US3726820A - Slip agent composition for spiral-wound paper cans - Google Patents

Abstract

PAPER ARTICLES HAVING A COATING OF VINYLIDENE CHLORIDE COPOLYMER AS A BARRIER TO MOISTURE PENETRATION ARE FURTHER COATED WITH AN AQUEOUS COMPOSITION TO IMPART "SLIP" TO THE COATED PAPER. THE "SLIP" COMPOSITION CONTAINS PARAFFIN WAX, SODIUM ALKYL SULFATE, A BINDER POLYMER SUCH AS STYRENE-MALEIC ANHYDRIDE COPOLYMER AND OXIDIZED POLYETHYLENE.

Description

United States Patent SLIP AGENT COMPOSITION FOR SPIRAL-WOUND PAPER CANS Merrill Bleyle, Waltham, and Charles T. Mitchell, Jr., North Reading, Mass, assignors to W. R. Grace & Co., Cambridge, Mass.

No Drawing. Original application June 30, 1964, Ser. No. 379,384, now Patent No. 3,400,008. Divided and this application Mar. 21, 1968, Ser. No. 734,186

Int. Cl. C08f 45/52 US. Cl. 260-285 R 2 Claims ABSTRACT OF THE DISCLOSURE Paper articles having a coating of vinylidene chloride copolymer as a barrier to moisture penetration are further coated with an aqueous composition to impart slip to the coated paper. The slip composition contains paraflin wax, sodium alkyl sulfate, a binder polymer such as styrene-maleic anhydride copolymer and oxidized polyethylene.

This application is a division of application, Serial No. 379,384 filed June 30, 1964 now US. 3,400,008.

Spiral-wound tubular paper cans have been adapted for packaging a number of materials. The spiral-wound tubes are made on a spiral winder. In brief, this machine consists of a stationary round steel mandrel over one end of which is looped an endless belt, while the other end has a traveling saw. The raw paper stock, i.e., flexible paperboard or paper of the type used in manufacturing paper cans, is slit into narrow rolls which are fed into the winder from either side.

Each web of paper passes over a glue roll and from there around the mandrel and under the endless belt at an angle of 45 to 60. The pressure of the moving belt causes the formed tube to rotate on the mandrel, thus drawing in more material and causing the formed tube to move forward in a helical motion along the mandrel. The continuous spiral tube may be cut to size on the winder or as a separate operation. The cut tubes are then placed in a press and the ends of the tube are flared to receive the can end.

Paper cans are normally provided with a foil lining or a film or coating of a material which bars moisture penetration. Representative of the moisture barriers are coatings formed from vinylidene chloride polymers. These -coatings, and moisture barrier materials in general, suffer from a lack of slip, i.e., the film-to-metal coefiicient of friction is high. This is a serious handicap in the formation of paper cans because it results in jamming of automatic machinery and difliculty in removing the tubes from the mandrel.

In actual operation, for example, the webs of paper are provided with the vinylidene chloride polymer coating. The coated Webs are fed into the belt loop and wrapped around the mandrel. This action produces a great deal of frictional heat and galling, i.e., wearing away by friction, of the coating. The mandrel, if uncooled, will heat up to 200 F. and the coating will adhere to the mandrel causing a shutdown and requiring cleaning and rethreading. The water cooled mandrel offers a slight improvement in that the temperature can be kept below 150 F., but gelling still occurs. The desired winding speed of 300 to 1000 feet per minute requires a slip coat of some type even on foil lined cans.

Various agents of different types have been proposed for use as slip agents, but most of the materials of the prior art have had one or more defects which detract from their usefulness on a practical commercial scale. They may not impart the desired slip; they may be 3,726,820 Patented Apr. 10, 1973 effective only in relatively large amounts so that use thereof increases the manufacturing cost of the cans too greatly; they may fail to give good slip at the higher temperatures to which the tube is subjected when it is exposed to heat developed by friction on the mandrel; or they may not have the hardness necessary to protect the barrier material from galling.

Specifically, one of the methods used to reduce the fraction between a steel mandrel and a vinylidene chloride polymer coated paper web was to apply a lubricant to the coating as the coated web was wound on the mandrel. Various water solutions and oils were applied, but these materials built up on the mandrel and resulted in streaks galling, and oversized can bodies. Another method was to top coat the vinylidene chloride polymer coating with a slippery material such as wax, oil, soap, and curing silicones. Many of the oil additives, floor waxes buffed and unpolished, metal stearate soaps, and silicone oils were found to increase the friction as measured by the angle indicative of the coefficient of friction.

The angle indicative of the coefiicient of friction was measured in the following manner. A steel block Weight was used which was 1.9 inches in height, 2 inches in width, and 4 inches in length, having at each end of the bottom a step 1 inch in length, 2 inches in width, and 0.25 inch in height, which was the surface in contact with the slip coated sheet being tested. The weight of the block was 4 pounds or 1 pound per square inch in the horizontal position. The slip composition was coated on kraft paper or similar type of paper and dried. The coated paper was attached to a smooth wooden board with Scotch tape with the uncoated side of the paper adjacent to the wooden board. The weight was placed on the coated surface of the paper, and the board was slowly tilted until slippage occurred. This angle was recorded as an indication of the static coefiicient of friction.

In measuring the angle indicative of the kinetic coeflicient of friction, the board was raised to a predetermined angle and the weight was then placed on the coated surface of the paper, and the weight was observed to see if slip occurred. The angle of the board was then changed in the proper direction, and the weight again was placed on the coated surface. The angle at which the weight slipped was reported as an indication of the kinetic coeflicient of friction.

It is a principal object of the present invention to provide a composition for use as a slip agent in the preparation of spiral-wound paper cans which overcomes the defects of the slip agents of the prior art. The slip agent composition of the instant invention is capable of forming extremely thin, smooth, and abrasive-resistant films.

The novel composition of the present invention comprises emulsion of paraffin wax, a sodium alkyl sulfate wherein the alkyl group is a C to C alkyl group, and an aqueous solution of a binder polymer.

While the above-described composition provides superior slip characteristics, it has been found that a still greater degree of slip can be provided by incorporating an emulsion of oxidized polyethylene.

The slip composition of the present invention is formulated as a homogeneous mixture to give a total solids content of between about 2 percent and 2.0 percent.

The solids are composed of about 5 to 35 percent by weight of parafiin wax, about 3 to 30 percent by weight of sodium alkyl sulfate, and between about 35.0 to 70 percent by weight of the binder polymer. In a preferred embodiment the composition comprises between 1.0 and 40 percent of oxidized polyethylene.

A composition having a solids content about 22.5 percent of oxidized polyethylene, 18.0 percent of paraflin wax, about 14.5 percent of the sodium alkyl sulfate, and

about 45.0 percent of the binder polymer is particularly effective in providing a film with good slip characteristics.

The sodium alkyl sulfate has the general formula ROSO Na wherein R is the C to C alkyl radical such as capric, lauric, myristic, palmitic and stearic. Preferably, the alkyl group contains to 18 carbon atoms. This component acts as a stabilizer and contributes to the formation of smooth continuous films. In this respect sodium lauryl sulfate is particularly preferred.

The binder polymer may be any polymer which is compatible with the other components of the instant composition and acts to bind them in forming a thin smooth clear film. It must also be capable of forming an aqueous solution. Representative binder polymers include polyvinyl alcohol, casein, carboxymethylcellulose, copolymers of an organic acid and styrene, and natural gums such as karaya gum and gum arabic. An ammonia solution of maleic anhydride-styrene copolymer (Lytron 820, Stymalon 1000A) is particularly effective as a binder in forming smooth'films with improved hardness.

Oxidized polyethylene may be prepared in a number of ways, several of which are disclosed in Great Britain Patent No. 581,279 to Whittaker et a1. One method cornprises heating the molten polymer on mixing rolls which permit good contact of the polymer with air in a temperature range of 140 to 250 C. for several hours. The oxidized polyethylene operable in the instant invention has a softening point of at least 110 C. and a melt index in the range of about 300 to about 5000. These oxidized polyethylenes can be emulsified by conventional methods and are commercially available in emulsion form.

The paraffin wax of the present invention should have a melting point of at least about 48 C. This wax can be emulsified by conventional methods and is commercially available in emulsion form.

The components of the instant composition may be mixed at room temperature and atmospheric pressure. To form a particularly smooth uniform blend of the components, an aqueous solution of the binder polymer is first formed. If the composition is to contain polyethylene emulsion, it is then mixed with the binder polymer solution until a uniform dispersion is produced. In a separate step, the emulsion of wax is thoroughly mixed with the sodium alkyl sulfate. The resulting wax-sodium alkyl sulfate mixture is mixed with the dispersion until a smooth homogeneous blend of the composition is produced. -Water is then added to the composition to form the final composition with the desired solids content.

The viscosity of the resulting slip composition is dependent upon the solids content and may be varied over a relatively Wide range. The particular viscosity used is determined to some extent by the method of application, but in general the lowest possible viscosity is preferred.

The method or means of depositing a coating of the slip agent on the substrate is not critical. Any type of coating mechanism or device which is capable of depositing a uniform amount in the desired thickness to the substrate may be employed. Special types which may be used in clude air knife coater, horizontal and vertical size presses, trailing blade, transfer roll, reverse roll, roller coater, gravure, bead coat, metering bar, spray coater and curtain coater. Deposition may be carried out in one or a number of applications, and the amount deposited is such as to provide a dry weight coating ranging between about 0.1 to 1.0 pound per 3000 square feet of paper. Dry weight coatings greater than 1.0 pound per 3000 square feet of paper do not provide improved slip characteristics to. any greater degree and any amounts in excess of that amount are merely wasteful. Dry weight coatings ranging from 0.2 to 0.5 pound per 3000 square feet of paper are particularly satisfactory.

The slip-coated substrate is then dried either in air or a suitable drying apparatus. Air-drying can be accomplished in less than 10 minutes while oven-drying can be effected within 10 to 30 seconds at an oven temperature of 120 to 130 C. The dried slip coating is odorless, clear and very glossy, and exhibits no separation between it and the substrate. The degree of adhesion is measured by the pressure-sensitive tape test in which a strip of tape is applied with the fingers to the dried slip coating and then rapidly pulled off. When subjected to this test, the slip coatings of this invention remain intact, indicating excellent adhesive properties.

Although film formation of the slip composition will take place by drying for about 8 minutes at room temperature, true coalescence requires somewhat higher temperatures. Excellent films are obtained by fusing the dried coatings for about 10 to 20 seconds at an oven temperature of 125 C.

Proportions used here and elsewhere herein refer to parts by weight. In the following examples the coefiicient of friction was determined according to ASTM D1894- 6lT. Procedure B, except that a Weight of 4.4 pounds was used.

EXAMPLE 1 A vinylidene chloride copolymer emulsion (Daran 210) was coated on one side of a large piece of flexible paperboard of the type used in forming spiral-wound paper containers. The paperboard was about 17 mils thick. Typical properties of the emulsion included the following:

Total solids About 60% Color Cream white.

Freezing point 36 F.

Particle size .13 avg. (micron) Specific gravity 1320:0015.

The polymer emulsion (Daran 210) was applied to the paperboard with a roller and then levelled with a N0. 6 Mayer rod. The coated paperboard was initially dried by passing it under infrared lights and then through an oven maintained at 250 F. The dried coated paperboard was then passed again under the infrared lights to fuse the dried vinylidene chloride polymer coating. The web speed was 350 feet per minute. The weight of the dried coating was approximately 8 pounds per ream (3000 sq. ft.).

A second coating of the vinylidene chloride polymer emulsion (Daran 210) was applied to the dried coating in the same manner except that a No. 4 Mayer rod was used and that drying temperatures of the first and second zones of the oven were maintained at 300 F. The weight of the dried coating was approximately 2.8 pounds per ream (3000 sq. ft.) A third coating of the vinylidene chloride polymer emulsion was applied in the same manner as the second coating, and the coating weight was approximately 3.6 pounds per ream (3000 sq. ft.). The total weight of the coating was approximately 14.4 pounds per ream (3000 sq. ft), and the total thickness of the paperboard and the coating was about 18 mils. The vinylidene chloride polymer coating was colorless, clear, smooth, continuous and glossy.

A slip composition wasformed comprising the followmg:

The styrene-maleic anhydride copolymer (Lytron 820) was a free flowing powder which had the following properties:

Specific gravity 1.14 to 1.16.

Particle size 100% through U.S. No. 40 sieve, 2% max. retained on U.S. No. 60 sieve, 25% max. retained on U.S. No. 80 sieve.

Softening temperature No softening below decomposition temperature.

Decomposition 210 C.

Temperature Chars on long exposure to 200 C. to 250 C.

Free styrene 1.0 max.

Acidity (acid No.) 180 to 190.

Equivalent weight 295 to 310.

The emulsion of oxidized polyethylene (Grex 39-1) had the following characteristics:

Solids percent 23 Viscosity, cps. 73 deg. F. (22% solids) 5-10 pH 8.5-9.5 Particle size, microns 0.05

Typical properties of the solid oxidized polyethylene Density, gms./ml., 73 deg. F 0.98-0.99 Penetration hardness, tenths of mm. (TA'PPI T639 sm-60) 0.5 Acid number 26-28 Viscosity, cps., 165 deg. C. 40,000 Melt index (ASTM D1238-62T) 400-600 Ring and ball softening point, deg. C. 140-145 The emulsion of the paraflin wax (Alwax 253A) had the following characteristics:

Acid and Type emulsionalkali stable Solids content, percent by Weight 40.

Specific gravity, lbs./ gallon 8.

Dilutability Infinite.

Wax present, percent on solids 100.

Average particle size, microns 0.5 to 1.5.

Melting point 123 F.

The solution of sodium lauryl sulfate (Duponol) had the following characteristics:

Chemical type Anionic.

Composition Sodium lauryl sulfate technical.

Molecular weight 302.

Physical appearance Pale yellow liquid.

Active ingredient, percent 30.0.

Unsulfated alcohol, percent 1.0.

Sodium chloride, percent 0.3.

Sodium sulfate, percent 0.7.

Viscosity, cps. at 80 F 200.

A solution of the ammonium hydroxide and styrenemaleic anhydride copolymer (Lytron 820) was formed. The emulsion of oxidized polyethylene (Grex 39-1) was then mixed with the solution until a uniform dispersion was formed. In a separate step the emulsion of paraflin wax was thoroughly mixed with the solution of sodium lauryl sulfate. The resulting mixture was then mixed with the dispersion until a uniform blend was produced to form a final composition having 8.9 percent solids and a viscosity of 2 cps. (LVF Brookfield Viscosimeter, No. 2 spindle at 60 rpm).

The slip composition was applied to the coated paperboard with a roller and then levelled with a No. 4 Mayer rod. The slip coated paperboard was initially dried by passing it under infrared lights and then through a first and second zone of an oven maintained at 300 F. The

dried coated paperboard was then passed again under the infrared lights to fuse the dried slip coating. The web speed was 350 feet per minute. The weight of the dried slip coating was approximately 0.2 pound per ream (3000 sq. ft.). The slip coating was clear, colorless, and very glossy.

The slip coated paperboard was then cut to strips about 6 /2 inches wide.

EXAMPLE 2 Spiral wound tubes of the coated paperboard strips prepared in Example 1 were formed in the conventional manner. The machine used consisted of a stationary round steel mandrel with an endless drive belt looped over one end of it. The drive belt was approximately 6 inches wide and was driven by two vertically mounted drums. The distance between the drums could be varied to adjust the tension on the belt.

Certain sections of the coated paperboard strips were passed over a glue roll and then fed into the belt loop and wound around the mandrel. The winding speed was at least 40 feet per minute. Due to the lack of friction between the slip coating and the mandrel, spiral tubes were formed quickly, and no difiiculty was experienced in removing the tubes from the mandrel. The limiting factor in the preparation of spiral-wound cans was not the slip coat or the frictional forces of the paperboard on the mandrel but other steps involved in the can manufacture. Therefore, 40 feet per minute is by no means the maximum speed at which the slip coat can be utilized.

A strip of the coated paperboard prepared in Example 1 was used to measure the degree of adhesion of the slip coating to the vinylidene chloride polymer coating.

Scotch tape was applied with the fingers to the slip coating and then rapidly pulled off. The slip coating remained intact.

The viscosity of the composition prepared in Example 1 was measured on an LVF Brookfield Viscosimeter. In addition, the viscosity of the same composition at various solids concentrations was measured. The results are shown below:

The slip characteristics of the slip composition prepared in Example 1 at varying dry weights and drying procedures were measured in the following manner:

A flexible standard bleached kraft paperboard with a standard clay coating (Moss-Cote Board) was used. This paperboard was about 15 mils thick. The vinylidene chloride polymer emulsion of Example 1 (Daran 210) was applied to the paperboard with a No. 8 Mayer rod. The coated paperboard was dried for 20 seconds in a forced-draft oven maintained at C. Several samples were prepared. One of these was used as a control. The slip composition was applied to the remaining samples with a Mayer rod. The slip coated samples were dried for 20 seconds in a forced-draft oven maintained at 125 C. Their slip characteristics are illustrated in the table below:

1 2 3 4 Control D 1 (3 i (I) rymg proce ure Slip Characteristics:

Angle indicative of coeificient of Friction:

Static deg 12 8 10 12 30+ Kinetic, deg 8 7 7 7 22% Coeificient of Friction (ASTM D1894-61T Procedure B):

Static 12 12 12 11 57 Kinetic..- 12 10 12 11 36 Dry coating wt. approx), lbs/ream (3,000 sq. ft.) 2 .3 4 3 l N o slip coat. 1 125 C. 20 sec. 3 Air dry 8 min.

8 As noted in the foregoing table, the instant composition Emulsion is capable of providing a very thin slip coating with slip Characteristics significantly better than that of the control, p rcent T 40. i.e., the vinylidene chloride polymer coated sample with- VISCOSItY P Brookfield, Splndle out a slip coating. In addition, as illustrated by Samples N9. 1, r-PJIu L ss than 0. 2 and 4, the slip coating formed by drying at an elevated Particle S126, microns Less than 0.1. temperature is somewhat better than that formed by air P range of 61161111031 stablllty 1 t0 drying.

EXAMPLE 3 Typical propertles of the solid polymer A slip coating composition Was prepared according to 10 D i gnL/cc 0920 to 0.935 the procedure of Example 1 containing the following con- Inherent viscosity, 1 12% Stltuentsi polymer in Tetra'lin at 135 C.) 0.5 to 0.9.

Average molecular weight 15,000 to 30,000. Parts by Weight Hardness, Shore D 45 to 48.

Dry w 15 Melting point (modified ring and O stgzrarge-maleic anhydride copolymcr (Lytron 4 ban method) Greater than 200 F .0 4.0 28% ammonium hydroxide.--. 1.2 Samples of vinylidene chloride polymer coated paper- 8.7 board were prepared as described above. One of the Emulsion of p fifi a 3 0% 20 samples was used as a control and contained no coating.

solids 1.0 4.0 soiution f Sodium lauryl lf t (pi i yj The remainder of the coated samples were each progg; Solids vided with the slip compositions of Examples 1 and 3 in three ditferent weights as illustrated in the table below:

SLIP CHARACTERISTICS Angle indicative of coefficient. Coeflicient of friction (ASIM M friction D189461T, Procedure B) a 61' Composition ibd Static, deg. Kinetic, deg. Static Kinetic Appearance 0 13.0 7.6 .14 .14 Example 1 (oxidized polyethylene) 4 8.0 7.5 .16 .16 }Very glossy surface.

s 8.0 .6.0 .13 .11 0 17.0 10.0 .15 .15 Example 3 (nonoxidized polyethylene) 4 15.0 10.0 14 14 }Du1l surface.

s 12.5 10.0 .14 .14 0 11.0 10.0 Example 4 (no polyethylene) g --}Du1l surface. Control 21: 0 "f5? ".36-

EXAMPLE 4 A slip coating composition was prepared according to the procedure of Example 1 containing the following constituents:

The emulsion of non-oxidized polyethylene (Poly EM 40") had the following characteristics shown in column 8.

As noted in the table above, the oxidized polyethylene provided the slip composition with slip characteristics significantly better than those provided by the other slip compositions.

In the following examples, various slip compositions containing oxidized polyethylene emulsion were prepared and the slip characteristics of each composition were measured. Samples of vinylidene chloride polymer-coated paperboard were prepared. The samples were then provided with a coating of a slip composition. The dry weight of each slip composition coating was about 0 .2 pound per ream (2000 sq. ft.).

The superior and preferred characteristics of the compositions which contain oxidized polyethylene emulsion are emphasized when compared with Example 5, which contains no polyethylene.

Example 5 Example 6 Example 7 Example 8 Percent by Parts by Percent by Parts by Percent by Parts by Percent by Parts by wet wt. solids Slip composition:

Styre ne-maleic anhydride copolymer ("Lytron wt. wet

wt.sol1ds wt.wet wt. solids wt.wet wt. solids wt.

45.0 4.0 39.2 4.0 38.1 4.0 28% ammonium hydr 1. 2 1. 2 1, 2 Water 78. 1 78. 1 78. 1 Emulsion of oxidized polyethylene (23% solids) (Grex 39-1) 22. 5 8. 7 19. 6 8. 7 19. 0 8, 7 Emulsion of parafin wax (40% solids) (Alwax 253A) 18.0 4. 0 15. 7 4. 0 30. 5 4. 0 Solution of sodium lauryl sulfate (32% solids) (D uponol) 15. 0 4. 0 25. 5 8. 0 12. 4 1, 0 Angle indicative of coetficient oi friction:

Static, deg- 11 12 12 Kinetic, deg 7 7 71 -8 Coltaefiici nt of friction (ASTM D1894-61T, Procedure Static 13 12 13 Kinetic .11 .12 11 Example 9 Example Example 11 Example 12 Percent by Parts by Percent by Parts by Percent by Parts by Percent by Partsby wt. solids wt.wet Wt. solids wt.wet wt. solids wt.wet wt. solids wt.wet

Slip composition:

Styrene-maleic anhydride copolymer (Lytron 82 52 0 4.0 37.7 4 0 58 0 4.0 28% ammonium hydroxide.-. 1.2 1. 2 1. 2 Water 78.1 78.1 78.1 Emulsion of oxidized polyethylene (23% solids) (Grex 39-1) 26.0 8. 7 35.0 16.0 0.0 4. 0 Emulsion of pai'aflin wax (40% solids) (Alwax 253A) 5. 2 l. 0 15. l 4. O 23. 2 4. 0 Solution of sodium lauryl sulfate (32% solids) (Duponol") 16. 8 4. 0 12. 2 4. 0 18. 8 4. 0 Angle indicative of ooefiiclent of friction:

Static, deg 16 13 18 18 Kinetic, deg 9 6 11 8 C(gfiieient of friction (ASTM D1894-61T, Procedure s'mfl .15 .19 .15 Kinetic .12 12 11 References Cited UNITED STATES PATENTS 2,964,487 12/1960 Chapman 26028.5 1S clalmed 3,234,158 2/1966 Pfluger 26028.5 A An aqueous composition for use as a slip agent hav- 3,328,325 6/1967 Zdanowski A ing a total solids content of between about 2 and 20 percent by weight, said solids being composed of about MQRRIS BM primary Examiner 22.5 percent emulsified oxidized polyethylene, 18.0 percent of emulsified paraffin wax, about 14.5 percent of MICHL Asslstant Exammer sodium lauryl sulfate, and about 45 percent of styrene- U 3 C1 X R maleic anhydride copolymer.

2. A film formed from the composition of claim 1. 106-145, 191, 197 C, 207; 11776