JP2907749B2 - Method for producing modified polypropylene resin foam, method for producing molded article, and foam and molded article obtained from those methods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a modified polypropylene resin foam, a method for producing a molded article, and a method for producing the same.
The present invention relates to a foam and a molded article obtained therefrom . More specifically,
The present invention can be used for heating in a microwave oven or the like, for example, and a method for producing a modified polypropylene resin foam which does not cause cracking even when used for storage and transportation at a low temperature, a method for producing a molded article,
And a foam and a molded article obtained from the production methods . Further, the modified polypropylene-based resin foam of the present invention and a molded article obtained therefrom can be used for applications of packaging materials, heat insulating materials, and structural materials.

[0002]

2. Description of the Related Art
As a food container that can be used for cooking in a microwave oven, a molded article made of a polypropylene foam is used. Since this molded article is excellent in heat resistance, heat insulation property and chemical resistance, it is excellent as a food container and very useful. However, there is a problem that the glass transition point is generally around 0 ° C., and the glass is broken when used for freezing at −30 ° C.

To improve the impact strength at low temperatures, a method of using a copolymer of propylene and ethylene, a method of mixing a polyethylene resin, a method of mixing various rubber resins or elastomers with a polypropylene resin, ethylene-propylene There is a method of mixing rubber and polyethylene resin. However, none of the methods sufficiently satisfy the conditions required for food containers.

More specifically, the method using a copolymer of propylene and ethylene is superior in the impact resistance at room temperature to the method using a propylene homopolymer. However, the impact resistance at low temperatures of both methods was slightly different. It is known that a method of mixing a polyethylene resin can obtain a foam having improved flexibility (Japanese Patent Application No. 6-260676). However, although this method improves flexibility, it has little effect on impact resistance.

[0005] Examples of the rubber-based resin used in the method of mixing various rubber-based resins include, for example, propylene-ethylene rubber, which is often used for improving the impact resistance of a polypropylene-based resin. When this propylene-ethylene rubber is mixed, at least 20 parts of the polypropylene resin are required to impart impact resistance at a low temperature.
It is necessary to add more than weight%.

When this method is used in a non-foaming step, it is common to extrude the foamed resin at a temperature several tens of degrees higher than the melting point of the polypropylene resin. Propylene-ethylene rubber can be mixed in a wide range with the polypropylene resin. However, in the case of having a foaming step, it is necessary to apply a sufficient tension to the resin in order to prevent the bubbles from being broken at the time of bubble growth. Therefore, it is necessary to lower the temperature of the resin to near the melting point. In general, a polypropylene resin having a low fluidity is used, so that a mixed state with other resins is deteriorated. As a result, only high-density foams with a high open cell ratio or foams with poor surface smoothness can be obtained, so that the mixing amount of the rubber-based resin is limited to a very small amount. Could not be granted.

Japanese Patent Application Laid-Open No. 6-212007 discloses a polypropylene block copolymer comprising polypropylene and an ethylene / α-olefin copolymer, and an ethylene / α-olefin copolymer. A polypropylene foam sheet using polyethylene as a base resin is described. This publication aims to obtain a polypropylene foam sheet having excellent impact resistance,
The example describes a foamed sheet using a polypropylene block copolymer containing an ethylene / propylene copolymer, an ethylene / 1-butene copolymer, and optionally polyethylene. However, according to the findings of the inventors of the present invention, it has been found that even the polypropylene-based foam sheet described in this publication has insufficient impact resistance at low temperatures.

In view of the above problems, the inventors of the present invention have:
As a result of diligent examination, it has excellent heat resistance, heat insulation and chemical resistance,
In particular, it does not crack during frozen storage at low temperatures and during transportation,
Method for producing modified polypropylene resin foam with excellent impact resistance, method for producing molded articles, and foaming obtained from these methods
The present invention was found by finding a body and a molded article.

[0009]

Thus, according to the present invention, 2% by weight or more of an ethylene-butene random copolymer is mixed with a polypropylene resin as a base resin, and a gas or a volatile foaming agent is further mixed. The present invention provides a method for producing a modified polypropylene resin foam, characterized in that the foam is extruded and foamed. Further, according to the present invention, it is possible to obtain
Of molded articles characterized by molding of expanded foam
Provided. Furthermore, according to the present invention, the modified polypropylene
A foam obtained by a method for producing a resin foam is provided.
Further, according to the present invention, it is obtained by the method for producing the molded article.
A molded article is provided.

Next , the polypropylene resin which can be used as the base resin in the present invention is not particularly limited, and any known resin can be used. Among known resins, a Z-average molecular weight Mz of at least 2.0 × 10 ⁶ or more and Mz / M
Propylene alone having w (weight average molecular weight) of 3.0 or more and having a camel-type molecular weight distribution curve (by gel permeation chromatography) having an overhanging curve indicating that the polymer region contains a branched polymer A polymer (referred to as a camel-type polypropylene-based resin) can be suitably used in the present invention. Further, a copolymer of ethylene and propylene containing 1 to 10% by weight of ethylene in the propylene homopolymer can also be used. In addition, this copolymer includes both a block copolymer and a random copolymer.

In the above resin, the Z average molecular weight Mz is
The average molecular weight at which the distribution on the higher molecular weight side is emphasized by measurement by gel permeation chromatography (hereinafter referred to as GPC), and means the average value of the cube of the molecular weight. The weight-average molecular weight Mw is an average molecular weight obtained when a measured physical property value is directly related to the weight of a polymer, and is 2% of the molecular weight.
Mean power. The GPC performed in the present invention
Is as follows.

Measuring device: GPC 150-C type (manufactured by Water) Measuring conditions: column KF-80M (manufactured by SHOdex)
Column temperature 145 ° C (polypropylene resin, hereinafter P
P) Injection temperature 145 ° C Pump temperature 60 ° C Sensitivity 32 Solvent used o-dichlorobenzene (1.0 ml / min) Scanning time 50 minutes Injection volume 400 μl If such a polypropylene resin is used, sufficient melt tension at the time of foaming can be obtained. Is obtained, and a foam having a desired density can be obtained.

Further, the polypropylene resin has a camel-type molecular weight distribution curve. The camel-type molecular weight distribution curve is, for example, as shown in FIG. Means a molecular weight distribution curve of a shape having a protrusion. The molecular weight distribution curve shows that certain components in the high molecular weight region have many branches. In FIG. 1, curve A indicates a camel-type polypropylene-based resin, and curve B indicates other polypropylene-based resins.

Specific examples of the polypropylene resin that can be used in the present invention include MH-8 manufactured by Mitsubishi Chemical Corporation, and A resin manufactured by Sumitomo Chemical Co., Ltd.
D571, S-131 and the like. In addition, camel-type polypropylene-based resins specifically include X-1005, PF-814, SD-632, and X11 manufactured by Himont.
277-22-1 and the like. In addition, PF-81
4, X-10005 is a propylene homopolymer, and S
D-632 and X11277-22-1 are propylene-ethylene block copolymers.

The base resin is mixed with an ethylene-butene random copolymer as a modifier in an amount of 2% by weight or more.
The ethylene-butene random copolymer usable in the present invention has a butene content of 5 to 30% by weight and a density of 0.8.
Those having 6 to 0.92 g / cm ² are preferred. In particular, the butene content is 10 to 25% by weight, and the density is 0.87 to 0.90.
g / cm ² is preferred.

The ethylene-butene random copolymer satisfying the above conditions is, for example, NO416 (22% by weight of butene) and NO372 (butene content of 1) manufactured by Sumitomo Chemical Co., Ltd.
3% by weight). The modified polypropylene resin foam of the present invention contains 98% by weight of a polypropylene resin.
Or less, preferably 98 to 60% by weight, 2% by weight or more, preferably 2 to 40% by weight of the ethylene-butene random copolymer.
% By weight. Here, when the content of the polypropylene-based resin is more than 98% by weight, the effect of improving the low-temperature impact resistance is small. On the other hand, if the amount of the ethylene-butene random copolymer is more than 40% by weight, the strength of the foam is reduced.

The modified polypropylene-based resin foam of the present invention includes polyethylene resins, α-olefin polymers, ionomers, ethylene-based resins and the like as long as physical properties such as foaming property, heat resistance and impact resistance are not impaired. Propylene rubber (E
A small amount of an elastomer such as P rubber) may be mixed. Further, an inorganic filler may be added to the base resin in an amount of 10 to 50% by weight based on the total resin amount in order to improve strength and durability and increase the amount. As inorganic fillers that can be used,
Although not particularly limited, silica, alumina, titanium oxide,
Examples include talc, clay, calcium carbonate and the like.

The modified polypropylene resin foam of the present invention preferably has a density of 0.6 to 0.02 g / cm ³ , more preferably 0.6 to 0.06 g / cm ³ . Here, if the density is larger than 0.6 g / cm ³ , the heat insulating property becomes poor, which is not preferable. The shape of the modified polypropylene resin foam is not particularly limited, and may have the shape of a sheet plate or a tube. When formed into a sheet plate, the thickness is usually 0.5 to 4.0 mm.

In the present invention, at least one surface of the above-mentioned modified polypropylene resin foam is provided with propylene homopolymer, ethylene-propylene copolymer, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, Also provided is a laminated foam formed by laminating sheets made of any one of chain ultra-low density polyethylene, ethylene-propylene rubber, and ethylene-butene random copolymer, or a mixture thereof. The sheets to be laminated include relatively thin sheets such as films. The thickness of the sheet is usually 0.02 to 1.0 mm, preferably 0.1 to 1.0 mm.

Further, the above-mentioned laminated foam may be coated with a nonwoven fabric, a metal foil, a decorative paper, a printed film or the like on the surface thereof in accordance with the use requiring a beautiful surface, as long as the object of the present invention is not hindered. They may be stacked. The present invention also includes a molded product obtained by molding the modified polypropylene resin foam and the laminated foam. The shape of the molded product is not particularly limited, but is preferably a food container shape such as a cup shape, a dish shape, and a lunch container shape.

Further, the modified polypropylene resin foam of the present invention can be produced by combining extrusion foaming, compression foaming, injection foaming and the like with methods such as block molding, plate molding and molding. . Hereinafter, a method for producing a foam using extrusion foam molding will be described. First, a modified polypropylene resin as a base resin is supplied to a foam extruder. As the foaming extruder, any device generally used in the art can be used.

A foaming agent is added to the base resin.
The foaming agent is not particularly limited, and any gas or volatile foaming agent can be used. In addition, if the above-mentioned camel-type polypropylene resin is used as the base resin, at the time of molding, since the melt viscosity is higher than the other base resins, sufficient properties can be obtained even when a gas or a volatile foaming agent is used. Can be produced.

[0023]

Examples of gaseous blowing agents include carbon dioxide, propane, neopentane, methyl ether, methane difluoride methane, and butane. In addition, the gas here means
It means that it is a gas at room temperature. On the other hand, examples of the volatile foaming agent include ether, petroleum ether, acetone, pentane, hexane, isohexane, heptane, isoheptane, benzene, and toluene. The volatile foaming agent was added in an amount of 0.5 to 100 parts by weight of the base resin.
It is preferable to set it to 20 parts by weight.

Of the above foaming agents, butane is particularly preferred. Further, a bubble regulator may be added. Examples of the foam control agent include inorganic powders such as talc and silica, acidic salts of polycarboxylic acids, and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate. The foam controlling agent is used in an amount of 0.01 to 1.0 with respect to 100 parts by weight of the base resin.
It is preferable to use parts by weight. Further, if necessary, an ultraviolet absorber, an antioxidant, a colorant, and the like can be added.

Here, the conditions for the extrusion foaming molding are such that the resin is melted by heating to 180 to 240 ° C. in an extruder, and then the temperature most suitable for foaming, ie, 145, is applied to a die.
It is preferred to inject while adjusting to １７175 ° C. and then extrude.

[0027]

Function: Production of the modified polypropylene resin foam of the present invention
The method is to etch the base resin polypropylene resin.
2% by weight or more of
Extruding foam by mixing gas or volatile blowing agent
It is characterized by excellent heat resistance, heat insulation and chemical resistance,
In particular, it does not crack during frozen storage at low temperatures and during transportation,
A modified polypropylene resin foam having excellent impact resistance is obtained.

It is not clear why the ethylene-butene random copolymer used in the present invention does not inhibit foaming properties of the polypropylene resin and improves impact resistance at low temperatures. Conceivable. In the case of a mixture of a polyethylene resin or an ethylene-propylene rubber and a polypropylene resin, since these are substantially incompatible resins, the polyethylene resin or the ethylene-propylene rubber may be present in the amorphous phase of the polypropylene resin. Conceivable. It is considered that the non-crystalline phase portion gives a non-uniform crystal structure during the progress of crystallization, that is, at the time of the growth of the foamed cells, and as a result, the expansion of the walls of the cell cells is reduced, thereby inhibiting the foaming property.

On the other hand, in the case of a mixture of the ethylene-butene random copolymer and the polypropylene resin, the ethylene-butene random copolymer has a low crystallization temperature. As a result, it is considered that the foamability is less reduced than the polyethylene resin or the ethylene-propylene rubber. On the other hand, since the amorphous phase of the polypropylene-based resin has an important influence on the impact resistance, the miscibility of the resin contained in the amorphous phase with the polypropylene-based resin is important. From this perspective,
This is probably because the ethylene-butene random copolymer and the amorphous phase of the polypropylene-based resin have better miscibility than other resins.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Examples 1 to 16 and Comparative Examples 1 to 15 First, the resins used in Examples and Comparative Examples are shown in Table 1 together with their properties.

[0031]

[Table 1]

As shown in Table 2, by combining the resins of Table 1, a foam was produced in the following steps. First, a base resin was mixed with a certain amount of a cell regulator, and this mixture was supplied to a foaming extruder comprising a first extruder and a second extruder having a diameter of 50 to 65 mm. In the supplied resin, the first
In the central zone of the extruder, butane is injected as blowing agent,
It was melt-kneaded. Thereafter, the resin was conveyed to the second extruder, poured into a mold having a diameter of φ80 mm maintained at a temperature most suitable for foaming, and further extruded from a slit having a die gap of 0.8 mm to obtain a tubular foam. . This tubular foam was taken out along a sizing drum having an outer shape of 205 mm and cut at one point on the circumference by a cutter to obtain a foam sheet having the density and thickness shown in Table 2.

Example 15 was repeated except that 15% by weight of talc was mixed with the base resin based on the total weight of the resin.
This is a foam sheet manufactured in the same manner as above. Further, in Example 16, 0.2 m was applied to one side of the foam sheet of Example 5.
m ethylene-propylene block copolymer (resin C)
Is a laminated foamed sheet having an overall density of 0.30 g / cm ³ obtained by laminating a resin consisting of Comparative Example 9 is a foam sheet manufactured based on the description in Examples of JP-A-6-212007.

The low-temperature impact height of the obtained foamed sheet was measured by the following method, and the evaluation results are shown in Table 2. Method for measuring impact height at low temperature A section (50 mm x 140 mm) of the foam sheet obtained in each of the examples and comparative examples is placed horizontally at the bottom of the constant temperature bath in a constant temperature bath at -30 ° C. Hold with clamps (distance between clamps 100 mm). Next, an iron ball (diameter: 41.3 mm, weight: 286 g) is dropped from the arbitrary height so as to drop vertically and almost to the center with respect to the held foam sheet.
Drop. The height at which cracks or cracks occurred in the foamed sheet was defined as the impact height. However, the values of the impact height shown in Table 2 are measured five times in each of the longitudinal direction and the lateral direction of the foam sheet, and the average value is shown. Further, in Table 2, ○ means the case where the value of the impact height is 100 mm or more, and × means the case where the value is less than 100 mm.

[0035]

[Table 2]

As shown in Table 2, the modified polypropylene resin foam of the present invention has better low-temperature impact resistance and a beautiful and smooth surface compared to the foam sheet of the comparative example. It is. Further, in Comparative Examples 11 to 13, phenomena such as poor dispersion of resin, breakage of air bubbles, and poor elongation occur.
It could not be made into a foam sheet. Further, Example 3
When the foamed sheets obtained in Comparative Examples 3 to 6 were molded into a shape shown in FIGS. 2 to 4 by a known method, the foamed sheet was produced in the same manner as when a foamed sheet of a polypropylene-based resin alone (Comparative Example 3) was molded. , And could be easily molded. In addition,
2 shows a top view (a) and a side view (b) of the cup container, FIG. 3 shows a top view (a) and a side view (b) of the dish-like container, and FIG. 4 shows a top view ( a) and side view (b)
Is shown.

[0037]

The method for producing the modified polypropylene resin foam of the present invention is based on the polypropylene resin as the base resin.
2% by weight or more of ethylene-butene random copolymer
Extrude and mix with a gas or volatile blowing agent.
It is characterized by that. Therefore, since the main component is a polypropylene-based resin having excellent heat resistance, it has excellent heat resistance, heat insulation, and chemical resistance, and does not cause cracking during frozen storage at low temperatures and during transportation, and has excellent impact resistance. A modified polypropylene resin foam having a wide operating temperature range can be obtained.

Further, an ethylene-butene random copolymer
Is mixed by 2 to 40% by weight,
To further improve the properties of porous polypropylene resin foam.
Can be. In addition, the polypropylene resin has a Z average
Particle size Mz is at least 2.0 × 10 ⁶With the above, Mz / Mw
(Weight average molecular weight) is 3.0 or more, and
The overhang of the curve indicating that the region contains a branched polymer
Camel type molecular weight distribution curve (gel permeation
(By chromatograph)
When melt viscosity increases, it is necessary to use a decomposable blowing agent
Use the same volatile foaming agent as styrene resin
A foam can be easily obtained by the foaming.

Further, a propylene homopolymer, ethylene-
Propylene copolymer, high density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-propylene rubber, ethylene-
The laminated foam formed by laminating sheets made of any one of butene random copolymers or a mixture thereof can also be used for applications requiring a beautiful surface.

The molded article formed from the above-mentioned foam can be suitably used particularly for containers used for cooking frozen foods in a microwave oven.

[Brief description of the drawings]

FIG. 1 is a graph showing molecular weight distribution curves of a camel-type polypropylene resin and other polypropylene resins.

FIG. 2 is a top view and a side view of a cup container according to an example of the present invention and a comparative example.

FIG. 3 is a top view and a side view of a dish-shaped container according to an example of the present invention and a comparative example.

FIG. 4 is a top view and a side view of a lunch container of an example and a comparative example of the present invention.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B29K 23:00 105: 04 (56) References JP-A-6-23895 (JP, A) JP-A-6-240065 (JP, A) JP-A-6-192500 (JP, A) JP-A-3-139535 (JP, A) JP-A-61-181841 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) ) C08J 9/00-9/42 B29C 44/00-44/60 B29C 67/20

Claims (6)

(57) [Claims] 1. A reforming method comprising mixing an ethylene-butene random copolymer in an amount of 2% by weight or more with a polypropylene resin as a base resin, further mixing a gas or a volatile foaming agent, and extruding and foaming. For producing high quality polypropylene resin foam. 2. An ethylene-butene random copolymer,
The method for producing a foam according to claim 1, wherein the foam is mixed at 2 to 40% by weight. 3. The polypropylene resin has a Z-average molecular weight Mz of at least 2.0 × 10 ⁶ or more, Mz / Mw (weight-average molecular weight) of 3.0 or more, and contains a branched polymer in a polymer region. The method for producing a foam according to claim 1, wherein the foam has a camel-type molecular weight distribution curve (based on gel permeation chromatography) having an overhang of the curve indicating: 4. The method according to claim 1, wherein
Molded article characterized by molding the obtained foam
Recipe. 5. The method according to claim 1, wherein
Foam obtained. 6. A molding obtained by the method according to claim 4.
Goods.