Laminated film or sheet and box-shaped vessel prepared therefrom

Abstract: A laminated film or sheet comprises poly-4-methyl-1-pentene laminated on a paper layer. By using poly-4-methyl-1-­ pentene having a low melting point, formation of cracks and other defects in the resin layer is prevented and the oil and fat impermeability is improved. If an intermediate layer of a specific polymer is formed in addition to the poly-4-methyl-1-pentene layer, the oil and fat impermeability is further improved. A box-shaped vessel (carton) and a release paper for an artificial leather can be prepared from this laminated film or sheet.

Description: The present invention relates to a laminate film or sheet comprising a layer of a specific resin and a paper layer, to a box-shaped vessel (hereinafter referred to as a "carton") prepared therefrom and to processes for the preparation of the film or sheet and vessel. Recently, cooking methods using an electronic oven have been rapidly introduced. A variety of foods such as dishes and cakes can be easily prepared using an electronic oven. When a food is cooked by an electronic oven, the food to be cooked is contained in a tray-shaped vessel formed of a laminate comprising, for example, an inner layer of a 4-methyl-1-pentene polymer and an outer paper layer, and the food is subjected to high-frequency heating. Foods to be cooked include foods containing oil and fat components such as butter and margarine, for example, pound cakes, and foods on which a sauce containing oil and fat components is poured to complete cooking after heating. It sometimes happens that after heating in an electronic oven or after pouring of a sauce containing oil and fat components after side heating, foods are preserved in a box-shaped vessel. Since the heretobefore used covering layer of a 4-methyl-1-pentene polymer has a high rigidity, fine cracks are sometimes formed in the covering layer. Moreover, when oil and fat components as described above are present, they permeate into the paper layer constituting the vessel over time, the paper layer as a whole becomes oily thus degrading the appearance of the vessel, and there is a risk of contamination of the hands or clothing with oil and fat components during handling. EP-A-345,031 discloses a laminated film comprising three layers, including a layer of a 4-methyl-1-pentene polymer and, inter alia, a paper substrate. The present invention provides a laminated film or sheet having at least two layers comprising (A) a layer of poly-4-methyl-1-pentene having a melting point of 190 to 230°C and (B) a paper layer; with the proviso that said film or sheet does not contain an intermediate layer between said layer (A) and said layer (B) of a propylene or polyester type polymer or of a poly-4-methyl-1-pentene having a lower melting point than that of the poly-4-methyl-1-pentene of layer (A). The present invention also provides a box-shaped vessel prepared from a laminate film or sheet as defined above. The present invention additionally provides a process for the preparation of a laminate film or sheet as defined above which comprises extrusion-coating poly-4-methyl-1-pentene having a melting point of 190 to 230°C to form a layer on the surface of a paper layer, while blowing gas at the layer being formed by the extrusion coating. The present invention further provides a process for producing a box-shaped vessel comprising folding a laminate film or sheet as defined above. In the laminate film, sheet or vessel of the present invention formation of cracks in the covering layer is prevented so that permeation of oil and fat components from a contained cooked food is prevented. The film, sheet or vessel has excellent oil and fat impermeability. In the laminate film or sheet of the present invention, the covering layer is formed of poly-4-methyl-1-pentene. The poly-4-methyl-1-pentene used in the present invention is a homopolymer of 4-methyl-1-pentene or a copolymer of 4-methyl-1-pentene with up to 20 mole%, preferably up to 12 mole%, of an α-olefin having 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 2-tetradecene or 1-octadecene. Crystalline poly-4-methyl-1-pentene is preferably used. This polymer can be prepared according to a known process, for example, the process disclosed in JP-A-59-206418. The MFR of the poly-4-methyl-1-pentene is preferably 5 to 1000 g/10 min, and poly-4-methyl-1-pentene having an MFR of 70 to 300 g/10 min is especially preferably used because the moldability and heat resistance thereof are very good. In general, an increase of the amount of the α-olefin to be copolymerized results in a lowering of the melting point, but the melting point is also influenced by the kind of the α-olefin, the catalyst used and other polymerization conditions. However, since the relationships between these factors and the melting point can be experimentally determined in advance, a person skilled in the art will easily obtain a poly-4-methyl-1-pentene having a desired melting point. If a layer of poly-4-methyl-1-pentene having a relatively low melting point of 190 to 230 °C is laminated with a paper layer, even under heating in an electronic oven, the above-mentioned oil and fat components do not permeate into the paper layer, and therefore a laminate film or sheet suitable as a vessel material can be provided. Papers customarily used as the material for boxes or cases, such as clay-coated paper and milk carton paper, can be used as the paper constituting the paper layer. However, use clay-coated paper is recommended because the permeation rate of oil and fat components can be maintained at a very low level even if pinholes or small cracks are formed in the poly-4-methyl-1-pentene layer by unexpected shock or rubbing or even if the oil and fat components happen to permeate from the end face of the laminated film or sheet. Moreover, since this clay-coated paper has excellent printability, the laminate sheet or film is suitably used as a base material to be printed on when a print layer is formed on the surface of the vessel according to need. The laminate film or sheet of the present invention can be prepared by extrusion-coating poly-4-methyl-1-pentene directly on the surface of a paper, or by extrusion-coating poly-4-methyl-pentene on the surface of a paper which has been subjected to an adhesiveness-increasing treatment according to a known method, for example by coating the paper surface with an anchor coat agent of an organic titanium, polyethyleneimine or isocyanate type compound or by bonding an adhesive polyolefin or high-pressure polyethylene as the undercoat to the paper surface. In the latter case, a laminated film or sheet having a three-layer structure is obtained. The poly-4-methyl-1-pentene has excellent adaptability to extrusion coating at a high speed, and therefore can be extrusion-coated at a high speed using an ordinary extrusion-coating apparatus. By this extrusion coating a laminate film or sheet having excellent mechanical properties and interlaminar adhesiveness can be obtained. If a gas such as air or nitrogen gas is blown to both the ends of the extruded film or sheet at the extrusion coating, neck-in or edge wave at both ends of the extruded film or sheet can be prevented, and in this case, if blowing of the gas is effected in the vicinity of the point of contact of the extruded film or sheet with the paper substrate from the side where the extruded film or sheet is not contacted with the paper substrate, the extrusion coating is accomplished at a high speed more stably. As the method for blowing a gas to the extruded film or sheet, there can be mentioned a method in which a metal tube such as an aluminium tube or copper tube or a conduit tube such as a thermoplastic resin tube is arranged downstream of a die, and a gas is blown to the extruded film or sheet of poly-4-methyl-1-pentene at an optional point in the course of up to the point of the contact of the film or sheet extruded from the die with the paper substrate, preferably in the vicinity of the contact point where the extruded film or sheet is coated on the paper substrate. The pressure of the gas to be blown is appropriately determined in view of the thickness of the extruded film or sheet to be coated. However, the pressure of the gas is generally 0.5 to 5 kg/cm²G. The aperture of the top end of a nozzle for blowing the gas is generally 1 to 50 mm² and preferably 5 to 10 mm². The distance between the top end of the nozzle and the extruded film or sheet is generally 2 to 100 mm and preferably 5 to 20 mm. If the top end of the blowing nozzle is directed to the outer side of the extruded film or sheet from the inner side thereof, the film or sheet is expanded by the blown gas and the effect of further narrowing neck-in is preferably attained. When the poly-4-methyl-1-pentene is extrusion-coated, the extrusion temperature is ordinarily 250 to 370 °C and preferably 290 to 340 °C. The extrusion-coating speed (the take-up speed of the covering material) is generally at least 100 m/min and preferably 150 to 500 m/min. The thickness of the poly-4-methyl-1-pentene layer and paper are not particularly critical, but the thicknesses of the poly-4-methyl-1-pentene and paper layers are generally 1 to 2000 um and 5 to 5000 µm, respectively, and preferably 5 to 50 µm and 100 to 600 µm, respectively. Known additives such as a weathering stabilizer, a heat stabilizer, an antistatic agent, an antifogging agent, an antiblocking agent, a slip agent and a colourant can be incorporated into the poly-4-methyl-1-pentene used in the present invention, so far as the intended objects of the present invention can be attained. The present invention is now further described in the following Examples. In the Examples, the melting point, MFR and initial modulus of elasticity were measured according to the following methods: Melting Point By using a differential scanning calorimeter (model DSC-II supplied by Perkin-Elmar), a sample was melted at 260 °C for 5 minutes, cooled to room temperature at a rate of 20 °C/min to effect crystallization and maintained at room temperature. An endothermic curve was determined at a temperature-elevating rate of 10 °C/min, and the peak temperature was designated as the melting point. The poly-4-methyl-1-pentene used in the present invention shows one endothermic peak or a plurality of endothermic peaks. When a plurality of peaks were observed, the highest peak temperature was designated as the melting point. MFR The MFR value was measured under a load of 5 kg at 260 °C according to ASTM D-1238. Initial Modulus of Elasticity The initial modulus of elasticity was measured according to ASTM S-790 (the test speed was adjusted to 5 mm/min). Example 1 A crystalline copolymer of 4-methyl-1-pentene with 1-octadecene (1-octadecene content of 6% by weight) [hereinafter referred to as "PMP (1)"] having a melting point of 226°C, MFR of 26 g/10 min and an initial flexural modulus of elasticity of 5000 kg/cm² was melted in an extruder having a screw diameter of 65 mm and laminated on a milk carton paper having a base weight of 290 g/m². The coating thickness of PMP (1) was 20 µm. A case having a size of 10 cm x 10 cm x 5 cm (depth) was prepared from the laminated paper so that the coating layer was located on the inner surface. Then, weighed 40 g of commercially available margarine (supplied by Yukijirushi Nyugyo) was placed in the case and heated for 30 seconds by an electronic oven (Type NE-A740 supplied by Matsushita Denki Sangyo). After the heating, the case was allowed to stand still at room temperature, and the number of days required for the margarine to exude to the outer surface of the paper layer was determined by visual inspection. A case prepared in the same manner as described above was charged with a starting powder of a chocolate cake (House Range Gourmet supplied by House Shokuhin) and water, and cooking was carried out for 3 minutes and 30 seconds using the same electronic oven as described above. After the cooking, exudation of the contents to the outer surface was examined without taking out the contents from the case. Similarly, a case prepared in the same manner as described above was charged with a starting powder of a butter cake (House Range Gourmet supplied by House Shokuhin) and water, and cooking was carried out at a set temperature of 190°C for 20 minutes in an oven. After the cooking, exudation of the contents to the outer surface was examined without taking out the contents from the case. The results obtained are shown in Table 1. Example 2 The procedures of Example 1 were repeated in the same manner except that a crystalline copolymer of 4-methyl-1-pentene with decene (decene content = 8% by weight) [hereinafter referred to as "PMP (II)"] having a melting point of 221°C, MFR of 26 g/10 min and an initial flexural modulus of elasticity of 400 kg/cm² was used instead of the PMP (I) used in Example 1. The results obtained are shown in Table 1. Comparative Example 1 The procedures of Example 1 were repeated in the same manner except that a homopolymer of 4-methyl-1-pentene [hereinafter referred to as "PMP (H)"] having a melting point of 242°C, MFR of 26 g/10 min and an initial flexural modulus of elasticity of 19000 kg/cm² was used instead of the PMP (I) used in Example 1. The results obtained are shown in Table 1. Comparative Example 2 The procedures of Example 1 were repeated in the same manner except that a crystalline copolymer of 4-methyl-1-pentene with 1-decene (1-decene content of 2.5% by weight) [hereinafter referred to as "PMP (III)] having a melting point of 237°C, MFR of 180 g/10 min and an initial flexural modulus of elasticity of 13000 kg/cm² was used instead of the PMP (I) used in Example 1. The results obtained are shown in Table 1.

Claims: A laminate film or sheet having at least two layers comprising (A) a layer of poly-4-methyl-1-pentene having a melting point of 190 to 230°C and (B) a paper layer; with the proviso that said film or sheet does not contain an intermediate layer between said layer (A) and said layer (B) of a propylene or polyester type polymer or of a poly-4-methyl-1-pentene having a lower melting point than that of the poly-4-methyl-1-pentene of layer (A). A film or sheet according to claim 1 wherein the thickness of the poly-4-methyl-1-pentene layer is 1 to 2000 µm and the thickness of the paper layer is 5 to 5000 µm. A film or sheet according to claim 1 or 2 wherein the melt flow rate of the poly-4-methyl-1-pentene is 5 to 1000 g/10 min. A box-shaped vessel prepared from a laminate film or sheet according to any one of claims 1 to 3. A process for the preparation of a laminate film or sheet as defined in any one of claims 1 to 3, which comprises extrusion-coating poly-4-methyl-1-pentene having a melting point of 190 to 230°C to form a layer on the surface of a paper layer, while blowing gas at the layer being formed by the extrusion coating. A process for producing a box-shaped vessel comprising folding a laminate film or sheet according to any one of claims 1 to 3.

Inventors: NORITOMI KATSUMI C O MITSUI PE, SHIGEMOTO HIROMI C O MITSUI PE, NORITOMI, KATSUMI, C/O MITSUI PETROCHEMICAL, SHIGEMOTO, HIROMI, C/O MITSUI PETROCHEMICAL
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1990
Main classification: B32B27
IPC codes: B32B27, B65D65