US3481755A - Indicia recording polyamide coating - Google Patents

Description

United States Patent 3,481,755 INDICIA RECORDING POLYAMIDE COATING Francis E. Gould, Princeton, N.J., assignor to Princeton Chemical Research, Inc., Princeton, NJ. No Drawing. Filed Apr. 25, 1966, Ser. No. 544,716 Int. Cl. B44c 1/22; B44m 5/00 U.S. Cl. 1178 6 Claims ABSTRACT OF THE DISCLOSURE Process of producing a polyamide film form material suitable for use as an embossing tape or as other indicia receiving means, which comprises dissolving a polyamide in a fluorinated alcohol solvent therefor, adding to such solution a non-solvent for the polyamide which is miscible with the fluorinated alcohol solvent, and casting this mixture on a suitable substrate to form an opaque film of such polyamide. The opaque film may be clarified by exerting pressure thereon, such as with a stylus or with a die so as to either to form indicia on selected portions of the film, or to clarify the entire film. Where the opaque film is cast on a pigmented substrate, the exertion of pressure on the film causes the pigmentation of the substrate to show through, whereby the indicia thus formed appears pigmented in the same color as the substrate.

This invention relates to an indicia recording polyamide coating. The invention more particularly relates to an article having a polyamide coating upon which indicia may be imprinted by the application of pressure.

It is well known that certain transparent plastic materials, such as certain polyvinyl chloride films maybe opacified by the application of pressure which distorts the films. These films are utilized in producing the well known and Widely marketed embossing tapes which are used for signs, labels, and the like. These tapes generally consist of a pigmented plastic film or foil which are overcoated with a transparent coating or layer of the plastic which will opacify. The tapes are fed through an embossing machine in which the desired letters to form the labels are impressed from the back through the tape so as to distort the tape forming a raised or relief letter, the distortion of the overcoat or laminate opacifying the same, rendering it white, so that the letters appear as raised white lettering on the pigmented tape background.

The tapes are generally provided with a pressure sensitive adhesive on the back protected with a peel-off sheet so that after imprinting of the desired lettering the peelotf backing is removed and the tape secured to a desired article by pressure. The known embossing tapes, however, which depend on the opacifying of the embossed regents of the top layer can only be used for forming white letters on a black or contrasting color background, and may not be used for the production of dark lettering or indicia on a lighter background.

An object of this invention is an opaque coating which may be selectively clarified by the application of pressure thus allowing the imprinting of darker contrasting indicia on a lighter background by the application of pressure.

A further object of this invention is an article having an opaque coating on a visually contrasting base which coating is capable of being selectively clarified by the application of pressure whereby indicia may be imprinted thereon.

A still further object of this invention is an embossing tape which may be embossed with darker characters or indicia on a lighter background.

A still further object of this invention is a novel process for casting a polyamide film so that the cast film is opaque but may be clarified by the application of pressure.

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These and still further objects will become apparent from the following description:

In accordance with the invention it has been discovered that if a polyamide film is cast from a solution of polyamide in a solvent also containing admixed therewith a liquid which is a non-solvent for the polyamide but miscible with the polyamide solvent, this film is opaque but may be selectively clarified by the application of pressure, as for example, with a stylus or die. Thus, by casting opaque polyamide film in the above matter as a coating on a visually contrasting base an article is formed which is capable of recording indicia thereon by the application of pressure. This application of pressure will selectively clarify the polyamide film, thus allowing the visually contrasting base to be seen through the clarified areas corresponding to the indicia.

A preferred article in accordance with the invention comprises an embossing tape consisting of a plastic tape, preferably with a conventional pressure sensitive adhesive backing and peelable protecting layer, which tape is coated with the polyamide coating in accordance with the invention. The base film is preferably of a darker contrasting color, such as a pigmented film, as for example, black. Additionally, the opaque polyamide coating may itself be overcoated with a further colored coating so that the tape appears as a colored tape and the indicia such as the letters imprinted thereon assume the contrasting color of the base layer.

The starting polyamide useful in accordance with the invention may be of any of the known or conventional polyamides or Nylon polymers and may .be polycondensates of diamines and dicarboxylic acids, such as 1,6- diaminohexane and adipic acid; and the acyclic polycondensates of e-caprolactam, u-butyrolactam, a-valerolactam, enanthiolactam, and the like, including their alkyl, aralkyl, and aryl derivates. The starting polyamides need only have sufficient molecular Weight so as to enable their casting into a solid film. There is no upper limit on the molecular weight, though a molecular weight range of between 15,000 and 8 million is generally preferred.

The solvent in which the polyamide is dissolved may be a fluorinated alcohol solvent. This fluorinated alcohol may be any primary, secondary or tertiary alcohol containing at least one fluorine atom. The alcohol may additionally contain up to 5 chlorine atom substituents. Most preferably the fluorinated alcohol solvents are monoand polyfluoro-substituted lower alcohols which may additionally contain chlorine substituents.

Examples of such alcohols include:

2,2,2-trifluoroethanol; 2,2-difluoroethanol;

2-fluoroethanol; 1,l,l,3,3,3-hexafluoroisopropanol, heptafluoroisopropanol; 1,1,2,3,3-pentafluoro- 1,3-dichloro-2-propanol; and 1,2,3-trifluoro- 1, 1, 3 ,3 -tetrachloro-2-prop anol.

The liquid, which is a non-solvent for the polyamide and miscible with the solvent fluorinated alcohol, may be any organic liquid which is non-reactive with the other constituents. Examples of such liquides include nonfluorinated aliphatic and alicyclic alcohols such as methanol, ethanol, isopropanol, and cyclohexanol; ketones, such as acetone and Z-butanone; tertiary amides, such as dimethylformamide, N-methyl pyrrolidone and dimethylacetamide; halogenated alkanes, such as methylene chloride and ethylene chloride; ethers, and nitro derivatives of aliphatic hydrocarbons, such as nitroethane and nitromethane, and the like.

Both fluorinated alcohol solvent and the non-solvent liquid should have a boiling point below 180 C., and preferably below C. The polyamide, the fluorinated alcohol solvent, and the liquid non-solvent for the polyamide which is miscible with the alcohol solvent are simply mixed together to form a solution. Generally, it is preferable to first dissolve the polyamide in the fluorinated alcohol solvent and then stir in the miscible liquid non-solvent. The amount of polyamide used in relationship to the fluorinated alcohol solvent may vary between about 1 and 40, and preferably 5 and weight percent. The weight ratio of the solvent alcohol to the non-solvent miscible liquid may range between about 1:1 to about 15: 1, and preferably about 3:1 to 6:1.

The mixing may be effected at any temperature at which the constituents remain liquid, but temperatures between about to 75 C. have been found most convenient. The solution can then be applied to the base, or substrate by any of the known or conventional coating techniques, as for example, brushing, spraying or dipping, and then the coating is allowed to dry, The drying may be effected at normal or lower temperatures, though it is generally preferable to use drying temperatures of C. and above, the upper temperature limitation simply being the temperature above which the polymer and/or substrate will be adversely affected by the heat.

The base or substrate may be any solid surface which should visibly contrast with the opaque dried polyamide film (which is white), or with the color of any overcoat which is used. The substrate may thus be a pigmented or unpigmented polymer film, as for example, films of polyvinyl chloride, polyesters, polyolefins, polycarbonates, and the like. The coating may additionally be effected on any suitable substrate, such as metal, glass, rubber, paper, wood or ceramics, which may either be colored or uncolored. In general the thickness of the coating layer is simply determined by the thickness at which the starting solution may be evenly applied. In general the dried coating will have the thickness between 0.1 and 6 mils, and preferably 1-3 mils.

It is also possible to cast the polyamide as a separable film which may be used per se, or which may be laminated on a backing. For this purpose the film is cast on a surface from which the same may be stripped, as for example, a polyethylene surface or a silicon-treated surface. After the casting the film is stripped and used per se, as for example, for forming clear indicia on a white background, or is subsequently laminated on a backing using, for example, a pressure sensitive adhesive.

It is also possible to cast the polyamide film on a transparent film and utilize the same per se, or as a laminate on another substrate. Thus, for example, polyamide film may be cast on a clear polyethylene, or polyolefin foil or film, or on a clear cellulose film. These films may then be laminated on any substrate of a contrasting color and a further film of a dyed resin may be cast thereon.

Examples of dyed resinous overcoats include those of polyvinyl chloride, polyvinyl butyral, polyvinylidene chloride, alkyds or polyvinyl esters, and the like. These may be applied by the conventional techniques, well known to those skilled in the art. The overcoat should, of course, be of a low enough density and thickness so that the substrate becomes at least partially visible when the polyamide film is clarified by the application of pressure.

By suitable election of the color of the substrate and by suitable coloring of the polyamide, as for example by the overcoat, it is possible to obtain almost any contrasting color combination for the indicia and background and thus, for example, almost any colored letters may be imprinted by pressure on almost any colored background.

The embossing tapes produced in accordance with the invention substantially correspond to those well known and conventional in the art, except for the opaque polyamide coating which is clarified by the embossing. Thus, aside from this coating, and the colored overcoat, the tapes have the conventional form and may be provided with a conventional pressure-sensitive adhesive layer which is covered by a peelable release backing. Pressuresensitive adhesive may, for example, consist of polyacrylates and natural and synthetic rubbers. The peelable release backing may be a thin film of polyethylene or paper. The tapes may be imprinted in conventional embossing machines, as for example conventional hand-type tape printers which are provided with raised die letters which are pressed into the film during the printing operation from the back.

When the coatings in accordance with the invention are applied to backings which cannot be embossed, the imprinting may simply be effected by the application of pressure, as for example, with the use of a stylus.

A clear sheet of film which is coated with the polyamide in accordance with the invention may be used as a master in a photoreproduction process in the same manner as an ordinary negative as the sheet is substantially opaque, except for the clarified areas where the indicia has been imprinted by pressure.

The following examples are given by way of illustration and not limitation.

EXAMPLE I A mixture of polycaprolactam (15 parts) and 2,2,2- trifluoroethanol (85 parts) is stirred until solution is effected. Added slowly with good stirrring at is n-buta- 1101 (22.5 parts).

Films were cast on polyvinylchloride pigmented with carbon black. The resulting opaque, white coating was printed via metal slug or stylus. The resulting black print on white background was excellent in color hiding and contrast.

EXAMPLE II The procedure of Example I is repeated employing a 2,2,2-trifluoroethanol solution of polyenanthiolactam with Z-butanone to produce a white, opaque polyamide coating. Similar results are obtained on printing.

EXAMPLE III The procedure of Example I is repeated by casting the polyamide coating on a polybutene-l surface impregnated with chrome yellow. A good yellow print on a white background is obtained.

EXAMPLE IV In a similar fashion to Example II using chlorinated polyethylene impregnated with hydrated chromium oxide, green print on a white surface is obtained.

EXAMPLE V Polycaprolactam (15 parts) in 2,2,2-trifluoroethanol '(85 parts) was warmed to and n-butanol (22.5 parts) added. The mixture was stirred to obtain a clear solution. Films were cast onto a polyvinylchloride film containing carbon black to obtain a white coating. The dried white coating was top-coated with a clear polyvinylbutyral film dyed with Majestic Yellow Toner (Imperial Color and Chemical Dep., Div. of Hercules Powder Co.) cast from methanol-toluene solution (:15). Imprinting the air-dried coating gave black letters on a yellow background.

EXAMPLE VI 'a fluorinated alcohol solvent to form a 1 to 40 weight percent solution of said polyamide, admixing with such solution a non-solvent for said polyamide in a Weight ratio of solvent to non-solvent of about 1:1 to 15:1 which is miscible with said fluorinated alcohol solvent; casting such admixture onto a suitable substrate and removing said solvent and said non-solvent by drying at a temperature of about 25 C. up to less than the temperature at which said polymer and said substrate are 'adversely affected thereby, whereby forming a substantially opaque article of said poly-amide.

2. Process as claimed in claim 1, wherein said fluorinated alcohol solvent is at least one member selected from the group consisting of 2,2,2-trifluoroethanol; 2,2-

difiuoroethanol; 2-fluoroethanol; 1,1,1,3,3,3 hexafluoroisopropanol, heptafluoroisopropanol; 1,1,2,3,3, pent-afiuoro-1,3-dichl0ro-2-propanol; and 1,2,3-trifluoro-l,1,3,3- tetrachloro-Z-propanol.

3. Process as claimed in claim 1, wherein said nonsolvent is at least one member selected from the group consisting of metanol, ethanol, isopropanol, cyclohexanol, acetone, 2-butanone, dimethylformarnide, N-methyl pyrrolidone, dimethylacetamide, methylene chloride, ethylene chloride, nitroethane and nitromethane.

4. Process as claimed in claim 1, wherein said polyamide is adhered to said substrate, and wherein pressure is imposed on selected portions of said polyamide, whereby to clarify such.

5. Process as claimed in claim 4, wherein said substrate is pigmented, and wherein said clarification of said polyamide permits the color of said substrate to appear as said indicia.

6. The product of the process of claim 1.

References Cited UNITED STATES PATENTS 2,352,725 7/ 1944 Markwood.

2,783,894 3/1957 Lovell et al. 26'r216 XR 2,848,752 8/1958 Bechtold 117-367 XR 3,031,328 4/1962 Larsen l1736.7 3,108,009 10/1963 Clancy et -a1. 1l736.7 XR 3,247,006 4/1966 Hoge et a1. 11736.7 3,340,135 9/ 1967 Avery.

20 DAVID KLEIN, Primary Examiner US. Cl. X.R.