United States Patent 19 11, 3,720,623 Cartmell Et Al

United States Patent 19 11, 3,720,623 Cartmell et al. (45 March 13, 1973 (54) ENCAPSULATED LIQUID CRYSTALS 3,499,112 3f 1970 Heilmeier et al............. 231230 LC X 75) Inventors: James W. Cartmell; Donald 3,578,844 5/1971 Churchill et al.................. 252/316X Churchill, both of Dayton, Ohio 3,600,060 8/1971 Churchill et al.................. 252/316X 73) Assignee: The National Cash Register Com Primary Examiner-Richard D. Lovering pany, Dayton, Ohio Attorney-E. Frank McKinney and Patrick P. Pacella 22 Filed: Feb. 8, 1971 (21) Appl. No.: 113,716 57 ABSTRACT A mixture of cholesteric liquid crystal material such as 52 U.S. Cl.............. 252/316, 231230 LC, 1 17137 R, cholesteryl nonanoate and nematic liquid crystal 1 17/100 A, 1171159, 2521403, 252/.408, material such as methoxybenzilidene-p-n-butylaniline 264/4, 350/160 P, 350/160 R is disclosed. The mixture can be encapsulated and em 51) Int. Cl..............................................Bo1j 13/02 ployed in temperature-sensitive visual display devices. 58) Field of Search ............... 252/316; 1171 100 A; The addition of nematic liquid crystal material to 231230 LC; 350/160 R, 160 P: 26414 cholesteric liquid crystal material enhances the brightness of films employing cholesteric liquid crystal 56) References Cited material and prolongs the usable life of the films. UNITED STATES PATENTS 6 Claims, No Drawings 3,341,466 9/1967 Brynko et al......................... 252/316 3,720,623 1. 2 ENCAPSULATED LIQUID CRYSTALS the usable lifetime. Also, by the addition of nematic liquid crystals, oleyl cholesteryl carbonate can be This invention relates to unencapsulated and encap eliminated from the mixtures, if desired. sulated mixtures of liquid crystals. This invention also The term "nematic' means "thread-like,' since relates to temperature-sensitive visual display devices. 5 materials in this state frequently assume a charac Most organic crystalline solids exhibit a distinct teristic thread-like texture when a thin section of the transition temperature at which the solid melts to an material is viewed between crossed polaroids. When a isotropic liquid state. Many compounds, however, ex nematic crystalline solid is heated in a capillary tube, hibit an intermediate phase such that on heating to a the crystals collapse sharply at the melting point and temperature (T), the solid melts to a highly colored 10 form a flowing turbid liquid. At a higher temperature, liquid state which can be optically anisotropic. On the turbidity of the nematic liquid crystal disappears further heating, the material undergoes one or more and the liquid becomes an ordinary isotropic liquid. An subsequent phase transitions finally becoming an opti example of a nematic liquid crystal is methoxybenzi cally anisotropic liquid. The intermediate phases com lidene-p-n-butylaniline. monly are called liquid crystals. A general discussion of 15 With respect to both cholesteric and nematic liquid liquid crystals is found in the publication, "Molecular crystals, the liquid crystal state often is called the Structure and the Properties of Liquid Crystals,' by G. mesomorphic state or mesophase. W. Gray, published in 1962 by Academic Press, New Accordingly, an object of this invention is to provide York and London. 20 unencapsulated and encapsulated mixtures of at least The liquid crystal state of most interest to this inven one cholesteric liquid crystal material and at least one tion is that most commonly exhibited by esters of nematic liquid crystal material. cholesterol called the cholesteric state. The domains of Another object of this invention is to provide tem aligned molecules in cholesteric liquid crystals are perature-sensitive visual display devices. capable of affecting a probing incident light in such a 25 Other objects, aspects and advantages of this inven manner that the probing light is reflected in a distinc tion will be apparent to one skilled in the art from the tive spectral hue, usually in bands, dependent on tem following disclosure and appended claims. perature. In most instances the effect is iridescent, de The cholesteric liquid crystals that can be employed pending on the quality of the incident light. This in this invention vary widely. Examples of the reflectance of light in relatively narrow bands is usually 30 cholesteric liquid crystals that can be employed in this referred to as light scattering. This light scattering is a invention are found on page 3 of the above-identified function of the physical ordering of the material in the U.S. Pat. application Ser. No. 798,237, now aban liquid crystal state rather than electronic absorption of doned. light as in the case of other dyes and absorbing Suitable chromatically responsive cholesteric liquid molecules. 35 crystal materials include, but are not limited to, the fol The particular color of the scattered light is a func lowing: cholesteryl halides, e.g., cholesteryl chloride, tion of the temperature of the liquid crystals. This fea cholesteryl bromide and cholesteryl iodide; cholesteryl ture has led to the use of liquid crystals for thermal nitrate and other mixed esters of cholesterol and inor mapping. Thin films of liquid crystals can indicate the ganic acids, cholesteryl esters of saturated and unsatu temperature of a substrate by the color of the film. 40 rated, substituted and unsubstituted organic acids, esp. Up to this time, the utility of cholesteric liquid cholesteryl esters of C to Caliphatic, monocarboxyl crystals in temperature-sensitive systems has been ic acids, e.g., cholesteryl nonanoate, cholesteryl severely limited for a number of reasons. For example, crotonate, cholesteryl chloroformate, cholesteryl in the light scattering state, cholesteric liquid crystals 45 chlorodecanoate, cholesteryl chloroeisosanoate, are a viscous, sticky liquid and require considerable cholesteryl butyrate, cholesteryl caprate, cholesteryl care in handling. Other problems are set forth in U.S. oleate, cholesteryl linolate, cholesteryl linolenate, Pat. application Ser. No. 798,237, filed Nov. 5, 1968, cholesteryl laurate, cholesteryl erucate, cholesteryl by Donald Churchill et al. One answer lies in the myristate, oleyl cholesteryl carbonate, cholesteryl hep encapsulation of cholesteric liquid crystals as de- 50 tyl carbamate, decyl cholesteryl carbonate; cholesteryl scribed in U.S. Pat. application Ser. No. 798,237. esters of unsubstituted or halogenated aryl, -alkenaryl, Another problem which besets these systems is the -aralkenyl, -alkaryl and -aralkyl organic acids, espe loss of color brightness over a period of time. cially cholesteryl esters of those organic acids contain Cholesteric liquid crystals used for thermal mapping ing an aromatic moiety and from seven to 19 carbon and other applications are generally a combination of 55 atoms, such as, cholesteryl p-chlorobenzoate, choles several esters, ethers or carbonates of cholesterol. By teryl cinnamate; cholesteryl ethers, e.g., cholesteryl adjustment of the components and proportions, it is decyl ether, cholesteryl lauryl ether, cholesteryl oleyl possible to select the temperature at which color ap ether, etc. pears and the temperature range over which color is Some exemplary mixtures of cholesteric liquid seen. One of the major components of commonly used 60 crystal materials which can be employed in accordance mixtures is oleyl cholesteryl carbonate. This compound with this invention include, but are not limited to, the is relatively unstable and contributes to the visual following: cholesteryl nonanoate, cholesteryl chloride deterioration of the system. and cholesteryl cinnamate; cholesteryl nonanoate and Encapsulated mixtures of at least one cholesteric cholesteryl chloride; cholesteryl nonanoate and choles liquid crystal and at least one nematic liquid crystal 65 teryl bromide; cholesteryl nonanoate, cholesteryl bro now have been found. The addition of nematic liquid mide and cholesteryl cinnamate; cholesteryl crystals enhances the brightness of films and prolongs nonanoate, cholesteryl iodide and cholesteryl cinna 3,720,623 3 4. mate; cholesteryl nonanoate, cholesteryl iodide and without the use of an added binder such as polymeric cholesteryl benzoate; cholesteryl nonanoate, choles film-forming material. teryl chloride and oley cholestery carbonate; choles If desired, an added binder matrix of polymeric teryl nonanoate, cholesteryl chloride and oleyl choles material can be used in manufacture of the display film teryl carbonate and cholesteryl bromide; oleyl choles wherein capsules which contain the mesomorphic teryl carbonate and cholesteryl iodide, oleyl cholesteryl material are dispersed in a liquid solution of polymeric carbonate and cholestery p-chlorobenzoate; etc. binder material and the resulting dispersion is cast onto Also, it should be understood that included within a substrate material and dried to yield a coated con the term cholesteric liquid crystalline mixtures can be struction of capsules embedded in a polymeric binder mixtures of two or more individual cholesteric materi O film. The substrate can be of any conventional sheet als. material, including glass, and a polymeric material of The nematic liquid crystals that can be employed in the same kind as that of the binder material or not, as this invention are alkoxybenzilidene-p-n-alkylaniline or desired or required by the intended purpose. Binder hydroxyalkoxybenzilidene-p-n-alkylaniline wherein material useful in the practice of this invention must be each alkoxy, hydroxyalkoxy or alkyl group has

Load more