US2227516A - Wax paper sheet and coating therefor - Google Patents

Description

Patented Jan. 7, 1941 UNITED, STATES,

assure wax PAPER sneer sun COATING runner-0a Randolph Spencer Seance, Toronto, Ontario, Canada, assignor to Appleton-d Paper Products, Ltd., Hamilton, Ontario, Canada No Drawing. Application Jul 11, 1938,

Serial No. 218,637

2 Claims. (CI. 91-68) This invention relates to an improved heat scalable, moisture proof, opaque wax paper sheet and to an improved wax composition coating for paper sheets or the like, which coating possesses the capacity when applied .to the sheet of rendering the coated sheet opaque, moisture resistant, and heat seal-able according to accepted commercial methods.

Waxed or coated sheets of this character are W commonly used as wrappers for food stuffs, such as bread, cake and the like. Such coatings usually consist in large part of wax such as parabin war.

licretofore waxed paper sheets have been of two hinds, namely, transparent or semi or partially transparent waxed sheets and opaque waxed sheets. Paraiiin wax which is commonly used as a coating material has a tendency to increase the trparency of the base sheet to which it is up W plied and unloaded sulphite tissue which is commoniy used as a base sheet to receive the coating is ore nearly transparent following the application of the coating than was the uncoated base sheet, Such sheets have a wide held of use and are marketed in large quantities. It is frequently desirable, however, to provide o. wax sheet which is opaque and to provide an opaque way paper sheet it has heretofore been the practice to employ an opaciiyine agent as a filler or loadino" octent in the iabrlcation of the base sheet. Tltonli dioxide (Title) because of its hiuh linden ol" rci'rocdon and the desirable white color which it imports to the sheet has been used as such ldller. finch loaded base sheet being substantially opoone was then treated with a want, such as llllitlt wan, to form a waxed opaque sheet.

.lln oblcct oi my invention is to provide on opnouo iprelerably purewhlte) moisture resistout, flexible, heat scalable wax composition coated M sheet oi paper or'the like wherein the characterlstlcc above enumerated reside in the coating.

l have developed a composition conslstino in lame part oi parailin wax with other suitable inyredlents hereinaiter specified, which composiyp tion may be applied in the conventional manner in n hot melt coating to an unloaded sulphite sheet or other suitable base sheet to produce o. cooled sheet which is opaque, moisture resistant, hoot scalable, and possesses a high degree oi pliyo ability. Such composition coating may be applied to one or both sides of the sheet or to local iced arms thereof.

Various decorative and novelty effects may be produced in an opaque wax sheet through the on use of my improved coating as compared with the opaque wax sheet where the opacity is due to the opacity of the base sheet. My improved sheet may have localized areas of transparency r translucency as compared with its 0th e opaque areas. One surface may carry the opaque coating while the opposite surface may carry the 5 conventional so-called transparent wax coating. The base sheet may have such opposite surface printed or decorated as desired before coating with the transparent wax coating so that the print or decoration will appear on the coated m sheet.

i may use an ordinary sulphite unloaded sheet as the base sheet to receive my improved coating. Because of the absorbency of such a base sheet w and the character of the coating a particularly secure bond is formed by the coating with the base sheet. If desired, however, loaded or shed paper sheets may be used. It grease resistance is desired a glassine base sheet may be used. Cellom phone or the like micht even be used. My coatinn is oi such a character as to form a particularly secure bond with any suitable base sheet and its high degree of flexibility and adhesion prevents cracking, breaking, or peelinp oi the coatiny M ircm the sheet as the sheet is wrapped or told in use.

in one preierred form. oi my invention as up plied to bread wrappers the paper sheet, printed as desired, is coated on the printed side with m par won or other suitable hot melt coating" oi reasonable transparency and on the reverse side with my improved composition. Such operation may be ndvontadeously carried out in o. wordne machine oi the Meyer type which per-nuts oppo- M site sides oi the sheet to be coated with dizdercnt compositions. l hrouoh the employment oi" suitable mechanism it is possible to produce a sheet possessing one or more bands oi creator or less transparency in the direction oi motion oi the sheet and in merited contrast with the opacity oi W the remainder of the sheet. The printing will stand out in, marked contrast ooainst the pure white baclryround enhanced ii desired by a transparent coating. M

The composition which i propose to employ comprises a suitable wax such as paramn wan carryiuc in suspension a suitable pigment, such as titanium dioxide. TiOc will not remain in suspension in molten paraflln wax alone. The viscosity of molten paraflln is low as is its specific gravity. T10: settles down very quickly in molten paraflln alone but I have i'ound that if certain substances of a rubbery consistency, such as natu red rubber .or certain synthetic materials possess- 55 ing similar characteristics are added in very small quantity to. the molten parafiin and placed in solution or what appears to be in solution therein that the TiO: will then remain in suspension for such period of time as to make the composition readily applicable topaper sheets as a hot melt,

coating.

I prefer to mix a small amount, for example, one to five parts of rubber, which may be in the form of crepe rubber sheets cut up fine, or smoked rubber sheets so disintegrated, with parts of wax, which wax may be in the form of paraffin wax. T'he rubber may be mixed with a relatively small amount of parafiin wax and stirred or otherwise incorporated therewith until it appears to go into solution therein and then this mixture may be reduced by the addition of the remaining paraflin to make up the 100 parts.

Whether the rubber actually goes into solution or a very fine dispersion is open to question but to all apearances it goes into solution and where the word solution" is used herein as referring to the rubber going into solution in the parafiin such interpretation is intended.

A suitable pigment, (T102 has been found highly suitable) is then added to the paraffinrubber solution and incorporated therein by passing the mixture through a paint mill or such in- -corporation is obtained in some other approved manner. The pigment is so thoroughly incorporated in the mixture that it will remain in suspension for several hours and for such an appreciable period of time that the coating may be used as a hot melt coating for paper with the pigment uniformly and finely distributed therethrough so that the coated sheet presents a uniform opaque appearance without spots or blotches in pigmentation.

Pigment may be added in varying amounts depending upon the degree of pigmentation desired. Sheets of varying opacity are used by the paper products manufacturer and it is obvious that the amount of opacifying substance could be varied as desired. Appreciable opacity is produced with the addition of three parts of the T102 with 100 parts of paraflin wax but to produce a substantially satisfactory commercially desirable high order of opacity of the wax sheet I have found it suitable to add fifteen parts of pigment in the 100 part mixture of the character above set forth. The percentage of TiO: may of course be varied not only depending on the degree of opacity desired and the character of the base sheet used but upon whether one or both surfaces of the base sheet are to be coated therewith and upon the thickness of the coating layer to be applied. It is readily possible to determine the amount required for the result sought. .The resulting liquid mixture is sufliciently fluid to be readily applied as a thin wax coating to a paper sheet either as a hot melt or in any other conventional manner. The pigment is so finely divided and distributed throughout the wax that the sheet presents a uniform pigmentation.

T102 is available in various commercial forms classified by the manufacturers as MO:HO: and WD. I have found the form known as TITA- NOX-A-MO very suitable but the other forms also are suitable. Other pigments may be employed; For example, zinc oxide though having a lower index of refraction and consisting of less finely divided particles is suitable for use. If zinc oxide is used it will be desirable to increase the percentage of pigment, for example, one-third over that of T102.

The substance of rubbery consistency in addition to serving to maintain the pigment in suspension in the paraflln also increases the security of the hot seal and increases substantially the anchorage of the coating upon the paper and increases substantially the flexibility of the coated sheet. Only a small amount of rubber is required. As low as one part to 100 parts of paraflin has an appreciable effect. Five parts of rubber to 100 parts of paraffin has proved to be ample and two to three parts has proved satisfactory.

It has been found that certain synthetic materials of a rubbery consistency may be substituted for the rubber particles of crepe or smoked rubber sheets. These synthetic substances might not even be termed true synthetic rubber. An example of such a synthetic material which has been found suitable is the polymer of iso-butylene (2 methyl propylene) known as Vistanex-Medium. In using this synthetic substance I have found it desirable to add a small amount of sodium benzoate. The sodium benzoate when added in a small trace to the paraflin bath mixture appears to increase the period of suspension of the pigment. Sodium benzoate alone will assist in maintaining titanium dioxide in suspension in paraflin but the perod of suspension attained thereby is very short as compared with the suspension period where the substance of a rubbery consistency is used. The amount of sodium benzoate might be as small as one-tenth of one part up to five parts in a mixture of approximately 100 parts.

The term rubbery substance or substance of a rubbery consistency is used herein to designate either natural rubber, synthetic rubber or substances of a rubbery consistency of the character specified herein.

Any suitable kind of wax may be used. Paraflin wax is commonly used and a preferred paraflin wax is one having a melting range of from 133 to 136 F. A. S. T. M. melting range. The melting range of the paraiiin used might vary from to F. Animal or vegetable waxes might be used though the price and the fact that such waxes tend to develop a rancid odor make them less to be desired than parafiin.

A simplified method of incorporating the rubbery substance in the solution and one which I prefer is to gradually add small fragments of pale crepe rubber sheets to a solution of molten paraffin heated to approximately 20 C. above its melt point while constantly subjecting said solution to violent agitation or stirring. Such agitation and temperature should be continued for the time required to bring the rubbery substance completely into solution, which should be accomplished within twelve hours or less.

What I claim:

1. A paper sheet provided with a flexible opaque moisture resistant heat scalable, surface coating characterized as applied to the sheet as a hot melt coating comprising a molten solution of paraffin wax and frubber carrying suflicient titanium dioxide in suspension to opacify the coating, the relative density of the molten paraflin wax and titanium dioxide being such that the titanium dioxide would not remain in suspension in the molten parafiin alone, the amount of rubber being suflicient to retain the'titanium dioxide in suspension in the molten wax and being within the range of one part of rubber to 3 to 7 parts of titanium dioxide in the solution, the

sum total of titanium dioxide and rubber not ex ceeding 20% of the paramn wax.

2. A coating composition for a sheet of paper or the like comprising one hundred parts of mo]- ten paraflin wax carrying in coiloida-l solution' one to three ports 01 a rubbery substance selected from a group consisting of rubber and the poly-- RANDOLPH SPENCER SOANES.