HETEROGENEOUS POLYMERS AND LATICES

Abstract: Latices useful in paper coating compositions contain heterogeneous polymeric particles comprising polymers based on e.g. styrene and e.g. butadiene, comprise in one domain about 1 to about 20 weight % of an alkenyl nitrile. The latices may be used to provide reasonable stiffness and en­ hance pick resistance.

Description: The present invention relates to latices of heterogeneous polymeric particles. Particles of such polymers may have clear and distinct zones of differing polymer structure as in the case of core/shell particles, or particles with an incomplete shell (continents). In some cases there is no distinct sharp dividing line between one polymeric structure and another; rather, there is a continuous gradual change in polymer composition between two loci on a polymeric particle. It is believed that such gradual change may occur for a number of reasons such as the solubility of monomers in a polymeric particle, or the gradual change in the composition of a monomer increment over time such as going from a high to low styrene content. In recent years there have been a number of patents directed to latices of heterogeneous polymeric particles. Such polymers have the potential to be tailored to specific end uses. It has been found that latices of polymers having substantially similar bulk compositions may behave in different manners depending upon the structure within the polymer particle. Belgium Patent 893,722 issued Jan. 3, 1983 in the names of A.R. Sinclair and E.H. Gleason assigned to Polysar International S.A., discloses a latex of a structured particle having a core of about 60 to 40% by volume of the particles comprising 55 to 65 parts by weight of a monovinylaromatic monomer; 45 to 35 parts by weight of a diolefin; 0.5 to 5 parts by weight of an ethylenically unsaturated acid, and 0.5 to 5 parts by weight of a primary amide or N-methylolacrylamide; and a shell comprising 40 to 60% by volume of the particles comprising 75 to 85 parts by weight of a monovinylaromatic monomer, 25 to 15 parts by weight of a conjugated diolefin, 0.5 to 5 parts by weight of an ethylenically unsaturated carboxylic acid and 0.5 to 5 parts by weight of a primary amide or N-methylolacrylamide. Papers coated with such latices have an improved gloss and pick. European Patent Application 0 040,419 in the name of D.I. Lee and T. Mundorf, assigned to The Dow Chemical Company published 25.11.81, also discloses latex of structured polymeric particles. The particles comprise from 20 to 45 parts by weight of a soft domain comprising 25 to 65 weight percent of a monovinylidene aromatic monomer, and from 75 to 35 weight percent of a conjugated diolefin; and from 55 to 80 parts by weight of a hard interpolymer comprising from 70 to 90 weight percent of a monovinylidene aromatic monomer and from 10 to 30 weight % of an aliphatic diene monomer. U.S. Patent 4,134,872 issued Jan. 16, 1979 in the name of D.I. Lee assigned to the Dow Chemical Company, discloses a similar type of structured polymeric particle except that both the core and the shell contain carboxylic acid monomers. Rohm and Haas Company have patents covering multi-component structured polymers. Much of this work is directed to polymers consisting mainly of acrylic acid or acrylate esters. Minor components in such systems include grafting agents such as alkyl esters of a,b-ethylenically unsaturated acids, active crosslinking agents such as glycols, or amides, and latent crosslinking agents such as carboxylic acids. Canadian Patent 916,340 issued Dec. 5, 1972 and United States Patent 4,107,120 issued Aug. 15, 1978 are representative of such art. Rhone-Poulenc Industries have patents to latices of grafted copolymer latices for use in the manufacture of non-wovens. The novel component in the Rhone-Poulenc patent is bis(2-chloroethyl) vinylphosphonate. European Patents 52,562 and 52,561 are representative of this Art. Japanese patent specification JP-A-6045696 relates to latices of polymeric particles, with an alkenyl-nitrile fraction. Those latices are heterogeneous, i.e. there is a core and a surface layer. British patent application specification GB-A 2101615 discloses a latex of heterogeneous polymeric particles with a first domain and a second domain, but without an alkenyl-nitrile fraction. None of the above art contemplates using alkenyl nitriles as a monomer. In the present invention the second domain contains e.g. 1 to 20% of an alkenyl nitrile. Paper manufacturers are seeking a latex binder which will provide a good balance of properties including good wet and dry pick, and acceptable paper stiffness at a low price. Unfortunately, these desiderata place conflicting demands on the latex manufacturer. To improve stiffness and gloss requires an increase in the so-called hard monomers with a resulting decrease in the soft monomers which give binding and pick properties. At best the latex manufacturer tries to achieve a balance of properties. Latices used in paper coating generally comprise a "hard" monomer and a "soft" monomer. Properties such as gloss and stiffness are attributed to the hard monomers and obtained at the expense of properties associated with soft polymers such as wet and dry pick. It is desirable to provide a polymer which provides a better balance of properties in a paper coating. The present invention provides a latex comprising 30 to 65 weight % of heterogeneous particles comprising: (A) 25 to 75 weight % of a first domain formed by emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (B) 75 to 25 weight % of a second domain formed by emulsion polymerization of a monomeric mixture having a bulk composition comprising (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or a C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and characterised by (v) the second domain comprises 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms. The present invention also provides a free radical emulsion polymerization process which comprises polymerizing an initial portion of the total monomers and subsequently polymerizing an increment portion of the total monomers wherein said initial portion comprises (A) 25 to 75 weight % of the total monomers used and comprises: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl radical or a C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or a C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and said increment comprises (B) 75 to 25 weight % of the total monomers used and comprises (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl radical or a C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and characterised by (v) 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms. The present invention also provides a method of manufacturing coated paper, characterised by the paper is coated with a composition comprising per 100 parts by weight of a pigment 5 to 25 parts by weight of polymeric solids of a latex, said latex comprising a latex as above. The present invention also provides a heterogeneous polymer characterised by (A) 25 to 75 weight % of a first domain formed by the emulsion polymerization of a monomeric mixture having a bulk composition comprising (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; and (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and 75 to 25 weight % of a second domain formed by the emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (v) 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms. As used in the description and claims the term domain refers to an area of the heterogeneous polymer particle polymerized from a monomer emulsion having a composition significantly different from the monomer emulsion(s) polymerized to form other domain(s) in the heterogeneous particle. As noted earlier in the description there may be instances where there is no clear dividing line between the polymeric compositions of one domain and another domain. Rather, there is a gradual transition in polymer composition from one domain to another. It is intended that the term be applicable to this situation as well as those where there is a relatively clear division such as a core/shell or continent situation. In the latex of the present invention the particles comprise 25 to 75% by weight of a first domain and 75 to 25% by weight of a second domain. Preferably the weight ratio of first domain to second domain ranges from 35:65 to 65:35, most preferably from about 40:60 to about 60:40. The first domain is formed by the emulsion polymerization of a monomeric mixture comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl radical or a C₁₋₄ alkanol radical, or a chlorine or bromine atom. (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin. (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acid; and (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical. Preferably the vinylaromatic monomer is present in the emulsion forming the first domain in an amount from 45 to 60 weight %. Preferably the conjugated diolefin is present in the emulsion forming the first domain in an amount from 35 to 55 weight %. Preferably the acid, aldehyde or ester monomer or monomer combination is present in the emulsion forming the first domain in an amount from 0.5 to 5 weight %. It should be noted that this weight % range may consist of an acid, aldehydes, or ester individually or a mixed blend such as acids-aldehydes, acids-esters, aldehydes-esters, or a blend of acids-aldehydes-esters. The amide is optionally present in the emulsion forming the first domain. It may, however, be used in amounts up to 10 weight %. If present, the amide is preferably used in an amount from 2 to 5 weight %. Vinylaromatic monomers are well known to those skilled in the art, e.g. styrene, a-methylstyrene, p-methylstyrene, chlorostyrene, bromostyrene, vinyl toluene, allyl toluene, divinyl benzene, vinyl pyridine, vinylnaphthalene, and t-butylstyrene. The most common monomers in this class are styrene, a-methylstyrene, p-methylstyrene, chlorostyrene, and bromostyrene. Some conjugated diolefins are butadiene, pentadiene, isoprene, hexadiene, heptadiene, octadiene, and nonadiene. The preferred diolefins are butadiene and isoprene. The acid, aldehyde and ester monomers are well known in the art. Some acid monomers are acrylic acid, methacrylic acid, butenoic acid, vinylacetic acid, fumaric acid, pentanoic acid, allylacetic acid, mesaconic acid, citraconic acid, vinyl acrylic acid, hexenoic acid, heptenoic acid, itaconic acid, octanoic acid, nonenoic acid and cinnamic acid. The ester monomers may be C₁₋₈ alkyl or alkanol derivatives of such acids and include lower alkyl acrylates and methacrylates such as butylacrylate and butylmethacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, ethylhexyl acrylate and ethylhexyl methacrylate. Some aldehydes are acrolein, methacrolein, pentenal, B-methylcrotonaldehyde, hexenal, isopropylacrolein, heptanal, octenal, ethyl-hexenal, and nonenal. The most common of the above monomers are acrylic, methacrylic, fumaric, itaconic and cinnamic acids, and their lower alkyl or alkanol esters, and acrolein, methacrolein, and cinnamaldehyde. If present the amide may be selected from e.g. acrylamide, methacrylamide, vinylacetamide, N-methyl methacrylamide, N-isopropyl acrylamide, N-methylol acrylamide, and N-methylol methacrylamide. Preferred amides are acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide. In the second domain the vinylaromatic monomers, the conjugated diolefin monomers, the acid, aldehyde, and ester monomers and the amide monomer, if present, may be selected from the same groups of monomers as those for the monomers of the first domain. This does not mean that it is necessary to use the same vinylaromatic monomer, diolefin monomer, acid, aldehyde, ester monomer and amide monomer (if present) in the first and second domain. In fact, it may be desirable to use different monomers within the same broad generic class in the first and second domain. This is particularly true for the functional monomers such as the acid, aldehyde, ester and amide monomers. This is also applicable to the diolefin monomers and the vinylaromatic monomers. For example, a first domain could contain divinyl benzene and butadiene and the second domain could contain p-methyl styrene and isoprene. In the second domain, the amide monomer is optional as in the first domain. The second domain contains, in addition to the foregoing monomers, an alkenylnitrile containing up to 6 carbon atoms. Some nitriles are acrylonitrile, butene nitrile, and pentene nitrile. The preferred nitrile is acrylonitrile. The ratio of the various monomers used in the second domain differs from the ratio of the monomers used in the first domain. The second domain comprises 75 to 25 weight %, preferably 60 to 40 weight % of the heterogeneous polymeric particles. The second domain is formed by polymerizing a monomeric mixture comprising (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer as described above; (ii) 25 to 40 weight % of a C₄₋₉ conjugated diolefin as described above; (iii) 0.5 to 10 weight % of the above described acid, aldehyde, and ester monomers; (iv) 0 to 20 weight % of the above described amides; and (v) 1 to 20 weight % of an alkenyl-nitrile containing up to 6 carbon atoms. Preferably the vinylaromatic monomer is present in the monomer emulsion forming the second domain in an amount from 45 to 60 weight %. Preferably the conjugated diolefin is present in the monomer emulsion forming the second domain in an amount from 30 to 40 weight %. Preferably the acid, aldehyde, ketone monomer is present in the monomer composition forming the second domain in an amount from 0.5 to 5 weight %. Preferably the amide is present in the monomer emulsion forming the second domain in an amount from 0.5 to 5 weight %. The alkenyl nitrile is present in the emulsion forming the second domain in an amount 1 to 20 weight %, preferably it is used in amounts 1 to 10 weight %; most preferably 3 to 8 weight %. The latices of the present invention may be prepared using conventional techniques and reagents for an emulsion polymerization system. The monomer emulsion may be stabilized with anionic or nonionic emulsifier, or a mixture of both. The polymerization may be initiated chemically by an initiation system or by heating the emulsion to the decomposition point of a free radical generating catalyst. The free radical catalyst may be a peroxide catalyst such as t-butyl peroxide, hydrogen peroxide, cumene hydroperoxide, or it may be a persulfate catalyst. The catalyst should be water soluble and is generally used in an amount 0.05 to 5 weight % based on the total monomers. The emulsion may contain 0.05 to 5 weight % of known chain transfer agents e.g. carbon tetrachloride or t-dodecyl mercaptan. Additionally, small amounts of electrolyte may be included in the emulsion. The techniques for emulsion polymerization are well known in the art and are generally disclosed in a number of texts including Synthetic Rubber, edited by G.S. Whitby, John Wiley & Sons Inc., New York, 1954; High Polymer Latices, D.C. Blackley, Maclaren & Sons Ltd., London, 1966; and Emulsion Polymerization, I. Piitma, Academic Press, 1982. It is generally preferred to conduct the polymerization without stopping the reaction between the addition of the emulsions forming the first and second domains. In this way the catalyst in the emulsion forming the first domain is also used in the polymerization of the second domain. It may be desirable to add small amounts of additional catalyst to the emulsion forming the second domain, usually not more than 1.5 parts by weight per 100 parts by weight of monomers. There are a number of processes which may be used to prepare heterogeneous polymers formed from monomer emulsions having different compositions. A seed process could be used where the seed is polymerized first and forms the first domain and the second domain is polymerized in the presence of the seed. The first and second domain could be polymerized by a batch process. It is also possible to use an incremental process where a small portion of an emulsion is polymerized and then an incremental monomer composition which may be a fixed or changing composition is added during the polymerization. The first or the second domain or both could be prepared by such a process. If desired the increment composition could be changed during polymerization to provide a heterogeneous polymer particle using a variable feed process. In the process the emulsion forming the first domain may be polymerized to completion prior to the addition of the emulsion forming the second domain. It may be desirable to start the addition of monomer emulsion forming the second domain at less than substantially complete conversion of the monomer mixture forming the first domain. For example, the addition of the emulsion forming the second domain may be added at about 60% or e.g. 75 to 90% conversion of the monomer emulsion forming the first domain. The emulsion is usually polymerized to a desired solids level, e.g. 50 to 55%, but may, if required be subsequently concentrated to a higher solids level. Conventional biocides may be added to the latex to prevent the growth of bacteria in the latex prior to its use. While the inventors were primarily interested in the application of latex in the commercial field, it must be recognized that the latex may be subject to conventional coagulation and drying procedures to produce a polymer comprising 25 to 75 weight % of first domain formed by the emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or alkanol radical or a chlorine or bromine atom, (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; and (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and 75 to 25 weight % of a second domain formed by the emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 45 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from , C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or alkanol esters of said acids, (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or a C₁₋₄ alkyl or alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (v) 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms. When the latex is used in conventional applications, it is useful in the art of coating paper. In coating paper the latex is compounded with fillers and other conventional additives such as co-binders and water retention aids. The paper coating compound may contain an additional dispersant, compatible with the latex, to disperse the filler. The weight ratio of filler to polymeric solids in the latex is usually in the range 100:25 to about 100:10 but may range as low as 100:5. Paper stock is then coated with the resulting compound and dried and callandered to produce a product having acceptable gloss and stiffness with enhanced pick resistance. The following examples are intended to illustrate the scope of the invention and are not intended as limiting. In the examples, "parts" refers to parts by weight. Experimental Latex A was prepared by the incremental polymerization of the following monomeric compositions: Monomer composition of the initial domain: Styrene 60 parts Butadiene 37.5 parts C₅ ethylenically unsaturated acids 2.5 parts After substantial polymerization of the initial domain an equal monomeric increment was added comprising: Styrene 52.0 parts Butadiene 31.5 parts A mixture of C₃ and C₅ ethylenically unsaturated acids 3.5 parts N-methylolacrylamide 5 parts Acrylonitrile 8 parts The resulting latex was stripped of residual monomer. Experimental Latex B was prepared by the incremental polymerization of the following monomer compositions: Monomer composition of the initial domain: Styrene 47.8 parts Butadiene 46.7 parts C₅ ethylenically unsaturated acid 3.1 parts N-methylolacrylamide 3.0 parts After substantial polymerization of the heel an equal monomeric increment was added comprising: Styrene 52.0 parts Butadiene 33.5 parts A mixture of C₃ and C₅ ethylenically unsaturated acids 2.9 parts N-methylolacrylamide 3.0 pacts Acrylonitrile 8.0 parts The resulting latex was then stripped of residual monomer. Latex A and B and a number of commercial available latices were compounded to provide a paper coating formula. The compound comprised: SPS Clay 100 parts Latex 10 parts Dispersant (Dispex-N-40) .25 part Thickener 1 part Caustic soda .18 part The compound was adjusted to 59% solids and a pH of 8. The paper was coated at 12 g of compound/m² using a hand coater. "Provincial" type paper was used as a base paper for binding power. The coated paper was dried at 130°C for 60 seconds and conditioned overnight at 23°C, 50% relative humidity. The sheets were callandered twice on each side at 60°C and 3000 kgf. The sheets were then conditioned an additional 4 hours. In the tests the gloss was measured on a Gardner PG 500 glossmeter. The brightness was measured on an Elrepho reflectance photometer. Ink absorbency was measured using a K & N test. Wet and dry pick were measured using 3804 Lorilleux Ink at 300 cm/sec. and 30 cm/sec. using an AlC₂ pick tester. The paper stiffness was measured using a Kodak Pathe Lester and a dynamic test (AFNOR NF 00 3025). 10 strips 150 mm long and 15 mm wide were tested in the direction of coating. The results of the testing are set forth in the Table below. As a comparison a series of commercially available latices suitable for use in paper coating compositions were compounded in the same formulation and tested in the same manner. The results are recorded in the Table below. Latex A B PL928 PL1212 Acrylate Latex (Acronal 320D) Gloss 75.6 72.3 74.7 78.1 75.8 K & N 12.9 13.2 12.4 15.3 17 Dry Pick 3804-300 174 128 210 93 93 Wet Pick 3804-30 1.37 1.30 .98 1.31 1.13

Claims: A latex comprising 30 to 65 weight % of heterogeneous particles comprising: (A) 25 to 75 weight % of a first domain formed by emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (B) 75 to 25 weight % of a second domain formed by emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or a C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and characterised by (v) the second domain comprises 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms, A latex according to claim 1, characterised by the first domain is 40 to 60 weight % and is formed by the emulsion polymerization of a monomeric mixture comprising (i) 45 to 60 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a bromine or chlorine atom; (ii) 35 to 55 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 5 weight % of at least one C₃₋₉ ethylenically unsaturated carboxylic acid; and (iv) 0 to 5 weight % of an amide of the formula wherein R is an alkenyl radical of up to 9 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical. A latex according to claim 2, characterised by the second domain is 60 to 40 weight % and is formed by the emulsion polymerization of a monomeric mixture comprising: (i) 40 to 60 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 40 weight % of a conjugated diolefin; (iii) 0.5 to 5 weight % of at least one C₃₋₉ ethylenically unsaturated acid; (iv) 0.5 to 5 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (v) 3 to 8 weight % of an alkenyl nitrile containing up to 6 carbon atoms. A latex according to claim 3, characterised by for the first and second domains: (i) said vinylaromatic monomer is selected from styrene, a-methyl styrene, p-methyl styrene, chlorostyrene, and bromostyrene; (ii) said conjugated diolefin is selected from 1,3-butadiene and isoprene; (iii) said ethylenically unsaturated acid is selected from acrylic acid, methacrylic acid, fumaric acid, and itaconic acid; and in said second domain (iv) said amide is selected from acrylamide, methacrylamide, N-methylolacrylamide and N-methylol methacrylamide; and (v) said nitrile is acrylonitrile. A free radical emulsion polymerization process comprising polymerising an initial portion of the total monomers and subsequently polymerizing an increment portion of the total monomers wherein said initial portion comprises (A) 25 to 75 weight % of the total monomers used and comprises: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl radical or a C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, a C₁₋₄ alkyl or a C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and said increment comprises (B) 75 to 25 weight % of the total monomers used and comprises (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl radical; a C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and characterised by (v) 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms. A process according to claim 5, characterised by said initial portion comprises 40 to 60 weight % of said total monomers used and comprises (i) 45 to 60 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a bromine or chlorine atom; (ii) 35 to 55 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 5 weight % of at least one C₃₋₉ ethylenically unsaturated carboxylic acid; and (iv) 0 to 5 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, or a C₁₋₄ alkyl or alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical. A process according to claim 6, characterised by said increment comprises 60 to 40 weight % of the total monomers used and comprises (i) 45 to 60 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 40 weight % of a conjugated diolefin; (iii) 0.5 to 5 weight % of at least one C₃₋₉ ethylenically unsaturated acid; (iv) 0.5 to 5 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (v) 3 to 8 weight % of an alkenyl nitrile containing up to 6 carbon atoms. A process according to claim 7, characterised by for said initial portion and said increment: (i) said vinylaromatic monomer is selected from styrene, a-methyl styrene, p-methyl styrene, chlorostyrene, and bromostyrene; (ii) said conjugated diolefin is selected from 1,3-butadiene, and isoprene; (iii) said ethylenically unsaturated acid is selected from acrylic acid, methacrylic acid, fumaric acid, and itaconic acid; and in said increment (iv) said amide is selected from acrylamide, methacrylamide, N-methylol-acrylamide, and N-methylol methacrylamide; and (v) said nitrile is acrylonitrile. A method of manufacturing coated paper, characterised by the paper is coated with a composition comprising per 100 parts by weight of a pigment 5 to 25 parts by weight of polymeric solids of a latex, said latex comprising a latex according to claim 1. A heterogeneous polymer, characterised by (A) 25 to 75 weight % of a first domain formed by emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 30 to 50 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of at least one member selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids; and (iv) 0 to 10 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen, a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (B) 75 to 25 weight % of a second domain formed by the emulsion polymerization of a monomeric mixture having a bulk composition comprising: (i) 40 to 70 weight % of a C₈₋₁₂ vinylaromatic monomer which may be unsubstituted or substituted by a C₁₋₄ alkyl or C₁₋₄ alkanol radical, or a chlorine or bromine atom; (ii) 25 to 40 weight % of a C₄₋₉ aliphatic conjugated diolefin; (iii) 0.5 to 10 weight % of one or more members selected from C₃₋₉ ethylenically unsaturated carboxylic acids, C₃₋₉ ethylenically unsaturated aldehydes, and C₁₋₈ alkyl or C₁₋₈ alkanol esters of said acids, (iv) 0 to 20 weight % of an amide of the formula wherein R is an alkenyl radical of up to 7 carbon atoms, R₁ is hydrogen or a C₁₋₄ alkyl or C₁₋₄ alkanol radical, and R₂ is hydrogen or a C₁₋₄ alkyl radical; and (v) 1 to 20 weight % of an alkenyl nitrile containing up to 6 carbon atoms.

Inventors: BLANPAIN, PETER RONALD JEFFREY, DEQUATRE, CLAUDE, LONGUET, MICHEL
Applicants: BASF AKTIENGESELLSCHAFT, POLYSAR FINANCIAL SERVICES S.A.
Application year: 1986
Main classification: C08F257
IPC codes: C08L25, C08F279, C08F257, C08F2, D21H19