US3260690A - Coated paper containers, method of coating and compositions therefor - Google Patents

Description

United States Patent 3,260,690 COATED PAPER CONTAINERS, METHOD OF COATING AND COMPOSITIONS THEREFOR Arthur F. Bohnert, hark Ridge, and William A. Vanick, Hinsdale, IlL, assignors to Enterprise Paint Manufacturing Company, Chicago, ill., a corporation of Illinois No Drawing. Filed July 31, 1961, Ser. No. 127,815 The portion of the term of the patent subsequent to July 31, 1978, has been disclaimer! 13 Claims. (Cl. 260-291) This invention relates to coatings for paper and more particularly to coated containers such .as drinking cups, milk cartons and the like used for receiving various foods and beverages, and method of coating the same.

The present application is a continuation-in-part of our co-pending application for patent, Serial No. 5,603, filed February 1, 1960, now US. Patent No. 2,994,677, as a continuation-in-part of then co-pending application for patent, Serial No. 631,060, filed December 28, 1956, and now abandoned.

Uncoated paper tends to become soggy when exposed to water and to noticeably stain when brought into temporary contact with various foods and/or liquids including coffee, tea, cocoa, milk, fruit juices and the like. Drinking cups which stain and show rings are distasteful to many users. Where the containers are to be used for hot beverages such as tea or coffee, protection of the paper by means of a coating is even more important since hot foods tend to disintegrate the paper and to stain it more readily than do cold liquids.

' While a number of different materials have been used for coating paper, none have been completely satisfact-ory from the point of view of providing a waterproof stain resistant coating for containers in which various foods and beverages might be placed. Two of the more commonly used materials have been vinyl chloride-vinyl acetate copolymer solutions and various blends and formulations of paraffin wax. The vinyl copolymers are usually embodied in a volatile organic solvent which can be evaporated to leave a thin coating of the vinyl co polymer on the paper. However, the ordinarily used solvents such as the ketones and esters are inflammable and thus present a fire hazard. Also the characteristic odors of the ketones and esters in which such resins are dissolved are both irritating and present a health hazard to workers coating containers therewith. Further, because it is almost impossible to completely remove all trace of solvent from the coating, a residual odor is left in the coated container which is highly unsatisfactory to those using such coated cups for drinking beverages and the like. Moreover, the organic solvents are relatively expensive, particularly when compared to water.

The various known parafline wax formulations previously used for coating containers also have their drawbacks. The wax not only has a tendency to flake and crumble from the paper but, in so doing, leaves flakes in the foods and beverage which are distasteful to most users. The wax also provides a taste which is annoying to some users. Moreover, paraffine wax formulations are generally applied hot and require special equipment with resultant high application costs. In the molten state, parafiine definitely presents a fire hazard. Likewise, it is well known that the parafiine wax, because of its low melting point, is not suitable for coating cups or other containers designed to withstand heat as encountered in hot coffee or tea. Such parafline wax formulations also are ordinarily somewhat opaque, particularly when in heavy films, and so are readily visible when applied over printing as on milk cartons, for example.

Thus a first and principal object of the present invention is to provide a coating for paper and/ or coated paper 3,26%,690 Patented July 12, 1966 ICC containers that will provide the desired waterproofing and stain resisting characteristics while avoiding or overcoming the disadvantages above mentioned for previously available coating materials.

Another important object of the present invention is to provide a coating for paper and/ or paper containers which will afford not only a measure of protection to the paper against disintegration and/or staining when brought into contact with hot fluids but will also have the added function of reducing heat transfer through the cup so as to provide a cup or container which can be held more comfortably in the fingers when filled with the hot liquid.

A further object of the invention is to provide such a coating which will not only increase the waterproofness of the paper but will also tend to eliminate the slight characteristic flavor of paper while at the same time itself being substantially free of odor and taste.

A further object of the invention is to provide a coating that will be not only relatively stable and unaflected by various foods and beverages placed in the containers but will be substantially non-blocking. By non-blocking is meant that when the containers are stacked one within the other they will not tend to stick or join together but may be readily separated and without injuring the coating. The advantages thereof will be readily apparent.

A further object of the invention is to provide a coating which will not only provide the desired waterproofing and stain resistance to the coated paper but will also supply a stiffening or reinforcing action on the paper when formed into a container such as a cup so as to provide strength and thereby increasing its utility while at the same time making it possible to employ paper stock of lighter weight so as to result in significant savings in cost of materials.

In obtaining these objects and others, it is proposed according to the present invention to coat paper and/or paper containers and the like from an aqueous emulsion of resin solids which will provide on evaporation of the water and fusion of the remaining resin solids, a thin continuous film affording the desired resistance to water. and staining.

As discussed above, those coatings previously available and used on paper containers ordinarily employed inflammable solvents in which the resin or other coating material was dissolved or dispersed and were therefore hazardous to use not only for health reasons but because of the danger of fire during the coating operation from sparks, static electricity, carelessly thrown matches, cigarettes and the like. Thus it is an important feature of the invention that the paper coating material is contained 1n a non-inflammable and inexpensive volatile vehicle, namely water.

Another advantage to be gained by the use of water as the volatile vehicle in which the coating material is dispersed is that the water in and of itself posseses no odor or taste. Therefore, where small residual traces of solvent remain in the coating, no persisting characteristic odor or taste remains to affect the beverage or other food placed in the coated container.

In some coating applications, particularly, for example, in forming milk cartons it is desirable to pre-coat the paper and then fold to shape. In this connection, a further object of the invention is to provide a means and method of coating to produce a film having all of the aforesaid advantages and features and which will additionally be sufficiently flexible as not to crack, flake or readily separate from the paper when it is folded.

A further object is to provide such a coating or film on paper which will also seal or fuse on the application of suitable heat and pressure to permit a water tight joint between portions of the paper when folded and brought together to form a container.

A further object of the invention is to provide a coating which on evaporation of the volatile constitutent will form a thin continuous film of material having the afore said characteristic and which will strongly adhere to the surface of the paper but will not deeply impregnate the paper whereby the desired protection may be obtained.

using a minimum amount of coating material.

Likewise it is an object of the invention to provide such a coating which will have little or no tendency toftake or peel and will be relatively flexible so that the coating will be useful for providing desired waterproofing and stain resistance to paper when either applied to finished products such as a drinking cup or carton or when applied to paper which is to be subsequently shaped into a container.

Many other objects and advantages as well as features of a coating material, the coated article and method of coating, according to the present invention, are or will become obvious to those skilled from the description thereof which is to follow.

Thus, in accomplishing the aforesaid objects, the inventors has found that a water emulsion of resin solids consisting essentially of polymeric material from the group consisting of (a) water emulsified styrene-butadiene copolymer alone or (b) water emulsified styrene-butadiene copolymer in admixture with water emulsified polystyrene may be prepared. 1

Such a coating composition can be conveniently and simply applied form or in the form of a cup, a carton, a plate or other container so as to obtain, on evaporation of the water, a thin, transparent, continuous film of resin having marked resistance to water penetration and staining by a variety of hot or cold liquids such as the aforementioned milk, coffee, tea, cocoa and fruit juices in addition to a variety of other foods. Such films have been found to be substantially tasteless and odor free as well as masking the taste of the paper on which the film is applied and imparting insulating qualities against heat.

Although the proportions of the several ingredients may be varied within relatively wide limits, as for example, the proportion of butadiene may range from a minimum of 1% to a maximum of 50% by weight of the total resin, a more satisfactory working range has proved to be obtained wherein the butadiene content is kept between 15 and 25%, with the preferred ratio being near 20 parts by weight of the butadiene moieties per 80 parts of the styrene moieties of the resin content.

Where the coating is being used on containers for food or beverages, it is a prime requisite of the selected plasticizer that it be oder and taste free as well as stable. In addition to possessing these properties butadiene is compatible with the polystyrene and/ or when in copolymerization with styrene moieties, it has no tendency to leach out or migrate from the film. Its other good film forming properties, plus its low cost, make it the plasticizer of preference.

Although an emulsion of polystyrene and styrenebutadiene copolymer or a styrene-butadiene copolymer esin used alone 'as the coating material will provide the major proportion of the protection and masking properties desired in the film, we have found that the addition of at least .625% by weight of a polyolefin or lower alkene polymer such as polyethylene and polypropylene based on the total solids present has the surprising and unexpected result of materially increasing the flow and other film forming characteristics of the resin and particularly the non-blocking and non-melting characteristics of the fused film. On the other hand we have also found that the amount of polyolefin should not be so large as to be incompatible with the other components of the emulsion and interrupt continuity of the fused film. For this reason we keep the polyolefin content below 50% by to paper, existing either in sheet stockweight of the total resin solids. Polypropylene might also be used in place of polyethylene.

The resins may be prepared by polymerization in an emulsified state or by emulsification of resins prepared by other methods as widely described in the literature. The proportions of water embodied in the emulsion can vary considerably, depending on the viscosity required for the particular method by which the coating is to be applied. Generally speaking, however, emulsions according to the present invention will comprise roughly 25 to 50% by weight of resin solids, the balance comprising water and including a small quantity of suitable emulsifying agent.

Although the coating material may be applied in any one of several ways as by dipping, spraying or flushing, containers such as coffee cups are conveniently coated by using a pair of jets one directed to focus a spray of the coating material onto the inner walls of the cup and a second jet located to direct coating material toward the bottom of the cup so as to completely cover the interior of the cup, including the rim if desired. It has been found that, although the Water in which the resins are contained, will readily penetrate the paper stock, the resin solids do not as readily penetrate and, instead, remain essentially on the surface of the paper as a thin layer which fuses, when heated, into a thin, clear transparent continuous film strongly bonded to the paper surface This may be accomplished for example by air-drying the coated paper stock or cups for about 10 minutes and then baking at 300 F. for two minutes. However, a preferred method for rapidly removing the water from the film and fusing the resin solids into a continuous film comprises directing air heated to a temperature in the vicinity of 250 F. onto the coated interior of the cups for roughly 1 minute or a time interval sufiicient to drive out the water without raising or otherwise blistering the remaining film of resin. The temperature of the thus directed air is then gradually increased over a period of roughly two minutes until it reaches a temperature between 350 and 400 F., at which temperature it is held for approximately 20 seconds or sufiicient to fuse the coating into a continuous film providing the desired Waterproofing and stain-resisting characteristics. The baking step is then followed by blowing air maintained at room temperature, or slightly below, onto the coated interior of the cups for approximately 30 seconds to cool and otherwise set the film so that there is no problem of the cups sticking when stacked or nested one Within the other. The aforesaid time cycle will vary somewhat with the size of the container being coated and/or thickness of the coating.

1 When coating flat paper stock, as it leaves the roll, one or both sides of the paper are brought into contact with the coating material and then between wiping blades or a knife as is known to those skilled in the art. Thereafter, the coated paper is subjected to air initially heated to 250 F. as before and which is gradually raised to the mentioned fusing temperature to near 400 F. The coated stock is then cooled to near room temperature.

In the formulation of our coating composition aqueous emulsions of the polyolefin may be prepared using an emulsifiable grade of the olefin polymer (i.e. which has been partially oxidized) or we may use an olefin polymer latex which is the direct product of an emulsion polymerization of the corresponding monomer.

For example, where an emulsifiable grade of polyethylene is used, a polyethylene emulsion may be prepared by heating 81 parts of thepartially oxidized polyethylene at approximately 250 F. until in a liquid state, then adding, in succession, 17 parts of oleic acid and 17 parts ofmorpholine as an emulsifying agent, the temperature being held at 225 to 235 F. After 2 to 5 minutes, the mix is gradually added with agitation to 400 parts of hot water until the desired emulsion is obtained.

Such a polyethylene emulsion we have found particularly satisfactory when added in an amount so that the polyethylene portions comprise about 1.5% or 1 to 2% by weight of the total solids contents of the coating emulsion. However, where the amounts are increased so that in the final film the polyethylene content exceeds 3.32% there is a noticeable browning efiect. This is apparently due to the slight discoloration which is imparted to the polyethylene when it is partially oxidized to an emulsifia-ble grade. Since the film has its most important utility as a coating for the interior of coffee cups, such a color may be erroneously interpreted as suggestive of a colfee-stained cup or at least one that is unclean.

At the same time we have also found that the nonblocking properties of the films are further improve-d as larger proportions of the emulsified polyethylene are added to the films. For this reason if the pap-er or cups to be coated have a color other than the conventional light pastel colors, or if the mentioned browning of the film is not objectionable, then larger amounts of the polyethylene can be used with beneficial results as far as the non-blocking properties of the coated paper cups are concerned. The polyolefins, however, being essentially inert have an incompatibility with the butadiene-styrene copolymer and polystyrene which comprise the balance of the films, particularly when present in large amounts, and where paper cups have been coated with emulsions containing polyethylene in excess of 50% by weight of the total solids thereof, coffee added to the cups noticeably stains the cups, indicative of the discontinuous or interrupted character of the film. However, in coatings where lesser amounts of polyethylene are present, the polyethylene particles are so distributed through the film as not to interrupt the continuity of the film but are effectively surrounded by the polystyrene and butadiene-styrene copolymer as to be confined thereby and yet available for imparting non-blocking properties to the film.

Polyethylene also may be prepared by polymerizing an aqueous emulsion of the monomer and using the resultant latex. In this case a much purer form of polyethylene is available and one characterized by an absence of color or odor as well as having greater resistance to acid and air oxidation. The emulsion polymers of polythylene are also of much higher molecular weight, in the order of 15,000 to 30,000, than the partially oxidized low molecular weight polyethylene which usually have a molecular weight of about 2,000. They are therefore also harder and more flexible. A typical emulsion will comprise about 40% by weight of solids of which approximately 4.0 to 6.5% represents the emulsifier and the balance the polyethylene particles. The emulsions comprise dispersions of very fine particle size (less than 0. 1 micron), have a viscosity of less than 100 (Brookfield, 25 C., spindle No. 1, 60 rpm.) and a pH range of chemical stability about 8.3. The coating emulsion which we prefer to use are anionic in character and so the selected polyethylene emulsions are also anionic. An appropriate anionic emulsifying agent would be dioctyl sodium sultosuccinate.

Properties of solid polyethylene isolated from its anionic latex are summarized below in comparison with the properties of an emulsifiablegrade or partially oxidized polyethylene:

Emulsion Partially Polymerized Oxidized Polyethylene Polyethylene Melting point (ring and ball method ASTM D36 26), F 215-230 196-201 Density, gins/cc 0. 920. 935 0.91 Inherent Viscosity (0.2%

130 C. dl./gm 0.5-0.9 0.1 Estimated Molecular Weight 15, 000-30, 000 000 Color White White to Yellow Hardness Shore D 45-48 30 Needle penetration (ASTM D552, 5009 In the case of the emulsion polymerized polyethylene, since the polyethylene has not been oxidized but exists in essentially its pure form, it is possible to add much larger amounts thereof to the coating emulsions and without effecting an undesired browning or yellow color to the deposited film. Therefore to obtain further improvement in the non-blocking property of the deposited film, we prefer to increase the amount of polyethylene to equal at least 5% by weight of the total solids content of the coating emulsion and up to a maximum of approximately 30%. Although it is possible to utilize up to about 50% by weight of polyethylene, that is to the limit where incompatibility of polyethylene starts to noticeably affect the continuity of the deposited film, beyond the 30% maximum mentioned there is a noticeable fall off in the gloss which the polyethylene imparts to the film. Actually we have noticed that as the amount of polyethylene content of the film is increased there is an accompanying increase in gloss as well as improvement in non-blocking properties, the optimum gloss being obtained in the range of approximately 8 to 20% although there is still appreciable high gloss up to the mentioned maximum polyethylene content of 30%. If gloss is not important, then, of course, the limit of polyethylene inclusion is determined only by the point at which its presence with the other components of the film produces a discontinuous film. Our tests indicate that although this point is not definite, 50% appears to be the maximum amount of polyethylene which a film can contain and still provide all the essential protective and good adherence properties which we desire in a coating.

Where the emulsion is tobe used for coating containers in which salad oils or other materials containing large amounts of oils or greases are to be placed, the resistance of the coating to such oils and greases can be improved by the addition of polyacrylic resins (lower alkyl acrylic or methacrylic ester polymers or copolymers) to the emulsion. The addition of the polya-crylics also appears to improve the non-wicking properties of the coating so that there is less penetration of the resin film 'into the paper.

Also if desired, the coating compositions may be modified by the addition of polyvinyl resins such as polyvinyl acetate. These provide a tougher and more flexible film on evaporation of the water. Thus, for example, where the coating material is to be applied to sheet stock which is to be later shaped into a container or other article, films modified with polyvinyl resin will have greater resistance to cracking during the necessary manipulation and/or bending and shaping of the coated paper. The polyvinyl resins also help to increase resistance of the films to attack by oils and greases. Likewise, the films may be modified by the addition of copolymers of styrene and natural or synthetic alcohol soluble resins as, for example: styrene-shellac copolymer, styrene-manila gum copolymer, styrene-maleic copolymer resins, and styreneallyl starch. These may be added to the coating emulsion to reduce tack, provide better leveling and more uniformly thin continuous films.

There follow typical examples of suitable coating compositions which may be formed and used in accordance with the present invention. In these examples, commercially available emulsions of styrene-butadiene resin copolymers have been modified by the additions of aqueous emulsions or polystyrene alone to obtain the required ratio of styrene moieties to butadiene moieties. The modifying resins are also added as aqueous emulsions and where necessary soft water has been added to obtain the required dilution or viscosity. Thus, in the following examples, Pliolite is an aqueous emulsion containing about 48% of styrene-butadiene resin in the ratio of 70 parts styrene to 30 parts by weight of butadiene. Dow 762W is an aqueous emulsion containing 48% of resin in the ratio of 33 parts butadiene to 67 parts of styrene by weight. Dow X2527 .4 is an aqueous emulsion embodying 48% resin in the ratio of 40 parts by weight of butadiene to 60 parts styrene and Dow 512L is an aqueous emulsion embodying 48% solids in the ratio of 60 parts by weight styrene to 40 parts butadiene. These are diluted with polystyrene resin emulsions such as U2001 which is an aqueous emulsion of polystyrene containing approximately 35% of polystyrene resins or the aqueous emulsion designated Monsanto 615 containing approximately 49% of polystyrene resin. Morton 1500 designates an aqueous emulsion of polystyrene which contains approximately 50% solids.

The polyethylene emulsions are either an emulsion prepared by using an emulsifiable grade of polyethylene as previously described or a commercially available emulsion where the polyethylene has been polymerized from an aqueous emulsion of the monomer as for example, the emulsion form of polyethylene sold under the trade name Poly Em which comprises about 40% solids.

A typical all-purpose formula particularly useful in coating containers to be used for drinking cups to contain hot beverages, such as coffee or tea, may be prepared using the emulsifiable grade of polyethylene so as to comprise:

Example I Gallons Styrene-butadiene copolymer emulsion (Dow 762W) 44 Polystyrene resin emulsion (U2001) 32 Emulsion of emulsifiable grade of polyethylene 4 Deionized water (soft water) 20 A composition having much less wicking and less odor will comprise:

Example 11 Gallons Styrene-butadiene copolymer emulsion (Pliolite 170) 55 Polystyrene emulsion (U2001) 40 Polyethylene emulsion (emulsifiable grade of polyethylene) 5 100 Another useful composition that may be formed will comprise:

Example III Gallons Styrene-butadiene copolymer emulsion (Dow 762W) 34 Polystyrene emulsion (Monsanto 615) 34 Polystyrene emulsion (U2001) 17 Polyethylene emulsion (emulsifiable grade of polyethylene) 8 Soft water 7 To The increased butadiene content of the following composition permits a much lower fusing temperature.

Example IV Gallons Styrene-butadiene copolymer emulsion (Dow X2527.4) 36.25 Polystyrene emulsion (U2001) 18.50 Polystyrene emulsion (Monsanto 615) 36.25

Polyethylene emulsion (emulsifiable rade S 5E51}:

ethylene) 9.00

100.00 The following composition is particularly colorless.

Example V Gallons Styrene-butadiene copolymer emulsion (Dow 762W) 55 Polystyrene emulsion (Monsanto 615) Polyethylene emulsion (emulsifiable grade of polyethylene) By reason of the higher polyethylene content in this particular composition better blocking resistance is ob tained than in the previous example.

Example VI Gallons Styrene-butadiene copolymer emulsion (Dow 762W) 49.00 Polystyrene emulsion (Monsanto 615) 35.25 Polyethylene emulsion 8.75 Soft water 7.00

The composition of the following is particularly useful for coating small cups and the like containers although it has somewhat lower resistance to grease than does the composition of Example I.

Example VII A formulation wherein a latex of emulsion polymerized polyethylene has been substituted for anemulsion of partially oxidized polyethylene toobtain improved non-blocking properties without discOloring the resultant film will comprise:

Example VIII Gallons Styrene-butadiene copolymer (Dow 512L) 49.5 Polystyrene (Morton 1500) 39.5 Emulsion polymerized polyethylene (Poly Em) 10.0 In the aforesaid example the polyethylene represents about 8.4% by weight of the total solids. By further increasing the polyethylene content still further improvements in gloss as well as non-blocking properties may be realized. The following is an example of a particularly useful composition containing 21.2% by weight of emulsion polymerized polyethylene on a solids basis.

Example IX Gallons Styrene-butadiene copolymer (Dow 5 12L) 41.0 Polystyrene (Morton 1500) 33.0 Emulsion polymerized polyethylene (Poly Em) 25.0

Thus1 it will be apparent from the above description al of have been demonstrated as obtainable in a convenient, simple, and practical manner.

Thus having described our invention we claim:

1. As a method of improving the resistance of paper to staining and penetration by ordinary foods and beverages, both hot and cold, the steps of coating a surface (a) water emulsified styrene-butadiene. copolymer and (b) Water emulsified polystyrene mixed with water emulexceeding approximately one-half thereof and the styrene moieties being not less than one-half thereof, removing the water from the aqueous 2. As a method of improving the resistance of paper to staining and penetration by ordinary foods and beverages, both hot and cold, the steps of coating a surface of the paper with a layer of an aqueous emulsion of polymeric material selected from the group consisting of (a) water emulsified styrene-butadiene copolymer and (b) water emulsified polystyrene mixed with water emulsified styrene-butadiene copolymer, said emulsion further containing an amount between about and 30% by weight of water emulsified polypropylene sufiicient to introduce non-blocking characteristics to the fused film left on the surface after heating, the butadiene moieties of said polymeric material not exceeding approximately one-half thereof and the styrene moieties being not less than one-half thereof, removing the water from the aqueous emulsion layer, thereafter fusing the remaining solids with heat into a continuous film, and then cooling to near room temperature to leave a clear transparent protective film strongly adherent to the paper.

3. As a method of improving the resistance of paper to staining and penetration by ordinary foods and beverages, both hot and cold, the steps of coating a surface of the paper with a layer of an aqueous emulsion of polymeric material consisting of water emulsified polystyrene and water emulsified styrene-butadiene copolymer, said emulsion further containing an amount between about 5% and 30% by weight of polyethylene polymerized from an aqueous emulsion of the monomer and having a molecular weight in the order of 15,000 to 30,000, said amount being sufi'icient to introduce nonblocking characteristics to the fused film left on the surface after heating without interrupting the continuity of the film, the butadiene moieties of said polymeric material not exceeding approximately one-half thereof and the styrene moieties being not less than one half thereof, removing the water from the aqueous emulsion layer, thereafter fusing the remaining solids with heat into a continuous film, and then cooling to near room temperature to leave a clear transparent protective film strongly adherent to the paper.

4. As a method of improving the resistance of paper to staining and penetration by ordinary foods and beverages, both hot and cold, the steps of coating a surface of the paper with a layer of an aqueous emulsion of polymeric material from the group consisting of (a) water emulsified styrene-butadiene copolymer and (b) water emulsified polystyrene mixed with water emulsified styrene-butadiene copolymer, said emulsion further containing an amount between about 5 and 30% by weight of water emulsified, water White polyethylene having a molecular weight in the order of 15,000 to 30,000, obtained by polymerizing an aqueous emulsion of the monomer, said amount being sufficient to introduce nonblocking characteristics and high gloss .to the fused film left on the surface after heating, the butadiene moieties of said polymeric material not exceeding approximately onehalf thereof and the styrene moieties being not less than one-half thereof, removing the water from the aqueous emulsion layer, thereafter fusing the remaining solids with heat into a continuous film, and then cooling to near room temperature to leave a clear transparent protective film strongly adherent to the paper.

5. A water emulsion coating composition free of organic solvent and consisting essentially of water emulsified resin solids, said emulsified resin solids constituting (I), as a major ingredient, polymeric material from the group consisting of (a) water emulsified styrene-butadiene copolymer and (b) a mixture of water emulsified styrene-butadiene copolymer and water emulsified polystyrene, and (II), as a modifier for the polymeric material water emulsified lower alkene polymer selected from the group consisting of polypropylene and polyethylene having a molecular weight in the order of 15,000 to 30,000 in an amount between about 5% and 30% by weight of the total resin solids, the butadiene moieties of said polymeric material comprising from about 15 to 25% by weight of the polymeric material, and the styrene moieties comprising the balance of said polymeric material, said composition being capable, when applied as a thin coating to paper and heated to the fusion temperature of the solids, of forming a thin continuous film that is strongly adherent to the paper, that is essentially tackfree and which provides the thus coated paper with marked resistance to penetration and staining by ordinary foods and beverages, both hot and cold.

6. A water emulsion coating composition according to claim 5 wherein the polyolefin comprises polypropylene.

7. A water emulsion coating composition free of organic solvent and consisting essentially of water emulsified resin solids, said emulsified resin solids constituting (I), as a major ingredient, polymeric material selected from the group consisting of (a) water emulsified styrene-butadiene copolymer and (b) a mixture of water emulsified styrene-butadiene copolymer and water emulsified polystyrene, and (II), as a modifier for the polymeric material, water emulsion polymerized, water white polyethylene having a molecular weight in the order of 15,000 to 30,000 in an amount between about 5% and 30% by weight of the polymeric material, the butadiene moieties comprising less than half by weight of the polymeric material and the styrene moieties comprising =the balance of said polymeric material, said composition being capable, when applied as a thin coating to paper and heated to the fusion temperature of the solids, of forming a thin continuous film that is strongly adherent to the paper, that is essentially tack-free and which provides the thus coated paper with marked resistance to penetration and staining by ordinary foods and beverages, both hot and cold.

8. A water emulsion coating composition free of organic solvent and comprised essentially of water emulsified resin solids, said emulsified resin solids constituting (I), as a major ingredient, a mixture of water emulsified styrene-butadiene copolymer and water emulsified polystyrene, and (II), as a modifier for the polymeric material, waiter emulsified waiter white polyethylene in an amount between about 5 and 30% by weight of the total resin solids, said polyethylene having a molecular weight in the to rder of 15,000 to 30,000, the styrene moieties of said copolymer and said polystyrene together exceeding by weight the ptoportion of butadiene moieties of the copolymer, said composition being capable, when applied as a thin coating to paper and heated to the fusion-temperature of the solids, of forming a thin continuous film that is strongly adherent to the paper, that is essentially tackfree and which provides the thus coated paper with marked resistance to penetration and staining by ordinary foods and beverages, both hot and cold.

9. Paper having at least one surface coated'with a baked-on, clear transparent, continuous film deposited from a water emulsion of polymeric material selected from the group consisting of (a) styrene-butadiene copolymer and (b) mixture of polystyrene and styrenebutadiene copolymer, wherein the styrene moieties of said polymeric material comprise the major portion thereof and the butadiene moieties comprise the minor portion thereof, said film further containing an amount of lower alkene polymer selected from the group consisting of polypropylene and polyethylene having a molecular weight in the order of 15,000 to 30,000 uniformly distributed through said polymeric material sufficient to impart nonblocking characteristics to the film without interrupting the continuity of the film and its clear transparent character, said amount of lower alkene polymer being between about 5% and 30% by weight of the film, said film strongly adhering to the surface of the paper but not deeply impregnating the paper, and said film imparting heat-insulating as well as nonblocking characteristics to the paper and improved resistance to penetration, staining and disintegration of .the paper by hot and cold bev- 1 l erages such as coffee, tea, milk, cocoa and fruit juices, said film further being essentially free of taste and odor while tending to mask the .taste of the paper over which it is coated.

10. A container formed of paper and having its interior surface coated with a baked-on, clear transparent, continuous film deposited from a Water emulsion of polymeric material from the group consisting of (a) styrene-butadiene copolymer and (b) mixture of polystyrene and styrene-butadiene copolymer, wherein the styrene moieties of said polymeric material comprise the major portion thereof and the butadiene moieties comprise the minor portion thereof,-said film further containing an amount of polypropylene uniformly distributed through said polymeric material suflicient to impart nonblocking characteristics to the film without interrupting the continuity of the film and its clear transparent character, said amount of polypropylene comprising from about 5% to 30% by Weight of the film, said film strongly adhering to the interior surface of the paper container but not deeply impregnating the paper, and said film imparting heat-insulating as well as nonblocking characteristics to the container and improved resistance to penetration, staining and disintegration of the paper when used to store hot and cold beverages such as coffee, tea, milk, cocoa and fruit juices, said film further being essentially free of taste and odor while tending to mask the taste of the paper over which it is coated.

11. A container formed of paper and having its interior surface coated with a baked-on, clear transparent, continuous film deposited from a water emulsion of polymeric material from the group consisting of (a) styrene-butadiene copolymer and (b) mixture of polystyrene and styrene-butadiene copolymer, wherein the styrene moieties of said polymeric material comprise the major portion thereof and the butadiene moieties comprise the minor portion thereof, Said film further containing between about 5% =to30% by weight, water white polyethylene having a molecular weight in the order of 15,000 to 30,000, uniformly distributed through said polymeric material, said film strongly adhering to the interior surface of the paper container but not deeply impregnating the paper, and said film imparting heat-insulating as Well as nonblocking characteristics to the container and improved resistance to penetration, staining and disintegration of the paper when used to store hot and cold beverages such as cotfee, tea, milk, cocoa and fruit juices, said film further being essentially free of taste and odor while tending to mask the taste of the paper over which it is coated.

12. A container formed of paper and having its interior sur ace coated with a baked-on, clear, transparent, high gloss continuous film deposited from a water emulsion of polymeric material consisting of a mixture of polystyrene and styrene-butadiene copolymer, wherein the styrene moieties of said polymeric material comprise the major portion thereof and :the butadiene moieties com- .prise the minor portion thereof, said film further containing an amount between about 5% and 30% by weight of a transparent, Water white polyethylene uniformly distributed through said polymeric material sufiicient to im- 5 part nonblocking characteristics and high gloss to the film without interrupting the continuity of the film, said polyethylene having a molecular Weight in the order of 15,000 to 30,000 and being the product of a polymerization of an aqueous emulsion of .the ethylene monomer, said film strongly adhering to the interior surface of the paper con- .tainer but not deeply impregnating the paper, and said film imparting heat-insulating as well as nonblocking characteristics to the container and improved resistance to penetration, staining and disintegration of the paper when used to store hot and cold beverages such as coffee, tea, milk, cocoa and fruit juices, said film further being essentially free of taste and odor while tending to mask the taste of the paper over which it is coated.

13. A water emulsion coating composition free of organic solvent and consisting essentially of water emulsified resin solids, said emulsified resin solids constituting (I), as a major ingredient, polymeric material selected from the group consisting of (a) water emulsified styrene-butadiene copolymer and (b) a mixture of water 25 emulsified styrene-butadiene copolymer and water emulsified polystyrene, (II) polyvinyl resin, and (III) as a modifier for the polymeric material, water emulsified lower alkene polymer selected from the group consisting of polypropylene and polyethylene having a molecular 3 weight in the order of 15,000 to 30,000 in an amount between about to 30% by weight of the total resin solids, the butadiene moieties of said polymeric material by weight of the polymeric and the styrene moieties comprising the balance 1, said composition being capable, when applied as a thin coating to paper and heated to the fusion temperature of the solids, of forming a thin continuous film that is strongly adherent to the paper, that is essentially tack-free and which provides the thus coated paper with marked resistance to penetration and staining by ordinary foods and beverages, both hot and cold.

References Cited by the Examiner UNITED STATES PATENTS 2,788,340 4/1957 Dannels 117-155 2,805,962 9/1957 Hendricks 26029.7 2,994,677 8/1961 Bohnert et a1 26029.7 5O FOREIGN PATENTS 558,748 12/1957 Belgium. 561,459 4/1958 Belgium.

MURRAY TILLMAN, Primary Examiner.

LOUISE P. QUAST, W. H. SHORT, Examiners. J. ZIEGLER, E. B. WOODRUFF, Assistant Examiners.

Claims (1)

1. AS A METHOD OF IMPROVIDING THE RESISTANCE OF PAPER TO STAINING AND PENETRATION BY ORDINARY FOODS AND BEVERAGES, BOTH HOT AND COLD, THE STEPS OF COATING A SURFACE OF THE PAPER WITH A LAYER OF AN AQUEOUS EMULSION OF POLYMERIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF (A) WATER EMULSIFIED STYRENE-BUTADIENE COPOLYMER AND (B) WATER EMULSIFIED POLYSTYRENE MIXED WITH WATER EMULSIFIED STYRENE-BUTADIENE COPOLYMER, SAID EMULSION FURTHER CONTAINING AN AMOUNT BETWEN ABOUT 5 AND 30% BY WEIGHT OF WATER EMULSIFIED LOWER ALKENE POLYMER FROM THE GROUP CONSISTING OF POLYPROPYLENE AND POLYETHYLENE HAVING A MOLECULAR WEIGHT IN THE ORDER OF 15,000 TO 30,000 WHICH IS SUFFICIENT TO INTRODUCE NON-BLOCKING CHARACTERISTICS TO THE FUSED FILM LEFT ON THE SURFACE AFTER HEATING WITHOUT INTERRUPTING THE CONTINUITY OF THE FILM. THE BUTADIDNE MOIETIES OF SAID POLYMERIC MATERIAL NOT EXCEEDING APPROXIMATELY ONE-HALF THEREOF, REMOVING MOIETIES BEING NOT LESS THAN ONE-HALF THEREOF, REMOVING THE WATER FROM THE AQUEOUS EMULSION LAYER THEREAFTER FUSING THE REMAINING SOLIDS WITH HEAT INTO A CONTINUOUS FILM, AND THEN COOLING TO NEAR ROOM TEMPERATURE SO AS TO LEAVE A CLEAR TRANSPARENT PROTECTIVE FILM STRONGLY ADHERENT TO THE PAPER.