ARTICLES HAVING PERMANENT INDICIA THEREON

Abstract: Permanent indicia can be applied to a surface consisting of a polymeric composition having a specific gravity less than about 1.35, and having a roughness average of at least about 2 mu m and an average peak width of less than about 200 mu m. The indicia are resistant to organic solvents, smearing and abrasion without a permatizing step. The surface can be, for example, the polymeric surface of a marker sleeve, preferably a heat-recoverable marker sleeve.

Description: ARTICLES HAVING PERMAJSΪET.INDICIA THEREON This invention relates to an article having permanent indicia thereon and to the use of such articles for marking electrical equipment, such as housings, wires and cables. In a preferred embodiment, the article is in the form of a heat recoverable marker sleeve suitable for use in marking wire and cable. Substrates such as wires, cables, equipment housing and the like are sometimes labeled with marker assemblies comprising a polymeric article marked with indicia, such as letters or numbers or -combinations thereof. To identify individual wires of a harness, a marker assembly may comprise a sleeve, preferably heat recoverable, of a poly¬ meric material such as a polyolefin, e.g. polyethylene, polyvinyl chloride, nylon or polyvinylidene fluoride. Relatively flat polymeric articles may be used for similarly marking large diameter cables, electrical equipment or the like. The indicia are generally typed onto the article using typewriting or similar printing equipment. For many uses, the indicia need to be permanent (i.e. durable), e.g. resistant to smearing, to being rubbed off (i.e. abrasion- resistant) and resistant to solvents which may contact the marker, as discussed more fully below. This latter require¬ ment is generally specified for aircraft wiring, which may come into contact with hydraulic fluid, liquid fuel, de- icing solvents or the like. The mark is generally rendered permanent by a heat treatment. This heat treatment, referred to as permatization, may take place by placing the sleeve in an oven or subjecting it to infrared radiation or in the case of heat-recoverable sleeves, by the heat applied during the heat-recovery step. See for example U.S. Patent No. 3,894,731 to Evans where infrared radiation is used to permatize the mark and U.K. Patent Application No. 2,181,142 where the mark is rendered permanent on application of heat during a heat shrinking step. An alternate technique of per¬ manently marking wires, cables or the like is the relatively expensive "hot stamping" technique which requires official equipment to mark the wire or cable with heated foil. One approach for the production of articles with permanent marks without the need for permatization is disclosed in commonly assigned copending application Serial No. 017,520 filed February 24, 1987, the entire disclosures of which are incorporated by reference. This application describes a multilayer article comprising a first substantially non-porous polymeric layer bonded to a second porous absorbent, polymeric layer. The porous layer is capable of being marked with indicia which are resistant to organic solvents, smearing or abrasion. The multilayer article is relatively complicated to manufacture. One method of manufacturing the article is to bond a first layer of polymeric material to a second layer of polymeric material containing a leachable particulate material and then leaching the particulate material from the second layer to render it porous. As discussed in the *520 application various solutions have been proposed for improving printability of polymeric materials but the issue of mark permanence is generally not addressed. We have now discovered that an article having a non-porous polymeric surface having certain roughness characteristics is capable of receiving permanent indicia. i.e. indicia resistant to organic solvents, smearing and abrasion. One aspect of this invention comprises an article for application to a substrate comprising: (a) unitary article consisting of a polymeric com¬ position having a specific gravity less than about 1.35, a surface of said article having a surface texture characterized by a roughness average of at least about 2 urn and an average peak width less than about 200 j am; and (b) indicia on said surface resistant to organic solvents, smearing and abrasion. Another aspect of this invention comprises an article for application to a substrate comprising: (a) an article having a nonporous surface layer con¬ sisting of a polymeric composition having a speci¬ fic gravity less than about 1.35, and having a surface texture characterized by a roughness average of at least about 2 μm and an average peak width less than about 200 jam; and (b) indicia on said surface resistant to organic solvents, smearing and abrasion. A further aspect of this invention comprises a method for producing an article having permanent indicia thereon, which method comprises: (a) selecting a unitary article consisting of a poly¬ meric composition having a specific gravity less than about 1.35, a surface of said article having a surface texture characterized by a roughness average of at least about 2 μm and an average peak width less than about 200 μm; and (b) applying to said surface in the desired pattern an ink containing a particulate pigment whereby permanent indicia resistant to organic solvents, smearing and abrasion are placed on the article. Yet another aspect of this invention comprises a method for producing an article having permanent indicia thereon, which method comprises: (a) selecting an article having a nonporous surface layer consisting of a polymeric composition having a specific gravity less than about 1.35, and having a surface texture characterized by a roughness average of at least about 2 μm and an average peak width less than about 200 μm; and (b) applying to said surface in the desired pattern an ink containing a particulate pigment, whereby permanent indicia resistant to organic solvents, smearing and abrasion are placed on the article. The indicia are permanent (i.e. resistant to organic solvents, smearing and abrasion) without the need of a permatizing treatment. FIGS 1-2 show profilometer tracings, each of a different surface showing the roughness profile of that surface. In accordance with this invention, permanent marking is obtained by applying ink to a surface having a surface texture characterized by a roughness average of at least about 2 μm, preferably at least about 2.5 μm and more preferably at least about 3 μm, and an average peak width (i.e. peak-to-peak width) less than about 200 μ , preferably less than about 150 um, most preferably less than about 100 um and in particular less than about 50 μm. The average peak-to-peak width is generally greater than about 1 μm, preferably greater than about 30 μm. The surface texture is measured according to American National Standard ANSI/ASME B46.1-1985 adopted October 7, 1985. In accordance with that standard, the surface texture is measured using a stylus method in which the stylus of a profilometer is passed over the sample surface so as to produce a graph of the surface texture. The roughness average is the arithmetic average of the absolute values of the measured profile height deviations taken within the sampling length and measured from the graphical center line. The values of roughness average and peak-to-peak width can vary depending on whether the stylus is moved in the direction of extrusion of the sample or perpendicular to the extrusion direction. The values specified above refer to the value in either direction of the sample. Profilometer tracings of surfaces suitable for receiving permanent indicia are shown in Figures 1 and 2. Figure 2 shows a surface on which permanent indicia are not obtained without a permatizing treatment. The average peak width is the arithmetic average of distance between adjacent peaks of the tracing. In Figure 1, the distance between one peak and an adjacent peak, i.e. a peak-to-peak width, is shown as "a". It has been found that permanence of the indicia depends on the texture of the surface to which they are applied. In one embodiment of the invention, the article is a unitary polymeric article, a surface of the article having the requisite surface texture. The term unitary article means an article that consists essentially of the same composition throughout and is generally made as a single layer extrusion. A layer of adhesive or the like can be applied to a surface of the article other than the surface to be printed. Such a layer is not regarded as part of the article. In a second embodiment, the article is a composite article having a nonporous surface layer having the desired texture. Such an article can be for example a dual wall article in which one of the layers has the desired texture. The other layer can be of any othe polymeric material, preferable one which bonds to the surface layer. The term nonporous, as used herein, means the substantial absence of pores and voids in the material of the surface layer. The surface layer in this embodiment is preferably at least about 10 microns thick. The article can be in the form of a film, sheet, slab, tube or any other shape to accommodate the substrate onto which it is to be applied. A surface having the desired texture can be produced by extruding the polymeric composition under conditions to -1- obtain melt fracture of the surface. These conditions are governed by the viscoelastic/shear relationship of the com¬ position which depends on the nature of the polymer, the nature of additives and fillers present, or the amounts of such additives and fillers. Extrusion of polymers under con¬ ditions to produce melt fracture is well known, see for example, "Capillary Flow of Molten Polyethylene - A photo¬ graphic Study of Melt Fracture", Transactions of the Society of Rheology, vol. 1, 203 (1957) J.P. Tordella; "A Comparison of Melt Fracture Initiation Conditions in Capillaries and Silts", Journal of Applied Polymer Science, vol 21,1177 (1977) J. Vlachopulos et al.;"Polymer Flow Instability: A Review and Analysis", J. Macromol. Sci.-Rev. Macromol Chem Vol. 16, 39-77 (1977-1978) E. Boudreaux Jr., et al. ; "A Unified Concept of Melt Flow Instability During Extrusion", J. Applied Polymer Science Vol. 22, 1781-1785 (1978) R. S. Lenk; "Instability in Polymer Processing", AICHE J. Vol. 22, 209-235 (1976) C. J. S. Petrie, et al.; and "Stretching Flow Instabilities at the Exiles of Extrusion Dies", J. of Non-Newtonian Fluid Mechanics Vol. 2, 37-47 (1977) F. N. Cogswell; the disclosures of which are incorporated herein by reference. Other methods of creating the desired surface texture include various physical and chemical treatments of the surface; for example, abrasion of the surface, stretching, laser treatment, ion beam treatment, plasma etching, solvent treatment and the like. Polymers that can be used include, for example, polyethylene, ethylene copolymers, e.g. ethylene-alkyl acrylate copolymers, such as ethylene-methyl acrylate and ethylene-ethyl acrylate copolymers, polyvinylidene chloride, nylons, such as nylon 66, nylon 11, and nylon 12, polyvinylidene fluoride and vinylidene fluoride copolymers, elastomers, such as butyl rubber, styrenebutadiene copolymers, other co- or terpolymers of the above and compositions comprising various polymer additives and fillers and blends of two or more polymers. The polymer composition can contain one or more additi¬ ves or fillers in an amount of up to about 60% fay weight of the polymer, preferably about 0.5 weight % to about 60 weight % and more preferably from about 5 weight % to about 50 weight %. Illustrative fillers and additives include for example, antioxidants such as alkylated phenols, e.g. those commerically available as Goodrite 3125, Irganox 1010, Irganox 1035, Irganox 1076, Irganox 1093, Vulkanox BKF, organic phosphite or phosphates, e.g dilauryl phosphite, Mark 1178, organic sulfides, sudas, dilauryl thio- dipropionate, e.g. Carstab DLTDP, dimyristyl thio- dipropionate, e.g. Carstab DMTDP,;distearyl thiodiproporionate, e.g Cyanox STDP, amines, e.g. Wingstay 29 etc; UV stabilizers such as [2,2'-thio-bis(4-t-octyl- phenolato). n-butylamine nickel, Cyasorb UV 1084, 3, 5-ditertiarybutyl-p-hydroxybenzoic acid, UV Chec Am-240; processing aids, e.g. zinc stearate, silicone oils/resin, PTFE poweder; flame retardants such as decabromodiphenyl ether, perchloropentacyclodecane, 2,2-bis(tetrabromo- phthalimido) ethylene; inorganic fillers such as titanium dioxide, antimony trioxide, zinc hydroxide, zinc oxide, basic zinc carbonate, iron oxide, etc, and the like. Mixtures of such fillers and additives can be used. Preferably, the polymeric composition has a specific gravity of less than about 1.35. Such compositions are spe¬ cified in certain military specifications such as MIL-I-23053. For application to individual wires and relatively small diameter cables, the article is preferably in the form of a tubular article, preferably heat-recoverable. Heat-recoverable articles are articles, the dimensional configuration of which may be made substantially to change when subjected to heat treatment. Usually these articles recover, on heating, towards an original shape from which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed. In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Patents 2,027,962, 3,086,242 and 3,597,372. As is made clear in, for example, U.S. Patent 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat-unstable form in a separate stage. In the production of heat-recoverable articles, the polymeric material may be crosslinked at any stage in the • production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently crosslinking the polymeric material, heating the article to a temperature above the crystalline point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape. The crosslinking can be effected by chemical means, e.g. with peroxides, or by irradiation or a combination of the two. Radiation employed can be of various types including charged particles, e.g. alpha particles or high energy electrons and electromagnetic radiation, e.g. gamma or ultraviolet radiation. Radiation doses of any desired amount can be used, although generally a dosage of from 1 to 50, preferably 2 to 20 Mrads will be sufficient. Illustrative processes for the preparation and use of marker sleeve assemblies can be found, for example, in U.S. Patents Nos. 3,894,731, 4,349,404 and 4,365,400 and European published patent application No. 295,918. The indicia are applied to the surface using conventional inks. Preferably the ink comprises carbon black in an appropriate vehicle. It is contemplated that any ink containing a pigment having a particle size of about 20 to about 80 microns can be used to provide permanent indicia on the surface. While not wishing to be bound by any theory, it is believed that the texture of the surface physically entraps pigment particles preventing them from being dislodged by abrasion or with solvents * ' Surfaces which do not exhibit the average roughness and peak width values are incapable of receiving permanent marks without a permatizing step, e.g. by heating. The terms "permanent" and "permanent indicia" or "permanent mark" as used herein mean that the indicia, or marks, are resistant to organic solvents, smearing and abrasion without having been subjected to a permatizing step. The degree of permanence required varies depending on the particular application. For use in wire and harnessing for military use, resistance to organic solvents and abrasion is of paramount importance. In this regard, it is necessary for the marked article to meet the requirements of Military Specification MIL-M-81531 and Military Standard MIL-STD-202, both of which are incorporated by reference herein. With respect to abrasion. Military Specification MIL-M-81531 requires that the markings or indicia be readable after being rubbed with an eraser 20 times. With respect to resistance to organic solvents. Military Standard MIL-STD-202 requires that the marks or indicia be readable after being immersed in a variety of organic solvents and then brushed with a toothbrush. These organic solvents include: mixtures of isopropyl alcohol and mineral spirits; an azeotrope mixture of trichlorotrifluroethane (FREON TF, a registered trademarks of E. I. DuPont de Nemours) and methylene chloride ? 1,1,1-trichloroethane; and an aqueous solution of butyl cellosolve and monoethanolamine. In addition to meeting the requirements of Military Standard MIL-STD-202, it is preferred that the markings or indicia be resistant to removal during prolonged immersion in the following organic solvents: JP-4 fuel (kerosene), Skydrol (a phosphate ester hydraulic fluid available from Monsanto Company), hydraulic fluid (petroleum based), aviation gasoline, lubricating oil (ester based) and anti-icing fluid (an aqueous mixture of gl cols) . These organic solvents are further specified in the Raychem Corporation Specification RT-1800/2, which is incorporated by reference herein. It is also preferred that the marked article according to the invention is resistant to dichloromethane which is representative of the class of halogenated solvents which include 1,1,1-trichloroethane and FREON mixtures. It is, of course, anticipated that the marked article according to the invention will be resistant to many other organic solvents as well as many inorganic solvents. It should be understood, then, that whenever throughout this specification the markings or indicia are stated to be permanent or durable they are resistant to organic solvents. smearing and abrasion, such resistance to organic solvents, smearing and abrasion shall be defined as indicated above. * The following examples illustrate the preparation of articles in accordance with this invention. Example 1. A formulation was prepared by blending the ingredients listed in Table I in a Banbury at high speed for 10 minutes at about 180°C. The resulting formulation was extruded at 115-163°C in the form of tubing. The tubing was irradiated in an electron accelerator at a dose of 20 Mrads. The tubing was heated to about 150°C and radially expanded, then cooled while maintained in the expanded configuration. Table I Component Percent by Weight Ethylene-methyl acrylate 51 σopolymer Flame retardant combination of: 40 Decabromo-diphenyl ether Antimony trioxide Zinc borate Magnesium hydroxide Trimethylol propane trimellitate 3 Stabilizers 4 Processing Aid 2 The composition had a specific gravity of 1.335. The surface texture of the expanded tubing was deter¬ mined using a Tancor Alpha Step 200 profilometer in accordance with the teaching of ANSI/ASME B46.1-1985. Measurements are made using a stylus having a diameter of 5 um, under a force of 5 milligrams over a 2000 micron length of sample. Figure 1 shows the profile of the surface of the tubing. The roughness average of the number shown in Figure 1 is 2.9 + 0.3 in the direction of extrusion and 2.6 + ^ 0.5 in the direction perpendicular to the extrusion. The average peak-to-peak width is 70 32 in the direction of extrusion and 108 52 in the perpendicular direction. Indicia were applied to the surface of the tube using black ink containing carbon black of particle size 25 milli¬ microns using a standard impact printer. The indicia were tested for permancence using the test procedures set forth above. The indicia were resistant to eraser rubs and the organic solvents. A slab was pressed of the formulation at 150°C and 25 pounds per square inch pressure. The surface texture of the slab was determined using a profilometer as above. The roughness average of the sample was 1.0 + 0.3 μm. The tex- ure is shown in Fig. 2. Indicia were applied to the surface as set forth above. The indicia were tested for permanence and failed both the eraser rub and solvent resistance testing.

Claims: What is Claimed is: 1. An article for application to a substrate comprising: (a) unitary article consisting of a polymeric com¬ position having a specific gravity less than about 1.35, a surface of said article having a surface texture characterized by a roughness average of at least about 2 μm and an average peak width less than about 200 μm; and (b) indicia on said surface resistant to organic solvents, smearing and abrasion. 2. An article in accordance with Claim 1, wherein said indicia comprise particulate carbon black. 3. An article in accordance with Claim 1, wherein said polymeric surface has an average roughness of at least about 3 um. 4. An article in accordance with Claim 1, wherein said polymeric surface has an average roughness of about 3 to about 4 jam. 5. An article in accordance with Claim 1, which is in the form of a polymeric tube. 6. An article in accordance with Claim 5, wherein the polymeric tube has been radially expanded after extrusion. 7. An article in accordance with Claim 6, wherein said tube is heat-recoverable. 8. An article in accordance with Claim 1, wherein said indicia are resistant to organic solvents, smearing and abrasion in the absence of heat treatment of the article subsequent to placing the indicia thereon. 9. An article in accordance with Claim 1 wherein said polymeric composition comprises an olefin polymer. 10. An article in accordance with Claim 1 wherein said polymeric composition comprises a copolymer of ethylene and an alkyl acrylate. 11. An article in accordance with Claim 10, wherein said polymeric composition further comprises one or more fillers in an amount of about 0.5 to about 60 parts by weight. 12. An article in accordance with Claim 11, wherein said filler ccomprises at least one flame retardant. 13. An article in accordance with Claim 12, wherein said filler comprises at least one processing aid. 14. An article for application to a substrate comprising: (a) an article having a nonporous surface layer con¬ sisting of polymeric composition having a specific gravity less than about 1.35, and having a surface texture characterized by a roughness average of at least about 2 μm and an average peak width less than about 200 μm; and (b) indicia on said surface resistant to organic solvents, smearing and abrasion. 15. A method for producing an article having permanent indicia thereon, which method comprises: (a) selecting a unitary article consisting of a poly¬ meric composition having a specific gravity less than about 1.35, a surface of said article having a surface texture characterized by a roughness average of at least about 2 μm and an average peak width less than about 200 μm; and (b) applying to said surface in the desired pattern an ink containing a particulate pigment whereby per¬ manent indicia resistant to organic solvents, smearing and abrasion are placed on the article. 16'. A method for producing an article having permanent indicia thereon, which method comprises: (a) selecting an article having a nonporous polymeric surface layer having a specific gravity less than about 1.35, and having a surface texture charac¬ terized by a roughness average of at least about 2 μm and an average peak width less than about 200 μm; and (b) applying to said surface in the desired pattern an ink containing a particulate pigment, whereby permanent indicia resistant to organic solvents, smearing and abrasion are placed on the article.

Inventors: CHAN CHI-MING, CHAN RANDOLPH WINSTON, NYBERG DAVID DOLPH, CHAN, CHI-MING, CHAN, RANDOLPH, WINSTON, NYBERG, DAVID, DOLPH
Applicants: RAYCHEM CORP, RAYCHEM CORPORATION
Application year: 1989
Main classification: B41M1
IPC codes: B41M1, B41M5, G09F3