This invention relates to the surface treatment of hollow plastic articles to provide thereon a surface receptive to inks, coatings, adhesives and the like and especially to the interior treatment of hollow containers to insure that interior coatings will adhere reliably and uniformly thereto.

Equations based on a simple model of surfaces and interfaces have been found useful for relating quantitatively several previously unrelated fields of surface chemistry {10-13). These equations introduce a new term — the London dispersion force contribution to the surface free energy (7d)—and make use of this term for the accurate calculations of surface tension, interfacial tension, contact angles, heats and free energies of immersion, heats and free energies of adsorption, and the long-range van der Waals attractive forces. The accuracy of predictions of values verifiable by experiment lead one to expect that predictions of un-verifiable quantities, such as the magnitude of attractive forces at solid-solid interfaces, are to be trusted. This approach should appeal especially to those who need to use the results of surface chemistry and would prefer to calculate from existing values rather than make new experimental determinations. It should also appeal to those teaching surface chemistry in that it relates for the first time several widely separated fields of surface chemistry. Most noteworthy is the ability to calculate heats and free energies of adsorption of gases on solid surfaces directly from measurements of surface tensions and contact angles. The calculation of the long range van der Waals attractive constant, A, from values of 7d is also very attractive.

A low-temperature, nonequilibrium plasmajet process for activation of polymer surfaces has been developed. A stream of oxygen is partially dissociated by a glow discharge, expanded to high velocity through an orifice into a region of lower pressure, and impinged on the desired surface. Parameters measured before and after treatment of a variety of polymers include weight, surface-bonding characteristics, and wettability. The weight loss of the polymer increases with exposure time, discharge power, and proximity to the atom source; its relation to the changes in surface properties is discussed.

A stream of atomic oxygen, produced by passing oxygen at low pressure through a radio-frequency coil, was allowed to impinge on films prepared from several dozen different polymers. The flow of oxygen radicals was regulated so that the reaction temperatures were between 40 and 70°C. The rapid reactions which occurred at the polymer film–oxygen radical interface were essentially unaffected by the presence of phenolic antioxidants over a wide range of concentrations but rate of reaction was greatly affected by the structure of the polymer. Bulk properties of the polymers were unchanged because the attack by atomic oxygen is limited to the surface of the polymer. In many instances a simple ablation of the surface was observed, but in some cases, especially polyethylene and polypropylene, a highly oxidized surface layer was created. These oxidized surface layers had remarkably low contact angles with water and should be of great interest in improving adhesion and other surface-dependent properties of polymers.

The rigid‐sphere theory of liquids is shown to yield an expression for the surface tension of a one‐component liquid which is essentially identical to an expression previously derived by the author employing a qualitative approach. Such a correlation suggests that the rigid‐sphere theory of liquids approach is applicable to a wide variety of nonpolar polymeric liquids.

The surface tension of polyethylene has been measured by the ring method over the temperature range 125–193°C. Because of problems with the viscousness of the liquid polyethylene, it was found convenient to use an Instron testing apparatus instead of the usual du Nouy torsion balance. The surface tension of the polyethylene decreased from a value of 28.5 dynes/cm. at 125°C. to 23.3 dynes/cm. at 193°C. with an average temperature coefficient of −0.076 dynes/cm./°C.

It is shown that structural joints can be formed between conventional epoxy adhesives and copolymer and terpolymer of chlorotrifluoroethylene, at temperatures well below the softening points of these polymers, without their prior surface treatment. An explanation of this low temperature behavior is given in terms of the surface tension of the adhesive, surface roughness, and the micro-Brownian motion of the polymers associated with the glass transition.

Data for the surface tension of molten polymers are scarce and relatively incomplete (1, 2). Schonhorn and Sharpe (3) have recently reported the surface tension of a molten polyethylene over a wide temperature range as measured with a strain gage type testing apparatus (4). In the present communication, we report the surface tension of a molten polypropylene as a function of temperature using techniques described previously (3). For this study we chose a completely atactic low molecular weight (in= 3,000) polypropylene, Epolene D-10, supplied by Eastman Chemical Products, Incorporated, Kingsport, Tennessee. This material was purified further by dissolving the polypropylene in xylene and then precipitating it with isopropyl alcohol. This process was repeated twice. The final product was colorless and probably had a higher in since low molecular weight fractions would tend to remain in the eluent. The details of the experimental procedures and standardization of the modified du Nouy technique are described elsewhere (3). The ring employed in this study was calibrated with a variety of low viscosity liquids. The manually operated du Nouy tensiometer was found to be inadequate because of the high viscosity of the liquid polymer and the sluggish response of the film under load. At the low crosshead speed of 0.02 in./min., no decay in force was noted when the crosshead was stopped. At higher crosshead speeds (> 0.05 in./min.) there was an increasingly large decay in the force as a function of time. By employing atactic polypropylene we were able to operate at lower temperatures. Dry preheated nitrogen was continually passed through the oven chamber to preclude oxidation of the molten polypropylene. Samples aged at 199OC. for an hour showed no change of surface tension with time. One hour is considerably longer than the time necessary for a determination. Measurements were repeated a minimum of three times for each recorded temperature.

This invention relates to corona treating of shaped articles and particularly articles of irregular shaped surface areas and made of synthetic resinous material such as polyethylene.

In a method for treating a surface of organic plastics material to improve the bonding or adhesion properties thereof (e.g. ink receptivity), the plastics material is passed between a current-conductive material and at least two electrodes spaced and electrically insulated therefrom and maintained at high voltage direct current of opposite polarity, the surface of the material to be treated being exposed to and spaced from the electrodes with the reverse side of the material in intimate contact with the current-conductive material, whereby a direct current corona aura is developed and maintained from the electrodes to the moving surface of the plastics material being treated. The electrodes are on the same side of the current-conductive surface, so that the corona, which increases in intensity with the speed of surface being treated, does not pass through the plastics material but operates on only one surface thereof. In one embodiment (Fig. 1, not shown), a D.C. voltage, e.g. 17,000 volts, is applied to each of alternate electrodes 20, intermediate electrodes 21 being of opposite polarity. The electrodes are sharp-pointed sections of a hacksaw blade. A film 23 made of e.g. polyethylene polypropylene, polystyrene is passed via rolls 24, 26 over a conductive plate 22 which is in contact with the film, and insulated from the D.C. supply. In Fig. 2 (not shown), a corona is developed in the air gap between film 23, passing round insulated metal roll 221, and electrodes 201, 211 of opposite polarity.

Contact time of activated gas with polymer film of as little as 1 sec. under these relatively mild conditions resulted in greatly improved adhesive joint strength for polyethylene. Longer contact times were required for polymers such as polytetrafluoroethylene. Helium, argon, krypton, neon, and xenon, and even hydrogen and nitrogen were all effective crosslinking agents although the latter also changed wettability of the surface. Adhesive joints were prepared by sandwiching 1041 films of polyethylene (Marlex 5003, Phillips Petroleum Co., Bartlesville, Oklahoma) and polytetrafluoroethylene (G-80, Allied Chemical Co., Morristown, New Jersey), before and after CASING, between epoxy-coated aluminum strips (3). The values obtained for tensile shear strengths of these joints are shown in Figure 1. In these instances, the polyethylene film was treated for 10 sec. and the polytetrafluoroethylene film was treated for 10 min.

Contact angle hysteresis was measured for a variety of liquids on condensed monolayers of 17-(perfluoroheptyl)heptadecanoic acid adsorbed on polished chromium. The hysteresis was shown to be simply related to the molecular volume of the liquid and to result from the penetration of liquid molecules into the porous monolayer. However, contact angle hysteresis was negligible when the average diameter of the liquid molecules was larger than the average cross-sectional diameter of the intermolecular pores. It is shown that it is possible to estimate intermolecular pore dimensions of such adsorbed monolayers by contact angle hysteresis measurements on a series of liquids having gradations in molecular volume. The results of this investigation reveal that liquid penetration, even into pores of molecular dimensions, is a cause of significant contact angle hysteresis, and it is also shown how liquids can be selected for contact angle investigations on organic solid surfaces so that there will be freedom from this source of hysteresis. The results also suggest that under these experimental conditions, liquid water, on the average, behaves as if it were associated in clusters of about six water molecules. Similarly, both ethylene glycol and glycerol behave as associated clusters of about two molecules.

A RECENT communication by Gray¹ illustrates a possible pitfall in the use of the theories of Fowkes^2–5 and Good and Girifalco^6,7 to estimate surface energies, and the various components of surface energy, from contact angles. This source of error is the incorrect identification of the surface tension terms, and the equating of the contact angle in a contaminated, experimental system to that in a system composed of properly pure components. Thus, Gray wrote Fowkes's equation in the form

A modified Wilhelmy plate technique has been developed for the measurement of surface tensions of viscous polymers. The method requires no knowledge of liquid density and provides a means of assuring a zero contact angle for the polymer on the plate. The surface tensions of several silicone polymers with viscosities as high 106 centipoises have been measured. The method has also been used to determine the surface tensions of several molten polyethylenes as a function of temperature over the range 115° to 215°C.

The present invention relates to the treating of plastic film materials and more particularly to a method and apparatus for improving the exposed surface adhesion qualities of films of plast'c such as polyethylene which have been applied to electrically conductive substrates such as metal foils.

The surface characteristics of shaped structures of fluorocarbon polymers containing at least five mole per cent. of recurring units of formula: wherein -X1 is -H, -F, -Cl or -CF3; -X2 is -H, -F, -R1 or R2; -R1 is an aryl or alkyl radical containing 1 to 8 carbon atoms and -R2 is -OR1, -CH2OR1, -CO.R1, -CH2CO.R1, -CO.OR1, -OCO.R1 or -CH2OCO.R1, are modified by subjecting the surface of such structures to the action of an electrical discharge having an energy level less than 15 electron volts in a gaseous atmosphere having a moisture content of not more than 3.5 gms. per cubic metre at 25 DEG C. Specified articles are sheets, rods, tubes, fabrics and filamentary articles. Specified polymers are the homopolymers and copolymers of vinyl fluoride, vinylidene fluoride, 1, 2-difluoroethylene, trifluoroethylene, 1-fluoropropylene and 1, 1-difluoropropylene; interpolymers of the above monomers with tetrafluoroethylene, hexafluoropropylene and chlorotrifluoroethylene; and interpolymers of the above monomers with olefins, halogen substituted olefins, vinyl and allyl esters, ketones and ethers, unsaturated acids and the esters, nitriles, amides, anhydrides and halides thereof, and vinyl heterocyclic compounds. The preferred articles are films, and the preferred polymers polyvinyl fluoride, polyvinylidene fluoride, copolymers of vinyl fluoride with vinyl acetate, tetrafluoroethylene or hexafluoropropylene, and copolymers of tetrafluoroethylene with ethylene. Preferred gaseous atmospheres are of oxygen, nitrogen and air. Examples describe the treatment of films of the following polymers in the specified atmospheres:-(1, 2 and 5) oriented polyvinyl fluoride in oxygen; (3) oriented polyvinyl fluoride in nitrogen; (4) oriented polyvinyl fluoride in air; (6) polyvinyl fluoride pigmented with titanium dioxide in air; (7) polyvinyl fluoride pigmented with titanium dioxide, chrome yellow, lamp black and phthalocyanine pigment in oxygen; (8) vinyl fluoride/vinylidene fluoride copolymer in nitrogen; (9) vinyl fluoride/vinyl acetate copolymer in oxygen; (10) vinyl fluoride/tetrafluoroethylene copolymer in air; (11) vinyl fluoride/hexafluoropropylene copolymer in oxygen; (12) vinyl fluoride/ethylene copolymer in nitrogen; (13) polyvinylidene fluoride in oxygen; and (14) tetrafluoroethylene/ethylene copolymer in air. The films may be laminated using conventional adhesives. Specifications 605,445, 920,860 and 923,846 are referred to.

The present invention relates to the treatment of plastic coated paper, and more particularly to the treatment of plastic coated paper to improve the adherence of ink and adhesives thereto. The principal utility of the invention at the present time resides in the treatment of polyethylene coated paper, and, for convenience, the invention will be described primarily in connection with tre-atment of such polyethylene coated paper. But it should be understood that the principles of the invention are applicable to the treatment of other plastics which may be coated on paper and which plastics exhibit generally similar response to the treatment of the invention, particularly polymers and copolymers of the lower olens. Similarly, the principles of the invention are also applicable to the treatment of certain plastic coated substrates other than paper.

This invention relates to treatment of organic thermoplastic polyme-ric surfaces to render the surfaces more wetta'ble by water and/or other liquids, more printable and dyeable and, in general, more adherable.

Further studies of a new and highly effective method for the surface treatment of low surface energy polymers for adhesive bonding are reported. Mechanisms are suggested for the increase in the cohesive strength in the surface region of polyethylene when it is exposed to activated species of inert gases. The technique is unique because, in contrast with results obtained with other methods, bulk properties of the polymer such as color or tensile strength and elongation are unaffected and surface properties such as wettability and dielectric properties such as surface conductivity are essentially unchanged.

The concept that the solubility parameter is a vector composed of hydrogen bonding, polar, and dispersion components is proposed and applied with success to prediction of the solubility of 33 polymers and resins in 90 solvents and 10 plasticizers. Solvents and plasticizers can be located as points in a three dimensional system, and regions of solubility are found for polymers and resins when solubility data are plotted. Non-interacting solvents which in a mixture become interacting have been found with better than 95% accuracy in over 400 cases.

The concept that the solubility parameter is a vector composed of hydrogen bonding, polar, and dispersion components is proposed and applied with success to prediction of the solubility of 33 poylmers and resins in 90 solvents and 10 plasticizers. The application of the solubility parameter concept is described. The three dimensional solubility parameter system based on the homomorph concept has been developed on the basis of polymer solubility. The same system has been applied to the characterization of dyes, nonionic emulsifiers, and pigments. The system is also useful for selecting solvents when protective coatings are formulated with more than one polymeric solute.

For substrates such as polyesters having limited capacity for hydrogen bonding or other specific interactions, thermodynamic compatibility of the substrate and adhesive is shown to be a key factor in promoting bondability to the substrate. Such compatibility occurs, as shown by Abere, when the cohesive energy densities (CED) or solubility parameters (δ = √CED) of substrate and adhesive are matched. Investigations with polyester film-adhesive-film model systems with the use of a variety of nonpolar (hydrocarbon) and polar (chlorinated compounds, ethers, esters) adhesives illustrate how compatibility promotes bondability to poly(ethylene terephthalate). The poor adhesion of polyester fibers to resorcinol–formaldehyde–latex (RFL) adhesives is attributed to the incompatibility of resorcinol (δ = 16.0) with the polyester (δ = 10.3). Adhesion to RFL was improved by substituting the more compatible n-hexyl resorcinol (δ = 12.5) for resorcinol in RFL adhesives. Currently, the best adhesive systems for polyester tire yarns are those (e.g., isocyanate–epoxy) involving formation of urethane polymers having matching δ values with poly(ethylene terephthalate).

A plot of the initial spreading pressures F sub ba or initial spreading coefficients S sub ba against the surface tensions of a homologous series of organic liquids b can be used to determine the critical surface tension for spreading on a second substrate liquid phase a. Straight-line relations are found for various homologous series. The intercept of that line with the axis of abscissas F sub ba 0, or S sub ba 0 defines a value of spreading for that series. This method is advantageous because it eliminates the need for measuring or calculating the contact angle of lens b floating on liquid a, it can be applied to any liquid substrate, and it is applicable even when spreading does not lie within the range of surface tensions of the members of the homologous series of liquids b. The value of spreading for the waterair interface was determined in this way using several homologous series of pure hydrocarbon liquids. The lowest value found was 21.7 dynescm at 20 deg C for the n-alkane series. Higher spreading values were obtained using olefins or aromatic hydrocarbons as the result of interaction between the unsaturated bond and the water surface. Since the results are analogous to those reported earlier for solid surfaces, it is concluded that the clean surface of water behaves as a low-energy surface with respect to low-polarity liquids. This result is to be expected if only dispersion forces are operative between each alkane liquid and water.

A technique has been developed for rapid and extremely accurate measurements of contract angles formed by liquids on the surface of small-diameter filaments. The light beam reflection technique first de- scribed by Langmuir and Sehaeffer (1) and recently by Fort and Patterson (2) for liquid drops on flat plates has been refined for use with filaments and microscope equipment.

The present invention relates generally to an improved method of treating surfaces of materials, such as synthetic resinous materials, to render these surfaces more adherent to substances such as printing inks, paints, lacquers and glues. More particularly, it relates to a process which comprises treating these materials with monatomic gases.

This invention relates to an improved method for treating the surface of plastic materials to render them capable of adhering to subsequently applied coatings such as printing inks, paints, pigments, adhesives, and various other materials which it may be desired to coat, print or otherwise attach to the treated surfaces.

A method is described for measuring the level of pretreatment of polyethylene films in terms of critical surface tensions. Drops of water-dioxan mixtures of various surface tensions are placed upon the pretreated films and their critical surface tensions assessed from the spreading behaviour of the liquids.

A suggestion is made for using this method as a process control test.

The critical surface tension γ_c of polyvinyl butyral has been measured with polyhydric alcohols and halogenated hydrocarbons. Despite variations in polymer composition (residual OH content) and modes of preparation, γ_c is found to be 24–25 dynes/cm. with the former class of liquids. The —CH₃ groups appears to predominate over —CH₂, ether oxygen, and OH groups present. Steric effect may account for this biasing of the γ_c values toward the lowest surface energy group present. Fowkes' relation based on dispersion force interactions only is found to fit the data reasonably well. Comparative data on polyethylene are also presented.

Sir: Padday and Uffindell produced a well organized and readable article, but unfortunately their mathematics is incorrect (by nearly one order of magnitude) because intermolecular potentials were integrated over molecular distances, breaking a fundamental principle of integral calculus.