Compositions: coating or plastic – Coating or plastic compositions – Natural resin or derivative containing
Reexamination Certificate
2000-10-13
2002-08-20
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Natural resin or derivative containing
C106S241000, C162S180000, C162S181500
Reexamination Certificate
active
06436181
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a sizing composition comprising an aqueous dispersion of a rosin material and a polyaluminium compound, and to a method of sizing a cellulosic fibre material.
BACKGROUND
One of the main properties of paper, paperboard and similar products is hydrophobation or resistance to penetration by water and other liquids, such as lactic acid, hydrogen peroxides solutions, etc. Hydrophobation also plays an important role in printing properties, affecting the way inks are adsorbed on paper products. The two main methods for conferring hydrophobic properties to paper products are internal sizing, which gives a hydrophobic effect in the entire paper structure, surface sizing, more or less limited to the actual surface structure, and a combination of both methods. The most common hydrophobic agents in internal sizing are rosin, synthetic sizing agents, such as alkyl ketene dimers, isocyanates, acid anhydrides and carbamoyl chlorides and combinations of both components.
It has recently been experienced, however, that the initial liquid packaging board resistance to edge penetration by lactic acid and hot hydrogen peroxide-containing solutions achieved by traditional products or methods is not always maintained over time, which often means economic, converting and end-use problems. In addition, deficient ink jet properties, such as wicking, drying time, color appearance, etc, also imply serious end-use problems.
It has been shown that internal sizing with a cationic rosin size (CRS), such as those disclosed in ES-8900750, GB-2159153, EP-O-200002, U.S. Pat. No. 3,966,654 and U.S. Pat. No. 4,199,369, or with a conventional anionic rosin size (emulsion, paste or soap) gives the finished paper good resistance to penetration by water, but it also has some drawbacks, such as some limitations in pH and temperature, the difficulty to give the paper a good resistance to penetration by acid liquids or the need to be used in comparatively high amounts to give a satisfactory sizing effect. On the other hand, rosin dispersions are widely used and cannot in all circumstances be replaced by synthetic sizing agents; rosin dispersions give, for example, a good adhesion to yankee cylinders.
Synthetic sizing agents react with the cellulose to give an irreversible bond. Although these sizing agents generally lead to a very good sizing effect, both to water and other liquids, they do also have some disadvantages. For example, sizing must be carried out at neutral or slightly alkaline pH's (between 7 and 8.5) to be effective, there is a risk of hydrolysis in water and synthetic sizing agents cannot give the finished paper a good resistance to penetration by hot peroxides. Moreover, although synthetic sizing agents give good ink holdout and brighter colors, some other ink jet properties are relatively poor, such as wicking, drying time or color-to-color bleed.
It is known to combine rosin and some synthetic sizing agents, which allows to overcome some of the aforementioned disadvantages when they both are used alone. For example, EP-A-0074544 discloses a method of sizing using cationic dispersions which contain as dispersed phase particles of fortified rosin as well as particles of the synthetic sizing agent. EP-O-275851 discloses a method of sizing utilizing the above cationic and anionic dispersions which further contain a polyaluminium compound. DE-A1-41 03 169 discloses a sizing composition including a conventional sizing agent together with an aluminium phosphate that contains on the average 1.5-3 phosphor atoms per aluminium atom. EP-O-693589 discloses a method of sizing paper and similar cellulose products containing precipitated calcium carbonate as a filler using the above dispersions. In WO 96/35841 a watersoluble inorganic alkali metal salt is added to improve the stability of cationic dispersions of sizing agents based on rosin and cellulose reactive material. U.S. Pat. No. 4,522,686 discloses a sizing composition in the form of an aqueous dispersion containing a cellulose-reactive sizing agent, fortfied rosin and a water-soluble, nitrogen containing dispersing agent, the last two components forming the elements of a CRS. EP-A-0 292 975 discloses a method for use in producing liquid packaging board. However, in the above publications there is no suggestion that there is a particular problem caused by the decrease in the resistance to edge-penetration by hot hydrogen peroxide-containing solutions, namely the board is within specifications at the reel, but, upon ageing, this resistance decreases to a level where it then remains constant. There is no suggestion, either, that there is a particular problem caused by deficient ink jet properties, such as wicking, drying time or color-to-color bleed.
Moreover, dispersions of sizing agents can exhibit stability problems whose practical consequences are a markedly increased viscosity, agglomeration and phase separation, which may lead to depositions, difficulty in dosing and deteriorated sizing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sizing composition and a method of sizing a cellulosic fibre material that reduce or eliminate the above disclosed problems associated with the prior art, and more particularly to provide a sizing composition with enhanced stability and which gives improved long time resistance to edge penetration by lactic acid and hot hydrogen peroxide-containing solutions when the composition is used for sizing cellulosic fibre materials such as paper, board and paper board.
According to the invention it has been found that the above problems may be alleviated or eliminated and superior results achieved by using as a polyaluminium compound in the sizing composition a polyaluminium phosphate sulphate (PAPS) compound. It has been found that polyaluminiumphosphate sulphates present in the sizing dispersion strongly enhances its sizing effect as compared to non-phosphate containing polyaluminium salts.
Thus, according to one aspect the present invention provides a sizing composition comprising an aqueous dispersion of a rosin material and a polyaluminium compound, characterised in that the polyaluminium compound is a polyaluminium phosphate sulphate compound.
According to another aspect the present invention provides a method of sizing a cellosic fibre material, such as paper, board or paper board, characterised in that the above sizing composition is added to the cellulosic fibre material in an amount of 0.01-5% by weight, calculated as dry sizing agent on dry cellosic fibres.
The dispersions according to the invention have low tendency to agglomerate and separate on storage, showing very good shelf life.
It has also been found that such dispersions used in the process for making a board for a container for consumable liquids gives its cut edges a high resistance to penetration by hot hydrogen peroxide and lactic acid and avoids the loss of such resistance upon ageing. Moreover, sizing with the dispersions described in the present invention give very good ink-jet properties such as wicking, drying time, color-to-color bleed or color appearance, overcoming the problems caused by a poor response. These surprising effects are even more unexpected since it was found that the use of a synthetic sizing agent, such as AKD, rosin size and alum or, alternatively, the use of combinations of rosin and synthetic sizing agents, such as those described in the aforementioned patents, did not give the same sizing effects. The polyaluminium compounds of the present invention differ substantially from the prior art polyaluminium compounds, especially the polyaluminium sulphates described for example in WO 94/01619 and EP-62015.
These and other advantages and characterising features of the present invention will appear from the following specification and the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The superior results achieved with the polyaluminium compound of the present invention are beleived to be due to the incorporation of phosphate into the polyalumi
Bisbal Tudela Josep Lluis
Gillberg Lars Ingemar
Birch & Stewart Kolasch & Birch, LLP
Brunsman David
Kemira Kemi AB
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