Composition for providing a vapour or moisture barrier coating for flexible wood fibre material, reprocessable as paste and process for reprocessing the material

The invention relates to a composition for making a coating, a barrier against moisture or vapor, for a flexible wood fiber material, reprocessable in the form of paste and a process for reprocessing it.

The process for reprocessing a flexible packaging material, having a vapor barrier coating, in which the coating can be mixed with cellulose fibers, to form a paste, allows the yarns to be processed as paste.

It is commonly practiced to add a polyethylene film on a paraffin coating or a polyvinylidene chloride (PVDC) coating on a paper substrate or between two sheets of paper, the respective paper substrate or sheets of paper being considered as linings, in order to obtain a flexible packaging with moisture barrier. Currently, all of these moisture barrier coatings are considered to be unable to be reprocessed as a paste.

In order to obtain flexible packaging materials, other resins having a low rate of moisture transmission, in the form of vapors, for example polyacrylates, polyvinyl acetates and the like are also used. However, at the same barrier performance, they are more expensive than paraffin, polyethylene and polyvinylidene chloride coatings.

Moisture barrier coatings, which are present in the moisture barrier packaging materials, are considered to be incapable of being reprocessable in the form of paste with the help of recycling facilities (retransformation in paste), in particular, because they introduce quality problems in the fiber recovery process, either by making the process difficult (clogging the screen) or by impurifying the finished product.

At present, over 20% of the entire quantity of paper and cardboard in the world is laminated as shown above, producing products that are incompatible with the recycling industry.

A disadvantage of packaging covered with polyethylene, paraffin or polyvinylidene chloride is that they are reprocessed and difficult to recycle and should usually be disposed of as unnecessary. The storage of packaging materials, with moisture barrier, has become an important issue for paper mills and their customers. The retransformation in the paste (recycling) of these materials poses special problems for the industry. The moisture barrier represents a challenge in recovering the useful fibers from these packaging materials, and most recycling factories are unable to overcome the problem of reprocessing them as a paste. At present, almost all of these moisture barrier packing materials are dumped in large quantities onto the field and cannot be retransformed into paste.

On the other hand, reprocessing of wood fiber packaging is an important source of wood fibers. In addition, due to the above difficulties, these materials should usually be disposed of as useless, but given recent environmental concerns, this is no longer acceptable. Wood fiber packaging reprocessing is an increasingly important source of wood fibers, and the waste of very expensive, high quality fibers is no longer tolerable as they represent millions of tons of waste materials.

Two methods are normally used for wood fiber reprocessing. The first method involves the forced breaking (fragmentation) of the source of wood fibers, such as those of the packaging material, in the constituent fibers, as a result of the reprocessing in the form of paste, while the rest of other material is sited with ordinary equipment. . The second method involves shredding the package, so that any additional material, such as the sheath, may be finely chopped into particles smaller than 1.6 mm, passing through a sieve, with fibers, for the pasta form. This second method is normally performed with additional equipment and / or additional chemicals, making it very costly.

RO 117922 Β1

Unfortunately, none of the prior art resins, with or without paraffin, which are used to provide coatings for flexible packaging, cannot be reprocessed, without additional manufacturing steps, making recycling difficult. In addition, the presence of the resin in the moisture barrier coating reduces the degree of use of the usable paste and, therefore, increases the amount of waste.

In the process of reprocessing as a paste, the paraffin-based barriers break 55 into very fine particles (smaller than 0.7 mm), which pass through the appropriate sieve and reach the paste that is sent to the paper machine as well as the water recirculation.

The problems related to the reprocessing of paraffin-based barriers are as follows:

- the paraffin particles clog the felt; 60

- the paraffin particles prevent the drying drum from working, causing the paper to break;

- the resin reaches the surface of the product being manufactured, giving rise to surface and printing problems and causing adhesions to the finished product;

- reducing the yield of usable paste. 65

On the other hand, when polyethylene is used as a vapor barrier coating, while it is in the pulping machine, it breaks into large pieces of film whose dimensions range from about 0.3 to 2.5 cm. Polyethylene causes clogging, requires stops for cleaning, and gives rise to solid waste.

Problems related to polyvinylidene chloride 70 barrier coatings are generally the same as for polyethylene coated barrier coatings.

As polyvinylidene chloride has the advantage of providing excellent vapor barrier coverage, a good oxygen barrier, and chemical resistance properties, at relatively low cost, it would be advantageous to manufacture paper rolls or the like. can be based on a flexible package, including a polyvinyl chloride-75-iden coating, which can be completely recycled and recovered.

However, in the known state of the art, any attempt to modify the ability of polyvinylidene chloride and other types of resins to be retransformed into paste, by adding materials or treating the packaging, in order to increase the hardness of the film, would result in a huge loss. of barrier properties, which, of course, is not acceptable. 80

Polyvinylidene chloride based coatings are known, for example, as shown in UK document 1,583,947, 04.02.1981. However, these coatings are used on paper to produce a transfer sheet. The patent shows nothing about recycling this coated paper and does not give any indication on how to produce a coating that can be retransformed into pulp together with the paper fibers. 85 In UK 2039789, 10.08.1980, the preparation of a dielectric coating from a dispersion of electrically insulating polymer and smectite clay dispersible in water is described. This patent does not show how to obtain a coating which is characterized by impermeability to water values, which, at the same time, can be processed as a paste when it is crushed into a paste mixture. 90 in Richard M.'s article Podhajny Study on Alternative Moisture Barrier Coatings, Converting Magazine, August 1995, the author suggests, as a matter of urgency, alternatives to polyvinylidene chloride, due to the polluting nature of polyvinylidene chloride when discharged into the waste stream. Although coatings with polyvinylidene chloride are known, with or without additives, it can be seen that a suitable formulation 95 has not yet been achieved, in which the coating remains with the paste, when it is recycled and therefore does not pollute the environment.

RO 117922 Β1 in the publication TAPPI, vol. 66, No. 11, pages 57 and 58, B. Alice and P. Lepoutre show that the viscosity of aqueous suspensions improves at low tangential stress, by using clay, calcium carbonate and a latex, which could be polystyrene.

JP A-06136698 presents a basic paper, made of wood pulp and a barrier layer containing polyvinylidene chloride latex, as a binder.

WO 93/13264 generally describes a lining material, which comprises a thermoplastic polymer, for example polyvinylidene chloride and an additive, which may be talc and / or silica, having filling properties and / or bleaching.

At the current rate, it will not be possible to maintain the traditional rate of supply of paper source, from forests, and there must be means of obtaining sufficient quantities of fiber to meet the demand.

It is an object of the present invention, therefore, to provide a polyvinylidene chloride coating with a moisture barrier, modified and capable of being processed in the form of a paste, for flexible packaging, from which a recyclable and / or packaging can be obtained capable of being seated, it is an excellent barrier to moisture in the form of vapors and oxygen barrier, having excellent chemical resistance properties and providing excellent cohesive force for paper rolling.

Another object of the present invention is to provide a modified, reprocessable polyvinylidene chloride coating in the form of paste, which, when applied to paper or a lining panel, provides a suitable barrier for moisture in the form of vapors. and does not affect the process of re-processing into pulp, paper machine or finished product.

Another object of the present invention is to provide a coating of modified polyvinylidene chloride, reprocessable in the form of paste, which, from the process of reprocessing in the form of paste, breaks into small particles, preferably below 1.6 mm. and defibrillate very easily, thus minimizing the amount of waste.

Another object of the present invention is to provide a barrier barrier coating, from which, when shredded, to yield particles that can pass through the sieve and disperse between fibers.

Another object of the present invention is to provide a polyvinylidene chloride coating, modified and retransformable into paste, which, upon recycling, does not give rise to solid waste, does not dissolve in technological water, does not affect the biological need for oxygen from the effluent and produce particles that are inert and not reactivated by heat.

Another object of the present invention is to provide a modified and retransformable barrier coating in industrially achievable paste, for example, based on polyvinylidene chloride, having generally the same barrier properties and at least nearly the same adhesion to paper as well as the coating with unmodified barrier and which, apart from the fact that it can be easily recovered, is reprocessable in the form of paste, with low costs.

Still another object of the present invention is to achieve a coating composition for a flexible packaging, having a current, improved rheology, so as to improve the flow properties and prevent the penetration of the coating in the porous papers, as is the case with chloride of chloride. Low viscosity polyvinylidene, commonly used.

Another object of the present invention is to provide a barrier coating, which does not require the use of complex equipment, which involves an associated chemical treatment, when recovering unused fibers.

Another object of the present invention is to provide a flexible barrier coating, which can be laminated to a base layer of the paper, without the use of an adhesive.

In accordance with the invention, these objectives are achieved with a composition for making a moisture or vapor barrier coating for a flexible material of

EN 117922 Β1 wood fiber, reprocessable in the form of paste, which contains a polymer emulsion which creates a barrier against moisture or vapor and wherein the respective emulsion polymer has a particle size distribution of less than 10pm, the polymer being chosen from the group consisting of polyvinylidene chloride, vinylidene chloride copolymer, methyl methacrylate and acrylonitrile 150 and mixtures thereof, characterized in that it contains an additive consisting of particulate material, selected from the group consisting of hydrated aluminum silicate, calcium carbonate, a polyvinyl acetate homopolymer and mixtures thereof and having a smaller average particle size from 10pm, the particulate material being capable of interstitial combination with the respective polymer particles and forming a coating on 155 flexible material, which retain the barrier properties against moisture or vapor, provided by the polymer and which, when reprocessed as a paste, are fragmented into pieces, generally smaller than 1.6 mm, the composition having a pH of less than or equal to about 2 and 6 ... 7.

Also, according to the invention, there is provided a process for reprocessing a 160 flexible wood fiber material, having on it a barrier coating against moisture or vapor, in which the flexible material is fragmented into the constituent fibers and particles of the coating, characterized by that the coating contains a mixture of polyvinylidene chloride and additive, in the form of particles selected from the group consisting of hydrated aluminum silicate, calcium carbonate, a homopolymer of polyvinyl acetate and mixtures thereof and having an average particle size of less than 10pm, the particulate material being capable of interstitial combination with said polyvinylidene chloride particles and forming a coating on the flexible material, which retains barrier properties against moisture or vapor, provided by polyvinylidene chloride, and which, when reprocessed as a paste, are fragmented into pieces, in general, smaller than 1.6 mm, the process comprising fragmentation of the flexible material, including coating coating on particles of which at least 95% are generally less than 1.6 mm, sizing and separating all larger particles 1.6 mm and the preparation of a paste of the remaining particles.

The invention has the advantage that it allows the recovery, in the form of valuable paper products, of flexible packages, covered with moisture barrier or 175 vapor coatings.

Although for the production of a vapor barrier coating according to the invention, numerous polymers, as is well known to those skilled in the art, could be used, preferred polymers include polyvinylidene chloride, a copolymer of vinylidene chloride, methyl methacrylate and acrylonitrile or mixtures thereof. 180 Similarly, with respect to the adhesive, hydrated aluminum silicate, calcium carbonate, a homopolymer of polyvinyl acetate and mixtures thereof are preferred, in practice, the most interesting polymer emulsion comprises polyvinylidene chloride.

The preferred polymer in the polymer emulsion is polyvinylidene chloride (PVDC), which is an excellent moisture barrier, because its molecular structure is capable of providing crystalline areas in which the polymer chains are aligned and arranged in an orderly manner. As analyzed in the study Study on alternative vapor barrier coatings from Converting Magazine^(R), August 1995, strong and interactive links are formed in these chains. The interactions between H and CI atoms are responsible for the strong attraction between PVDC chains, forming a three-dimensional, 190-dense crystalline network.

When re-transforming into a paste, in an ordinary crusher, the mechanical force applied to the coating is not sufficient to break the links between these chains and to produce particles smaller than 1.6 mm, because the obtained particles are normally larger than 6 mm.

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By adding selective additives in polyvinylidene chloride, such as hydrated aluminum silicate and calcium carbonate with an average particle size of about 10μ and choosing a critical pH, the composition still retains its crystalline character, but due to the presence of additives, it remains possible to crush to produce smaller particles.

As mentioned above, the pH of the solution is a critical size. For example, in the case of hydrated aluminum silicate, the pH value should generally be less than or equal to 2. In the case of calcium carbonate, the pH value should normally be between 6 and 7.

Obviously, too high a concentration of additives would rapidly decrease the moisture resistance of the formed vapor barriers. It was found that particles of the desired fineness may still be produced when polyvinyl acetate is used as an additive. This additive is not as good as hydrated aluminum silicate or calcium carbonate to provide a mixture with a good retransformation capacity in the paste, however, it has a less negative influence on the imperviousness of the vapor barrier coating. On the other hand, the combined use of polyvinyl acetate and calcium carbonate gives excellent results in terms of reshaping ability and impermeability. Other additives, which give satisfactory results, include polystyrene, polyacrylate emulsions and the like.

The following are examples of embodiments of the composition and process according to the invention, in connection with FIGS. 1 ... 4, which represents:

FIG. 1, paper obtained by using virgin cellulose fibers;

- Figure 2, paper obtained by re-transforming the paste into a flexible packaging, having a vapor barrier, according to the invention;

- fig. 3, paper as in fig. 1, at which the vapor barrier is PVDC (polyvinylidene chloride);

- Figure 4, paper as in Figure 1, in which the vapor barrier is polyethylene.

It will be readily observed that, in practice, the coating of the known state of the art is not retransformable into the paste, as is accomplished by the present invention on paper, which is equivalent to a paper made from virgin vibes.

Example 1. The coating composition is prepared by mixing 80 parts of a polyvinylidene chloride emulsion, which is sold under the trade mark SERFENE 2022, with 20 parts of a hydrated aluminum silicate slurry, bearing the trade mark OMNIFIL. The pH value of this mixture, which contains 54.5% solid material, is adjusted to 2.1 and using this mixture a coating is formed on a flexible wrapping paper product. For reprocessing as a paste, the coated product is broken (fragmented) into particles smaller than 1.5 mm, which, in practice, allows the entire coating to be re-transformed into paste.

MVTR (moisture vapor transmission rate, 100% RH, 37.8 ° C) 25 g / m²coating on the lining plate: 15 g / m²/day.

Example 2. Repeat the operations from Example 1, except that OMNIFIL is replaced by 10 parts calcium carbonate, sold under the trademark PULPRO 3 and 10 parts of a polyvinyl acetate homopolymer, sold under the trademark DARATACK 7IL. The pH value is set to 6.2. The mixture contains 55.7% solid material. When re-transforming into paste, particles smaller than 1.2 mm are obtained.

MVTR: 4 g / m²/day.

Example 3. Repeat the operations from example 1, except that 66 parts of SERFENE 2002 emulsion are used with 27 parts of DARAN SLI 12^(R) which is a copolymer of vinylidene chloride, methyl methacrylate and acrylonitrile and 7 parts of DARATACK 7IL.

The pH value is set to 2.1. The mixture contains 51.5% solid material. When re-transforming into paste, particles smaller than 1.5 mm are obtained.

RO 117922 Β1

MTVR: 1.5 g / m^{1 2 3}/day.

Example 4. Repeat the operations from example 1, except that 85 parts 245 of SERFENE 2022 are used with 15 parts of DARATACK 7IL. The pH value is adjusted to 2.1 and the mixture contains 50.8% solid material. When retransformation into the paste, particles smaller than 1.5 mm are obtained, which allows all the coating to be retransformed into the paste.

MVTR: 4 g / m²/ day 250

Example 5. Repeat the operations from example 1, except that 75 parts of SERFENE 2022 are used with 15 parts PULPRO 8 (trademark for calcium carbonate as slightly coarser particles than PULPRO 3) and 10 parts DARATACK 7IL. The pH value is adjusted to 6.2 and the mixture contains 58% solid material. Particles smaller than 1.5 mm are obtained when retransformation into the paste. 255

MVTR: 8 g / m²/day

Example 6. Repeat the operations from Example 1, except that 75 parts of SERFENE 2022 are used with 11 parts PULPRO 8 and 14 parts LZTRON 604 (trademark for an emulsion made of spherical, light, hard and uniform polystyrene polymer particles. ). The pH value is set to 6.1 and the mixture contains 54% solid material. At 260 retransformation in the paste, particles smaller than 1.6 mm are obtained.

MVTR: 5 g / m²/day

It can be seen that, in all examples, the particles are equivalent in size with the fibers still in use, which means that they can be easily reprocessed and that, in practice, the rate of moisture vapor transmission is equivalent to that of chloride of 265. polyvinylidene (PVDC).

The tests performed with the paper coated with a composition according to the invention show that, by retransformation in the paste, in proportion of 97%, particles smaller than 1.6 mm are obtained, after 30 minutes of retransformation in the paste.