Abstract:
Disclosed are UV-cured heat transfer labels prepared from a mixture containing at least one thermoplastic resin, at least one material for solvating the thermoplastic resin, the solvating material being either a solvent or liquid monomer, and at least one photo-initiable material which initiates curing of the composition.

Description:
This application is a continuation of application Ser. No. 08/514,401, filed Aug. 11, 1995, now abandoned. 
    
    
     FIELD OF INVENTION 
     The present invention is directed to heat transfer labels, for application to substrates, wherein the labels are screened onto carrier film or webs, cured with the UV radiation, and then applied to the substrate with application of heat and pressure. 
     BACKGROUND OF THE INVENTION 
     Heat transfer labels are used to decorate items by effecting transfer of the label to the item upon application of heat and pressure. The labels consist of inks containing a thermoplastic which softens and flows when heated so that it conforms to the decorated surface. Currently, known thermoplastic ink systems are solvent or water-based type systems, with solvent-based systems predominating. 
     Ultraviolet-curing ink systems which cure upon exposure to ultraviolet light are generally known in the art. NOR-COTE INTERNATIONAL provides UV-curing inks for the screen printing industry known as Series 02, Series 70, and Series 80. These inks, however, have not performed adequately when applied to webs used to apply heat transfer labels. With application of heat and pressure, these labels did not transfer to styrene or acrylonitrile-butadiene-styrene (ABS) copolymer, which are the most readily decorated substrates, regardless of the variance of temperature, pressure, and time. Under-curing the ink provided transfer of some of the ink to the substrate as a ghost-image, but it does not offer any adhesion to the part. Simply affixing tape over the label and removing the tape resulted in the removal of the label as well. 
     More recently, ink manufacturers, including Craig Adhesives &amp; Coatings Company, of Newark, N.J. have developed coatings that will accept writing, glue or hot stamp decoration while maintaining good intercoat adhesion. However, when tested for use as heat transfer inks, new coatings did not provide enough thermoplasticity and tack for transfer and adhesion to ABS, styrene or other common substrates. 
     For an ink to be effective in the preparation of a heat transfer label, it must soften and develop tack at a temperature above room temperature and possess sufficient cohesive strength to transfer completely from the carrier web to the substrate to be decorated. Once adhesion has been established on the substrate, it must be strong enough to retain the complete image as the carrier web is removed from the ink and substrate. Once the decorated part has cooled to room temperature, the ink must pass minimal adhesion tests, normally specified in the industry by applying an adhesive tape to the ink surface and pulling the tape away from the substrate at right angles to the surface in an attempt to remove the image with the tape. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide heat transfer labels that are alternatives to those presently available and which will exhibit good adhesion and resistance to removal when applied to common substrates such as ABS or styrene. It is a further object to develop such labels from inks cured with UV radiation. Such labels would not emit volatile organic compounds during the process and would also exhibit improved abrasion resistance and chemical resistance when compared to the existing solvent-based or water based ink systems. 
     Generally, the UV-cured heat transfer labels of the present invention are prepared from a mixture containing at least one thermoplastic resin, at least one material for solvating the thermoplastic resin, the solvating material being either a solvent or liquid monomer, and at least one photo-initiable material which initiates curing of the composition. The presence of the photoinitiable material, hereinafter referred to as an initiator, initiates a curing reaction within the ink upon exposure to UV radiation. It is often preferable to include an oligomer in the composition as well, since coating strength and solvent resistance appear to be improved with the introduction of an oligomer that reacts with an initiator. 
     Conventional ingredients may be included in the compositions, such as pigments or viscosity-reducing additives such as fused silica, dispersing aids, defoaming agents and other surface modifying materials. 
     While not wishing to be bound by any theory, the presence of the photocuring initiators is believed to provide enhanced physical and chemical properties normally not found in solvent or water-based heat transfer inks, while the presence of the thermoplastic resin is believed to provide good mechanical adhesion to the labelled substrates. 
     Another aspect of the present invention is a clear topcoat layer which also cures upon exposure to UV radiation. The heat transfer labels constituted of the UV curing inks previously described can be printed directly upon the UV topcoats. While it is believed that the UV-curing inks of the present invention exhibit an acceptable degree of abrasion resistance and chemical resistance in ordinary situations, the combination of a UV curing ink and a UV topcoat will provide additional wear resistance when necessary. 
     Substrates suited for labelling with the present invention include acrylonitrile-butadiene-styrene copolymer, polystyrene, polyethylene, polycarbonate, polypropylene, blends thereof, aluminum, and stainless steel. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the UV curing heat transfer labels of the present invention, a thermoplastic resin is dissolved in either a solvent or a monomer and incorporated into a finished photoinitiated ink system. It should be understood that any solvent or monomer which can dissolve the thermoplastic resin component and remain compatible with the other components of the labels are acceptable. Those which are suitable include: 2-butoxyethyl acetate, Aromatic 100 (a blend of C9 aromatic hydrocarbons), Aromatic 150 (a blend of C10 aromatic hydrocarbons), and cyclohexanone. Suitable monomers for dissolving the thermoplastic resin component include esters of acrylic acid and methacrylic acid such as lauryl acrylate, isobornyl acrylate, 2-phenoxyethyl acrylate, glycidyl methacrylate, tetraethoxylated nonylphenol acrylate, and propoxylated neopentyl glycol diacrylate. 
     Thermoplastic resins suitable for the heat transfer labels of the present invention include epoxies, polyurethanes, polymethacrylates, polyethylene vinyl acetates, polyvinyl chlorides, chlorinated halogenated polyolefins such as chlorinated and fluorinated polyolefins, and polystyrene. 
     Additionally, thermoplasticity (i.e.--adhesion) can be promoted by preparing a coating made from monofunctional acrylates. Oligomer can be added to improve the physical and chemical properties of the finished coating with the understanding that the heat transfer temperature, the minimum temperature at which transfer occurs, increases with increasing dilution of the polymerized monofunctional acrylate. 
     Suitable photocurable monomer initiators include benzophenone, alpha ketone, thiophenyl morpholinopropanone (Irgacure 907), morpholinophenylaminohexanone (Irgacure 369), cyclohexylphenyl ketone (Irgacure 184), hydroxyphenylpropanone (Darocur 1173), and isopropylthioxanthone (Quantacure ITX), alkylated benzophenone (Esacure TZT), diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (Lucirin TPO), and poly 4-(2-hydroxy-2-methylpropionyl) alpha-methyl styrene (Escacure KIP-100F). Irgacure 907, 369, 184 and Daracur 1173 are products available from Ciba-Geigy. Quantacure ITX is a product from Biddle Sawyer. Esacure TZT and KIP-100F are products of the Sartomer Corporation. Lucirin TPO is a product of the BASF Corporation. Generally, suitable initiators as those which produce free radicals upon exposure to UV radiation. 
     Coating strength and solvent resistance is improved by including photoinitiable oligomers in addition to photoinitiable monomers within the UV curing heat transfer label. Two suitable initiators of this kind are a urethane acrylate designated as CN 966J75 and an epoxy acrylate designated as CN 104, both available from Sartomer, Inc. Concentrations of up to 30% based on total resin weight have been effective. Higher concentrations can provide a curable film, but heat transfer properties appear to be compromised. 
     Curing can be effected by a Fusion Systems light source, using either a doped mercury type &#34;D&#34; or &#34;V&#34; lamp. The &#34;D&#34; outputs in the wavelength range of 340-390 nm. The &#34;V&#34; lamp outputs in the 400-430 nm. range. The choice of pigment and initiator dictate which range (i.e.--lamp) to use, and the selection process would be readily understood by the artisan skilled in printing with traditional UV curing inks. 
     The following examples illustrate the suitable compositions of the present invention and the beneficial results achieved thereby. The Examples are not intended to limit the scope of the present invention in any way. 
     &#34;Parts&#34;, as used in the following Examples, refers to parts by weight. 
    
    
     EXAMPLE 1 
     A heat transfer ink was prepared by combining 80 parts CN104 oligomer, 42.7 parts glycidyl methacrylate, 54.7 Elvacite 2016 available from ICI Acrylics of Wilmington, Del., 90.7 parts isobornyl acrylate, 20 parts Irgazin DPP Red BO available from Ciba Pigments of Newport, Del., 7.5 parts Irgacure 369, 0.8 parts AntiTerra U-100 available from BYK Chemie, U.S.A., Wallingford, Conn. and 4 parts Lithene PL, available from Special Electric Co., Inc. Cleveland, Ohio. The ink was printed onto a continuous polyester web (film) using a flat polyester screen wherein a polyurethane squeegee is passed over the screen forcing the ink through openings in the screen. The squeegee can be actuated manually or mechanically, both having been tried. The polyester screen had a stencil of emulsion firmly bound to the screen which defined an image to test graphic print quality. The printed image was then passed under a Fusion Systems UV lightsource at 27 ft/min using a doped mercury type &#34;D&#34; lamp emiting in the 340-390 nm output range. After curing, the coating was placed on flat test coupons of various materials and transferred to the coupon from the film at temperatures ranging from 350-400° F. and 300 pounds force per square inch of part area. A one-half (0.5) ton vertical stamping press, manufactured by Kensol, Inc. was used to transfer the label. Air pressure to the cylinder was adjusted to accommodate the areas dewatered. Materials accepting the coating with complete adhesion included ABS, high impact polystyrene (HIPS), and polycarbonate. 
     EXAMPLE 2 
     A heat transfer ink was prepared by combining 16.75 parts CP 164 chlorinated polyolefin, available from Eastman Chemical, 44 parts isobornyl acrylate, 44 parts glycidyl acrylate, 22.65 parts CN 104 oligomer, 20.1 parts lauryl acrylate, 6 parts Irgacure 1173, and 3 parts Irgacure 369. The ink was screened onto a carrier web and cured at 27 feet per minute under 300 Watts/inch UV light using an electrodeless lamp emitting most strongly in the 340 nm to 390 nm range. After curing, the coating was placed on a flat polyethylene test coupon and transferred from the film at 450° F. and 300 pounds force per square inch of part area. 
     EXAMPLE 3 
     Example 2 was repeated with the omission of lauryl acrylate, CN 104, and Irgacure 369 with good transfer and adhesion results on polyethylene. 
     EXAMPLE 4 
     Example 2 was repeated with the inclusion of 2 parts Lithene PL, 1 part of AntiTerra U-100, and 10.1 parts Irgazin DPP Red BO. Results on polyethylene showed good transfer and adhesion. 
     EXAMPLE 5 
     A heat transfer label was prepared from 100 parts isobornyl acrylate, 20 parts glycidyl acrylate, 47.6 parts thermoplastic resin, 59 parts CN 104 oligomer, 2.3 parts Lithene PL,, 31.9 parts titanium dioxide, 3 parts CI Pigment Blue 15:3, 0.7 parts AntiTerra U-100, 6.8 parts Darocure 4265, 5.23 parts Irgacure 369, 1.3 parts Quantacure ITX, 28.3 parts polytetrafluoroethylene beads, and 3-7 parts fused silica to obtain proper printing viscosity. The thermoplastic resins used in this composition included Elvacite 2013, Acryloid B-66, and Piccotex 120. All labels transferred to HIPS and ABS with good adhesion. In adhesive tape testings using 3M Brand Scotch Tape 810, no removal of design was observed. 
     EXAMPLE 6 
     A heat transfer label was prepared from 102.5 parts isobornyl acrylate, 17.5 parts CP 164, 18.5 parts lauryl acrylate, 5 parts Darocure 369, 3 parts Monarch 120 carbon black, available from Cabot Corporation, Boston, Mass. and 0.1 part AntiTerra U-100. The ink was screened onto a carrier web and cured at 27 feet per minute under 300 Watts/inch UV light using an electrodeless lamp emitting most strongly in the 340 nm to 390 nm range. The coating was transferred to polyethylene at 450° F. and polypropylene at 400° F. Good transfer and adhesion were obtained. 
     The experiment was repeated with 10.3 parts Monarch 120 instead of 3 parts, curing with two passes of irradiation under the same conditions. Transfer was good, as was adhesion. 
     EXAMPLE 7 
     A series of thermoplastic resins were evaluated and shown to offer a UV curable coating with the ability to transfer to HIPS with good adhesion. These included: 
     A--26% CP 343-1 (Eastman Chemical) in isobornyl acrylate 
     B--18.2% Phenoxy Resin PKHC (Phenoxy Associates) in 70:30 isobornyl acrylate: glycidyl acrylate 
     C--40% Piccolastic D125 (Hercules) in isobornyl acrylate 
     D--20% Elvax 40W (DuPont) in isobornyl acrylate 
     E--40% Piccotex A 100 (Hercules) in isobornyl acrylate 
     F--14% VYHD (Union Carbide) in 82:18 isobornyl acrylate: glycidyl acrylate 
     G--33.3% Epon 1009F (Shell) in 70:30 isobornyl acrylate:glycidyl acrylate 
     
         ______________________________________Parts (by weight)______________________________________Resin Solution A     162.6Resin Solution B  146Resin Solution C         200Resin Solution D              150Resin Solution E                   200Resin Solution F                        140Resin Solution G                             180AntiTerra U-100     1.3     1.3    1.3  1.3  1.3  1.3  1.3Lithene PL     2.4     2.4    2.4  2.4  2.4  2.4  2.4Titanium Dioxide     120     120    120  120  120  120  120Cab-O-Sil TS-610     8       4      6    3    5.8  2.4  6Darocur 4265     12      12     12   12   12   12   12______________________________________ 
    
     All of the above were screened onto a carrier web and cured at 40 feet per minute under 400 Watts/inch UV light using an electrodeless lamp emitting most strongly in the 400 nm to 430 nm range. After curing the coating was transferred to high-impact polystyrene (HIPS) from the film at 380° F. Good adhesion was observed in all applications. 
     EXAMPLE 8 
     A hard, clear topcoat was prepared from 100 parts CN 964E75, 120 parts dipentaerythritol-pentaacrylate, 3.3 parts Lithene PL, 100 parts triethoxylated trimethylolpropane triacrylate, and 14 parts Darocure 1173. The ink was screened onto a carrier web and cured at 27 feet per minute under 300 Watts/inch UV light using an electrodeless lamp emitting most strongly in the 340 nm to 390 nm range. Onto this layer was screened a heat transferable coating prepared from 60 parts 2-phenoxyethyl acrylate, 40 parts Elvacite 2016, 20 parts CN 966J75, 12 parts tetraethoxynonylphenol acrylate, 2 parts Lithene PL, and 9 parts Darocure 1173. Transfer was made from the carrier web to ABS or HIPS at 350° F. with good adhesion. 
     Comparison Example 1 
     A commercial UV curing coating Craigcoat 1077HS from Craig Coat Adhesive was cured at 40 feet per minute and 400 Watts/inch. This material contains an acrylate ester of bisphenol A-epoxy, monomeric and oligomeric multifunctional acrylates and benzophenone. The resulting film was immediately tested and partially transferred at 380° F. onto HIPS with poor adhesion. Three hours after curing the film, the coating did not transfer to the part at all under the test conditions. 
     Comparison Example 2 
     Another commercial UV curing ink Nor-Cote 8010195A (black) was tested. Alone, a film was produced on curing which did not transfer to either ABS or HIPS. 
     EXAMPLE 9 
     37.5 parts of 40% Acryloid B-66 in 2-butoxyethanol acetate were added to 85 parts of Nor-Cote 8010195A. The resulting ink was screened onto a carrier web and forced hot air dried to remove solvent. The ink was cured at 40 feet per minute under 300 Watts/inch UV light using an electrodeless lamp emitting most strongly in the 340 nm to 390 nm range. The coating was tested for transfer, transferring completely with good adhesion to ABS and HIPS. The experiment was similarly performed replacing the Acryloid B-66 solution for Elvacite 2046 at the same concentration. Results were the same, showing good transfer and adhesion to ABS and HIPS. 
     Table 1 sets forth a list of components used in the present disclosure. 
     
                       TABLE 1______________________________________Name    Generic Description                 Component  Manufacturer______________________________________Aromatic   blend of C9 hydro-                 solvent    Exxon Chemical100     carbon                   CompanyAromatic   blend of C10 hydro-                 solvent    Exxon Chemical150     carbon                   CompanyButyl   2-butoxyethyl acetate                 solvent    Union CarbideCellosolve                       Chemicals &amp;Acetate                          Plastic Co.Cyclohexa-   cyclohexanone solvent    Union Carbidenone                             Chemicals &amp;                            Plastics Co.SR 335  lauryl acrylate                 monomer    Sartomer                            CorporationSR 506  isobornyl acrylate                 monomer    Sartomer                            CorporationSR 379  glycidyl methacrylate                 monomer    Sartomer                            CorporationSR 339  2-phenoxyethyl                 monomer    Sartomer   acrylate                 CorporationCD 504  tetraethoxylated                 monomer    Sartomer   nonylphenol acrylate     CorporationSR 9003 propoxylated  monomer    Sartomer   neopentyl                Corporation   glycol diacrylate   epoxies*      thermoplastic                 resin   polyurethanes*                 thermoplastic                 resin   polymethacrylates*                 thermoplastic                 resin   polyethylene vinyl*                 thermoplastic   acetates*     resin   polyvinyl chlorides*                 thermoplastic                 resin   chlorinated   thermoplastic   polyolefins*  resin   polystyrene*  thermoplastic                 resinEsacure TZT   alkylated     initiator  Sartomer   benzophenone             CorporationEsacure alpha hydroxy ketone                 initiator  SartomerKIP 100F                         CorporationIrgacure 907   thiophenyl    initiator  Ciba-Geigy   morpholinopropanoneIrgacure 369   morpholinophenyl-                 initiator  Ciba-Geigy   amino-   hexanoneIrgacure 184   cyclohexlphenyl                 initiator  Ciba-Geigy   ketoneDarocure   hydroxy-      initiator  Ciba-Geigy1173    phenylpropanoneQuantacure   isopropylthioxanthone                 initiator  Biddle-SawyerITXEsacure TZT   alkylated benzo-                 initiator  Sartomer   phenone                  CorporationLucirin TPO   diphenyl (2,4,6,-                 initiator  BASF Corp.   trimethylbenzoyl)   phosphine oxideEsacure KIP-   poly 4-(2-hydroxy-                 initiator  Sartomer100F    2-methylpropionyl)       Corporation   alpha-methyl styreneCN 966J75   urethane acrylate                 oligomer   Sartomer, Inc.CN 104  epoxy acrylate                 oligomer   Sartomer, Inc.Elvacite   methyl/n-butyl                 thermoplastic                            ICI Acrylics2016    methacrylate  resin   copolymerIrgazin DPP   CI Pigment Red 254                 pigment    Ciba-GeigyRed B0Lithene PL   polybutadiene surfactant Special                            Electric Co,                            Inc.Tipure  TiO.sub.2 CI Pigment                 Pigment    DuPont   white 6CI Pigment   CI Pigment Blue 15:3                 Pigment    Ciba-GeigyBlue 15:3SST     PTFE beads    filler     Shamrock                            Chemical Corp.Elvacite   methyl/n-butyl                 thermoplastic                            ICI Acrylics2013    methacrylate  resin   copolymerAcryloid   methyl/butyl  thermoplastic                            Rohm and HaasB-66    methacrylate  resin      Company   copolymerPiccotex 120   alpha methyl styrene/                 thermoplastic                            Hercules, Inc.   vinyl toluene resin   copolymerCP 164  modified chlorinated                 thermoplastic                            Eastman   polyolefin    resin      ChemicalDarocure   2-benzyl-2-   initiator  Ciba-Geigy369     (dimethylamino)-1-    4-(4-morpholinyl)   phenyl!-1 butanoneAnti-Terra   salt of polyamine                 dispersing BYK-ChemieU-100   amides and high                 additive   USA   molecular weight         Corporation.   acidic esters.Darocure   2-hydroxy-2-methyl-1                 initiator  Ciba-Geigy4265    phenge - propanone   and diphenyl (2,4,6-   trimethyl benzoyl)   phosphine oxideCP-343  modified chlorinated                 thermoplastic                            Eastman   polyolefin    resin      ChemicalPhenoxy Phenoxy resin thermoplastic                            PhenoxyResin PKHC            resin      AssociatesPiccolastic   Polystyrene   thermoplastic                            Hercules, Inc.D125                  resinElvax 40W   ethylene vinyl acetate                 thermoplastic                            DuPont   copolymer     resinPiccotex   alpha methyl  thermoplastic                            Hercules, Inc.A100    styrene/vinyl toluene                 resin   copolymerVYHD    vinyl chloride/acetate                 thermoplastic                            Union Carbide   copolymer     resinEpon 1009F   Bisphenol     thermoplastic                            Shell   A/Epichlorohydrin                 resin   based epoxy resinCab-O-Sii   treated fumed silica                 thickener  CabotTS-610                           CorporationCN964E75   Urethane acrylate                 Photoinitiable                            Sartomer                 oligomer   CorporationSR 399  dipentaerythritolpenta-                 Monomer    Sartomer   acrylate                 CorporationSR 454  triethoxylated                 Monomer    Sartomer   trimethylolpropane       Corporation   triacrylateCraigcoat   high performance UV                 commercial ink                            Craig Adhesives1077HS  curing overprint         &amp; Coatings,   varnish                  Inc.Nor-Cote   screen Printing UV                 commercial ink                            Nor-Cote8010195A   ink, black               InternationalMonarch 120   carbon black  Pigment    Cabot   CI Pigment black 7       CorporationElvacite   n-butyl/isobutyl                 thermoplastic                            ICI Acrylics2046    methacrylate  resin   copolymer______________________________________ *Generic terms only