JPH08120106A - Polyolefin-based resin foam - Google Patents

Abstract

PURPOSE: To obtain a foam capable of keeping foaming properties of a polypropylene-based resin and having high heat resistance and high cushioning performance. CONSTITUTION: This polyolefin-based resin foam has at least >=2.0×10<6> of Z average molecular weight, Mz and >=3.0Mz/Mw (weight average molecular weight) and contains a mixed resin composed of 60-95wt.% of a polypropylene- based resin having a camel type molecular weight distribution curve (by gel permeation chromatograph) having projections of a curve which exhibits that it contains a branched polymer in a high polymer region and 40-5wt.% of one or more kinds of polyethylene-based resins having <=10Mz/Mw as a substrate resin.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyolefin resin foam. More specifically, the present invention relates to a thermoformable polyolefin resin foam useful for use as a cushioning packaging material for home appliances, precision instruments, food packaging, automobile interior materials, heat insulating materials, anti-condensation materials and the like.

[0002]

2. Description of the Related Art Generally, it is excellent as a material used for applications such as buffer packaging materials for home electric appliances, precision instruments, food packaging, automobile interior materials, heat insulating materials, anti-condensation materials, etc. Polyolefin resin foams are required because of their flexibility, mechanical strength and chemical resistance. The low-density polyethylene foam is excellent in physical properties such as flexibility and elongation because of its low melting point, and is used in many fields. However, due to its low heat resistance, it is not suitable for use in contact with high-temperature substances or for thermoforming.

A low-density polyethylene foam having improved thermoformability is a cross-linked polyethylene foam, which has a cross-linked structure and is therefore excellent in heat resistance. As the crosslinking method, a method using a chemical crosslinking agent, a method using ionizing radiation, etc., a silane-modified polyethylene-based resin is produced by graft-polymerizing a silane compound onto a polyethylene-based resin, and the resin is treated with a silanol catalyst and water. A so-called water-crosslinking method is known in which crosslinking is performed below. However, any crosslinking method requires extremely complicated steps, is expensive in equipment, and is industrially very disadvantageous.

Further, both low-density and cross-linked polyethylene foams are often unsuitable as cushioning materials and packing materials for heavy goods because of their strength. Even if it is cross-linked, the heat-resistant temperature is 120
It has been reported that a foam having a heat resistance and a buffering property higher than that of about 0 ° C has not been reported so far. On the other hand, polypropylene resin is superior to polyethylene resin in heat resistance and strength. However, the polypropylene-based resin has an extremely low melt viscosity above the crystal melting point and cannot hold foamed bubbles, so that it easily breaks. Therefore, the conventional polypropylene-based foam can only obtain a sheet having a high open cell rate, and it is difficult to obtain a foam having closed cells and excellent mechanical properties and heat resistance. That is, the conventional polypropylene resin foam has a density of 0.
Low-foamed product of 5g / cm ³ or more, or density of 0.03
Only highly foamed products with g / cm ³ or less were obtained.

A low foam having a density of 0.5 g / cm ³ or more is
It is manufactured by adding a decomposable or reactive foaming agent to a polypropylene resin and supplying it to a molding extruder. Further, a highly foamed material having a microcellular structure having a density of 0.03 g / cm ³ or less is disclosed, for example, in Japanese Patent Publication No. 46-41474. That is, the crystalline polypropylene resin is dissolved in an activating liquid such as methylene chloride, fluorotrichloromethane, perfluorocyclobutane. The activating liquid is evaporated to precipitate the solid polymer by extruding the resulting solution from a zone above the vapor pressure of the solution but no above 1000 PSi to a substantially low pressure zone. It is then produced by cooling the polymer orientation to a temperature at which it freezes and extruding.

[0006] As intermediate foams of the above two examples, those having a density of about 0.3 g / cm ³ are also found, but they are open cells, not closed cells, and have good mechanical properties. It was hard to say the body. Therefore, in order to perform extrusion foam molding of a polypropylene resin like a polystyrene resin, it is necessary to widen the temperature range in which extrusion foaming is possible and increase the melt viscoelasticity in the temperature range above the melting point. Therefore, attempts have been made to increase the molecular weight of the polypropylene resin and to make it a copolymer resin with other olefins. However, although the resin modification by these means gave good results for the extrusion processability of the non-foamed sheet, the thermoformability of the non-foamed sheet, and the physical properties of the molded product, the melt viscosity suitable for extrusion foaming was obtained. It did not give elasticity.

Further, one of the reasons why the polypropylene resin has a special melt viscoelasticity may be that the polypropylene resin is an extremely linear polymer. Therefore, attempts have been made to solve the problem by crosslinking the resin. According to this attempt, although a slight improvement in foamability was observed, the polypropylene resin has the property that crosslinking and decomposition proceed at the same time.
It was extremely difficult to obtain the expected effect.

However, in recent years, the Z-average molecular weight Mz is at least 2.0 × 10 ⁶ and Mz / Mw is at least 3.0, and the molecular weight distribution curve by gel permeation chromatography includes a branched polymer in the high molecular region. A density of 0.02 is obtained by using a camel-type polypropylene resin that has a shape with a curved overhang.
It has been reported that a foam of 5 to 0.5 g / cm ³ can be obtained by an inexpensive extrusion molding method using a polystyrene resin (JP-A-1-92460). The foam obtained by this method is a foam with a high closed cell ratio and excellent heat resistance, heat insulation, and mechanical properties, but lacks elasticity and is used in fields requiring high shock absorbing performance. could not.

As a method for imparting elasticity to a polypropylene resin, an ethylene-propylene copolymer having an ethylene content of 1 to 10 mol%, low / medium / high density polyethylene, polybutene, and an ethylene-vinyl acetate copolymer are used. , Ethylene-ethyl acrylate, ethylene-1-butene copolymer, propylene-1-butene copolymer, modified polyolefin having polar groups such as unsaturated carboxylic acid and its derivatives, 1: 2 type polybutadiene, linear low Method of mixing at least one elastically modified polymer selected from high-density polyethylene (Japanese Patent Publication No. 62-22787), 0.1-1
Propylene random copolymer containing 5% by weight of ethylene units 100 to 20 parts by weight, propylene block copolymer containing 0 to 15% by weight of ethylene units 0 to
Polypyrpyrene resin 90 to 40 containing 80 parts by weight
A method of mixing 10 to 60 parts by weight of an ultra-low density ethylene copolymer having a density of 0.910 g / cm ³ or less with respect to parts by weight (JP-A-3-109444), and a homopolypropylene having a melt flow rate adjusted to 10 to 90 parts by weight. % And linear low-density polyethylene 90 to 10% by weight (JP-A-4-59840) and the like have been reported.

Although it is known that polyethylene resin is mixed with polypropylene resin to give elasticity as described above, the mixture of polyethylene resin causes roughening of cells, increase of open cell ratio, and immediately after extrusion. There is a problem that the amount of shrinkage increases and the foamability is impaired. Therefore, the inventors of the present invention, as a result of earnest study, by an inexpensive method,
The present invention has been accomplished by finding a polyolefin resin foam that maintains the foamability of polypropylene resin, has high heat resistance, and has a high degree of cushioning performance.

[0011]

According to the present invention, the Z-average molecular weight Mz is at least 2.0 × 10 ⁶ or more and the Mz / Mw (weight average molecular weight) is at least 3.0, and the polymer is 60 to 95% by weight of a polypropylene resin having a camel-type molecular weight distribution curve (by gel permeation chromatograph) having a curve overhang indicating that a region contains a branched polymer, and Mz
Provided is a polyolefin-based resin foam characterized by using a mixture of 40 to 5% by weight of one or more polyethylene-based resins having a Mw of 10 or less as a base resin.

Further, according to the present invention, the Z-average molecular weight Mz
Is at least 2.0 × 10 ⁶ or more, Mz / Mw (weight average molecular weight) is 3.0 or more, and a camel-type molecular weight distribution curve ( Polypropylene resin 60 having gel permeation chromatograph)
~ 95% by weight, calorific value during crystallization is 110 mJ / mg
Provided is a polyolefin-based resin foam characterized by using, as a base resin, a mixture of 40 to 5% by weight of one or more of the following polyethylene-based resins.

In the present invention, the Z-average molecular weight Mz is the average molecular weight by which the distribution on the highest molecular weight side is emphasized as measured by gel permeation chromatography (hereinafter referred to as GPC), and is the average of the cube of the molecular weights. Means a value. The weight average molecular weight Mw is an average molecular weight obtained by GPC measurement when the measured physical property is directly related to the weight of the polymer, and means an average value of the square of the molecular weight.

The GPC measuring method used in the present invention is as follows. Measuring device: GPC 150-C type (manufactured by Water) Measuring condition: column KF-80M (manufactured by SHODEX)
Column temperature 145 ° C (polypropylene resin, P
P), 135 ° C (polyethylene resin, hereinafter PE) Injection temperature 145 ° C (PP), 135 ° C (PE) Pump temperature 60 ° C (PP), 55 ° C (PE) Sensitivity 32 (PP), 64 (PE) used Solvent o-dichlorobenzene (1.0 ml / min) Scanning time 50 minutes (PP), 42 minutes (PE) Injection volume 400 μl (PP), 200 μl (PE) The polypropylene-based resin usable in the present invention is defined by the above definition. A polypropylene having a camel-type molecular weight distribution curve having Mz of at least 2.0 × 10 ⁶ or more and Mz / Mw of 3.0 or more, and having a curve overhang indicating that the polymer contains a branched polymer. It is a resin. Mz less than 2.0 × 10 ⁶ or Mz / M
When w is less than 3.0, sufficient melt tension cannot be obtained at the time of foaming, and a foam having a desired density cannot be obtained.

Further, the polypropylene resin usable in the present invention has a camel-type molecular weight distribution curve. The camel-type molecular weight distribution curve means, for example, a camel spine in a high molecular weight region as shown in FIG. It means a molecular weight distribution curve having an overhanging shape. The molecular weight distribution curve shows that certain components in the high molecular weight region have many branches. In FIG. 1, a curve A shows a camel-type polypropylene resin that can be used in the present invention, and a curve B shows a polypropylene resin that cannot obtain a sufficient melt tension during foaming.

The camel-type polypropylene resin satisfying the above conditions is specifically X-1000 manufactured by Highmont Co.
5, PF-814, SD-632, X11277-22
-1 etc. are mentioned. The polyethylene resin effective for obtaining the foam of the present invention has an Mz / Mw ratio of 10 or less and /
Alternatively, it is a polyethylene resin whose calorific value during crystallization is 110 mJ / mg or less.

The method for measuring the amount of heat generated during crystallization performed in the present invention is as follows. Measuring device: DSC Model 200 (manufactured by Seiko Co., Ltd.) Measuring condition: Temperature rising / falling rate 10 ° C / min Measuring temperature range -40 ° C → 220 ° C → -40 ° C → 220
C was repeated.

When the Mz / Mw ratio is more than 10, when mixed with the polypropylene resin, phenomena such as a high open cell rate, coarse cells, and large shrinkage immediately after extrusion occur, which are excellent. No foam can be obtained.
The cause of this is not clear, but it is considered that the so-called sea-island structure becomes non-uniform as the molecular weight distribution becomes wider, resulting in the phenomenon as described above.

The amount of heat generated during crystallization is 110 mJ / m.
Even when it is larger than g, phenomena such as coarse cells and a high open cell rate occur, and similarly a good foam cannot be obtained. It is considered that this is because the heat generated during crystallization hinders the solidification of the bubble film during the growth of the foam cells, which causes the phenomenon as described above. Specific examples of the polyethylene resin satisfying the above conditions include HE-30 (manufactured by Mitsubishi Petrochemical Co., Ltd.) and VL-100 (manufactured by Sumitomo Chemical Co., Ltd.).

Furthermore, when a mixed resin of two or more polyethylene resins is used, even if the heat of crystallization of one of the polyethylene resins exceeds 110 mJ / mg, If the heat of crystallization of the mixed resin is adjusted to 110 mJ / mg or less as a whole by adjusting the mixing ratio, the foamability is not hindered. When two or more polyethylene resins are mixed, the functions (mechanical strength, elongation, elasticity, etc.) required for the intended use of the foam can be widely controlled by the polyethylene resin used.

Among the resins having an Mz / Mw ratio of 10 or less and a heat of crystallization of more than 110 mJ / mg as a whole, the polyethylene resin usable in the present invention is specifically NUCG-0851 (Nippon Unicar Co., Ltd.). Manufactured), UE-
320 (manufactured by Mitsubishi Petrochemical Co., Ltd.) and the like. The mixing ratio of each resin in the base resin of the present invention is 60 to 95% by weight of polypropylene resin and 40 to 5% by weight of polyethylene resin. When the polypropylene resin is less than 60% by weight and the polyethylene resin is more than 40% by weight, heat resistance is deteriorated, which is not preferable. On the other hand, polypropylene resin is more than 95% by weight and polyethylene resin is 5%.
If it is less than wt%, elasticity is not improved, which is not preferable.

Other resins may be added to the base resin of the present invention as long as the purpose thereof is not impaired. Examples of resins that can be added include ethylene / propylene random copolymer resins, ethylene / propylene block copolymer resins, ethylene / butene / propylene copolymer resins, ionomers, and ethylene / propylene rubbers. The polyolefin resin foam of the present invention has a density of 0.025.
It is possible to provide a foam having excellent mechanical properties and heat resistance, which has closed cells of 0.5 g / cm ³ or less, an open cell rate of 80% or less, and a tensile elastic modulus of 10 MPa or less.

Further, a method for producing the polyolefin resin foam of the present invention by using extrusion foam molding will be described. First, a base resin made of a polypropylene resin and a polyethylene resin in a predetermined mixing ratio is supplied to a foaming 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 of a decomposable foaming agent, a gaseous or volatile foaming agent can be used. In addition,
Since the base resin used in the present invention has a higher melt viscosity than the conventional base resin at the time of molding, it is necessary to produce a foam having sufficient properties even if a gas or volatile foaming agent is used. You can

Examples of the decomposable foaming agent include inorganic decomposable foaming agents such as ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium nitrite, calcium azide, sodium azide, sodium borohydride, azodicarbonamide and azobis. Azo compounds such as sulfolamide, azobisisobutyronitrile and diazoaminobenzene, nitroso compounds such as N, N'-dinitrosopentanemethylenetetramine and N, N'-dimethyl-N, N'-dinitrosoterephthalamide, Examples thereof include benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide and p, p'-oxybisbenzenesulfonyl semicarbazide, p-toluenesulfonyl semicarbazide, trihydrazinotriazine and barium azodicarboxylate. These foaming agents may be used alone or in combination. Further, the addition ratio of the decomposable foaming agent is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the base resin. Further, a known foaming auxiliary agent may be added in order to control the decomposition temperature, the amount of generated gas and the decomposition rate.

Examples of the gas foaming agent include carbon dioxide gas, propane, neopentane, methyl ether, dichlorodifluoromethane, butane and the like. 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 addition ratio of the volatile foaming agent is 0.5 with respect to 100 parts by weight of the base resin.
It is preferably about 20 parts by weight.

Of the above-mentioned foaming agents, butane is particularly preferable. 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 cell regulator is 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, an ultraviolet absorber, an antioxidant, a coloring agent, etc. can be added if necessary.

The polyolefin resin foam of the present invention can be used for applications such as home electric appliances, precision instruments, cushioning packaging materials for food packaging, automobile interior materials, heat insulating materials, anti-condensation materials and the like.

[0029]

The polyolefin resin foam of the present invention has an Mz of at least 2.0 × 10 ⁶ and an Mz / Mw of 3.0.
60 to 95% by weight of a polypropylene resin having a camel-type molecular weight distribution curve which is the above and has an overhang of a curve indicating that the polymer contains a branched polymer.
And a mixed resin of 40 to 5% by weight of one or more polyethylene-based resin having Mz / Mw of 10 or less as a base resin, so that the foamability of the polypropylene-based resin is maintained and heat resistance is improved. A foam having high properties and a high degree of cushioning performance is obtained.

Furthermore, since the polyethylene-based resin is composed of one or more kinds, and the resin as a whole has a calorific value during crystallization of 110 mJ / mg or less (according to differential scanning calorimetry), a foam having fine cells is formed. The properties (mechanical strength, elongation, elasticity, etc.) of the foam obtained are controlled according to the intended use of the foam. In addition, the polyolefin resin foam has a Mz of at least 2.0 × 10 ⁶ and a Mz / Mw of 3.0 or more, and a camel type with a curve overhang indicating that the polymer contains a branched polymer. Polypropylene resin having a molecular weight distribution curve of 60 to 95% by weight, and the calorific value during crystallization is 110 mJ
/ Mg or less of one or more polyethylene-based resin 40 ~
By using a mixed resin with 5% by weight as the base resin, the polypropylene resin maintains the foamability and has high heat resistance,
A foam having a high degree of cushioning performance is obtained.

[0031]

EXAMPLES The present invention will be described in more detail below with reference to examples. Examples 1 to 5 and Comparative Examples 1 to 4 Table 1 shows physical properties of the polypropylene resin (resin A) and the polyethylene resins (resins B to F) used in the examples and the comparative examples.

[0032]

[Table 1]

Foams were produced by combining the resins as shown in Table 2 in the following steps. First, a base resin is mixed with a certain amount of a bubble control agent, and the mixture is calibrated with a diameter of 90
It was supplied to a foam extruder having a diameter of -115 mm. Butane was injected as the blowing agent in the central zone of the first extruder. After being melt-kneaded by the first extruder, the resin was conveyed to the second extruder and poured into a die having a diameter of 90 mm and kept at a temperature most suitable for foaming. Then, it was extruded from a slit having a die gap of 0.5 mm to obtain a tubular foam. Furthermore, outer diameter 380
The sheet was taken along with a sizing drum of mm and cut with a cutter at one point on the circumference to obtain a sheet-shaped foam. The properties of the obtained foam are shown in Table 2 together with the foaming conditions (the amount of the foaming agent, the amount of the cell regulator and the foaming temperature).

The foamed sheet was evaluated by the following method.・ Evaluation of surface condition: When the surface of the foamed body does not have wrinkles, roughness, bubble bleeding and the like immediately after extrusion, the result is indicated by ○, and when the phenomenon occurs, it is indicated by ×. Cell diameter: The cell diameters in three directions were averaged, and when the cell diameter was less than or equal to the cell diameter of the foamed sheet obtained in Comparative Example 1 with 100% polypropylene-based resin, it was marked with ◯, and when it was larger, it was marked with x.

Open cell ratio (%): The open cell ratio equal to or lower than the open cell ratio of the foamed sheet obtained in Comparative Example 1 with 100% polypropylene resin was rated as ◯, and the higher value was rated as x. The open cell rate is a value measured by the following method. Measuring device: Air Pycnometer (Toshiba Beckman, model -930) Calculation method: Open cell ratio (%) = (apparent volume-measured value)
× 100 / apparent volume-For imparting elasticity, each of the obtained foams was subjected to a tensile test at room temperature, and the elastic modulus obtained was
A case of 10 MPa or less, which shows a significant difference from the elastic modulus of the foamed sheet obtained in Comparative Example 1 with 100% polypropylene resin, was marked with ◯, and a case of more than 10 MPa was marked with x. The tensile test was performed according to JIS K-6301 using Tensilon UCT-10T (manufactured by Orientec).

[0036]

[Table 2]

As is clear from Tables 1 and 2, when a polyethylene resin having a heat of crystallization of more than 110 mJ / mg was mixed, only a foam having coarse cells was obtained, resulting in poor elasticity ( Comparative Examples 3 and 4). However, when two polyethylene resins are mixed, the heat of crystallization of the polyethylene resin mixture is 110 mJ / mg.
If the amount is below, the heat of crystallization of one of them is 110 mJ.
It can be seen that a good foam is obtained even when the amount exceeds / mg (Examples 4 and 5).

Further, Mz / Mw in the GPC curve is 1
When it is greater than 0, it can be seen that a beautiful foam cannot be obtained due to surface roughness such as poor mixing (Comparative Example 2).

[0039]

The polyolefin resin foam of the present invention has Mz of at least 2.0 × 10 ⁶ and Mz / Mw.
Is 3.0 or more, and a polypropylene resin 60 to 9 having a camel-type molecular weight distribution curve having a curve overhang indicating that the polymer contains a branched polymer.
Since the base resin is a mixed resin of 5 wt% and 40 to 5 wt% of one or more polyethylene resins having Mz / Mw of 10 or less, the foamability of the polypropylene resin is maintained. However, it is possible to obtain a foam having high heat resistance and a high degree of cushioning performance.

That is, in the foam of the present invention, by selecting a polyethylene-based resin which does not impair the foamability of the polypropylene-based resin, the polypropylene-based resin is provided with a lack of elasticity, and the foamability and appearance of the polypropylene-based resin are reduced. It has no synergistic effect and has a synergistic effect that it can be manufactured at low cost with general manufacturing equipment, and is very useful.

Further, the polyethylene resin is made of one or more kinds, and the resin as a whole has a calorific value at the time of crystallization of 110 mJ / mg or less (according to the differential scanning calorimetry). Can be obtained, and
The properties (mechanical strength, elongation, elasticity, etc.) of the foam can be controlled according to the use of the foam. The polyolefin resin foam has an Mz of at least 2.0 × 10.
^{60 to} 95% by weight of a polypropylene resin having a camel-type molecular weight distribution curve having a Mz / Mw of 3.0 or more and 3.0 or more, and a curve showing that a branched polymer is contained in a high molecular region, and a crystal. The heat generation amount at the time of conversion is 1
By using as a base resin a mixed resin of 40 to 5% by weight of one or more polyethylene resins of 10 mJ / mg or less, the foamability of the polypropylene resin is maintained, the heat resistance is high, and the high buffer performance is obtained. It is possible to obtain a foam having

[Brief description of drawings]

FIG. 1 is a graph showing a molecular weight distribution curve of a camel-type polypropylene resin and a conventional polypropylene resin.

Claims (3)

[Claims] 1. A Z-average molecular weight Mz of at least 2.0 ×
A camel-type molecular weight distribution curve (gel permeation chromatograph) having an Mz / Mw (weight average molecular weight) of 3.0 or more at 10 ⁶ or more and a curve that indicates that a branched polymer is contained in the high molecular region. 60 to 95% by weight of a polypropylene-based resin having Mz
A polyolefin resin foam characterized by using a mixture of 40 to 5% by weight of one or more polyethylene resins having an Mw of 10 or less as a base resin. 2. The foam according to claim 1, which comprises at least one polyethylene resin, and the resin as a whole has a calorific value during crystallization of 110 mJ / mg or less (by differential scanning calorimetry). 3. A Z-average molecular weight Mz of at least 2.0 ×
A camel-type molecular weight distribution curve (gel permeation chromatograph) having an Mz / Mw (weight average molecular weight) of 3.0 or more at 10 ⁶ or more and a curve that indicates that a branched polymer is contained in the high molecular region. According to the present invention, a mixture of 60 to 95% by weight of a polypropylene resin and 40 to 5% by weight of one or more polyethylene resins having a calorific value of 110 mJ / mg or less during crystallization is used as a base resin. A polyolefin resin foam characterized by the following.