US3525668A - Method for improving the wet strength and water resistance of paper - Google Patents

Description

United States Patent U.S. Cl. 162--169 2 Claims ABSTRACT OF THE DISCLOSURE Applying an aqueous dispersion of 40 to 90% by weight of bitumen, 6. to 45% by weight hydrocarbon wax, and 1 to 20% by weight of a copolymer of an olefin and an olefinic alcohol ester has been found to impart improved wet strength and water resistance to paper.

This invention relates to compositions useful for improving the water resistance of paper. More particularly, it relates to compositions which, when blended in vari ous paper stocks, significantly decrease the water absorption and produce a great increase in wet strength of the paper without impairing its dry strength.

In various applications of paper and paper board, it is exceedingly important that the materials be resistant to water impregnation. For example, in commerce many items are packaged for shipment and sale in paper or cardboard wrappings, etc. When it is probable that the items will come in contact with moisture, a coating is usually applied to the package to prevent passage of moisture into the package with consequent damage to the article and the container. Thus, frozen food containers are usually coated with wax or plastic compositions for this purpose. However, for many applications where moisture contact is not inevitable, the application of coatings to the exterior of packages, etc. is usually uneconomical due to the substantial cost of coating materials and applicators. However, since occasional moisture contact has serious effects on uncoated paper materials, it is highly desirable to incorporate within the matrix of fibers in the paper, substances which will increase the moisture resistance and wet strength of the paper. Among the materials that have been employed for this purpose have been various bituminous (especially asphaltic) materials and waxes. However, none of these materials have been found entirely satisfactory. Asphaltic materials have been found to produce an insufiicient decrease in water absorption and increase in wet strength. Wax, while significantly decreasing water absorption, produces a substantial decrease in the dry strength of the paper and only a nominal increase in wet strength.

It is therefore desirable to incorporate into the paper fibers a material which will provide dry strength retention while increasing water resistance and wet strength.

It has now been found that paper materials of excellent water resistance and having high dry and wet strengths result from the incorporation in the paper or fiber board of minor amounts of a composition comprising an aqueous dispersion of a bitumen, a hydrocarbon wax and a copolymer of an olefin and an olefinic alcohol ester.

The dispersion which comprises the composition is analogous to anionic or cationic bituminous emulsions. These emulsions are well described in the art and are generally prepared by stirring a bituminous phase and an aqueous phase in the presence of an emulsifying agent. Examples of the emulsions and various methods of their preparation may be found in the literature, e.g., in U.S. Pats. 2,481,374, U.S. 2,601,597, U.S. 3,026,266 and U.S. 3,271,240. The particular type of emulsion is not im- 'ice portant to this invention, as either cationic or anionic emulsions may be employed and their method of preparation is not of consequence. Thus, any number of materials (acid or bases) may be used for emulsifying agents.

However, it may be noted that, in accordance with the prior findings of the art, smallparticle size of the emulsions is preferred in order to eliminate plugging of paper equipment and appearance of spots on the paper; thus, the use of agents which result in small particles of the emulsion is preferred. Examples of suitable emulsifiers include fatty acids such as oleic, palmeic, lauric, stearic, naphthenic, and oxidized hydrocarbons, tall oil acid, rosin acid and mixtures of these materials.

The preferred olefin-olefinic alcohol ester polymers which are employed in the compositions are polymers of olefins of from 2 to 4 and esters of olefinic alcohols of 2 to 4- carbon atoms and monocarboxylic acids of from 1 to 12 carbon atoms. The monocarboxylic acid moiety is preferably derived from an alkanoic acid. Polymers of this type are well known in the art and are usually derived from the reaction of an olefin with an ester derived from an olefinic alcohol and a monocarboxylic acid. Suitable olefins which may be reacted with the ester to produce the polymers include ethylene, propylene, butylene and isobutylene. The olefinic alcohols from which the esters is derived include vinyl alcohol, allyl alcohol, 2 butenol, l-butenol, etc. The monocarboxylic acid from which the ester derived is an acid of from 1 to 12 carbon atoms. Thus. suitable acids include formic, acetic, propionic, butanoic, hexanoic, octanoic, lauric, etc.

As examples of suitable bituminous materials which may be employed in the compositions of this invention may be cited asphalts which are characterized by penetration values in the range from about 0 to about 30 at 77 F. (ASTM D5-52) and by softening points in the range from about 160 to about 260 F. (ASTM D36-26, Ring and Ball Method) may be used- Preferably the asphalts will have a softening point of from about 180 to about 230 F. and a penetration of about 0 to 15.

Suitable bitumens include all kinds of asphalts which are capable of emulsification when heated to from about 300 to about 450 F., irrespective of the manner of their production; thus, steam-refined, solvent-refined ad airblown asphalts may be used.

High melting coal-tar pitches such as those recovered in coal-tar production from horizontal coke ovens, gaswork retorts, blast furnaces, etc. having substantially similar penetration values and softening points and similar viscosities which permit emulsification when heated to 300450 F., also may be employed in the compositions of the invention.

Included among other bituminous materials which may be used are the so-called native asphalts, wurtzilite, Gilsonite and Montan wax; these materials may be emulsified and employed in the compositions in the same manner as the more typical asphalts.

The polymers may be prepared by any suitable method. Ordinarily, free-radical polymerization is utilized with a free-radical producing catalyst, which is oxygen or an organic peroxide. The materials are reacted at high pressures and temperatures from about 150 to 250 C. However, the most suitable methods of producing these polymers comprise reacting an olefin and the ester of an unsaturated alcohol under free-radical conditions at a pressure from about -200 atmospheres, the temperature in the order of -250" C., and distilling to remove unreacted materials. The preferred polymers have molecular weights of from about 100,000 to 1,000,000.

Examples of the materials which may be obtained commercially are the Elvax polymers marketed by Du Pont,

Inc. These polymers are produced by the reaction of ethylene with vinyl acetate. The polymers are available in a number of molecular weight ranges, and a range of from 100,000 to 500,000 is suitable for the purposes of this invention.

The waxes employed in the composition are preferably petroleum waxes or, more preferably, parafiin waxes. Parafiin wax is a solid, crystalline, hydrocarbon mixture wholly derived from that portion of crude petroleum commonly designated paraffin distillates, from shale distillates, or from hydrocarbon synthesis, by low temperatures solidification, an expression, or by solvent extraction. It is distinguished by its solid state at room temperature, relatively slight deformation at this temperature, even under considerable pressure, and low viscosity, from 35- 45 SSU at 210 F. when melted. Although the paraffinic waxes are most desirable, microcrystalline waxes and mixtures of microcrystalline and paraflinic waxes may also be employed in the compositions of the invention. Natural waxes such as beeswax, etc. may also be used.

In order to form the aqueous dispersion used for the treating composition, the wax and the copolymer may be blended together and then emulsified and blended further with the bituminous emulsion before the treating composition is added to the paper-making fibers. Alternatively, the wax and copolymer may be blended with heat into the bituminous mix and emulsified by conventional methods. Emulsifying agents which may be employed include the same cationic and anionic emulsifying agents previously mentioned in conjunction with the bitumens. In order to disperse the materials on the cellulosic fibers, the emulsion or emulsions are dispersed into the wet pulp stock from which the products are made.

The treating compositions are employed in concentrations sufiicient to give from about 0.5% to by weight of solids in the dry paper. The ratio of bitumen to waxcopolymer may vary from about 9:1 to about 1:1. The ratio of wax to copolymer in the wax-copolymer combination may vary from about 9:1 to about 3:2. Thus, in the total composition, the concentration of solids of the respective materials is from about 40 to 90% bitumen, from about 6 to 45% wax and from about 1 to 20% of the copolymer. It is preferred that the bituminous portion comprise from about 75 to 85% of the composition, and the wax from about 60 to 80% of the wax-polymer portion.

minutes. The samples were tested in a Mullen tester to determine dry strength. The sheet of each sample was immersed in water for 10 minutes, and the amount of water absorbed by 36 square inches of surface in 10 minutes in centigrams was measured and recorded as immersion number. The wet sheet was then tested in the Mullen tester to determine its wet strength. The wax employed in the samples was a paraffin wax having a softening point of about 150 F.

The following materials were employed:

1) By ordinary emulsion forming methods, such as that described in US. Pat. No. 2,481,374, previously referred to, an emulsion was prepared from the following materials: 53.5% of a steam-refined asphalt having an ASTM ring and valve softening point of 190 F.; 2% pinewood resin; .65% bentonite clay; .40% NaOH; 43.5% water. The emulsion has a pH of about 10.2.

(2) An experimental, small-particle-size emulsion was prepared employing the same asphaltic bases as in emulsion 1, 1% of the pinewood resin, 1% tall oil, .5% bentonite clay, .4% NaOH. This emulsion contains an ingredient designed to effect small particle size in the finished emulsion. The average particle size above 0.9 micron was 1.1 microns.

(3) An emulsion of a hydrocarbon wax was prepared by blending a paraffin wax having a melting point of 154-156 F. AMP with anionic emulsifiers and water. This emulsion was combined with bituminous emulsions (1) and (2) to form other additives.

(4) 30% by weight of an ethylene-vinyl acetate copolymer having a melt index of 5-7 (ASTM D12-38 modified) was combined with of the same wax as in emulsion (3).

(5) The wax emulsion described in (3) was combined with the asphaltic emulsion of 1).

(6) The wax-copolymer emulsion of (4) was combined with the asphaltic emulsion of (1).

(7) The wax-copolymer emulsion of (4) was combined with the asphaltic emulsion of (2).

In preparing the samples the various emulsions were used to size the hand sheets.

Data from the above-mentioned test are included in Table I. Ratios of the various sizing constituents are given. Additionally, the wet strength to dry strength ratio times 100 is included, this figure being a reliable determinant of the eifectiveness of the waterproofing size.

TABLE I.EFFECT OF TREATING AGENTS UPON PAPER Treating agent, weight percent of Wet total dispersion strength] Drain Dry Wet dry Test Additive ry time, Mullen, Mullen, Immersion strength No. No Bitumen Wax Copolymer sheet seconds p.s.i. p.s.i. No. X100 0 25 117 22 222 18. s 3 0 100 0 1 34 86 26 110 30.2 3 0 100 0 3 32 96 36 112 37.5 3 0 100 0 5 31 74 24 as 32.4 4 0 70 3o 1 32 115 51 106 44. 4 4 0 70 30 3 31 53 101 62.4 4 0 70 30 5 31 9s 70 71 71.5 1 0 0 1 28 116 33 121 28. 4 1 100 0 0 3 33 115 45 112 39.1 1 100 0 0 5 34 120 56 103 46. 6 5 s0 20 0 5 33 54 89 51.4 5 60 40 0 5 32 96 41 89 42.7 5 40 60 0 5 32 82 31 93 37.8 6 s0 14 6 5 32 114 66 79 58.0 6 60 2s 12 5 32 104 60 77 57.6 6 40 42 1s 5 33 86 69 70 80.2 2 100 0 0 1 2s 87 51 127 58.6 2 100 0 0 3 31 84 42 115 50.0 2 100 0 0 5 34 99 43 43.4 7 s0 14 6 5 33 85 88 69 97.8 7 60 2s 12 5 34 78 59 79 75.6 7 40 42 1s 5 34 72 72 78 100.0

In order to demonstrate the advantage of the wax- What 1scla1med1s: polymer modified asphalt treating compositions of this 1. A method of imparting Wet strength to cellulosic 70 materlals from papermakmg fibrous pulp stock which invention, a Kraft pulp was treated with varying quantities of this emulsion, with a bituminous emulsion and with a wax emulsion. The fiber freeness was 650 and the pH of the pulp was about 4.3. Five percent alum retention acid was employed in this sheet, and sheets were thus prepared from the pulp and dried at 300 F. for 20 ethylene and vinyl acetate, said minor portion of said treating composition being sufiicient to give from about 0.5 to 10 percent by weight of solids in the dry paper.

2. The method of claim 1 wherein the composition is dispersed by emulsifying the bitumen, (A), and a mixture of the hydrocarbon Wax, (B), and the copolymer, (C), separately, and incorporating them Within the pulp stock.

References Cited UNITED STATES PATENTS 6 3,158,531 11/1964 Rohrer 162-171 XR 3,291,767 12/ 1966 Zaayenga.

OTHER REFERENCES Casey, Pulp and Paper, Interscience Publishers, Inc., 2nd edition, vo1.II (1960), p. 1154.

S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner U.S. Cl. X.R.