SE190101C1 - - Google Patents

Description

Inventors: JJ Golner and WB Baird Jr. Priority Begried March 16, 1961 (USA) The present invention relates to: sealing or welding polyolefins and in particular to an improved process for welding oriented films of polyolefins under the influence of heat by applying pull or layer on the foils.

Oriented polyolefin foils or oriented polyester foils should be sealed or joined together by means of sealing or welding devices under the action of heat, it has since been shown by Bilge that the Mien shrinks in the heated area and that the sealing seam becomes weakened or wrinkled. This is due to the fact that the oriented foils at the Mr thermoplastic foils hitherto used in the welding temperatures become brittle or opaque, contract and in the vicinity of the welding seam have a very low or no adhesion resistance.

The use of fitting layers to sink the temperature at which a good weld can be obtained is well known. For example, U.S. Pat. No. 2,824,019 states that in the case of the polyethylene terephthalate foils oriented for good sealing or welding, a considerable shrinkage of the foil occurs and in that salt a poor welding time occurs, while by applying a certain coating mass to the foil temperature is reduced, and a strong non-deformed weld is obtained. A similar finding is disclosed in U.S. Pat. No. 2,820,735, according to which benzyl alcohol is proposed to improve the weldability of polyethylene terephthalate films at lower temperatures.

Oriented polyolefin foils including irradiated foils show the same similarities in welding as the oriented polyester foils, although they differ in their chemical and physical properties. At the temperatures in question, only poor welding summers are obtained, with consequent deformation or brittleness.

As a result, according to the present invention, a process salt is proposed for a better sealing or welding of oriented polyolefin foils or films. Furthermore, the new method makes it possible to weld such products of oriented polyolefins and specially oriented polyethylene or polypropylene films with each other or with similar materials.

It has been established that there are two classes of coating varnishes which, when carefully applied to oriented polyolefin foils, allow sealing or welding at such low temperatures that no appreciable shrinkage occurs.

Delta is achieved according to the invention by coating a foil substrate with a certain oriented thermoplastic polymer monoolefin, such as polyethylene or polypropylene, on at least one surface with one of the following two special coatings: A coating varnish which consists in a solution of a mixed polymer of vinyl chloride and vinylidene chloride, such as e.g. it under the trade name K4eon. 222 »by B. F. Goodrich Chemical Co. manufactured polyvinyl chloride emulsion polymer, which is present in a solution ay 4 & parts by weight of vinylidene chloride and 60 parts by weight of polyvinyl chloride in acetone.

A coating varnish consisting of a pair of polyvinyl alcohol butyrals and containing some unreacted polyvinyl alcohol residues, such as that of the Union Carbide Plastics Company under the name "Bakelite XXHL" marketed vinyl butyral resin. This resin is dissolved in a mixture of 70 parts by weight of denatured 95% ethyl alcohol and 30 parts by weight of acetone.

The film or foil material or bar foil used for the present invention may be an oriented polyethylene of medium or higher specific gravity, a polypropylene and a mixed polymer of ethylene and propeller. Medium and specific gravity polyethylenes have a specific gravity of 0.926 to 0.940, and higher specific polyethylenes have a specific gravity of 0.941 to 0.970. A suitable high specific gravity polyethylene having an average value of 0.940 is, for example, that of W. It. Grace & Co. under the name »GREX 2001» promote the product. Of course, any polyethylene of medium or higher specific gravity can be used. A suitable polypropylene is, for example, that of the Finn Hercules Powder Co. Inc. under the name »Pretax» saluforda polypropylene. The polyethylene may preferably be irradiated per se, for example by electrons, x-rays, gamma rays, etc. for example, according to U.S. Pat. No. 2,877,500.

The polyolefin film can be oriented in either one or two mutually perpendicular directions and is usually stretched 100 to 700% in the longitudinal direction and 100 to 900% in the transverse direction.

Since polyethylene and polypropylene as an edge are relatively inert, and then due to the surface properties an adhesion of the coatings on these foils responds to achieve, the surface is pre-treated with the foils for better adhesion of the multilayered compositions. A suitable method for treatment or transformation of the surface consists of e.g. in flame treatment according to U.S. Pat. No. 2,968,576, and a discharge treatment or glow discharge treatment according to British Pat. No. 808,730. The oxidative influence exerted on the foils by such a treatment process increases the uptake capacity and retention capacity of the bar foils. According to the invention, at least one of the polyolefin foils is to be treated. Such a people, in which only one surface has been pretreated and according to the invention has been coated with the coating mass in question, can with good result be welded together with another foil under the action of heat, in that it is folded. coated the surface and welds the foils surface to surface in heat. In cases where the foils are to be welded together with the back and front or overlapping, ie. When a coated side is to be joined to an uncoated side, it is necessary to subject the uncoated side to the above-mentioned surface treatments in order to obtain one. completely satisfactory welded.

In the following, the invention will be described in more detail in the form of exemplary embodiments. In the first examples (Table I), a 0.013 mm thick biaxially oriented polypropylene film is subjected to the flame treatment according to U.S. Pat. No. 2,968,576. The coating composition is then paginated and dried in air until complete removal of the solvent. The coated side of the foil is then folded in and welded under vfirme with itself at 116 °. The coatings can be applied with ordinary devices, for example with an offset device or a direct application device. The foils can also be coated by dipping or spraying. The layer thickness can be up to 0.001 to 0.025 mm, although in the examples 0.06 mm thick layers were used. Layers smaller than 0.001 mm or stiffer than 0.025 mm are also possible. The pressure required for welding in an automatic packaging machine of approximately 0,6 kglem2 is sufficient. Various coating compositions were examined, each time measuring the clarity, the hall strength, the adhesion shape and the heat weld shape at 116 ° C at the coated films.

The adhesion was measured in that it was continued to separate the coating from the substrate by means of pressure-sensitive adhesive strips. For example, scotch-tape from the Minnesota Mining and Manufacturing Company with a pressure-sensitive surface can be pressed onto the coated foil and then quickly peeled off. A good adhesion of the coating composition is present when the peeled adhesive strip is included with only very little or no dried coating composition. The hall strength was determined by tearing with the fingernail on the coated surface of the foil, whereby damage or peeling of the layer was noted Table I.

Example The plastic base for the coating mass The clarity of the coating mass Adhesion at the base of Hall strength 3 Flexibility at 21 ° G4 ° G Welding shape at 116 ° G a 1 AYAF excellent excellent good good good good toothy good 2 AYAT excellent good moderately good moderately poor 3 BUTVAR BR moderately poor good good good bad bad 4 XYHL and PVPIVA-3utmarkt good good good good • little sticky bad fairly good - —3 XYHLutmarkt good good good 6Geon 222utmarkt excellent good good good good good good good ring sticker Coated on coated surface. b Coated on uncoated surface. c Coated on uncoated but untreated surface. 1 Butvac BR— Shawinigan Resins Corporation— a stable dispersion of a plasticized polyvinyl butyral in water.

PVIIVA 1-335 —Vinylpyrrolidone as a 50% solution in isopropanol / vinyl acetate in a ratio of 30:70 AYAF »Bakelite» vinyl acetate polymer with a non-hazardous molecular weight of 15,000 and a tensile strength of 2600 AYAT »Bakelite * and tensile strength of 4200 XYHL - »Bakelite * vinyl butyral resin with 80.7% vinyl butyral, 19.0% vinyl alcohol and 0.3% vinyl acetate as white powder.

Geon 222 B.F. modified polyvinyl chloride resin containing 40 parts of vinylidene chloride and 60 parts of polyvinyl chloride. 2 Matt according to the adhesive strip method. 3 Matt according to fingernail test.

The masses given in Examples 5 and 6 in Table I have the properties which are necessary for good welding. The masses according to Examples 1 to 4, on the other hand, are unsatisfactory in one or more houses.

Example 7. A polyethylene film having a thickness of 0.013 mm and a specific gravity of 0.94, irradiated with approximately 12 megarads and stretched in the longitudinal and transverse directions, was subjected to a flame treatment and then coated with a 17.5% loaning. of polyvinyl chloride / polyvinylidene chloride (60:40) »Geon 222» in acetone. After drying in air until complete removal of the solvent, the coated side of the foil was folded in and welded together at 116 ° C. There was only a very small shrinkage of the film and the resulting weld seam was excellent. The coated side could also be pulled over a shiny welding plate of 116 ° C and thereby welded as.

Example 8. A 0.013 mm thick and biaxially oriented polypropylene film was subjected to a flame treatment as previously described and the side thus treated was then coated with a 17.5% solution of the polyvinyl chloride / polyvinylidene chloride mixture according to Example 7. After drying in air the coated side was welded with the uncoated side at 116 ° C. The uncoated foil side was then subjected to a flame treatment and at one time an attempt was made to weld the coated side with the uncoated side. The resulting weld seam was excellent and the joke could be separated without tearing the foil.

Claims (6)

Patent claim: A method of welding oriented or irradiated films of polyethylene, polypropylene and blended polymers thereof having an average specific gravity of 0.925, characterized in that the surfaces welded together at each edge are pretreated to improve adhesion and that at least one of the pre-treated surfaces is coated with a coating composition consisting of a mixed polymer of vinyl chloride and polyvinylidene chloride or of a mixture of at least 80% polyvinyl butyral, at least 17% polyvinyl alcohol and at least 0.3% polyvinyl acetate, after which the surfaces thus treated welded together. A method according to claim 1, characterized in that the surface intended for pre-treatment is pre-treated by an oxidizing treatment. 3. A method according to claim 12, characterized in that the film is constituted by a biaxially oriented, irradiated polyethylene film having an average specific gravity of more than 0.925 or a biaxially oriented polypropylene film. 4. Weldable, oriented or irradiated polyethylene or polypropylene or blended polyinerate foil of these polyolefins having an average specific gravity of 0.925 as a starting material in carrying out the method according to claims 1-3, characterized in that one or had the surfaces for better adhesion of a coating is modified and that at least one of these modified surfaces is either coated with a polyvinyl chloride / polyvinylidene chloride blend polymer or with one of at least 80% polyvinyl butyral, at least 17% polyvinyl alcohol and at least 0.3% polyvinyl acetate. Weldable foil according to claim 4, characterized in that the foil is biaxially oriented. Weldable foil according to claims 4 to 5, characterized in that the pre-treated or modified surface consists of an oxidized surface. Request publications: