FI90793C - Method for reducing the permeability of paper or board and the substance used in the method - Google Patents

Description

90793

The method for reducing the permeability of paper or board and the substance used in the method

The invention relates to a method for reducing the permeability of paper or board 5, as the product obtained has e.g. a sufficiently good barrier property for the passage of gases and vapors, such as water vapor, required in the packaging industry. Despite this property, according to the method, the paper or board treated as waste hello mail can be treated, e.g. by composting or recycling, the product back into a raw material for the fiber-using industry (i.e. problems). The invention 15 also relates to a substance by means of which the above-mentioned properties are obtained.

Tightening environmental protection requirements have led to e.g. packaging materials must be disposed of by users after use, which does not cause environmental problems. In other words, packaging waste must be able to be either reused as an industrial raw material or disposed of, for example, by composting, which requires that the material as a whole is naturally volatile and does not produce chemicals that are hazardous to the environment when decomposed.

These requirements mean that, especially in packaging sites where packaging is required to have barrier properties (e.g. barrier properties) against e.g. water vapor permeability, the solutions traditionally used - such as papers in which the barrier property is obtained by laminating a plastic film to the paper - lead to in the treatment of seasonal material at high cost due to the poor degradability and non-recyclability of 35 materials. Some commonly used polymers with good barrier protection, such as products containing polyvinylidene chloride, can also not be disposed of by incineration due to the danger of hydrogen chloride gas and dioxin formed in 2 tanks.

The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a paper product which, while providing sufficient barrier properties, is reusable as a raw material for paper and can in addition be disposed of by composting or allowed to decompose, e.g. in landfills.

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The method according to the invention is based on the application of a dispersion product having a modified starch component to the surface of paper or board. The dispersion product can also be applied between the layers of paper or board, whereby the polymer layer formed when the dispersion dries provides the necessary barrier protection. When applied between layers, the dispersion also forms sufficient adhesion between the layers, so that a separate gluing treatment is not required.

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It is already known that papers can be treated with products containing wax dispersions to provide moisture protection. It is also known that these products usually contain synthetic polymer dispersions, such as styrene butadiene, acrylate, or polyvinyl acetate latexes, which are commonly used to provide adequate adhesion. Latexes generally account for a large proportion of the total solids content of the polymer dispersion. Examples of the described technology can be found in 30 patent literature. See, e.g., GB 1,593,331 (J. Vase, Kemi

Oy) and Finnish patent application no. 901928 (Neusiedler AG) describe a technology similar to that shown.

The technique of these inventions provides adequate water vapor barrier protection. However, when the proportion of latex composed entirely of synthetic materials is high, the recyclability properties of the product deteriorate due to the accumulation of interfering substances from the latex during pulping. On the other hand, if the proportion of wax dispersion in the vapor barrier is increased too much, the adhesion and gluability properties of the dispersion will suffer, as will the printability of the treated surface due to the rejection of the ink.

The starting point of the present invention has been to overcome the above drawbacks by preparing the dispersion so that it contains components which promote the degradability of the synthetic product in the environment as well as at various stages of the recycling processes. This is accomplished either (A) by incorporating naturally occurring polymer chains into the latex polymer at the manufacturing stage, especially from starch, or (B) by replacing a significant portion of the latex polymer with a starch-synthetic copolymer of the starch and synthetic material. . It has been found that paper products treated with dispersions prepared in this way pulp with a lighter-20 bomb than papers treated with latices prepared by conventional recipes. In addition, the dispersion tensions formed during pulping tend to have a much lower tendency to form interfering substances, which is a serious problem in the recycling of paper products treated with synthetic binders. The amount of synthetic monomer can in the extreme case be very small, even zero. Although the properties of the dispersion thus prepared deteriorate to the extent that the adhesion of the coating remains low, the dispersion 30 may have use in less demanding applications.

The uses of the dispersions prepared according to the invention, as already indicated above, are mainly packaging materials and wrappers, which are expected to provide a certain degree of protection against moisture and moisture. In these applications, the use of dispersion can replace traditional plastic / paper laminate solutions, which are non-recyclable, and in addition, their degradation in nature for plastics is extremely slow.

Paper products made using dispersions made in accordance with the present invention, on the other hand, are relatively well degradable in nature. Compared to products made with fully synthetic latexes, the degradability is also better because the starch parts contained in the dispersion and the polymer backbone provide a natural attachment site for naturally occurring degrading hydrolysis enzymes. A polymer dispersion prepared in the above-described manner, which gives better recycling and degradability properties, already provides reasonable barrier properties per se. If necessary, the vapor barrier properties can be further modified by adding to the mixture, e.g. a wax dispersion.

The following describes ways in which the polymers that make up the dispersion body can be prepared.

20 (A) Preparation of latex from starch in polymer backbone.

The principle is that in the preparation of the latex by the emulsion polymerization process, an aqueous solution is used as the reaction medium, which, in addition to the usual excipients, such as catalyst initiators (persulphates, peroxides) and surfactants, is added. In this case, under the influence of the initiators on the starch backbone, radicals are formed which act as the initial centers of the polymerization reaction. That is, in addition to the normal fully synthetic material formed in emulsion polymerization, a starch graft copolymer material is formed in which the polymer chains formed from the synthetic monomers used are covalently attached to the starch backbone.

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Since natural starch, regardless of its origin, is a very high molecular weight compound and, as a result, its aqueous solution already has a high viscosity at very low solids content, the molecular size of the starch must be calculated first, or preferably by using commercially available, usually oxygenated digested starch grades. If oxidative cleavage is desired to be carried out in connection with the reaction, it is possible in a manner known per se, preferably as a first step in the reaction using oxidizing initiators acting as polymerization catalysts.

15 In order for the viscosity of the final polymer dispersion to be within a usable range and reproducibly constant, care must be taken to ensure that the degree of degradation of the coating is always exactly desired. This can be done, for example, by viscosity analysis, end group analysis or gel permeation chromatography. In the following examples, hydrogen peroxide-oxidized commercial potatoes from Raisamyl 302P with a viscosity of 10-30 mPas at 10 ° C as a 10% solution, or native potato starch digested with Bacillus alpha-alpha as shown in the example.

Example 1: 30 (Al) 34.30 g of oxidized RKD Rylamyl 302P was slurried in 150 g of water and transferred to a pressure vessel. The temperature of the mixture was raised to 100 ° C for 20 min. for the time to dissolve the starch grains. The mixture was then cooled to 70 ° C and a solution of 2.5 g of sodium lauryl sulfate in 50 ml of water was added. To this mixture, a monomer mixture containing 116.8 g of styrene and 73.9 g of butadiene washed with a lye solution and 3.0 g of acrylic acid was gradually added over a period of 6 hours. From the second pressure bed, an initiator solution containing 3.0 g of ammonium persulfate in 70 g of water was added. The polymerization reaction was allowed to proceed for 12 hours. The product was a white dispersion with a solids content of 45.8% and a viscosity of 890 mPas, measured on a Brookfield LVT viscometer at a No. 2,100 rpm speed.

Measurements were performed after the product was neutralized with NaOH to pH 6.8. The calculated starch content of the product is 13%.

Example 2: (A2) 34.5 g of oxidized starch was slurried in 150 g of water and boiled for 20 minutes to dissolve the starch. To the solution was added 2.5 g of sodium lauryl sulfate in 50 ml of water, as well as a catalyst-20 solution and a monomer solution according to Example 1. The composition of the monomer solution in this case was 146 g of vinyl acetate and 22 g of butyl acrylate. The reaction was allowed to proceed for 14 hours. The neutralized product had a dry matter content of 40.8% and a viscosity of 600 mPas at 25 ° C.

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Example 3 (A3) 49.4 g of oxidized starch was slurried in 370 ml of water and the mixture was boiled for 20 minutes to extract the starch. An inert atmosphere was introduced into the reaction mixture by a stream of nitrogen. 0.1 g of CuSO 4 was added and a monomer mixture consisting of 72 g of acrylic acid and 53 g of acrylonitrile was added dropwise over 1.5 h. At the same time, 6 g of 30% hydrogen peroxide was charged to the reaction mixture within 2 hours. The reaction was allowed to proceed at 70 ° C for 11 hours. The product was a white dispersion with a dry matter content of 26.3%.

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Example 4: (B1) Preparation of a starch copolymer. 250 g of native pe-5 russet starch with a moisture content of 16% was slurried in 220 g of water. To the suspension was added 0.05 U / kg of B. licheniformis thermostable alpha-amylase with an activity of 984 U / ml. The temperature of the suspension was gradually raised to 90 ° C with good stirring and kept at this temperature for 30 min. I drive. To stop the enzyme activity, 0.5 ml of 30% hydrogen peroxide was added and the temperature was lowered to 60 ° C. A stream of nitrogen was introduced into the reaction mixture, 0.2 g of CuSO 4 was added and 38 g of styrene and 6 g of 30% hydrogen peroxide were added dropwise simultaneously over 1.5 hours. The reaction was allowed to proceed for a further two hours, after which the resulting white dispersion was cooled to room temperature. The viscosity of the dispersion at 25 ° C was 670 mPas and the solids content was 51.8%.

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Example 5: (B2) The preparation of the starch graft copolymer was carried out as in Example 3 using butyl acrylate (75 g) as the grafting monomer. The amount of starch was 209 g and it was slurried in 217 g of water. The product obtained was a yellowish dispersion with a viscosity at room temperature of 610 mPas and a solids content of 50.5%.

30 Example 6.

This example illustrates the compositions of the final paper spreads containing the dispersions of Example 1-4 and the reference formulations, as well as the properties of the papers treated therein. LD460 is a styrene-butadiene latex, manufactured by Raision Lateksi Oy, RN1125 is a vinyl acetate acrylate latex, manufactured by Rasional δ ΟΥ, waxes are a wax dispersion containing M paraffin wax with a melting range of about 50-70 ° C.

The dispersion was applied by means of a laboratory baling machine (En-5 dupapp) to cardboard (basis weight 190 g / m2), from which water vapor permeability values (WWP) were measured according to the big 258-1974 method (unit g / m2 / 24h.) PM = amount of applied dispersion dry ( g / m2).

10 The value PA in the table describes the pulpability properties of the treated board. The value is defined as follows: the treated board is decomposed according to the method SCAN-C 18:65. Laboratory sheets (basis weight approx. 100 g / m2) were prepared from the stock. The quality of the sheet was rated on a scale of 0 to 15 5, where 0 indicates good pulpability (no build-up due to surface treatment agent) and 5 poor quality (high surface treatment agent selection or unevenness due to poor pulp decomposition).

20 Table 1.

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 LD460 100 - - - - 70 70 60 90 RN1125 - 100 - - - - - 25 A1 - 100 go - - - - A2 ---- 100 ----- A3 _____ 100 ---- B1 ______ 30 - 30 - 30 B2 _______ 30-- waxes - - - 10 - - - - 10 10 PM 17.8 20.2 19.9 18.7 21 .0 20.3 19.4 20.3 20.1 18.0 0 35 WWP 29 98 32 7 36 4 27 38 8 5 151 PA 5322001114 0

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Example 7.

In this example, a laminate product is formed from two cartons by means of a dispersion 5 prepared according to the invention. Dispersions R3, R6 and R8 were applied to the board in a quantity corresponding to about 20 g / m2 solids. After this, another sheet of the same board was pressed onto the treated surface, and the laminate product thus formed was allowed to dry. The gluing result was evaluated on the basis of the fiber tear formed when separating the 10 paperboard layers (complete fiber tear = excellent adhesion). Vapor barrier values were also measured for the laminates.

15 Table 2.

Fiber breakage WWP (g / m2 / 24h) 20 R3 Perfect 29 R6 Perfect 9 R7 Perfect 28 R9 Låhes perfect 12 25

Claims (13)

A method of reducing permeability in paper or paperboard by coating the paper or cardboard with a coating agent containing one or more polymer dispersions, characterized therein, using a coating agent in which the polymer dispersion contains a component containing modified starch . 15 2. A process according to claim 1, characterized in that, as a starch-containing component, a product obtained by emulsion polymerization of an enriched, split-phase aqueous phase with a monomer mixture is used, by feeding the monomer mixture into aqueous phase containing 2 to 50%. strength based on the solid substance of the finished dispersion. 3. A process as claimed in claim 2, characterized in that, as the starch-containing component of the polymer dispersion, a product obtained by using a monomer mixture containing styrene and butadiene is used. 4. A process according to claim 2, characterized in that, as the starch-containing component of the polymer dispersion, a product obtained by depleting a monomer mixture containing vinyl acetate and a (methyl, ethyl, propyl or butyl) ester of acrylic acid is used. lower alcohols. 5. A process according to claim 2, characterized in that, as the starch-containing component of the polymer dispersion, a product obtained by using a monomer mixture containing acrylic acid and acrylonitrile is used. 5 6. A process according to claim 1, characterized in that as the starch-containing component of the polymer dispersion, a product prepared by grafting an unsaturated monomer to the split starch is used in a quantity of 0 to 50% of the starch. 7. A process according to claim 6, characterized in that as the starch-containing component of the polymer dispersion, a product produced by grafting styrene monomer to the split starch is used. 8. A process according to claim 6, characterized in that, as the starch-containing component of the polymer dispersion, a product obtained by grafting an ester monomer of acrylic acid and lower alcohols to the split starch is used. Coating agent for the process according to claim 1, characterized in that it consists of a polymer dispersion containing from 10 to 100% of one of the starch-containing components prepared according to any one of claims 2-8, and 90% of a starch-free component, and 0-30% of a wax dispersion. 10. Coating agent according to claim 9, characterized in that the starch-free component is styrene-butadiene latex. II. Coating agent according to claim 9, characterized in that the starch-free component is vinyl acetate-acrylate latex. 12. Coating agent according to claim 9, characterized in that the wax used in the dispersion has a melting point of about 50-70 ° C. 13. A method according to claim 1, characterized in that the coating agent is applied between two or more paper and / or cardboard layers and the layers are joined to each other with the coating agent. II