The CASING (crosslinking by activated species of inert gases) treatment of polypropylene film in both oxygen and nitrous oxide is shown to be an effective surface treatment for conventional adhesive bonding. A crosslinked surface extending to a depth of about 300 Å, apparently independent of exposure time, is produced in both excited oxygen and nitrous oxide.

Corona treatment improved bonding between sheets of cellulose and synthetic polymers. The bond strength increased at higher temperatures of pressing. Physical changes in the surface were detected microscopically after corona treatment in air. Sheets treated in pure nitrogen made strong bonds although the surface treated in nitrogen was indistinguishable from the untreated surface.

A new definition for work of adhesion W_a is applied to computationally define the dispersion γ_s^d and polar γ_s^d components of the solid surface tension γ_s = γ_s^d + γ_s^d for twenty-five low energy substrates. These calculated surface properties are correlated with surface composition and structure. Surface dipole orientation and electron induction effects are respectively distinguished for chlorinated and partially fluorinated hydrocarbons. Published values for critical surface tension of wetting γ_c are correlated with both γ_s^d and γ_s.

The solubility parameters of a broad spectrum of solvents and chemicals are calculated from vapor pressure data using an expression derived from the relationship of Haggenmacher. In the case of high boiling liquids, the available vapor pressure data are found to be unreliable when extrapolated to room temperature and an alternate method of calculation is proposed. A structure correlation is made using the method of Small and new values of the molar cohesion constants are developed. The problem of associations of certain molecular species is discussed and the concept of chameleonic character introduced as a qualitative explanation.

The reaction of a radiofrequency-excited oxygen plasma with the surfaces of cured and uncured polymethylsiloxane produces intense hydroxylation of the surface region as followed by FMIR spectroscopy. Characteristic infrared features indicative of intraor intermolecular hydrogen bonding are evident. Plasma oxidation differs markedly from thermal oxidation processes. Reactions of polymethylsiloxane with nitrogen and air plasmas were also investigated and compared to corona reactions of oxygen, nitrogen, and air. In air corona, nitrogen moieties appear to be introduced. The behavior of polymethylsiloxane surfaces in oxidizing acids is also described.

A modification of the Good-Girafalco-Fowkes-Young equation is used to calculate nondispersion interactions I_SL^P at the interface for nine polymeric solids and four polar series of liquids. The relationship of I_SL^P to work of adhesion W_A and the spreading coefficient S_e is shown. A linear relationship is found to exist between I_SL^P and γ_L^P, the nondispersion energy component of the liquids, for the series of polar liquids and the solids studied. The slopes of the I_SL^P vs. γ_L^P curves vary depending upon the polymer surface. Intercepts of the curves may be a measure of π_s, the reduction in the surface energy of the solid resulting from adsorption of vapor from the liquid.

Critical surface tensions γ_e of nine representative polymer surfaces with four series of polar liquids differed considerably from commonly accepted values. The Good-Girafalco-Fowkes-Young equation is used to explain the results, and it is shown that if certain precautions are observed, the equation may be used to predict γ_c of solid polymers for “standardized” series of liquids. The theoretical concepts of Fowkes and Good are shown to be compatible with Zisman's approach to the determination of γ_c. Serious errors may result, however, in the evaluation of contact angle data from misuse of the theoretical concepts of Fowkes or from misinterpretation of critical surface tension values as determined by the Zisman technique. Curve of cos θ vs. γ_L are straight lines only for one particular series of liquids and normal curves are of power form. It is suggested that many of the experimental contact angle data in the literature may be reinterpreted, including those for poly-(styrene), human skin, nylon 11, poly(ethylene), and monolayers of perfluorolauric acid.

It is generally accepted that the surface tension of fluoropolymers is approximately equal to the sum of a polar and nonpolar term. The first paper in this series described an empirical method for approximating the nonpolar term, and this paper proposes a similar approach for determination of the polar term, based upon contact angle measurements of polar liquids. The method is applicable to other solid surfaces provided suitable contact angle liquids are available.

Surface tension is frequently expressed as the sum of a polar and a nonpolar term. In this paper an empirical approach is proposed for approximating the nonpolar term γ_sd of the surface tension of fluoropolymers. The experimental data were obtained from contact angle measurements employing a series of linear alkanes. These data are plotted by two different methods to evaluate γ_sd. The critical surface tension γ_e obtained from nonpolar contact angle liquids should reasonably approximate the γ_sd of the fluoropolymer surface. This work is based on classical molecular interactions, many concepts of which were established in earlier reports by Fowkes, Good, and Zisman.

The wetting properties of a series of polyacrylates containing the fluoroalkyl group have been studied. Where n is 7 and 9, the polyacrylates are highly crystalline at room temperature. Since the polymers were prepared under atactic free-radical conditions and the polyacrylates with shorter alkyl groups (where n is 3 or 5) were not crystalline at room temperature, the crystallinity is presumed to occur as a result of side-chain packing and not involve the backbone. The polymers become more wet-table (higher γ_c) as polymer crystallinity was reduced by quenching or heating past T_m. Correlations have been made between the work of Zisman and co-workers on the wetting properties of various fluorinated acid monolayers and the wetting properties of these fluoroalkyl acrylates. The results obtained in this study concerning the influence of polymer crystallinity on surface wetting are discussed in relation to the findings of Schonhorn and Ryan on the wettability of polyethylene single crystal aggregates.

The surface free-energies of the polyethers, polyethylene glycol, polypropylene glycol, polyepichlorohydrin, and polybutylene glycol, their mixtures and their random and block copolymers were determined by means of the pendant drop method. In all cases, except that of random copolymers, surface excesses of the low surface-energy component have been found. In the mixtures of homopolymers the behavior of surface excess isotherms depends on the molecular weight of the two components, while in block copolymers it depends on the degree of polymerization of the base unit. The Belton and Evans Equation for perfect solutions and the Prigogine equation for r-mer solutions have been applied to the experimental data.

Contact angles of water, glycerol, formamide, ethylene glycol, 1-bromonaphthalene, and bromobenzene were measured in the temperature range 5–160° on surfaces of polyethylene, polystyrene, polyacetal, polycarbonate, poly(ethylene terephthalate), and poly(tetrafluoroethylene-co-hexafluoropropylene). Stable advancing and receding angles were found and these varied linearly with temperature except in the range where solubility or swelling was evidence. Superheated water wet all the polymers to a greater degree than predicted. For the fluoropolymer all the liquids showed a negative temperature coefficient of the contact angle, both advancing and receding, ranging from 0.03 to 0.1 deg/°C. For the other polymers coefficients for advancing angles were nearly all negative and ranged from 0.03 to 0.18 but most receding angle values were positive; several liquid-polymer pairs showed a negligible coefficient. Temperature coefficients of the critical surface tension and of the dispersion surface tension of each solid were evaluated. Correlations of these derived quantities are discussed.

The surface tensions of a series of poly(isobutylenes) in the molecular weight range 400–3000 have been determined at 24°C. These results, together with surface tension values from the literature for poly(dimethyl siloxanes) and three series of different pure chain-molecule homologues, are found to exhibit a linear dependence on (molecular weight)^{$\text{−2}\text{2}$}. A simple free-volume argument seems to be consistent with this empirical observation.

The surface tensions of polyethylene, polyisobutylene, and polyvinyl acetate, and the interfacial tensions of polyethylene/polyvinyl acetate and polyisobutylene/polyvinyl acetate systems have been measured by the pendent drop method in the temperature range up to 200°C. The results are analyzed in terms of the equations of Fowkes and of Girifalco and Good, and suggest that the conformational restriction of polymer molecules imparts a limitation on the extent of interfacial contacts and sharp phase boundaries in these systems. Several quantities of interest in adhesion, such as contact angle, spreading coefficient, and work of adhesion are also discussed.

Metallized polyethylene terephthalate film produced by first subjecting a surface of the film to a reducing flame, and thereafter depositing on the treated surface a coating of metal, e.g., aluminum, deposited from a vapor of the metal.

This application is a continuation-in-part of our copeuding application Ser. No. 469,317, filed July 2, 1965 now abandoned.

This invention relates to a process for the improvement of the adhesion of vacuum-deposited metal to linear polyester film. More specifically, it relates to the flame treatment of polyethylene terephthalate film to promote the adhesion of vacuum-deposited metal.

Apparatus for treating the exterior surfaces of plastic objects to improve their adherency to and compatibility with inks and adhesives comprising a pair of electrodes spaced apart from each other, means including a source of electric current of sufficient intensity to produce a spark discharge across the gap between said electrodes, electrical conducting means connecting said electrodes and said source, and means for positioning the objects in the gap between said electrodes, and electrodes being arranged with regard to the size and configuration of the objects to provide a nearly direct electron path around the objects whereby desired portions of the object surfaces may be passed over by the spark discharges during the passage of the latter along said path from electrode to electrode.

The theory of the flotation of a fiber-shaped solid by a liquid of lower density is presented in detail. Within the usual range of fiber diameters and densities, provided the cross section shows no protruding cusps, a very small positive contact angle is sufficient to float the fiber. If the contact angle is zero, the fiber will sink. The critical surface tension (CST) of a fiber surface can therefore be estimated by placing samples of the fiber on a series of liquids of progressively increasing surface tensions. The CST lies between the surface tensions of the liquid in which the fiber just sinks and the liquid in which it just floats. Agreement with the classical method is excellent.

A simple apparatus and technique are described for measuring contact angles of liquids on small-denier fibers. This technique is based on the level-surface method and can be used to obtain either advancing or receding contact angles. Contact angles determined by this method are accurate and precise and the apparatus is inexpensive, rugged, easy to operate, and suitable for routine work.

Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm−1 in PE, and 887 and 910 cm−1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found.

Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm⁻¹ in PE, and 887 and 910 cm⁻¹ in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found.

Heterogeneous nucleation and crystallization of FEP Teflon and nylon 6 melts against high energy surfaces (i.e., gold) produce an interfacial region, in these polymers, of high mechanical strength. Dissolution of the metal substrate rather than removal by mechanical means results in a polymer surface which is amenable to conventional structural adhesive bonding. Nucleation and crystallization of the polymer melts in contact with phases of low surface energy (e.g., vapor) result in the generation of weak boundary layers.

A method for measuring the surface energy of solids and for resolving the surface energy into contributions from dispersion and dipole-hydrogen bonding forces has been developed. It is based on the measurement of contact angles with water and methylene iodide. Good agreement has been obtained with the more laborious γ_c method. Evidence for a finite value of liquid-solid interfacial tension at zero contact angle is presented. The method is especially applicable to the surface characterization of polymers.

This invention relates to a process for preparing poly: vinylbutyral sheeting which has a decreased tendency to block. More specifically, this invention relates to treating polyvinylbutyral by electrical discharge in a nitrogen atmosphere and thereby obtaining a surface on the sheeting that has a decreased tendency to adhere to itself or to other similarly treated polyvinylbutyral sheets.

his invention relates to a method by which substantial improvement can be obtained in the electric glow discharge treatment of polyolefin, such as polyethylene or polypropylene, structures to improve the anchorage characteristic of a surface thereof. More particularly, the invention is concerned with improving processes and apparatus for treating polyethylene or other thermoplastic film or article to render its surface adherent to printing inks or other coating materials, wherein the surface treatment is accomplished by means of an electric glow discharge, as for example, in accordance with the disclosure of the copending applications of Kaghan and Stoneback, Ser. No. 540,137, filed Oct. 12, 1955, and issued Nov. 11, 1958, as U.S. 2,859,481 and of Berthold and Pace, Ser. No. 359,352 filed June 3, 1953, and issued May 3, 1960, as U.S. 2,935,418. This application is a continuationin-part of our copending application Ser. No. 602,506 filed Aug. 7, 1956, now abandoned.

This invention relates to a method by which substantial improvement can be obtained in the electric glow discharge treatment of polyolefin, such as polyethylene or polypropylene, structures to improve the anchorage characteristic of a surface thereof. More particularly, the invention is concerned with improving processes and apparatus for treating polyethylene or other thermoplastic film or article to render its surface adherent to printing inks or other coating materials, wherein the surface treatment is accomplished by means of an electric glow discharge, as for example, in accordance with the disclosure of the copending applications of Kaghan and Stoneback, Ser. No. 540,137, filed Oct. 12, 1955, and issued Nov. 11, 1958, as U.S. 2,859,481 and of Berthold and Pace, Ser. No. 359,352 filed June 3, 1953, and issued May 3, 1960, as U.S. 2,935,418. This application is a continuationin-part of our copending application Ser. No. 602,506 filed Aug. 7, 1956, now abandoned.

The interfacial tension along the boundary formed between two immiscible polymer liquids has been measured by the pendant drop method. The polymers employed for the study are polyethylene, polydimethylsiloxane, poly(ethylene oxide), polytetrahydrofuran, poly(vinyl acetate) and an ethylene-vinyl acetate copolymer. Surface tensions of these polymers (against air) were also determined by the same technique. The values of interfacial tension between polyethylene and each of the five polar polymers, together with the surface tension data, were utilized to calculate the separate contributions to the surface tension by dispersion and dipole interaction forces, in accordance with the procedure proposed by Fowkes. The interfacial tension between two polar polymers was then analyzed in terms of these separate components of forces. An empirical relation has been shown to correlate the dipole interaction term in interfacial tension with the individual dipole force components of the two polar polymers involved.

A web of polythene &c. or a plastics article such as a bottle is treated to render its surface more receptive to printing ink by subjecting it to an elongated electrical discharge between two electrically conducting electrodes such as 2, 3, the discharge traversing a gaseous medium only and the surface to be treated entering and leaving the discharge on the same side thereof. The plastics material to be treated may alternatively be polyethylene terephthalate or a polyolefine. The discharge is preferably of the corona type and may be accompanied by sparking, the discharge being caused by either direct or alternating current. A potential between 20-60 thousand volts and a frequency between 60-3,000 c.p.s. may be employed. The web 1, Fig. 4, may be treated by four pairs of electrodes as shown, one electrode of each pair being connected to a high tension source 13 via a resistor such as 6, and the web being arranged over insulating guide rollers 10, 101 and 4, 41. The electrodes are preferably in the form of knife edges, brushes or combs, and one electrode may be a heated wire. A web moving in a linear path, Fig. 1 (not shown), may be similarly treated.

A process for flame treating and heat sealing an uncoated biaxially oriented heat shrinkable film formed from a homogeneous blend of low density and high density ethylene polymers and copolymers comprising passing the film through a flame fed by a fuel of paraflinic and olefinic hydrocarbons, said fuel having a fuel equivalency when mixed with oxygen-enriched air of between 0.95 and 1.05, with said film being supported as it traverses the flame on a surface maintained at a temperature from about room temperature to 40 C., said film being exposed to the flame for a time between .0005 and .1 second; and heat sealing the flame treated film to itself or to another such film similarly treated.

The critical surface tension of wetting (γ_c) for certain branched-chain polymeric fluoroalkyl acrylates and methacrylates was obtained. Polymeric materials utilized in this study can be represented by the repeating units

Zisman's critical surface tension has been widely used as an appoximate value to the surface free energy of solids. Attempts to correlate the critical surface tension with the bulk properties have been reported previously. Howeer, none of these is quantitiatively reliable. In this work, we developed a modified Hildebrand-Scott equation that permits prediction of the critical surface tension for polymers from molecular constitution with good accuracy.