It has been shown that the determining factors in the wetting of low-energy solid surfaces are the nature of the atoms in the surface and their physical packing. Of all solid organic polymers polytetrafluoroethylene is known to have the lowest surface energy and thus the lowest critical surface tension of wetting (y_c). In this study the wettability of a series of copolymers of tetrafluoroethylene with hexafluoropropylene by a variety oforganic and inorganic liquids was examined; the results show that these solid plastics have critical surface tensions which are even lower than that of solid polytetrafluoroethylene. As anticipated, the progressive increase in the proportion of perfluoromethyl side chains in the polymer introduces a higher concentration of exposed-CFs groups in the surface which in turn progressively reduces y_c. By extrapolation y_c of a polyhexafluoropropylene has been calculated to give the value of 15 dynes/cm.

THE nature of active nitrogen, the mechanism of its afterglow¹, and its gas phase reactions with organic molecules² have been discussed. I have now investigated a heterogeneous active nitrogen reaction at a polymer surface.

This invention relates to the treatment of polyethylene resins and relates more particularly to the treatment of polyethylene resin sheet material in order to make the surface of said material receptive to printing inks.

Articles, such as films, of polyethylene resins have been employed extensively in the arts because of the numerous advantages of these lightweight, relatively inert, tough materials. However, it has been found very difficult to provide decorative or informative matter on the surfaces of such articles, since these surfaces are not receptive to printing inks. Thus, while the inks may be applied readily to the surface of the polyethylene resin material, they do not adhere well thereto and are easily rubbed off.

It is therefore an object of this invention to provide an article of polyethylene resin having a surface which is receptive to printing inks.

This invention relates to a method of treating sheets and other articles of plastic material to improve the anchorage or adherence characteristics of the surfaces thereof. More particularly, the invention is concerned with a method of treating polyethylene sheets or articles to improve the anchorage or adherence characteristics of the surfaces thereof whereby various coating materials including printing inks applied thereto are tightly adhered thereto.

Surface shaping of articles, e.g. embossing; Apparatus therefor by electric discharge treatment

In order to obtain information on the wettability of some polymers, the sliding of water drops down tilted polymer slides has been examined. The angle of sliding is defined as the limiting angle between the slide and the horizontal plane at which the drop moves at a uniform rate, and can be taken as a measure of the wettability of the surface.

In previous investigations2 the heats of fusion and heat capacities of BiCl3, BiBrs, HgCl2, CdCl2, CdBr2 and Cdl2 near the meltingpoint were measured. However, the heat contents relative to 298.15 K. were not published for these halides at the melting point. Since it recently was pointed out3 that such data would be of value, the Hm. p.—ff29S. iK increments as well as the heat capacities (assuming they are constant) of the solid salts for the same temperature range are listed in Table I.

Although the agreement between the heat content increment of this study and that of an earlier work4 for CdCl2 is poor, the present value as well as those of all the other salts except the bismuth halides are in excellent agreement with literature estimates6 (Table I). Included in Table I with the heat capacities for the temperature range 298 K. to the melting point are those values found near the melting points of the salts.

The effect of varying the chemical constitution of a material on its ability to adhere may be determined to a good first approximation by the nature and packing density of the atoms or molecular radicals in the solid surface. This general conclusion was established by experiments on the wetting of liquids and solids, by the effect of the constitution of polymeric solids on friction, and by the overriding effect of monomolecular adsorbed films on adhesion. The reversible work of adhesion W sub A of a liquid to a low-energy solid can be calculated approximately from the contact angle and liquid surface tension. Both W sub A and the maximum capillary rise in pores and crevices are parabolic functions of the liquid surface tension. The resulting data are discussed in terms of surface constitutive effects, changes in W sub A and in the internal stress concentrations developed as the adhesives solidify.

The present invention relates to the surface treatment of thermoplastic tubing for the reception of protective and decorative coatings, printing inks, adhesives and the like in a manner which causes them to readily and firmly adhere thereto, and has particular reference to a method of and apparatus for improving the adherence characteristics of exterior and interior surfaces of polyethylene or the like thermoplastic tubing by the application of a high voltage electrical stress accompanied by corona discharge as the tubing is extruded in substantially continuous lengths.

A simple apparatus and technique are described for measuring contact angles formed by liquid drops on solid surfaces. The procedure is a modification of one described 25 years ago by Langmuir and Schaeffer. It is based on observation of the angle at which light from a point source is reflected from a liquid drop surface at its contact point with a solid. The technique gives results the same, within experimental error, as those obtained by other investigators who used the usual “drop profile” method. The apparatus has the advantages of ease of construction and operation, ruggedness, and low cost coupled with high precision and accuracy.

This invention relates to a method of electrically treating polyethylene film to improve the anchorage characteristics of its exposed surface whereby various materials such as printing ink or adhesive may be firmly secured thereto. More particularly, it relates to the use of an electrically conductive treating roll coated with a phenol-formaldehyde resin, in the process of passing a polyethylene film through an electrical discharge between an electrode and a dielectrically coated conductor roll.

A review of the author's investigations of the equilibrium contact angles of pure liquids on low- and high-energy solid surfaces, both bare and covered with a condensed monomolecular adsorbed film, includes the critical surface tension of wetting and the effect of homology on spreading by pure liquids, the causes of nonspreading on high-energy surfaces, and the existence and properties of autophobic liquids and oleophobic monolayers. Constitutive relationships are summarized in a table of critical surface tensions of wetting. The theory and application of the retraction method of preparing adsorbed monolayers from solution and the conditions for mixed films are presented. Studies of the wetting behavior of solutions of various surfactants and the resultant explanation of the function of a wetting agent are generalized to include nonaqueous systems. Following estimates of the reversible work of adhesion of liquids to solids, the part played by wetting in obtaining optimum adhesion by adhesives is outlined, and a fundamental explanation is given of constitutive effects in the development of strong adhesive joints. Future areas of research on wetting and adhesion are indicated.

In his opening remarks at the first symposium in this series Professor Robert Good pointed out that Galileo in the 17 century was quite likely the first investigator to observe contact angle behavior with his experiment of floating a thin gold leaf on top of a water surface. Since that time contact angle measurements have found wide application as a method for determining the energetics of surfaces. This, in turn, has a profound effect on the wettability and adhesion of liquids and coatings to surfaces.

The effect of roughness on the wettability of an idealized sinusoidal surface has been studied with a digital computer. The equations of Wenzel and of Cassie and Baxter are discussed in relation to the model. The heights of the energy barriers between metastable states of a drop are seen to be of utmost importance in determining the magnitude of contact angle hysteresis.

An experimental study of the wettability of rough surfaces over an extremely wide range of roughness is described. The theoretical wettability behavior of an idealized, rough surface agrees well with that of real surfaces. The theoretically predicted minimum in the curve of receding contact angle vs. roughness, for systems of high intrinsic contact angle, is experimentally verified.

Adhesion of polymers was determined as a function of temperature. The influence of the bonding times and temperatures indicates that the performance is established largely by the extent of wetting at the polymer-substrate interface. Considerations based on surface free energies show that most practical systems should exhibit complete wetting at equilibrium. The problem appears to involve establishing factors which retard or preclude wetting. Low substrate surface energy, high polymer viscosity, substrate topography, selective adsorption, and coacervation may be involved.

Certain aspects of the adsorption theory of adhesion are developed more fully than has been done previously. The consequences of nonreciprocity of spreading are pointed out, and are used to develop a more general practical point of view with respect to the adhesive bonding of materials of low-surface free energy. The system epoxy adhesive-(nonsurface-treated) polyethylene, normally considered nonadherent, is investigated experimentally in some detail. It is shown how this system, without material modification, can be made adherent. An area of study for possible adhesives for materials of lowsurface free energy is suggested.

This invention relates to a novel apparatus for treating the surface of plastic articles with a corona discharge, and more particularly to an apparatus for the treatment of the surface of an article made from a hydrocarbon resin with a corona discharge in order to render the surface more readily printable, which apparatus is located on one side only of the plastic article.

The effect of surface heterogeneity on the wettability of an idealized heterogeneous surface has been studied with the aid of a digital computer. Surface heterogeneity permits the existence of a large number of metastable configurations. Contact angle hysteresis is discussed in terms of a balance between the vibrational energy of a drop and the heights of the energy barriers between allowed metastable states.

This invention relates to surface and interior modification of thermoplastic resinous bodies, and is particularly useful in the treatment of resin plastics which are normally non-adherent or only slightly adherent to inks, adhesives, and other coatings. The invention is particularly useful in the treatment of such substantially non-adherent plastics as polyethylene and polypropylene, but is also useful in the treatment of polyvinyl chloride, polyvinylidene chloride, and copolymers, homologues, and mixtures thereof.

This invention pertains to the surface treatment of film, and more particularly to the flame treatment of the surface of polyvinyl fluoride film whereby to enhance the ad herability characteristics of said surface.

Polyvinyl fluoride is noted for its attractive properties, and in film form possesses an unusual combination of excellent resistance to outdoor weathering exposures, a high degree of physical toughness, chemical inertness, abrasion resistance, resistance to soiling and the action of solvents as well as an amazing retention of these properties at both low and elevated temperatures. The above combination of properties not only suggests many areas of use for polyvinyl fluoride in the form of self-supporting films, but also the use of such films as the outer layers of a wide variety of laminar structures destined chiefly for outdoor use wherein the polyvinyl fluoride films serve to upgrade less functional substrates, imparting to the final structure a degree of utility not to be found solely in either film or substrate.