CA1256238A - High strength pigment binders for paper coatings containing carboxylated vinyl ester ethylene interpolymers - Google Patents
High strength pigment binders for paper coatings containing carboxylated vinyl ester ethylene interpolymersInfo
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Abstract
ABSTRACT OF THE DISCLOSURE
High strength pigment binders for paper coating having increased water retention and stability are disclosed. The coating compositions comprise an aqueous synthetic polymer latex and pigment and may contain other additives used in the art of pigmented paper coating. The latex comprises a dispersed interpolymer of a vinyl ester, ethylene a poly-ethylenically unsaturated comonomer and a ethylenically unsaturated mono- or dicarboxylic acid.
High strength pigment binders for paper coating having increased water retention and stability are disclosed. The coating compositions comprise an aqueous synthetic polymer latex and pigment and may contain other additives used in the art of pigmented paper coating. The latex comprises a dispersed interpolymer of a vinyl ester, ethylene a poly-ethylenically unsaturated comonomer and a ethylenically unsaturated mono- or dicarboxylic acid.
Description
~S6238 HIGH STRENGTH PIGMENT
BINDERS FOR PAPER COATINGS CONTAINING
CARBOXYLATED VINYL ESTER ETHYLENE INTERPOLYMERS
The present invention is directed to high strength pigment binders for paper coating having increased water retention and stability. The coating compositions comprise a synthe-tic polymer latex and pigment and may include other additives used in the art of pigmented paper coating.
The latex comprises a dispersed interpolymer of a vinyl ester, ethylene, a polyethylenically unsaturated comonomer and an ethylenically unsatur-ated mono- or dicarboxylic acid.
In the preparation of a coated paper web there is used a pigment, such as clay or the like, which is then compounded with a latex binder 1~ or adhesive material to produce a composition known in the art as a coating "color" for use in coating a cellulose web, e.g. a paper or paperboard web. Substantial quantities of the binder are used, and accordingly, the composition and characteristics of the binder are of great importance in determining the qualities of the finished coated web.
It has been recognized by the paper industry that increased dry strength properties may be provided to these latex binders by the in-clusion therein of carboxylate functionalities. There has however been difficu`lty encountered in providing carboxylic functionality in excess of about 2% by weight to vinyl ester containing latex polymer com-- . . , , -, : ~ ' . . ~ : . ,. -1~2S~
positions due to excessive alkaline swellabili-ty of the resultant latex particles. This swellability, in turn, produces unacceptable latex thickening at these pH values and consequent problems in the transport of such materials in conventional latex handling equipmert where vis-cosities less than about 1 Pa.s (1000 cps.) are generally employed.
It has now been found that substantially higher levels of carboxy-lation, with a synergistic improvement in coating strength, may be ach-ieved with reduction in alkaline swellability by incorporation in the interpolymer of one of a specific class of polyethylenically unsa-turat-ed comonomers.
The present invention provides a pigmented paper coating composi-tion comprising an aqueous synthetic polymer latex binder, pigment, and sufficient alkali to achieve a pH of 6 to 10, the latex comprising dis-persed therein an interpolymer which consists essentially of:
a~ a vinyl ester of an alkanoic acid having 1 to 13 carbon atoms interpolymerized with the following comonomers:
b) from 15 to 40% by weight ethylene, sufficient to achieve a Tg of 0 t~ -40C.;
c) from 2 to 15 milliequivalents per 100 grams (a) and (b) of a polyethylenically unsaturated comonomer selected from the group con-sisting of triallyl cyanurate, triallyl isocyanurate, diallyl maleate, diallyl fumarate, divinyl benzene, and diallyl phthalate;
d) from 25 to 65 milliequivalents per 100 grams (a) and (b) of an ethylenically unsaturated mono- or dicarboxylic acid or a half ester thereof characterized in that the alkali response of the polymer latex is substantially reduced wi-th respect to latices lacking component (c) , ,: : ,. : .
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while the coating strength of the resultant pigmented paper coa-ting is substantially improved thereover.
The vinyl ester monomers which may be utilized herein include the vinyl esters of alkanoic acids having from 1 to about 13 carbon atoms.
Typical examples include: vinyl formate, vinyl acetate, vinyl propion-ate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl 2-ethyl-hexanoate, vinyl isooctanoate, vinyl nonoate, vinyl decanoate, vinyl pivalate, vinyl versatate, etc. Of the foregoing, vinyl acetate is the preferred monorner because of its ready availability and low cost.
Generally, any ethylenically unsaturated mono or dicarboxylic acid may be used to provide the carboxyl functionality. Examples of suit-able acids include the monocarboxylic ethylenically unsaturated acids such as acrylic, vinyl acetic, crotonic, methacrylic, tiglic; the di-carboxylic ethylenically unsaturated acids such as maleic, fumaric, itaconic, maleic, citraconic, hydromuconic, allylmalonic; as ~ell as the corresponding half ester of those dicarboxylic acids, such as mono-(2-ethyl hexyl) maleate, monoethyl maleate, monobutyl maleate. Substan-tial improvements in strength are shown at levels of greater than 25 milliequivalents per 100 grams of the ethylene comonomer with amounts greater than 40 milliequivalents being preferred.
The resultant paper coating latex compositions are characterized by reduced alkali response and increased water retention in the latex state with improved properties of dry strength imparted to the final paper sheets coated therewith. Thus, while latex compositions prepared with levels of carboxylic functionality in excess of about 25 milliequi-valents per hundred and particularly in excess of about 40 milliequiva-lents per hundred will generally exhibit substantial increase in vis-~;~5~623 !!3 cosity a-t alkaline pH's, compositions prepared with 2 to 15, preferably 4 to 7, milliequivalents of polyethylenically unsaturated monomer per 100 part comonomer as taught herein exhibit little or no increase in vis-cosity under the same conditions. Moreover, in addition to the increase in coating strength which may be expected as a result of the increase in carboxyl functionali-ty, further increases in coating strength are observ-ed when the pigmented coating binders are prepared with the latices taught herein. It will be recognized by one skilled in the art tha-t the preferred level of polyethylenically unsaturated comonomer will vary pro-portionately depending upon the particular type and level of acid used.
To prepare the interpolymer latices used in the coating compositionsherein the vinyl ester, ethylene, the polyetnylenically unsaturated monomer and -the carboxylic acid are interpolymerized in an aqueous medium under pressures less than about 130 atmospheres in the presence of a catalyst, and an emulsion stabilizing amount of an anionic or a nonionic surfactant or mixtures thereof, the aqueous system being maintained by a suitable buffering agent, if necessary, at a pH of 2 to 6. The poly-merization is performed at conventional temperatures from about 21-107C
(70-225F), preferably from 49-79C (120-175F), for sufficient time to achieve a low monomer content, e.g. from 1 to about 8 hours, prefer-ably from 3 to about 7 hours, to produce a latex having less than 1.5 percent, preferably less than 0.5 weight percent, free monomer. Conven-tional batch, semi-continueous or continuous polymerization procedures may be employed and are taught, for example in U,S. Patents 3,708,388 issued Jan. 2, 1973 to M. K. Lindemann et al.; 3,404,112 issued Oct. 1, 1968 to M. K. Lindemann et al.; 3,71~,099 issued Jan. 30, 1973 to G. Biale; and 4,164,488 issued Aug. 14, 1979 to B. V. Gregorovich et al.
- . :
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' : " ' - ' ' ' ' ' ~5~X3~3 The polymeriza-tion is initiated by a water soluble free radical in-itia-tor such as water soluble peracid or salt therof, e.g. hydrogen per-oxide, sodium peroxide, lithium peroxide, peracetic acid, persulfuric acid or the ammonium and alkali metal salts thereof, e.g. ammonium per-sulfate, sodium peracetate, lithium persulfate, potassium persulfate,sodium persulfate, etc. A suitable concentration of the initiator is from 0.05 to 5.0 weight percent and preferaby from 0.1 to 3 weiyht percent.
The free radical initiator can be used alone and thermally decompos-ed to release the free radical initiating species or can be used in com-bination with a suitable reducing agent in a redox couple. The reduc-ing agent is typically an oxidizable sulfur compound such as an alkali metal metabisulfite and pyrosulfite, e.g. sodium metabisulfite, sodium formaldehyde sulfoxalate, potassium metabisulfite, sodium pyrosulfite, etc. The amount of reducing agent which can be employed throughout the copolymerization generally varies from about 0.1 to 3 weight percent of the amount of polymer.
The emulsifying agent can be any of the nonionic or anionic oil-in-water surface active agents or mixtures thereof as are generally em-ployed in emulsion polymerization procedures. When combinations of emul-sifying agents are used, it is advantageous to use a relatively hydro-phobic emulsifying agent in combination with a relatively hydrophilic agent. The amount of emulsifying agent is generally from about 1 to about 10, preferably from about 2 to about 8, weight percent of the mono-mers used in the polymerization. Latex stabilizers such as sodium vinyl sufonate may also be present in amounts up to about 0.5% by weight. It will also be recognized that some portion of the carboxylic acid monomer may provide the stabilizing function in addition to the strength increase.
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The emulsifier usecl in the polymerizaton can also be added, in it entirety, -to the initial charge to the polymerization zone or a portion of the emulsifier, e.g. from 90 to 25 percent thereof, can be added continuously or intermittently during polymerization.
The preferred in-terpolymerization procedure is a modified batch process wherein the major amounts of some or all the comonomers and em-ulsifier are charged to -the reaction vessel after polymerization has been initiated. In this manner, control over the copolymerization of monomers having widely varied degrees of reactivity can be achieved.
It is preferred to add a small portion of the vinyl ester initially and -the remainder o-f the vinyl ester and other comonomers intermittently or continuously over the polymerization period which can be from 0.5 to about 10 hours, preferably frorn about 2 to about 6 hours.
The ethylene content of the interpolymer depends on the ethylene content of the aqueous polymerization medium. Factors which control ~he ethylene content of the polymerization medium include the partial pressure of ethylene in the vapor phase over the medium, the tempera-ture of polymerization and the degree of mixing between the vapor phase and the liquid medium. Generally, the polymerization is performed at temperatures from 49-79C l120-175F) and, at these temperatures, ethylene partial pressures from 345-6895 x 103 Pa (50-1,000 psig) preferably from 1724-5171 x 103 Pa (250-750 psig.) are sufficient to incorporate from 1 to 30, preferably from 5 to 25, weight percent -ethylene in the polymer. The reaction medium is preferably agitated with a stirrer, however, other agitation can be used as sparging the liquid with recirculated ethylene from the vapor phase. In the pre-ferred procedure, the ethylene partial pressures is maintained con-.' , . . . , ', .
'.' .', ;".:
:~L25~2 stant throughout the polymerization period so that this monomer is con-tinuously supplied at a constant rate.
The latices are produced and used at relatively high solids con-tents, e.g. between 35 and 70% although they may be diluted with water if desired. The preferred contents of solids are from 40 to 60, and, most preferred, from 50 to about 60 weight percent.
The particle size of the latex can be regulated by the quantity of non-ionic or anionic emulsifying agent or agents employed. To obtain smaller particles sizes, greater amounts of emulsifying agents are used.
As a general rule, the greater the amount of the emulsifying agent em-ployed, the smaller the average particle size.
The actual paper coating composition comprises the interpolymer latex together with pigment, such as clay and the usual paper coating additives which may include other cobinders, such as polyvinyl alcohol, protein, e.g. casein or soy protein, or starch, as is well known to those skilled in the art.
The pigment used in the papermaking compositions may be any of those conventionally employed. Generally, at least a portion of the pigment comprises clay and for this portion, any of the clays custom-arily used for coating paper, including the hydrous aluminum silicatesof kaolin group clays, hydrated silica clays, and the specific types of clays recommended in Chapters 10-16 of "Kaolin Clays and their Indus-trial Uses," by J. M. Huber Corp., New York, NY (1949). In addition to clay itself, there may be utilized other paper pigments such as, for example~ calcium carbonate, titanium dioxide, blanc fixe, lithopone, zinc sulfide, or other coating pigments including plastics, for example polystyrene, in various ratios, e.g. up to 50%, preferably up to 35%, , .
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by weigh-t of the clay. Adclitionally, the composition may also contain other additives such as zinc oxide and/or a small amount oF a dispersing or stabilizing agent such as tetrasodium pyrophosphate. In general, the paper coating composition comprises 100 parts pigment containing 65-100 parts clay and 0-35 parts secondary pigment; 0.01-0.5 parts dispersing or stabilizing agent; 3-30 parts interpolymer latex (solids basis); 0-25 parts co-binder; 0-0.2 parts defoamer and sufficient water to provide the desired level of solids. The modification of the coating color using these materials will be within the knowledge of those skilled in the art.
The coating compositions produced herein may be applied to fibrous paper webs using any of the conventional coating devices including, but not limited to, those referred to as trailing blade coaters, air knife coaters, roll coaters and the like.
In the examples which follow all parts of polyethylenically unsat-urated comonomers and carboxylic acid are based on parts per 100 parts by weight of the combined vinyl ester and ethylene component. In test-ing the latices and coating colors, the following test procedures were followed:
75 Gloss was meausured using a Gardner Glossmeter.
Brookfield viscosity values were obtained using Spindle ~2 at 20 rpm and/or 100 rpm as indicated.
Dry Strength values on paperboard were determined using an IGT
Dynamic Pick Tester or an AIC 2-5 Tester, the ink as indicated, a "B"
spring setting and 35 kg. load.
EXAMPLE I
Two latices were prepared using an interpolymer of 85% vinyl ace-tate, 15% ethylene, and 5 parts monoethyl maleate (35 milliequivalents - : ' . ' : , .. . .. . . . .
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,: ' ~ . ' . , " : , ' 9 ~2S;~i~3 51 per 100). To one of the interpolymers was added 0.~ parts diallyl mal-eate (6 milliequivalents per 100) in accordance wiih the teachings herein.
The Brookfield viscosity of the resultant latices ~50% solids) were recorded at varying pH ranges in order to test the alkali response of the latices. Viscosity values are shown in Table I.
TABLE I
Brookfield Viscosity (Latex) Parts DiallylPa.s (cPs.) Maleate pH 6.0 7.0 ~.0 9.0 0.4 0.06 2.000 20.150 60.000 -(60)(2000) (20,150)(60,000) 0 0.0612.000 67.000 (60)(12,000) (67,000) agglomerated ~ -As can be seen from the above results, the presence of the diallyl maleate served to substantially reduce the alkali sensitivity of the car-boxylated interpolymer latex. One set of colors (designated Group A) were prepared using 100 parts clay, 16 parts latex (dry resin weight), 0.3 parts carboxymethyl cellulose and 0.1 part tetrasodium pyrophosphate.
Another set ~Group B) were prepared from 100 parts clay, 5 parts latex, 7 parts ethylated starch co-binder and 0.1 part tetrasodium pyrophos-phate. In both sets, the resultant coating colors, which at 55% solids level had a pH of 8.0, were compounded using conventional techniques known in the art of paper coating such as are described by R. H. Mosher in "The Technology of Coated and Process Papers" (Chemical Publishing Company, Inc., New York, 1952).
In order to better illustrate the reduction in alkali sensitivity, Brookfield viscosity measurement of the coating colors were also made at pH 9.5.
The coating colors were then applied to the wire side of several : . ~ : . . ' . :, ::
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~2~6:23~1 sheets of 56.7 kg./278.7 m2 125 lb./3000 ft.2 bleached board to a final weight of 4.5 kg. (10 lb.) per 278~7 m.2 (3000 ft.2) square feet. The sheets were machine calendered by 1 pass at 77C (170F), 90.7 kg. per 2.54 cm. (200 lb. per linear inch) and then conditioned overnight before testing. The test results are shown in Table II.
TABLE II
pH 8 pH 9.5 Parts Brookfield Brookfield 75 Diallyl MaleateViscosity Viscosity Gloss IGT
Pa.s (cps.) Pa.s (cps.) (#5 Ink) 20 rpm100 rpm 20 rpm100 rpm Group A:
0.4 2.050 0.670 2.750 0.915 (20~0)(670) (2750)(915) 43 400 0 2.150 0.730 6.600 2.180 (2150)(730) (6600)(2180) 44 320 Group B:
0.4 2.650 0.940 2.750 0.990 (265Q)(940) (2750)(990) 52 215 0 2.700 0.970 4.150 1.550 (2700)(970) (4150)(1550) 53 95 As the above results show, the dry strength of the coating color ~as measured by IGT values) is substantially increased by the use of both the diallyl maleate and the monoethyl maleate.
EXAMPLE II
Another series of latices were prepared using an interpolymer of 70%
vinyl acetate, 30% ethylene and varying amounts of acrylic acid and dial-lyl maleate. In each case a small amount of sodium vinyl sulfonate (SVS) was also added as latex stabilizers. The Brookfield viscosity of the re-sultant latice (50% solids) of varying pH ranges and the coating strength of colors prepared with the corresponding latices are shown in Table III.
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TABLE III
pH (latex) Diallyl Acrylic Pa.s (crs.) IGT
Latex Maleate Acid SVS 7.0 8;0 9 0 #6 Ink A <0.100 0.100 0.100 - 0.75 O.S (<100) (100) (100) 230 B <0.100 0.100 0.100 0.35 0.75 0.5 (<100) (100) (100) 370 C <0.100 0.200 0.350 ~ 2.0 0.5 (<100) (200) (350) 310 D <0.100 0.100 0.200 0.35 2.0 0.5 (<100) (100) (200) 420 E 1.000 2.500 2.500 - 3cO 1.0 (1000) (2500) (2500) 330 F 0.200 0.350 0.400 0.35 3.0 1.0 (200) (350) (400) 480 G <0.100 <0.100 <0.100 - - 3.0 (<100) (<100) (<100) 190 H 0.35 - 3.0 not measured 250 (ConYersions to milliequivalents: 0.35 parts diallyl maleate = 5~4 meq., 0.75, 2.0 ml 3.0 parts acrylic acid = 10.4, 27.8 and 4.2 meq. respect-i vely . ~
As the above results show, the addition of acrylic acid and diallyl ma7eate substantially improves the coating strength of pigment binders while effectively suppressing the alkali response of the polymer latex.
Thus, a comparison of samples C and E shows that when the levels of car-boxyl functionality are increased, with an increase in IGT strength, the alkali response of the latex is also increased. Surprisingly, when the diallyl maleate is added (Samples D and F) the strength values are even further increased yet the alkali response is substantially reduced. As a control to illustrate the necessity of using carboxyl functionality, a sample (G) was prepared using high le~els of sodium vinyl sulfonate.
No substantial increase in wet strength was obtained thereby. Sample H
shows some increase as a result of the addition of the diallyl maleate.
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A conventionally employed acrylate paper coa-ting latex was tested as a control with the aforementioned series and found to give an IGT
strength value of 480 thus showing that the use of higher levels of carboxylic functionality will provide an ethylene vinyl acetate based paper coating binder comparable to those binders conventionally employ-ed in the industry.
When interpolymers are prepared using other vinyl esters, and/or triallyl cyanurate, triallyl isocyanurate, diallyl fumarate, divinyl benzene or diallyl phthalate and/or other carboxylating agents compar-able results will be obtained.
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BINDERS FOR PAPER COATINGS CONTAINING
CARBOXYLATED VINYL ESTER ETHYLENE INTERPOLYMERS
The present invention is directed to high strength pigment binders for paper coating having increased water retention and stability. The coating compositions comprise a synthe-tic polymer latex and pigment and may include other additives used in the art of pigmented paper coating.
The latex comprises a dispersed interpolymer of a vinyl ester, ethylene, a polyethylenically unsaturated comonomer and an ethylenically unsatur-ated mono- or dicarboxylic acid.
In the preparation of a coated paper web there is used a pigment, such as clay or the like, which is then compounded with a latex binder 1~ or adhesive material to produce a composition known in the art as a coating "color" for use in coating a cellulose web, e.g. a paper or paperboard web. Substantial quantities of the binder are used, and accordingly, the composition and characteristics of the binder are of great importance in determining the qualities of the finished coated web.
It has been recognized by the paper industry that increased dry strength properties may be provided to these latex binders by the in-clusion therein of carboxylate functionalities. There has however been difficu`lty encountered in providing carboxylic functionality in excess of about 2% by weight to vinyl ester containing latex polymer com-- . . , , -, : ~ ' . . ~ : . ,. -1~2S~
positions due to excessive alkaline swellabili-ty of the resultant latex particles. This swellability, in turn, produces unacceptable latex thickening at these pH values and consequent problems in the transport of such materials in conventional latex handling equipmert where vis-cosities less than about 1 Pa.s (1000 cps.) are generally employed.
It has now been found that substantially higher levels of carboxy-lation, with a synergistic improvement in coating strength, may be ach-ieved with reduction in alkaline swellability by incorporation in the interpolymer of one of a specific class of polyethylenically unsa-turat-ed comonomers.
The present invention provides a pigmented paper coating composi-tion comprising an aqueous synthetic polymer latex binder, pigment, and sufficient alkali to achieve a pH of 6 to 10, the latex comprising dis-persed therein an interpolymer which consists essentially of:
a~ a vinyl ester of an alkanoic acid having 1 to 13 carbon atoms interpolymerized with the following comonomers:
b) from 15 to 40% by weight ethylene, sufficient to achieve a Tg of 0 t~ -40C.;
c) from 2 to 15 milliequivalents per 100 grams (a) and (b) of a polyethylenically unsaturated comonomer selected from the group con-sisting of triallyl cyanurate, triallyl isocyanurate, diallyl maleate, diallyl fumarate, divinyl benzene, and diallyl phthalate;
d) from 25 to 65 milliequivalents per 100 grams (a) and (b) of an ethylenically unsaturated mono- or dicarboxylic acid or a half ester thereof characterized in that the alkali response of the polymer latex is substantially reduced wi-th respect to latices lacking component (c) , ,: : ,. : .
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while the coating strength of the resultant pigmented paper coa-ting is substantially improved thereover.
The vinyl ester monomers which may be utilized herein include the vinyl esters of alkanoic acids having from 1 to about 13 carbon atoms.
Typical examples include: vinyl formate, vinyl acetate, vinyl propion-ate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl 2-ethyl-hexanoate, vinyl isooctanoate, vinyl nonoate, vinyl decanoate, vinyl pivalate, vinyl versatate, etc. Of the foregoing, vinyl acetate is the preferred monorner because of its ready availability and low cost.
Generally, any ethylenically unsaturated mono or dicarboxylic acid may be used to provide the carboxyl functionality. Examples of suit-able acids include the monocarboxylic ethylenically unsaturated acids such as acrylic, vinyl acetic, crotonic, methacrylic, tiglic; the di-carboxylic ethylenically unsaturated acids such as maleic, fumaric, itaconic, maleic, citraconic, hydromuconic, allylmalonic; as ~ell as the corresponding half ester of those dicarboxylic acids, such as mono-(2-ethyl hexyl) maleate, monoethyl maleate, monobutyl maleate. Substan-tial improvements in strength are shown at levels of greater than 25 milliequivalents per 100 grams of the ethylene comonomer with amounts greater than 40 milliequivalents being preferred.
The resultant paper coating latex compositions are characterized by reduced alkali response and increased water retention in the latex state with improved properties of dry strength imparted to the final paper sheets coated therewith. Thus, while latex compositions prepared with levels of carboxylic functionality in excess of about 25 milliequi-valents per hundred and particularly in excess of about 40 milliequiva-lents per hundred will generally exhibit substantial increase in vis-~;~5~623 !!3 cosity a-t alkaline pH's, compositions prepared with 2 to 15, preferably 4 to 7, milliequivalents of polyethylenically unsaturated monomer per 100 part comonomer as taught herein exhibit little or no increase in vis-cosity under the same conditions. Moreover, in addition to the increase in coating strength which may be expected as a result of the increase in carboxyl functionali-ty, further increases in coating strength are observ-ed when the pigmented coating binders are prepared with the latices taught herein. It will be recognized by one skilled in the art tha-t the preferred level of polyethylenically unsaturated comonomer will vary pro-portionately depending upon the particular type and level of acid used.
To prepare the interpolymer latices used in the coating compositionsherein the vinyl ester, ethylene, the polyetnylenically unsaturated monomer and -the carboxylic acid are interpolymerized in an aqueous medium under pressures less than about 130 atmospheres in the presence of a catalyst, and an emulsion stabilizing amount of an anionic or a nonionic surfactant or mixtures thereof, the aqueous system being maintained by a suitable buffering agent, if necessary, at a pH of 2 to 6. The poly-merization is performed at conventional temperatures from about 21-107C
(70-225F), preferably from 49-79C (120-175F), for sufficient time to achieve a low monomer content, e.g. from 1 to about 8 hours, prefer-ably from 3 to about 7 hours, to produce a latex having less than 1.5 percent, preferably less than 0.5 weight percent, free monomer. Conven-tional batch, semi-continueous or continuous polymerization procedures may be employed and are taught, for example in U,S. Patents 3,708,388 issued Jan. 2, 1973 to M. K. Lindemann et al.; 3,404,112 issued Oct. 1, 1968 to M. K. Lindemann et al.; 3,71~,099 issued Jan. 30, 1973 to G. Biale; and 4,164,488 issued Aug. 14, 1979 to B. V. Gregorovich et al.
- . :
.
-.
.
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' : " ' - ' ' ' ' ' ~5~X3~3 The polymeriza-tion is initiated by a water soluble free radical in-itia-tor such as water soluble peracid or salt therof, e.g. hydrogen per-oxide, sodium peroxide, lithium peroxide, peracetic acid, persulfuric acid or the ammonium and alkali metal salts thereof, e.g. ammonium per-sulfate, sodium peracetate, lithium persulfate, potassium persulfate,sodium persulfate, etc. A suitable concentration of the initiator is from 0.05 to 5.0 weight percent and preferaby from 0.1 to 3 weiyht percent.
The free radical initiator can be used alone and thermally decompos-ed to release the free radical initiating species or can be used in com-bination with a suitable reducing agent in a redox couple. The reduc-ing agent is typically an oxidizable sulfur compound such as an alkali metal metabisulfite and pyrosulfite, e.g. sodium metabisulfite, sodium formaldehyde sulfoxalate, potassium metabisulfite, sodium pyrosulfite, etc. The amount of reducing agent which can be employed throughout the copolymerization generally varies from about 0.1 to 3 weight percent of the amount of polymer.
The emulsifying agent can be any of the nonionic or anionic oil-in-water surface active agents or mixtures thereof as are generally em-ployed in emulsion polymerization procedures. When combinations of emul-sifying agents are used, it is advantageous to use a relatively hydro-phobic emulsifying agent in combination with a relatively hydrophilic agent. The amount of emulsifying agent is generally from about 1 to about 10, preferably from about 2 to about 8, weight percent of the mono-mers used in the polymerization. Latex stabilizers such as sodium vinyl sufonate may also be present in amounts up to about 0.5% by weight. It will also be recognized that some portion of the carboxylic acid monomer may provide the stabilizing function in addition to the strength increase.
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The emulsifier usecl in the polymerizaton can also be added, in it entirety, -to the initial charge to the polymerization zone or a portion of the emulsifier, e.g. from 90 to 25 percent thereof, can be added continuously or intermittently during polymerization.
The preferred in-terpolymerization procedure is a modified batch process wherein the major amounts of some or all the comonomers and em-ulsifier are charged to -the reaction vessel after polymerization has been initiated. In this manner, control over the copolymerization of monomers having widely varied degrees of reactivity can be achieved.
It is preferred to add a small portion of the vinyl ester initially and -the remainder o-f the vinyl ester and other comonomers intermittently or continuously over the polymerization period which can be from 0.5 to about 10 hours, preferably frorn about 2 to about 6 hours.
The ethylene content of the interpolymer depends on the ethylene content of the aqueous polymerization medium. Factors which control ~he ethylene content of the polymerization medium include the partial pressure of ethylene in the vapor phase over the medium, the tempera-ture of polymerization and the degree of mixing between the vapor phase and the liquid medium. Generally, the polymerization is performed at temperatures from 49-79C l120-175F) and, at these temperatures, ethylene partial pressures from 345-6895 x 103 Pa (50-1,000 psig) preferably from 1724-5171 x 103 Pa (250-750 psig.) are sufficient to incorporate from 1 to 30, preferably from 5 to 25, weight percent -ethylene in the polymer. The reaction medium is preferably agitated with a stirrer, however, other agitation can be used as sparging the liquid with recirculated ethylene from the vapor phase. In the pre-ferred procedure, the ethylene partial pressures is maintained con-.' , . . . , ', .
'.' .', ;".:
:~L25~2 stant throughout the polymerization period so that this monomer is con-tinuously supplied at a constant rate.
The latices are produced and used at relatively high solids con-tents, e.g. between 35 and 70% although they may be diluted with water if desired. The preferred contents of solids are from 40 to 60, and, most preferred, from 50 to about 60 weight percent.
The particle size of the latex can be regulated by the quantity of non-ionic or anionic emulsifying agent or agents employed. To obtain smaller particles sizes, greater amounts of emulsifying agents are used.
As a general rule, the greater the amount of the emulsifying agent em-ployed, the smaller the average particle size.
The actual paper coating composition comprises the interpolymer latex together with pigment, such as clay and the usual paper coating additives which may include other cobinders, such as polyvinyl alcohol, protein, e.g. casein or soy protein, or starch, as is well known to those skilled in the art.
The pigment used in the papermaking compositions may be any of those conventionally employed. Generally, at least a portion of the pigment comprises clay and for this portion, any of the clays custom-arily used for coating paper, including the hydrous aluminum silicatesof kaolin group clays, hydrated silica clays, and the specific types of clays recommended in Chapters 10-16 of "Kaolin Clays and their Indus-trial Uses," by J. M. Huber Corp., New York, NY (1949). In addition to clay itself, there may be utilized other paper pigments such as, for example~ calcium carbonate, titanium dioxide, blanc fixe, lithopone, zinc sulfide, or other coating pigments including plastics, for example polystyrene, in various ratios, e.g. up to 50%, preferably up to 35%, , .
.. . . .
. ' ' , -. ' . ~ ~; ' , .
.
.
- . ' ~5i~233~
by weigh-t of the clay. Adclitionally, the composition may also contain other additives such as zinc oxide and/or a small amount oF a dispersing or stabilizing agent such as tetrasodium pyrophosphate. In general, the paper coating composition comprises 100 parts pigment containing 65-100 parts clay and 0-35 parts secondary pigment; 0.01-0.5 parts dispersing or stabilizing agent; 3-30 parts interpolymer latex (solids basis); 0-25 parts co-binder; 0-0.2 parts defoamer and sufficient water to provide the desired level of solids. The modification of the coating color using these materials will be within the knowledge of those skilled in the art.
The coating compositions produced herein may be applied to fibrous paper webs using any of the conventional coating devices including, but not limited to, those referred to as trailing blade coaters, air knife coaters, roll coaters and the like.
In the examples which follow all parts of polyethylenically unsat-urated comonomers and carboxylic acid are based on parts per 100 parts by weight of the combined vinyl ester and ethylene component. In test-ing the latices and coating colors, the following test procedures were followed:
75 Gloss was meausured using a Gardner Glossmeter.
Brookfield viscosity values were obtained using Spindle ~2 at 20 rpm and/or 100 rpm as indicated.
Dry Strength values on paperboard were determined using an IGT
Dynamic Pick Tester or an AIC 2-5 Tester, the ink as indicated, a "B"
spring setting and 35 kg. load.
EXAMPLE I
Two latices were prepared using an interpolymer of 85% vinyl ace-tate, 15% ethylene, and 5 parts monoethyl maleate (35 milliequivalents - : ' . ' : , .. . .. . . . .
: - . . : :
,: ' ~ . ' . , " : , ' 9 ~2S;~i~3 51 per 100). To one of the interpolymers was added 0.~ parts diallyl mal-eate (6 milliequivalents per 100) in accordance wiih the teachings herein.
The Brookfield viscosity of the resultant latices ~50% solids) were recorded at varying pH ranges in order to test the alkali response of the latices. Viscosity values are shown in Table I.
TABLE I
Brookfield Viscosity (Latex) Parts DiallylPa.s (cPs.) Maleate pH 6.0 7.0 ~.0 9.0 0.4 0.06 2.000 20.150 60.000 -(60)(2000) (20,150)(60,000) 0 0.0612.000 67.000 (60)(12,000) (67,000) agglomerated ~ -As can be seen from the above results, the presence of the diallyl maleate served to substantially reduce the alkali sensitivity of the car-boxylated interpolymer latex. One set of colors (designated Group A) were prepared using 100 parts clay, 16 parts latex (dry resin weight), 0.3 parts carboxymethyl cellulose and 0.1 part tetrasodium pyrophosphate.
Another set ~Group B) were prepared from 100 parts clay, 5 parts latex, 7 parts ethylated starch co-binder and 0.1 part tetrasodium pyrophos-phate. In both sets, the resultant coating colors, which at 55% solids level had a pH of 8.0, were compounded using conventional techniques known in the art of paper coating such as are described by R. H. Mosher in "The Technology of Coated and Process Papers" (Chemical Publishing Company, Inc., New York, 1952).
In order to better illustrate the reduction in alkali sensitivity, Brookfield viscosity measurement of the coating colors were also made at pH 9.5.
The coating colors were then applied to the wire side of several : . ~ : . . ' . :, ::
:. :.
, .
- . . . . . .
:
~2~6:23~1 sheets of 56.7 kg./278.7 m2 125 lb./3000 ft.2 bleached board to a final weight of 4.5 kg. (10 lb.) per 278~7 m.2 (3000 ft.2) square feet. The sheets were machine calendered by 1 pass at 77C (170F), 90.7 kg. per 2.54 cm. (200 lb. per linear inch) and then conditioned overnight before testing. The test results are shown in Table II.
TABLE II
pH 8 pH 9.5 Parts Brookfield Brookfield 75 Diallyl MaleateViscosity Viscosity Gloss IGT
Pa.s (cps.) Pa.s (cps.) (#5 Ink) 20 rpm100 rpm 20 rpm100 rpm Group A:
0.4 2.050 0.670 2.750 0.915 (20~0)(670) (2750)(915) 43 400 0 2.150 0.730 6.600 2.180 (2150)(730) (6600)(2180) 44 320 Group B:
0.4 2.650 0.940 2.750 0.990 (265Q)(940) (2750)(990) 52 215 0 2.700 0.970 4.150 1.550 (2700)(970) (4150)(1550) 53 95 As the above results show, the dry strength of the coating color ~as measured by IGT values) is substantially increased by the use of both the diallyl maleate and the monoethyl maleate.
EXAMPLE II
Another series of latices were prepared using an interpolymer of 70%
vinyl acetate, 30% ethylene and varying amounts of acrylic acid and dial-lyl maleate. In each case a small amount of sodium vinyl sulfonate (SVS) was also added as latex stabilizers. The Brookfield viscosity of the re-sultant latice (50% solids) of varying pH ranges and the coating strength of colors prepared with the corresponding latices are shown in Table III.
. . ;- , :: , ~ - . , . :
: . . . , , , : ~ .
, :- : ' :
5~;i2~
TABLE III
pH (latex) Diallyl Acrylic Pa.s (crs.) IGT
Latex Maleate Acid SVS 7.0 8;0 9 0 #6 Ink A <0.100 0.100 0.100 - 0.75 O.S (<100) (100) (100) 230 B <0.100 0.100 0.100 0.35 0.75 0.5 (<100) (100) (100) 370 C <0.100 0.200 0.350 ~ 2.0 0.5 (<100) (200) (350) 310 D <0.100 0.100 0.200 0.35 2.0 0.5 (<100) (100) (200) 420 E 1.000 2.500 2.500 - 3cO 1.0 (1000) (2500) (2500) 330 F 0.200 0.350 0.400 0.35 3.0 1.0 (200) (350) (400) 480 G <0.100 <0.100 <0.100 - - 3.0 (<100) (<100) (<100) 190 H 0.35 - 3.0 not measured 250 (ConYersions to milliequivalents: 0.35 parts diallyl maleate = 5~4 meq., 0.75, 2.0 ml 3.0 parts acrylic acid = 10.4, 27.8 and 4.2 meq. respect-i vely . ~
As the above results show, the addition of acrylic acid and diallyl ma7eate substantially improves the coating strength of pigment binders while effectively suppressing the alkali response of the polymer latex.
Thus, a comparison of samples C and E shows that when the levels of car-boxyl functionality are increased, with an increase in IGT strength, the alkali response of the latex is also increased. Surprisingly, when the diallyl maleate is added (Samples D and F) the strength values are even further increased yet the alkali response is substantially reduced. As a control to illustrate the necessity of using carboxyl functionality, a sample (G) was prepared using high le~els of sodium vinyl sulfonate.
No substantial increase in wet strength was obtained thereby. Sample H
shows some increase as a result of the addition of the diallyl maleate.
~- ~ . .. . . .
... . : :~ - . .
. - .
: - ,, . , .:
. ~ ..
.
~25623~
A conventionally employed acrylate paper coa-ting latex was tested as a control with the aforementioned series and found to give an IGT
strength value of 480 thus showing that the use of higher levels of carboxylic functionality will provide an ethylene vinyl acetate based paper coating binder comparable to those binders conventionally employ-ed in the industry.
When interpolymers are prepared using other vinyl esters, and/or triallyl cyanurate, triallyl isocyanurate, diallyl fumarate, divinyl benzene or diallyl phthalate and/or other carboxylating agents compar-able results will be obtained.
: ....
.
Claims (10)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An aqueous pigmented paper coating composition, comprising an aqueous synthetic polymer latex binder, pigment, and sufficient alkali to achieve a pH of 6 to 10, the latex comprising dispersed therein an interpolymer which consists essentially of:
a) a vinyl ester of an alkanoic acid having 1 to 13 carbon atoms interpolymerized with the following comonomers:
b) from 15 to 40% by weight ethylene, sufficient to achieve a Tg of 0 to -40°C;
c) from 2 to 15 milliequivalents per 100 grams (a) and (b) of a polyethylenically unsaturated comonomer selected from the group con-sisting of triallyl cyanurate, triallyl isocyanurate, diallyl maleate, diallyl fumarate, divinyl benzene and diallyl phthalate; and d) from 25 to 65 milliequivalents per 100 grams (a) and (b) of an ethylenically unsaturated mono- or dicarboxylic acid or a half ester thereof characterized in that the alkali response of the polymer latex is substantially reduced with respect to latices lacking component (c) while the coating strength of the resultant pigmented paper coating is substantially improved thereover.
a) a vinyl ester of an alkanoic acid having 1 to 13 carbon atoms interpolymerized with the following comonomers:
b) from 15 to 40% by weight ethylene, sufficient to achieve a Tg of 0 to -40°C;
c) from 2 to 15 milliequivalents per 100 grams (a) and (b) of a polyethylenically unsaturated comonomer selected from the group con-sisting of triallyl cyanurate, triallyl isocyanurate, diallyl maleate, diallyl fumarate, divinyl benzene and diallyl phthalate; and d) from 25 to 65 milliequivalents per 100 grams (a) and (b) of an ethylenically unsaturated mono- or dicarboxylic acid or a half ester thereof characterized in that the alkali response of the polymer latex is substantially reduced with respect to latices lacking component (c) while the coating strength of the resultant pigmented paper coating is substantially improved thereover.
2. The composition of Claim 1, wherein the carboxylic acid component is selected from the group consisting of acrylic acid, vinyl acetic acid, crotonic acid, methacrylic acid, tiglic acid, maleic acid, fumaric acid, itaconic acid, maleic acid, citraconic acid, hydromusonic acid, allyl-malonic acid, mono(2-ethylhexyl) maleate, monoethyl maleate and mono-butyl maleate and wherein the vinyl ester is selected from the group consisting of vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl 2-ethylhexanoate, vinyl isooctanoate, vinyl nonate, vinyl decanoate, vinyl pivalate and vinyl versatate.
3. The composition of Claim 2, wherein the carboxylic acid component is monoethyl maleate.
4. The composition of Claim 2, wherein the vinyl ester is vinyl acetate.
5. The composition of Claim 1, wherein the polyethylenically unsaturat-ed comonomer is diallyl maleate.
6. The composition of Claim 1, wherein the polyethylenically unsaturat-ed comonomer is present in an amount of 4 to 7 milliequivalents per 100 grams (a) and (b).
7. The composition of Claim 1, wherein the mono- or dicarboxylic acid is present in amounts of 40 to 65 milliequivalents per 100 grams (a) and (b).
8. The composition of Claim 1, wherein the coating comprises 100 parts of the pigment, 0.01-0.5 parts dispersing agent, 3-30 parts (solids) latex, 0-25 parts co-binder, 0-0.2 parts defoamer and sufficient water to obtain a solids level of 35 to 70 weight percent.
9. A fibrous web coated with the aqueous pigmented paper coating com-position of Claim 1, the coating being that deposited upon the evapora-tion of water from the aqueous coating composition applied to the web.
10. The fibrous web of Claim 9, wherein the coating composition has a solids content of 35 to 70% and the latex is present, on a latex solids basis, in the amount of 3 to 30 parts by weight per 100 parts of the pigment.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US58005584A | 1984-02-14 | 1984-02-14 | |
| US580,055 | 1984-02-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1256238A true CA1256238A (en) | 1989-06-20 |
Family
ID=24319474
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000472300A Expired CA1256238A (en) | 1984-02-14 | 1985-01-17 | High strength pigment binders for paper coatings containing carboxylated vinyl ester ethylene interpolymers |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS60185893A (en) |
| CA (1) | CA1256238A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20120021237A1 (en) * | 2010-07-20 | 2012-01-26 | Celanese International Corporation | Vinyl ester/ethylene-based binders for paper and paperboard coatings |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2543452C3 (en) * | 1975-09-29 | 1980-06-12 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Venting device for ink supply systems of inkjet writing devices |
| JPS542409A (en) * | 1977-06-01 | 1979-01-10 | Dainippon Ink & Chemicals | Composition for paper coating |
-
1985
- 1985-01-17 CA CA000472300A patent/CA1256238A/en not_active Expired
- 1985-01-28 JP JP1274385A patent/JPS60185893A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60185893A (en) | 1985-09-21 |
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