JP2926290B2 - Polypropylene resin foam sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed sheet of a polypropylene resin, and more particularly to a foamed sheet which is easy to recover and is used as various packaging materials such as food packaging and various kinds of product members. The present invention relates to a polypropylene resin foam sheet that can be processed next.

[0002]

2. Description of the Related Art A foam sheet made of polypropylene resin is used as a foam sheet which can be formed secondarily such as food packaging.
Is used. Since the polypropylene resin is a crystalline resin, it is excellent in heat resistance and the like. However, the crystalline polypropylene resin has a very low melt viscosity above the melting point of the crystalline melting point, cannot retain the foamed bubbles, and easily breaks. Therefore, the conventional polypropylene foam sheet has a high open cell rate. It was difficult to obtain a foam sheet having good mechanical properties and excellent heat resistance having closed cells. The conventional foamed polypropylene resin sheet is a low foamed product having a density of 0.5 g / cm ³ or more, or a high foamed product having a density of 0.03 g / cm ³ or less.

That is, a low foam sheet having a density of 0.5 g / cm ³ or more is produced by adding a decomposable or reactive foaming agent to a polypropylene resin and supplying it to a sheet molding and extruding apparatus. A highly foamed sheet having a microcellular structure having a density of 0.03 g / cm ³ or less is disclosed in, for example, Japanese Patent Publication No. 46-4 / 1976.
No. 1474, a crystalline polypropylene resin is dissolved in an activating solution such as methylene chloride, fluorotrichloromethane, perfluorocyclobutane, etc., and the resulting solution is higher than the vapor pressure of the solution but 1000 PSi. Extruding foam from an area no higher than to a substantially lower pressure area, thereby evaporating the activating liquid, precipitating solid polymer and freezing the orientation of the polymer. There is.

[0004] An intermediate foam of these two examples has a density of 0.
Although those having around 3 g / cm ³ are also found on the market, they are almost open cells, and hardly any closed cells, and therefore, it is hard to say that the foam sheet has good mechanical properties. However, in recent years, it has been found that some polypropylene resins can be obtained from foamed sheets having a density of about 0.3 g / cm ³ by extrusion foaming methods such as polystyrene resins.

The polypropylene resin has a Z-average molecular weight Mz of at least 2.0 × 10 ⁶ , Mz / Mw of at least 3.0, and a molecular weight distribution curve determined by gel permeation chromatography. A camel-type polypropylene-based resin having a shape with a curve overhang indicating that the region contains a branched polymer (hereinafter, may be simply referred to as a camel-type polypropylene-based resin).
It is. However, the foam sheet used alone with this resin is brittle, and when food is stored in a cup or tray molded with the foam sheet and frozen and stored, it often breaks due to impact or the like. . Further, when this foam sheet is used as a packaging material, there is a drawback that packaging is difficult due to lack of flexibility.

In order to improve this disadvantage, it has been proposed to blend a propylene copolymer resin obtained by copolymerizing a polypropylene resin with an α-olefin such as ethylene (see Japanese Patent Application No. 4-92990). However, considering recovery of polypropylene in order to recycle such a polypropylene resin blend, it is not preferable because the blend contains a polyethylene resin of a different kind of resin.

[0007]

The inventor of the present invention is a polypropylene-based resin foam sheet which can be subjected to secondary processing such as thermoforming used as various packaging materials and various product members including food packaging. In addition, the molded article obtained from the polypropylene-based resin foamed sheet has excellent brittleness at a low temperature, and is a result of various studies on a foamed sheet made of a polypropylene-based resin that gives characteristics such as easy recovery. The purpose of the present invention is to provide a polypropylene-based material which can be easily recovered and can be subjected to secondary processing such as thermoforming used as various packaging materials and various product members including food packaging. An object of the present invention is to provide a foamed polypropylene resin sheet having a low open cell ratio and excellent mechanical properties.

[0008]

The gist of the present invention is that the density is 0.025 to 0.5 g / cm ³ (the expansion ratio is 2 to 30 g / cm ³ ).
Times), wherein the polypropylene resin has a Z-average molecular weight Mz of at least 2.0 × 10 ⁶ , Mz / Mw of at least 3.0, and gel permeation. The chromatographic molecular weight distribution curve is a camel-type polypropylene resin (A) having a protruding shape of a curve indicating that the polymer region contains a branched polymer, and an atactic amorphous polypropylene (A). A polypropylene resin foam sheet characterized by being a mixed resin with B), wherein the amount of the camel-type polypropylene resin (A) is 30 to 95% by weight and the atactic amorphous polypropylene (B) is 7
It is preferable that the mixing ratio is 0 to 5% by weight.

That is, in the present invention, the foaming characteristics of the camel-type polypropylene resin and the foamed sheet obtained by foaming are obtained by blending the same type of atactic polypropylene resin with the camel-type polypropylene resin (A).
Since the foamed sheet is made of a single polypropylene component while maintaining the excellent mechanical properties of the sheet, it is easy to recover.

Further, the present invention will be described in detail. The method for measuring a gel permeation chromatograph (hereinafter referred to as GPC) performed in the present invention is as follows. Measurement device: Waters, GPC 150-C type Measurement condition: Column KF-80M 2 pieces (SH
ODEX) Column temperature 145 Inject. Temperature 145 Pump temperature 60 Sensitivity 32 Solvent used O-dichlorobenzene (1.0 ml
/ Min) Run time 50 minutes Inject. Volume 400μl

The information obtained by the GPC is as follows. (1) Mn number average molecular weight: the most basic average molecular weight obtained by measuring physical properties directly related to the number of molecules of a polymer, and depends on the total number of molecules. (2) Mw weight average molecular weight: the average molecular weight determined when the measured physical property value is directly related to the weight of the polymer, and is the root mean square of the molecular weight, and depends on the higher polymerization degree molecule than Mn. (3) Mz z average molecular weight: the highest average molecular weight,
It is the cube mean of the molecular weight.

The polypropylene resin effective for obtaining the foam of the present invention is a polymer having an Mz of about 2.0 × 10 ⁶ or more and an Mz / Mw ratio of about 3.0 or more. Since the polydispersity index Mw / Mn could not be distinguished between a polypropylene resin that gives good foaming properties and a polypropylene resin that gives only insufficient foaming properties, the numerical value is less important. In addition, the molecular weight distribution curve of the polypropylene resin giving good foaming properties by GPC is always in a shape with an overhang in the polymer region.
It has a shape like the back of a camel. In the present invention, such a curve is called a camel type, and a polypropylene resin exhibiting such a curve is called a camel type polypropylene resin. On the other hand, the molecular weight distribution curve B of the polypropylene resin giving only insufficient foaming property has a simple mountain shape showing a normal distribution. The molecular weight distribution of the camel-type polypropylene resin indicates that most parts of the polypropylene resin are linear, but certain components with high molecular weight have many branches.

The camel type polypropylene resin (A) used in the present invention is considered to be produced by the method of US Pat. No. 4,916,198, and is a branched polymer such as polypropylene resin sold by Himont. Belongs to this.

Camel type polypropylene resin (A)
The GPC curve has a camel-shaped overhang shape,
Although it is possible to obtain a closed-cell foam sheet by itself,
It is brittle and does not have good mechanical properties. Therefore,
Further, in order to improve the mechanical properties, in the present invention, the propylene resin is mixed with an atactic polypropylene resin of the same kind.

On the other hand, the atactic polypropylene resin used in the present invention is an amorphous polypropylene resin having no stereoregularity. Since it is an amorphous polypropylene resin, it is highly flexible and resistant to impact at low temperatures. . Furthermore, it has excellent adhesiveness, good gas permeability, and low density.

The ratio (A) :( B) of the camel type polypropylene resin (A) to the atactic polypropylene resin (B) is preferably from 95 to 30: 5 to 70.
This is because if the atactic polypropylene resin is 5 parts by weight or less, the flexibility is lost, and if it is above 80 parts by weight, the foaming does not occur. In the present invention, in addition to the above resin mixture, a nucleating agent such as talc which is usually used, a lubricant,
A compounding agent such as a deterioration inhibitor may be added and used.

Although the method for producing the foamed polypropylene resin sheet of the present invention is not particularly limited, a twin extruder is usually used and the hopper of the first extruder is used.
Is supplied with a composition mainly composed of the above resin mixture. Further, a physical foaming agent such as butane is supplied from the middle of the extruder, melt-kneaded, and then supplied to the second extruder. After cooling, the resin temperature is adjusted, and the resin is extruded and foamed from a mold. Next, the present invention will be described in more detail with reference to examples.

[0018]

[Examples and Comparative Examples]

Example 1 In a molecular weight distribution curve, 90% by weight of a camel-type homopolypropylene resin having a protruding curve indicating that a branched polymer is contained in a high molecular weight region, PF814 (manufactured by Himont Co.) A resin obtained by mixing 10 parts by weight of Ubetak UR079 (manufactured by Ube Lexen Co., Ltd.), which is a polypropylene resin, and 100 parts by weight of hydrocellol HK (Boshrimger Im).
The mixture was added to an extruder. As an extruder, a first extruder having a foaming agent injection port in a cylinder (50 mmφ in diameter, L / D = 2)
An extrusion foaming apparatus having a structure in which 2) and a second extruder (65 mmφ in diameter, L / D = 25) having a cooling oil jacket in a cylinder was connected in series was used. The above mixture is supplied from a hopper to a first extruder, heated and melted at about 210 ° C. while kneading and transferring with a screw, and a blowing agent (butane) is supplied from a supply port to 4.5 parts per 100 parts by weight of the resin. Injected in a ratio, kneaded, put into the second extruder, 170 ℃
Cooled to 80mm diameter, 0.75m slit thickness
The sheet extruded from the m is taken along a cooled cylinder having a diameter of 205 mm to have a thickness of 2.12 m.
m, a density of 0.138 g / cm ³ , a basis weight of 293 g / m ² , and a flexible foam sheet having a width of 640 mm were obtained. The results of a tensile test using Tensilon UCT-10T (manufactured by Orientec) are shown in Table 1. After being used for packaging, the sheet was pulverized by a pulverizer, and then melted by an extruder to form pellets. 20 parts of the pellet resin, PF814
Hydrocellol HK (Boshrimger I) was added to 100 parts by weight of a resin obtained by mixing 72 parts (manufactured by Himont) and 8 parts of Ubetak UR079 (manufactured by Ube Lexen).
0.2 part (mgelheim). It was extruded under the same conditions with the above-mentioned extruder to obtain a sheet. The obtained homopolypropylene resin foam sheet has a thickness of 2.1.
0 mm, density 0.141 g / cm ³ , basis weight 296 g /
m ² , a beautiful sheet rich in flexibility was obtained.

Example 2 A sheet was prepared under the same conditions as in Example 1 except that the composition was changed to 80 parts by weight of PF814 (manufactured by Himont) and 20 parts by weight of Ubetac-UR079 (manufactured by Ube Industries).
The obtained foamed sheet has a thickness of 2.10 mm and a density of 0.1.
A highly flexible foamed sheet having a weight of 42 g / cm ³ , a basis weight of 298 g / m ² and a width of 640 mm was obtained. This is Tensilon UC
The results of a tensile test using T-10T (manufactured by Orientec) are shown in Table 1.

Example 3 A sheet was prepared under the same conditions as in Example 1 except that the composition was changed to 50 parts by weight of PF814 (manufactured by Himont) and 50 parts by weight of Uberexen UR079 (manufactured by Ube Lexen). The obtained foam sheet has a thickness of 1.20 mm, a density of 0.253 g / cm ³ , a basis weight of 303 g / m ² , and a width of 638 m.
m was obtained. The results of a tensile test using Tensilon UCT-10T (manufactured by Orientec) are shown in Table 1.

Comparative Example 1 A sheet was prepared under the same conditions as in Example 1 except that the formulation was changed to 100 parts by weight of PF814 (manufactured by Himont). The obtained foam sheet has a thickness of 2.55 mm, a density of 0.114 g / cm ³ , a basis weight of 290 g / m ² , and a width of 641 m.
m foamed sheet was obtained. This is Tensilon UCT-10
Table 1 shows the results of a tensile test using T (manufactured by Orientec).

[0022]

[Table 1]

[0023]

As described above, in the present invention,
By using the atactic polypropylene resin mixed with the camel type polypropylene resin, a polypropylene resin foam sheet having excellent mechanical properties such as a low open cell rate and a high elongation can be obtained. Since it is composed of the polypropylene-based resin alone, it has an effect that the polypropylene resin can be easily recycled.

[Brief description of the drawings]

FIG. 1 shows a molecular weight distribution curve by GPC of a camel type polypropylene resin used in the present invention and a general polypropylene resin.

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C08J 9/00-9/42

Claims (2)

(57) [Claims] (1) a density of 0.025 to 0.5 g / cm;
^{3. A} foamed polypropylene resin sheet having an expansion ratio of 2 to 30 times, wherein the polypropylene resin has a Z-average molecular weight Mz of at least 2.0 × 10 ⁶ and Mz / Mw
Is at least 3.0 and the molecular weight distribution curve determined by gel permeation chromatography is a camel-type polypropylene having a shape with a protrusion of the curve indicating that the polymer region contains a branched polymer. Resin (A)
And a atactic amorphous polypropylene (B). 2. The polypropylene resin according to claim 1, wherein the polypropylene resin (A) which is a camel type has a mixing ratio of 30 to 95% by weight and the atactic amorphous polypropylene (B) has a mixing ratio of 70 to 5% by weight. Resin foam sheet.