Ethylene vinyl acetate compositions for paper saturation

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: PA1 (a) a vinyl ester of an alkanoic acid interpolymerized with: PA1 (b) 5 to 30% by weight of ethylene; PA1 (c) 0.5 to 6% by weight of an N-methylol containing copolymerizable monomer; PA1 (d) 1 to 5% by weight of an olefinically unsaturated carboxylic acid; PA1 (e) 0.2 to 3% by weight of a latex stabilizer; and PA1 (f) 0 to 1% by weight of at least one polyunsaturated copolymerizable monomer.

BACKGROUND OF THE INVENTION 
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 ("nonwovens") usually contain substantial amounts of long 
synthetic fibers which are bonded using chemical, mechanical or thermal 
techniques and which generally contain little or no hydrogen bonding. In 
contrast, paper is generally comprised substantially of shorter cellulose 
fibers which are hydrogen bonded using conventional paper manufacturing 
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 
waterproof or greaseproof, or adhesive, or to size them, to make them 
glossy. Many of these treatments 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 completely different requirements than does a saturant 
type binder which is used to impregnate or saturate the paper web thereby 
giving the paper integrity. 
More particularly, a saturant is used to impart a combination of tensile 
strength and stretch to the paper sheet, a property often referred to as 
"toughness". Other desirable properties which a saturant provides to the 
paper sheet include wet strength, folding endurance, flexibility, internal 
tear, edge tear, delamination resistance and resistance to physical 
degradation and discoloration due to heat and light aging. While the 
addition of certain comonomers, including N-methylol containing monomers, 
has been suggested in order to improve the 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, fail 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 in the manufacture of 
masking tape, book cover stock, and label stock. As 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. 
SUMMARY OF THE INVENTION 
We have now found that paper may be prepared by: 
I. saturating a web containing cellulose fibers with an aqueous 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) 5 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 
(f) 0 to 1% by weight of at least one polyunsaturated copolymerizable 
monomer; and 
II. subjecting the saturated sheet to temperatures above 100.degree. C. 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. They are also characterized by excellent 
color retention and resistance to degradation by light or ultraviolet 
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 reaction. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
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. 
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. 
The olefinically-unsaturated carboxylic acids of component (d) are the 
alkenoic 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 amounts 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 monomers 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 alkenoates, 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, for example, 
ethylene glycol diacrylate, ethylene glycol dimethacrylate, butanediol 
dimethacrylate; lower alkylene bis-acrylamides and lower alkylene 
bismethacrylamides, for example, methylene bis-acrylamide; triallyl 
cyanurate, etc. 
In accordance 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 acetate 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 
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 the case of the slow addition, some of the vinyl acetate is 
generally charged initially, and the remainder pre-emulsified with the 
N-methylol component 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 
persulfate, 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, 
as redox catalysts in amounts of 0.01 to 3% by weight, preferably 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. The emulsifiers can be anionic, cationic or non-ionic 
surface-active compounds. Suitable anionic emulsifiers are, for example, 
alkyl sulfonates, alkylaryl sulfonates, alkyl sulfates, sulfates of 
hydroxylalkanols, alkyl and alkylaryl disulfonates, sulfonated fatty 
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 sulfonium salts. Examples of 
suitable non-ionic emulsifiers are the addition products of 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 block 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 polymerization 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 useful to 
work in the presence of customary buffer systems, for example, in the 
presence of alkali metal acetates, alkali metal carbonates, alkali 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 completed reaction product is then allowed 
to cool to about room 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 may 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 produced the stable carboxylated 
vinyl acetate-ethylene-N-methylol acrylamide interpolymer latex 
characterized above, with the copolymer having an ethylene content of 5 to 
30%, a glass transition temperature of between -30.degree. and +15.degree. 
C., an intrinsic viscosity of 1 to 2.5 dl./g., and an average particle 
size of 0.1 to 2.mu., and the latex having a solids content of up to 60% 
or more. They are crosslinked at elevated temperature in a weakly acid pH 
range. Since acid catalysts accelerate the crosslinking, before the binder 
is applied it is optionally mixed with a suitable catalyst for the 
N-methylol components. Such acid catalysts are mineral acids or organic 
acids, such a 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. The 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 recognized 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 about 8 to about 20 
pounds per 3000 square feet are especially useful in the invention, 
although heavier or lighter papers can be use 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. 
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 about 0.1 to about 65 percent may be employed depending 
upon the polymer to fiber ratio desired in the saturated product, although 
the usual solids range is from about 10 to 50 percent. A majority of 
products are made within the range from about 10 to about 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 performance. 
The heat treatment which effects curing of the paper saturant may be 
performed by subjecting the dried saturated sheet to temperatures of 
100.degree. C. to 200.degree. C. 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 temperatures above about 100.degree. C. 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 100.degree. C. may be employed, although about 1 to 
about 7 hours at about 105.degree. C. are most generally used. Practical 
equivalent time-temperature relationships may be used.

The following examples are given to illustrate the present invention, but 
it will be understood that they are intended to be illustrative only and 
not limitative of the invention. In the examples, all parts are by weight 
unless otherwise indicated. 
The following test procedures were utilized in evaluating the binders 
prepared herein: 
Basis weight--Weight in pounds of a ream of paper 24 inches.times.36 inches 
per 500 sheets, weighed at 50 percent relative humidity and 22.degree. C. 
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 per 
minute. The test is performed on a strip 1 inch wide, and reported in 
pounds per inch. 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 Edge tear-machine direction--The tear strength is determined on an 
Instron tester using a Finch Stirrup in the lower jaw. Jaw speed is 12 
inches per minute. The test is performed on a strip 1 inch wide and 
reported pounds per inch. 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.times.7 inches and evaluated with one 
kilogram tension. TAPPI Method T423m-50. 
Delamination resistance machine direction--This test indicates the 
resistance to internal splitting of a sheet. Resistance to delamination is 
tested by heat sealing a 1.0".times.5" sample between two strips of Bondex 
Rug Binding Tape. Heat sealing is done on a Carver press at 135.degree. C. 
for 30 seconds at minimal pressure. Strength is measured by Instron 
testing at a crosshead speed of 5 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.times.3 inch sample. Results are 
reported in grams. 
Saturation 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), 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 fiber (about 39% pickup). The 
saturated web was then air dried and cured at 175.degree. C. for 45 
seconds. Aging studies were run on samples aged at 266.degree. F. for 30 
minutes. 
In the case of the heavier weight stock (30 pounds), the emulsion was 
diluted to 25% solids and formulated with 0.5% aerosol O.T. based on 
polymer solids. A creped web of cellulose fiber was saturated using a 
two-roll padder. The emulsion was applied to achieve a final sheet 
composition of 22 parts binder to 78 parts fiber (about 28% pickup). The 
saturated stock was dried on a drum type drier and cured at 150.degree. C. 
for 3 minutes. Aging studies were done on samples aged at 110.degree. C. 
for 3 hours. All elevated temperated cure and aging times and temperatures 
refer to use of a laboratory forced air oven. 
EXAMPLE 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 alkyl aryl polyethylene oxide sulphate (3 moles ethylene 
oxide), 40 g (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 acetate, 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 acetate (2000 g) was added and 
the reactor was pressurized to 750 psi with ethylene and equilibrated at 
50.degree. C. for 15 minutes. 
The polymerization was started by metering in a solution of 25 g. tertiary 
butyl hydroperoxide in 250 g of water and 20 g sodium formaldehyde 
sulfoxylate in 250 g water. The initiators were added at a uniform rate 
over a period of 51/4 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 g 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 65.degree. C. to 
70.degree. C. by 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. 
This procedure resulted in a polymeric composition of ethylene, vinyl 
acetate, N-methylol acrylamide and acrylic acid (E/VA/NMA/AA) in a 
25:75:3:1 ratio. 
EXAMPLE II 
This 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 g (of a 20% w/w solution in water) 
sodium alkyl aryl polyethylene oxide sulphate (3 moles ethylene oxide), 6 
g (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 vinyl sulfonate, 2 g 
sodium formaldehyde sulfoxylate 0.5 g sodium acetate, 5 g (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 50.degree. C. for 15 minutes. The polymerization 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 
61/2 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) sodium alkyl aryl polyethylene oxide sulphate (3 mole 
ethylene oxide), 60 g (of a 70% w/w solution in water) alkyl aryl 
polyethylene oxide (30 mole ethylene oxide), 1 g sodium acetate, 60 g (of 
a 25% w/w solution in water) sodium vinyl sulfonate in 600 g water. 
During the polymerization, the temperature of the reaction was maintained 
at 55.degree.-60.degree. C. by means of cooling and the pressure at 750 
psi of ethylene by adding it when necessary. At the end of the additions 
of monomers and catalysts, the emulsion was 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; 
______________________________________ 
Composition 
Emulsion 
E VA NMA AA Polymeric Procedure 
______________________________________ 
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 
5 25 75 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. 
______________________________________ 
Testing on 22 Pound Stock 
Tensiles (lbs/inch) 
______________________________________ 
Emul- Basis MD* 
sion Wt 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 
5 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 32.5 16.5 16.0 8.0 8.0 3.4 
SBR 30.6 15.2 15.5 6.9 7.4 3.2 
______________________________________ 
Finch Edge Tear 
Elmendorf Tear 
(lbs/inch) (grams) Delam. 
Emulsion Dry Aged Dry Aged Ounces 
______________________________________ 
1 3.4 3.2 32 30 45 
3 4.1 2.3 28 26 47 
4 3.1 3.7 32 32 47 
5 3.9 3.1 36 36 49 
6 4.1 3.3 44 38 50 
7 3.3 2.9 36 38 44 
SBR 3.9 4.1 34 30 48 
______________________________________ 
MD = Machine Direction 
CD = Cross Direct 
The results of the testing presented above illustrate that the optimum 
balance of strength and tear properties (comparable to those obtained the 
styrene butadiene rubbers) can be obtained only by the combination of 
carboxyl containing monomer and N-methylol containing monomer. Thus, 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 
performance. Moreover, the papers prepared using the emulsions of the 
invention exhibited excellent color retention when compared with the SBR 
saturated papers. 
______________________________________ 
Test on 26 Pound Stock 
Tensiles 
______________________________________ 
Emul- Basis MD 
sion Wt Dry MD Wet MD Aged 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 
______________________________________ 
Finch Edge Tear Elmendorf 
Emulsion 
Dry Aged Dry Aged Delam. MIT 
______________________________________ 
9 1.9 1.5 32 28 35 857 
1 2.3 1.9 30 30 42 902 
4 2.1 1.7 36 30 41 * 
3 1.9 1.8 33 30 44 * 
SBR 1.7 1.7 26 28 43 929 
______________________________________ 
*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) polymerization procedures and tested as 
described above. 
______________________________________ 
Tensiles 
______________________________________ 
Emul- Basis MD 
sion Wt. Dry MD Wet MD Aged CD Dry CD Wet 
______________________________________ 
1 38.5 21.1 12.3 20.5 16.5 8.2 
1 37.6 21.0 11.8 19.9 15.0 7.2 
2 36.6 18.2 9.3 19.0 13.1 6.0 
2 37.4 16.8 7.7 16.8 11.8 4.6 
______________________________________ 
Finch Edge Tear 
Elmendorf 
Emulsion Dry Aged Dry Aged Delam 
______________________________________ 
1 5.4 4.0 52 44 54 
1 4.9 3.3 46 46 51 
2 7.1 5.4 48 48 30 
2 7.6 6.6 54 54 26 
______________________________________ 
The above results illustrate the differences in properties obtained using 
emulsions prepared by the batch and slow-addition polymerization 
techniques. While a good balance 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 may be made in 
the embodiments 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.