Stock material or miscellaneous articles – Hollow or container type article – Paper containing
Reexamination Certificate
2000-01-18
2003-03-11
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Paper containing
C428S034300, C427S391000, C427S411000
Reexamination Certificate
active
06531196
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coated board comprising at least one polymer-based coat which prevents the penetration of liquids and gases. Furthermore, the invention comprises a process for manufacturing the board, and dishes and packaging, such as food packaging formed from the board
DISCUSSION OF RELATED ART
The board used for packaging liquid foods and other products sensitive to spoiling must, for the sake of the durability of the product, be impermeable to liquid and gas. Such packaging board prevents airborne oxygen from penetrating to the inside of the package and, consequently, the product from spoiling and, respectively, the aromas which evaporate from the product from escaping from the package. In board used for disposable containers, it is important to have a liquid-resistant coat which protects the board from wetting.
One known method for rendering product packaging impermeable to liquid and gas is to provide the board used for the packaging with a metal foil. However, the disadvantages of such packaging include high manufacturing costs, non-biodegradability of the foil layer, problems of regeneration of the packaging material, and the unsuitability of the packaging for heating in a microwave oven.
Because of the said problems associated with metal foil, a shift has been made in food packaging to increased use of boards in which the impermeability to liquid and gas has been achieved by means of one or more polymeric barrier layers. Among polymer materials, especially EVOH has excellent barrier properties but, for example, polyamide is also usable for the purpose. By combining various polymer materials, an impermeability substantially corresponding to that of aluminum foil has been achieved, but owing to the required successive barrier and bonding agent layers the board becomes complicated in structure and the consumption of polymer material is high.
The special problems of EVOH in packaging boards include its mechanical weakness and sensitivity to moisture. During the heat sealing of the board, the EVOH layer tends to be perforated by the steam escaping out of the board. In these respects polyamide is a material more durable than EVOH ,but its barrier properties are not equal to those of EVOH. There are known packaging boards in which the solution to the problem has been sought through a suitable combining of EVOH and polyamide. A common problem associated with on-line coating of boards with polymers continues to be the risk of sticking during the rolling subsequent to the drying of the coat. The sticking will damage the coat, which should specifically be unbroken and continuous in order to provide the desired impermeability to oxygen and water vapors. The large amount of polymeric material present in the coating layers also detract from the pulpability of the board during its recycling.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a board provided with a polymer-based coat impermeable to liquids and gases, substantially avoiding the said disadvantages associated with known coated boards. Board according to the invention is characterized in that the coat is formed on the board during its manufacture from a polymer dispersion applied as on-line coating, to which dispersion talc particles have been added so that the talc will constitute. 30-80% of the total weight of the dried coat.
In the coated board according to the invention, impermeability to water, water vapor, oxygen and aromas can be achieved by means of suitable batching of talc, in addition to which the coat is impermeable to fats and oils. The barrier properties of the coat are based on the presence of a very pure talc made up substantially of small, flaky particles, typically less than 50 &mgr;m in size, while the polymer closing the gaps between the talc particles forms a continuous phase which finally ensures the impermeability of the coat. It should be noted that calling the coat polymer-based refers to the presence of the. said continuous polymer phase and not to the polymer necessarily constituting the largest ingredient proportion in the coat, a fact which can be observed even from the range of the weight proportion of talc.
Besides the achievable barrier properties, the talc-containing coat of board also has many other advantages over known coating materials. The talc-containing coat is not sensitive to moisture; it protects the board from wetting so that the board retains its mechanical strength. The coating is thus especially suitable. for disposable containers and for packaging of liquid foodstuffs. The talc-containing coating compound is also suitable, without problems, for on-line coating processes which are in use, and the coating does not have a tendency to stick when the completed board is wound on a roll. The coating withstands heating, for which reason the coated board is suitable, for example, for baking containers. The coating also improves the mechanical properties of the board by increasing its stiffness.
Furthermore, the talc-containing coating has good printing properties owing to the fact that its surface is not hydrophobic. It is possible to carry out printing without a corona treatment, which is required by many other polymers, such as polyethylene, used as coatings.
Since the presence of talc in the coating compound reduces the amount of polymeric coating material, the coated board according to the invention is better pulpable and thus easier to recycle than known boards having corresponding barrier properties. For the same reason the use of talc is preferable in terms of the compostability and biodegrability of the board.
DETAILED DESCRIPTION OF INVENTION
A talc-containing coat is in itself transparent, which maybe an advantage in some uses of the board. On the other hand, the talc-containing coating compound can be easily colored by adding pigments to the polymer dispersion forming the coat, applied onto the board.
The oxygen and water vapor barrier properties of a talc-containing coat depend on the basis weight of the coat and the amount of talc therein. Generally speaking, the dry weight of an individual talc-containing coat on either side of the board may vary within a range of 2-40 g/m
2
. Preferably the weight of the coat is 5-40 g/m
2
, by means of which it is possible to achieve impermeability of the coat to water vapor, and most preferably within a range of 8-20 g/m
2
, in which case the coat can be made impermeable to oxygen, a so-called High Barrier coating with an oxygen permeability below 100 cm
3
O
2
/m
2
·d. The proportion of talc is 30-80%, preferably 40-75%, of the weight of the dried coat.
Polymers suitable for the polymer basis of a coat according to the invention for a board include styrene butadiene, styrene acrylate, acrylate or vinyl acetate polymers and copolymers, or blends of these. The polymer may be prepared by using a monomer blend containing as its principal components vinyl acetate and a (methyl, ethyl, propyl or butyl) ester of acrylic acid and/or methacrylic acid and/or lower alcohols, or by using a monomer blend containing as its principal components styrene and a (methyl, ethyl, propyl or butyl) ester of acrylic acid and/or methacrylic acid and/or lower alcohols or by using a monomer blend containing as its principal components a (methyl, ethyl, propyl or butyl) ester of acrylic acid and/or methacrylic acid and/or lower alcohols and/or a copolymer of these. The said polymers form polymer latexes, i.e. polymer dispersions, which can be combined with talc particles and be applied onto board as a coat in which dispersed polymer particles join one another as a polymer phase which binds the talc particles together. Furthermore, polylactides, polyhydroxybutyrates/polyhydroxy-valerates, modified starches and other biopolymers which are compostable or entirely biodegradable can be mentioned as usable polymers which are especially advantageous.
The colorability, already pointed out above, of a talc-containing coat is an especially advantageous property, in particular in the packaging of foods whi
Aho Yrjö
Kimpimäki Tomi
Nurmi Kari
Penttinen Tapani
Santamäki Kimmo
Birch & Stewart Kolasch & Birch, LLP
Hon Sow-Fun
Pyon Harold
Stora Enso Oyj
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