Abstract:
A product shelf life monitoring system comprises a label substrate bearing upon a limited portion of its area an active indicator composition responsive to varying temperature over time to effect a visible change in color density or the like. The susceptibility of the indicator composition to similarly respond to incidence of vagrant ultraviolet light is ameliorated by application of an area of ultraviolet light absorbent composition in register above the indicator composition and extending at most only slightly beyond the periphery of the area of indicator composition. In this manner, the remaining area of the label is preserved for ultraviolet light responsive implementations, and only a minimal, economical amount of ultraviolet light absorbent composition is expended.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to systems, and elements, components, and compositions therefor, for monitoring and indicating the elapse of a predetermined integral of ambient conditions, such as time, temperature, humidity, actinic radiation, vaporous atmosphere, and the like, to which such a system has been exposed. Typically, for example in monitoring a thermal ambient, a composition comprising an indicator system is formulated to exhibit a readily discernible property variation, such as a change of color or color density, upon the elapse of a given time-temperature integral, and the system, often in the form of a label, is associated with a product of foodstuff, medicament, or the like the useful shelf life, i.e., the safe or potent utility, of which is known to expire substantially concurrently with the elapse of the given time-temperature integral.  
           [0002]    In particular, the present invention relates to responsive compositions of shelf life systems comprising substituted diacetylenic monomer components which exhibit a distinct color change as a result of and generally concomitant with a solid state polymerization effected by the ambient condition integral; typically, as in the case of a time-temperature indicator (TTI) system, the integral of time and temperature. More particularly, through incorporation of integral elements for isolating actinic stimuli, the invention provides means for achieving TTI systems and compositions of remarkable durability, sensitivity, and responsiveness which yield significant functional and economic improvements while greatly reducing the consumption of highly priced components and resources.  
           [0003]    Substituted diacetylenic monomers useful in the present invention have been studied and utilized in TTI systems for many years. Such utility of numerous monomers comprising at least two conjugated acetylene groups (—C≡C—C≡C—) and their unique physico-chemical properties, e.g., responsiveness to temperature change by transforming into contrastingly colored solid state polymerization reaction products, have, for instance, been described by Patel et al. (U.S. Pat. No. 3,999,946). The synthesis of these monomers and their implementation in useful TTI and other shelf life indicator compositions are discussed there at length by Patel et al. and continue to be valid in formulating embodiments of the present invention. Likewise, the use of these diacetylenic monomer shelf life system components and improvements thereon, including assymetric substitutions and complexes, and improved methods of monomer synthesis, have been described at length by Patel (U.S. Pat. No. 4,384,980) and Preziosi et al. (U.S. Pat. No. 4,788,151). Such useful descriptions and examples of the basic diacetylenic monomer components of the present invention are incorporated herein by reference.  
           [0004]    While the consistent and predictable response of these diacetylenic monomer compositions to thermal stimuli provides a basis for highly functional and reliable TTI system products, a similar contemporary color-generating solid state polymerization response to other ambient actinic stimuli, such as ultraviolet radiation, significantly compromises their utility in such systems. This detraction has been recognized long since even by Patel et al who suggested the use of active ultraviolet light-absorbing compounds, such as benzophenones, benzotriazoles, and the like to mitigate these results. Thus, diacetylenic monomer composition TTI products comprising sheet elements, such as labels or marker tabs, bearing a localized deposit of active monomer indicator composition have had laminated thereto an overlying film comprising a UV-absorbing composition. While such a fabrication practice has provided a TTI product with significantly reduced sensitivity to UV stimuli, the expanse of UV-blocking film usually far exceeds that needed to cover the relatively small deposit of active TTI composition component. As a result, a significant amount of expensive UV-absorber composition utilized in the fabrication process serves no advantageous purpose and merely represents a wasted cost factor resource. Further, in some TTI product applications the complete expanse of UV-blocking material prevents the selective employment of otherwise useful areas of a TTI label.  
           [0005]    The present invention obviates the noted shortcomings and disadvantages of prior diacetylenic monomer composition TTI system products and provides such products which yield highly effective and improved results while greatly reducing costs and achieving significant savings in fabrication time and material resources.  
         SUMMARY OF THE INVENTION  
         [0006]    TTI system products of the instant genre generally comprise a self-adhesive substrate label having deposited or printed on its face surface an isolated area or spot of coating or ink composition comprising a selected active diacetylenic monomer compound. In practice, economics favor such a fabrication of a multiplicity of TTI label units, as in a repetitive printing operation upon a continuous web of release sheet-backed substrate moving at high speed past printing or composition application stations.  
           [0007]    In order to provide the noted protection from anticipated vagrant exposure to actinic ultraviolet light during label use, the fabrication process has typically included a “downstream” station at which a continuous web of transparent film bearing a UV-absorbent, or UV-blocker, composition is laminated upon the printed, active monomer face of the label substrate web. To ensure thorough coverage of UV-absorbent composition upon active monomer depositions, the overlay film is normally applied coextensive with the substrate web. A subsequent, final operation in the fabrication stream may be utilized to die-cut and remove extraneous adhesive-backed substrate and overlay film, leaving the desired multiplicity of individual TTI labels on the release sheet backing support web. Along with the excess areas of UV-blocker composition remaining on each label surface, the extraneous overlay film material discarded in this final fabrication operation represents substantial waste of this composition which amounts to a significant component of product cost.  
           [0008]    In a preferred embodiment of the present invention, a printing or coating station is situated downstream from the point of active diacetylenic monomer composition application and effects deposition of UV-blocker composition directly upon and in substantial register with the active monomer deposition to provide the latter component optimum protection from incident UV radiation. As in the past, additional printing stations may be provided in the fabrication process for application of desired indicia, such as reference color patches, use instructions, and advertising.  
           [0009]    The selective location, according to the invention, of UV-blocker composition only over those areas occupied by active monomer provides additional advantages beyond the direct saving in cost of otherwise wasted UV-absorbent composition. Since, in this improvement, the major extent of the label area is devoid of UV-blocker, indicia may be applied to various portions of that area at a later time and at a greater rate and diversity, and thus more economically, by means of UV-cured printing inks.  
           [0010]    Further, and of particular significance in expanding the capabilities of the diacetylenic monomer compositions into multiple response indicator systems, portions of a label face outside the UV-blocker protected TTI site may be employed as sites for indicators, including selected diacetylenic monomer compositions, dedicated as responsive to UV-radiation, thereby incorporating into a single label indicators for both time-temperature and time-radiation integrals relevant to the shelf life of an associated product. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]    The present invention will be described with reference to the accompanying drawing of which:  
         [0012]    [0012]FIG. 1 depicts in plan view the general conformation and functional response of a time-temperature indicator (TTI) system device of the prior art typically comprising an active diacetylenic monomer indicator composition and a UV-protective overlay film;  
         [0013]    [0013]FIG. 2 depicts in elevational cross-section, taken at  2 - 2  in FIG. 1( a ), the structure of the prior art TTI system device;  
         [0014]    [0014]FIG. 3 depicts in elevational cross-section, taken at  3 - 3  in FIG. 4, the structure of a TTI system device embodying the present invention;  
         [0015]    [0015]FIG. 4 depicts in plan view multiple TTI system devices embodying the present invention;  
         [0016]    [0016]FIG. 5 presents graphic data depicting the UV-protective efficacy of a device embodying the present invention; and  
         [0017]    [0017]FIG. 6 presents graphic data depicting the comparative UV-protective efficacy of a device embodying the present invention and one of the prior art. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0018]    As seen in FIG. 1( a ), a TTI system label  10  of the prior art typically comprises a self-adhesive substrate  11  upon which is printed a spot  13  of active diacetylenic monomer indicator composition. A threshold reference color body, such as shown in the form of a ring  15  surrounding spot  13 , is printed in close proximity to the active indicator composition and is provided in a color tone closely approximating the color density which will be developed in indicator spot  13  upon accumulation of the time-temperature integral predetermined to be representative of the shelf-life beyond which the intended associated product, e.g., a foodstuff, such as fish or fowl, or a medicament, such as vaccine or medicine, is expected to lose its utility or potency. As an example of such an expired shelf-life, the indicator composition spot  17  of the label in FIG. 1( b ) is shown to have polymerized under the influence of ambient temperature beyond the threshold integral period to yield a tone which is far darker than that of reference color ring  15 .  
         [0019]    The TTI label product may generally bear additional indicia  12  presenting identifying or instructional text and the like. Further, in order to mitigate the effect of incident UV-light on active indicator composition  13 , a sheet of transparent film  18 , a section only of which is shown in FIG. 1( a ), bearing a UV-absorbent blocker composition has often been coextensively laminated to the face of label substrate  11 .  
         [0020]    [0020]FIG. 2 depicts in greater detail a typical construction of the prior art TTI label of FIG. 1. Such a label  20  comprises a release sheet  21  support for label substrate  11  of stable paper or film, e.g., biaxially oriented polypropylene, and its pressure-sensitive self-adhesive coating  23 . The selected area, or spot,  13  of active diacetylenic monomer indicator composition is deposited on substrate  11 , preferably as an ink or lacquer in a screen, gravure, or other printing operation. A body of reference color, such as a registered ring  15 , is printed upon composition  13  to provide a means of ready comparison with polymerization color density level during progression of the target shelf-life. After application of additional desired indicia (not shown), UV-blocking overlay film  18  is laminated, preferably by means of an integral self-adhesive layer (not shown), upon the resulting composite label device.  
         [0021]    In contrast to the foregoing structure of the prior art, the TTI system label  30  of the present invention is fabricated in a manner to yield the device depicted in FIG. 3. While similar release sheet support web  21  and self-adhesive label substrate  11 ,  23  materials may be employed to carry the active indicator spot  13  of diacetylenic monomer composition, the present invention departs from past practice by applying a UV-blocking component layer  33 , preferably as a printed UV-absorbent transparent lacquer ink composition, directly over active monomer component  13 . The area of applied layer  33  may be in precise register with that of active spot  13 ; however, the simpler application may preferably be such that layer  33  extends to some degree beyond the area of monomer  13  to thus obviate concern of excessive and costly register control parameters. Such application provides the additional benefit of encompassing the monomer deposition with UV-blocker to minimize lateral exposure to vagrant radiation. In this manner, the UV-sensitive monomer component of the TTI system label is accorded optimum protective coverage with UV-blocker composition  33  while requiring only a minimum amount of such composition and avoiding in great measure the previously encountered costly waste.  
         [0022]    A color contrast comparison reference component  15  may be printed in turn with other desired indicia according to prior practice, but with the advantageous exception that improved and highly preferred UV-setting compositions and inks may now be employed without concern of deleteriously affecting the active monomer indicator composition with processing UV light. The utility of reference component ring  15  remains as with prior TTI labels in that, as seen in FIG. 4, the color density change progression of indicator  13  may be observed at any time through visible-transparent UV-blocker film  33  revealed at the annular opening in reference ring  15 . As an optional component to provide protection from physical abrasion or abuse, substantially inert, transparent film  38  may be applied over the label product in the manner previously employed with a UV-blocker overlay film  18 .  
         [0023]    In addition to a capability for subsequent application of printed indicia  42 , such as point-of-sale information, in label areas now unobstructed by UV-blocker, a further advantageous embodiment afforded by the invention may be seen in FIG. 4 which generally depicts a multiplicity of TTI system labels  40  as typically arranged in series during continuous printed fabrication on a section of carrier web  21 . Areas of label substrate  11  not otherwise occupied by active TTI components, and being devoid of UV-blocking composition, are now available to support active components of a responsive system, represented generally at  42 , for indicating an integral of time and UV-light exposure, that is, one constituting an indicator of shelf life vis-à-vis ultraviolet light to which an associated foodstuff or other product may, along with excessive heating, be susceptible. The limited and localized disposition of UV-absorbent composition achieved in systems of the present invention has enabled such expanded and complementary indicator utility.  
         [0024]    Representative implementations of the present invention may be seen more specifically in the following examples.  
       EXAMPLE I  
       [0025]    An active TTI system indicator composition comprising a commonly used substituted diacetylenic monomer was prepared by first ball milling about 9.0 parts by weight of 2,4-hexadiyn-1,6-bis (ethylurea) and 25 parts n-butanol for about 16 hours to obtain a fine particle dispersion which was then mixed with a lacquer solution of about 8.3 parts of ethyl cellulose and 60 parts n-butanol. The mixture was then thinned to a desired printing ink consistency with up to about 85 parts of n-butanol.  
         [0026]    A UV-blocker ink composition of printable consistency was prepared by thoroughly mixing about 3.5 parts by weight of 2-2′ dihydroxy- 4 -methoxybenzophenone, 2.5 parts Orosol Yellow dyes, and 2.1 parts ZnO into a lacquer base prepared with about 18.4 parts nitrocellulose, 5.0 parts 2-ethylhexyl-2-cyano-3,3-diphenyl acrylate, and 1 part silicone-based flow adjunct in a solvent mixture of about 45 parts ethyl- 3 -ethoxy propionate, 5.7 parts isopropanol, 11.4 parts ethyl acetate, and 5.4 parts diacetone alcohol.  
         [0027]    The above indicator ink composition was printed as a series of spot images of about 6 mm diameter on a first length of continuous strip substrate web of white-pigmented biaxially oriented polypropylene in a Gallus R250 (Gallus, Inc., Philadelphia, Pa.) rotary screen printing press utilizing a 39%, 180μm screen. A second length of substrate web was likewise printed with indicator composition, and at a subsequent press station the buff-colored indicator spots were over-printed in similar manner with the above UV-blocker ink as substantially registered images of about 8 mm diameter. Samples were taken from the two printings for comparative testing in the following manner.  
         [0028]    Sample sections (A and B) were taken from the first length of printed strip web without UV-blocker overprint. Sample (A) was sealed within an opaque foil envelope for use as a control and sample (B) was retained for use as is. A third sample (C) was taken from the second length of printed web having UV-blocker overprint for use as is. These samples and control were exposed together to mid-day sunlight (at about 22° C. and 25% relative humidity) with measurements of indicator spot color density being taken at regular intervals with a commercial reflection densitometer (X-Rite  404 ) operating in the cyan mode until a predetermined threshold color density of a sample was observed.  
         [0029]    Results of these tests are shown in FIG. 5 as traces of the relative color density change data. As anticipated, data  53  of the enclosed control sample (A) showed no color density change. Data  55  of the unprotected sample (B) indicator spots showed an increase in color density at a regular rate to a final dark blue-black during the nearly 3 hour test period, thus confirming the susceptibility of the active indicator composition to the polymerizing influence, at least in part, of ultraviolet light. Data  57  of indicator sample (C) comprising UV-blocker overprint according to the invention, on the other hand, showed substantially no change in color density during the test period, thereby indicating the high efficacy of the overprint embodiment. The offset of these latter data from those of control sample (A) are attributable to the color initially imparted by UV-blocker composition dyes.  
       EXAMPLE II  
       [0030]    The comparative efficacy of the present invention and the prior art with respect to exposure over a more limited wavelength range of ultraviolet light, such as would normally be encountered in artificial lighting of refrigerated foodstuff display counters, was tested in the following manner. Samples (D and E) of plain and UV-blocker overprinted active indicator composition were prepared in the manner of Example I with the exception of utilizing as the active substituted diacetylenic monomer component a co-crystallized 2:1 mixture of 2,4-hexadiyn-1,6-bis (ethylurea) and 2,4-hexadiyn-1,6-bis(propylurea). A comparative sample (F) according to the prior art was prepared by laminating a commercial UV-blocker film over a portion of sample (D) plain active indicator composition web material.  
         [0031]    The prepared samples were exposed to about 2800 lux under a fluorescent light fixture in a constant ambient of about 4° C. to substantially simulate storage in a commercial food market display case. As in Example I, regular measurements were made of active indicator composition color density and the relative color density change data were plotted to provide the results shown in FIG. 6. The substantially regular increase in UV-initiated color density in plain sample (D) is represented in the data of trace  63  and is seen to reach a maximum during the  9  day test period. The limited increase in color density of the prior art sample during the same period in overlay-protected sample (F) is shown in the data of trace  65 , while trace  67  data from sample (E) shows the lesser rate of UV-initiated color increase achieved by the greater efficacy of the present invention arrangement.  
         [0032]    Other TTI system label devices were prepared according to the present invention utilizing various monomer components described in the above-noted patent specifications to achieve a range of time-temperature integral endpoints representative of numerous foodstuff and medicament shelf lives. In each instance, in addition to the readily calculable savings in reduced materials waste, the devices responded with improved efficacy as compared with prior art products.  
         [0033]    It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in the light of the foregoing description and examples, and such embodiments and variations are intended to likewise be included within the scope of the invention as set out in the appended claims.