Equil EX2009
`Akamai Techs. v. Equil IP Holdings
`IPR2023-00332
`
`

`

`5,902,846
`
`1
`HIGH-PERFORMANCE OVERPRINT
`VARNISHES COMPRISING COMPOSITE
`SMA LATICES
`
`BACKGROUND OF THE INVENTION
`
`1. Technical Field of the Invention
`
`The present invention relates to novel overprint varnishes,
`and, more especially,
`to high-performance overprint var-
`nishes comprising composite latices prepared by polymer-
`izing at least one hydrophobic monomer within a matrix
`solution/dispersion of a particular styrene/maleic anhydride
`(SMA)resin.
`By “overprint varnishes” are intended surface-
`improvementprotective compositions designed to impart to
`treated surfaces, for example printed or unprinted papers and
`cardboards, enhanced resistance to external agents and
`influences, and,in particular, enhancedresistance tofriction,
`moisture, and temperature, and even an improved
`appearance, for example improved glossiness.
`2. Description of the Prior Art
`Conventional overprint varnishes comprise aqueous com-
`positions based on composite latices of the styrene/acrylate
`polymer-styrene/maleic anhydride resin type.
`Thus, EP-A-675,177 (Goodrich) describes shell/core lati-
`ces prepared via the polymerization of mixtures of hydro-
`phobic monomers, such as butyl methacrylate, 2-ethylhexyl
`acrylate, and styrene in an aqueous styrene/maleic anhydride
`resin solution, this resin being rendered soluble bysalifica-
`tion with a volatile nitrogenous base such as ammonia.
`
`SUMMARYOF THE INVENTION
`
`It has now unexpectedly and surprisingly been determined
`that especially high-performance overprint varnishes could
`be formulated from related composite latices exhibiting the
`following properties/characteristics:
`(a) the styrene/maleic anhydride resin has a low molecular
`weight ranging from 500 to 5,000 and an acid number
`of at most 500;
`(b) the amount by weightof this styrene/maleic anhydride
`resin in the resin/hydrophobic monomer copolymer
`mixture ranges from 5% to 50%; and
`(c) the glass transition temperature of the hydrophobic
`monomer copolymersis less than 30° C.
`
`DETAILED DESCRIPTION OF BEST MODE
`AND SPECIFIC/PREFERRED EMBODIMENTS
`OF THE INVENTION
`
`Moreparticularly according to the present invention, the
`subject composite latices are prepared via conventional
`technique which entails providing a styrene/maleic anhy-
`dride resin solution by hot or warm dissolution of the resin
`in water,
`in the presence of ammonia or of a volatile
`nitrogenous base, then in dispersing therein the mixture of
`hydrophobic monomers, the free-radical polymerization of
`which is next carried out conventionally in the presence of
`water-soluble initiators, such as ammonium, potassium, or
`sodium persulfate, or in the presence of hydrogen peroxide
`and oxidation/reduction catalysts. The polymerization tem-
`perature advantageously ranges from 40° to 90° C., and
`preferably from 65° to 85° C. The solids concentration
`advantageously ranges from 20% to 60%. The polymeriza-
`tion may be carried out per a process utilizing a sealed
`reaction vessel, or semi-continuously. In the first event, the
`monomer and the initiator are added intheir totality to the
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`oligomer solution at the beginning of polymerization, and
`the temperature of the reaction medium is maintained con-
`stant and stirring continues for a period of from 2 to 4 hours
`In the second event, two dosing pumps permit the continu-
`ous addition, first, of the monomer mixture and, second, of
`the initiator solution to the polymer solution maintained at
`constant temperature whilestirring continuously. The mono-
`mers and the initiator are added over a time period of from
`30 minutes to 4 hours, depending on the quantity and nature
`of the monomers to be added. At the end of the pouring
`operations, the reaction medium is maintained at constant
`temperature and stirred continuously for a period of time of
`up to 4 hours.
`The styrene/maleic anhydride resin may advantageously
`be partially esterified with a linear or branched hydrocarbyl
`alcohol having a hydrocarbon-containing chain incorporat-
`ing from one carbon (methanol) to 18 carbon atoms, or with
`mixtures of such alcohols.
`
`The hydrophobic monomers are polymerized because of
`the presence of sites of ethylenic or acrylic unsaturation
`within their molecular structure. Particularly exemplary
`such monomers according to the invention include styrene
`and derivatives thereof and (meth)acrylic esters. These
`monomers may be used either alone or in admixture to
`prepare a copolymer having the desired glass transition
`temperature. Adjustmentof the glass transition temperature
`is a technique well known to this art. The qualification
`“hydrophobic” applies, as is conventional
`for
`these
`formulations, not to one particular comonomer, but to the
`entire composition. As will be seen in the examples below,
`comonomer compositions may be prepared which comprise
`a small proportion of monomers which are not specifically
`hydrophobic, or even clearly hydrophilic, and which are
`ordinarily added to these mixtures to adjust the glass tran-
`sition temperature (Tg) or latex stability.
`The overprint varnishes according to the invention are
`preferably compositions comprising 30% top 90% compos-
`ite latex and from 5% to 20% polyethylene wax emulsions.
`They provide a highly advantageous compromise between
`two conflicting properties of the resinous constituents, 1.e.,
`the increase in the hardness of thefinal film, at the expense
`of a nevertheless acceptable sensitivity to water provided by
`the hydrophilicity thereof. The overprint varnishes formu-
`lated according to the invention are advantageously applied
`to preprinted papers,
`rigid cardboard boxes used for
`packaging, including those for foodstuffs, multi-layer bags,
`paper plates, packaging for microwave-heatable products,
`magazine covers, and glossy papers.
`In order to furtherillustrate the present invention and the
`advantages thereof,
`the following specific examples are
`given, it being understood that same are intended only as
`illustrative and in nowise limitative.
`
`In said examples to follow, the latices were characterized
`by means of the tests described below.
`The molecular weight of the resin was calculated by GPC
`in a solvent medium containing tetrahydrofuran and 5%
`acetic acid on “PL-Gel” chromatographic columns.
`Particle size was measured using a Coulter N4SD appa-
`ratus.
`
`Viscosities were measured at 23° C. using a Brookfield
`RV viscosimeter.
`
`Estimation of resistance to temperature was a visual test
`entailing exposure of a section of cardboard coated with a
`thin film of overprint varnish for 10 seconds on a metalplate
`heated to 200° C. and observation of the changes occurring.
`Glossiness was measured at a 600 angle in accordance
`with Standard No. ASTM D-523.
`
`

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`5,902,846
`
`3
`Water-resistance was assessed either by a Cobbtest or, in
`general, by placing a drop of water on the varnished surface
`and by monitoring the change of appearance after 15 sec-
`onds and 1 minute.
`
`EXAMPLE1
`
`Preparation of composite latices
`
`4
`Heat-resistance agent (ZnO): 3
`Leveling agent (glycol ether): 4
`28% ammonia: 1.2
`Water: 7.7
`A varnish was obtained from the composite latex(a) of
`Example 1, the varnish(b) being from the composite latex(b)
`of that same example.
`
`EXAMPLE3
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`Comparative performances of the overprint
`varnishes
`
`Each varnish prepared in Example 2 (varnish(a), varnish
`(b)) was applied to a sheet of cardboard using a polishing
`film-spreader and dried at 175° C. for 1 minute. Heat-
`resistance, gloss, and water-resistance were measured or
`observed by meansofthe tests described above. The results
`obtained are reported in the following Table:
`
`TABLE
`
`
`
`
`
`Latex(a) according to the invention (latex having a 30%
`concentration of SMA):
`240 g of a copolymerresin of styrene and maleic anhy-
`dride having a molecular weight of 1,600 and an acid
`number of from 465 to 495, 1,110 g demineralized water,
`and 136.8 g 28%. ammonia in water were successively
`introduced into a glass three-necked 3-liter reaction vessel
`equipped with a mechanicalstirrer. All reagents were heated
`to 60° C. andstirred continuously until the copolymer of low
`molecular weight had dissolved, which provided a dispers-
`20
`ing effect. The solution was heated to 85° C., and then a
`mixture of 207.2 g styrene, 341.6 g butyl acetate, 5.6 g
`Varnish Gloss at 60° C._Water-resistanceHeat-resistance
`acrylic acid, and 5.6 g acrylamide, and a mixture of a
`solution of 10 g (NH,)S,O, in 200 g water was added under
`a nitrogen atmosphere and while understirring, the opera-
`tion being carried out continuously, as indicated above, for
`two hours using dosing pumps in the copolymer solution
`previously prepared and at 85° C. The reaction medium was
`maintained for another two hours at 85° C., then cooled
`under mild stirring.
`A latex having the following characteristics was obtained.
`Dry solids content: 45.6%
`Brookfield viscosity at 23° C.: 1,000 mPa.s pH: 9
`Average particle diameter: 70 nm
`Latex(b): Composite latex according to the prior art (latex
`having a 65% concentration of SMA)
`520 g of a copolymerresin of styrene and maleic anhy-
`dride having a molecular weight of 1,600 and an acid
`number of from 465 to 495, 840.4 g demineralized water,
`and 296.4 g ammonia in a 28% concentration in water were
`successively introduced into a glass three-necked 3-liter
`reaction vessel equipped with a mechanical stirrer. All
`reagents were heated to 60° C. and stirred continuously until
`the copolymer of low molecular weight had dissolved,
`which provided a dispersing effect. The solution was heated
`to 85° C., and then a mixture of 103.6 g styrene, 170.8 g
`butyl acetate, 2.8 g acrylic acid, and 2.8 g acrylamide, and
`a mixture of a solution of 5 g (NH,).S.0. in 200 g water was
`added undera nitrogen atmosphere and while understirring,
`the operation being carried out continuously, as indicated
`above, for two hours using dosing pumpsin the copolymer
`solution previously prepared and at 85° C. The reaction
`medium was maintained for another two hours at 85° C.,
`then cooled under mildstirring.
`A latex having the following characteristics was obtained.
`Dry solids content: 45.6%
`pH: 9
`Average particle diameter: 66 nm
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`EXAMPLE 2
`
`Overprint varnish formulations
`
`An overprint varnish composition was formulated con-
`taining composite latices and a polyethylene wax emulsion,
`in accordance with the formula (percentages by weight):
`Composite latex: 76
`Polyethylene wax emulsion: 8
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`a
`b
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`Good
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`Good
`Poor
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`While the invention has been described in terms of
`
`the skilled artisan will
`various preferred embodiments,
`appreciate that various modifications, substitutions,
`omissions, and changes may be made without departing
`from the spirit thereof. Accordingly, it is intended that the
`scopeof the present invention be limited solely by the scope
`of the following claims, including equivalents thereof.
`Whatis claimedis:
`
`1. An overprint varnish which comprises a composite
`latex, said composite latex comprising the copolymerizate of
`at least one hydrophobic monomerwithin an aqueoussolu-
`tion of a styrene/maleic anhydride resin, said styrene/maleic
`anhydride resin having a molecular weight ranging from 500
`to 5,000 and an acid numberof at most 500, and the amount
`by weight of said styrene/maleic anhydride resin in said
`copolymerizate ranging from 5% to 50%.
`2. The overprint varnish as defined by claim 1, said at
`least one hydrophobic monomer comprising styrene or
`derivative thereof, or a (meth)acrylic ester.
`3. The overprint varnish as defined by claim 1, further
`comprising a polyethylene wax emulsion.
`4. The overprint varnish as defined by claim 3, comprising
`from 30% to 90% of said composite latex and 5% to 20% of
`said polyethylene wax emulsion.
`5. The overprint varnish as defined by claim 1, said
`styrene/maleic anhydride resin being salified with ammonia
`or a nitrogenous base.
`6. The overprint varnish as defined by claim 1, said
`styrene/maleic anhydride resin being partially esterified with
`at least one linear or branched alkanol having from 1 to 18
`carbon atoms.
`
`7. The overprint varnish as defined by claim 1, said
`composite latex comprising the free-radical copolymerizate
`of said at least one hydrophobic monomerwithin an aqueous
`solution of said styrene/maleic anhydride resin.
`8. The overprint varnish as defined by claim 1, said
`copolymerizate having a glass transition temperature of less
`than 30° C.
`9. The overprint varnish as defined by claim 1, having a
`pH of about 9.
`10. The overprint varnish as defined by claim 1, further
`comprising a heat-resistance agent.
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`5,902,846
`
`5
`11. An overprint varnish which comprises a composite
`latex and a polyethylene wax emulsion, said composite latex
`comprising the copolymerizate of at least one hydrophobic
`monomer within an aqueous solution of a salified styrene/
`maleic anhydride resin, said styrene/maleic anhydride resin
`having a molecular weight ranging from 500 to 5,000 and an
`acid numberof at most 500, the amount by weight of said
`styrene/maleic anhydride resin in said copolymerizate rang-
`ing from 5% to 50% and said copolymerizate having a glass
`transition temperature of less than 30° C.
`12. A substrate coated with a dried film of the overprint
`varnish as defined by claim 1.
`13. A paper, cardboard or packaging substrate coated with
`a dried film of the overprint varnish as defined by claim 1.
`14. A substrate coated with a dried film of the overprint
`varnish as defined by claim 11.
`15. A paper, cardboard or packaging substrate coated with
`a dried film of the overprint varnish as defined by claim 11.
`16. The copolymerizate of at
`least one hydrophobic
`monomer within a matrix of a styrene/maleic anhydride
`resin, said styrene/maleic anhydride resin having a molecu-
`lar weight ranging from 500 to 5,000 and an acid numberof
`at most 500, and the amount by weight of said styrene/
`maleic anhydride resin in said copolymerizate ranging from
`5% to 50%.
`
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`17. The copolymerizate as defined by claim 16, having a
`glass transition temperature of less than 30° C.
`18. The copolymerizate as defined by claim 17, said at
`least one hydrophobic monomer comprising styrene or
`derivative thereof, or a (meth)acrylic ester.
`19. The copolymerizate as defined by claim 17, said
`styrene/maleic anhydride resin being salified.
`20. The copolymerizate as defined by claim 17, said
`styrene/maleic anhydride resin being partially esterified with
`at least one linear or branched alkanol having from 1 to 18
`carbon atoms.
`
`21. The overprint varnish of claim 1, wherein said styrene/
`maleic anhydride resin does not contain grafts of said
`hydrophobic monomer.
`22. The overprint varnish of claim 11, wherein said
`styrene/maleic anhydride resin does not contain grafts of
`said hydrophobic monomer.
`23. The copolymerizate of claim 16, wherein said styrene/
`maleic anhydride resin does not contain grafts of said
`hydrophobic monomer.
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