US3340135A - Laminar means for changing color in response to embossment - Google Patents

Description

p 5, 1967 R. s. AVERY 3,340,135

LAMINAR MEANS FOR CHANGING COLOR IN RESPONSE TO EMBOSSMENT Filed May 6, 1963 IN Fzone of sfrerch 1 f2 QM] I0 40o 351} F 4 INVENTOR.

RAY S. AVERY 52 BY ATTORNEYS United States Patent 3,340,135 LAMINAR MEANS FOR CHANGING COLOR IN RESPONSE TO EMBOSSMENT Ray S. Avery, Bradbury, Califi, assignor to Avery Adhesive Products, Inc., San Marino, Califi, a corporation of California Filed May 6, 1963, Ser. No. 278,143 4 Claims. (Cl. 161-120) The present invention relates to a composite sheet or tape structure which changes color in response to embossment.

It has long been recognized that various plastic sheet and tape materials change color or opacity when coldstretched. The color, or degree of opacification, may vary abruptly as a function of elongation of a threshold region to give good definition or contrast between the original and new color states corresponding respectively to prethreshold and post-threshold elongations. This threshold region is generally near the yield point of the material.

Elongation may be expressed as a ratio of stretched length to original length, or stretch ratio. Elongations within the threshold region correspond to a range of such ratios which may be designated the threshold range and which is narrower than the entire range of stretch ratios. The latter range starts at 1 and extends to the ultimate value corresponding to rupture.

In an important aspect, the invention provides a composite sheet or tape which is selectively responsive to less than all of the several types of mechanical deformations (bending, drawing, etc.) involved in the embossing of straight or curved lines on the label or .tape. Embossing dies which define such lines are usually arranged in the form of alpha-numeric characters and like symbols. Previously known sheets or tapes which have generally acceptable color change properties exhibit an undesirable lack of selectivity as between the kinds of mechanical deformations in which a color change response is desired (embossing) and other kinds of mechanical deformation Where a color change response is not desired (e.g. bending). These previously known tapes include laminar combinations of a color change material provided with adhesive and with a backing sheet to protect the adhesive.

According to one aspect of the present invention, sheets -or tapes may be provided which exhibit a color change response that is both sensitive to embossing and remarkably insensitive to bending, thereby greatly irnproving selectivity as between embossing and other forms of mechanical deformation.

Since embossing itself represents a combination of mechanical deformations including bending, it appears that in this aspect the present invention relates to a color change phenomenon which is selectively responsive to less than all types of mechanical deformations involved in embossing. Under many conditions this may be readily confirmed by respectively comparing embossments formed with the said pair of dies in (1) previously known sheets or tapes and (2) sheets or tapes of the present invention. Such comparisons demonstrate for example the elimination of undesirable color changes at the embossment root while desirably retaining color change at the crest and regions adjacent to the crest.

In a particularly important aspect, the present invention provides a color change tape having better efiective adhesion and conformability than previously known color contrast sheets and tapes.

In another respect, the invention also makes possible a good intensity of background color even when undercoated colors or colored adhesives or colored bases are relied upon to provide the background or field against which is contrasted the color change areas of the color change material itself, and furthermore even when the film material has relatively poor transparency.

The present invention contemplates the combination of a relatively mobile color change face sheet or tape (or cast film or coating) with a base which, when embossed as part of the face-bace combination, has less mobility, or less tendency to draw, than does the face. This aids in peaking or promotion of strain concentration precisely where color change is desired over the embossment crests. The result is a good color change response to embossment, even when the face material consists of a fairly thin film (say one or two mils in thickness) which in its uncombined state will not give a color change response to embossment, or will respond, and then rather raggedly, only at the very tips and roots of the embossments where the mating dies form corner bends in the film material.

Optionally, the present invention can eliminate perceptible color change at the roots of the embossment. This is an improvement over the best color changing sheets or tapes previously known which, under the same embossing conditions, exhibit an undesirable color change or halo effect at the roots of the embossments, so that the lines forming each embossed character are (as is desired) set oif by primary contrast color regions at the embossment crests but (as is not desired) are somewhat obsoured and degraded by halos, i.e. secondary contrast color regions which extend along the roots of the embossed lines in spaced relation to the primary contrast regions.

The features of the invention will be more fully appreciated after a discussion of the accompanying illustrations which are in a schematic or diagrammatic form.

FIGURES 1A and 1B are diagrammatic non-scaled illustrations of a film of material which is uncombined or entirely self supporting.

FIGURES 2A and 2B are diagrammatic non-scaled illustrations of a combined color changing face and base according to the present invention. FIGURES 2A and 2B respectively illustrate the combination before and after embossment.

FIGURE 3 is a diagrammatic and smaller but likewise non-scaled illustration of an embossed web combination illustrating certain aspects of the invention.

FIGURE 4 is a view similar to FIGURE 3 also illustrating certain aspects of the invention.

An uncombined face layer 10 is shown in FIGURE 1 for purposes of exposition, but it will be understood that this face layer does not in itself constitute an embodiment of the invention. On the contrary, the invention contemplates combining the face 10 with a suitable base, or forming the base 10 on a suitable base as by coating, as more fully dis-cussed below. However certain preliminary considerations make it desirable to illustrate an uncombined face layer 10 in FIGURE 1. The face layer 10 may include compounded stocks of acrylonitrile-butadiene-styrene, polystyrene or polyvinyl chloride with suitable plasticizers, stabilizers, and lubricants, the base resins being provided in particulate form and being compounded with the additives and sheeted as by coating as described below, or by calendering, extruding or formation on a planishing press. The color change material compounding steps may be conventional steps as described for example in US. Patent 2,925,625, but as above mentioned, the base resin particles or agglomerates which are employed as the primary sheeting ingredient may comprise acrylonitrile-butadiene-styrene, or polystyrene type resins. However annealed or unannealed polyvinyl chloride may be employed, but care should be taken that the mobility relationships described herein are established, as by suitable plasticizing or other modifying of the contemplated face or base material, or employment of metallic, partially metallic, fibrous, or partially fibrous bases. For example,

other factors being equal, best performance may be achieved by staying below the lowest thicknesses previously thought to be at all operative (say below 3 mils) in order to provide increased mobility of the color change material in its self supporting state.

With such modifications the layer is in a condition such that even if it is an annealed polyvinyl chloride film its embossment may not embody previously contemplated color change methods inasmuch as only bending, and not permanent embossment as such, may accomplish color change. Only the outside corners of bends formed in the film may opacify or change color. Thus, for example, when the color change film is embossed at the region 11 as shown in the FIGURE 1B, the embossment does not change color in regions adjacent the tip of its crest, although it may change color at the corner bend region 12 at the very tip of the crest and also at the corner bends at the roots 13. Thus the color changes do not essentially result from embossment, as such, but from secondary mechanical deformations occurring only at the very tips and roots Where the mating dies form sharp corner bends in the film.

To obtain a good color change effect, it is necessary that the color change extend over the crest of the embossment and Well down the sides. In the case of the unsupported film 10', an adequate color change in response to embossment does not occur. Apparently in the critical areas, the stretch ratio does not exceed the threshold range. For discussion there may be chosen a vicinity 1 such that this vicinity forms part of the critical area after deformation of the tape shown in FIGURE 1B. At this vicinity 1 there may be selected any two points such that between them there is an arbitrarily small length a. Some stretching of the tape must occur as the film changes from the condition of FIGURE 1A to the condition of FIGURE 13, and this change means that elongation at the vicinity 1 will be of a certain amount which may be designated A a (the two selected points will move apart by this amount) so that at the vicinity 1 the ratio of elongation of the tape is:

If the designation t is applied to any ratio which is well within the threshold range previously referred to, the following relationship is implied by the lack of color change at vicinity 1:

This relationship results from the relative mobility of the film 10. A corollary of this mobility is the drawing action which occurs around the roots of the embossment as it is formed, as indicated by the arrows 16. This drawing action in turn is a reflection of the fact that some of the material forming the final embossment 11 is supplied or replaced from the illustrated zone of stretch 17. The limits of the zone of stretch are the limits beyond which no stretching of the film 10 occurs as an incident of embossment. As mobility is used in the present description with respect to a web (film, sheet or base), the smaller the zone of stretch of the web, the less the mobility of the web, and the greater the zone of stretch, the greater the mobility.

The extent of the zone of stretch for a particular film, sheet or base may be determined by direct examination, with or without use of a grating or printed patterns as references to show where stretching begins in cases where reference points cannot be established by simple observation of the Web. The bounds of the stretched portion of the web can also be determined as those locations Where sensitive thickness measurements indicate the web commences to depart in the thinning-down direction from its normal thickness in the neighborhood of the embossment.

As will later be discussed at more length, the base on which the color change face sheet or tape 10 is supported must act as an anchoring agent or immobilizer so as to reduce mobility at the color change face and thereby concentrate and localize stresses, rather than acting as a mobile agent to equalize or ease peak stresses produced in the drawing operation.

The color change face is quite mobile as compared to the base, or conversely stated, the base is quite immobile so that the drawing action of an embossing step is limited to the region of the embossment and particularly the drawing components thereof, and it is there that embossing stresses and strains are concentrated.

FIGURE 2 illustrates a face film 10 which may in all respects be identical to that illustrated in FIGURE 1, but which is combined with or formed on a supporting base 20. The base 20, when embossed as part of a facebase combination, exhibits less tendency to draw than does the face. Thus the zone of stretch of the combined face and base is substantially less than that of the face film alone, as indicated in FIGURE 2. Advantageously the zone of stretch of the base alone is substantially less than that of the face film alone. The extent of the zones of stretch may be determined as previously described.

As a result of the reduced extent of the zone of stretch of the combination shown in FIGURE 2, there is little or no drawing action similar to that indicated by the arrows 16 in FIGURE 1 when the combination illustrated in FIG- URE 2 is embossed at the embossment 21. The result is a good color change response to embossment over the crest of the embossment 21 and down the sides thereof, as illustrated at 22. Furthermore, substantially no perceptible color change occurs at the roots 23 of the embossment. This is an improvement over the best color changing sheets or tapes previously known which, under the same embossing conditions, exhibit an undesirable color change or halo effect at the embossment roots. As previously mentioned, this halo effect means that the lines forming each embossed character are degraded by the color change at the roots. Such color change at the roots is spaced from the primary contrast color region, hence the term halo.

While present experimental models of the invention do in fact eliminate halo effect, as just described, enhancement of the color change capacity of the face-film may be advantageously accomplished according to the general teachings of the invention without necessarily accomplishing also the elimination of halo efiect.

If along the length of the tape at a vicinity 2 in the tape combination shown in FIGURE 2A, corresponding to the vicinity 1 of FIGURES 1A and 13, there are again selected any two points such that between them there is an arbitrarily small length a (the same as the length a in FIGURES 1A and 1B), then following embossment and as shown in FIGURE 2B, the elongation at this vicinity will be by the amount A 42 (the two selected points will move apart by this amount) so that at the vicinity 2 the ratio of elongation of the tape is:

If the designation 2 continues to apply as before to the same ratio as before, such ratio being any ratio which is Well within the threshold range previously referred to, the following relationship is implied by the color change at vicinity 2:

Therefore as between the tape of FIGURES 2A and 2B and the tape of FIGURES 1A and 1B:

In this expression the first and third terms are the stretch ratios of arbitrarily small identical lengths a of tape at respective locations 2 and 1, which locations strictly correspond to each other as to their position in the embossment. Although the locations 2 and 1 strictly correspond, the stretch ratio at location 2 exceeds the ratio t which in turn exceeds the stretch ratio at location 1.

Thus, the ratio of elongation at the region 2 exceeds the threshold range, and this occurs continuously along regions which extend well down the sides of the embossment as well as over the top thereof. Top color change however, does not undesirably rely on bending of the material, with much of the stress and strain failing to accomplish color change and instead'merely being dissipated by stretching over a large zone of stretch, but rather results from the peaking or promotion of strain concentration precisely where the color change is desired-up and over the sides and peak of the embossment crests.

It should be noted that the base 20 may comprise a single sheet or tape layer bound to the layer 10, or alternatively may itself be a laminar structure (which may include a removable backing) so long as it exhibits a markedly lower mobility than the face material alone. Generally it is advantageous to limit the face to less than 4 mils thickness and to have the thickness of the combination exceed 10 mils. The base 20 (whether laminar or non-laminar) thus exceeds the thickness of the face 10. It may comprise any plastic or fibrous web structure having the requisite low degree of mobility as compared to the face 10.

Any suitable adhesive may be employed between the base 20 and the face film 10, but the bonding should be firm, that is, it should resist substantial shear deformation or slipping of the face sheet 10 to thereby impose on the face sheet 10 the mobility restrictions described above. In suitable instances direct cohesion between the layers may be relied upon.

Many known adhesives otherwise suitable for mounting labels or the like exhibit a relatively good peel back release, particularly when known release coating are provided on the surface to be released, but, prior to release, such known adhesives exhibit a high resistance to interfacial slipping or shear deformation. In this respect, the invention contemplates the provision of a face 40 generally similar to the face 10 together with a base 50 generally similar to the base 20. The base 50 may be a selfreleasing material or may be provided on its front or inner face 51 with a suitable release coating, and it is combined with the face 40 by means of an adhesive 47. The mobility relationships described above are provided so that the face 40 has good color change characteristics upon embossment, as at an embossed region 41. However, following embossment, the supporting base 50 may be peeled away as indicated in FIGURE 3 thereby providing a highly flexible label consisting solely of the adhesive coated face 40.

Again, it is advantageous to limit the face 40 to less than 4 mils thickness and to have the thickness of the combination of elements 40 and 50 exceed 10 mils so that the thickness of the base 50 exceeds the thickness of the face 40.

The relatively great flexibility and conformability of this product achieves a better adhesion than the relatively rigid known color changing tapes even when other factors, such as the adhesive formulation, are identical. Furthermore, conformability of the product to a variety of surface shapes is obviously enhanced.

The base 50 may also be laminar so that only a portion of it is removable, the other portion remaining permanently associated with the face 40, as shown in FIGURE 4 where the base 50 is illustrated as a laminar base 50a which includes a removable portion 52 and a portion 53 which remains permanently associated with the face 40. The adhesive 47a which may be ultimately employed to mount the product is located between the layers 52 and 6 53 of the base 50a. The inner face 54 of the layer 52 may be provided with a suitable release coating.

Again it is advantageous to limit the face 401: to less than 4 mils thickness and to have the thickness of the combination of face 40a and base 50:: exceed 10 mils so that the thickness of the base 50a substantially exceeds the thickness of the face 40a. The removable portion 52 of the product here exceeds the combined thickness of the remaining portions 40a and 53.

The portion 53 may be a thin fibrous material such as impregnated or ordinary paper or fabric. It may be a metallized or colored or colorless plastic, or a metal sheet or foil. In one embodiment that was made, the layer 53 comprised aluminum sheeting of foil having an anodized surface on which the face 40a was applied as a liquid coating. The coating comprised acrylonitrile-butadienestyrene which was dissolved in a solvent which served as a coating vehicle. The applied coating was dried to a, thickness of 1.5 mils. The anodized surface apparently promoted good cohesion or bonding at the interface of the layers 40a and 53. It will be understood that coatings rather than preformed films may be similarly employed as the face material 10 URES 2A and 2B.

The adhesive employed in the embodiment of FIG- URES 2A and 2B, or in the embodiment of FIGURE 3, may include a colorant such as a dye or pigment, or the rear or inner surface of the face 10, 40 or 40a may include a separate colorant. In cases where the base 20 or 50 is to remain permanently adhered to the face 10 or 40, the background color may be provided by colorants included in the base. The background color may be provided by the base portion 53 in the embodiment of FIG- URE 4. Good intensities of such background color areas are achieved when very thin face films such as one of two in the combination shown in FIG- mil films are employed. As above described, the present invention makes possible the embossment of such extremely thin face films which can be much clearer or transparent and involve far less loss by way of light diffusion or the like than the thicker color change films of the prior art. Any requirement that color change films of the prior art be annealed can be expected to be removed, although annealed films may be employed if desired.

The prior art found it necessary for color change material to be compounded with colorants included in them in order to achieve good intensity of background color. The present invention contemplates the provision of colors, if desired, in the face, but, as justed pointed out, good intensity of background color can be expected with the present invention without resort to inclusion of colorants in the face.

Color change enhancement according to the present invention is best achieved by a rigid immobile face-base bond, as by use of rigid immobile heat seal adhesives or solvent cements, or by direct face-base cohesion. However somewhat softer adhesives such as those of the pressure sensitive type may be employed without losing the color change enhancement advantages of the invention. Particularly when the somewhat softer adhesives are used, tapes or sheets such as those shown in FIGURES 2 and 3 are remarkably insensitive to bending. They may be bent to a radius of a small fraction of an inch in either direction without showing any color change. In many instances they may actually be creased with the face 10 on the inner side without showing any apparent color change. Thus they represent a substantial improvement in colorchange-response selectivity as between (1) embossing as such and (2) bending.

As will be clear from the above, the color change face may not be a preformed film in some instances, but may be a cast film or a coating applied by employing a solvent or dispersing agentrsuch coatings do not necessarily employ acrylonitrile-butadiene-styrene as a base resin. For example a polyvinyl chloride material suitable for making a preformed face such as that shown in U.S. Patent 2,925,625 may instead be dissolved in solvents or dispersed (as in a water emulsion) to form a fluid which is then applied and dried on a base as a thin coating with retention of latent color change characteristics providing there is a good final bond between the dried face and the base. This is to be contrasted with sheeting the material as with calenders, planishing presses or extruders which cannot achieve the thinnesses contemplated or preferred in the present invention.

The invention is not restricted to the slavish imitation of each and every one of the details and features described above which have been set forth merely by Way of example with the intent of most fully setting forth the teaching of the invention. Obviously devices may be provided which change, eliminate, or add certain specific details and features without departing from the invention.

What is claimed is:

1. An article for contrast color embossment comprising a face film of latently color changing material which is however so thin as not show, in its self supporting state, a color change response to the mechanical drawing action which is incident to embossment, said face film being combined with a thicker supporting base, the face film, in the combination, being a patently color changing material showing a color change response to the mechanical drawing action which is incident to embossment, said backing being operable to concentrate color changing stress in said face film along convex embossed portions of said face film and being operable to resist the occurrence of color changing stress in the face film along concave embossed portions of said face film.

' 2. An article as set forth in claim 1 in which the base taken alone being less readily drawable by embossing dies than is the face film taken alone, whereby the embossment-responsive color change capacity of the face is enhanced by concentration of the facial stresses and re- 8 sultant strains which are generated by embossment of the combination.

3. An article for contrast color embossment as set forth in claim 1 wherein said face film has a thickness not greater than four mils and the total thickness of said article including the thickness of said face film and said supporting base is at least ten mils, the combination of said face film and supporting base being bendable in either direction to a radius of a small fraction of an inch without producing any significant color changing stress in said face film.

4. An article for color contrast embossment comprising a face film of color changing material which is however so thin as to show, in its self-supporting state, a substantial halo effect in color change response to the mechanical drawing action which is incident to embossment, said face film being combined with a thicker support base, said face film, in combination with said base, being a color changing material showing greatly reduced halo effect in color change response to the mechanical drawing action which is incident to embossment, said backing film being operable to concentrate the color changing stress in said face film along convex embossed portions of said face film and being operable to resist the occurrence of color changing stress in the face film along the concave em-. bossed portions of the face film.

References Cited UNITED STATES PATENTS v 2,996,822 8/1961 Souza 156-219 X 3,036,945 5/1962 Souza -5. 16l120 X 3,198,688 8/1965 Yoder 156-209 X 3,240,932 3/1966 Haines 11736.7 X

M. BERGERT, Primary Examiner.

H. F. EPSTEIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,340 ,135 September 5 1967 Ray S. Avery It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1, line 16, for "of", second occurrence, read at line 57, for "said" read same column 2, line 28, for "contrast" read contrast color column 7, line 20 for "not" read not to Signed and sealed this 29th day of October 1968.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting ()fficer Commissioner of Patents

Claims (1)

1. AN ARTICLE FOR CONTRAST COLOR EMBOSSMENT COMPRISING A FACE FILM OF LATENTLY COLOR CHANGING MATERIAL WHICH IS HOWEVER SO THIN AS NOT SHOW, IN ITSELF SUPPORTING STATE, A COLOR CHANGE RESPONSE TO THE MECHANICAL DRAWING ACTION WHICH IS INCIDENT TO EMBOSSMENT, SAID FACE FILM BEING COMBINED WITH A THICKER SUPPORTING BASE, THE FACE FILM, IN THE COMBINATION, BEING A PATENTLY COLOR CHANGING MATERIAL SHOWING A COLOR CHANGE RESPONSE TO THE MECHANICAL DRAWING ACTION WHICH IS INCIDENT TO EMBOSSMENT, SAID BACKING BEING OPERABLE TO CONCENTRATE COLOR CHANGING STRESS IN SAID FACE FILM ALONG CONVEX EMBOSSED PORTIONS OF SAID FACE FILM AND BEING OPERABLE TO RESIST THE OCCURRENCE OF COLOR CHANGING STRESS IN THE FACE FILM ALONG CONCAVE EMBOSSED PORTIONS OF SAID FACE FILM.

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