Field of the invention

The invention relates to the field of plastic-coated disposable board packages and containers. In particular, the invention discloses a method of treating a surface of a disposable container, and a disposable container, the surface of which is treated to enhance the friction of the surface and to improve its insulation properties.

Prior art

Disposable packages, plates, trays, drinking cups or glasses are made of board for storing, distributing and serving cold and hot meals and drinks. Typically, the plates and trays are containers that are formed of one piece and pressed to shape in moulds. A conventional cup structure is a mantle that is formed into a truncated cone having one seam, and a board bottom is attached to said cone by an annular seam. The properties of board that are preferable for the disposable container application include stiffness, good printability, an advantageous price and biodegrad- ability; its inadequate properties, again, include a tendency to wet, minor porosity and defective insulation capacity.

Board, particularly when coated with plastic, is a slippery material in various condi- tions. A package, disposable plate or cup that is slightly wet on the surface slips in the hands of a user or on surfaces, where it is placed. The thermal insulation of plastic-coated board is also unsatisfactory for many applications. The factors affecting the insulation properties of disposable containers include, among others, selection of material, thickness of the layers and the design. Regarding materials, board is not a particularly good insulation material because of its tightness. Correspondingly, plastic layers are generally thin, and not very good in insulation.

Regarding cups, in particular, with takeaway cafes becoming more and more popular, an increasing number of hot drinks are carried to jobs or cars after purchasing them. Generally, the drink is then not drank right after pouring it into the coffee cup, and thus the drink should remain hot in the cup. Furthermore, the significance of the appearance and the touch and feed properties of the disposable cup are emphasized. A self-evident solution is to add wings, a handle(s) or an ear(s) to the cup; however, this will not ensure that the liquid remains hot. If the cup is not provided with wings, the user holds the cup by its walls, which should then be able to insulate the heat transfer by convection from the contents to the hands or to the environment and/or vice versa. Published patents or patent applications have disclosed various technical arrangements. Efforts have been made to increase the insulation thickness of the sleeve by different outer sleeve applications, e.g., by the techniques presented in the published application US2006231606 or the abstracts of the patent specifications JP2007168820 and JP2007215974. The outer sleeve applications contain corrugated board, grip wrap or double-wall solutions, wherein the consumption of material thus increases in an undesired manner.

The patent specification WO20060429908 describes a solution for improving the insulation capacity, wherein the sleeve part of a board cup is first creased with ridges that are at distances of no more than 0.8 mm from each other, and a dispersion of a heat-expanding polymer is added as varnish into the cavities thus created, which dispersion is not named in the specification. The whole board cup is heated to at least 100 ⁰ C, where the surface treatment agent expands. The insulation is based on the combined effect of the creases and polymer. The prior art discloses a method, wherein the cup is heated to make the PE plastic bubble, and through that, to possibly provide a better heat insulation. However, in this case, it has been necessary to use deviating plastic approaches (e.g., HDPE - board - LDPE), i.e., the amount of material is thus increased.

However, the known prior art solutions

require a separate acquisition of conversion equipment and/or use of extra material. Thus, the price of the disposable container increases.

The patent specification WO2007147935 relates to seaming and its problems in the manufacture of board cups. The specification describes a method of manufacturing board cups, wherein the plastic of the seam areas of the sleeve blank is softened and melted by heating with a laser, the seam areas are laid on top of each other and pressed together to form the side seam and/or bottom seam of the cup.

With respect to the solutions of the prior art above, there is a further need to improve the insulation and the gripping quality of the surface of the disposable containers manufactured of board.

The available English translation of the patent specification JP9301356, which relates to the field of manufacturing easy-to-open liquid packages, discloses a method of locally treating the surface of a blank that consists of board that is coated on two sides thereof. The surface of the separate pull tab that is attached to the liquid package is perforated mechanically and heated by an air flow hotter than the melting point of the thermoplastic resin and cooled with cool air, whereby the surface is roughened, enabling a better grip for the user of the package. However, the specification discloses no solution to treat the walls of the liquid- containing package. Neither do the measures carried out on the pull tab enhance the insulation quality of the package walls.

The English translation of the specification JP 2007069936 describes a method of forming air venting holes in the outermost polymer layer of the liquid packaging board, so that the heat pulse of the heat sealing does not cause pinholes in the inner polymer layer. Making the air venting holes removes the plastic layer from the board in the treated sites. In other words, the thickness of the plastic layer in the treated sites is smaller compared with untreated sites (Fig. 1 of the specification). The English translation of another specification JP 6170959 describes the making of vent holes in the manufacture of materials that are intended for breathable packages. The point-form holes are made by a laser. Removing the material does not increase the insulating capacity.

There is still a need to develop methods, by which plastic-coated board can be treated in a controlled manner by locally influencing the surface roughness and thickness, preferably for heat insulation purposes.

General description of the invention

Surprisingly, the inventors of the present invention have observed that, by treating target sites of a plastic-coated disposable container by locally heating them, the surface of the disposable container can be roughened. The surface is preferably also foamed, which in the end product results in a deceleration of heat convection through the packaging material and in an increase in the thickness of the plastic layer of the surface. These changes cause changes in the surface of the disposable container that is to be handled by the user or that comes into contact with the environment, which in addition to the insulation capacity, also increase the friction between the disposable container and the fingers or the surface, reducing the compression force that is needed to hold the container or keep it in place, and may also provide a possibility to reduce the basis weight of the board. Regarding the user, the changes that affect the appearance of the container and a pleasant touch and feel are also significant. The product properties serve the end user of the disposable container.

The surface is treated, so that its properties can be rendered appropriate for the end use. The advantages achieved by the embodiments of the invention include, jointly or separately, a better heat insulation capacity, higher friction between the hand and the cup, or the table top or other plane and the plate or tray, a more comfortable feel in the hand provided by an embossing, a visually more pleasant and improved appearance, information conveyed by the embossing (cf. printing).

Requiring no special materials, the method can also bring about cost- effectiveness.

In the surface-treatment method, which is the first object of the invention, the- disposable container or its blank that is manufactured from at least one blank of plastic-coated board is, optionally, first moistened, then heated momentarily for less than 1 sec to a temperature that is at least the softening point of the plastic at tar- get sites of the blank surface and, finally, the surface is allowed to cool. The method according to the invention is described in detail in Claim 1.

The second object of the invention comprises a disposable container consisting of plastic-coated board, a surface of which is treated at target sites of said surface, preferably in a grip area, so that the plastic is locally foamed. The disposable con- tainer according to the invention is described in detail in Claim 6.

Short description of the drawings

Fig. 1 shows the application of the invention to a disposable board cup. The cup is presented both as a perspective view and as flat parts, which comprise a sleeve blank 1 and a bottom blank 2. The grip areas 11 and 21 of the cup are marked with diagonal lines.

Fig. 2 shows the application of the invention to a disposable board plate. On the left, the disposable plate 3 is shown as a perspective view of a three-dimensional piece and, on the right, as a blank. The grip area 31 of the plate is marked with diagonal lines.

Fig. 3 shows the application of the invention to a disposable board tray. On the left, there is a perspective view of the tray 4. On the right above, the tray is shown directly from below. On the right below, there is the outer surface of the flat tray blank. The grip area 41 of the tray is marked with diagonal lines. Fig. 4 shows the application of the invention to a disposable board package. On the left, the package 5 is shown in an upright perspective view and, on the right, there is a perspective view of the same package turned over. The grip areas 51 of the package are marked with diagonal lines. Fig. 5 shows a SEM image of the surface of the plastic-coated board packaging material as a 100-fold enlargement. The surface is treated according to an embodiment of the invention, whereby the blank of the disposable container, which is made of plastic-coated board blank, is first heated by a laser for less than 1 sec to a temperature that is higher than or as high as the softening point of the plastic and, finally, the surface is allowed to cool, so that the plastic layer at the treated site is thicker than at an untreated site.

Fig. 6 shows a SEM image of the surface of the plastic-coated board packaging material as a 100-fold enlargement, wherein the surface is first moistened by aerating the sample at a relative humidity of 80% and, thereafter, treated by a laser according to another embodiment of the invention.

Fig. 7 shows the differences of height of the surface of the plastic-coated board (15 gsm LDPE) packaging material, when writing at different powers of the laser. In the upper left corner, the powers are so high that the LDPE surface is already destroyed instead of foaming. It can be concluded from the figure, that an expan- sion of about 50 μm can be achieved at a specific power density.

Detailed description of the invention

The invention discloses a method of treating a surface of a disposable container. In the surface-treatment method, the blank of the disposable container, which is manufactured from at least one blank of plastic-coated board, is first momentarily heated at target sites of the blank surface for less than 1 sec to a temperature, which is higher than or as high as the softening point of the plastic.

It has been observed that momentary heating provides the product manufactured by the method with advantageous properties. Instead of slowly heating the entire blank or package, i.e., in an oven, a dot-form high-density energy point is focused on a target site of the surface. In this way, markings are made on the surface, which are typically dots and/or lines. When so desired, the markings can also be used to create similar visual effects as printing does. Naturally, by making the dots and/or lines very close to each other, an impression of a treated area is obtained. However, it is essential to the invention that the plastic of the blank's or package's surface that is to be treated is not treated throughout the area, but treated and untreated areas can be distinguished on the surface, the thicknesses of their plastic layers being different. The difference of height depends, among other, on the materials used (the strength of the board and the thickness of the plastic layer), pos- sible moistening and the power density of the momentary heating.

To produce the temperature needed in heating, a power density suitable for the method is selected. Those skilled in the art are capable of selecting the parameters used, e.g., for heating by laser. When selecting the power density, reference can be made, e.g., to the publication Gane, P. A. C, Buri, M., Spielmann D.C., Neuenschwander, B., Scheidiger, H., Battig, D., Mechanism of post-print laser marking on coated substrates: factors controlling ink ablation in the application of high brightness calcium carbonate, J. Graphic Techn., 1.1, p. 37-48, which disclosed the mathematical method according to Formula 1.

The energy density can be calculated by the Formula 1 :

PE = E/A = P _Laser /(v 2 d) (1) wherein P = power, W v = velocity, m/s d = diameter of the beam

The point-form and momentary heating provided by the laser is considerably pref- erable in the method of the invention. In particular, together with moistening, focusing the laser power on the evaporation of water simultaneously with softening the plastic advances the conversion of the structure of the dense plastic layer into one containing cavities and, thus, one that binds gases, among others, water vapour and air, to the structure.

The invention is not limited to the use of laser only, but the heating can be carried out by any other quick and locally focusable heating method, e.g., a quick hot air blowing. According to the invention, this treatment is also carried out on a very small area at a time and so that a difference of height can be observed between the treated and untreated surface.

Increasing the thickness of the plastic layer in this context refers to an increase in the porosity of the existing plastic layer. In some embodiments, it can even be stated that the plastic layer produces foam locally. No extra plastic material is brought into the layer. In other words, the grammage of plastic per square meter of board g/m ² remains the same, but due to waviness or foaming, its height is different from that of untreated plastic, when measured by a profilometer or a height indicator. The terms thickness and height herein refer to the same thing, i.e., the average dimension of the plastic layer on the surface of the board from the boundary surface of the board and plastic to the outer surface of the plastic, as defined in the experimental part. Experimentally, a distinct difference was provided in the thickness of the plastic layer between the treated and untreated surfaces. According to an embodiment, the treated surface was at least 75% and, at the most, several hundred percents thicker than the untreated one.

After heating, the plastic that has formed bubbles or foam cools quickly, as energy is exerted on the surface only momentarily. According to the invention, the cooled surface remains upraised and a difference of height can be measured between the treated and untreated surface. This deviates, e.g., from heating that is applied in connection with seaming, wherein the plastic surface should stay molten so long that the surfaces to be seamed can be pressed against each other, whereby efforts are made to repress the plastic layers as thin and tight as possible.

In the method according to the invention, it is essential for the formation of the difference of height that the surface cools quickly without being adhered to another surface, pressed or smoothed when hot. The energy that is brought locally in point-form exits quickly and no special cooling is generally needed. However, the use of cooling is not excluded.

The surface is treated at target sites. The target site is not the surface of the whole blank or finished container or package. The marking is preferably made on a so- called grip area. In the case of some embodiments, the grip area refers to an area, where the user of the disposable container or package most likely grabs it with his or her hands or fingers in relation to typical use. In the case of other embodiments, such as disposable plates and trays, the grip area refers to the site of the surface that comes into contact with the environment, particularly the plane, on which the plate or tray lies. In the case of board packages, both the grip area of the user's hand and the area that comes against the surface can be considered.

The method is most typically applied for providing insulation and/or frictional properties on the outer surface of the package or container. In that case, the inner plastic layer of the package remains intact and insulates humidity and other contents from the board layer. In these applications, the contents of the package do not come into contact with the treated surface. In some applications, however, it is desirable to treat the inner surface of the package. In some of these applications, the measures taken may even include deliberately making small pinholes on the surface.

The method can be applied to a disposable container or its blank, which is made of board and coated with thermoplastic polymer, i.e., plastic. The disposable container in this context refers to containers and packages, which are intended to be used for a short period only and which are disposed of after using them once. Typical disposable containers include drinking cups and glasses with or without lids, board plates, trays and cartons, and boxes, packages, casings, etc. In the field, the blank generally refers to a part, which is cut or stamped from a flat board into a desired shape, and moulded from a two-dimensional shape into a three- dimensional one by typical board moulding and/or seaming methods. Coating can be provided on one or both sides of the board; however, preferably on both sides. It is not critical for the invention, whether the blank is rendered a disposable con- tainer before or after treating the surface. For example, regarding board cups that are made of two pieces by seaming, it is preferable to carry out the treating before combining the sleeve blank and the bottom blank, but it can also be carried out after combining thereof. Instead, in the case of disposable plates, the treating can be carried out on a plate that is already shaped by means of the mould.

Those skilled in the field know various sandwich-type boards that contain selected layers, depending on the scope of application. Typical layers comprise liquid or moisture barrier layers, gas barrier layers, flavour barrier layers etc. Various combinations of these are known. Grades that fulfil specific terms include liquid packaging boards and those suitable for use in food products. It is essential for the in- vention that the surface treatment is carried out on an object that consists of plastic-coated board. The invention can be implemented for the combination of these materials, wherein the thermoplastic quality and softening of the plastic in combination with the insulation capacity and heat resistance of the board makes the treating possible. The wetting properties of the board, in particular, provide an ad- vantageous effect in the method according to some embodiments of the invention.

The plastic that is used as surface layer can be a thermoplastic that is acceptable for the application. The grades suitable for the treating according to the invention preferably include polyethylenes (PE), polypropylenes (PP), polyamides (PA) and polyethylene terephthalate (PET). Other alternatives include, among biodegrad- able plastics, polylactic acid PLA, plasticised starch derivatives, etc. Those skilled in the art are familiar with the softening points or softening temperatures of these plastic grades and can thus select the power density required.

Embodiment without moistening

In the surface-treatment method that comprises one embodiment of the invention, the disposable container or its blank, which is manufactured from at least one blank consisting of plastic-coated board or paper, is first heated quickly for less than 1 sec to a temperature, which is higher than or as high as the softening point of the plastic at target sites of the blank surface and, finally, the surface is allowed to cool, so that the thickness of the plastic layer at the treated site is different from that at an untreated site. The treated site is preferably thicker. This heating is thus carried out without moistening the blank.

The inventors have observed that heating without moistening is a measure that stresses the plastic layer. At lower powers, the plastic is foamed, forming differences of height between the treated and untreated sites. By experiments, it has been observed that when lasering dry board, some very small holes, pinholes, are formed in the plastic. By adjusting the power, the hole content can be affected, if desired.

The board thus treated provides advantages in applications, wherein an undamaged plastic surface on top of the board is not necessary, but the holes may even be of benefit. It could be perceived that such an application be, for example, a package made of board that is plastic-coated on both sides, wherein a part of the inner surface of the package is treated according to the invention, whereby the roughened part increases friction between the package and its contents, while the liquid of the contents can be absorbed into the board layer through the small holes.

By doing this, the breathability of the package can also be adjusted in a controlled manner. For example, in packages wherein a freshly baked product is packed, the moisture evaporating from said product should be conveyed outside the package in a controlled manner, while the product should yet be protected from drying dur- ing storage, the method according to the invention provides the desired properties.

Embodiment, the first step of which comprises moistening

In one preferred embodiment of the surface-treatment method of the invention, the blank of the disposable container, which is manufactured from at least one blank consisting of plastic-coated board, is first moistened, then heated momentarily for less than 1 sec to a temperature, which is higher than or as high as the softening point of the plastic at target sites of the blank surface and, finally, the surface is allowed to cool or, alternatively cooled, so that the plastic layer at the treated site is thicker than at an untreated site. The mass of the plastic layer does not increase, but the thickening is caused by the effect of the unbroken or broken gas bubbles that are formed to the plastic layer.

In other words, the method comprises at least the successive stages i-iii, wherein the blank or the ready moulded disposable container

i. is moistened; ii. the plastic at target sites of the blank surface is momentarily heated for less than 1 sec to a temperature, which is higher than or as high as the softening point of the plastic; and iii. the surface is allowed to cool. The first one of the successive stages of the method is moistening. The meaning of this stage is to enhance the bubbling of the plastic surface and the changing of the structure during the momentary heating. The inventors have observed that when energy is supplied to the sandwich structure, the water in the structure becomes hot, evaporates and its volume grows. It tries to exit and it is allowed to exit momentarily through the molten plastic layer. Locally, the steam pressure and the temperature of the plastic surface go up enough to provide bubbling. The gas bubbles push the molten plastic material out of their way. When cooling, the volume of water vapour and the other gasified substances also decreases, but the shaped plastic remains porous. When exiting the structure, the water vapour forms in the molten plastic passages and bubbles, which remain in the plastic after the water vapour has exited and the surface has cooled. In other words, instead of a dense film, the plastic is reformed into a more porous form. In applications, where the plastic surface preferably remains unpierced, the moistening surprisingly provides better controllability to the treatment.

When the plastic-coated board, such as an LDPE/board structure, which is normal to disposable containers, is aerated at a relative humidity of about 50-90%, the moisture content of the board increases. Particularly, the fibrous part of the sandwich structure binds water. In some cases, specific plastic layers can also bind moisture. In practice, at its simplest, the moistening is thus implemented so that the finished blank or disposable container is stored long enough in a storage, where the moisture content is raised. Depending on the storage humidity, the moisture contents vary; e.g., the moisture content of cup board has been about 10-11.5% when stored at a relative humidity of 85%, about 7.5-8.5% when stored at a relative humidity of 70% and about 5.5-6.5% when stored at a relative humid- ity of 50%.

According to an especially preferred embodiment, the method comprises at least the successive stages i-iii, wherein the blank or readily moulded disposable container that consists of board that is plastic-coated at least on one surface thereof

i. is moistened; ii. the plastic on target sites of the blank surface is momentarily heated by a laser for less than 1 sec to a temperature that is higher than or as high as the softening point of the plastic; and iii. is allowed to cool or is alternatively cooled.

A technique alternative to the moistening technique presented above comprises manufacturing the board so that its moisture content remains higher than normal. Those skilled in the art know techniques, by which the moisture of plastic-coated board can be adjusted during manufacture. In a process presently used, cup board is run to a moisture content of over 8% by the board machine in production. After coating with PE, the board slightly dries, but remains moist. Without binding ourselves to any technique, by which the plastic-coated board is rendered its desired moisture content, the moisture of the board at the moment or treating the surface should preferably be at least 5%. Those skilled in the art know the methods of obtaining the desired moisture level. The effect of moisture on the foaming of the plastic layer is examined in Example 2.

The surface of the moistened plastic/board sandwich structure is heated extremely quickly using a quick momentary heating method. The water absorbed by the board and evaporated under the effect of the energy supplied is discharged through the plastic surface, foaming the plastic layer of the surface in a very limited area. From the parts of the container, to which no heating is directed, moisture gradually evaporates and does not penetrate through the softened plastic layer; hence, it neither breaks nor foams the same. Since the entire container or blank is not heated, the difference between the treated and untreated surface is provided. One way of observing and measuring the difference is to examine the height differences of the treated and untreated surface by a profilometer (Fig. 7). The plastic layer that comes to the outer surface of the finished container, on which the frictional and insulation properties are of the greatest importance, is most preferably heated. The visual properties, visible markings similar to printing and touch and feel properties, which are provided by the method, are also at their best when the treating is provided on the outer surface.

At its simplest, foaming can be carried out by a laser. Under the effect of the laser beam, the thermoplastic polymer is heated momentarily beyond its softening point, and after the beam has passed, the plastic solidifies again. The fibrous layer under the plastic coating dries quickly. The water exiting the fibres tends to exit through the molten plastic layer. The control route of the laser beam forms embossing on the treated surface.

Products according to the invention

The different embodiments of the product according to the invention encompass various board-based disposable containers.

The product according to the invention is characterized in that its structure comprises board and thermoplastic resin. The plastic layer of the product is selected from among thermoplastics, as described above. A selected area in the plastic of the surface comprises treated areas, the thickness of the plastic of which has a difference of height of at least 10 μm, more preferably 20 μm and most preferably 50 μm compared to the thickness of the plastic in untreated areas. A site in the surface treated according to the invention is preferably thicker than an untreated one. Treating the surface according to the invention increases the friction of the surface. The importance of friction to disposable products is emphasized due to the small consumption of material required of the products and the lightness that nec- essarily follows. A light container does not stay easily in place, e.g., on surfaces, or it slips through the fingers. The local static friction of the treated sites in the disposable containers according to the invention is at least 5%, preferably 10% and more preferably 50% better than that of untreated sites.

At its smallest, a sitecan be selected to be treated, the area of which is only about two square centimetres and, at its largest, even more than 90% of the surface area of the disposable container; however, not the whole area. The portion of the target site of the surface is preferably less than 50% of the entire surface area.

According to an embodiment, the disposable container is a board drinking cup. An example of manufacturing the drinking cup is the method disclosed as a phase diagram in Fig. 7 of the patent application FI20040242, wherein a curved mantle blank is seamed with a side seam to form a piece with the shape of a truncated cone, the piece forming the walls of the cup and being seamed tightly to a bottom blank. Various solutions related to the details of the cup are well-known in the field and can be applied together with the invention. When applying the method according to the invention to a board cup, it is preferable to heat treat the grip area of the mantle blank. Fig. 1 shows the mantle blank (1) and the grip area (11) that is marked on the same. The grip area (21) of the bottom blank (2) or the bottom of the finished cup can also be treated according to the invention. The heating pat- terns that are made in the grip area can be freely selected. Without limiting ourselves thereto, let us mention, e.g., a marking that extends around the cup as a wraparound; a marking that forms text, a trademark or a graphical representation, a marking of a label type, a marking with the shape of a palm, a uniform marking that covers the entire grip area or one that consists of repeated shapes, etc. Con- sidering the technical implementation of the invention, the shape and the graphical content of the marking are not limiting.

According to another embodiment, the disposable container is a disposable plate formed from plastic-coated board. Typically, such a plate is manufactured from one blank, which is creased and/or pressed to shape in a mould. Applying the sur- face-treatment according to the invention to the disposable plate is illustrated in Fig. 2, which comprises the grip area (31) of the disposable plate (3), which is marked with diagonal lines. The stages of treatment are preferably carried out on a plate that is already shaped, but the treatment of a flat blank can also be implemented. Regarding the disposable plate, the grip area functions particularly to in- crease friction between the bottom of the plate and the surface, on which the plate is placed (e.g., a table, tray, etc.). The grip area can also be an annular periphery that follows the bottom of the plate, or it can form a pattern(s), as described in connection with the cup application.

A further embodiment is a disposable tray, such as a food tray, which is formed from plastic-coated board. Examples of trays formed from board and their manufacture are disclosed in patent specifications FM 17933 and FI20040415. Regarding the food tray, the present method can be employed in the grip surface on the bottom of the tray, in particular. In that case, the tray containing extremely hot food does not burn the surface it is placed on, but the surface-treatment according to the invention insulates heat and decelerates its convection to the plane it is placed on. Fig. 3 shows an image of the food tray (4) according to the invention as a perspective view and from below, and of the grip area (41) that is applied thereto.

According to a further embodiment, the disposable container is a package formed from plastic-coated board, such as the one example of the liquid board package (5) that is shown in Fig. 4, and one of its grip areas (51). A preferred object of application comprises medical packages, wherein the markings can help to identify and grip the package. The disposable container according to the invention is also suitable for packages of household products, such as mild detergents, textile treatment agents etc. Other typical examples include food packages, which can optionally be liquid-tightly and/or hermetically closed. For example, in board packages of frozen products, the surface-treatment according to the invention can be used to decrease the slippiness of the plastic surface that is a consequence of circumstances. The insolation capacity can provide a mutual advantage: for the user, the surface of the package does not feel as cold as without the treatment and, on the other hand, no heat is transferred to the package from the hands of the user. Examples of liquid and/or air-tightly closed food packages include juice, milk, soup and yoghurt containers etc. In these products that are often cold-stored, the surface treatment according to the invention improves adhesion to the package, e.g., when pouring or emptying. The insulation capacity is important in preventing the product inside the package from warming because of the heat of the user's hand. The visual properties of the outer surface also influence marketing and the user convenience.

In the following, the invention is described by means of examples, which should not be considered so as to limit the scope of the invention.

Experimental part

The results of the method according to the invention and the technical effects of the disposable container according to the invention were examined by tests. Changes in thickness were measured in two different ways. By a profilometer (Fig. 7) and a thickness gauge (Table 1). Furthermore, friction measurements were taken from board cups, the surfaces of which were treated by a laser (Table 2). Example 1

Plastic-coated cup board was used in the tests.

The tests were carried out by a carbon dioxide laser, a 50 W Linx SL500 marking laser. The diameter of the laser beam used was 400 μm. The samples were made at a power of 40 W and a marking speed of 15 m/s, and at a power of 25 W and a marking speed of 5 m/min, whereby the power density used was 0.012 J/mm ² .

When the beam diameter was 250 μm, the power 25 W and the speed 9 m/s, the calculated power density obtained was also 0.012 J/mm ² .

Table 1 compares the behaviour of different plastic materials when treated by the method according to the invention. The other factors were kept constant.

Table 1

The coating plastic of the PE-coated cup board burnt slightly, turning into yellowish brown. The plastic also had holes, which is not desired in all embodiments. The larger beam size was of benefit.

The PET-coated cup board behaved similarly, but the plastics in it escaped easier in full, not resulting in holes but in a groove.

Considering all plastic grades, it could be stated that increasing the power density increased the risk of forming holes in the plastic layer.

When foaming was carried out on the outer surface of the cup, the small pinholes had no effect on or meaning for the plastic on the inside. Example 2, comparison between unmoistened and moistened board

The profilometer was used to measure the moister PE only. The tests were conducted by the Linx SL500 carbon dioxide marking laser, using a laser power of 25 W. The diameter of the laser beam used was 400 μm. The samples photographed by SEM were made using a marking speed of 9 m/s.

The test samples, of which cups were made, were aerated at a RH of 85% and at 25°C for about two weeks (Fig. 6). The corresponding lasering was also carried out on the same sample, which was not aerated (Fig. 5). The moisture of the boards was not measured.

The moister sample formed clearly larger bulges and the plastic did not break as easily.

Example 3, friction measurements

The friction of the surface treated according to the invention was examined by measuring both the static and the dynamic friction by a friction measuring device. The samples consisted of cup board, which was coated with a LOPE layer with a weight of 12 g/m ² . The moisture of the samples was about 10% (± 1%). The friction was measured between the surface (pi) and the bottom (po) of the board, respectively. The references consisted of the same material, which was not treated. The measurements were carried out on three parallel samples (a, b, c), of which the mean value was measured. The results are in Table 2.

Table 2

On the basis of the results, it could be stated that treating the surface according to the invention increases friction. Especially advantageous is the higher static fric- tion, which in use is a useful property for light-weight disposable products. On the basis of the results, the static friction in these tests was improved by about 10%. Example 4, marking on the inner surface of the cup

Lasering slightly weakened the adhesion of the plastic of the back side to the fibrous layer. This was observed, when foaming was made on the inner surface of the cup; hot water was poured into the cup and the water penetrated its inner sur- face through the pinholes of the plastic. The moistened fibrous layer was detached from the plastic on the outer surface of the cup and water bubbles and "blisters" were created under the intact plastic of the outer surface.