JPS6131403A - Plastic container - Google Patents

Abstract

PURPOSE:A lightweight container, consisting of a specific propylene based polymer or ethylene based polymer, having improved impact resistance particularly at low temperatures, and most suited to trays, containers, etc. for use in refrigerators. CONSTITUTION:A container obtained from (A) a propylene based polymer having <=5g/10min melt index and >=70wt% constituent units thereof consisting of propylene units or (B) ehtylene based polymer having within 0.05-10g/10min range melt index and >=50wt% constituent units thereof consisting of ethylene units to make the time integration value (Ft) of the contraction force produced in heating the polymer (A) or (B) at the melting point or above satisfy the formula I in the case of the polymer (A) and formula II in the case of the polymer (B) respectively. Preferably, propylene homopolymer or block polymer containing copolymerized ethylene in the form of block is used as the polymer (A), and high-density polyethlene is used as the polymer (B).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lightweight plastic container that has excellent impact resistance particularly at low temperatures.

Conventionally, plastic containers have been used in a wide variety of fields in various shapes because they are lightweight.

However, although containers made of polyethylene or polypropylene are inexpensive, they have low impact strength and are not particularly suitable for transporting heavy objects.

The present inventors have researched a wide range of methods for producing sheets using olefin polymers such as polyethylene and polypropylene, and have recognized that polyethylene or polypropylene polymer sheets with extremely excellent impact resistance can be obtained. The inventors have recognized that by configuring the container using different materials, it is possible to obtain a container that is extremely lightweight and has excellent performance especially at low temperatures, leading to the present invention.

That is, the present invention uses a propylene polymer having a melt index of 5 f/10 minutes or less and in which 70'M or more of its constituent units are propylene units, or a propylene polymer having a melt index in the range of 0.05 to 10 f/10 minutes. The material is not made of an ethylene polymer in which 50% by weight or more of its constituent units are ethylene units, and the time integral value (Ft) of the shrinkage force generated when heated above the melting point satisfies the following formula. It is a plastic container.

(In the case of propylene polymers, 0.51#-min/ai≦Ft≦451#Q min/-preferably 10 g#e min/cII≦Ft≦20kF-min/-what; in the case of ethylene polymers, 0. 5 kf-min/aI≦Ft≦2Qlcfe min/-preferably 10 g#min/ai≦Ft≦151#min/-The time-integrated value (Ft) of the contractile force is measured as follows.

A test piece of 105 m in diameter and 50 m or more in length is cut out from the container and used as a sample. Using a tensile p testing machine with a constant ms, the tank was kept at a temperature at which the material was completely fermented (185°C for propylene polymers, 150°C for ethylene polymers), and The distance is set to 30 degrees, and the force and time of shrinkage of the sample due to heat are measured under no tension.

Ft is calculated from the height and half-value of this peak.

If there is directionality in the maximum Ft value, it is expressed as the median value, but
The container of the present invention preferably has physical properties such as sufficient impact resistance, preferably within 3.

The propylene-based polymer in the present invention is a polymer in which 70% by weight or more, preferably 85% by weight or more of its constituent units are propylene units, such as propylene homopolymer, random or block polymers with ethylene or other olefins. Copolymer.

A copolymer of propylene, maleic anhydride, and acrylic acid is used), and the melt index is sf/10 minutes or less. Particularly suitable are propylene homopolymers and block copolymers obtained by copolymerizing ethylene into blocks.

In addition, the ethylene polymer in the present invention is a polymer in which 90% by weight or more, preferably 85% by weight or more of the constituent units thereof are ethylene units, such as low density polyethylene, high density polyethylene, propylene, 1-butene, etc. ,
Random or block copolymers of ethylene and other olefins other than ethylene such as 1-hexene, copolymers of ethylene and diene monomers such as butadiene, polar monomers such as ethylene and N-vinylcarbazole, etc. It is a copolymer with a melt index of 0.05 to 0.1710 minutes. A particularly preferred ethylene polymer is high density polyethylene.

Other polymers, additives, fillers, colorants, flame retardants, stabilizers, etc. can be added to the polymer within a range that does not impair the effects of the present invention.

The container obtained by extrusion molding, injection molding, press molding, etc. according to the conventional method for the above polymer has a time-integrated value of shrinkage force of 0.5) #-min/cd or less, It has poor impact resistance.

An example of a manufacturing method for obtaining a container having specified physical properties from the polymer is as follows.0 A sheet obtained by a normal extrusion method is heated to a temperature very close to the melting point of the sheet. A rolled sheet is obtained by simultaneously biaxially rolling (rolling ratio 3 to 10 times) at (±5°C, preferably ±3°C) for 30 seconds or more, preferably F'i 2 minutes or more (rolling ratio 3 to 10 times) using a cooling press. . The desired container can be obtained by subjecting the thus obtained rolled sheet to any desired shaping or processing such as air pressure molding or press molding.

The container according to the present invention has high impact resistance, is lightweight, and has excellent workability. In addition, the -9 container according to the present invention has particularly good impact resistance at low temperatures, so it is suitable for use as containers for trays, containers, etc. used in extremely cold regions, refrigerators, and freezers. It has a characteristic that its shape can be freely selected due to its good properties.

In the above container manufacturing method, a more suitable container can be manufactured by variously changing the rolling conditions. The container satisfies any of the following conditions.

(a) Difference between the melting point (Th) of the polymer in a container and the melting point (Tp) of the polymer in a state where the container is heated and melted and then allowed to cool (Δ'r, 'rh-'rp) is 3
The angle should be at least 8 degrees, especially at least 8 degrees.

0 The notched Izod impact strength value of the material sheet at 0°C is 40 pieces/100 or more, preferably 70] #.3
/3 or more, the same Izot impact strength at -30℃ is 3
0 Moan・DIE/C1t1 or more preferably 45 Gin・cII
I/e must be 10g1 or higher.

Furthermore, the impact strength of the trowel is A8TM D 256 Km
If the material sheet has anisotropy, the value is shown as an average value. Similarly to the Ft value, if there is anisotropy in the impact strength, it is preferably within 0. Conventionally, the rolling temperature is low in conventional uniaxial rolling using rolling rolls, When rolled near the melting point, the molding ratio is extremely large, so the desired molded product cannot be obtained from this material to date (C)
After heating to 120°C for propylene polymers and 85°C for ethylene polymers for 1 hour, allow to cool to room m, and after standing for at least 24 hours, the rate of change in thickness at the same point of the container is 5 kg. Below, preferably 3 inches or less.

Note that the melting point in the above refers to a differential scanning calorimeter (DSC).
) Yota samples 5 to 20F were heated at 10℃/in a nitrogen atmosphere.
It is defined by the temperature corresponding to the peak of the maximum endothermic peak when the resin crystals are melted by increasing the temperature at a heating rate of 1 min.

The present invention will be explained in more detail below with reference to Examples.

Example 1 Melt index (hereinafter abbreviated as MI) 12/10
By keeping a 6-inch thick block of polypropylene homopolymer (melting point 164°C) at 165°C for 3 minutes using a hydraulic press and rolling it to a thickness of 1 piece, and then cooling it with a cooling press. A sheet with a thickness of 1 was was obtained.

The sheet was molded into a circular cup-shaped container having a thickness of 0.5 wax as shown in FIG. 1 using an air pressure molding machine equipped with a far-infrared heating device. Various physical property values of this container were measured and the results are shown in Table 1.

Example 2 Polyethylene with MI of 0.5 f/10 min (melting point) 32
℃) A block-like material with a thickness of 12 m was maintained at 132° C. and rolled for about 3 minutes using a hydraulic press, and then cooled with a cooling press to obtain a rolled sheet with a thickness of 2 cm. A rectangular container with a thickness of 1.5 m as shown in FIG. 2 was molded from a sheet of lintel using a press mold equipped with a steam heating device. In the same manner as in Example 1, each harvest property value was measured and the results are shown in Table 1.

Comparative Example 1 Using the same polypropylene as used in Example 1, a sheet having a thickness of 1 inch was obtained by melt extrusion. Using the same apparatus as in Example 1, a circular container having a thickness of 0.5M was formed from the sheet by air pressure forming. This container was used in the same manner as in Example 1 to measure various physical properties, and the results are shown in Table 1.

Comparative Example 2 A circular container with a thickness of 1.5 m was molded according to Comparative Example 1 using Ml-0.8F/10 min polyethylene.

Various physical property values of the container were measured and the results are shown in Table 1.

10-1.Measuring the material sheet before forming according to ASTM D256

[Brief explanation of drawings]

1 and 2 are perspective views showing an example of a container according to the present invention, with FIG. 1 showing a circular container and FIG. 2 showing a rectangular tray. In the figure, 1 indicates a circular container body, and 2 indicates a rectangular tray body.

Claims (1)

[Scope of Claims] A propylene polymer having a melt index of 5 g/10 minutes or less and in which 70% by weight or more of its constituent units are propylene units, or a melt index of 0.05 to 0.05.
It is in the range of 10 g/10 minutes, is made of an ethylene polymer in which 50% by weight or more of the constituent units are ethylene units, and the time integral value (Ft) of the shrinkage force generated when heated above the melting point is as follows. A plastic container made of a material that satisfies the formula. (a) For propylene polymers: 0.5kg・min/cm^2≦Ft≦45kg・min/cm
^2 (b) For ethylene polymers: 0.5 kg/min/cm^2≦Ft≦20 kg/min/cm
^2