WO1993011300A1

WO1993011300A1 - A method for reducing the permeability of paper and board and a substance for the method

Info

Publication number: WO1993011300A1
Application number: PCT/FI1992/000305
Authority: WO
Inventors: Antti Hamunen; Kari Nurmi
Original assignee: Raision Tehtaat Oy AB
Current assignee: Raisio Oyj
Priority date: 1991-11-25
Filing date: 1992-11-11
Publication date: 1993-06-10
Anticipated expiration: 1994-05-25
Also published as: FI90793C; NL9220027A; NL194977C; GB2287420B; DE4294110T1; CA2124194A1; FR2685018B1; FI915541L; SE9401765D0; FI90793B; GB9408432D0; FI915541A0; SE9401765L; GB2287420A; SE505439C2; FR2685018A1

Abstract

The invention concerns the permeability of paper and board substrate. The permeability of the substrate is reduced by coating it with a modified coating mixture, which is based on a polymer dispersion containing at least one modified starch component. The polymer is prepared preferably by grafting monomers onto the modified starch structure.

Description

A method for reducing the permeability of paper and board and a substance for the method

The object of this invention is a method for reducing the permeability of paper and board in which state the treat¬ ed product possesses sufficiently good barrier prop¬ erties against gases and vapours such as water vapour as required in the packaging industry, for example. Despite possessing this property, paper or board treated in ac- cordance with this method is readily disposable as waste by, for example, composting or recycling the product back as raw material for the fibre-consuming industry (i.e. the product can be re-pulped; i.e. disintegrated into fi¬ brous material without causing problems when used again in papermaking) . The invention also involves the substance by means of which the aforementioned properties are achieved.

Increasingly strict regulations pertaining to environ- mental protection have led to a situation in which the manufacturers of packaging materials, for example, are required to organize the post-consumption treatment of the resultant waste in an environment-friendly manner. In other words, packaging waste has to be either recycled to provide industria^'' raw material or it has to be disposed of by composting, i-αr example. If the latter option is resorted to, then the material as a whole must be biode¬ gradable without releasing any environmentally hazardous chemicals.

The above requirements mean that the continued use of conventional solutions (e.g. papers whose non-permeabi¬ lity has been achieved by a plastic film lamination) lead to high costs because of the material's poor degradabili- ty and unsuitability for recycling. This is so in packag¬ ing situations where the package is required to possess barrier properties against water vapour, for instance. Certain commonly used polymers that possess good barrier properties (e.g. products containing polyvinyl chloride) cannot be disposed of by burning because of the hazard caused by hydrogen chloride gas and dioxin.

The purpose of this invention is to eliminate the above shortcomings and to make available a paper product which, while offering adequate barrier properties, ^"can be re¬ cycled as raw material for the paper industry or disposed of by composting or left to decompose in landfills, for instance.

The method in accordance with the invention is based on spreading onto the surface of paper or board a dispersion product containing a component that includes modified starch. The said dispersion product can also be spread between the layers making up paper or board in which case the polymer layer formed when the dispersion dries pro¬ vides the required barrier protection. When spread be¬ tween the layers, the dispersion also forms an adequate adhesion between the layers and thus no actual gluing treatment is needed.

It is known that papers can be treated with products con¬ taining wax dispersions in order to provide them with protection against moisture. It is also known that the said products usually contain commonly used synthetic polymer dispersions such as styrene butadiene, aerylate or polyvinyl acetate latexes that provide the products with adequate adhesion. The proportion of latexes in the total polymer dispersion's solid matter content is gene¬ rally high. Examples of the above technology are to be found in patent literature; e.g. GB 1 593 331 (J. Vase, emi Oy) and the Finnish patent application 901928 (Neu- siedler AG) contain descriptions of this technology.

The technology in accordance with these inventions pro¬ vides an adequate barrier against water vapour. However, seeing as the proportion of latex composed entirely of synthetic substances is high, the product's recyclabili- ty is impaired as a result of the latex-based disturban¬ ce substance accumulation when such material is made into pulp. On the other hand, if the proportion of wax disper¬ sion is in the vapour barrier substance is raised excess¬ ively, the dispersion's adhesive and gluing properties are impaired as is also the printability of the treated surface due to its ink repelling property.

The present invention's point of departure has been to avoid the aforementioned shortcomings by preparing the dispersion so that it contains components that promote the disintegration of the synthetic product in nature and during the various stages of recycling processes. This has been executed either (A) by joining natural polymer chains (especially starch) to the latex polymer at the manufacturing stage or (B) by replacing a significant part of the latex polymer with a combination polymer - starch graft copolymer - consisting of starch and a syn¬ thetic substance. It has been observed that paper prod¬ ucts treated with thus manufactured dispersions are more readily made into pulp than papers treated with latexes made according to conventional recipes. Moreover, the dispersion residuals formed in conjunction with pulping to be considerably less likely to form disturbance resid¬ uals that cause serious problems in the recycling of pa¬ per products treated with synthetic adhesives. In extreme cases, the amount of synthetic monomers can be low - even nil. Actually, the properties of a dispersion manufac¬ tured in this manner are impaired in that the coater sub¬ stance's adhesion is low but still such a dispersion may find use in less demanding situations.

As is pointed out in the above, applications for ^r sper- sions manufactured in accordance w th the invent..,-... are mainly in conjunction with packaging materials and wrap- pings that are required to possess certain moisture and vapour barrier properties. In these cases the dispersion can be used in place of conventional plastic/paper la¬ mination solutions that are non-recyclable as well as being very slowly degradable in nature on the part of their plastic component.

When dispersions manufactured in accordance with the pre¬ sent invention are used, the resultant paper products degrade relatively quickly in nature. When compared to products made using fully synthetic latexes, the degra- dability of products treated with dispersions manufac¬ tured in accordance with this invention is also better because the starch components contained by the dispersi- on and polymer structure offer a natural substrate for - naturally occurring decomposing hydrolytic enzymes. A polymer dispersion offering better recycling and degra¬ ding properties, and manufactured in the manner descri¬ bed in the above, has reasonable barrier properties to offer as such. When necessary, the vapour barrier pro¬ perties can be further modified by means of additives such as a wax dispersion.

The following is a description of ways according to which polymers forming the structure of the dispersion can be manufactured.

(A) Manufacturing of latex containing starch in a poly¬ mer structure.

The principle here is that the reaction medium used in the manufacturing of latex by means of the emulsion polymerization method is a water solution containing con¬ ventional additives such as initiators acting as cata- lysts (persulphates, peroxides) and surface-active sub- . stances and starch dissolved into the water phase by heating. When this is the case, the initiators cause radicals to form onto the starch structure and these rad¬ icals then act as the initial centres of the polymeri¬ zation reaction. In other words, in addition to the fully synthetic material formed in normal emulsion polymeri- zation, one obtains starch graft copolymer material in which the polymer chains formed of the synthetic monomers used are covalently attached to the starch structure.

Since native starch - regardless of its origin - is a macromolecular compound and water solutions of it have very high viscosities even in very low solid matter con¬ centrations, one must first reduce the molecular size of the starch or better still use commercially available starch qualities which have usually been split up by means of oxidization. In the event that the user wishes to carry out the oxidization-based splitting up in con¬ junction with the reaction, this can be done using a known art method advantageously as the first stage in the reaction by using the oxidizing initiators acting as polymerization catalysts.

In order that the viscosity of the polymer dispersion obtained as the end product might fall within the appro¬ priate range and that it might be a replicable constant, one must take great care to ensure that the degree of splitting of the starch is always precisely that which is required. This can be done by means of viscosity determi¬ nation, end group analysis or gel permeation chromatogra- phy. The initial starch used in the following examples is either a commercial, hydrogen peroxide oxidized potato starch Raisamyl 302P with a viscosity of 20-30 Pas when 2d as a 10% solution at a temperature of 60 °C or na¬ ve potato starch that has been split up enzymatically by alpha-amylase possessing temperature stability with respect to Bacillus licheniformis in the manner described, in the example. Example 1 :

(Al) 34.30 g of oxidized starch Raisamyl 302P were added to 150 g of water and then transferred into a pressure- proof reactor vessel. The temperature of the mixture was raised to 100 °C for a period of 20 minutes in order to dissolve the grains of starch. Following this the mixtu¬ re was cooled down to 70 °C after which a solution con¬ taining 2.5 g of sodium lauryl sulphate in 50 ml of wa- ter. A monomer mixture containing 116.8 g of styrene,

73.9 g of butadiene washed with a solution of lye and 3.0 g of acrylic acid were then gradually added to the mix¬ ture over a period of two hours. Initiator solution con¬ taining 3.0 g of ammonium persulphate in 70 g of water was added from another pressure burette. The polymerizat¬ ion reaction was then allowed to proceed for 12 hours. The end product was a white dispersion with a solid mat¬ ter concentration of 45.8% and a viscosity of 890 mPas as measured by a Brookfield LVT viscometer using measuring head no. 2 at 2100 r/min. The measurements were conducted after the product had been neutralized with NaOH to a pH of 6.8. The product's calculatory starch concentration was 13%.

Example 2:

' (A2) 34.5 g of oxidized starch were added to 150 g of water and boiled for 20 minutes in order to dissolve the grains of starch. Following this 2.5 g of sodium lauryl sulphate in 50 ml of water were added to the solution as was the catalyst solution and the monomer solution as mentioned in connection with 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 dry matter concent¬ ration of the neutralized product was 40.8% and its vis¬ cosity was 600 mPas at a temperature of 25 °C. Example 3: 49.4 g of oxidize- tarch were added to 370 g of water and boiled for 20 mi-iutes in order to dissolve the grains of starch. The reaction mixture was provided with an inert atmosphere by means of a flow of nitrogen. Next, 0.1 g of CuS0₄ was added followed by the addition during a period of 1.5 hours of a monomer mixture com¬ posed of 75 g of acrylic acid and 53 g of acrylic nitri¬ te in drops. This was accompanied by the concurrent ad- dition to the reaction mixture of 6 g of 30% hydrogen peroxide given over a period of 2 hours. The reaction was allowed to proceed for 11 hours at a temperature of 70 °C. The product thus obtained was a white dispersion with a dry matter concentration of 26.3%.

Example 4:

(Bl) Starch copolymer production. 250 g of native potato starch with a moisture content of 16% were mixed into 220 g of water. This was followed by adding 0.05 U/g of starch of alpha-amylase possessing a temperature stabi¬ lity with respect to B. licheniformis and with an acti¬ vity value of 984 U/ml. While mixing the suspension vi¬ gorously, its temperature was raised to 90 °C and kept there for 30 minutes. As a means of stopping enzymatic activity 0.5 ml of 30% hydrogen peroxide was added and the temperature was brought down to 60 °C. A flow of ni¬ trogen was led into the reaction mixture, 0.2. g of CuS0₄ were added, and 38 g of styrene and 6 g of 30% hydrogen peroxide were administered in drops at the same time for a period of 1.5 hours. The reaction was allowed to pro¬ ceed for another 2 hours at the end of which the result¬ ant white dispersion was cooled down to room temperature. The dispersion's viscosity at 25 °C was 670 mPas and its solid matter concentration was 51.8%.

Example 5: (B2) Starch graft polymer was produced in the manner described in Example 3 above using butyl acrylate (75 g) as the monomer to be grafted. The amount of starch was 209 g and it was added to 217 g of water. The resultant product was a yellowish dispersion with a room tempera¬ ture viscosity of 610 mPas and a solid matter concentra¬ tion of 50.5%.

Example 6:

This example describes the compositions of the formula¬ tions finally spread onto paper surface, containing dis¬ persions according to examples 1-4 and control formula- tions and the properties of papers treated with them.

LD460 is a styrene butadiene latex, manufactured by Rai- sion Lateksi Oy, RN1125 is a vinyl acetate acrylate la¬ tex, manufactured by Rasional Oy, vahad is a wax disper¬ sion containing paraffin with a melting range of c. 50- 70 °C.

Using a laboratory coater machine (Endupapp) , the dis¬ persion was spread onto board (grammage 190 g/m ) . The board was then measured for its water vapour permeability (WWP) in accordance with the ISO 258-1974 method (unit: g/m²/24h) . PM= amount of dispersion spread (g/m²) .

The value PA in the table depicts the pulpability pro¬ perties of treated board. The value is obtained as fol- lows: the treated board was broken down in accordance with the method SCAN-C 18:65. The pulped material was made into laboratory sheets (grammage: c. 100 g/m²) . The sheet quality was assessed using a scale of 0 - 5 in which 0 indicates good pulpability (no accumulations of surface treatment material observed) and 5 indicates poor pulpability (numerous accumulations of surface treatment substance or unevenness due to incomplete breaking down of material)

Example 7:

In this example two pieces of board are made into a lami¬ nated product by means of a dispersion manufactured in accordance with the invention. Dispersions R3, R6 and R8 were spread onto boards using amounts that corresponded to c. 20 g/m² of solid matter. Immediately after this step another sheet of the same board was pressed against the treated surface and the thus formed laminated product was then allowed to dry. The outcome of the gluing oper¬ ation was assessed on the basis of the fibre tear pro¬ duced when the two layers were separated from one another (total fibre tear = excellent adhesion) . The laminates were also measured for their vapour barrier values.

WWP (g/nτ/24h)

29

28

12

Claims

PATENT CLAIMS:

1. A method for reducing the permeability of paper or board by coating paper or board with a coater consisting of one or more polymer dispersions, characterized in that the polymer dispersion used in the coater substance con¬ tains a component containing modified starch.

2. A coater substance for a method as claimed in claim 1, characterized in that the component containing starch has been prepared by emulsion polymerization of dissolved, split up starch in water phase by means of a monomer mix¬ ture by feeding the monomer mixture into a water phase containing 2-25% of starch as calculated from the finish- ed dispersion's solid matter.

3. A coater substance as claimed in claim 2, character¬ ized in that the polymer dispersion s starch-containing component has been prepared using a monomer mixture con- taining styrene and butadiene as its main components.

4. A coater substance as claimed in claim 2, character¬ ized in that the starch-containing component of the poly¬ mer dispersion has been prepared using a monomer mixture containing esters of vinyl acetate and acrylic acid and lower alcohols (methyl, ethyl, propyl or butyl) as its main components.

5. A coater substance as claimed in claim 2, character- ized in that the polymer dispersion's starch-containing component has been prepared using a monomer mixture con¬ taining acrylic acid and acryl nitrate as its main com¬ ponents.

6. A coater substance as claimed in claim 1, character¬ ized in that the polymer dispersion's starch-containing component has been prepared by grafting to the split up starch unsaturated monomer in amounts corresponding to 0- 50% of the amount of starch.

7. A coater substance as claimed in claim 6, character- ized in that the polymer dispersion's starch-containing component has been produced by grafting a styrene monomer onto split up starch.

8. A coater substance as claimed in claim 6, character- ized in that the polymer dispersion's starch-containing component has bee prepared by grafting onto the split up starch an ester monomer formed of acrylic acid and lower alcohols.

9. A coater substance for reducing the permeability of paper or board, characterized in that it contains a poly¬ mer dispersion containing 10-100% of starch-containing polymer component and 0-90% of a starch-free component and 0-30% of a wax dispersion.

10. A coater substance as claimed in claim 9, character¬ ized in that the starch-free polymer dispersion is styrene butadiene latex.

11. A coater substance as claimed in claim 9, character¬ ized in that the starch-free polymer dispersion is vinyl acetate - acryl latex.

12. A coater substance as claimed in claim 9, character- ized in that the melting point of the wax used in the dispersion is c. 50-70 °C.

13. A method as claimed in claim 1, characterized in that the coater substance is spread between two or more paper and/or board layers and that the layers are bound to one another using the coater substance. AMENDED CLAIMS

[received by the International Bureau on 21 April 1993 (21.04.93); original claims 1 and 5 amended; other claims unchanged (2 pages)]

1. A method for reducing the gas and vapour permeability of paper or board by coating it with a coater consisting of one or more polymer dispersions, characterized in that the polymer used in the coating dispersion at least partly consists of modified starch.

2. A coating substance for a method as claimed in claim 1, characterized in that the component containing starch has been prepared by grafting of dissolved, split up starch in water phase by means of a monomer- mixture by feeding the monomer mixture into a water phase containing 2-25% of starch as calculated from the finished disper- sion's solid matter.

3. A coating substance as claimed in claim 2, character¬ ized in that the polymer dispersio 's starch-containing component has been prepared using a monomer mixture con- taining styrene and butadiene as its main components.

4. A coating substance as claimed in claim 2, character¬ ized in that the starch-containing component of the poly¬ mer dispersion has been prepared using a monomer mixture containing esters of vinyl acetate and acrylic acid and lower alcohols (methyl, ethyl, propyl or butyl) as its main components.

5. A coating substance as claimed in claim 2, character- ized in that the polymer dispersion's starch-containing component has been prepared using a monomer mixture con¬ taining acrylic acid and acryl nitrile as its main com¬ ponents.

6. A coating substance as claimed in claim 1, character¬ ized in that the polymer dispersion's starch-containing component has been prepared by grafting to the split up starch unsaturated monomer in amounts corresponding to 0- 50% of the amount of starch.

7. A coating substance as claimed in claim 6, character- ized in that the polymer dispersion's starch-containing component has been produced by grafting a styrene monomer onto split up starch.

8. A coating substance as claimed in claim 6, character- ized in that the polymer dispersion's starch-containing component has been prepared by grafting onto the split up starch an ester monomer formed of acrylic acid and lower alcohols.

9. A coating substance for reducing the permeability of paper or board, characterized in that it contains a poly¬ mer dispersion containing 10-100% of starch-containing polymer component and 0-90% of a starch-free component and 0-30% of a wax dispersion.

10. A coating substance as claimed in claim 9, character¬ ized in that the starch-free polymer dispersion is styrene butadiene latex.

11. A coating substance as claimed in claim 9, character¬ ized in that the starch-free polymer dispersion is vinyl acetate - acryl latex.

12. A coating substance as claimed in claim 9, character- ized in that the melting point of the wax used in the dispersion is c. 50-70 °C.

13. A method as claimed in claim 1, characterized in that the coating substance is spread between two or more paper and/or board layers and that the layers are bound to one another using the coating substance.