Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-05-02
2004-08-24
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S048000, C524S317000, C524S313000, C524S503000, C524S297000, C524S310000
Reexamination Certificate
active
06780903
ABSTRACT:
The present invention relates to dispersions of biodegradable polymers. The invention particularly concerns a process for the preparation of a hydrophobic polymer dispersion characterized by a) forming a mixture of a biopolymer, a plasticizer, dispersion auxiliaries and water, b) heating up the mixture in order to obtain a paste-like composition, and c) diluting the paste-like composition in water.
The current emphasis on an environmentally friendly attitude and green values is opening up new markets for products based on renewable natural resources. Such trends can be observed within the sectors of, e.g. the packaging industry, the sanitary industry and the glue industry, where recyclability, reuse, compostability, biodegradability and lack of environmental strain are demands of today. The trend of replacing products based on petrochemistry by processed biopolymer products is also emphasized. Starch and its derivatives constitute a particularly interesting initial material for the production of biodegradable polymer products. Other important biodegradable or compostable polymers include, among others, polycaprolactone, polylactide and other lactic acid based polymers and copolymers, such as polyester urethanes.
Polymer dispersions are used, e.g., in the coating of paper and board in order to improve their water resistance. Dispersions used in the paper industry today contain, in addition to fillers, various synthetic latexes which are quite poorly degraded in a biological environment.
Solutions are previously known where modified starch components have been used for the preparation of paper coating dispersions. Thus, a hydrophobic coating composition is known from WO Published Application No. 93/11300 which is based on a polymer dispersion containing a starch derivative having a polymer containing styrene and butadiene monomers grafted thereto. Thus, this solution does not use any of the biodegradable components which would be compatible with the demands for recyclability made on the products.
The present invention aims at achieving a hydrophobic dispersion whereby at least most and preferably essentially all of its components are biodegradable. The invention especially aims at providing a dispersion whose polymer component mainly comprises a biodegradable polymer (below also termed “biopolymer”), advantageously starch or a derivative thereof and/or lactic acid based polymers and copolymers. The invention further aims at providing a process for the preparation of hydrophobic dispersions.
The invention is based on the surprising observation that stable dispersions can be prepared from many biodegradable polymers by forming a paste-like composition of the polymer in question, a plasticizer, dispersion auxiliaries and water, which composition is dispersed in water. No solvents are then required for preparing the dispersion. Thus, according to the present process
the polymer used is a biodegradable polymer which is admixed with a plasticizer, auxiliaries and water in order to form a premixture,
the premixture is heated in order to provide a paste-like composition, and
the paste-like composition is diluted/dispersed in water.
In more detail, the method according to the invention is characterized by a process for the preparation of a hydrophobic polymer dispersion, characterized by a) forming a mixture of a biopolymer, a plasticizer, dispersion auxiliaries and water, b) heating up the mixture in order to obtain a paste-like composition, and c) diluting the paste-like composition in water.
The invention offers considerable benefits. Thus, the raw materials of the polymer dispersion according to the present invention are mainly based on renewable natural resources and are biodegradable/compostable. The method is particularly well suited for finely divided/powdery polymers. The starch component may be derived from any native starch; it need not be, e.g., a starch rich in amylose. No solvents requiring removal by evaporation need be used for formulating the dispersion, instead, the dispersing may be performed in a conventional disperser or even a mixer. There is no need to dry the polymer prior to dispersing.
Films made from the dispersion are quite resistant to water and can be exploited to greatly improve the water resistance of paper or board. The dispersions also have good adherence properties. Thus, the novel polymer dispersions can be used for coating paper or board, as primers, as adhesive component in water-soluble adhesives (e.g. labelling adhesives) or as a component in paint or lacquer. The examples 10 and 11 deal with the use of the dispersions for improving the water resistance of paper coating latexes. As will emerge from the examples the dispersions can be used for partly or entirely replacing synthetic binders (e.g. 10 to 90% of a synthetic binder, 90 to 10% of the present dispersion).
The suitability of the dispersions for use as lamination adhesives is examined in Example 5 and it will emerge that a plastic film laminated onto paperboard using the dispersion could not possibly be detached without breaking the board surface. Example 7, then, assesses the drying properties of the dispersions when used as paint vehicle, and it is found that films made from the dispersions are plastic-like and dry quickly. Therefore, the dispersions are excellently suited for use as paint vehicles. It has also been found that the dispersions can be used as lacquers for the surface treatment of wood and other materials. They are also suitable in the production of hydrophobic cast films and as binders in materials based on cellulose fibres. The water resistance of the dispersions can be further improved by modifying them using cross-linking chemicals. If desired, these can be combined with the use of wax.
In the following the present invention is examined in greater detail by means of a detailed description and a number of working examples.
According to the invention, dispersions of biodegradable polymers are advantageously prepared in three steps whereafter the dispersions can be treated further using modifying chemicals in order to achieve e.g. improved water resistance. If required, the dispersions can also be homogenized.
First, a mixture is formed of the biopolymer, dispersion auxiliaries (including protective colloids, if any) and water. Depending on the biopolymer, the mixture may also contain, for example, a polymer plasticizer and other adjuvants and auxiliaries. The mixture contains a part of the total amount of water in the dispersion. Advantageously, 10 to 90%, preferably about 20 to 80%, of the total amount of water in the final dispersion is contained in the mixture, whereby the premixture contains advantageously 1 to 200 parts by weight, preferably about 50 to 150 parts by weight of water, to 100 parts by weight of the polymer. The aim is to provide a sufficiently stable and viscous mixture. The mixture is stirred to provide a homogeneous mass by applying intensive stirring.
The dispersion auxiliaries are most advantageously dissolved or mixed into the water to be added into the premixture before being intermixed with the polymer.
During the second step of the process the mixture is heated to about 20 to 100° C., preferably about 40 to 60° C. The temperature varies according to the polymer used and the composition of the dispersion. Stirring is continued at the temperature in question until a suitably paste-like mixture results. In the case of certain polymers no actual heating step is required and the paste-like mixture is instead obtained by continuing the stirring at room temperature.
The stirring times are usually equally divided between the formation of the mixture and the heating step. Depending on the amounts of the materials, the mixture is stirred for about 1 min to 24 h, advantageously about 10 min to 2 h, during the first step of the process, and for about 1 min to 24 h, advantageously about 10 min to 2 h, during the second step of the process. The total stirring time is typically between about 5 min and 4 h.
During a third step of the process the rest of the calc
Hamara Jouni
Heikkilä Maija Elina
Mikkonen Hannu
Peltonen Soili
Acquah Samuel A.
Birch & Stewart Kolasch & Birch, LLP
Rajguru U. K
Valtion Teknillinen Tutkimuskeskus
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