US2388326A - Moistureproof sheet - Google Patents

Description

Patented Nov. 6, 1945 MOISTUREPBOOF SHEET William L. Hyden and James A. Mitchell, Kenmore, N. Y., asslgnors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 27, 1943, Serial No. 473,700

8 Claims.

This invention relates to the production of coated structures. More particularly, it relates to moistureproofing coating compositions containing a new type of slip-promoting agent and the use of such coating compositions in the production of thin, non-fibrous, optionally transparent sheets and films suitable for moistureproof wrapping tissue having a coating which is substantially non-tacky through a wide range of temperature conditions.

Thin transparent sheets and films of nonflbrous cellulosic materials containing moistureproof coatings are well known as wrapping tissue. In general, the coatings of such sheets and films comprise a film-forming constituent such as a cellulose derivative or a resin, a moistureproofing agent such as a wax, a blending agent such as a resin, and a plasticizer. Such moistureproofing coating compositions and methods for compoundin and applying the same are disclosed in detail in U. 8. Patent No. 1,737,187 to Charch and Prindle, and French Patent No. 718,440 to Charch.

Difficulty has long been experienced in the hantiling and storing or such sheets and films because of their lack of slipperiness and adherence of contiguous sheets to each other. These difliculties are caused by at least two factors. One factor is that some of the constituents of the moistureprooflng composition may be inherently tacky; this is especially so in the case of heat-sealing moistureprooflng compositions. A second factor is that the surfaces of these sheets are so smooth that, when they lie in close juxtaposition, they have a tendency to exclude air from between them, thus causing a vacuum action which renders it very diflicult to separate the sheets and at the same time to increase the area of contact, thus increasing the coefliclent i friction. This smoothness is not overcome and, in fact, is accentuated by the ordinary constituents of the moistureproofing composition, particularly the moistureprooflns agent, since it apparently forms a smooth continuous phase in order to prevent the passage of moisture.

Furthermore, it has been observed that these handling difficulties are greatly augmented by a slight rise in temperature. A sheet, and especially a sheet coated with a moistureproot heat-sealable composition, which proves perfectly satis- Iactory as to suri'ace conditions at ordinary room temperatures may become very tacky and unmanageable when stored in heated places or when subjected to abnormally high room temperatures. Similar conditions have been found to arise in the use or automatic wrapping machinery. As long as such wrapping tissue is manually applied to packages, a slight degree 01' stickiness and frictional resistance, while an inconvenience, is of no considerable consequence. It becomes of extreme importance, however, when such adherence and frictional resistance are increased by the transmission of heat or the heat developed by friction in an automatic machine. It is found actually that even a difference oi 1 or 2 may cause a sticking of the material to some part or other of the machine and completely foul its operation. Furthermore, due to the high speeds developed in such automatic machinery, normal adherence and frictional resistance, even of the same degree as can be tolerated in manual operation, are objectionable even in the absence of a temperature rise. l

An attempt has been made to overcome the adhesive tendency inherent in these films by the use of a thin layer or talcum powder. This method has the disadvantage, however, that while it lessens the adhesion of the sheets, it stains the film.

It has also been proposed to incorporate in the moistureprooflng coating compositions which are to be applied to the fllm small amounts oi finely divided, organic solvent-insoluble, high-melting, polymeric organic materials, such as insoluble polyvinyl halide polymers, insoluble urea-formaldehyde resins, polyvinyl alcohol, alkyd resins produced by condensing to an insoluble stage polyhydric alcohols such as ethylene glycol, polyglycols, HO(CH1CH2O)H, propane-1,2-diol, trimethyl'ene glycol, glycerols, polyglycerols,

HO (CHrCHOI-ICI-IrO) "H pentaerythritol, hexitols (e. g., mannltol), hexahydrocyclohexane, trimethylolethylmethane, 2- amino-2-methyl-1,3 propanedicl with polybasic acids such as oxalic, HOCC(NH:)nCOOH, malic, tartaric, maleic, iumaric, citric, aconitic, tricarballylic, diglycolic, dilactic, benzophenone-2,4' dicarboxylic. phthalic, diphenic, naphthalic, camphoric, tetrahydrophthalic, 3-6-endomethylenen -tetra-hydrophthalic acid; insoluble phenol-ab dehyde resins produced. for example, by condensing to an insoluble stage phenol and formaldehyde, and insoluble polyamides and polyesters. Since these solid materials are in finely divided form and since the coating bath is of relatively high viscosity, it is possible to disperse these solid particles in the bath and apply evenly to the surface of the film. The presence of such solid matter produces numerous points of separation between contiguous sheets in stacked relation -r between the surface of the sheet and other smooth surfaces, and thus insures generally good surface slip. However, most 01' the organic solvent-insoluble, high-melting, polymeric organic materials suffer from one or more defects which detract from their usefulness as slip agents. For example, many of these materials adversely affect the transparency of the film. Some, while satisfactory at ordinary temperatures, do not give good slip at higher temperatures, 1. e. above 100' F. Others are difllcult to prepare in the requisite uniform physical condition and still others cannot be easily reduced to proper particle size.

It is, therefore, an object of this invention to provide means for overcoming the tackiness of non-fibrous sheets and films, which means is free of the objectionable features pointed out above.

Another object of this invention is to provide a moistureproofing, heat-scalable coating composition for non-fibrous sheets and films, which composition contains stably dispersed therein an organic solvent-insoluble, high-melting, solid organic material which effectively reduces the tackiness of the dry coating.

A still further object is to produce a wrapping tissue comprising a non-fibrous, clear, transparent base sheet or film coated with a moistureproof, heat-scalable, non-tacky coating, which coating remains non-tacky even at substantially elevated temperatures and does not adversely affect the clarity of the base sheet or film.

These and other objects will more clearly appear hereinafter.

We have discovered that finely divided organic solvent-insoluble 1,2-dihydronaphthalene polymer can be readily dispersed in the usual moistureproofing heat-sealable coating compositions for Cellophane and like wrapping tissue, to form a stable dispersion which, when dried, is free of tackiness throughout the range of temperatures normally encountered in handling and processing such wrapping tissue, and which at the same time does not adversely affect the clarity of the tissue.

The above objects, therefore, are accomplished by our invention which comprises dispersing in the usual moistureprooiing coating composition comprising generally a film-former such as cellulose nitrate, polyvinyl butyral, chlorinated rubber, etc.; a plasticizer such as dibutyl phthalate, a moistureproofing agent such as paraiiln wax; a blending agent such as gum damar, ester gum, etc.; a volatile solvent mixture for these constituents; and, if desired, an agent to render the coating heat-scalable; a small amount of finely divided 1,2-dihydronaphthalene polymer. The resulting coating composition is applied in the usual way to a base film, e. g. regenerated cellulose, and the solvent is thereafter removed to form a clear, non-tacky coating.

The preparation of 1,2-dihydronaphthalene polymer which shows no signs of melting or decomposing under 200 C. and which is useful for the purposes of our invention, is described by Scott and Walker in an article in Industrial and Engineering Chemistry, 32, page 312 (1940), and in Scott, U. S. Patent No. 2,181,770.

The particle size of the 1,2-dihydronaphthalcne polymer must be within the range of from about 0.1 to about 3.0 microns in its greatest linear di-- mension, and preferably the particle size should be within the range of from 0.25 to 1.5 microns.

The amount of 1,2-dihydronaphthalene polymer to be incorporated in the coating composition will vary somewhat with the particular composition. However, it should be within the range assaszo of 0.05 to 10.0% by weight of the solids content of the composition and preferably should be from 0.08 to 1.0% by weight of the solids present in the composition.

As will be apparent from the description hereinafter, the coating compositions containing 1,2- dihydronaphthalene polymer can be used in the production of moistureproof sheets from thin, non-fibrous, transparent base sheets and films normally used for wrapping tissue. These materials may include sheets or films of regenerated cellulose whether they be made by the viscose process, the cuprammonium process, or by any other manufacturing technique; cellulose ethers, such as ethyl, benzyl or glycol cellulose; cellulose esters, such as cellulose nitrate or cellulose acetate; lowly etherifled or esterified materials, such as lowly etherified ethyl cellulose, lowly etherified benzyl cellulose or lowly etherifled glycol cellulose and lowly esterified cellulose nitrate or lowly esterified cellulose acetate; gelatin, casein or the like. The materials may also include film-forming compounds, such as rubber hydrochloride (Pliofllm) cyclized rubber (Pliolite) vinyl resins, such as polyvinyl acetate, polyvinyl acetals and also polyvinyl alcohol.

The moistureprooflng and preferably heatsealing coating compositions modified according to our invention are applied to the base film by any of the conventional methods known to the art, 1. e. by dipping, spraying, roller-coating, brushing, or the like.

The solvent may be removed and the coating material subjected to an elevated temperature at least equal to the melting point of the wax whereby a clear, transparent, molstureproof film may be obtained. The technique of this procedure is set forth in Charch and Prlndle, U. S. Patent No. 1,737,187.

The following examples illustrate specific embodiments of our invention. Quantities are given in parts by weight unless otherwise indicated.

Example I The following composition was coated on 300 gauge regenerated cellulose film containing 15% glycerol:

The moistureproof film produced in the above manner possessed a surface of good slip and storage characteristics without materially affecting transparency.

Example [I The following composition was coated on 300 gauge regenerated cellulose film:

Parts 1,2-dihydronaphthalene polymer 0.4 Chlorinated rubber (6668% chlorine) 63.7 Paraflin wax, melting point 60 C. 8.0 Chlorinated paraflln wax (42% chlorine) 28.0 Calcium salt of hydrogenated rosin 0.3

Toluene 550.0

Results similar to those described in Example I were obtained.

assasoc Example If] The following composition was coated on cellulose acetate film:

Parts 1,2-dihydronaphthalene polymer 0.08 Pliolite (deformation point 30 C.) 10.00 Paraflin wax, melting point 60 C. 1.00 Xylene 90.00

Results similar to those in Example I were obtained.

Example IV The following composition was coated on polyvinyl alcohol film:

To give a solution of 12% effective solids.

Results similar to those in Example I were obtained.

Example V The following composition was cast as a selfsustaining film:

Parts 1,2-dihydronaphthalene polymer 0.1 Cellulose acetate 17.0 Dimethyl cellosolve phthalate 3.0 Acetone 80.0

The film was transparent and possessed good surface slip and storage characteristics.

Example VI The following composition was coated on cellulose acetate film: Parts 1,2-dihydronaphthalene polymer 0.4 Butyl methacrylate polymer 94.0 Paraflin wax, melting point 60 C 6.0 Toluene 730.0

Results similar to those in Example I were obtained.

Example VII The following composition was coated on regenerated cellulose film: Parts 1,2-dihydronaphthalen polymer 0.3 Polyvinyl butyral (10% hydroxyl) 95.0 Paraffin wax 5.0 Toluene 900.0

Results similar to those in Example I were obtained. 7

Example VIII The following composition was coated on regenerated cellulose film: Parts 1,2-dihydronaphthalene polymer 0.4 Ethyl cellulose (medium viscosity) 60.0 10 Ester gum Dibutyl phthalate 10.0 Paraffln wax 5.0 Toluene 580.0

Ethyl alcohol Results similar to those in Example I were obtained.

While this invention has been described chiefly in terms of a coating composition applied to a. base film of regenerated cellulose or other material. it will be understood that it is equally applicable to the preparation of self-sustaining films which are formed by extrusion or casting or other means from a solution in which the 1,2-dihydronaphthalene polymer is suspended.

The surface conditioning agent of the present invention, when incorporated in coating compositions for use with wrapping tissue, has been found to give a product which is eminently suited for use upon automatic wrapping machinery. For such use it is necessary that the tightly wound rolls of material supplied for use upon such machines unwind and deliver the film very smoothly and evenly through the machine. Even though rolls of such material have been tightly wound and stored at somewhat elevated temperatures, it is found that there will be substantially no sticking between the surfaces of the film, allowing it to unroll with great ease and freedom from tears. marred surfaces and other blemishes. It is furthermore essential that such material will pass evenly and smoothly through the whole course of the wrapping machine without adherence to various ortions of said machine. Very often. certain heated elements form a part of such machine, said elements generally being used for the formation of heat seal at a certain sta e of the wrapping operation. Should the adjacent parts of the machine become warm by conduction or convection of said heating elements, serious trouble may result in the operation of the machine by sticking of the wrapping tissue to these surfaces. The present invention produces a wrapping tissue which is far less likely to adhere to such surfaces than wrapping tissues previously available.

Where the coated material is in the form of sheets, said sheets may be stacked and stored for long periods of time without any appearance of adhesion between the sheets so stacked. Such sheets may be readily separated and handled manually or by machinery.

The method and specific agent of this invention produce an improved surface without adversely affecting clarity to the extent encountered in the use of the previously known insoluble slip-promoting agents. 1,2-dihydronaphthalene polymer is also more easily dispersed and remains dispersed longer than the materials heretofore employed to promote slip.

Since many changes and modifications can obviously be made from the details of the above description without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited except as set forth in the following claims.

We claim:

1. An article of manufacture comprising an organic, non-fibrous. transparent base sheet material coated with a moistureprooiing composition having incorporated therein finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.1 to about 3.0 microns.

2. An article of manufacture comprising an organic, non-fibrous, transparent base sheet material coated with a moistureprooflng composition having incorporated therein finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

3. An article or manufacture comprising an organic, non-fibrous, transparent base sheet material coated with a moistureproofing composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight or the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.1 to about 3.0 microns.

4. An article of manufacture comprising an organic, non-fibrous, transparent base sheet material coated with a moistureproofing composition having incorporated therein from about 0.08% to about 1.0% by weight, based on the weight or the composition, of finely divided 1,2- dihydronaphthaiene polymer of a particle ize having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

5. An article of manufacture comprising a non-- fibrous, transparent celiulosic base sheet coated with a moistureproofing composition having in corpora-ted therein from about 0.05% to about 10% by weight, based on the weight of the composition, oi finely divided 1,2-dihydronaphtha1ene polymer of a particle size having a maximum linear dimension within the range of from about 0.1 to about 3.0 microns.

8. An article of manufacture comprising a nonflbrous, transparent ceilulosic base sheet coated with a moistureprooflng composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight of the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

7. An article of manufactur comprising a nonfibrous, transparent regenerated cellulose base sheet coated with a moistureproofing composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight oi the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

8. An article of manufacture comprising a nonfibrous, transparent regenerated cellulose base sheet coated with a moistureproofing heat-sealing composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight of the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

WILLIAM L, HYDEN. JAMES A. MITCHELL.

CERMFICATE OF CORRECTION Patent No. 2,588,526.

November 6, 1945.

WILLIAM L. HYDEN, ET AL.

It is hereby certified that errorappesrs in the pr of the above numbered patent requiring correction as follows:

line no, for that portion of the formula reading "HOCC read ond column,

inted specification Page 1, sec- -HO0C--- and that the said Letters Patent should be read with this correction therein that the same may conform to the record Patent Office of the case in the Signed and sealed this 22nd day of January, A. D. 19116.

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

ing a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

3. An article or manufacture comprising an organic, non-fibrous, transparent base sheet material coated with a moistureproofing composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight or the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.1 to about 3.0 microns.

4. An article of manufacture comprising an organic, non-fibrous, transparent base sheet material coated with a moistureproofing composition having incorporated therein from about 0.08% to about 1.0% by weight, based on the weight or the composition, of finely divided 1,2- dihydronaphthaiene polymer of a particle ize having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

5. An article of manufacture comprising a non-- fibrous, transparent celiulosic base sheet coated with a moistureproofing composition having in corpora-ted therein from about 0.05% to about 10% by weight, based on the weight of the composition, oi finely divided 1,2-dihydronaphtha1ene polymer of a particle size having a maximum linear dimension within the range of from about 0.1 to about 3.0 microns.

8. An article of manufacture comprising a nonflbrous, transparent ceilulosic base sheet coated with a moistureprooflng composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight of the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

7. An article of manufactur comprising a nonfibrous, transparent regenerated cellulose base sheet coated with a moistureproofing composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight oi the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

8. An article of manufacture comprising a nonfibrous, transparent regenerated cellulose base sheet coated with a moistureproofing heat-sealing composition having incorporated therein from about 0.05% to about 10% by weight, based on the weight of the composition, of finely divided 1,2-dihydronaphthalene polymer of a particle size having a maximum linear dimension within the range of from about 0.25 to about 1.5 microns.

WILLIAM L, HYDEN. JAMES A. MITCHELL.

CERMFICATE OF CORRECTION Patent No. 2,588,526.

November 6, 1945.

WILLIAM L. HYDEN, ET AL.

It is hereby certified that errorappesrs in the pr of the above numbered patent requiring correction as follows:

line no, for that portion of the formula reading "HOCC read ond column,

inted specification Page 1, sec- -HO0C--- and that the said Letters Patent should be read with this correction therein that the same may conform to the record Patent Office of the case in the Signed and sealed this 22nd day of January, A. D. 19116.

(Seal) Leslie Frazer First Assistant Commissioner of Patents.