JPS6236062B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an olefin polymer sheet used in the technique of forming containers by deep drawing the sheet. More specifically, the present invention relates to a sheet that can be stably molded over a wide range of temperatures when molded using vacuum or pressure molding, and that can yield containers that are deeply squeezed with uniform wall thickness. Conventionally, polystyrene,
Amorphous resins such as high-impact polystyrene, ABS, and vinyl chloride have been used. However, recently, due to problems such as the toxicity of monomers contained in such molding resin components, the elution of plasticizers, and the hygiene of fillers in rubber components, polyolefin resins that do not have such concerns have appeared. It was requested. In general, simple polyolefin resins such as polyethylene and polypropylene are crystalline resins, so it is difficult to squeeze them deeply below their melting point, and even if it is possible,
Since the molded product recovers from strain over time, it cannot be deep drawn as a result. On the other hand, above the melting point, the viscosity of the resin decreases rapidly and temperature changes are large, so the viscosity differs at various locations in the plane and thickness direction of the sheet, resulting in a disadvantage that the thickness unevenness of the molded product increases. The present invention improves these drawbacks of sheets made of polyethylene and polypropylene alone. That is, the present invention has a melt flow rate of 2.0.
A composition consisting of 95-50% by weight of polyethylene with a melt flow rate of 3.0 g/10 minutes or less and 5-50% by weight of isotactic polypropylene with a melt flow rate of 3.0 g/10 minutes or less was molded by a conventional method without a stretching process. This sheet is suitable for manufacturing deep-drawn containers with uniform thickness, and when this sheet is deep-drawn by the forming method described below, the temperature range in which the sheet can be formed stably is wide, A molded product with even thickness can be obtained. Containers obtained from the sheet of the present invention can be used not only for foods, frozen desserts, lactic acid drinks, and other applications where solving the aforementioned problems are strictly required, but also for filling other articles and liquids. The sheet of the present invention can also be used as a sheet-like membrane drawn into the same shape as the sand mold used in the V process of casting to stabilize the sand mold and prevent sand from entering the casting. The sheet of the present invention can also be used as a sheet in a technique in which adhesive or pressure-sensitive adhesive is applied to one side of the sheet, deep drawing is performed, and the sheet is simultaneously laminated onto a container made of other materials such as paper or metal. Melt flow rate used in the present invention: 2.0g/
Polyethylene of 10 minutes or less is an ethylene homopolymer or copolymer that can be produced by a high-pressure method or a coordination catalyst, and copolymer monomers for such a copolymer include propylene, n-butene-1, n- Pentene-1, n-hexene-1, n-heptene-1
Examples include α-olefins having 3 to 20 carbon atoms such as 1, n-octene-1, n-decene-1, and 4-methylpentene-1. Such a polymer may be a copolymer of two or more of the above copolymerizable monomers and ethylene, but the ethylene content is at least 50% by weight. In this case, the method for measuring the melt flow rate (hereinafter referred to as MFR) of polyethylene is based on JIS K 6760. There is a limit to MFR because if the MFR exceeds 2.0g/10 minutes, the sagging during sheet heating will increase and the thickness of the molded product will become more uneven. As for the lower limit of MFR, it can be said that there is no practical limit, as even polyethylene having substantially no fluidity may be formed into a sheet by a molding machine. In addition, the melt flow rate used in the present invention
Isotactic polypropylene of 3.0 g/10 minutes or less refers to a propylene homopolymer that can be produced using a coordination catalyst, or a block copolymer or random copolymer of propylene and an α-olefin having 2 or 4 to 20 carbon atoms. Polymer (propylene content 50% by weight)
(above), and has crystallinity with a boiling heptane extraction amount of 60% by weight or less. The method for measuring MFR of polypropylene is based on JIS K 6758. If the MFR is larger than this, the sag of the sheet will be large and the thickness unevenness of the molded product will also be large. The lower limit of MFR is the same as that of polyethylene. The blending ratio of such polyethylene and polypropylene used in the present invention is 95 to 50% by weight of polyethylene and 5 to 50% by weight of polypropylene. The restriction on the composition is that the polyethylene content must be equal to or higher than the polypropylene content, and in a system where the polypropylene content is greater than the polyethylene content, the result is similar to that of polypropylene alone, and deep drawing cannot be performed. Further, if the amount of polypropylene is less than 5% by weight, there is no improvement effect. The blended composition of polyethylene and polypropylene, which is the composition of the sheet of the present invention, can be prepared using known blending methods such as extruder, Banbury, roll, etc.
Obtained using a kneader such as a Brabender plastogram. Usually, the compound is kneaded in an extruder or the like to form a pellet-like compound and then processed into a sheet, but it is also possible to directly form a sheet by dry blending the two components of polyethylene and polypropylene. It is of course possible to use additives such as antioxidants, weatherability improvers, antistatic agents, lubricants, and pigments in the composition of the sheet of the present invention. The sheet of the present invention to be subjected to deep drawing is formed by a conventional forming method. For example, extrusion molding using a T-die,
It can be obtained by a molding method such as press molding or calendar molding, but in the case of a thin product, it can also be obtained by inflation molding or the like. Examples will now be shown, in which the following method was used to evaluate the thickness unevenness of the molded product and the molding temperature range in which the thickness unevenness does not occur. The test specimen, a 150μ thick sheet, was placed in a 250mm x 250
It is sandwiched between two plate-shaped aluminum frames measuring mm x 3 mm and having a central hole of 150 mm in diameter, and set horizontally in an air pressure forming machine. Next, slide the heater heated to 350 to 450°C in the pressure forming machine to a height of 15 cm above the sheet surface. When the sheet is heated and changes from translucent to transparent, remove the heater and insert a push-in plug wrapped in felt with a tip radius of 40 mm at a speed of 300 mm/sec to 210 mm.
Push to a depth of mm. The aperture ratio is 1.4. After cooling, the push-in plug is removed and the thickness unevenness of the molded product in the push-in direction and circumferential direction is evaluated. Additionally, thermo tape is applied to the top surface of the sheet, and the temperature range in which a molded product with uniform thickness can be obtained is evaluated based on the change in color. Example 1 Propylene homopolymer pellets with MFR 3.0 g/10 min were added to polyethylene pellets with MFR 2.0 g/10 min and density 0.950 at 5, 10, 20, 30, 40, 50, 60, 80
The composition containing % by weight was blended using a Henschel mixer, and the T-die molding machine (screw diameter
35mm, L/D=22), 150μ at molding temperature 230℃
It was molded into a thick sheet and various items were examined. Table 1 shows the results of comparison with polyethylene and propylene homopolymer alone. From this, 5 to 50% by weight of polypropylene to polyethylene,
It has been found that if it is added preferably in an amount of 10 to 40% by weight, stable molding can be achieved and molded products with even thickness can be obtained. Example 2 Example 1 for a composition in which 50% by weight of propylene homopolymer with an MFR of 3.0 g/10 minutes was added to 50% by weight of polyethylene with an MFR of 0.03, 1.0, 2.0, and 3.0.
It was made into a sheet using the same method as above, and various studies were conducted. As a result, it is desirable that the MFR of polyethylene be as low as possible; if the MFR exceeds 2.0 g/10 minutes, the sheet will sag significantly and the thickness will become noticeably uneven. The results are summarized in Table 2. Example 3 MFR0.05, 3.0, 4g/10 for 50% by weight polyethylene with density 0.954g/ ^cm3 at MFR2.0g/10 minutes
Propylene homopolymer at 3.0 g/10 min.Propylene-ethylene block copolymer with 15 wt.% ethylene content and crystalline propylene-ethylene random copolymer with 3.5 wt.% ethylene content at MFR3.0 g/10 min. Compositions containing 50% by weight of each polymer were formed into sheets in the same manner as in Example 1, and various studies were conducted. The results are shown in Table 3. From this, the polypropylene blended is also low.
MFR is desirable, and when MFR exceeds 3.0 g/10 minutes, the sheet sag is large and the thickness unevenness is large.
The MFR of polypropylene is limited to 3.0 g/10 minutes or less. Furthermore, similar effects were confirmed when polypropylene was used alone, as a block copolymer, or as a random copolymer.

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[Table] Example 4 Regarding a composition in which 10% by weight of propylene homopolymer pellets with an MFR of 0.05 g/ ¹⁰ minutes were added to polyethylene pellets with an MFR of 0.03 g/10 minutes and a density of 0.940 g/cm3, Example 1 and A sheet formed in the same manner and, as a comparative example, a stretched sheet was obtained by stretching this sheet using a uniaxial stretching device so that the area ratio was 2 times and 5 times that of the original sheet. We conducted an evaluation. Tearability was evaluated by cutting out the deep-drawn portion of the deep-drawn body obtained in the evaluation of thickness unevenness and determining how easy it was to tear it by hand. As shown in Table 4, the results show that deep-drawn stretched sheets are easily torn, and deep-drawn containers formed using this method tear in the stretching direction due to falling or deformation stress. This poses problems in practical terms, such as the filling material leaking.

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Claims (1)

[Claims] 1. A resin composition consisting of 95-50% by weight of polyethylene with a melt flow rate of 2.0 g/10 minutes or less and 5-50% by weight of isotactic polypropylene with a melt flow rate of 3.0 g/10 minutes or less is subjected to a stretching process by a conventional method. An olefin polymer sheet for deep drawing, which is formed by forming the sheet without undergoing any process.