PROCESS OF ROUGHENING THERMOPLASTIC FILMS AND ROUGHED PLASTIC FILMS

Abstract: The invention relates to process for roughening thermoplastic films and roughed films. The invention further relates to process for preventing thermoplastic packaging films from slipping on each other and a suitable system for such purpose. The essence of the roughening process is that practicles consisting of the same polymer as that of the film and/or other plastic material being able to weld together with that, and having suitable size and/or abrasion resistance are brought to the surface to be roughened of semi-finished product having sufficient reserved heat content to maintain condition appropriate for welding said particles on said thermoplastic film surface to be roughened or on one or on both film surfaces being re-heated to such temperature and are dispersed in suitable closeness and configuration and that condition of the roughened surface is maintained until desired welding process is completed. Process for preventing thermoplastic packaging films from slipping on each other characterised in that a system comprising films to be stacked - at least one of which is roughed - and has protrusions of suitable closeness on its surface; a binding element having a loose fibrous structure and stability is placed on the film or on its specified parts, on the entire surface or on surface part(s); said binding element comprises fibres of such closeness and layer thickness that between the fibres of the binding element and the protrusions of the roughed film a mechanical joint is formed.

Description: Process of roughening thermoplastic films and roughed plastic films Technical Field The invention relates to process of roughening thermoplastic films and roughed films. In the present context the term of "film" also includes plastic products of different thicknesses such as plates, sheets, pellicles, which may optionally be supplied with a base or may be covering layers as well. The invention further relates to process for prevention thermoplastic packaging films from slipping on each other and a suitable system for such purpose. The technical term "films" also means plate-like products of differ¬ ent thickness varying from entirely thin to markedly thick. Background Art It is known that the process for production of thermoplastic films starting from the appropriate mixtures or granules is made so that the un¬ processed material is melted or moulded by heating and the desired product is formed in a tool by die-casting or pressing the material through the gap of an extruding die. The gap does not necessarily determine a flat film, for example in case of hose-like products it can be round shaped as well. In order to gain its final shape and for the purpose of its stabilisation at leaving the gap of the tool or being taken out of the mould the moulded product is congealed by cooling. Most often the cooling is made by blowing cold air on. After cooling undesired deformation does not occur any more, so cutting to size, winding etc. can take place. The quality of films' surfaces is depending mostly on the surface of the tool; in general that is completely plain. Similarly to the manners as stated above thermoplastic films can be moulded by heat transmission again and may be subjected to further proc¬ essing. In connection with the products prepared from plastic films it often creates difficulties that film products, for example folders put on top of each other, are slipping on each other, which can cause falling out of documents, thus the pieces of paper can get dirty and damaged or spoiled. In the same way, in case of plastic sacks instead of the earlier conventional sacks made ot textile put on top of each other, when setting up upper sacks, in case of the smallest displacement of the centre of gravity plain surfaces lying on each other can slip on each other and say nothing of shake which takes place in the course of shipment and interplant transport. Until now slipping of plastic sacks had been tried to prevent in differ¬ ent ways. The most obvious procedure seemed to be to coat sack surfaces lying on each other with adhesive. This solution has raised the problem of choosing the adhesive and the quality of the adhesive. Mostly, when adhe¬ sive an excellent quality was used, it was difficult to pull the sacks apart without the consequence of damaging (deterioration) of the plastic film, while using an adhesive of poor quality due to the insufficient adhesion strength, the task could not be deemed to be solved either. As an other type of solution it was tried to create antislip surfaces by forming unevenness from the material of the film. According to a typical so¬ lution of that kind the film was embossed from the direction of the internal side of the sacks so that bumps were formed on the external side of the sacks. According to an other solution based on a similar principle grooves were formed in the die casting machine before the gap which created ribs on the films' surface in the direction of the material's movement. By this means the problem was solved in part only because the slipping could only be prevented perpendicularly to the line of the aforementioned ribs, the product was able to slip freely in the other direction. Antislip surface on extruded film sheets was tried to create aiso by forming tips and cavities between the tips on the cylinders forwarding the film by which formations rising from the sur¬ face were created. Although these formations were theoretically suitable to prevent slipping in any directions, the required effect it could neither provide. According to an other solution also known from the prior art unproc¬ essed plastic granules were mixed with extraneous substance which could not be incorporated homogeneously into the basic plastic and humps were formed. However in the course of that kind of method the extruder and the connected passing cylinders were exposed to abrasion, so the tool was get- ting deteriorated early and besides it was impossible to keep control over the disposal of humps as it would have been required. A procedure was also applied, where humps were formed on both sides of the film by mixing the raw material with some chemical additive. The drawback of that procedure is its high cost, because the additive, having a high price, was demanded in quite large quantities, and also that both sides of the product were provided with humps, which limited the scope of utilisa¬ All of the aforementioned procedures are costly, uneconomical and are not as efficient as it would be required These methods are used be- cause until now there are no adequate processes which would solve the problem favourably A further disadvantage of all these solutions is that humps and formations rising from the surface are covered by the material of the film itself and, although they are subjected to greater abrasion effect, their resistance to abrasion is equal to that of the other parts of the film The common disadvantage of the solutions described above is that, due to its extenuation or its having extraneous substance particles implied in its structure, the tensiie strength of the product is reduced Disclosure of Invention The object of the invention is to provide a process of forming suitable antislip films for further use which eliminates the deficiency and drawbacks of the methods known from the state of the prior art without modifications in well known technologies and tools The invention is based on the recognition that if particles consisting of the substance of the film and/or other plastic material being able to weld to- gether with that, and having suitable size are brought to the melted film, then the temperature of the particles at their sides looking on the film surface will increase and also themselves will be melted at least partly and will be welded together with the film Standing out of the surface at least partly, these particles make the surface rough According to the present invention the surface of the moulded film, as a semi-finished article, just leaving the gap of the extruder die during the manufacturing process can as well be roughened as, by reheating it, that of previously finished film. The substantial quality of the particles used for the creation of roughed surfaces should be selected so that their abrasion resistance and similarly the particle size are suitable for this purpose. If desired, a homoge¬ neous fraction of particles such as particles representing a fraction sepa¬ rated by passing through a sieve, are applied to the surface. The film can be heated with any of the methods known from the state of the prior art, for example with blowing on hot air, electrical heating etc. The particles may be applied in well ordered or disordered configura¬ tion to the entire surface or to specified surface areas such as edges or, if demanded, in spots, repeating the application once or several times depend- ing on the desired pattern. For example the pattern may be formed by using templates or otherwise. The process according to the present invention is extremely economical, because no special chemical additives and no change of the tool for preparation of the film are needed and similarly, the particular conditions and parameters of the manufacturing procedure are remaining the same. Quite often it is sufficient to rough one side of the product only, however, in accor¬ dance with the present invention optionally film made rough either both sides or only one side may be prepared as well. Thus the essence of the present invention is that practicles consisting of the substance of the film and/or other piastic material being able to weld together with that, and having suitable size and/or demanded abrasion resis¬ tance are brought - to the surface to be roughened of semi-finished product having sufficient reserved heat content to maintain condition appropriate for welding of the thermoplastic film surface to be roughened or - to one or both film-surfaces re-heated to such temperature and are dis¬ persed in suitable closeness and configuration and that condition of the roughened surface is maintained until desired welding process is completed. The invention also relates to the roughed films characterised in that they at least on one side of them on the entire surface or on specified areas of the surface, comprise protrusions consisting of particles having substance of the film and/or other plastic material being able to weld together with the substance of the film, which are welded into the surface and at least partly standing out of the surface. The invention further relates to process for preventing plastic packag¬ ing films from slipping on each other, which process can prevent slipping in case of even more significant external effects than it was mentioned above. It is based on the recognition that the connection between two roughed sur- faces can be made even more firm if a particular binding element is placed between them. Best Mode for Carrying Out the Invention The essence of the process is that a system comprising films to be fixed - at least one of them is roughed - and a binding element is formed applying a roughed film with protrusions of suitable closeness on its surface; a binding element having a loose fibrous structure and individual stability is placed on the film or on its specified parts, on the entire surface or on sur¬ face part(s) which binding element comprises fibres of such closeness and layer thickness that between the fibres of binding element and the protru- sions of the roughed film a mechanical joint is formed. The welding surface between the film surface and the particles form¬ ing the protrusions is preferably such that the inter-section of the particles and the plane of the film does not cover the shape of projection of particles viewed perpendicularly to said film sheet According to one preferable aspect of the present invention roughed film sheets are used on both surfaces of the binding element. According to a further preferable aspect of the present invention the binding element is fixed to one of the two film sheets; by sticking, welding or sewing. It is also preferable if the thickness of the binding film reaches at most up to or more preferably is less than the greatest value of the projection of the particles in the surfaces, roughed with plastic particles, of the two film sheets to be connected with each other. Suitably a binding element based on plastic, having well ordered or disordered fibrous structure, such as non-woven fabric, forming veiled film and having reticular structure, prepared by thermo-fleece technology is used. When in practical use, 'roughed plastic film-binding element-roughed plastic film 1 tripartite system is built, the resulted three-member joint will be strong enough to withstand also greater mechanical stress without slipping At the same time the joint can be broken off simply, because though in the direction of the slipping on each other the layers are stabilised, in case of necessity elements can easily be lifted off each other. For the mechanical joint of the surfaces if is needed that there are bigger protrusions of lower density or smaller protrusions taking place closer to each other in the surface, so a certain part of the surface needs to com¬ prise protrusions. The relation between size and closeness of protrusions is determined by several factors such as the thickness of the film and its resis¬ tance to mechanical stress or that can be decided depending on the field of application. Geometric shape of particles is important because in case of plainly lying, lenticular, archedly rounded particles, where the welding line is long, the fibres taking place between the particles obviously can not keep on holding them as it would be desired, they slide off, they do not get stuck in cavities between them. As it was mentioned above, the binding element has a fibrous struc¬ ture and, in addition, it must have suitable stability to prevent the particles from tearing it apart and the fibres from slipping off it when stress in the direction of slipping arises. In addition the structure of the binding element must be loose enough to let the protrusions penetrate into the fibrous struc¬ ture. As binding element may be used a fabric with disordered structure, fleece, felt, etc., where fibres are bound together by using known procedures such as adhesive way, sewing, spot-welding etc. Films made suitable for the purpose of packaging are usually wound and stored in rolls, at the utilisation they are cut to size and the packaging is carried out. The place where the binding element will get into is already deter- mined at the roughening process of the film, accordingly at production of the film, when smooth film, which, from the invention point of view, is described as a semi-finished product, is in the appointed places of its surface made rough with taking the desired position of the binding element into account but it is also possible to provide the smooth finished film with roughness in the places where necessary. Films may contain a self adhesive layer on their surface, if required, too. The system according to the present invention is characterised in that it comprises roughed film on which protrusions are taking place in suitable closeness and on the roughed film or on specified parts of its surface it has a binding element having a loose fibrous structure and individual stability which contains fibres of such closeness and layer thickness that between the fibres of the binding element and the protrusions of the roughed film a mechanical joint is formed. Industrial Applicability More particularly, the process for roughening films according to the present invention is illustrated by the following examples relating to manufac¬ turing of plastic sacks. EXAMPLES Example 1 Tubular film used as starting material for manufacturing plastic sacks is processed by moulding and extrusion of the polyethylene raw material so that the temperature of the film's substance just leaving the round shaped gap of the tool is 195 °C. The tubular film - as it is usual in blown hose ex¬ trusion processes - is drawn up to the cooling tower and in the usual way to form a balloon air is blown inside of the hose enclosed by the tool and a pair of lifting nip-rolls. By setting the parameters such as air volume entrapped in the balloon, the speed of rotatron of the screw of the extrusion machine and the pull off speed, finished film of 0.150 mm thickness and 700 mm width is prepared. According to the present invention particles consisting of the film's substance are brought to the surface with air flow concentrically or in sepa¬ rate segments separately together before blowing the cooling air on. The film is cooled by the cooling air to the point of congelation, so after that no changes of sizes can occur. After the extrusion the finished film tube is fur¬ ther processed in accordance with the technology suitable for sack manufacturing. The present invention is further illustrated by an antislip system as follows: Example 2 Plastic granules are usually packaged in plastic sacks of 25 kg of weight and these sacks are transported on pellets put on top of each other in stacks in quantities of more than 1000 kgs each. To prevent such sacks from I I slipping up on each other, sacks are prepared from roughed films. The sacks are prepared from gusseted tube on a packaging machine. To prevent slipping both sides of the film tube, excepting the part which is gusseted, is made rough so that at least 50 protrusions pro square centimetres should be on the roughed parts of the surface. Thus the filled sacks lie on each other with their roughed parts of surfaces. Fleece bands of 10 cm of width and 30 cm of length are used as binding elements. When the packaging machine finished filling up a sack, that is forwarded on a conveyer to the stacking ma¬ chine. A piece of fleece band is placed on each sack lying on the moving conveyer before reaching the stacking machine so that it takes place lengthwise in the middle of the sack. The sacks are put on each other by the stacking machine so that each sack should come into contact with an other sack being in contact with itself and taking place in the upper line directly. This contact is mediated by the binding element on a part of the common contact surface. The fibres of the binding element are clinging to the upper and lower sacks and fasten them to each other with a mechanical joint and prevent them from slipping on each other.

Claims: What we claim is: 1. Process of roughening thermoplastic films characterised in that particles consisting of the substance of the film and/or other plastic material being able to weld together with that, and having suitable size and/or demanded abrasion resistance are brought to the surface to be roughened of semi-finished product having sufficient reserved heat content to maintain condition appropriate for welding of the thermoplastic film surface to be roughened or to one or both film surfaces re-heated to such temperature and are dispersed in suitable closeness and configuration and that condition of the roughened surface is maintained until desired welding process is completed. 2. A process as claimed in claim 1 wherein plastic particles are brought to the film with air flow before cooling. 3. A process as claimed in claim 1 or claim 2 wherein piastic particles are blown with pre-heated air flow to the outside surface of the tubular film just coming out from the gap of the tool. 4. A process as claimed in claim 3 wherein plastic particles are brought to the outside surface of the film before forming or cooling. 5. A process as claimed in any of claims 1 to 4 wherein plastic particles are blown to the film concentrically or in full width of the film. 6. A process as claimed in any of claims 1 to 5 wherein plastic particles are blown to the film periodically and/or each segment separately or each stripe separately. 7. A process as claimed in any of claims 1 to 6 wherein the particles are grains. 8. Roughed piastic films characterised in that they at least on one side of them on the entire surface or on specified areas of the surface comprise protrusions consisting of particles having substance of the film and/or other plastic material being able to weld together with the substance of the film, which are welded into the surface and at least partly standing out of the surface. 9. Process for prevention thermoplastic packaging films from slipping on each other characterised in that a system comprising films to be fixed - at least one of them is roughed - and a binding element is formed apply¬ ing a roughed film with protrusions of suitable closeness on its surface; a binding element having a loose fibrous structure and individual stability is placed on the film or on its specified parts, on the entire surface or on surface part(s) which binding element comprises fibres of such close¬ ness and layer thickness that between the fibres of binding element and the protrusions of the roughed film a mechanical joint is formed. 10. A process as claimed in claim 9 wherein the welding surface between the film surface and the particles forming the protrusions is preferably such that inter-section of the particles and the plane of the film does not cover the shape of projection of particles viewed perpendicularly to said film sheet. 1 1. A process as claimed in claim 9 or claim 10 wherein roughed film sheets are used on both surfaces of the binding element. 12. A process as claimed in claim any of claims 9 to 11 wherein the binding element is fixed to one of the two film sheets. 13. A process as claimed in claim 12 wherein the binding element is stacked to one of the two film sheets. 14. A process as claimed in claim 12 wherein the binding element is welded to one of the two film sheets. 15. A process as claimed in claim 12 wherein the binding element is sewn to one of the two film sheets. 16. A process as claimed in any claims of 9 to 15 wherein the thickness of the binding film reaches at most up to, preferably is less than the great¬ est value of the projection of the particles in the surfaces, roughed with piastic particles, of the two film sheets to be connected with each other. 17. A process as claimed in any claims of 9 to 16 wherein the binding ele¬ ment based on plastic having well ordered or disordered fibrous struc- ture such as a non-woven fabric, forming veiled film and having reticular structure prepared by thermo-fleece technology is used. 18. System for prevention thermoplastic packaging films from slipping on each other characterised in that it comprises roughed film on which pro¬ trusions are taking place in suitable closeness and on the roughed film or on specified parts of its surface it has a binding element having a loose fibrous structure and individual stability and which contains fibres of such closeness and layer thickness that between the fibres of the binding element and the protrusions of the roughed film a mechanical joint is formed.

Inventors: MANDZSU JOZSEF JR, MANDZSU JOZSEF SR, MANDZSU ZOLTAN, MANDZSU, JOZSEF, JR., MANDZSU, JOZSEF, SR., MANDZSU, ZOLTAN
Applicants: MANDZSU JOZSEF JR, MANDZSU JOZSEF SR, MANDZSU ZOLTAN, MANDZSU, JOZSEF, JR., MANDZSU, JOZSEF, SR., MANDZSU, ZOLTAN
Application year: 1998
Main classification: B29C59
IPC codes: B29C59, B29C65, B29C70, B29C71, B65D30, B65D33, C08J5