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, a layer of a further specified resin and a paper layer, to a box-shaped vessel (hereinafter referred to as "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 by 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, a layer of a 4-methyl-1-pentene polymer as the inner layer of the vessel and paper layer as the outer layer of the vessel, 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 hand or clothing with oil and fat components during handling. The present invention provides a laminated film or sheet having at least three layers comprising an outer layer of poly-4-methyl-1-pentene, an intermediate layer of poly-4-methyl-1-pentene having a lower melting point than that of the outer layer, and a paper layer; with the proviso that said film or sheet does not comprise an intermediate layer of a propylene or polyester type polymer. 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 a poly-4-methyl pentene on the surface of a paper layer to form an intermediate layer and extrusion-coating a poly-4-methyl-1-pentene having a higher melting point than that of the intermediate layer to form an outer layer on the intermediate layer while blowing gas at the outer 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. The melting point of the poly-4-methyl-1-pentene of the outer layer is preferably 220 to 245°C, and the melting point of the poly-4-methyl-1-pentene of the intermediate layer is preferably 190 to 230°C. If the covering layer is divided into two layers composed of poly-4-methyl-1-pentenes differing in characteristics and the intermediate layer is formed of poly-4-methyl-1-pentene having a lower melting point, the resistance to permeation of oil and fat components is highly improved. 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 poly-4-methyl-1-pentene constituting the outer layer of the laminate of the present invention has excellent adaptability to extrusion coating at a high speed, and therefore can be extrusion-coated at a high speed by 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/cm 2 G. The aperture of the top end of a nozzle for blowing the gas is generally 1 to 50 mm 2 and preferably 5 to 10 mm 2 . 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. A crystalline homopolymer of 4-methyl-1-pentene or a crystalline copolymer of 4-methyl-1-pentene with up to 20 mole%, preferably up to 12 mole%, of other α-olefin such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-tetradecene or 1-octadecene, which has a melting point of 220 to 245 °C, especially 225 to 240 °C, is preferably used as the poly-4-methyl-1-pentene of the outer layer. 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 of the outer layer 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 since the moldability and heat resistance thereof are very good. The MFR of the poly-4-methyl-1-pentene of the intermediate layer is within the same range as that of the above-mentioned poly-4-methyl-1-pentene of the outer layer, but the melting point is generally 190 to 230 °C, preferably 200 to 230 °C. This polymer can also be prepared according to the process disclosed in JP-A-59-206418. A polymer having a melting point within the above-mentioned range can be obtained by increasing the copolymerized amount of the α-olefin over the amount of the comonomer used for the production of the poly-4-methyl-1-pentene of the outer layer. 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 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. As is apparent from the foregoing description, there is a substantial difference between the melting points of the poly-4-methyl-1-pentenes used in the outer and intermediate layers. The melting point ranges of both the polymers partially overlap each other, but it is indispensable that the poly-4-methyl-1-pentene of the outer layer should have a melting point higher than the melting point of the poly-4-methyl-1-pentene of the intermediate layer. In the present embodiment, by forming one layer of poly-4-methyl-1-pentene having a higher rigidity and an intermediate layer of poly-4-methyl-1-pentene having a lower melting point and a lower rigidity, even if the laminated film or sheet is heated in an electronic oven, oil and fat components as mentioned above do not permeate into another layer, that is the paper layer, through these two layers, and therefore the laminated film or sheet is very suitable as a material for a vessel. The extrusion temperature adopted for extrusion-coating two poly-4-methyl-1-pentenes constituting the outer and intermediate layers on the paper substrate is generally 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. In the laminate film or sheet of the present embodiment, the thicknesses of the outer layer, intermediate layer and paper layer can be optionally selected, but the thicknesses thereof are generally 1 to 2000 µm, 1 to 2000 µm and 5 to 5000 µm, respectively, and preferably 5 to 50 µm, 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 in each of the two poly-4-methyl-1-pentenes used in the present invention, so far as the attainment of the intended objects of the present invention is not inhibited. By adopting a laminate structure as used in the present invention for the laminated film or sheet, even if oil and fat components contact the outer poly-4-methyl-1-pentene layer, the carton prepared from this laminate film or sheet has excellent oil resistance, and therefore can be advantageously used as a tray to be used for cooking in an electronic oven, a carton for a food containing oil and fat components, such as a cake or a bun, and other packaging vessels. Since the laminated film or sheet of the present invention has excellent oil resistance and heat resistance, the laminated film or sheet can be advantageously used as a release paper for the production of an artificial leather. More specifically, the laminated film or sheet is passed through between a nip roll and an embossing roll to form a convex-concave embossed pattern or grain pattern on the surface of the poly-4-methyl-1-pentene layer, and the patterned surface of the poly-4-methyl-1-pentene layer is coated with a PVC sol or polyurethane solution as the starting material of an artificial leather. The obtained laminate is heated in an oven to cure the PVC or polyurethane layer. Then, the release paper comprising the poly-4-methyl-1-pentene and paper is peeled from the obtained cured body, whereby an artificial leather member composed of PVC or polyurethane, which has the embossed pattern or grain pattern transferred on the surface thereof, can be obtained. Since this release paper for an artificial leather is heated to cure the PVC or polyurethane layer coated on the surface thereof, the release paper should have an excellent heat resistance. Since the poly-4-methyl-1-pentene constituting the outer layer of the laminated film or sheet of the present invention has a high melting point, a high heat resistance is manifested. When the PVC or polyurethane layer having the embossed or grain pattern transferred thereon is separated by peeling, there is a risk of the pattern-forming outer layer of the poly-4-methyl-1-pentene will separate together with the PVC or polyurethane layer. However, in the present invention, since the outer layer and paper layer are tightly bonded to each other through the intermediate layer of poly-4-methyl-1-pentene, peeling of the outer layer together with the PVC or polyurethane layer can be prevented. Accordingly, the laminated film or sheet of the present invention can be used as an excellent release paper for an artificial leather. 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(I)"] having a melting point of 226°C, an MFR of 26 g/10 min and an initial flexural modulus of elasticity of 5000 kg/cm 2 , and a crystalline copolymer of 4-methyl-1-pentene with 1-decene (1-decene content of 2.5% by weight) [hereinafter referred to as "PMP(II)"] having a melting point of 237°C, an MFR of 180 g/10 min and an initial flexural modulus of elasticity of 13000 kg/cm 2 were independently melted in extruders having a screw diameter of 65 mm, and the melts were laminated on a milk carton paper having a base weight of 290 g/m 2 using a coextrusion two-layer die. The total coating thickness was 30 µm, and each of the coating layers had a thickness of 15 µm. A case having a size of 10 cm x 10 cm x 5 cm (depth) was prepared from the obtained laminated paper so that the coating layer was located on the inner surface of the case. 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 changed 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 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 octadecene (octadecene content of 4 % by weight) [hereinafter referred to as "PMP (III)"] having a melting point of 229°C, an MFR of 10 min and an initial flexural modulus of elasticity of 8000 kg/cm 2 was used instead of PMP (I) used in Example 1. The obtained results are shown in Table 1. Comparative Example The procedures of Example 1 were repeated in the same manner except that PMP (II) was used for both of the coextruded layers. The results obtained are shown in Table 1. Example 1 Example 2 Comparative Example Structure inner layer PMP(II) (15 µm) PMP(II) (15 µm) PMP(II) (15 µm) intermediate layer paper PMP(I) (15 µm) PMP(III) (15 µm) PMP(II) (15 µm) Number of days for exudation of margarine exudation did not occur for 20 days, and test was stopped same as in Example 1 4 Number of days for exudation of chocolate cake (electronic oven) ditto same as in Example 1 3 Number of days for exudation of butter cake (oven) ditto same as in Example 1 5 Note Unit of each parenthesized value is µm.

Claims: A laminate film or sheet having at least three layers, comprising an outer layer of poly-4-methyl-1-pentene, an intermediate layer of poly-4-methyl-1-pentene having a lower melting point than that of the outer layer and a paper layer; with the proviso that said film or sheet does not comprise an intermediate layer of a propylene or polyester type polymer. A film or sheet according to claim 1 wherein the poly-4-methyl-1-pentene of the outer layer has a melting point of 220 to 245°C. A film or sheet according to claim 1 or 2 wherein the poly-4-methyl-1-pentene of the intermediate layer has a melting point of 190 to 230°C. A film or sheet according to any one of claims 1 to 3 wherein the thickness of the outer layer is 1 to 2000 µm, the thickness of the intermediate layer is 1 to 2000 µm, and the thickness of the paper layer is 5 to 50000 µm. A box-shaped vessel prepared from a laminate film or sheet according to any one of claims 1 to 4. A process for the preparation of a laminate film or sheet as defined in any one of claims 1 to 4 which comprises extrusion-coating a poly-4-methyl pentene on the surface of a paper layer to form an intermediate layer and extrusion-coating a poly-4-methyl-1-pentene having a higher melting point than that of the intermediate layer to form an outer layer on the intermediate layer while blowing gas at the outer 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 4.

Inventors: NORITOMI KATSUMI, SHIGEMOTO HIROMI, NORITOMI, KATSUMI, SHIGEMOTO, HIROMI, NORITOMI, KATSUMI, C/O MITSUI PETROCHEM. IND. LTD., SHIGEMOTO, HIROMI, C/O MITSUI PETROCHEM. IND. LTD.
Applicants: MITSUI CHEMICALS INC, MITSUI CHEMICALS, INC.
Application year: 1990
Main classification: B32B27
IPC codes: B32B27