Process for the Production of Coated Cellulose Cardboard, Coating Composition and Coated Cellulose Cardboard So Obtained

Europäisches Patentamt *EP001114894A1* (19) European Patent Office

Office européen des brevets (11) EP 1 114 894 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) Int Cl.7: D21H 25/04, D21H 19/16, 11.07.2001 Bulletin 2001/28 D21H 19/18, D21H 23/22

(21) Application number: 01100339.9

(22) Date of filing: 04.01.2001

(84) Designated Contracting States: • Tocchio, Cesare AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU 20121 Milano (IT) MC NL PT SE TR • Cavallini, Eugenio Designated Extension States: 20121 Milano (IT) AL LT LV MK RO SI • Sampietro, Dario 20121 Milano (IT) (30) Priority: 05.01.2000 IT MI200004 • Marucci, Mino Leo 20121 Milano (IT) (71) Applicant: Reno de Medici S.p.A. 20121 Milano (IT) (74) Representative: Trupiano, Federica Brevetti Europa S.r.l., (72) Inventors: Corso di Porta Ticinese, 3 • Dell’aria Burani, Giovanni 20123 Milano (IT) 20121 Milano (IT)

(54) Process for the production of coated cellulose cardboard, coating composition and coated cellulose cardboard so obtained

(57) A process for the production or coated cellulose • a catalyst/quenching agent cardboard comprises the following steps: • a graft initiating/regenerating system

providing a substrate of cellulose cardboard, allowing graft polymerization to occur on the cellu- applying on said substrate a coating composition lose material forming the cardboard substrate. comprising:

• at least an acrylic monomer and/or prepolymer, • a covering/waterproofing means • a solvent/dispersing means EP 1 114 894 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 1 114 894 A1 2

Description said cardboard, that is degradable and suitable for use in containers and packages also for alimentary sub- [0001] The present invention relates to a process for stances. the production of coated cellulose cardboard for differ- [0011] Another further object of the invention is to pro- ent uses, depending on the type of coating applied. 5 vide compositions for coating cellulose cardboard suit- [0002] The present invention also relates to the coat- able to realize a coating having excellent waterproofing ing composition, as well as the coated cardboard so ob- and hydrophobic characteristics and that is intimately tained. and irremovably attached to said cardboard. [0003] By the term "cardboard" there is intended to [0012] These and still other objects and related ad- indicate in the present invention all the types of paper, 10 vantages that will result from the following description board and cardboard of any size and thickness. are achieved by a process for the production of coated [0004] As is known, the cardboard intended for con- cardboard, which process, according to the present in- taining hygroscopic products or products containing wa- vention, comprises the following steps: ter and/or fats, or products degraded by humidity, is wa- terproofed and made hydrophobic by coating or cover- 15 - providing a substrate of cellulose cardboard, ing the same with a film from waterproof material, sub- - applying on said substrate a coating composition stantially a protective layer realized from plastic materi- comprising: al, such as polyethylene and the like. [0005] Coating is substantially an operation by which • at least an acrylic monomer and/or prepolymer, the surface of raw cardboard is covered, by way of ex- 20 • a solvent/dispersing means, ample by means of rollers and/or metal- or air-blades, • a catalyst/quenching agent with coating products in the form of emulsions or aque- • a graft initiating/regenerating system ous suspensions, which are so coated on the cardboard in various layers or thicknesses obtained by as many - allowing graft polymerization to occur on the cellu- "passages", depending on the intended use. In order to 25 lose material forming the cardboard substrate. Said increase the resistance of the cardboard to the passage graft polymerization occurs spontaneously as a of humidity and steam, according to the known tech- function of the time and/or the catalyst added. Al- niques the cardboard sheet is "coupled" with preformed ternatively, graft polymerization may be promoted sheets or films from plastic materials such as polyethyl- and/or accelerated by heating at a temperature ene, vinylidene chloride copolymers and the like, obtain- 30 comprised between 80°C and 150°C or any other ing in this way coated cardboard comprising at least a suitable means, such as irradiation or the like. cardboard layer and one or more layers or preformed sheets from such waterproof materials. In these cases, [0013] More particularly, said substrate of cellulose the bond between the cardboard layer and the coating cardboard is comprised of a cardboard sheet in the for- is only of a physical nature. 35 mation step or a cardboard sheet in the finishing step. [0006] Generally, said coated cardboard solves the [0014] In other words, the coating composition is ad- problem of preventing the passage of humidity satisfac- vantageously applied onto the cardboard during card- torily, but requires particular working processes carried board working without needing to have recourse to a out by means of delicate and often laborious techniques. specific coating step on the sheet after the preparation [0007] With the transparent protective paints of vari- 40 of the mix, in this case preferably by spraying, or on the ous type, for instance acrylic, that are applied on the sheet after drying, in the finishing step by means of a cardboard sheet, one obtains a barrier effect hindering roller or blades, avoiding in this way a whole working the passage of humidity, which is however lower than step. that achieved by using the aforementioned coupling [0015] Preferably, said monomer and/or prepolymer technique. Besides, this process is very onerous, as it 45 is an acrylic monomer or prepolymer of the formula is necessary to apply several paint layers. [0008] It is also known that if microfractures occur in the protective/barrier layer, the effectiveness of the whole barrier layer is irremediably jeopardized. It suffices, in fact, that steam comes in touch with the underlying 50 cardboard in one single point to cause water to spread in the time on all the cardboard sheet, moistening it. [0009] Object of the present invention is to realize a process for the production of coated cardboard provided with a coating film intimately and irremovably attached 55 to said cardboard. wherein X is -OR or -COOR and R is an alkyl, phenyl [0010] Another object of the invention is to realize a group or an alkyl group, having preferably 1 to 10 carbon coated cardboard with a coating film stably attached to atoms.

2 3 EP 1 114 894 A1 4

[0016] In particular, there has been advantageously • The product is hydrophobic. used as acrylic monomer or prepolymer an ethylenacryl- • The coating formulation applied to the cellulose ic acid-based dispersion of prepolymers, such as "Pri- cardboard has a uniform thickness. macer" 4983-48R, produced by Michelman Inc., and a • The coated cardboard is suitable for use in food in- latex comprising carboxylated acrylic prepolimers, such 5 dustry. as Hycar 26288 produced by BF Goodrich, Cleveland, Ohio, USA. [0026] As is known, by "chemical graft" there is in- [0017] Said covering/waterproofing means is consti- tended to indicate the process through which a given tuted of a combination of paraffin and anionic/non ionic material is attached to a different material by means of emulsion polyolefin wax, such as Michem 70750 Emul- 10 a chemical bond. sion produced by Michelman Inc., or Aquabead 270 E [0027] The chemical graft is constituted by the activa- of the Micro Powders Inc., Tarry Town, New York. tion of the substrate. Once the substrate is activated, [0018] Said solvent/dispersing means is constituted chains of monomers connected by carbon-carbon of a monomer substance comprising a mix of trimethyl- bonds growth on the substrate and become whiskers. propane and ethoxylated triacrylate, such as the SR344 15 These whiskers impart the substrate new, interesting Monomer of SR9035 Monomer, produced by Sartomer. permanent properties without damaging the existing [0019] Said graft initiating/regenerating system is positive characteristics of these materials. constituted of ferrous ammonium sulfide and hydrogen [0028] As said, the bond between the grafted polymer peroxide. and the substrates has a covalent nature and the grafted [0020] The graft initiator may also consist of the sys- 20 polymer cannot be detached from the substrate, as it is tem of metal ions Fe++/Fe+++,Co++,Cu++, and the per- substantially a growth of polymer chains on said sub- oxide may be selected from among water soluble cata- strate. lysts such as hydrogen peroxide, urea peroxide, ammo- [0029] As is known, cellulose is a natural carbohy- nium, and potassium peroxide. drate polymer (polysaccharide) consisting of anhydrous [0021] The monomers and prepolimers have collater- 25 glucose units bridged by an oxygen bond to form essen- al functional X groups that can react with one another tially straight molecular chains. and the further prepolymers included in the formulation, [0030] The chemical graft on cellulose can be de- generating an organic covering made up by graft- scribed as being a process that activates the cellulose crossed atomic bonds. The functional groups of mono- molecule, binding the monomers to the reactive centers, mers and prepolimers may be comprised of hydroxy 30 followed by chain propagation, such that polymer groups, carboxy groups, amine secondary and/or terti- branches form that are bond to the main cellulose mol- ary groups. The molecular ratio of the functional groups ecule. of the reactive components is so adjusted as not to leave [0031] According to the present invention, said coat- any free group once the reaction has ended. ing composition has the following composition ex- [0022] Substantially, the X group defines the property 35 pressed as percentage by weight: or properties obtained. In many cases, several monomers are utilized and often more than a property can be - acrylic monomer and or prepolymer 25 to 50% altered in one of the process steps. These chains, - covering/waterproofing means 15 to 25% whose length can be controlled, are permanently bound. - solvent/dispersing means 10 to 35% [0023] The bond between the grafted polymer and the 40 - catalyst/quenching agent 0,001 to 0,1% substrates is of a covalent nature, and therefore the - initiating/regenerating system about 0,0001% grafted polymer cannot be detached from the substrate. In substance, the chemical graft is a growth of polymer [0032] According to the present invention, in the case chains on the skeleton of a substrate. The grafted pol- of a cellulose molecule, the chemical graft is substan- ymer chains are constituted of vinyl monomers or mon- 45 tially obtained through the extraction of an hydrogen at- omers containing suitable functions, for instance, hy- om from the hydroxy group of the molecule. As indicated droxy, carboxy, epoxy, amine groups, etc. above, cellulose molecules have active labile hydrogen [0024] The "permanent" properties that can be atoms (-CH2 OH) that can be activated in the presence achieved include uninflammability, abrasiveness, abra- of a graft initiator causing the growth of the free radicals sion resistance, slidability, stain-repulsion, improve- 50 ("X"). The free radicals so produced in the process ini- ment in ionic-exchange characteristics, protection from tiates the graft polymerization. UV rays, water absorption power, gas-impermeability, [0033] The initial graft ion spurs the action and the bactericide and antifungal properties, as well as many whole process behaves as a self-catalytic one. A minor other ones. part of the initial graft ions (10-100 ppm) suffices there- [0025] According to the present invention, the coating 55 fore to develop the graft polymerization process. composition is attached to the cellulose cardboard [0034] All the reactions indicated above occur in the through a graft-based chemical bond. The so obtained presence of a peroxide that simultaneously regenerates coated cardboard has the following properties: the graft initiator, forming a free radical.

3 5 EP 1 114 894 A1 6

[0035] The graft polymerization can be terminated by a radical combination, for instance, between a free rad- PARTS BY WEIGHT ical and one of the substrate polymerized radicals. Ac- (B.F. Goodrich) cording to the amount of catalyst, the polymerization reaction proceeds more or less, and it is thus possible to 5 Acrylic copolymer 306,00 adjust as one wishes the length of the chain and sub- Hycar 26288 (latex) stantially the characteristics of the covering film real- (Micropowders Inc.) ized. Aquabead 270 E [0036] The following examples of practical application (Wax emulsion) 234,00 are reported only by way of illustrative non limiting em- 10 Water 153,00 bodiments of the invention. Isopropyl alcohol 45,00 (Sartomer) EXAMPLE 1 Monomer SR 9035 0,40 Graft initiator [0037] A pre-calculated amount of an acrylic polymer 15 together with paraffin and the emulsified polyethylene Ferrous ammonium sulfide waxes are charged in a vessel, followed by the addition (1% solution) 0,001 of the catalyst, the graft initiator system and the other Hydrogen peroxide (28%) 0,001 elements of the composition. The components are taken according to the concentration ratio and the order spec- 20 EXAMPLE 3 ified in the formulation of the coating composition. The contents is then mixed until a uniform solution is ob- [0041] The modalities are those indicated in Example tained. 1. Formulation of the coating composition: [0038] The formulation is then ready to be used in the industrial application. 25 PARTS BY WEIGHT [0039] In the laboratory, the formulation was coated (B.F. Goodrich) on the cardboard by means of a Meyer rod. However, in the industrial use, the formulation is coated with paper Acrylic copolymer 374,0 production machines. The coated cardboard was then Hycar 26288 submitted to a 100°C treatment for 10 minutes. Formu- 30 (Micropowders Inc.) lation of the coating composition: Aquabead 270 E 286,00 Deionized water 44,00 PARTS BY WEIGHT Isopropyl alcohol 44,00 (Michelman Inc.) solvent 35 Dispersion of (Sartomer) acrylethylene acid 52,00 Monomer SR 9035 0,400 copolimers Ferrous ammonium sulfide Primacer 4983-48R (1% solution) 0,001 (Michelman Inc.) 40 Hydrogen peroxide (28%) 0,001 Michem 70750 emulsion 26,00 Deionized water 16,00 EXAMPLE 4 Isopropyl alcohol 18,4 [0042] The modalities are those indicated in Example solvent 45 1. Formulation of the coating composition: Deionized water 27,6 Monomer SR344 0,01 PARTS BY WEIGHT Graft initiator Ferrous ammonium sulfide (B.F. Goodrich) (1% solution) 0,001 50 Acrylic copolymer 270,00 Hydrogen peroxide 0,001 Hycar 26288 (Micropowders Inc.) EXAMPLE 2 Aquabead 270 E 270,00 Deionized water 153,00 [0040] The modalities are those indicated in Example 55 Isopropyl alcohol 45,00 1. Formulation of the coating composition: (Sartomer) Monomer SR 344 0,40

4 7 EP 1 114 894 A1 8

(continued) 3. The process according to claim 1, characterized in that said substrate from cellulose cardboard is con- PARTS BY WEIGHT stituted of a cardboard sheet in the formation step, Graft initiator or a cardboard sheet in the finishing step. Ferrous ammonium sulfide 5 (1% solution) 0,001 4. The process according to claim 1, characterized in Hydrogen peroxide (28%) 0,001 that said monomer and/or prepolymer is an acrylic monomer or prepolymer

EXAMPLE 5 10

[0043] The modalities are those indicated in Example 1. Formulation of the coating composition:

PARTS BY WEIGHT 15 (B.F. Goodrich) Acrylic copolymer 234,00 Hycar 26288 (Micropowders Inc.) 20 wherein X is -OR or -COOR and R is an allyl, phenyl Aquabead 270 E 307,00 group or an alkyl group, having preferably 1 to 10 Deionized water 153,00 carbon atoms. Isopropyl alcohol 45,00 (Sartomer) 5. The process according to claim 4, characterized in Monomer SR 344 0,40 25 that said acrylic monomer or prepolymer is a dis- Graft initiator persion of ethylenacrylic acid copolymers. Ferrous ammonium sulfide 6. The process according to claim 4, characterized in (1% solution) 0,001 that said acrylic monomer or prepolymer is a latex Hydrogen peroxide (28%) 0,001 30 comprising carboxylated acrylic copolymers.

Claims 7. The process according to claim 1, characterized in that said covering/waterproofing means . is consti- 1. A process for the production of coated cardboard, tuted of a combination of paraffin and emulsion an- 35 characterized in that it comprises the following ionic/non ionic polyolefin wax. steps: 8. The process according to claim 1, characterized in - providing a substrate of cellulose cardboard, that said solvent/dispersing means is constituted of - applying on said substrate a coating composi- a mix of isopropyl alcohol and deionized water. 40 tion comprising: 9. The process according to claim 1, characterized in • at least an acrylic monomer and/or prepol- that said catalyst/quenching means is constituted ymer, of a monomer substance constituted of a mix of tri- • a covering/waterproofing means methylpropane and ethoxylated triacrylate. 45 • a solvent/dispersing means • a catalyst/quenching agent 10. The process according to claim 1, characterized in • a graft initiating/regenerating system that said graft initiator/regenerator is constituted of ferrous ammonium sulfide and hydrogen peroxide. - allowing graft polymerization to occur on the 50 cellulose material forming the cardboard sub- 11. A coating composition according to claims 1 and 4, strate. characterized in that it has the following composition expressed in parts by weight: 2. The process according to claim 1, characterized in that said polymerization is carried out by heating at - acrylic monomer and or prepolymer 25 to 55 a temperature comprised between 80°C and 50% 150°C, or other suitable means, such as irradiation - covering/waterproofing means 15 to 25% or the like. - solvent/dispersing means 10 to 35% - catalyst/quenching agent 0,001 to 0,1%

5 9 EP 1 114 894 A1 10

- initiating/regenerating system about 0,0001%

12. A coated cardboard according to claim 1, characterized in that it comprises a substrate from cellu- 5 lose cardboard and a film from polymer material attached to said substrate by means of chemical graft.

6 EP 1 114 894 A1

7 EP 1 114 894 A1

8 EP 1 114 894 A1