United States Patent 19 11) 4,045,383 Koff 45) Aug. 30, 1977 (54) STABLE EMULSIONS AND IMPROVED (56) References Cited TEMPERATURE MONITORING FILMS FOREIGN PATENT DOCUMENTS PREPARED THEREFROM 1,138,590 1/1969 United Kingdom (75) Inventor: Arnold Koff, West Orange, N.J. OTHER PUBLICATIONS (73) Assignee: Hoffmann-La Roche Inc., Nutley, Chem. Abstract 48:225 h. N.J. Chem. Abstract 64:17,361 g. 21 Appl. No.: 651,010 Primary Examiner-Theodore Morris Attorney, Agent, or Firm-Samuel L. Welt; Bernard S. 22) Filed: Jan. 21, 1976 Leon; William M. Farley 57 ABSTRACT Related U.S. Application Data Improved temperature monitoring films formed from (63) Continuation of Ser. No. 221,408, Jan. 27, 1972, stable emulsions containing compounds capable of ex abandoned, which is a continuation-in-part of Ser. No. isting in the cholesteric liquid crystalline phase which 885,353, Dec. 15, 1969, abandoned. are protected and stabilized against aging, and the atmo 51 Int. C.’................................................ C09K 3/34 sphere by the inclusion of an antioxidant are provided. (52) U.S. C. ................................... 260/8; 23/230 LC; The thus-formed film materials are used in thermogra 106/135; 252/299 phy and/or thermometry. 58) Field of Search ........................ 106/135; 252/299; 260/8; 428/1; 23/230 LC 3 Claims, No Drawings 4,045,383 1. 2 viewed, has an apparent color which is a complement of STABLE EMULSONS AND MPROVED the color of the light transmitted through the film. TEMPERATURE MONTORING FILMS The terms "light” and "color" as used herein have a PREPARED THEREFROM broad connotation of referring to electromagnetic radi ation generally, rather than to solely visible radiation. The phenomenon of selective scattering as exhibited RELATED APPLICATION by cholesteric liquid crystalline films is independent of This is a continuation, of application Ser. No. 221,408 whether the light illuminating the film is polarized or filed Jan. 27, 1972, now abandoned which is a continua not. The color and intensity of the scattered light de tion-in-part of U.S. Pat. application Ser. No. 885,353, 10 pends upon the temperature of the scattering material filed Dec. 15, 1969, now abandoned, the benefit of the and upon the angle of incidence of illumination. date of which is hereby claimed. Because of the thermochromic properties of choles teric liquid crystals, films containing them are useful for BACKGROUND OF THE INVENTION detecting temperature patterns on various objects, i.e., Liquid crystalline materials have properties that are 15 thermography and/or themometry. This temperature intermediate those of a true liquid and a true crystal pattern is manifested by an irredescent color pattern since they have an ordered structure while also having exhibited by compounds in their cholesteric liquid crys fluidity. These materials are known and are character talline phase. ized or identified by one of three phases or structures Compounds capable of existing in the cholesteric known as the smectic phase, the nematic phase, and the 20 liquid crystalline phase exhibit thermochromic proper cholestric phase (a special form of the nematic phase). ties at temperature ranges which are unique for that The present invention is concerned with materials ex compound. Therefore, the particular cholesteric liquid hibiting a cholesteric liquid crystalline phase. crystalline compound or mixtures of compounds uti Compounds with the cholestric liquid crystalline lized to detect a temperature pattern can be varied to structure exhibit certain characteristics which are mark 25 result in color sensitivity at the particular temperature edly different from those having the smectic or the range being measured. At the lower temperature within nematic structures. The characteristic properties of the range, which can be varied from fractions of a de compounds with the cholesteric liquid crystalline struc gree to several degrees of temperature, the color exhib ture may be summarized as follows: (1) they are opti ited is in the red end of the spectrum and at the higher cally negative, in contrast to the smectic and nematic 30 temperature within the range, the color is in the violet structures which are optically positive; (2) the choles end of the spectrum. Intermediate temperatures result in teric liquid crystalline structure is optically active and intermediate colors, e.g., green. Thus, for example, if it shows strong optical rotatory power; (3) when illumi is desired to measure and detect the temperature pattern nated with white light, the most striking property of the of a particular portion of the anatomy of a person sus compounds with the cholesteric liquid crystalline struc 35 pected of having a blood circulatory disorder or a tu ture is that they scatter light selectively to give vivid mor, a composition which shows a color change at the colors. The color and intensity of the scattered light appropriate temperature can be formulated. Further depends upon the temperature of the scattering material more, cholesteric liquid crystals have been utilized to and upon the degree of incidence of illumination. A determine faults of metal parts of machines and air cholesteric material exhibits a scattering peak having a planes by non-destructive testing techniques. band width of about 200 angstroms that occurs in or Previously, it has been found that in order to more between the infrared and ultraviolet portions of the easily visualize the colors exhibited by cholesteric liquid spectrum; (4) in the cholesteric structure, one circular crystals, it is advantageous to utilize a black back polar component of the incident beam is completely ground. However, the use of a black background gives unaffected. For the dextro cholesteric structure, it is 45 rise to problems which make the use of cholesteric only the circular polarized beam with counterclockwise liquid crystals for detecting temperature patterns diffi rotating electric vector which is reflected. (The sign of cult and uneconomical. One problem is that the black rotation refers to an observer who looks in the direction background must be painted on in the form of a paint or of the incident light.) Levo cholesteric structures have a spray and then the liquid crystals must be applied to the reverse effect; (5) when circular polarized light is 50 the black background so the colors can be readily ob scattered from these materials, the sense of polarization served. Because of the problems involved, the adapt is unchanged. In ordinary materials, the sense of circu ability of these systems is limited. Further, these meth lar polarization is reversed; (6) the mean wave length of ods are disadvantageous since the oily cholesteric liquid the reflected band depends upon the angle of incidence crystals must be applied to the black background as a of the beam. The relationship can be roughly approxi 55 solution in a volatile solvent, thus causing obvious dan mated by the Bragg difraction equation for birefringent gers. Furthermore, the removal of the background and materials. These enumerated properties effectively de particularly the liquid crystals themselves is difficult fine cholesteric liquid crystals. particularly where large areas are concerned. These Thin films of cholesteric liquid crystals exhibit a prop methods are also disadvantageous since it is very diffi erty upon interaction with light, which may be termed 60 cult if not impossible to get a uniformly even coating of "selective scattering". The term "scattering' is used the liquid crystals upon the background, thus rendering rather than "reflection' in order to distinguish from the the pattern unreliable. Furthermore, by the known effect occurring on mirror surfaces wherein light is methods, the re-use of the liquid crystals is, for practical reflected at an angle equal to the angle of incident light. purposes, impossible. A scattered light ray may leave the scattering material 65 In instances wherein the black background is painted at an angle unrelated to the angle of the incident light. or sprayed on a plastic film prior to the application of A selectively scattering film, when observed with light liquid crystals, as well as wherein no plastic film is impinging the film on the same side as that which is utilized, problems arise since the liquid crystals age and 4,045,383 3 4. are unstable when exposed to the atmosphere causing color between 36 C. and 37.5 C, a homogeneous partial decomposition of the compounds and loss of mixture of 46.0 parts of cholesteryl nonanoate, 8.0 parts color intensity and either a shift in the color-tempera cholesteryl oleyl carbonate and 6.0 parts cholesteryl ture response. Even in the case wherein the liquid crys chloride can be used. tals are protected from the atmosphere, e.g., minute 5 The antioxidants useful in this invention are those transparent liquid walled capsules, aging and other which do not adversely affect the color-temperature problems arise. This is true since films formed contain response of the cholesteric liquid crystals and which ing these materials tend to be rough and the protected also do not mask the colors. Typical suitable antioxi liquid crystalline material can be rubbed off, thus caus dants are butylated hydroxytoluene (BHT), butylated ing losses of color intensity and thermographic reliabil 10 hydroxy anisole (BHA), nordihydroguaiaretic acid ity. Furthermore, the thin walls of the capsules can (NDGA), 6-ethoxy-1,2-dihydro-2,2,4-trimethylquino shatter under pressure, thus exposing unprotected liquid line (EMO), dl-a-tocopherol, tertiary butylhydroqui crystals to the atmosphere. none (TBHQ), 1,5-dihydroxynaphthalene (1,5-DHN) or It is more advantageous to use a film of the choles mixtures thereof. The amount and identity of antioxi teric liquid crystals, preferably on a flexible substrate 5 dant used can vary, however, preferably from about blackened prior to the application of liquid crystals, 0.2% to about 1.75% based on the weight of the choles since the utilization of a black paint or spray to serve as teric liquid crystals is suitable.