DE1648266B1 - Device for the optical display of surface temperatures - Google Patents

Description

The invention relates to temperature sensitive display devices using an encapsulated liquid substance that reacts to changes in temperature iridescent, d. H. passes through the spectral colors.

The phenomenon of color change that occurs in certain types of so-called liquid crystals of reflected light is well known. The greatest importance in the class of liquid crystals, in which the named play of colors occurs when the temperature changes, have certain cholesterol derivatives with the general structural formula

CH ₃

CH ₃

CrI - CH-2 - CrIo - CHo - CrI

CH ₃

R-X-i

wherein X is a chemical compound selected from the group consisting of esters, ethers and carbonates and R is a hydrocarbon radical from the saturated or unsaturated alkyls, aryls, aryl-substituted alkyls, alkyl-substituted aryls, and halogen- and nitro-substituted ones derived from the aforementioned substances Compounds containing group. Other suitable cholesterol derivatives are those in which X represents a halogen and R is not included in the molecular structure. Any of these connections can as molecular mass as a function of temperature in at least three different physical Forms occur. Below an external given for certain connections Conditions characteristic transition temperature occur the cholesterol derivatives as solid crystalline Phase on while it is above another certain transition temperature in a liquid isotropic state with an irregular molecular arrangement. When moving out of the solid crystalline phase with strictly ordered molecular arrangement into the liquid isotropic phase with irregular, Disordered molecular arrangement as a result of an increase in temperature exists in these compounds at least one mesophase, d. H. a phase that is between the solid and the liquid State lies. It is true that a compound in the aforementioned mesomorphic state becomes common referred to as "liquid crystal", but the term "mesomorphic" used in the following is more precise and more accurate. There are three mesophases, the smectic, the nematic and the cholesteric, which, however, need not all appear in a given connection. Possess cholesterol compounds in its mesophase a liquid, molecular isotropic, coherent structure, with domains aligned molecules are randomly distributed in separate layers and are conspicuous Reflect light. A general discussion of mesophases and mesomorphic compounds is in the publication "Molecular Structure and the Properties of Liquid Crystals" by G. W. Gray, published 1962 by Academic Press, New York and London. Under suitable conditions are the domains of aligned molecules in the within a given Temperature range in the cholesteric mesophase mass in a position striking on it To influence light in such a way that it is clearly visible as a function of the temperature Spectral color, usually in ribbons, is reflected, in most cases depending on the Type of incident light an iridescent effect, d. H. a play of colors results.

There is a particularly expedient method for creating a system with this "play of colors" in the use of thin films of mesomorphic substances, which act as the cholesteric mesophase be provided on an opaque or clear, colored or colorless support can. To make the iridescence of these fabrics clearly visible, a film with a thickness of a few hundredths of a millimeter can be used, whereby by applying such a film to a black, opaque carrier gives a good contrast. Such a carrier prevents weakening of reflected iridescent light, since it does not reflect any light itself or none from behind allows incident light to pass through. In addition, such a carrier has the advantage that those surfaces the device above and below that for achieving the cholesteric mesomorphic state required temperature limits, appear black in incident light. The usual one The color effect achieved in a film made of cholesteric-mesomorphic material is one that ranges from red to blue Spectral color bands or areas composed of brilliant color samples. The colors are one Function of the temperature change of the film, the system being a higher temperature in general Light with a shorter wavelength is reflected, although exceptions are known from the literature which the wavelength of the reflected light increases with increasing temperature. Of course is above and below the temperatures required for a visually recognizable colored display Depending on the type of system to be examined and the type of incident light, there may also be a reflection ultraviolet and infrared light present to a greater or lesser extent.

With a few exceptions, the systems used for temperature determination and display exist from two or more mesomorphic compounds so selected and combined with one another, that a color change occurs within a certain temperature range.

Although mixtures of these cholesterol derivatives result in functional systems, it is one

3 4

general rule that the temperature at which is that which consists of small capsules and is stratified Coloring occurs, not the color generation temperature that the capsules each have a liquid core a certain of the compounds used contain one or more substances that are addressed by the, but is generally lower than the temperature range showing a cholesteric meso temperature, in which the phase takes on the highest temperature, and that the nuclei are influenced by a light parameter containing fabric for the first time is encased in a permeable color, capsule wall forming fabric, and sometimes even lower than closed.

the color generation temperature of the substance with the lowest die in the device according to the invention Temperature parameters. The used capsules can be produced by any suitable encapsulation process, the capmorph Substances in temperature-sensitive systems be of the desired small dimensions, strictly limited for the following reasons: The finished products to be used for coating

1. Preferably, in such a mixture of one or more f ^ ^sun have a size of 10 to mesomorphic compounds in the form of a 50 ^ m but it has _ shown that other film containing systems occurs useful in the ^decision-15 capsule Great siad wherein However, at speaking working temperatures a crystal! - Use of larger capsules for a data presentation of large areas. Through this inconsistent device, a lower visual crystallization can result in the individual dissolving power. In the encapsulated Kristallisierungsstellen from a concentration of a mesomorphic compounds existing Filmschichder active substances are caused, WO ²⁰ th contact said, together with these existing from the other components of a hanging-wet films of these substances such mesomorphic mixture is separated at exposed. Disadvantages do not arise. This separation of the components leads to encapsulated material cast and then

a) to a reduced accuracy and dried layers are dry to the touch

Intensity of the color change in the case of the ²⁵ S ⁵ Sf ¹ . Relatively insensitive to abrasion

desired temperature and practically immune to contamination by solute

b) to abnormal color change activity in fabrics, and not subject to rapid decay

other temperatures. ^through sal ctive crystallization as a result of nucleation,

2. A mesomorphic cholesterol derivatives in which m and cases where crystallization begins, oily liquid above their melting temperatures ³ ° <jif ^s through the capsule walls in a wide Auskeiten. Are they as a film on any surfaces clue is changed.

present, then the wet film is subject to the ^F ™, the invention enables the use of a wide variety of harmful influences, e.g. B. one of different capsules differing in their contents and their premature aging and different one sensitivity range in effects from the environment. So the ³⁵ takes such a film layer. On such a system, the surface easily liquefies dust particles, the different capsules can be used for temperature displays as undesirable nucleation sites for crystallization purposes or for the display of data! versation can work. Further, such different temperatures serve Em such a system films easily with other materials in its demand ¹ Ff *, for example, consist of layers of which ready money come into contact, resulting in containing ⁴ ° every one, two or more kinds of capsules, a disorganization the mesomorphic material which m the following characteristic Memory and may ^paint a change in the thickness can differ from one another:
in certain areas, resulting in a) temperature response range,
Change the sensitivity of the system result in b) size of the liquid core,
would. ⁴⁵ c) type and thickness of the substance forming the capsule wall,

3. The mentioned mesomorphic wet film systems d) Type of mesomorphic substances.

tend to have abnormal discoloration. ,. . . ,,,,,.

hold in case the slightest contamination of the _A ^These ™ ^d "also serve some other features

System through various solutes up ^{to 'em f "r de} * Relevant use overall

occurs. Already such contamination can achieve ⁵ ° One suitable crisp control

at a given temperature, at which ^normal- _v Dle, ^Wa * ^{de the one} containing the mesomorphic substance

wisely no color change occurs, capsules can be made of colored material

Iridescence or iridescence can cause great problems, for example the task of a color filter for the

Shifts in the temperature of color generation according ^to and that of the mesomorphic substances

effect up or down. ⁵⁵ to meet this i ^m reflected light. By using dyes, the capsule walls

The object of the invention is to make them tinted easily. To isolate such a controlled thermotropic liquids or system can be used in devices, protect, in that they are in the form of droplets with which the iridescent effect are surrounded in all of its transparent walls, ie the 60 spectral width is not desired.
Form cores of small transparent capsules, and one embodiment of the invention will furthermore distribute these capsules as a thin layer on a subsequent carrier, which is suitable in more detail with reference to the drawings, in order to record a temperature.

to create display device. F i g. 1 a shows a greatly enlarged schematic

The subject of the invention is therefore a front 6g side view of a carrier sheet 1, one surface of which

direction for the optical display of surfaces is provided with a coating of capsules 2,

temperatures, characterized in that the cholesterol derivative in liquid or solid

controlling surface with a mass containing state;

5 6

Fig. Ib shows again the sheet of Fig. La, is brought, which represent the temperature at which however here the capsule contents in the choleste- the layer in question experiences a color change, ric mesomorphic state. In Fig. 4 a, the surface of the screen has so much of

The carrier 1 can consist of any desired thickness of the infrared or infrared emitted by the energy source 11 thin, translucent, or opaque, 5 absorbs radiation as is necessary to the colored or colorless material. In Fig. La to bring the temperature of the capsules to 25 ° C, that is and Ib is a film of normal thickness as the support at the temperature at which the color change in the turns. For certain applications it can occur for each layer representing digits “2” and “5”. That but be more expedient to a solid body as a result of the warming so that is visually recognizable To use carrier for the encapsulated substance. An OK display of the surface temperature. In Fig. 4 b Another possibility is the encapsulated, more radiation was absorbed, and the temperature temperature sensitive substances as liquid pulp too was over the coloring temperature range of the first use, whereby the color change phenomenon remains the type of the encapsulated substance and until the color is the same as with the dried layer. temperature range of a second type of substance in one F i g. la should be the capsule coating at a temperature 15 additional layer representing the numbers "3" and "0" rature above or below the temperature- increased. This means that the number "25" becomes the range represent, in which the capsule contents are brought into disappearance, and then appears the its mesomorphic phase. Fig. Ib represents the number "30". It thus becomes a direct temperature the same capsule coating is achieved within the Coloring the marked temperature range. 20 corresponding to the shape of the numbers to be displayed The hatching of the capsules in FIG. 1b serves only for surface areas with corresponding encapsulated me-Ied to represent a color change and should somorphous substances is achieved.

do not suggest a specific color. For the coating in FIG. 5 is another possible application '

can capsules with a diameter of 5 to the invention shown in which the encapsulated meso-1000 μΐη or even above can be used. Furthermore, 25 morphic substances for the representation of data can be used depending on the circumstances and the use. The capsules are made for a display purpose the coating a capsule layer or sheet 12 applied as a coating, and by several superimposed capsule layers for touching or bringing a heated writing use come. Different types of characters, e.g. B. an embossing type 13, a Dar areas 30 different types of position of the corresponding character out-capsules on the same surface contain. If desired, the carrier can be called. Mesomorphic by appropriate choice also be provided with a layer of paint, as can be done in systems sensing and indicating devices FIGS. 1 a and 1 b by the layer 3 on which a clearly visible coloration is produced Carrier 1 is illustrated. at significantly above or below room

The F i g. Figures 2 and 3 show the use of a 35 temperature supply temperature values. Display screen 4 with a coating of only one. There now follow specific examples of an encapsulation

Type of an encapsulation process containing cholesteric substance as well as the tempeseln for the production, those used on a support of self-supporting temperature sensitive display devices Material is applied. An infrared radiation mesomorphic substance, source 5 is aimed at the display screen, the 4 ° n · · 1 1

Infrared beam is formed by a template 6. example 1

The 1.25 g of acid-extracted pig skin gelatin passing through the template 6 with

Infrared rays are absorbed by the display screen 4 from a bloom strength of 285 to 305 g and one isosorbed and lead to an increase in the temperature from pH 8 to 9 as well as 1.25 g rubber temperature of the screen surface, so that a coloring 45 arabic were with 125 g of distilled water when changing with a contour corresponding to the shape of the template from a temperature of 55 ^° C. in a Waring mixer section is produced. stirred, so that a solution with a pH value

In Fig. 3 the encapsulated material is revealed as a coating of about 4.5. After the solution was formed applied to a display screen 7, which the same the pH by adding dropwise a Color and structure as the unheated 50% by weight aqueous sodium hydroxide encapsulated Has fabric. When set to 6.0 from a power source 8 solution. Then the system became Infrared rays by means of a focusing lens system 9 a solution of 2 g of cholesteryl propionate in 8 g A cholesteryl oleate is added to the display screen. The cholesterol derivatives Warming of the capsules in the area of the impacting were in the Waring mixing vessel on a droplet jets, which emulsifies the characteristic iridescence and visible size of about 10 to 50 μm and becomes pH-bar of the image. Of course, the value of the system by adding one drop by drop can also use 14 weight percent aqueous acetic acid solution in the practice of the invention any other energy sources using sam lowered. The addition of acid has been so long Find. For the sake of simplicity, the figures are continued until the individual, liquid walls Infrared lamps shown. 60 having capsules to form aggregates with a

In the F i g. 4a and 4b is the practical conical diameter of 25 to 100 μm. In Use of the invention as a directly readable temperature - this final state was the pH of the system Temperature display device 10 shown in which more than about 5.

a temperature sensitive system is used. Then the whole fluid system became one

The device is od on its front side with inde- 65 ice bath with continued stirring. Like. To below pendently responsive layers comparable 1O ⁰ C cooled. At 10 ° C, 0.6 ecm of an encapsulated mesomorphic substance was provided, with each 25% by weight aqueous solution of pentane layer corresponding to the contour of the numbers on diol, a chemical hardening agent for the gelatin,

added to the mixing vessel, after which the system is about Was stirred for 12 hours slowly returning to room temperature. After that were the capsule walls solid and hardened, and the capsule system was passed through a wire mesh screen with openings a size of 74 μπι cast. The crowd, which passed through the screen was suitable for coating the desired carrier. Under Using a coating device, the capsules were poured through the sieve together with the penetrated equilibrium liquid in a wet thickness of more than 0.05 mm, but less than 0.25 mm on a blackened, approximately 0.13 mm thick polyethylene terephthalate film applied and then dried in the air at about 25 ° C. Was the temperature At one point on the coating "rises," then a temperature gradient pattern appeared concentric rings, starting from a blue central ring over all spectral colors up to to red, corresponding to the temperature gradient falling outwards. By increasing the temperature or lowering of the point concerned, an expansion or contraction of the rings takes place. The system according to Example 1 showed the first color transition brought about by the mesophase at about 25 ° C and remained in its mesomorphic phase up to 30 ° C. Groups of adjacent expanding and contracting rings intersected and each color obtained was a function of temperature of the corresponding surface area.

Example 2

The encapsulation procedure of this example is the same as that of example 1, except that another mixture of cholesterol derivatives was used. In this example, cholesteric mesomorphs instead of cholesteryl propionate and the cholesteryl oleate of Example 15 g of cholesteryl propionate and 5 g of cholesteryl nonanoate used. This was the case with regard to the color change and the transition temperatures System very similar to the system of Example 1, the mixing ratio being chosen with the intention was to adjust the behavior of the system to the usual room temperature, which is also the purpose of example 1 was.

Example 3

Here were two different mixtures of cholesterol derivatives separately, encapsulated using the method described in Example 1 and the capsules applied as a mixture to a blackened carrier film. The cholesteric mesomorphic mixtures was

a) Oleyl cholesteryl carbonate and cholesteryl nonanoate in a ratio of 1: 1 and

b) Oleyl cholesteryl carbonate and cholesteryl nonanoate in a ratio of 1: 3.

A maximum sensitivity to incident light with a strong 5500 Å component possessed system a) at 34.5 ° C and system b) at 48.8 ° C.

The visual effect of such a coated capsule mixture was almost the same as in the previous examples, with the exception that the iridescence occurs in two sequences, starting with two different temperatures. When heating a point on the coating, the first appeared Follow concentric colored rings around the heated point. The point on the coating still became further to one above the color generation temperature of the first encapsulated substance, but below that Color generation temperature of the second encapsulated substance lying temperature heated, then appeared the test point is black again, but with a remaining color ring, which is due to the static Temperature gradients at a certain distance from the center of the heat source, d. H. of the warmed Test point, found. When the latter was further heated, a second group of colored rings began to appear and move outwards. These rings never made it to the first rings, however a visually recognizable display of the temperature at two different points on the coated Carrier revealed.

When the coated carrier film as a whole was heated, the film also reflected the changing ones Colors, however, not in the form of rings, but the entire carrier film appeared in the same way Colour. First there was a first color sequence based on one encapsulated substance and then with another Heating as a result of the second encapsulated substance a second color sequence comes about, with the film in between at temperatures between the different color generation temperatures for a while appeared black. As the film cooled, the color changes occurred in reverse order on. If capsules with different cholesteric mesomorphs with overlapping color change temperature ranges are combined then the reflected colors are combined, resulting in different responses depending on the ratio and the resolving power of the capsule system gives a different appearance. As explained above, systems with smaller capsules give a higher degree of resolution.

Example 4

Using the method described in Example 1, capsules were prepared, the mixtures of oleyl cholesteryl carbonate (OCC) and cholesteryl nonanoate (CN) in corresponding proportions and showed reflection properties in incident white light, which are recorded in the following table:

50
cape
selart (OCC) / (CN)
Weight
percent Color generation
temperature
in ° C
for reflected
Light from
5500 Ä temperature
area
in ° C
for reflected
Light from
6000 to 4500 Ä 55 1
2
3 25/75
50/50
65.2 / 34.8 48.8
34.5
28.3 48.5 to 49.8
34.3 to 35.4
28.1 to 29.1

These three encapsulated substances No. 1, 2 and 3 were (as in Example 1) individually on a blackened film, but applied in a pattern consisting of squares, in such a way that the individual Squares overlapped so that two or three layers were superimposed in different places. When heated this sample showed each of the three encapsulated substances as described above Color change phenomenon, whereby a color change on the simply coated surfaces, two color

009525/114

changes to the double-coated areas and three color changes to the triple-coated Surfaces occurred. The main objective of this example was to show that overlapping layers the mesomorphic substances work independently of each other and that the layers are transparent from what the strong iridescent effect also results when encapsulated with other mesomorphs Fabrics are covered.

Claims (5)

Claims: IO 1. Device for the optical display of surface temperatures, as indicated by that the surface to be controlled is coated with a mass consisting of small capsules, and that the capsules each contain a liquid core with one or more substances that are to be displayed Temperature range a cholesteric mesophase assume, and that the cores surrounded by a translucent, capsule wall forming substance are. 2. Apparatus according to claim 1, characterized in that the mass is a mixture contains several types of capsules, which differ in their content due to their different response temperatures differ from each other. 3. Apparatus according to claim 1 or 2, characterized in that the capsules have one or more of the following compounds contain: cholesteryl propionate, cholesteryl oleate, cholesteryl nonanoate and oleyl cholesteryl carbonate. 4. Device according to one or more of the preceding claims 1 to 3, characterized in that that the thickness of the capsule walls is between 12 and 250 μηα. 5. Display device according to claims 1 to 4 , characterized in that the carrier is blackened. 1 sheet of drawings