HEAT SEALABLE COVER MATERIAL WITH FRICTION SURFACE

Abstract: On the surface of a cover material agent increasing friction is spread on a paper-based underlay. The agent contains solid particles attached to the surface of the material with the help of a heat-resisting polymer bonding agent the temperature resistance of which is at least 160 DEG C, preferably at least 180 DEG C. On the reverse of the material at the same region as the friction-increasing agent there is a heatsealable area of adhesion (3). The cover material is an end cover sheet (4) to be attached to the end of a paper roll.

Description: HEAT SEALABLE COVER MATERIAL WITH FRICTION SURFACE The invention relates to a cover material on the surface of which agent increasing friction is spread, the underlay of the agent being a paper-based material. Spreading friction agent on the surface of a paper- or plastic-based cover material is known, among others, from the Finnish patent applications 873577 and 873854, as well as the Swedish lay-open print 451019. The purpose of the friction agent in the aforesaid Finnish patent applications is to prevent sliding of packagings, such as sacks, made of paper and plastic materials, and they employ various agents increasing surface coarseness, for example, hot-melt spread using a screening technique, or a mixture of bonding agent and microscopic particles spread using a printing method. The Swedish lay-open print is concerned with a plastic cover film for timber piles, on the upper surface of which there are anti-sliding spots preferably made of asphaltic mixture. The papers employ as friction surfaces materials selected for their good frictional properties and perhaps good spreadability. For example, the hot-melt referred to in the Finnish patent application 873577 must be one that rapidly solidifies into the desired screen pattern. Cover materials have been previously used for conventional packaging purposes, for example as sacks, equipped with traditional friction agents. The purpose of the present invention is to present a novel cover material which takes into consideration the treatment of the material in connection to the forming of the packaging. For this purpose, the cover material according to the invention is characterized in that the agent contains solid particles attached to the surface of the material with the help of a heat-resisting polymer bonding agent the temperature resistance of which is at least 160 C°, preferably at least 180 C°, and on the reverse of the material, at the same region as the friction-increasing agent there is a heatsealable area of adhesion. The polymer bonding agent being heat-resisting, the cover material can be utilized in applications where it acts as the material to be heatsealed to a packaging. Then the reverse of the material has a layer of heatsealable plastic. A good example of such a cover material is the end cover sheet of a paper roll which covers the end of a paper roll and protects it. Such an end cover sheet is heatsealed to the rest of the roll on the end press of a packaging machine which end press is in contact with the outer surface of the end cover sheet. Due to the heat-resisting friction-increasing agent, the outer surface of the end cover sheet maintains its good frictional properties in spite of the heatsealing process, and when paper rolls are piled up excessive tying of paper rolls for transportation can be avoided thanks to the improved frictional properties of the rolls, thus also avoiding any damage to the paper in the roll that tying could cause. In the following, the invention is described in more detail with reference to the attached drawing where Figure 1 shows a cross section of a cover material according to the invention, and Figure 2 shows one embodiment of a cover material according to the invention. Figure 1 shows a cover material the supportive layer of which is a paper-based material (1), for example kraft paper or board. On the outer surface of the paper-based material (1) a friction surface (2) is formed by spreading onto the surface (1) friction-increasing agent. This agent contains solid particles attached to the underlay and to each other with the help of a heat-resisting polymer bonding agent. Viewed from the side of the friction surface, on the reverse of the material (1) there is a heatsealable area of adhesion (3) which can be made of some suitable plastic layer attached to the inner surface of the paper-based material, for example a layer of polyethylene. Figure 2 shows one preferred embodiment of a cover material according to the invention. The cover material is in this case an end cover sheet (4) used particularly in automated paper roll packaging machines. This is an outer end cover sheet which will form the outermost surface of the ends of paper roll packagings. In practise, the end cover sheet is pressed with a heated end press (visualized by arrow P) against the folded wrapping material on the end of the paper roll (R), under which wrapping material there may even be an inner end cover sheet to protect the paper in the roll. The end cover sheet then adheres to the folded wrapping material with the help of the heatsealable area of adhesion (3) when the plastic of the area of adhesion melts. The heated end press is then in contact with the friction surface (2). Automated paper roll packaging machines on which the aforesaid operations are carried out are previously known and not described here in more detail. In the following, the agents used in the friction surface (2) and the methods for their spreading are described in more detail. The friction surface consists of bonding agent and solid particles which together make the surface coarse to the extent that its friction coefficient increases compared to the untreated surface. The bonding agent is a heat-resisting polymer the temperature resistance of which is at least 160 C°, preferably at least 180 C°. According to the most preferable alternative the temperature resistance is at least 200 C°. Temperature resistance means that the polymer does not break, melt or soften in a given temperature so that the friction surface would be damaged. This is particularly beneficial in heatsealing where a high temperature is directed also to the friction surface. The polymer bonding agent is preferably a resin. The heat-resisting resin can be some thermosetting plastic, such as phenol formaldehyde resin, melamine resin or urea formaldehyde resin. 95 In principle, the bonding agent can also be a thermoplastic, the softening point of which is above the aforesaid temperature values. The thermoplastic can in this case be a thin coating on top of the base paper and its surface forms a coarse friction surface. For example the softening point of straight thermoplastic polyester polymers is clearly 100 above 200 C°. As solid particles, a fine mineral agent can be used, such as silicon dioxide crystals. One composition that can be presented as an example and in no way limiting the 105 invention is a melamine resin as a bonding agent sold under the trade name Dynomel M-345, and a silicon dioxide as a friction agent sold under the trade name Ludox HS 40. The friction-increasing agent can be spread as a friction surface (2) on top of a paper 110 underlay using conventional coating methods, for example a spray method or a printing method. In practise, only a thin layer is enough to increase friction. It is also possible that the friction surface is not formed by a layer covering the entire surface area but the underlay is only partly covered, for example at specific regions. 115 Although the invention is described above mainly with reference to an end cover sheet, the invention can also be applied to other cover materials to be attached to packagings.

Claims: 120 Claims 1. A cover material on the surface of which agent increasing friction is spread, the underlay of the agent being a paper-based material (1), characterized in that 125 the agent contains solid particles attached to the surface of the material with the help of a heat-resisting polymer bonding agent the temperature resistance of which is at least 160 C°, preferably at least 180 C°, and on the reverse of the material, at the same region as the 130 friction-increasing agent there is a heatsealable area of adhesion (3) . 2. A cover material according to claim 1, characterized in that it is an end cover sheet (4) to be attached to the end of a paper roll. 135 3. A cover material according to claim 1 or 2, characterized in that the polymer bonding agent is heat-resisting resin. 4. A cover material according to one of the above claims, characterized in that the solid particles are minerals, for example silicon dioxide crystals. 140

Inventors: NOKKONEN AARNO, NOKKONEN, AARNO
Applicants: NOKKONEN AARNO, UPM KYMMENE OYJ, NOKKONEN, AARNO, UPM-KYMMENE OYJ
Application year: 1998
Main classification: D21H19
IPC codes: B32B29, B65D85, D21H19