CA1287452C

CA1287452C - Ethylene vinyl acetate compositions for paper saturation

Info

Publication number: CA1287452C
Application number: CA 519892
Authority: CA
Inventors: James L. Walker; Marie E. Yannich
Original assignee: Ablestik Laboratories
Current assignee: Ablestik Laboratories
Priority date: 1985-10-07
Filing date: 1986-10-06
Publication date: 1991-08-13
Anticipated expiration: 2008-08-13
Also published as: DK476486A; FI864027A0; ATE38864T1; FI864027A; DK167229B1; EP0218954B1; US4659595A; EP0218954A1; NO863927D0; NO171737B; NO863927L; AU6352386A; DK476486D0; DE3661276D1; JPS6297997A; NO171737C; AU562733B2

Abstract

ABSTRACT

Saturated paper products characterized by an excellent balance of toughness, strength, fold, tear and delamination resistance comprising a sheet of loosely bonded cellulose fibers saturated with an aqueous emulsion prepared by the emulsion polymerization of:
a) a vinyl ester of an alkanoic acid interpolymerized with:
b) 5 to 30% by weight of ethylene;
c) 0.5 to 6% by weight of an N-methylol containing copolymerizable monomer;
d) 1 to 5% by weight of an olefinically unsaturated carboxylic acid;
e) 0.2 to 3% by weight of a latex stabilizer; and f) 0 to 1% by weight of at least one polyunsaturated copolymerizable monomer.

Description

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ETHYLENE VINYL ACETATE COMPOSITIONS FOR PAPER SATURATION

The present invention is directed to a process for saturating paper, particularly paper which is to be used for the manufacture of masking tape and label stock where superior wet strength, edge tear and delamination resistance are required.
Nonwoven fabrics (nnonwovensn) usu~lly contain substantial amounts of long synthetic fibers which are bonded using chemical, mechanical or ther-mal techniques and which generally contain little or no hydrogen bonding.
In contrast, paper is generally comprised substantially of shorter cellu-lose fibers which are hydrogen bonded using conventional paper manufac-turing techniques.
In practice coatings are then applied as post-treatments to the already formed paper sheets or nonwovens for a variety of purposes, i.e., to strengthen them or apply a functional coating so as to make them water-proof or greaseproof, or adhesive, or to size them, to make them glossy.Many of these treatm~nts are mutually exclusive and each has its own particular problems. Thus, a pigmented coating composition which, for example, is used to provide a glossy coating such as found on paper used for magazines has ccmpletely different requirements than does a saturant type binder which is used to impregnate or saturate the paper web thereby giving the paper integrity.

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More particularly, a sa~urant is used to irnpart a combination of tensile strength and stretch to the paper sheet, a property often referred to as "toughnessn. Other desirable properties which a saturant provides to the paper sheet include wet strength, folding endurance, flexibility, internal tear, edge tear, delamination resistanoe ana resistance to physical degradation and discoloration due to heat and light aging. ~hile - the addition of certain comonomers, including N methylol containing monomers, has been suggested in order to improve ~he strength properties of the saturants, the use of these crosslinking agents has been found to detract from other properties such as edge tear and fold endurance. These saturants of the prior art, therefore, ail to provide the required balance of properties for use in stringent applications such as in the case of papers which are to be used as base stock Ln the manufacture of masking tape, book cover stock, and label stock. ~s a consequence, styrene butadiene rubber based latices are generally used for these industrial applications although these latices are deficient in the areas of color, light and ultraviolet stability.
We have now found that paper rnay be prepared by:
I. saturating a web containing cellulose fibers with an aqueous 2~ emulsion prepared by the emulsion polymerization of:
a) a vinyl ester of an alkanoic acid having 1 to 13 carbon atoms interpolymerized with the following comonomers:
b) S to 30% by weight of ethylene;
c) 0.5 to 5% by weight of an N-methylol containing copolymerizable monomer;
d) 1 to 5~ by weight of an olefinically unsaturated carboxylic acid;
e) 0.2 to 3~ by weight of a latex stabilizer; and t7452 f) 0 to 1~ by weight of at least one polyunsaturated copolymerizable nomer; and II. subjecting the saturated sheet to temperatures above 100C to remove excess water and to effect cure of the saturant.
The resultant paper products are characterized by an excellent balance of toughness, wet strength, fold, edge tear and delamination resistance and, as such, are especially suitable for use as masking tape, book cover stock, label stock and the like. m ey are also characterized by excellent color retention and resistance to degradation by light or ultra-violet radiation.
While the aqueous emulsions utilized herein may be prepared using batch or slow-addition polymerization techniques, we have found that those prepared by the batch process provide superior results.
As used herein, the term "batch" refers to a process whereby all the major monomers are charged to the reactor intially with the functional monomer(s) added uniformly and concurrently with the initiators. In contrast, the term "slow-addition" refers to a process wherein water, emulsifying agents and optionally a minor portion of the monomers are initially charged in the reactor and the remainder of the monomers then added gradually with the initiators over the course of the re~ction.
The vinyl esters utilized herein are the esters of alkanoic acids having from one to about 13 carbon atoms~ Typical examples include:
vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl 2-ethyl-hexanoate, vinyl isoctanoate, vinyl nonoate, vinyl decanoate, vinyl pivalate, vinyl versatate, etc. Of the foregoing, vinyl acetate is the preferred monomer because of its ready availability and low cost.

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The N-methylol component is generally N-methylol acrylamide or N-methylol methacrylamide although other mono-olefinically unsaturated compounds containing an N-methylol group and capable of copolymerizing with ethylene and the vinyl ester may also be employed.
m e olefinically-unsaturated carboxylic acids of componen~ ~d) are the aIkenoic acids having from 3 to 6 carbon atoms or the alkenedioic acids having from 4 to 6 carbon atoms, like acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaric acid, or mixtures thereof in amoun~s sufficient to give between 1 and 5~ by weight, of monomer units in the final copolymer. In addition, certain copolymerizable monomers which assist in the stability of the copolymer emulsion, e.g., vinyl sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid are used herein as latex stabilizers. These stabilizers are added in amounts of from about 0.2 to 3~ by weight of the monomer mixture.
Optionally, polyunsaturated copolymerizable monomer~ may also be present in small amounts, i.e., up to about 1~ by weight. Such comonomers would include those polyolefinically-unsaturated monomers copolymerizable with vinyl acetate and ethylene, such as lower alkenyl lower aIkenoates, for example, vinyl crotonate, allyl acrylate, allyl methacrylate; di-lower alkenyl alkanedioates, for example, diallyl maleate, divinyl adipate, diallyl adipate; dilower alkenyl benzenedicarboxylates, for example, diallyl phthalate; lower alkanediol di-lower alkenoates, Eor example, ethylene glycol diacrylate, ethylene glycol dimethacrylate, butanediol dimethacrylate; lower alkylene bis-acrylamides and lower alkylene bis-methacrylamides, for example, methylene bis-acrylamide; triallyl cyanurate, etc.

~ 28745~

In accordanoe with the procedure utilized herein the vinyl acetate, ethylene, N-methylol acrylamide and the carboxylic acid are polymerized in a aqueous medium under pressures not exceeding 100 atmospheres in the presence of a catalyst and at least one emulsifying agent, the aqueous system being maintained, by a suitable buffering agent, at a pH of 2 to 6, the catalyst being added incrementally. In the preferred embodiment where a batch process is used, the vinyl aoe tate is suspended in water and thoroughly agitated in the presence of ethylene under the working pressure to effect solution of the ethylene in the vinyl acetate up to the substantial limit of its solubility under the condition existing in the reaction zone, while the vinyl acetate is gradually heated to polymerization temperature. The homogenization period is followed by a polymerization period during which the catalyst, which consists of a main catalyst or initiator, and may include an activator, is added lS incrementally, and the N-methylol and carboxylic acid components are similarly added incrementally, the pressure in the system being maintained substantially constant by application of a constant ethylene pressure if required. In ~he case of the slow addition, some of the vinyl acetate is generally charged initially, and the remainder pre-emulsified with the N-methylol comF~nent and carboxylic acid and added incrementally.
Suitable as polymerization catalysts are the water-soluble free-radical-formers generally used in emulsion polymerization, such as hydrogen peroxide, sodium persulfates, potassium persulfate and ammonium persulate, as well as t-butyl hydroperoxide, in amounts of between 0.01 and 3~ by weight, preferably 0.01 and 1% by weight based on the total amount of the emulsion. They can be used alone or together with reducing agents such as sodium formaldehyde-sulfoxylate, iron-II-salts, sodium dithionite, sodium hydrogen sulfite, sodium sulfite, sodium thiosulfate, ~l2~37~5~

as redox catalysts in amounts of 0.01 to 3~ by weight, preerably 0.01 to 1~ by weight, based on the total amount of the emulsion. The free-radical-formers can be charged in the aqueous emulsifier solution or be added during the polymerization in doses.
The dispersing agents are all the emulsifiers generally used in emulsion polymerization, as well as optionally present protective colloids. It is also possible to use emulsifiers alone or in mixtures with protective colloids. m e emulsifiers can be anionic, cationic or non-ionic surface-ac~ive compounds. Suitable anionic emulsifiers are, for example, alkyl sulfonates, aLkylaryl sulfonates, alkyl sulfates, sulfates of hydroxylalkanols, alkyl and alkylaryl disulfonates, sulfonated atty acids, sulfates and phosphates of polyethoxylated alkanols and alkylphenols, as well as esters of sulfosuccinic acid. Suitable cationic emulsifiers are, for example, alkyl quaternary ammonium salts, alkyl quaternary phosphonium salts and ternary sulEonium salts. Examples oE
suitable non-ionic emulsifiers are the addition products o 5 to 50 moles of ethylene oxide adducted to straight-chained and branch-chained alkanols with 6 to 22 carbon atoms, or alkylphenols, or higher fatty acids, or higher fatty amides, or primary and secondary higher alkyl amines; as well as blocX copolymers of propylene oxide with ethylene oxide and mixtures thereof. Preferably nonionic and/or anionic emulsifiers are used as emulsifying agents in amounts of 1 to 6~ by weight of the polymerisate.
The polymerlzation is carried out at a pH of between 2 and 7, preferably between 3 and 5. In order to maintain the pH range, it may be 2S useful to work in the presence of customary bufer systems, for example, in the presence of alXali metal acetates, alkali metal carbonates, alkali --` 128~45~

metal phosphates. Polymerization regulators, like mercaptans, aldehydes, chloroform, methylene chloride and trichloroethylene, can also be added in some cases.
The reaction is generally continued until the residual vinyl acetate content is below about 1%. The campleted reaction product is then allowed to cool to about roam temperature, while sealed from the atmosphere. The pH is then suitably adjusted to a value in the range of 4.5 to 7, preferably 5 to 6 to insure maximum stability.
The saturants used herein ma~ also contain other materials as are normally incorporated into paper products. Such other materials include flame retardants, fillers, pigments, dyes, softeners, post-added surfactants and catalysts and/or crosslinking agents for the latex polymer. These materials, if present, are employed in conventional amounts.
By following the procedure described above, particularly the initial saturation of the polymerization mixture with ethylene before polymerization is initiated, there can be produoed the stable carboxylated vinyl acetate-ethylene-N-methylol acrylamide interpclymer latex characterized above, with the copolymer having an ethylene content o~ 5 to 30~, a glass transition temperature of between -30 and +15C, an intrinsic viscosity of 1 to 2.5 dl./g., and an average particle size of 0.1 to 2u, and the latex having a solids content of ~p to 60~ or more. They are crosslinked at elevated temperature in a weakly acid pH range. Since acid catalysts accelerate the crosslinkingr before the binder is applied it is optionally mixed with a suitable catalyst for the N-methylol oomponents.
Such acid catalysts are mineral acids or organic acids, such as phosphoric acid, tartaric acid, citric acid, or acid salts, such as chromium-III

, . : , .

salts, aluminum chloride, ammonium chloride, zinc nitrate or magnesium chloride, as known in the art. m e amount of catalyst is generally about 0.5 to 2~ of the total emulsion polymer solids.
Paper webs obtained from bleached or nonbleached pulp may be saturated using the saturants of the invention. Additionally, those webs obtained by the unbleached sulfite, bleached sulfite, unbleached sulfate (kraft), semibleached and bleached sulfate processes may also be employed as may wet laid nonwoven webs prepared from blends of natural cellulose and synthetic fibers. It will be recogni~ed that those fibers having a bonding surface which is activated by an aqueous medium will have a lesser degree of fiber to fiber bonding when formed into a sheet if the fiber refining is at a minimum and wet pressing of the sheet is at a minimum.
The process of the invention is particularly advantangeous for use with specialty paper webs intended for use in tape or stock applications which require the saturation of the paper web in order to modify the structural properties such as the toughness, delamination resistance and tear strength of the paper. The paper employed in the invention can be a conventional paper containing a wet-strength resin so that it will more readily withstand the impregnation step. Papers having basis weights (by the procedure of TAPPI T 140) of the order of from 8 to 20 pounds per 3000 square feet (3.6 to 9 kg per 275 square meters) are especially useful in the invention, although heavier or lighter papers can be used if desired.
Also, the web of paper can be composed of two or more plys of such paper.
The paper should contain enough wet strength resin so that it will maintain its integrity after absorbing a minimum of about two times its own weight of water. Such papers are well known in the art.

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g Saturation of a dry sheet or web may be accomplished in the following manner. Roll stock of unsaturated base paper is passed through the saturating bath and then through the squeeze rolls or it may be impregnated using a shower head as the saturating head at the squeeze roll. Excess saturant is removed by squeeze rolls, saturate vehicle is evaporated by passing the sheet over heated can dryers, and the dried sheet is wound up in a roll. Other methods of saturation including foam saturation, saturation from a print roll, etc. may also, of course, be employed. As alternate drying methods, a festoon or tunnel dryers may be used.
The ratio of dry saturant polymer to fiber for a given base sheet is controlled primarily by the dry solids of the saturant. A secondary but minor control is effected by the nip pressure on the squeeze rolls.
Saturant solids of 0.1 to 65 percent may be employed depending upon the polymer to fiber ratio desired in the saturated product, although the usual solids range is from 10 to 50 percent. A majority of products are made within the range from 10 to 100 parts of dry saturant per 100 parts by weight of fiber. In general, pickups in the range of 20 to 50 parts appear to be optimum, both from the standpoint of economics and physical property performanoe .
m e heat treatment which effects curing of the paper saturant may be performed by subjecting the dried saturated sheet to temperatures of 100C
to 200C prior to winding the sheet into a roll. Alternatively the curing may be effected by winding the dry saturated sheet up in the roll at temFeratures above about 100C after which the roll is stored at a like temperature for a predetermined length of time. The curing reaction in this case is stopped by rewinding the roll to reduce the temperature.

Heat treatments of 0.5 to 20 hours at temperatures above 100C. may be employed, although 1 to 7 hours at about 105C. are most generally used.
Practical equivalent tLme-temperature relationships may be used.
In the following examples, all parts are by weight and all temperatures in degrees Celsuis unless otherwise indicated.
m e following test procedures were utilized in evaluating the binders prepared herein:
8asis weight - Weight in pounds (and kilograms) of a ream of paper 24 inches x 36 inches (61 x 91 cm) per 500 sheets, weighed at 50 percent relative humidity and 22C. Essentially the same as TAPPI Methods T410m-45.
Dry tensile strength-machine and cross direction - The breaking strength as determined on an Instron tester having the upper jaw travel at 1 inch (2.54 cm) per minute. The test is performed on a strip 1 inch (2.54 cm) wide, and reported in pounds per inch (kilograms per centimeter). TAPPI Method T404ts-66.
Wet tensile Strength - This is obtained in the same manner as the dry tensile with exception that the strips are tested after soaking in 1%
Aerosol OT for 10 minutes. TAPPI Method T456 m-49.

Finch Ed e tear-machine direction. m e tear strength is determined g on an Instron tester using a Finch Stirrup in the lower jaw. Jaw speed is 12 inches (30.48 cm) per minute. The test is performed on a strip 1 inch (2.54 cm) wide and reported pounds per inch (kilograms per centimeter).
TAPPI reference T4700s~66.
MIT fold-cross direction - Fold endurance is tested with an M.I.T.
Fold Tester. Samples are cut into 1.5 mm x 7 inches (17.78 cm) and evaluated with one kilogram tension. T~PPI Method T423mr50.

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1 1 _ Delamination resistanoe machine direction - This test indicates the resistance to internal splitting of a sheet. Resistanoe to delamination is tested by heat sealing a 1.0" x 5" (2.54 x 12.7 cm) sample between two strips of Bondex Rug Binding Tape. Heat sealing is done on a Carver press at 135C for 30 seconds at minimal pressure. Strength is measured by Instron testing at a crosshead speed of 5 (12.7 cm) inches per minute.
Elmendorf tear - crossdirection - TAPPI method T41 4ts-65 is used to _ measure the internal tearing resistance of the paper. Tear Strength is measured on an Elmendorf Tear Tester using a 2.5 inch x 3 inch (6.35 x 7.62 cm) sample. Results are reported in grams.
&turation Procedure - The saturation procedure employed varied -depending on the basis weights of the stock:
In the case of light weight stocks (22 and 26 pound) (9.9 and 11.7 kg), the emulsion was diluted to 30% solids and applied to a creped web of cellulose fibers using a two-roll padder in an amount sufficient to achieve a final sheet composition of 28 parts binder to 72 pounds (32.4 kg) fiber (about 39~ pickup). m e saturated web was then air dried and cured at 175C for 45 seconds. Aging studies were run on samples aged at 266F for 30 minutes.
In the case of the heavier weight stock (30 pounds) (13.5 kg), the emulsion was diluted to 25% solids and formulated with 0.5~ aerosol O.T.
based on polymer solids. A creped web of cellulose iber was saturated using a two-roll padder. The emulsion was applied to achieve a final sheet composition of 22 parts binder to 78 parts iber (about 28~ pickup).
The saturated stock was dried on a drum type drier and cured at 150C for 3 minutes. Aging studies were done on samples aged at 110C for 3 hours.
All elevated temperated cure and aging times and temperatures reEer to use of a laboratory forced air oven.

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Exam~_e I
This example describes the batch preparation of the emulsion polymers utilized as saturants in accordance with the present invention.
A 10 liter stainless steel autoclave equipped with heating/cooling means, variable rate stirrer and means of metering monomers and initiators was employed. To the 10 liter autoclave was charged 450 g (of a 20~ w/w solution) sodium aIkyl aryl polyethylene oxide sulphate ~3 moles ethylene oxide), 40 9 (of a 70% w/w solution in water) alkyl aryl polyethylene oxide (30 mole ethylene oxide), 90 g sodium vinyl sulfonate (25~ solution in water), 0.5 g sodium aoe tate, 5 g (of a 1% solution in water) ferrous sulfate solution, 2 g sodium formaldehyde sulfoxylate and 2500 g water.
After purging with nitrogen all the vinyl aoe tate (2000 9) was added and the reactor was pressurized to 750 psi with ethylene and equilibrated at 50C for 15 minutes.
The polymerization was started by metering in a solution of 25 g.
tertiary butyl hydroperoxide in 250 9 of water and 20 9 sodium formaldehyde sulfoxylate in 250 g water. The initiators were added at a uniform rate over a period of 5-1/4 hours.
Concurrently added with the initiators over a period of 4 hours was an aqueous solution of 280 g N-methylol acrylamide (48% w/w solution in water), 45 9 of acrylic acid, 100 g of sodium alkyl aryl polyethylene oxide (3 mole ethylene oxide) sulfate (20~ w/w solution in water), 1.5 g of sodium acetate in 400 g of water.
During the reaction the temperature was controlled at 65C to 70C ~y means of jacket cooling. At the end of the reaction the emulsion was transferred to an evacuated vessel (30 L) to remove residual ethylene from the system.

~2~37452 This prooedure resulted in a polymeric composition of ethylene, vinyl acetate, N-methylol acrylamide and acrylic acid (E~V~/NMA/AA) in a 25:75:3:1 ratio.

Example II
m is example describes the preparation of an emulsion similiar to that described in Example I but using the slow-addition polymerization procedure.
To the 10 liter autoclave was charged 90 9 ~of a 20~ w/w solution in water) sodium aLkyl aryl polyethylene oxide sulphate (3 moles ethylene oxide), 6 9 (of a 70% w/w solution in water) alkyl aryl polyethylene oxide (30 moles ethylene oxide), 20 g (of a 25% w/w solution) sodium vin~l sulfonate, 2 9 sodium fonmaldehyde sulfoxylate 0.5 9 sodium acetate, 5 9 (of a 1% w/w solution in water) ferrous sulphate solution and 2000 g water. After purging with nitrogen, 300 g vinyl acetate were charged to the reactor. The reactor was then pressurized to 750 psi with ehtylene and equilibrated at 50C for 15 minutes. m e polymeri~ation was started by metering in a solution of 35 g tertiary butyl hydroperoxide in 250 g water and 35 g sodium formaldehyde sulfoxylate in 250 g water over a period of 6-1/2 hours.
Concurrently added with the initiators over a period of 4 hrs was a pre-emulsified blend of 3075 g. vinyl acetate, 150 g (48% w/w solution in water) N-methylol acrylamide, 45 g acrylic acid, 810 g (of a 20% w/w solution in water) sodi~m aLkyl aryl polyethylene oxide sulphate (3 mole ethylene oxide), 60 9 (of a 70~ w/w solution in water) alkyl aryl polyethylene oxide (30 le ethylene oxide), 1 g sodium acetate, 60 g (of a 25% w/w solution in wa~er) sodium vinyl sulfonate in 600 9 water.

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During the polymerization, the temperature of the reaction was maintained at 55-60C by m~ans of cooling ana the pressure at 750 psi of ethylene by adding it when necessary. At the end of the additions of monomers and catalysts, the emulsion WRS transferred to an evacuated vessel following the procedure in Ex 1.
Using procedures similar to those described in Examples I or II, a series of emulsions having the following polymeric compositions were prepared;

Emulsion Composition Polymeric Procedure E V~ NMA AA
1 25 75 3 1 batch 2 25 75 3 1 slow addition 3 25 75 3 1* batch 4 25 75 3 2 batch 3 3 batch 6 25 75 3 3.5 batch 7 25 75 2.5 5 batch 8 25 75 1.5 5 batch 9 25 75 3 0 batch *In this sample itaconic acid was used in place of acrylic acid.

For comparitive purposes, an emulsion (9) was prepared with no carboxyl containing comonomer. Emulsions 1-9 were then used to saturate various paper stocks and the papers subjected to tests as described above.
Tests were also done using styrene butadiene rubber (SBR) latices such as are conventionally used for saturation of label and tape stocks.
Testinq on 22 Pound Stock (Standard Units) Tensiles in_lbs/inch Emulsion Basis Wt MD* Dry MD Wet MD Aged CD* Dry CD Wet 1 29.1 15.1 13.3 9.3 5.6 4.8 3 30.0 16.4 14.1 7.5 8.1 4.6 4 29.3 14.9 14.3 10.4 6.8 4.3 29.7 15.3 14.8 8.3 7.9 4.6 6 30.2 16.0 14.7 7.7 7.7 4.5 7 32.; 16.5 16.0 8.0 8.0 3.4 35 SBR 30.6 15.2 15.5 6.9 7.4 3~2 MD=Machine Direction CD=Cross Direct Testing on 9.9 kg Stock (Metric Units) Tensiles in kg/cm EmulsionBasis Wt MD* Dry MD Wet MD Aged CD* Dry CD Wet 1 1.31 2.67 2.36 1.65 .99 .85 3 13.5 2.91 2.50 1.33 1.43 .81 4 13.2 2.64 2.53 1.84 1.20 .76 13 4 2.71 2.62 1.47 1.40 .81 6 13.6 2.83 2.60 1.36 1.36 .80 7 14.6 2.92 2.83 1.42 1.42 .60 SBR 13.8 2.69 2.75 1.22 1.31 .57 MDcMachine Direction CD=Cross Direct Finch Edge Tear Elmendorf Emulsion(lbs/inch) (kg/om) (~rams) Delamination Dry Aged Dry Aged Dry A~ ~ (Z ? (kg) 1 3.4 3.2 .60 .57 32 30 45 1.26 3 4.1 2.3 .73 .41 28 26 47 1.32 4 3.1 3.7 .55 .66 32 32 47 1.32 3.9 3.1 .69 .55 36 36 49 1.38 6 4.1 3.3 .73 .58 44 38 50 1.41 7 3.3 2.9 .58 .51 36 38 44 1.23 SBR 3.9 4.1 .69 .73 34 30 48 1.35 me results of the testing presented above illustrate that the opti-mum balance of strength and tear properties (comparable to those obtained the styrene butadiene rubbers) can be obtained only by the c.ombination of carboxyl containing monomer and N-methylol containing monomer. m us, the use of as little as 1 part acrylic acid gives a saturant having a good balance of properties, while the use of higher levels of acrylic acid, even in conjunction with lower levels of NMA, results in optimum perf-ormanoe. Moreover, the papers prepared using the emulsions of the invent-ion exhibited excellent color retention when compared with the SBR

saturated papers.

374~i2 Test on 26 Pound Stock (Standard Units) Tensi es in lbs/inch Emulsion Basis Wt MD Dry MD Wet MD ~ged CD Dry CD Wet 9 32.3 16.4 11.4 14.6 9.4 5.9 1 33.7 18.6 9.6 17.2 9.5 5.2 4 34.4 18.0 13.0 16.4 10.2 4.6 3 35.2 15.3 12.8 15.1 10.2 6.3 SBR 34.1 17.9 8.5 18.3 10.2 3.8 Test on 11.7 kg. Stock (Metric Units) Tensiles in kg/cm Emulsion Basis Wt MD Dry MD Wet MD Aged CD Dry CD Wet 9 14.5 2.91 2.02 2.59 1.66 1.04 1 15.2 3.29 1.70 3.05 1.68 .92 4 15.5 3.19 2.30 2.91 1.81 .81 3 15.8 2.71 2.27 2.67 1,81 1.12 SBR 15.3 3.17 1.51 3.24 1.81 .67 Finch Edge Tear Elmendorf Emulsion(lbs/inch) (kg/cm) (grams) Delam. MIT
Dry Aged Dry Aged Dry Aged (oz) (kg) 9 1.g 1.5 .34 .27 32 28 3S15.7 857 1 2.3 1.9 .41 .34 30 30 42t8.9 902 2.1 1.7 .37 .30 36 30 4118.4 *
3 1.9 1.8 .34 .32 33 30 4419.8 *
SBR 1.7 1.7 .30 .30 26 28 4321.5 929 * Not tested The above test results show a similar pattern to that observed previously. The sample containing NMA but no acid ~9) fails to exhibit the required balance of properties.
In the following test, different lots of emulsions corresponding in composition to those of Emulsions 1 and 2 were prepared by batch ~Emulsion 1) and slow addition (Emulsion 2) polymeriza~ion procedures and tested as described above.

~LZ~37452 Tensiles (Standard Units) Emulsion Basis Wt. MD Dry MD Wet MD Aged CD Dry _CD Wet 1 38.5 21.1 12.3 20.5 16.5 8.2 1 37.621.0 11.8 19.9 15.0 7.2 2 36.618.2 9.3 19.0 t3.1 6.0 2 37.416.8 7.7 16.8 11.8 4.6 Tensiles (Metric Units) Emulsion Basis Wt. MD Dry MD Wet ~D Aged CD Dry CD Wet 1 17.3 3.74 2.18 3.63 2.92 1.45 1Q 1 16.9 3.72 2.09 3.53 2.66 1.27 2 16.5 3.22 1.65 3.37 2.32 1.06 2 16.8 2.98 1.36 2.98 2.09 0.81 Finch Edge Tear Elmendorf Emulsion(lbs~inch) ~kg/cm) (grams) Celamination Dr,~ 99~ Y~ 9~ 5~ 9~d (Z) (kg) 1 5,4 4.0 0.96 0.71 52 44 54 1.52 1 4.9 3.3 0.87 0.58 46 46 51 1.43 2 7.1 5.~ 1.26 0.96 48 48 30 0.84 2 7.6 6.6 1~35 1.17 54 54 26 0.73 The above results illustrate the differences in properties obtained using emulsions prepared by the batch and slow-addition polymerization techniques. While a good balanoe of strength, tear and delamination is obtained using emulsions prepared by the slow addition, the optimum balance of properties are obtained when the emulsions are prepared using a batch polymerization procedure.
It will be apparent that various changes and modifications ~ay be made in the embcdiments of the invention described above, without departing freom the scope of the invention, as defined in the appended claims, and it is intended therefore, that all matter contained in the foregoing description shall be interpreted as illustrative only and not as limitative of the invention.

Claims

1. A saturated paper product characterized by an excellent balance of toughness, strength, fold, tear and delamination resistance comprising a web containing cellulose fibers saturated with an aqueous emulsion prepared by the emulsion polymerization at a pH of 2 to 7 of:

(a) a vinyl ester of an alkanoic acid having l to 13 atoms interpolymerized with the following comonomers:

(b) 5 to 302 by weight of ethylene;

(c) 0.5 to 6% by weight of an N-methylol containing copolymerizable monomer;

(d) 1 to 52 by weight of an alkenoic acid having from 3 to 6 carbon atoms or an alkenedioic acid having from 4 to 6 carbon atoms;

(e) 0.2 to 3a by a weight of a latex stabilizer; and (f) 0 to 1a by weight of at least one polyunsaturated copolymerizable monomer said web fibers being saturated with said composition in an amount of from about 10 to 100 parts by weight on a solids weight basis per 100 parts by weight of fibers.

2. The paper of claim 1, wherein the aqueous emulsion is prepared using batch polymerization procedures.

3. The paper of claim 1, wherein the vinyl ester is vinyl acetate.

4. The paper of claim 1, wherein the N-methylol containing comonomer and is N-methylol acrylamide or N-methylol methacrylamide.

5. The paper of claim 1, wherein the olefinically unsaturated carboxylic acid is selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid.

6. The paper of claim 1, wherein the latex stabilizer is vinyl sulfonic acid or 2-acrylamido-2-methylpropane sulfonic acid.

7. The paper of claim 1, wherein there is additionally present up to 1% by weight of a polyunsaturated co-polymerizable monomer selected from the group consisting of vinyl crotonate, allyl acrylate, allyl methacrylate, diallyl maleate, divinyl adipate, diallyl adipate, diallyl phthalate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, butanediol dimethacrylate, methylene bis-acrylamide and triallyl cyanurate.

8. The paper of claim 1 which additionally contains an acid catalyst in an amount of 0.5 to 2% by weight of the emulsion polymer solids.

9. A process for manufacturing a paper product characterized by an excellent balance of toughness, strength, fold, tear and delamination resistance which comprises the steps of:

(I) saturating a web containing cellulose fibers with a composition comprising and aqueous emulsion prepared by the emulsion polymerization at a pH of 2 to 7 of:

(a) a vinyl ester of an alkanoic acid having 1 to 13 atoms interpolymerized with the following comonomers:

(b) 5 to 30% by weight of ethylene;

(c) 0.5 to 6% by weight of an N-methylol containing copolymerizable monomer;

(d) 1 to 5% by weight of an olefinically unsaturated carboxlyic; alkenoic acid having from 3 to 6 carbon atoms or an alkenedioic acid having from 4 to 6 carbon atoms:

(e) 0.2 to 3% by a weight of a latex stabilizer; and (f) 0 to 1% by weight of at least one polyunsaturated copolymerizable monomer;
said web fibers being saturated with from about 10 to 100 parts by weight on a solids weight basis per 100 parts by weight of fibers with said composition; and (II) subjecting said saturated sheet to temperatures above 100°C. to remove excess water and to effect cure of the saturant.

10. The paper of claim 9, wherein the aqueous emulsion is prepared using batch polymerization procedures.

11. The paper of claim 9, wherein the vinyl ester is vinyl acetate.

12. The paper of claim 9, wherein the N-methylol containing comonomer and is N-methylol acrylamide or N-methylol methacrylamide.

13. The paper of claim 9, wherein the olefinically unsaturated carboxylic acid is selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid.

14. The paper of claim 9, wherein the latex stabilizer is vinyl sulfonic acid or 2-acrylamido-2-methylpropane sulfonic acid.

15. The paper of claim 9, wherein there is additionally present up to 1% by weight of a polyunsaturated co-polymerizable monomer selected from the group consisting of vinyl crotonate, allyl acrylate, allyl methacrylate, diallyl maleate, divinyl adipate, diallyl adipate, diallyl phthalate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, butanediol dimethacrylate, methylene bis-acrylamide and triallyl cyanurate.