, etc. concrete and cement have a low density and a high stiffness (Young's modulus). It is also an advantage that characteristics of the present materials can be adapted easily, if required.

Thereby the present invention provides a solution to one or more of the above mentioned problems and drawbacks.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a method of producing a copy of an original 3-dimensional element, such as an optical element, according to claim 1.

In an example of the present method step (II) comprises A1) coating the copy with a reflective coating, thereby forming a mirror surface. The coating can be applied by advanced techniques, such as vacuum sputtering, or can be applied directly, such as by a metal foil, such as an aluminium foil. For rather complex surfaces advanced techniques are preferred, e.g. in terms of quality.

In an example of the present method step (II) comprises A2) filling the mold with an optically transparent material. Thereby for instance a lens may be obtained. It is noted that for a lens typically two molds are required, i.e. a "top" mold and a "bottom" mold. If a lens as planar at one side one mold would be sufficient. The molds can be filled with a glassy material, or a glass forming material, such as the present silicate (see below).

In an example of the present method the concrete or cement is grinded before use to an average particle size of 0.2-20 pm, preferably 0.5-5 pm, with a median size of 1-3 pm. It has been found that by grinding particles to the above ranges the cement or concrete remains is characteristics, can be handled as required, and provides a smoother surface. The smoother surface provides a better reproduction of the original, which for some application is beneficial, such as for optical quality of optical elements.

In an example of the present method the concrete or cement further comprises an additive, preferably in an amount of 0.1-2 wt.%, with an average particle size of 0.05-0.2 pm, such as a geopolymer, such as fumed silica. It has been found that a surface of the copy remains somewhat rough, typically on a micrometer scale. In view of e.g. optical quality of the coating being formed it is preferred to have a smooth surface, e.g. having a low as possible surface roughness. Surface roughness is quantified by the vertical deviations of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small the surface is smooth. Also waviness of a surface is preferably as low as possible. Surface roughness is typically considered to be a high frequency, short wavelength component of a measured surface, and hence being relevant for an (optical) quality thereof. Surface roughness can be characterized by measuring amplitude parameters based on vertical deviations of a roughness profile from a mean or median line. One can simply take an arithmetic average of absolute values of amplitudes (Ra)· It is also preferred that a maximum valley depth and a maximum peak height (of the amplitudes) are as small as possible. Surface roughness is typically difficult to control during manufacturing of an original or a copy. Roughness is typically determined with a roughness profiler. With the present addition of an additive and/or grinding of the ce-ment/concrete a surface roughness Ra (arithmetic averages of absolute values) of 100-1000 nm can be obtained. Such a surface roughness is found to be good enough for many applications, including the present optical applications.

In an example of the present method the concrete or cement further comprises a surfactant, preferably in an amount of 0.1-2 wt. %. The surfactant can for instance improve the packing density of cement or concrete, e.g. providing a denser structure. It has been found that a better "copying" behaviour of the surface the fresh cement c.q. concrete was poured on is obtained, e.g. in terms of surface roughness, details of the original surface being copied, etc.

In an example of the present method before step Al) or A2), respectively, the mold is coated with an aqueous composition for forming a coating. Said composition comprises (i) water, and optional co-solvents, the co-solvents being selected from glycerol, and alcohols, such as ethanol and methanol, (ii) one or more of an in water dissolvable cyclic and single chain silicate (Si02+n2n ) , such as silicate (SiCh2-) , and orthosilicate (SiCq4-) , pyrosilicate (Si2076~) , such as a monovalent cation thereof, and components that form a silicate such as SiC>32~ in water, wherein the silicate is capable of forming a glassy structure in contact with polyvalent cations under ambient conditions, optionally (iii) platelet nanoparticles, the nanoparticles being suspended in the liquid, and optionally (iv) a geopolymer with an average particle size of 0.05-0.2 pm, such as fumed silica.

With said composition not only the surface roughness can be improved (further), but also a maximum valley depth and maximum peak height (of the surface) have been improved, to about +500 nm, respectively. Also characteristics of the surface, such as hydrophobicity, release behaviour, etc. can be improved.

The invention makes use of non-toxic and environmentally friendly components. These components are biocompatible, i.e. an impact on the biological environment is considered minimal. The composition has as a main liquid water, or may be formed primarily from water. Other solvents may be present, such as glycerol and alcohols. It has been found that these co-solvents for certain applications improve optical properties of the coating as well as durability.

The present silicate forms a glassy structure upon contact with a polyvalent cation, the cation being provided by a surface on which the silicate is provided. The silicate provides a conformal coating to a surface to which it is applied. The coating closely follows a texture and form of the surface to which is provided.

The present composition does not or at the most to a small extent penetrate into a surface to which it is applied. So surprisingly the present composition may be applied directly to a surface and provides advantageous effects. The composition may also be applied to the surface after setting of the concrete/cement has been (partly)completed; a "finishing touch" is achieved by dipping or pouring e.g. Sodium Silicate that smoothes the slightly rough surface, by reaction of sodium silicate with calcium and forming calcium silicate.

For some specific applications it has been found that in order to have improved barrier properties further platelet nanoparticles are preferably present. Platelet nanoparticles have dimensions wherein a length, and likewise a width, thereof is significantly larger than a height thereof, such as at least a factor 5 larger. A height of the nanoparticles is typically in the order of a crystallographic axis thereof, or a few times the axis, such as 1-50 nm or more. The width and length of the nanoparticles are from 10 nm - 5 pm, preferably from 25 nm-1 pm, more preferably from 50 nm-500 nm, such as from 100 nm-250 nm.

The nanoparticles are typically suspended in the aqueous composition. Once a glassy structure is formed it has been found that the nanoparticles are incorporated therein.

It is an important characteristic of the present composition that once applied onto a surface, the surface providing polyvalent cations, a coating is formed immediately, i.e. within a short time frame. As such properties of a surface are not changed significantly, e.g. by penetration of the composition or components thereof into the surface .

In an example of the present method an amount (wt.%) of silicate is larger than an amount of nanoparticle. It has been found that nanoparticles may be added in a relative (compared to silicate) low amount, such as less than 30 wt. % thereof. As such the nanoparticle perform their action, without jeopardizing functionality of the silicate glass.

In an example of the present method (ii) the silicate is present in an amount of 1- 50 wt.%, based on a total weight of the composition, preferably 2-30 wt.%, more preferably 5-20 wt.%, such as 10-15 wt.%, and/or wherein the polyvalent cation is one or more of calcium, iron, copper, strontium, cobalt, zinc, magnesium, and nickel, and is preferably non-toxic, such as calcium, iron, and magnesium, preferably calcium or iron.

In an example of the present method (iii) the nanoparticles are one or more of a natural or artificial clay, the clay preferably a monovalent cation clay, comprising one or more of H+, Na+, K+, Li+, such as a TOT-clay (or 2:1 clay), such as a kaolin clay, such as kaolinite, dickite, halloysite and nacrite, a smectite clay, such as bentonite, montmorillo-nite, nontronite and saponite, an illite clay, a chlorite clay, a silicate mineral, such as mica, such as biotite, le-pidolite, muscovite, phlogopite, zinnwaldite, clintonite, and allophane, and platelet like polymers, and/or wherein the nanoparticles are present in an amount of 0.01- 12 wt.%, preferably 0.1- 10 wt.%, more preferably 0.5- 5 wt.%, such as 1-3 wt.%, based on a total weight of the composition.

In an example of the present method the clay is Na-montmorillonite, and/or wherein the composition is applied in an amount of 1-1000 ml/m2, such as 100-500 ml/m2.

In an example of the present method the reflective coating comprises one or more of a metal, such as Al, Zn, Cu, Ag, a metal salt, such as tin(II)chloride, a dielectric, a reflective coating, such as a paint. A metal like Al is very suitable for the present application.

In an example of the present method the reflective coating has a thickness of 5 nm-1000 nm, preferably 20-500 nm, such as 100-250 nm. The reflective coating is preferably not too thin in view of wear and clearly not thicker than necessary. It comes as a surprise that very thin coatings are suited for the present applications.

In an example of the present method the reflective coating is applied by spraying, Chemical vapour deposition (CVD), sputtering, vacuum deposition, or flame spraying, such as acetylene spraying of A1. In other words many techniques are suitable for applying a coating. Depending on required characteristics one or another of these techniques may be chosen .

In an example of the present method the fluid concrete or cement is reinforced, such as by one or more of nettings, chicken wire, cotton, fibre, carbon, polymer, and cellulose. With (a small amount of) readily available materials the present copy elements can be reinforced, thereby improving durability, strength and ) optical) quality of the elements.

In an example of the present method the mold comprises at least one part, such as 4-10 parts. The present method is relatively flexible, in that a copy can be made in parts. Such may be relevant for relatively large and/or relatively complex structures, such as a large mirror. In such a case it may be necessary to provide a (further) support in order to (re)construct the larger element.

In an example of the present method a surface of the mold is pre-treated before making a copy, such as by polishing, burnishing or grinding. Such can be done with relatively simple means, such as with grinding paper, with a solution comprising finely dispersed particles, etc. In view of quality of a final product it is noted that such polishing or grinding may relate to a delicate process.

In a second aspect the present invention relates to an optical element obtainable by the present method, such as a mirror, a lens, a laser window, an optical prism, polarising optics, UV and IR optics, an optical filter, a 3-dimensional optical element, a 2-dimensional optical element, and (spectacle) glasses.

In an example the present optical element is one or more of spherical, aspherical, trough-shaped, and parabolic.

In a third aspect the present invention relates to a product comprising an optical element according to the invention, such as a solar cooker, a solar concentrator, such as a mirror, and a lens, a cooking instrument,

In an example the present product further comprises a protective layer, such as an optical transparent coating, such as a polyacrylate, and optionally an anti-reflective coating, such as a magnesium fluoride coating.

In a fourth aspect the present invention relates to a use of an optical element according to the invention, for providing a diffuse focus.

In a fifth aspect the present invention relates to a product comprising an element obtainable by the present method, such as a construction element, a building element, a reflective concrete or cement element, and reflective concrete or cement.

The one or more of the above examples and embodiments may be combined, falling within the scope of the invention.

EXAMPLES

An experimental procedure varies somewhat depending on the precise characteristics of the smooth, curved, etc. surface of the original.

In an example, inventors used ordinary Portland Cement and mixed this with water in 0.4 water to cement ratio. Initially inventors added surfactant to avoid any entrapment of bubbles, but it has been found that such also supports close packing of cement particles. Inventors fixed the original glass lens in a plastic beaker and poured the cement paste in the beaker. The samples were kept in a sealed condition to avoid water evaporation. After 4 days the samples were taken out from the mould using compressed air. To enhance smoothness of the surface the samples were coated with a saturated sodium silicate solution and then rinsed with tap water. Depending on the exposure time to the sodium silicate solution the roughness is alleviated in a controllable fashion, although this was not investigated in any detail.

The copy was then provided with a metallic reflective coating. Before sputtering A1 on the curved surface of cement, the sample needed to be dried for about a day, which was achieved at 40°C until constant weight. After drying the samples were covered w'ith A1 using a sputtering machine.

The invention is further detailed by the accompanying figures, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

FIGURES

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

Fig. 1A-C show objects made with the present method.

Fig. 2 shows a solar concentrator.

Fig. 3 shows a building.

DETAILED DESCRIPTION OF THE FIGURES

Fig. 1A-C show curved objects made with the present invention. The curved surface of the objects (inner part) reflects the curvature of the original quite precise. The surface is remarkably smooth; without any further effort a shiny appearance of the surface is obtained, reflecting a surface having a roughness which is smaller than parts of a micrometer .

Fig. 2 shows a solar concentrator which can easily be made with the present invention, such as in parts.

For stimulating imagination, fig. 3 shows an example of a building (Landerbrook Place Office Building) with curved structures. The curved structures are made of glass. The glass can be made by the present invention, as copies. Likewise, instead of glass, the building could be formed of concrete, the concrete being provided with a reflective coating.

Claims

A method of making a copy of an original 3-dimensional element, such as an optical element, comprising the steps of (I) making a mold of the original element comprising the steps of a) providing an original element, b) coating the original element with concrete mortar or liquid cement, c) allowing the concrete mortar or liquid cement to harden, and d) removing the original element, thereby obtaining the mold, (II) making a copy of the original element.

The method of claim 1, wherein step (II) comprises A1) coating the copy with a reflective coating, or A2) filling the mold with an optically transparent material.

Method according to any one of the preceding claims, wherein the concrete or cement is ground before use to an average particle size of 0.2-20 µm, preferably 0.5-5 µm, with a median size of 1-3 µm.

A method according to any one of the preceding claims, wherein the concrete or cement comprises an additive with an average particle size of 0.05-0.2 µm, such as a geopolymer, such as smoked silica, and / or a surfactant.

A method according to any one of the preceding claims, wherein before step A1) or A2) respectively, the mold is coated with an aqueous composition to form a coating, wherein the composition comprises (i) water, and optional co-solvents, wherein the co-solvents are selected from glycerol and alcohols, such as ethanol and methanol, (ii) one or more of a water-soluble cyclic and single-chain silicate (SiO 2 + n 2 n ~), such as silicate (SiO 32-), and orthosilicate (SiO 44 ~) pyrosilicate (Si 2 C> 76 ~), such as a monovalent cation thereof, and constituents forming a silicate such as SiC> 32 ~ in water, the silicate being capable of forming a glassy structure in contact with polyvalent cations under ambient conditions, optionally (iii) plate-shaped nanoparticles, wherein the nanoparticles are suspended in the liquid, and optionally (iv) a geopolymer with an average particle size of 0.05-0.2 µm, such as smoked silica.

The method of any one of claims 2-5, wherein the reflective coating is one or more of a metal such as Al, Zn, Cu, Ag, a metal salt such as tin (II) chloride, a dielectric, a reflective coating, such as a paint, and / or wherein the reflective coating has a thickness of 5 nm-1000 nm, preferably 20-500 nm, for example 100-250 nm, and / or wherein the reflective coating by spraying, chemical vapor deposition (CVD), sputtering, vacuum deposition or flame spraying, such as acetylene spraying from Al, is applied.

A method according to any one of the preceding claims, wherein the liquid concrete or cement is reinforced, for example by one or more of nets, chicken wire, cotton, fiber, carbon, polymer and cellulose.

A method according to any one of the preceding claims, wherein the mold comprises at least one part, such as 4-10 parts.

A method according to any one of the preceding claims, wherein a surface of the mold is pretreated before making a copy, for example by polishing or grinding.

An optical element obtainable with a method according to any one of the preceding claims, such as a mirror, a lens, a laser window, an optical prism, polarizing optics, UV and IR optics, an optical filter, a 3-dimensional optical element, a 2-dimensional optical element, a window, and (glasses) glasses.

The optical element of claim 10, wherein the element is one or more of spherical, aspherical, trough-shaped, and parabolic.

A product comprising an optical element according to claim 10 or 11, such as a solar cooker, a solar concentrator, such as a mirror, and a lens, and a cooking instrument.

The product of claim 12, further comprising a protective layer, such as an optically transparent coating, such as a polyacrylate, and optionally an anti-reflective coating, such as a magnesium fluoride coating.

Use of an optical element according to claim 10 or 11, for providing a diffuse focus.

A product comprising an element obtainable by a method according to any one of claims 1-9, such as a building element, a building element, a reflecting concrete or cement element, and reflecting concrete or cement.