US 3196063 A
Description (OCR text may contain errors)
COATED PAPER AND METHOD OF PRODUCING THE SAME Filed March 28, 1962 July 20 1955 l.. J. PAQUIN ETAL 3 Sheets-Sheet l O o All'jo ozjooo Nm mmozzs o... ...UI l I I om ozu m Qmnznomu m Lm im m om bm m wm mUmDOw IIIIIKMQDEPXM July 20, 1965 L.. J. PAQUIN ETAL 3,196,063
COATED PAPER AND METHOD OF PRODUCING THE SAME Filed March 28, 1962 3 Sheets-Sheet 2J 37 `..OCI n July 2o, 1965 l.. J. PAQUIN ETAL 3,196,063
COATED PAPER AND METHOD OF PRODUCING THE SAME Filed March 28, 1962 3 Sheets-Sheet 5 United States Patent 3,196,063 COATED PAPER AND METHD F PRGiDUClNG THE SAME Leon I. Paquin and Owen D. Mosher, Glens Falls, N.Y., and Glenn M. Violette, Greenwich, NJ., assignors to International Paper Company, New York, N.Y., a corporation of New York Filed Mar. 2S, 1962, Ser. No. 183,304 Claims. (Cl. 16h-250) The present invention relates to an improved method of producing coated paper and to the coated paper produced thereby, and more particularly to a method of producing polyolefin coated paper having heightened resistance, i.e., improved barrier properties, to the passage of gases such as water vapor and solvents such as fats and oils.
This is a continuation-in-part of our copending application Serial No. 80,584, filed January 4, 1961, now Patent No. 3,161,560.
In recent years paper coated with polymers and copolymers of the lower oleiins have been widely used in the packaging of products, including both solids and liquids. Polyethylene has been the most widely used material for this purpose, and the invention will be described primarily in connection with polyethylene. However, the principles of the invention are applicable generally to the polymers and copolymers `of the lower olelins, e.g., propylene, ethylene and butylene, which may be extruded in molten form and deposited on a moving paper web. The term lower olefins as used herein is intended to mean the polymers and copolymers .of propylene, ethylene and butylene. The principles of the invention are also applicable to substrate materials other than paper which have dielectric constants similar to paper.
The coating of a polyolen, such as polyethylene, upon paper is usually accomplished by passing the extruded polyethylene lm and the paper simultaneously between two pressure rolls and thereby bonding the hot film thoroughly to the paper. One of the pressure rolls is usually rubber-covered and is shielded by the paper web. The other of the pressure rolls is conventionally metalcovered, e.g., chrome-plated and serves to secure the release of the hot extruded polyethylene film. In this regard, it has been found that the use, on the premise tha-t its excellent release properties are well known, of a hot pressure roll having a silicone rubber covering in place of the high cooling capacity chrome-plating does not successfully prevent the sticking of the hot extruded polyethylene to such pressure roll and the resultant production-halting breaking of the paper web. It has also been found that, even at relatively low speeds, the polyethylene film that forms the paper coating must be chilled from extruding temperatures of from about 260 to 315 C. to near room temperatures by the chrome-plated roll in a fraction of a second in order to release therefrom. It appears, therefore, that shock cooling is a requiste of the successful coating of paper with polyolens.
A brief analysis of the nature of polyolefins, using polyethylene as a typical example, is necessary to a proper understanding of what the problem is. Polyethylene molecules are either linear or side-chained and compositions containing them are readily identifiable by their molecular weights, molecular weight distributions, densities, percentages of chain branchings, and melt indices. Polyethylenes made by low temperature, low pressure catalytic processes tend to contain higher percentages of linear molecules and, because such molecules lend themselves to the growth of compact, dense crystals as the polymers cool and solidify, they are known as linear or high density polyethylenes. Linear polyethylenes are from about to crystalline in structure with an amorphous remainder. Polyethylenes made by high pressure, high temperature processes tend to contain higher percentages of side-chained molecules and, because such molecules do not lend themselves to the growth of crystals as the polymers cool and solidify, they are only from about 60% to 70% crystalline with an amorphous remainder. The linearity of the molecules then is a factor in the crystallinity and the density of the solids they compose. I-t is not, however, the sole factor, so that, if it were possible to produce purely linear polyethylene with no molecules having side chains, it would be conceivable that the polymer would pass from being amorphous when melted to being 100% crystalline and having a maximum density of 1.0 when cooled to a solid form. The thermal history of a polyethylene is also relevant and, if such thermal history is unfavorable to the growth of crystals therein, the solid will have a diminished crystallinity and density. It is typical, for instance, for a polyethylene having a high density in the range of 0.945 to 0.950, when supplied, to lose such density appreciably, i.e., down to 0.930 to 0.938, when coated on paper by customary extrusion methods. Polyethylenes of medium density (0.925 to 0.940) and of low density (0.918 to 0.925) show similar, if less dramatic, losses. Hence, it is on account of at least these two factors that all commercially available grades of solid polyethylenes are partly crystalline, partly amorphous mixtures having a density less than 1.0. Densities set for-th herein should be understood to be in terms of grams per cubic centimeter.
Practical consequences iiow from the mixed character of solid polymers and copolymers of olefins. Where, for
instance, a solid polyethylene has a high amorphous content, it has. superior gloss, transparency, and elongation properties. Such pnoperti-es are desirable in free films, but they have little or no value in captive films, e.g., paper coatings. As paper coatings, polyolenic films have value almost only when they have good barrier properties, i.e., resistance to the passage of gases such as water vapor and solvents such as fats and oils, these agents being harmful either to the paper itself or to the products wrapped, covered, or contained thereby or perhaps being desirably prevented from escaping from the packaged goods out through the coated papers. Such barrier properties are, of course, a function of the density of the finished coated papers and therefore of the amount of crystallinity of the films coating the papers.
Short of seeking to produce purely linear polyethylenes capable of being 100% crystalline in the solid state, then the most immediate solution to the problem of improving polyolefnic coating films and their barrier properties must be and has been taken to lie in the direction of affording the films the thermal history most favorable to crystal growth possible and, 'throughout their production and application, in maintaining, in preventing any decline in, in restoring any decline in, or even in a heightening of the amount `of crystallinity in any of the polymers and coaisance polymers with which one can coat paper. More particularly, it has been taken to lie in the direction of ascertaining any bad effects on the thermal history of such coating films of their being shock-chilled to enable their release from the pressure roll bonding them and thereafter overcoming or at least mitigating such effects. So much then for the problem giving rise to and the objects satisfied by Ythe present invention.
It has now been found that, in a continuous process of coating paper with a film of a compound selected from the group consisting of polymers and copolymers of lower olefins, the pressure rolls commonly employed to bond the film to paper can be eliminated, thereby reducing equipment purchase and maintenance costs, andtthat shock chilling to obtain film release from one of the pressure rolls can be eliminated, thereby affording the film a thermal history consonant with either an effort to obtain improved barrier properties for smaller amounts of film raw material or an effort tomaintain at or improve to a point approaching the theoretical maximum barrier properties of a given amount of film material. Thus, in our copending application Serial No. 80,584, filed January 4, 1961, we have described and claimed a process for producing improved polyethylene film coated papers in which the hot extruded film is applied to the paper pneumatically.
In the method of the present invention, a highly concentrated electric field is created and used to `apply the hot extruded film to the paper. The method of the present invention has been found to yield results at least equal to those lof our aforementioned copending application and far superior to those of the'conventional practices described above, particularly as regards obtaining a high moisture vapor barrier at low coating weights. Another important advantage of the present invention over the conventional `practices and over the method of our aforementioned copending application has been `in the ease of obtaining a good polyethylene-paper adhesion at low coating weights.
The principal object of the present invention has been to provide a novel and improved method of coating a substrate such as paper with a film of a polymer or copolymer of the lower olefins, such as polyethylene.
Another object of the invention has been to provide such a method in which superior moisture vapor'barrier characteristics are achieved.
Still another object of the invention has been to provide such a method in which electrostatic forces are used to produce adhesion of the film to the substrate.
A further object of the invention has been to provide such a method which is especially adapted vto high speed operation. y Y
Another object of the invention has been to provide a polyethylene coated paper having improved moisturevapor barrier characteristics as compared to a paper coated with the same thickness of polyethylene by prior processes.
Other and further objects, features and advantages of the invention will appear more fuliy from the following description of the invention. v
The invention will 'now be described in greater detail with reference to the appended drawings, in which:
FIG. 1 is a schematic diagram illustrating one form of apparatus for practicing the method of the invention;
FIG. 2 is a schematic diagram illustrating the operation of FIG. 1; and
FIGS. 3-12 are schematic diagrams each illustrating a respective modified form of apparatus for practicing the method of the invention.
Referring now to the drawings and more particularly to FIG. 1, a continuous web 2f@ of paper from an unwind stand or other suitable source passes over a roll 21. The roll 21 is provided to pre-coat a surface of the web 2t) with an adhesion promoter or primer such as Adcote Chemical Companys Shawnad 313 which is a water-based solution containing 20% solids. The adhesion promoter, diluted to contain 1.5% solids, is contained in Va trough El 2.2 and is applied to one surface of web Ztl as the web contacts roll 2i. The roll 2f is in turn provided with the adhesion promoter by contact with roll 23 which extends into the trough 22. As the web 20l advances, rolls 21 and Z3 rotate, keeping a fresh supply of adhesion promoter on the surface of roll 2. The use yof an adhesion promoter or primer is not essential, but it has been found desirable,
particularly at low coating weights.
The web 2d leaving `roll 2l passes around steam heated rolls 24 and 25, idler rolls 26, 27 and 28, steam heated rolls Z9 and 3?, an electrically grounded backing roll 3ft, an idler roil 32 and a cooling roll 33. The web leaving the cooling roll 33 goes on to a winding roll, although other treatment Zones may beV positioned between the cooling roll and the winder. The grounded roll 31 and the cooling roll 53 are preferably driven rolls and the stem heated rolls may be driven if desired.
An extruder 34 and die 3S are positioned -to extrude a thin film 3d of polyethylene or other plastic downwardly so as to contact a surface ofthe paper web 2f? as the paper is passing around the roll 31. If the paper has been precoated, the pre-coated surface faces outwardly of the roll 31 so as to contact the film.
From rolli onwardly, the paper web 2% has adhered to one surface thereof a thin film of polyethylene. The conventional practice in the past has been to cause the polyethylene film toy adhere to the paper surface by'causing the paper and the film to pass between two pressure rolls, as described above. In the method of copending application referred to above, adhesion of the polyethylene film to the paper surface is produced by pneumatic means. ln accordance with the method of the present invention, electrostatic charges are used to apply the hot extruded polyethylene film to the paper with sufficient pressure to produce adhesion ofthe hlm to the paper.
More particularly, air in the region of convergence of the polyethylene film and the paper is ionized, and the ions are caused to impinge on the polyethylene film. The ionsrcarry a charge and when they impinge on the polyethylene film the latter becomes charged. Since lthe paper is essentialy uncharged, or yat least possesses a different charge, a charge differential will exist between the polyethylene film and the adjacent paper. The resultant electric field between the polyethylene film and the paper will cause the film to be attracted to the paper.
The attractive field between the polyethylene and the paper must exist in the region of convergence between the polyethylene and the paper and hence the source of ions must be located so that the polyethylene film in the region `of convergence will be charged to create the attractive field.
The charge density V'on the polyethylene surface could be expressed in terms of coulombs, While the attractive force Vresulting from the charge differential could be considered as a field strength expressible inkcoulornbs per square centimeter. The greater the strength of this field the greater will be the force with which the polyethylene film is-urged into contact with the paper surface.
vIn FIG. l the source of ionization is shown as a series of six horizontal wires vertically spaced yin a vertical plane. VThe wires, which are designated by the reference numeral 37 extend across the width of the polyethylene film with the top wire approximately at the height of the top of Vroll 31. The wires 3'7 might be, for example,
3 mil tungsten wires separated from each other by a distance of not less than about Ms. The wires 37 are suitably held in a holder 3S under sufficient tension to resist the substantial pull which will be experienced in the direction of the grounded backing roll 31. The spacing between the wires 37 and thel polyethylene film may be of the order of tto 2, depending on the film thickness and the voltage applied to the wires. This voltage, which is supplied equally to the various wires 37, depending on electrical field configuration may be of the order of 3,000 to 50,000 volts, and may be positive, negative or alternating. It has, however, been found more desirable to use a negative voltage on the wires. The voltage source is designated by the block 39 in FIG. 1 and may be of any suitable type.
The high voltage on the wires 37 ionizes the air in the immediate vicinity of the wires, and under appropriate conditions this can be observed as a corona discharge in the immediate vicinity of the Wires. The corona should be limited to the region of the wires and preferably should not extend to the polyethylene film. The ions migrate away from the vicinity of the wire and some of them impinge on the polyethylene, resulting in an attractive electrostatic force between the polyethylene film and the paper, as described above.
A substantial proportion of the ions produced in the vicinity of the wires 37 will tend to travel in directions in which they will not impinge on the polyethylene film or at least not in the region of convergence between the polyethylene film and the paper. Various means can be used to concentrate the ion flow so as to maximize the ion flow into the polyethylene film in the region of converge'nce thereof with the paper. For example, air ow may be used to direct the ions in the desired direction. Or charged shields may be provided to inhibit ion flow except in the desired direction.
The foregoing physical explanation for the method of the invention is believed to be accurate but even if it should prove not to be accurate or to be incomplete, nevertheless Vthe method of the invention can be practiced to advantage as herein described and claimed.
In the arrangement of FIG. 1 the diameter of the backing roll 321 is preferably relatively small, e.g., about 2 inches. The roll surface may be steel or may have a dielectric coating such as nylon, Hypalon (a chlorosulfonated polyethylene sold by E. I. du Pont de Nemours & Co.), Mylar (a polymerized ethylene glycol terephthalate), or Teflon (a tetrauorethylene plastic). The dielectric coating is particularly desirable with small diameter backing rolls such as the 2" diameter referred to, in order to minimize any tendency for arcing or sparking across the high voltage gap between the wires and the backing roll.
The polyethylene film 36 leaving the die 35 will generally havev a temperature of about 600 F. but will cool so as to contact the paper at a temperature in the range 'of about 450-475" F. The paper web which contacts the polyethylene is preferably heated by the steam rolls to minimize chilling of the polyethylene; typically the paper temperature might be of .the order of 150 F. to 240 F. at the backing roll 31. The heating of the paper also promotes adhesion of the polyethylene film to the paper.
When using small diameter backing rolls, e.g., the 2" roll suggested for FIG. 1, the force on the polyethylene will tend to cause the polyethylene lm to wrap around the roll, i.e., to contact the paper at a point in advance of the expected point of tangency of the film and the roll. This effect is graphically illustrated in FIG. 2 where the .film 36 is shown a-s having a bow 3ft above the expected point of tangency 31. Because of the bow 36', the polyethylene film 36 contacts the paper 20 at point 31, which is in advance of the point 31'. The
distance between points 31 and 31" may be termedthe amount of wrap or extra length of contact between the paper and the film. In general, the higher the applied voltage on the discharge wires 37 the greater will be the Wrap. However, the usable applied voltage is limited by the requirement that arcing between the wires and the grounded backing roll be avoided. The amount of wrap obtained is also dependent on speed and will decrease as speed increases. For example, with a field strength of ordinary magnitude and using a 2" diameter 6 backing roll, visible wrap will substantially disappear at paper speeds of about 400 per minute.
In applying the polyethylene film to the paper substrate, there are two major factors to be accommodated. One is to achieve good adhesion of the polyethylene to the paper, and the other is to achieve a good moisture Vapor transfer resistance (hereinafter termed M.V.T.R.).
With respect to adhesion, for some applications of the product of the invention it is sufficient that the polyethylene film be tightly bonded to the paper substrate so that delamination will not occur. Such an application might be as an inner wall of a multi-wall bag construction. But for other applications, where appearance of the product is important, it is desirable that the adhesion be uniform so as to avoid a patterned appearance. A patterned appearance may be in the form of visible lines in the polyethylene surface, areas of dull appearance, or in general regions whose light reflectance differs from the remaining surface. The presence of such regions seems to have little or no relation to the overall polyethylenepaper adhesion or the product M.V.T.R., but is undesirable from an appearance standpoint for many packaging applications where a uniform surface appearance is desirable.
It is believed that this patterned effect results from areas having a different degree of adhesion to the substrate. It has been found that irregularities in the electrode structure relative to the film face are associated with the patterned effect and probably produce this effect, or at least vary the wrapping force on the polyethylene which in turn produces the pattern. The use of point sources instead of wires tends to produce a severe line patterned effect unless the point sources are located very close together, as in a ne wire brush.
The patterned effect has been found to be greater as the density of the paper substrate is increased, and it appears that to avoid a patterned effect on the product it is best to use low to medium density papers as the substrate. In general, it has been found difficult to avoid excessive patterning effect with a paper substrate density greater than about 75 seconds per 100 cc. measured by official standard T460 m-49 (April 1949) of the Technical Association of the Pulp and Paper Industry.
To obtain a satisfactory appearance, it is desirable that the paper substrate be uncoated. Thus the method of the invention, so far as is presently known, is best applicable -t-o coating polyethylene on a low to medium density uncoated paper.
The numerical M.V.T.R. figures set forth below are in terms of grams of moisture vapor transferred per square inches of sample per 24 hours, after extrusion and lamination. The Itesting was in accordance with recognized testing procedure using a General Foods cabinet Iheld at 100 F. and from 90 to 95% relative humidity.
Some lspecific examples of the method of the invention will now be given. The .apparatus used was that of FIG. 1, using a 2 diameter grounded backing roll and six 3 mil tungsten wires spaced ls apart in a vertical plane tand spaced 1/z inch from a vertical plane tangent to the adjacent side of the backing roll. The backing roll had .a s Hypalon covering. The voltage applied to the electrode wires was .a negative 30,000 volts, producing an input current flow (at volt-s) of 0.55 amps. The paper was a 40 lb. unbleached kraft paper heated to about F. The polyethylene was a Ihigh density Bakelite #7501.
The results of four tests (three specimens each) are tabulated in Table I. In Table I and in the other tables set forth, paper weight is in pounds per ream, i.e., pounds per' 3000 square feet. Coating weight is likewise set forth in terms of pounds per ream (3000 square feet).
TABLE I Trial Coated Coated Paper Film MVTR-gms. number' Specimen Weight thickness Weight Weight 100 sq. in./
pounds inches pounds pounds 24 hours Average; 52. 9 0. 0045 39. 0 13. 2 .37
Average. 40. 1 6. 9 88 3 1 40.0 14.3 .38 2 40. 4 14.7 .38 3 41.0 l 14.0 .as
Average. 55. 0 0. 0046 40. 5 14. 5 38 Average. 47. 2 0. 0042 39. 3 7. 9 73 Further examples of the invention are set forth below in Tables III and HI for Various coating Weights of po-ly- 25 ethylene on a 40 lb. unbleached kraft paper substrate.
Table II is for density polyethylene (S45-.950), while Table III is for low density polyethyene (S18-.925).
Trials Nos. 1, 2, 3 and 4 of Table II are the same as the trials of Table I.
the trials was the same as that described for Table I except for trials 9, 10, 11, 12, 17, 18, 19 and 20, which differed in that three tungsten Wires were used in place of n for all six, as described below in connection with FIG. 3.
The standard method referred to is that employing pressure rolling and shock chilling.- The coating weights and thicknesses'set forth for the standard method are those which would be required to achieve the same M.V.T.R. reading as that shown in the tables for the cor- Qn responding trial using t-he method Iof the invention. The pounds orV mils saved columns represent the saving in polyethylene coating Weight or thickness by using the method of the invention rather than the standard method.
TABLE II H :gh density PE Equiv. coatings Lbs. or mils Coat Thiekfor saine MV TR saved Trial wt. ness MV TR standard method Percent number lbs. mils saved Lbs. Mils Lbs. Mils Average percent 47 TABLE III Low density PE Equiv. coatings Lbs. or mils Coat Thielrfor same MVTR saved Trial wt. ness MV TR standard method Percent number lbs. mils saved Lbs. Mils Lbs. Mils Average percent.
FIG. 3 shows a modified electrode structure for carrying out the method of the invention. FIG. 3 is similar to FIG. 1 but shows three parallel wires 37 in a holder 38 and arranged in a vertical plane in place of the six wires shown in FIG. 1. In FIG. 3 the wires are preferably spaced about 1A" apart. The backing roll 31 of FIG. 3 might be, for example, a 111/16 nylon covered steel roll, and the roll-wire spacing might be l/2.- The electrode wires are preferably tungsten, but might be m-ade of other material, eg., Nichrome wire. One or two wires could be used in place of the three wires of FIG. 3 -or the six wires of FIG. 1, but at least three wires are preferred.
FIG. 4 is similar to FIGS. 1 and 3 except that the electrode wires are disposed in a curved surface concentric wit-h roller 31. When six 'wires are used, the spacing between adjacent wires is preferably about 1/s, but for three wires the spacing is preferably about 1A". The roll 31 in FIG. 4 might be identical with the roll shown in IFIG. 3.
FIG. 5 shows the electrode structure as six parallel wires disposed in a horizontal plane with a spacing of about Ma" between adjacent wires. The vertical position of the electrode wires is preferably at the point of convergence of the polyethylene and paper, but satisfactory results have been achieved with the electrode structure moved somewhat up or down from that position.
tFIGS. 6 and 7 show the electrode wires disposed in planes tilted 30 above and 30 below the horizontal, respectively.
FIG. 8 shows an arrangement in which the electrode wires are divided into two groups of three, with each group lying in a respective vertical plane. These planes might be, for example, 1A apart.
LFIG. 9 shows an electrode structure in which the wires 6U .are replaced with two parallel bands 37' of .003 brass shim stock 1/2" wide and spaced about 1/2 from backing roll 31. A single band 37 has also been used success- '.fully. The ban-ds 37 have been successfully replaced with one or two 1/2" wide bands of copper screen wire (200 mesh).
FIG. 10 illustrates the use of a large diameter backing roll. In FIG. 10, the backing roll 311 might be, for example, an 18 diameter chill roll having a high gloss or matte finish. In FIG. 10 the electrode wires 3-7 lare arranged in a vertical plane, as in lFIG. 1, with the uppermost horizontal wire approximately at the level of the point of convergence of the polyethylene film 36 and the paper 20. An electr-ode structure of the type shown in FIG. 7 can be used to advantage with a large diameter backing roll.
SFIG. 11 shows the use of a large diameter backing roll, as in FIG. 10, but the electrode 37A mounted in holder 38 is formed from a tube having an axially extending slit cut out of the side facing the backing roll, The tube 37A might be, for example, a 7z diameter copper tube and the slit might be 3&6 wide. The slit should extend for the full Iwidth of the electrode.
In FIG. 12 the electrode 37B is formed .by a series of razor blades having their sharp edges facing the backing roll. The razor blades should be mounted so that little or no gap exists between t-he adjacent blades, or a single elongated sharp edged blade should be lused in place thereof. As in the case of the electrode structures described, the electrode structure of FIG. 12 should extend across the complete wid-th of the polyethylene and the holder should provide a firm mounting so that the electrode elements are held rigidly in position. The holders may be made of strong plastic or other suitable insulating material.
Satisfactory results have been achieved also using a 4" diameter grounded steel backing roll wit-h a 'ii/32" thick Hypalon cover and a 1 mil thick aluminum foi-l cover over the Hypalon.
While the invention has been described in connection 19 with specific embodiments thereof and in la specific use, various modifications thereof will occur to those skilled in the .art without departing from the spirit and scope of the invention as set forth in the appended claims.
What is claimed is:
1. The continuous process of coating a paper substrate with a film of a compound selected from the group consisting of polymers and copolymers of lower olefns, comprising the steps of extruding the film, advancing said substrate through a selected region, directing said extruded film along a path in which said extruded film and said substrate converge in said region, and ionizing the air in said region thereby subjecting said extruded film in said region to the action of an electric field whereby said film is forced into intimate bonding contact withsaid substrate.
2.. The continuous process of coating a paper substrate with a film of a compound selected from the group consisting of polymers and copolymers of lower olefins, comprising the' steps of extruding the film, advancing said substrate over and in contact with a grounded conductive roller located in space .adjacent the point of extrusion, directing said extruded film along a path through a region of convergence with and into contact with said substrate 'while the latter is passing over said roller, and ionizing the air in said region of convergence thereby subjecting `saidfilm in said region of convergence thereof with said substrate to the action of an electric field whereby said film is forced into intimate bonding contact with said substrate.
3. The process of claim 2 in which said substrate is maintained .under substantial longitudinal tension while passing over said roller whereby said substrate is restrained against motion in a direction away from said rolle-r and toward said film.
'4. The continuous process of coating a paper substrate with a film of a compound selected from the group consisting of polymers .and copolymers of lower olefins, comprising the steps of extruding the film, advancing said substrate over and in contact with a grounded conductive roller located in space adjacent the point of extrusion, directing sa-id extruded .lm along a path through a region of convergence with and into contact with said substrate while the latter is passing over said roller, and subjecting the air in the space adja'cent said region of convergence of said extruded film and said substrate to a thigh voltage ionized liield whereby electrically charged ions produced by said field contact said extruded film in said region of convergence and force said film into intimate bonding contact with said substrate.
5. The continuous process of coating a paper substrate with a film of a compound selected from the group consisting of polymers .and copolymers of lower olefins, comprising the steps of extruding the film, advancing said substrate over and in contact with a grounded conductive roller located in space adjacent and beneath the point of extrusion, directing said extruded film Ialong a path through a region of convergence with and into contact with said substrate while the latter is passing over said roller, and applying a high voltage between an electrode structure and said roller, said electrode structure being ,disposed in space adjacent the region of convergence of said Ifilm and said substr-ate, said voltage being sufficiently high to ionize the air in said space adjacent said region of convergence whereby resulting ions impinge upon said extruded .film in said region of convergence and force said extruded film into intimate bonding contact with said substrate.
16. The process of claim 5 in which said voltage is of the order of 3,000 -to 50,000 volts and in which the spacing between said electrode structure and said roller is about 1A inch to 2 inches.
7. The continuous process of coating a paper web with Ia polyethylene film, comprising the steps of heating said web, passing said heated web over a horizontally arcanes i l disposed grounded metal roller, extruding a polyethylene iilrn .in space above said roller whereby said lm p-asses vthrough a region of convergence with and contacts said paper While the .latter is passing around said roller, maintaining said web under substantial tension whereby said paper tightly contacts said roller, and applying a high voltage between said roller and an electrode structure .positioned .adjacent the region of convergence of said lm and said web whereby the air adjacent said electrode structure is .ionized and ions impinge on said film, said voltage and the relative spacing of said iilm and said structure being yselected'so that the attractive force prioduced between said i-lrn and said paper web will force said film into intimate bond-ing contact with said web.
8. Theprocess of claim 7 in which said attractive force is substantially uniform across the width of said film.
9. Thev continuous process of coating a paper web with a polyethylene film, comprising the steps of heating said web, passing said heated web over a horizontally disposed grounded metal roller, extruding a polyethylene film in yspace above said roller whereby said iilm passes through .a region of convergence with andcont-.acts said paper while the latter is pass-ing around said roller, maintaining said web under substantial tension whereby said paper tightly cont-acts `said roller, and creating an ionized electricale'ld in said region of convergence of suftcient strength to produce an electrical charge dierential be- V'tween said `iilm and said paper web in the region of con- References Cited by the Examiner UNlTED STATES PATENTS 2,052,131 8/36 Chappell 204-183 2,690,206 9/54 `Mueller 15 6-501 3,003,892 10/ 61` Shannon 117-47 3,018,189 1/ 62 Traver 117-47 FOREIGN PATENTS 1,104,679 4/61 Germany.
OTHER REFERENCES Stiefeling: Electronic Surface Treating of Polyethylene 'Film reprint from Plastics World, November 19-62.
EARL M BERGERT, Primary Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,196,063 July 20, 1965 Leon J. Paquin et a1.
It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
In the grant, lines 2 and 3, for "Glenn IVIe Violette, of
Greenwich, New Jersey," read Glenn M. Violette, of Greenwich, New York, in the heading to the printed specification, line 5, for "Glenn M. Violette, Greenwich, N. J. read Glenn M. Violette, Greenwich, N. Y. column l, line 57, for "requiste" read requisite column 4', line 29, fter "of" insert the column 7, line 26, after "for" insert high Signed and sealed this 28th day of December 1965.
ERNEST W. SWIDER EDWARD I. BRENNER Attesting Officer Commissioner of Patents