MXPA97005526A - Method and composition to provide a recyclable water barrier coating recyclable for flexib packaging - Google Patents

Abstract

The present invention relates to the composition comprising a polymer emulsion containing, for example, polyvinylidene chloride with a particle size distribution of less than 10 microns and an additive with, generally, the same size distribution, for example silicate. of aluminum, calcium carbonate, polyvinyl acetate polystyrene, polyacrylates, in emulsion or powder that is capable of a combination in the interstices with the polymer particles. The composition has a critical pH between 2 and 7. The method for repulping or recycling the coated packaging is also presented.

Description

METHOD AND COMPOSITION TO PROVIDE A BARRIER COAT OF RECYCLABLE HUMID VAPOR FOR FLEXIBLE PACKAGING. DESCRIPTION OF THE INVENTION The present invention relates to a method and composition for providing a recyclable wet vapor barrier coating for flexible packaging as well as a flexible package provided with that coating. More particularly, the invention concerns a method for reprocessing a flexible packaging material having a coating over which is a wet vapor barrier, wherein the coating is allowed to mix with the cellulose fibers to form a pulp, allowing that the fibers adapt to form a pulp. The invention also relates to a flexible package that is provided with a coating that allows it to be reprocessed to paper products of some value. It is common practice to add a polyethylene film, a wax coating or a polyvinylidene chloride (PVDC) on a paper substrate or between two sheets of paper, the paper substrate and the paper sheets are mentioned as linings, with the purpose to obtain a flexible packaging with wet vapor barrier. At present all of these wet barrier coatings are considered non-recyclable.

Other resins are also used to give flexible packaging materials that have low moisture vapor transmission rates, such as polyacrylates, polyvinyl acetates and the like. However, for barrier functions, they are more expensive than coating them in wax, polyethylene and polyvinylidene chloride. Moisture barrier coatings that occur in wet barrier packaging materials or rather moisture are considered by recycling facilities or mills as non-recyclable, mainly because they introduce quality problems in the fiber recovery process , either by saturating the process (covering the screen or grid) or by contaminating the finished product. At present more than 20% of all paper and cardboard produced in the world are laminated as indicated above, which gives products that are incompatible with the recycling industry. A disadvantage with polyethylene, wax or PVDC in coated packages is that they are difficult to reprocess and usually should be discarded. The elimination of wet barrier packaging materials has become an important factor for paper mills and their customers. The recycling or repulping in these materials establishes special problems for the industry. The wet barrier presents a challenge to recover the useful fiber from these packing materials, and most of the recycling facilities are unable to overcome the problems of repulping them. At present almost all moisture barrier packaging materials are disposed of in trash cans and are not recyclable. On the other hand, the reprocessing of packages based on wood fiber constitutes an important source of wood fibers. In addition, due to the above mentioned difficulties, this matter should usually be considered and with recent concerns about the environment, this is not acceptable. The reprocessing of packaging based on wood fiber, and the manufacture of high quality and expensive fibers is no longer tolerable, since they represent millions of tons of waste material. Two methods are commonly used to reprocess wood fibers. The first method includes breaking the source of wood fiber, such as those present in a packing material, into constituent fibers as a result of repulpation, while any other material is removed by conventional equipment. The second method includes disrupting the packing so that any additional material such as the coating will break down into thin particles smaller than 1.6mm which will pass through the sieve or screen with the fiber to form the pulp. This second method is usually performed with additional equipment and chemical agents, which makes it expensive. Unfortunately, none of the prior art resins with or without wax that are used to provide coating for flexible packaging can be reprocessed at an additional manufacturing stage, with the result that recycling is difficult. In addition, the presence of wax in the wet vapor barrier coating lowers the yield of the available pulp and therefore increases the amount wasted. In the repulping process, the wax-based barriers break into very thin particles (less than 0.7 mm) that pass through the sieve and end up forming the pulp that is sent to the paper machine, as well as to the slurry. The problems associated with the repulpamiento of barriers based on wax eon lae eiguientee: -the particles of wax cover the felts; -the particles of wax make gummy to the deposit eecador ocaeionando the rupture of the paper; -the wax ends up accumulating on the surface of the product resulting in problems of surface and impurity and causing adhesion in the finished product; and - decreasing the yield of ueable pulp. On the other hand, when polyethylene is used as the wet vapor barrier coating, the repulper is on and breaks into large pieces of film whose sizes range from about 0.2 cm to 2.5 cm in length. Polyethylene causes plugging of the screen requiring detention time to clean and generate solid waste. The problems associated with polyvinylidene chloride barrier coatings are generally the same as those encountered when the coating is made of polyethylene. Since PVDC, has the advantage of providing a coating with an excellent vapor barrier, good oxygen barrier, as well as chemical resistance properties at a low cost, it would be commercially beneficial for the manufacture of paper rolls or the like to be able to rely on a flexible packaging that includes a PVDC coating, which could be completely recycled and reprocessed. However, in the present state of the art any attempt to modify the recyclability of the PVDC, and other types of reein by adding materialee or treating the packing to increase the hardness of the film, would result in a tremendous loss of barrier properties. ' which is unacceptable. Coatings based on PVDC are known, for example, from the English patent l 583 947, dated February 4, 1981, by Frederic Douglae Hough. However, eetoe revestments are used on paper to produce a transfer sheet. The patent says nothing about the recycling of that coated paper and gives no directive to produce a coating that can be re-pulped together with the paper fiber. The British patent 2 039 789, published on August 10, 1980, by the inventor Adrián Beville Fellows, describes the separation of a dielectric coating from a dispersion of an electrically insulating polymer and a water-dispersible emectite clay. There is no teaching in that patent to provide a coating that is characterized by being impermeable to water vapor, so long as it is recyclable by breaking into a pulp mixture. Richard M. Podhajny in MThe search for alternative wet-barrier coating "Converting Magazine, August 1995, suggests that alternatives to PVDC are urgently needed due to the pollution character of the PVDC, when it is allowed to throw it into a stream of garbage. Because PVDC coatings, with or without additives, are known, it seems that a suitable formulation in which the coating remains with the pulp when it is recycled, and therefore does not contaminate the environment, has not been achieved.

B. Alinee and P. Lepoutre in TAPPI Journal, vol. 66, No. 11, page 57 and 58, preeve that the viecocity of aquatic euepeneiones improves with a small tear using clay, calcium carbonate and a latex that could be polyetheirene. JP A 06 136 698, pre-presents a baee paper made of wood pulp and a barrier layer containing PVDC latex, as a binder. WO 93/13264, generally describes a liner material comprising a thermoplastic polymer such as PVDC latex and a talc or silica additive having a filler or whitening properties. At present, it will not be possible to maintain the traditional role of the source of the paper's incest of forests, and it is necessary to find means to obtain sufficient fiber by filling the demand. It is therefore an object of the present invention to provide a coating of polyvinyl chloride which is a barrier to moisture vapor and recyclable for flexible packaging and obtains recyclable or siflable packaging and which constitutes an excellent barrier against moist vapor and oxygen, having Excellent chemical retention properties and providing sufficient bond re-bonding for paper lamination. It is another object of the present invention to provide a repulpable polyvinylidene chloride coating, which when applied to the liner plate or to the paper provides a barrier to the suitable wet vapor and does not interfere with the process of repulpation in the paper machine or finished product. It is another object of the present invention to provide a repulpable modified polyvinylidene chloride coating, which in doing so is broken into small pieces, preferably less than 1.6mm, and which is easily broken down by keeping the amount of waste to a minimum. It is another object of the present invention to provide a barrier coating of moisture vapor that upon breaking of particles that pass through the screen and that dissipate within the fiber. It is another object of the invention to provide a repulpable polyvinylidene chloride coating, which does not generate solid water when recycled, which does not dissolve in the water of the process and which does not contribute to the demand of biological oxygen in the effluent and which produces particles. that they are inert and not reactivated by the heat. It is another object of the invention to provide a commonly used repulpable modified barrier coating, such as one based on PVDC, and having generally the same barrier properties and when about the same adhesion on the paper that barrier coating does not modified and that in addition to recover can be recycled with low cost. It is another object of the invention to provide a flexible packaging coating composition having an improved normal rheology to improve the flow properties and to prevent the coating from penetrating into the porous papers as is the case with the PVDC of low tear viscosity. which is normally used It is another object of the invention to provide a barrier coating that does not require the use of complex equipment, which implies a chemical treatment associated with recovering virgin fibers. It is another object of the present invention to provide a flexible barrier coating that can be laminated onto a base layer of paper and need to be glued. According to the invention, a composition is proposed to provide a repulpable moist vapor barrier, for flexible packaging material, which comprises a polymer emulsion wherein the polymer in the emulsion has an average particle size 10 microns, and a consistent additive of particulate material with an average micron size and which is capable of a combination in the interstices with the average particles and which produces a coating on the flexible packaging material which preserves the properties of barrier to wet steam provided by the polymer and that when repulpated or recycled breaks into parts generally smaller than approximately 1.6mm. The pH of the composition should be such that it allows the coating to break into parts generally smaller than 1.6mm. Also according to the invention, a method is provided for reprocessing a flexible paper packaging material having a wet vapor barrier coating wherein the packing material is broken into the constituent fibers and the coating particles according to the method of the invention, the coating comprises a mixture containing polyvinylidene chloride and a particulate additive which is capable of combining in the interstices with particles of polyvinylidene chloride and of a coating on the flexible paper packing material which preserves the properties provided by the polyvinyl chloride. The method includes breaking the packing material including the particulate coating where at least about 95% is less than 1.6mm, sifting and separating particles larger than 1.6mm, and producing a pulp from the remaining particles. Although many polymers can be used to produce the vapor barrier coating, according to the invention, the technicians know that the preferred polymers include polyvinylidene chloride, a copolymer of vilididene chloride, methyl methacrylate, and acrylonitrile, or mixtures thereof. same. Similarly with respect to the adhesive, preferred are aluminum hydrous silicate, calcium carbonate, a polyvinyl acetate homopolymer and mixtures thereof. In practice, the most interesting polymer emulsion comprises polyvinylidene fluoride. The preferred polymer emulsion polymer is polyvinylidene chloride which is an excellent barrier against moisture, since its molecular structure makes it possible to provide crystalline regions where the chains of the polymer are aligned and arranged in an orderly manner. As discussed in "The Search for Alternative Wet Barrier Coatings," Converting Magazine, August 1995, ee form strong interactive links in that chain. The interactions between the H and Cl atoms are responsible for the strong attractions between the PVDC chains, forming a dense, three-dimensional crystal lattice. When repulping in a standard crusher, the mechanical force applied to the coating is not sufficient to break the bonds between these chains and produce particles smaller than 1.6 mm, since the particles are larger than 6mm By adding selected additives to the PVDC, such as hydrated aluminum silicate and calcium carbonate with an average particle size of less than 10 microns, and selecting a critical pH, the crystallinity still remains in the composition, but crushing becomes possible by producing larger particles. small due to the presence of additives. As mentioned above the pH of the solution is critical, for example, with aluminum silicate hydrate, the pH should be less than or equal to about 2, with calcium carbonate the pH should normally be between 6 and 7. Obviously a Too large a concentration of additives quickly lowers the moisture resistance of the formed barrier, it has been found that particles with the desired fineness can be produced if polyvinyl acetate is used as an additive. This additive is not as good as hydrated aluminum silicate or calcium carbonate to provide a good repulpable mix, but it has a minor negative effect on coating impermeability. On the other hand, the combined use of polyvinyl acetate and calcium carbonate gives excellent results with regard to repulpability and impermeability, other additives that give satisfactory results include polyethylene, polyacrylate and the like. BRIEF DESCRIPTION OF THE DRAWINGS. The invention is illustrated by means of the accompanying drawings which are illustrative in the drawings: FIGURE 1 depicts a paper obtained using virgin cellulose fibers; FIGURE 2 represents a paper obtained by repulping a flexible package with a vapor barrier according to the invention; FIGURE 3 depicts a paper as in Fig. 1, where the vapor barrier is PVDC; FIGURE 4 represents a paper as in Fig. 1, wherein the vapor barrier is polyethylene; It is immediately seen that in practice the coating of the prior art is not repulpable, while the process of the present invention provides a paper that is subetanially equivalent to that produced with virgin fiber. The invention is further illustrated by means of the following examples. EXAMPLE 1.

The coating composition is prepared by mixing 80 parts of an emulsion of polyvinylidene chloride sold under the trademark SERFENE 2022, with 20 parts of a hydrated aluminum silicate in slurry sold under the trademark OMNIFIL, the pH of the mixture containing 54.5% of solid material, it is adjusted to 2.1 and a coating is formed using the mixture that is applied to a flexible packaging paper product. In repulping or recycling, the coated product is broken into particles smaller than 1.5mm, which allows practically the entire coating to re-pulp. The MVTR (wet steam tranemieion rate) 100% R.H. 37.8 * C, 25 g / m2 coating on lining plate: I5.g / m2 / day. EXAMPLE 2 Example 1 was repeated except that OMNIFIL was replaced by 10 parts of calcium carbonate sold under the trademark PULPRO 3 and 10 parts of a polyvinyl acetate homopolymer sold under the trademark DARATACK 7 IL. The pH was adjusted to 6.2, the mixture contained 58.7% solid material. The pulping process resulted in particles smaller than l.2mm. MVTR: 4 g / m2 / day. EXAMPLE 3 Example 1 was repeated but 66 parts of SERFENE 2022 were used with 27 parts of DARAN SL 12 (M.R.) which is a copolymer of vinylidene chloride, methyl methacrylate and acrylonitrile and 7 parts of DARATACK 7IL. The pH was adjusted to 2.1, the mixture contained 51.5% solid material; the repulpated resulted in particles less than 1.5mm. MVTR: 1.5 g / m2 / day. EXAMPLE 4 Example 1 was repeated except for 85 parts of SERFENE 2022, were used with 15 parts of DARATCK 7IL. The pH was adjusted to 2.1, and the mixture contained 50.8% solid material. The repulpation resulted in particles smaller than 1.5mm, which allowed all the coatings to return to pulp. MVTR: 4 g / m2 / day. EXAMPLE 5 Example 1, ee was repeated but 75 parts of SERFENE were used with 15 parts of PULPRO 8, (mark for a somewhat coarser calcium carbonate particle than PULPRO 3), and 10 parts of DARATACK 7IL. The pH was adjusted to 6.2 and the mixture contained 58% of the solid material, the repulpation gave particles smaller than 1.5mm. MVTR: 8 g / m2 / day. EXAMPLE 6 Example 1 was repeated, but 75 parts of SERFENE 2022, with 11 parts of PULPRO 8, and 14 parts of LYTRON 604, (mark for an emulsion of uniform hard light spherical polystyrene spherical polymer particles), the pH of the mixture was 6.1 and contained 54% solid material. The repulpamiento resulted in smaller particles of 1.6mm. MVTR: 5 g / me / day. It is seen, therefore, that in all the examples the particles are equivalent in size to the virgin fibers which can easily be reprocessed and that the wet vapor tranemieion rate is in practice equivalent to the PVDC. Eneayoe made with paper coated with a compound according to the invention, showed that the repulpation gives about 97% particles smaller than? .6mm, after 3? Min. of repulpamiento.

Claims (7)

1. REIVINDI CAC I ON ES 1.- A composition to provide a repulpable or recyclable barrier resistant to wet vapor for flexible packaging material characterized in that it comprises: a polymer emulsion that provides a barrier to wet vapor and where the polymer in the emulsion has a finer particle size distribution of approximately 10 micrae; an additive consisting of particulate material having an average particle size of less than about 10 microns being capable of combining in the intermetations with polymer particles and producing a coating on the flexible packaging material which preserves the properties of the wet vapor barrier, given by the polymer, and that at the eometeree to repulpamiento or recycling it breaks in part and generally smaller than around 1.6mm; the composition has a pH, between about less than 2 and 8, and is selected so as to allow the coating to break into generally less than about 1.6mm portions, with the polymer selected from the group consisting of polyvinylidene chloride, a chloride copolymer of vinylidene, methyl methacrylate and acrylonitrile, as well as mixtures thereof.
2. 2.- composition according to claim 1, characterized in that the additive is selected from the group consisting of hydrated aluminum silicate, calcium carbonate, polyvinyl acetate homopolymer, and mixtures thereof.
3. 3. Composition according to claim 1, characterized in that the polymer emulsion comprises polyvinylidene chloride.
4. 4. Composition according to claim 3, characterized in that the additive consists of a slurry of hydrated aluminum silicate, the pH of the composition adjusted to less than 2.
5. 5. Composition according to claim 3, characterized in that the additive comprises calcium carbonate, the pH being approximately between 6 and 7. 6. Composition according to claim 3, characterized in that the additive comprises a polyvinyl acetate homopolymer with the pH being approximately 2.0. 7. A composition for providing a repulpable wet vapor barrier coating for flexible material, which comprises: a polymer emulsion containing polyvinylidene chloride, wherein the polyvinylidene chloride in the emulsion has an average particle size distribution more fine than 10 microns; an additive containing an aluminum silicate emulsion hydrated into particles with an average particle size distribution finer than 10 micrae; the composition has an approximate pH of 2.0; the particulate hydrated aluminum silicate is capable of a combination in the interstices with polyvinylidene chloride particles and produces a coating on the flexible packaging material which preserves the moist vapor barrier properties provided by the polyvinyl chloride and which when it is repulped or recycled it breaks into generally smaller parts of approximately 1.6mm. 8. A composition for providing a repulpable moist vapor barrier for flexible packaging material, which comprises: a polymer emulsion containing polyvinylidene chloride, wherein the polyvinylidene chloride in the emulsion has an average particle size distribution finer than about 10 microns; an additive containing particulate calcium carbonate, with an average particle size distribution finer than about 10 microns; the composition has an approximate pH of
6. 6.0; the particulate material is capable of a combination in the interstices with particles of polyvinyl chloride and of giving a coating on the flexible packaging material that preserves the moist vapor barrier properties, given by polyvinyl chloride, and that upon repulping breaks in parts usually less than approximately 1.6mm. 9. Compoeition according to claim 8, wherein the additive additionally contains a polyvinyl acetate polymer with the same average particle size distribution as the calcium carbonate. 10. A method for reprocessing a flexible paper packaging material that has over it a wet vapor barrier coating, wherein the packaging material is broken or separated into constituent and particulate coating fibers, characterized in that the coating comprises a mixture containing polyvinylidene chloride, and a particulate additive having an average particle size of less than 10 microns, capable of combining in the intermetations with polyvinylidene chloride particles and of coating the flexible paper packing material , which preserves the wet vapor barrier properties donated by polyvinyl chloride, the method also comprises breaking the packing material including the particulate coating of which at least about 95% are generally less than 1.6mm, sifting and separating all particles smaller than 1.6mm and produce a pulp with the remaining particles. RESUMEN The composition comprises a polymer emulsion containing, for example, polyvinylidene chloride with a particle size distribution of less than 10 micron and an additive with generally the same size distribution, for example aluminum silicate, calcium carbonate, polyvinyl acetate polystyrene, polyacrylates, in emulsion or powder that is capable of a combination in the interstices with the polymer particles. The composition has a critical pH between 2 and
7. 7. The method for repulping or recycling the coated package is also presented.