JPH08217889A - Polypropylene sheet and container - Google Patents

Abstract

PURPOSE: To obtain a polypropylene sheet having good transparency and excellent thermoformability and obtain a propylene container by carrying out thermoforming of the sheet. CONSTITUTION: This polypropylene sheet comprises a composition composed of a polypropylene and an olefinic elastomer and in the sheet, the olefinic elastomer is dispersed in the propylene sheet as fiber having 0.005-0.4μm average diameter. This polypropylene container comprises a thermoformed body of the polypropylene sheet. The polypropylene sheet is produced by melt-extruding the composition of the polypropylene with the olefinic elastomer into a sheet-like material, cooling the material and rolling the material at a temperature lower than the melting point of the crystal. The polypropylene container is produced by thermoforming the polypropylene sheet by a method such as vacuum forming or air pressure forming.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polypropylene sheet which is suitably used as a packaging material for foods, pharmaceuticals, cosmetics, stationery and the like, has excellent transparency and is excellent in thermoformability such as vacuum forming, and a sheet thereof. The present invention relates to a polypropylene container obtained by thermoforming.

[0002]

2. Description of the Related Art Polypropylene sheets are widely used as packaging materials for foods, stationery, etc. because they are low in cost and excellent in mechanical strength and heat resistance. Since it is easy to recycle, it is expected as a substitute for polyvinyl chloride and polystyrene sheets. However, conventional polypropylene sheets are inferior in transparency as compared with polyvinyl chloride and polystyrene sheets, and thus their use is limited.

[0003]

As a means for improving the transparency of a polypropylene sheet, a method of producing a sheet from a composition obtained by adding a crystallization nucleating agent to a propylene-ethylene random copolymer has been proposed. Although the sheet produced by the method is recognized to have an effect of improving transparency to some extent, the drawdown due to heating during thermoforming is large,
There is a drawback that wrinkles and uneven thickness are likely to occur.

A method has also been proposed in which polypropylene is melt-extruded into a sheet shape, cooled, and then rolled at a temperature lower than the crystal melting point. However, the sheet produced by such a method has a large shrinkage due to heating during thermoforming. However, there is a drawback that the sheet is apt to be damaged or improperly shaped. Furthermore, this method requires a relatively high pressure of 5 kg / cm ² or more in order to faithfully transfer the die shape in thermoforming, which causes improper shaping due to air leakage from the die mating surface and die clamping due to high pressure. Therefore, there is a problem that the life of the mold is shortened.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, a polypropylene sheet composed of a composition in which a specific elastomer is mixed with polypropylene, wherein the elastomer has an average diameter 0.0
It was found that a polypropylene sheet having fibrous dispersion of 05 to 0.4 μm has good transparency and good mold shape transferability even when thermoforming is performed at a relatively low pressure. The present invention has been completed.

That is, the present invention comprises a composition of polypropylene and an olefinic elastomer, wherein the olefinic elastomer forms fibers having an average diameter of 0.005 to 0.4 μm and is dispersed in polypropylene. A characteristic polypropylene sheet.

In the present invention, the polypropylene constituting the polypropylene sheet may be a propylene homopolymer, a block copolymer of propylene and an α-olefin other than propylene, a random copolymer, a copolymer such as a graft copolymer. Can be mentioned. Examples of α-olefins other than propylene include ethylene, butene-1, pentene-1, and hexene-1, and the copolymerization ratio of these α-olefins is 10 mol% or less. It is suitable for exhibiting. Further, as the polypropylene in the present invention, a mixture of the above-mentioned propylene homopolymers or copolymers can also be used. Among these, a propylene homopolymer excellent in rigidity and transparency is particularly preferable.

The melt index of polypropylene is
In order to satisfactorily perform the molding process described below, 0.3 to 10
It is preferably in the range of g / 10 minutes.

In the present invention, the olefinic elastomer is an olefinic soft resin having rubber-like elasticity although it is thermoplastic because it does not have a cross-linking structure like rubber. Of these, an olefin-based soft resin having a Vicat softening point of 130 ° C. or lower is preferable. Such olefin elastomers include ethylene and α-other than ethylene.
Examples thereof include a copolymer with an olefin and a copolymer of propylene and an α-olefin other than propylene. Here, the α-olefin has 3 to 1 carbon atoms.
The α-olefin of 2 is preferable, and specifically, propylene, butene-1, pentene-1, 4-methylpentene-
1, hexene-1, heptene-1, octene-1, and the like. In the present invention, particularly preferable olefin elastomer is an ethylene content of 10 to 90 mol%.
Propylene-ethylene copolymer, butene content 10-6
An ethylene-butene copolymer of 0 mol% may be mentioned.

[0010] The melt index of the olefin elastomer is, in order to favorably perform the molding process described later,
It is preferably in the range of 0.3 to 10 g / 10 minutes.

In the polypropylene sheet of the present invention, the above-mentioned olefin elastomer has an average diameter of 0.
It is important that fibers of 005 to 0.4 μm are formed and dispersed in polypropylene. When the average diameter of the olefin elastomer is less than 0.005 μm, the effect of improving thermoformability is not sufficient and the object of the present invention cannot be achieved. Further, when the average diameter exceeds 0.4 μm, the transparency is lowered, which is not preferable. The average diameter of the fibers of the olefin elastomer is preferably in the range of 0.01 to 0.1 μm in consideration of better thermoformability and transparency.

The blending amount of the olefinic elastomer with respect to polypropylene is not particularly limited, but polypropylene 1
1 to 100 parts by weight, preferably 5 to 100 parts by weight
80 parts by weight, and more preferably 8 to 50 parts by weight are preferable in order to enable thermoforming at a relatively low pressure and to improve transparency.

In the present invention, it is effective to add a crystallization nucleating agent to the above resin component, if necessary, in order to improve the transparency. Examples of the crystallization nucleating agent include talc; silica; metal salts of aromatic phosphoric acid compounds such as methylene (2,4-tert-butylphenyl) phosphate; sodium benzoate, sodium toluate, p-ter.
Metal salts of aromatic monocarboxylic acids such as sodium t-butylbenzoate; sorbitols such as 1,3,2,4- (dimethylbenzylidene) sorbitol; polymer nuclei such as poly (3-methyl-pentene-1) Examples thereof include agents. In particular, metal salts of aromatic phosphoric acid compounds, metal salts of aromatic monocarboxylic acids, sorbitols, organic crystallization nucleating agents such as polymer nucleating agents are preferable, and among them, sorbitols are effective in improving transparency. Most suitable. Although the addition amount of the crystallization nucleating agent is not particularly limited, it is preferably in the range of 0.0001 to 1 part by weight with respect to 100 parts by weight of the resin component.

Further, if necessary, additives such as a stabilizer, an antistatic agent, a lubricant, an antifogging agent, an ultraviolet absorber, an antiblocking agent, and a coloring agent can be appropriately added.

The thickness of the polypropylene sheet of the present invention is not particularly limited, but it is usually 0.1 to 2.0 in order to impart sufficient practical strength, high transparency, flexibility and heat resistance.
It is preferably in the range of mm. Further, as described above, the polypropylene sheet of the present invention has the average diameter of the dispersed fibers of the polyolefin-based elastomer of 0.005 to 0.4 μm, but the crystal orientation coefficient of polypropylene itself is 0. 20 to 0.90 and a fibril diameter of 0.01 to 0.4 μm are preferable in terms of transparency, mechanical strength, and heat resistance.

The polypropylene sheet of the present invention may be obtained by any method, but can be suitably produced by the method described below. That is, a method of obtaining a sheet by melt-extruding a composition in which polypropylene is mixed with an olefin elastomer into a sheet, cooling the composition, and then rolling the composition at a temperature lower than the crystal melting point can be mentioned.

The method of melt extruding a composition obtained by blending polypropylene with an olefin elastomer into a sheet and cooling the composition can be carried out by a known technique. For example, polypropylene is mixed with a predetermined amount of an olefin elastomer by a mixer such as a tumbler, and the resulting mixture is melt-kneaded and pelletized in an extruder. The obtained composition is supplied to an extruder, melted at a resin temperature of 200 to 280 ° C., extruded in a sheet form from a die, and cooled with a cooling roll having a surface temperature of 20 to 100 ° C., preferably 30 to 80 ° C. to form a sheet. There is a way to

As the roll rolling method, the following method can be preferably adopted. A method in which the sheet cooled by the cooling roll is sufficiently preheated before passing it between the rolling rolls and then rolled at a temperature not lower than the preheating temperature and lower than the crystal melting point of the sheet can be suitably adopted. Preheating before rolling is a very important step for the present invention, and preheating causes the polyolefin-based elastomer to have an average diameter of 0.005 to 0.4 μm.
m fibers can be dispersed in polypropylene. Further, a polypropylene sheet having the above-mentioned specific crystal orientation coefficient and fibril diameter can be manufactured.

The preheating temperature varies depending on the thickness of the sheet to be preheated, but it is preferable to preheat so that the sheet temperature before rolling satisfies the following formula.

80 + 35 × t1−15 × t1 / t2 ≦ T ≦ 155 + 15 × t
1-27 × t1 / t2 (where T is the sheet temperature before rolling (° C.), t1 is the sheet thickness before rolling (mm), and t2 is the sheet thickness after rolling (mm).) When the sheet temperature is higher than the range of the above formula, stretching unevenness due to rolling occurs and a uniform sheet cannot be obtained, and the effect of improving transparency is poor, which is not preferable. On the contrary, if the sheet temperature is too low, not only rolling becomes difficult, but also
The average diameter of the fibers of the polyolefin elastomer is 0.
It is not preferable because the thickness cannot be 4 μm or less and the effect of improving transparency is poor. Also, the fibril diameter of polypropylene itself cannot be reduced to 0.4 μm or less.

The method of adjusting the sheet temperature before rolling to the above temperature includes a method of passing the sheet between preheating rolls whose surface temperature is adjusted so that the sheet temperature before rolling becomes the above temperature, and an indirect heating method such as a far infrared heater. Examples thereof include a method of preheating and a method of passing the sheet through a medium such as air or water heated to a predetermined temperature. Among these, the method of using a preheating roll is preferable because the temperature can be easily adjusted.

Next, the rolling is preferably carried out at a surface temperature of 120.
It is carried out by passing the sheet between rolling rolls at ˜160 ° C., more preferably at 130 to 155 ° C. The rolling is preferably performed so that a rolled sheet having a crystal orientation coefficient of 0.2 to 0.9 and a fibril diameter of 0.01 to 0.4 μm can be obtained. For this purpose, it is preferable that the thickness of the rolled sheet be within the range of 1 / 1.5 to 1 / 3.5 of the original sheet thickness. The rolling can be repeated a plurality of times if necessary.

The polypropylene sheet of the present invention is thus obtained. Furthermore, the polypropylene container of the present invention can be manufactured by thermoforming the above polypropylene sheet. As the thermoforming method, a known method can be adopted without any limitation. For example, there is a method of forming by direct heating with a hot plate or indirect heating with a far-infrared heater using a vacuum forming machine, a pressure forming machine, or a vacuum pressure forming machine combining these. In this case, it is desirable to perform thermoforming at a relatively high pressure in order to ensure good mold transferability, but a range in which air leakage from the mold mating surface and decrease in mold life are unlikely to occur, for example, 2-4
It is preferable to perform thermoforming in the range of kg / cm ² . The sheet surface temperature at the time of thermoforming needs to be lower than the melting point of polypropylene in order to obtain a container having excellent transparency. Usually, it is preferable to select from the range of 130 to 165 ° C. from the viewpoint of transparency of the obtained container.

The polypropylene container thus obtained is
The average diameter of the fibers of the polyolefin elastomer is 0.
It is 005 to 0.4 μm. Further, it is preferable that the polypropylene itself has a crystal orientation coefficient of 0.30 to 0.95 and a fibril diameter of 0.01 to 0.4 μm from the viewpoint of transparency, mechanical strength and heat resistance.

[0025]

INDUSTRIAL APPLICABILITY The polypropylene sheet of the present invention is a polypropylene sheet having a transparency comparable to that of polyvinyl chloride and polystyrene sheets and excellent thermoformability even though it is polypropylene. Moreover, since the polypropylene container obtained by thermoforming this polypropylene sheet has good transparency, it is suitable as a container for food, stationery or cosmetics trays, lids, cups, packs, etc., and also as a PTP packaging container for pharmaceuticals. Can be used.

[0026]

EXAMPLES Examples are shown below for specifically explaining the present invention, but the present invention is not limited to these examples. In the following examples and comparative examples,
The crystal orientation coefficient is "advances in xray
Analysis (Advances in X-ray Analysis) ", Volume 6,
by the method described in p231 (1963),
The fibril size is “Journal of Polymer Sience”, Volume 27, p8
7 (1958).

Examples 1 to 3 100 parts by weight of a propylene homopolymer having a melt index of 0.9 g / 10 min, a propylene-ethylene copolymer having a melt index of 1.5 g / 10 min as an olefin elastomer and a Vicat softening point of 110 ° C. A polypropylene composition in which a polymer (ethylene content: 15 mol%) was blended in a ratio shown in Table 1 was melted by a twin-screw extruder having a screw diameter of 65 mm, and extruded into a sheet form from a die having a die width of 1300 mm. 0.6m after cooling with a cooling roll
The thickness of the sheet was m. The sheet was preheated by passing it through four preheating rolls with the surface temperature of each roll set to the values in Table 1. The sheet temperature before rolling was measured by a contact type thermometer and was as shown in Table 1. Continued
The preheated sheet was rolled by a pair of rolling rolls having a surface temperature of 135 ° C. so that the final sheet thickness would be 0.3 mm. This rolled sheet is C in the MD direction (extrusion direction)
Table 1 shows the crystal orientation coefficient and fibril diameter of the uniaxially oriented sheet in which the axes are oriented. In addition, the average diameter of the olefinic elastomer inside the obtained sheet was measured with a transmission electron microscope, and the haze of the sheet was measured according to JIS.
The results measured by K7105 are shown in Table 1.

Subsequently, this sheet was vacuum-pneumatic molded at various sheet pressures at a sheet surface temperature of 162 ° C. by a vacuum-pneumatic molding machine, and 160 mm × 100 mm × depth 30 m.
m container was molded. For moldability evaluation, the minimum compressed air pressure is displayed for those in which the mold shape can be faithfully transferred, and “Mold failure” is displayed for those with poor appearance such as wrinkles and breaks, and those in which the mold shape is not transferred well. Was displayed.

Comparative Example 1 A 0.3 mm sheet was obtained in the same manner as in Example 2 except that rolling was not performed in the sheet manufacturing process. The obtained sheet was a non-oriented sheet, and no fibril structure was observed. Table 1 shows the results of measuring the average diameter of the elastomer inside the obtained sheet, the haze of the sheet, the moldability, and the like.

Comparative Example 2 0.3 m in the same manner as in Example 2 except that the olefin elastomer was not added.
m sheets were obtained. Haze of the obtained sheet, moldability,
Others were measured, and the results are shown in Table 1.

Examples 4 to 6 100 parts by weight of a propylene homopolymer having a melt index of 0.9 g / 10 min, an ethylene-butene copolymer having a melt index of 1.3 g / 10 min as an olefin elastomer and a Vicat softening point of 55 ° C. Polymer (butene content 1
(0 mol%) was used in the proportion shown in Table 1 to obtain a rolled sheet and a container in the same manner as in Example 1. The results are shown in Table 1.

Examples 7 to 9 100 parts by weight of a propylene homopolymer having a melt index of 0.9 g / 10 min, a propylene-ethylene copolymer having a melt index of 1.5 g / 10 min as an olefin elastomer and a Vicat softening point of 85 ° C. A polypropylene composition was prepared by blending a polymer (ethylene content: 20 mol%) in the proportion shown in Table 1 and 0.3 part by weight of 1,3,2,4- (dimethylbenzylidene) sorbitol as a crystallization nucleating agent. A sheet and a container were prepared in the same manner as in Example 1. The results are shown in Table 1.

[0033]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area // B65D 1/09 B65D 1/00 B

Claims (2)

[Claims] 1. A polypropylene comprising a composition of polypropylene and an olefin elastomer, wherein the olefin elastomer forms fibers having an average diameter of 0.005 to 0.4 μm and is dispersed in the polypropylene. Sheet. 2. A polypropylene container comprising a thermoformed body of the polypropylene sheet according to claim 1.