JP2001226510A - Polypropylene resin foam, its molded article and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low cost polypropylene resin foam excellent in heat resistance, heat insulating properties and oil resistance. SOLUTION: The polypropylene resin foam is produced by blending a polypropylene resin having a melt tension in a specific range and a free-terminal long chain branch with a polypropylene resin having a melt tension in a specific range and a ratio of weight average molecular weight to number average molecular weight in a specific range to obtain a polypropylene resin blend and extruding and foaming the resin blend as a substrate resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin foam, and is mainly used as a food container such as a tray, a bowl or a cup.

[0002]

2. Description of the Related Art In recent years,
With the spread of microwave ovens and the increase of convenience stores, consumers can cook food for heating at home,
Cooking at stores is increasing. Therefore, heat resistance is important as a container for cooking in a microwave oven, and oil resistance is also important in the case of foods containing a large amount of oil. Further, such a container is required to have a heat insulating property as a handling property after cooking.

[0003] As a material satisfying heat resistance, oil resistance and heat insulation, polypropylene resin is one of the preferable materials because of its resin properties. However, since the polypropylene-based resin is a crystalline resin, the melt viscosity becomes extremely low above the melting point of the crystalline melting point, and there is a problem that the foamed bubbles cannot be retained and are easily broken. For this reason, it has been difficult to obtain a resin foam having closed cells having high open cell ratio, good mechanical properties, and excellent heat resistance in the conventional polypropylene resin foam.

To solve such a problem, Japanese Patent Application Laid-Open No.
By using polypropylene having a free-end long-chain branch, which is considered to be produced by a method disclosed in Japanese Patent Application Laid-Open No. 21704 or JP-A-2-69533, it is possible to obtain a low closed cell rate and an excellent external appearance. It is known that foams of high density can be obtained. As such a resin, for example, a product sold as a foaming grade by Montel S.D.
fax PF-814, Pro-fax SD-632
and so on. However, by using these resins, a foamed resin material having heat resistance, oil resistance, and heat insulating properties can be obtained, but a polypropylene resin having a free long chain branch is expensive, which results in an increase in product cost. ing.

[0005] In addition, since the polypropylene resin is very susceptible to the influence of air oxidation, there is a problem that the physical properties of the obtained product decrease with time. In the case of a polypropylene resin having a free-end long-chain branch, the tendency appears more strongly. It is known to add a stabilizer to reduce the effects of air oxidation,
In a polypropylene resin having a free terminal long chain branch,
The effect of the addition of the stabilizer was low, and it was necessary to increase the addition amount. As the amount of stabilizer added increases, the cost of the product rises accordingly, and further a new problem arises in that the added stabilizer coarsens the cell diameter, resulting in an increase in the open cell ratio and a decrease in surface smoothness. There was a problem that the quality was adversely affected. On the other hand, although the purpose is different, as a result of realizing a low cost and preventing a decrease in physical properties of the product, an expensive polypropylene resin having a long chain branch at a free end and a lower cost general PP resin are used. A foam made of a resin mixture of the following has been proposed.

For example, in Japanese Patent Application Laid-Open No. 6-192460, in order to improve the impact resistance of the obtained foamed sheet,
A foamed sheet comprising a mixed resin of a PP resin having a specific molecular weight distribution (having a branched polymer in a polymer region) and a propylene-based copolymer and having a density of 0.5 to 0.025 g / cm ³ has been proposed. ing. Also, Japanese Patent Laid-Open No. 7-2
No. 68121, in order to improve the appearance quality of the obtained foamed sheet, the melt tension is 6 g or more, 20
g and the ratio of the weight average molecular weight to the number average molecular weight is 7 or more and less than 20.
0 parts by weight, the melt tension is 1 g or more, less than 6 g, and the value of the ratio of the weight average molecular weight to the number average molecular weight is 4 or more,
A foamed sheet comprising a polypropylene-based resin mixture comprising 10 to 90 parts by weight of a polypropylene-based resin of less than 7, an inorganic filler and a foaming agent and having a foaming ratio of 1.4 to 5.0 times has been proposed. However, the above melt tension is 6 g or more and less than 20 g and the weight average

When the ratio of the molecular weight to the number average molecular weight is 7 or more,
Since the expansion ratio of a foam obtained using a polypropylene resin having a molecular weight of less than 20 is as low as 1.5 to 1.6 times, the heat insulating property is inferior. In order to improve the heat insulating properties of such a foam sheet, it is necessary to increase the thickness of the foam sheet. To do so, it is necessary to increase the amount of polypropylene resin used,
The problem that the cost rises arises. Therefore, the above-mentioned polypropylene resin is not sufficient in that it simultaneously satisfies both heat insulation and cost reduction.

The present invention has been made in order to solve such problems, and provides a foam which is inexpensive and has excellent heat insulating properties, heat resistance and oil resistance, a molded article thereof, and a method for producing the same. Is what you do.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies and have found that by mixing two or more types of polypropylene resins having a specific range of melt tension and a ratio of weight average molecular weight to number average molecular weight. , Density 0.5g / c
The present inventors have found that a foam having a cell density lower than m ^{3 and} a low open cell ratio can be obtained at low cost, and have completed the present invention. That is, according to the present invention, the melt tension is 6 to 40.
g and a polypropylene-based resin (a) having a free-end long-chain branching in an amount of 10 to 50% by weight, a melt tension of 0.01 g to less than 1 g, and a ratio of a weight average molecular weight to a number average molecular weight of 3 to A polypropylene-based resin foam is provided which is extruded and foamed using a polypropylene-based resin mixture consisting of 90 to 50% by weight of the polypropylene-based resin (b) of No. 8 as a base resin.

Further, according to the present invention, the melt tension is 20 to 40 g and the polypropylene resin (a) having a free terminal long-chain branching is 10 to 50% by weight, and the melt tension is 0.01 to 6 g. And extrusion-foaming using a polypropylene-based resin mixture consisting of 90 to 50% by weight of a polypropylene-based resin (b) having a ratio of a weight average molecular weight to a number average molecular weight of 3 to 8 as a base resin. Is provided.

According to the present invention, the melt tension is 20 to 40 g, the polypropylene resin (a) having a long chain branch at a free end is 10 to 50% by weight, and the melt tension is 0.01 to less than 1 g. It is characterized by being extruded and foamed using, as a base resin, a polypropylene-based resin mixture consisting of 90 to 50% by weight of a polypropylene-based resin (b) having a ratio of a weight average molecular weight to a number average molecular weight of 3 to 8. Is provided.

Further, according to the present invention, there is provided a molded article obtained by heat-molding the above-mentioned polypropylene resin foam. Further, according to the present invention, the base resin and the foaming agent constituting the above-mentioned polypropylene-based resin foam are melt-kneaded with an extruder, and then extruded and foamed through a mold attached to the extruder tip. A method for producing a polypropylene resin foam is provided.

[0013]

Embodiments of the present invention will be described below. In the present invention, two types of polypropylene resins having a predetermined melt tension and a ratio of a weight average molecular weight to a number average molecular weight as shown below are used in combination.

The melt tension of the polypropylene resin (a) used in the present invention is 6 to 40 g, preferably 20 to 40 g, particularly preferably 20 to 30 g. If the melt tension is lower than 6 g, good foaming properties cannot be obtained. If the melt tension is higher than 40 g, the flowability becomes extremely poor and a gel is easily formed, and the extrusion processability is lowered. The value of the ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight of the polypropylene resin (a) is 7
To 20 are preferable, and 7 to 15 are more preferable. When this value is lower than 7, good foaming properties are hardly obtained, and when it exceeds 20, a gel is easily generated, and the appearance tends to be deteriorated. Such a polypropylene-based resin (a) has free terminal long-chain branching in the molecular structure due to electron beam crosslinking and the like, and has a higher melt tension than ordinary polypropylene.

The polypropylene resin (a) includes, for example, homopolypropylene and ethylene-propylene copolymer satisfying the above conditions.
For example, Pro-fax, a product sold as high melt tension polypropylene manufactured by Montel SDK Sunrise
PF-814 (homopolypropylene), Pro-fa
x SD-632 (ethylene-propylene block copolymer) and the like. By using a polypropylene resin (a) having a free terminal long chain branch having a melt tension of 20 g or more, a resin having a wider range of melt tension is selected as the polypropylene resin (b) having no free terminal long chain branch. it can. This is because the higher the melt tension of the polypropylene resin (b), the higher the melt viscosity and the lower the resin temperature to near the melting point, but the higher the melt tension of the polypropylene resin (a). This is considered to increase the overall tension.

The melt tension of the polypropylene resin (b) used in the present invention is from 0.01 to 6 g, preferably from 0.01 to less than 1 g. If the melt tension is lower than 0.01 g, the tension is too low, so that when the secondary molding is performed on a container or the like, a sagging phenomenon occurs during heating, and a good molded product cannot be obtained. On the other hand, when the melt tension exceeds 6 g, the melt viscosity becomes high, so that it becomes difficult to lower the resin temperature to near the melting point. As a result, the obtained foam is likely to be an open cell, and the quality is reduced.

The value of the ratio between the weight average molecular weight and the number average molecular weight of the polypropylene resin (b) is from 3 to 8, preferably from 4 to 6. If this value is less than 3, the elasticity is low and the secondary moldability deteriorates, and if it exceeds 8, it becomes difficult to lower the resin temperature uniformly, and a foam having a low open cell ratio, that is, a foam having a high heat insulating property is obtained. It is difficult to obtain. Examples of such a polypropylene resin (b) include homopolypropylene and ethylene-propylene copolymer satisfying the above conditions. The mixing ratio of the former in the base resin composed of the polypropylene resin (a) and the polypropylene resin (b) is 10 to 50% by weight,
Preferably it is 15 to 40% by weight. When the mixing ratio of the polypropylene-based resin (a) is less than 10% by weight, it is difficult to improve the foaming property of the polypropylene-based resin (b), and when it exceeds 50% by weight, an inexpensive product is provided. One of the challenges of

The foaming agent used in the present invention includes various volatile foaming agents and decomposition type foaming agents. Examples of the volatile foaming agent include hydrocarbons such as propane, butane and pentane, and halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane and difluoroethane. Examples of the decomposable foaming agent include an organic foaming agent such as azodicarbonamide and dinitrosopentamethylenetetramine, and a combination of an organic acid such as sodium bicarbonate or citric acid or a salt thereof with a bicarbonate.

In some cases, carbon dioxide, nitrogen gas, water and the like can be used as appropriate. These foaming agents may be used alone or in combination of two or more. To the base resin of the polypropylene-based resin foam of the present invention, in addition to the above-described foaming agent, for example, talc, sodium bicarbonate-citric acid, etc., adjust the size of bubbles during foaming. Bubble regulators, pigments, stabilizers,
Various additives such as a filler and an antistatic agent may be added as long as the effects of the present invention are not impaired. As the filler, for example, talc, clay, calcium carbonate, silica,
An inorganic filler such as magnesium hydroxide is preferable, and it is preferable to add 5 to 50 parts by weight based on 100 parts by weight of the base resin. Further, the polypropylene-based resin foam of the present invention, in order to improve the appearance and strength of food containers and the like, a film made of non-foamable resin on one or both sides of a sheet-like resin foam as its raw material They may be stacked.

The resin constituting the film is not particularly limited, but is preferably a resin mainly composed of the same type of propylene resin as the resin foam. In addition, you may laminate | stack a gas barrier film depending on a use. Examples of the gas barrier film include ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyvinylidene chloride, polyamide, polyester, polyacrylonitrile, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-based methyl methacrylate-butadiene copolymer,
Nylon 6, biaxially stretched nylon, biaxially stretched polyethylene terephthalate, biaxially stretched polypropylene, high-density polyethylene, ionomer resin (for example, Surlyn®), or a metal-deposited film alone or a combination of these polymers is used. Can be

The thickness of the gas barrier film is as follows:
It is 5 to 300 μm, preferably 25 to 200 μm.
The film may be a stretched film or a non-stretched film,
The thickness of the film layer is usually 0.02 to 1.0 mm, preferably 0.1 to 1.0 mm. In this film layer, for example, talc, clay, calcium carbonate, silica,
An inorganic filler such as magnesium hydroxide may be included. Lamination of the film is performed by a conventional method such as a heat lamination method or a co-extrusion method. Further, the polypropylene-based resin foam of the present invention may have a nonwoven fabric, a metal foil, a decorative paper, a printing film, etc. on the surface thereof in accordance with the use in which the beautifulness of the surface is required, as long as the object of the present invention is not hindered. May be laminated.

The polypropylene resin foam of the present invention comprises:
It is manufactured by a method in which a base resin composed of a polypropylene-based resin (a) and a polypropylene-based resin (b) and a foaming agent are melt-kneaded with an extruder, and then extruded and foamed through a mold attached to the extruder tip. The polypropylene-based resin foam produced in this manner is formed into, for example, a sheet-like foam having a thickness of 0.5 to 10.0 mm, preferably 0.5 to 3 mm. If the thickness is less than 0.5 mm, the strength is low, and the heat insulating property decreases, which is not preferable. On the other hand, if the thickness exceeds 10.0 mm, the secondary formability deteriorates, which is not preferable.

The obtained polypropylene resin foam is 0.1 to 0.45 g / cm ³ , preferably 0.18 to 0.4 g / cm ³ .
It has a density of about 0.45 g / cm ³ . If the density is lower than 0.1 g / cm ³ , the strength becomes weak, which is not preferable. On the other hand, if it is higher than 0.45 g / cm ³ , the heat insulating property is undesirably reduced. The polypropylene-based resin foam as described above is heat-molded by a conventional method, and is processed into a molded article having a form suitable for various purposes and uses.

In the present invention, the melt tension of the polypropylene resin is determined by the following method.
Using a Capillograph PMD-C manufactured by Toyo Seiki Seisaku-Sho, Ltd., heat the polypropylene resin to 230 ° C.
The molten polypropylene resin is nozzleed with a piston extrusion type plastometer (2.095 mm in diameter, 8 m in length)
m), the piston is extruded in a string while maintaining the lowering speed of the piston at a constant speed of 10 mm / min. Then, the string is passed through a tension detecting pulley located 35 cm below the nozzle, and then wound up by a winding roll. 66m / min ² ratio of about, gradually by gradually increasing the take-up speed until the string-like material is cut, and the tension (g) at the time that the burnt-out and the melt tension of the resin. However, the winding speed is 60
In the case where the string-like material was not cut even at a speed exceeding m / min, the tension (g) at a winding speed of 60 m / min was defined as the melt tension of the resin.

In the present invention, the value of the ratio of the weight average molecular weight to the number average molecular weight of the polypropylene resin can be determined by gel permeation chromatography under the following conditions. Measuring device: GPC 150-C manufactured by Waters Column: UT-806M 3 pieces (SHOdex) Column temperature: 145 ° C Injection temperature: 145 ° C Pump temperature: 55 ° C Solvent used: o-dichlorobenzene Flow rate: 1.0 ml / min

In the polypropylene resins (a) and (b) used in the present invention, the presence or absence of long chain branch at the free end can be determined by observing the elongation characteristics of the resin according to the method described in JP-A-62-121704. Confirmed by Specifically, it is measured using a Toyo Seiki Seisakusho Melten Rheometer. A measurement sample of a polypropylene-based resin is prepared, and the relationship between elongational viscosity (μ) and time (t) measured under the conditions of a measurement temperature of 180 ° C. and a strain rate of 0.5 second ⁻¹ is plotted (see FIG. 1). In the obtained curve, the one having a tendency that the elongational viscosity rises with time and becomes sharper as the breakage point is approached is a polypropylene resin having a free-end long-chain branch. On the other hand, although the elongational viscosity increases to some extent with time, it does not show a sharp increase as it approaches the breaking point, but on the other hand, decreases to the breaking point, but the polypropylene type which does not have free-end long-chain branching Resin.

[0027]

The present invention will be described below based on examples and comparative examples. Examples 1 to 8 and Comparative Examples 1 to 9: In these Examples and Comparative Examples, polypropylene resins (a) -1 to 3 having the properties shown in Table 1 and polypropylenes having the properties shown in Table 2 System resins (b) -1 to 6 were used, respectively. Resins (a) -1 to 3 showed a tendency for the elongational viscosity to rise sharply, indicating that they had free-end long-chain branches. On the other hand, (b) -1 to 6 did not show a sharp increase in the elongational viscosity and showed that they did not have free-terminal long-chain branches.

The resins and additives were dry-blended at the composition ratios shown in Tables 3 and 4, and this mixture was mixed with a tandem extruder comprising a first extruder and a second extruder having a diameter of 50 to 65 mm. It is supplied through a hopper of an extruder having a diameter of 50 mm and melted by heating. Then, butane (isobutane / normal butane = 35/65) is used as a foaming agent.
Was press-fitted and melt-mixed. In Examples 5 and 6, butane (isobutane / normal butane = 70/30) was used as a blowing agent. Next, after being transferred to a 65 mm diameter extruder and uniformly cooled, it is extruded and foamed at a discharge rate of 20 kg / hour from a cylindrical die having a diameter of 60 mm, and the inside of the obtained cylindrical foam is cooled with water at about 20 ° C. The outer surface is cooled and formed by blowing air with an air ring larger than the diameter of the mandrel, and the outer surface is cut with a cutter at one point on the circumference. A resin foam having a thickness and a density shown in Table 1 was obtained.

Example 9: An unstretched polypropylene resin film having a thickness of 50 μm was laminated on one surface of the foamed sheet obtained in Example 1 by a heat lamination method. As described above, the properties and evaluation of the obtained foamed sheet were respectively performed by the following methods. -Average bubble diameter: Measured according to ASTM D-2842-69. -Open cell ratio: Measured by an air pycnometer (air comparison specific gravity meter) method. -Secondary formability: The obtained foamed sheet was L156 mm, W126 mm, H30 mm using a foamed styrene sheet molding machine.
After being molded into a gratin container, the state of the molded product was observed, and the following evaluation was performed. …: Good molded product that does not correspond to the following △ and × △: Poor elongation at the time of molding, resulting in a locally thin portion ×: Breakage, etc., making it difficult to mold into a predetermined shape Property: 150 cc of water was placed in the container obtained above, heated in a microwave oven of 1500 w for 50 seconds, and evaluated when taken out with bare hands. ○: Can be taken out without any problem △: Feel hot and difficult to hold for a long time ×: Hot and difficult to take out

[0030]

[Table 1]

PF814: Homopolymer manufactured by Montell SDK Sunrise SD632: Propylene-ethylene block copolymer manufactured by Montell SDK Sunrise PF716: Homopolymer manufactured by Montell SDK Sunrise

[0032]

[Table 2]

PM600A: Homopolymer manufactured by Montell SDK Sunrise, Inc. PM801Z: Homopolymer manufactured by Montell SDK Sunrise, Inc. J704WA: Propylene-ethylene block copolymer manufactured by Grand Polymer F-104: Homopolymer manufactured by Grand Polymer EA-7: manufactured by Nippon Polychem Homopolymer PS201A: Homopolymer manufactured by Montell SDK Sunrise

[0034]

[Table 3]

[0035]

[Table 4]

As apparent from Tables 3 and 4, the polypropylene resin foam of the present invention has a small open cell ratio and is excellent in secondary moldability and heat insulation. Further, the foamed sheet obtained by laminating the polypropylene resin unstretched film obtained in Example 9 was excellent in the secondary moldability and the heat insulating property, and was more excellent in the strength and the appearance.

[0037]

According to the present invention, it is possible to reduce the use ratio of an expensive polypropylene resin having a long chain branch at a free end, to obtain a low-density polypropylene resin foam having few open cells. it can. As a result, a polypropylene-based resin foam excellent in heat resistance, heat insulation, and oil resistance can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between elongational viscosity (μ) and time (t) of a polypropylene-based resin measured by a Toyo Seiki Seisakusho Melten Rheometer.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08L 23/10 C08L 23/10 // B29K 23:00 B29K 23:00 105: 04 105: 04 105: 16 105: 16 B29L 9:00 B29L 9:00 (72) Inventor Saburo Fujii 2615 Sampuri All II 205 F Term (Reference) 4F074 AA24 AA98 AC00 AG01 BA37 BA38 CA22 CE02 CE46 CE98 DA34 4F100 AA00A AA00B AA00C AA01AH AK01B AK01C AK07A AK07B AK07C AL05A AT00B AT00C BA01 BA02 BA03 BA04 BA05 BA06 BA07 BA10B BA10C BA15 CA01 CA23A CA23B CA23C DJ01 DJ01A EH17A EJ02A GB23 JA13A JA15 JA20A JB01 J02A01 J03A02A03 J02A01 J03A02A03 BB151 BP021 DE077 DE206 DE237 DJ017 DJ037 DJ047 EA016 EB066 EF076 EQ016 ES006 FD017 FD326 GG01

Claims (9)

[Claims] 1. A polypropylene resin (a) having a melt tension of 6 to 40 g and a long chain branch at a free end.
10 to 50% by weight and the melt tension is 0.01 to 1
g and a ratio of the weight average molecular weight to the number average molecular weight of 3 to 8 is a polypropylene resin (b) 90 to 50.
A polypropylene-based resin foam, which is extruded and foamed using a polypropylene-based resin mixture consisting of 1% by weight as a base resin. 2. A polypropylene resin (a) having a melt tension of 20 to 40 g and a long chain branch at a free end, 10 to 50% by weight, and a melt tension of 0.0
1 to 6 g, and a polypropylene resin (b) 90 to 5 having a ratio of the weight average molecular weight to the number average molecular weight of 3 to 8
A polypropylene-based resin foam obtained by extrusion foaming using a polypropylene-based resin mixture containing 0% by weight as a base resin. 3. A polypropylene resin (a) having a melt tension of 20 to 40 g and a long chain branch at a free end, 10 to 50% by weight, and a melt tension of 0.0
A polypropylene resin (b) 90 having a weight average molecular weight to a number average molecular weight of 3 to 8 which is less than 1 g and 1 to 8 g;
A polypropylene-based resin foam obtained by extrusion-foaming using a polypropylene-based resin mixture of about 50% by weight as a base resin. 4. The polypropylene resin foam according to claim 1, wherein the inorganic filler is contained in an amount of 5 to 50 parts by weight based on 100 parts by weight of the base resin. 5. A sheet-like foam having a density of 0.18 to 0.45 g / cm ³ and a thickness of 0.5 to ³ mm, according to any one of claims 1 to 4, The polypropylene resin foam according to the above. 6. The polypropylene resin foam according to claim 1, wherein one or more films are laminated on at least one surface of the polypropylene resin foam. . 7. The polypropylene resin foam according to claim 6, wherein at least one layer of the film is a polyolefin resin containing an inorganic filler. 8. A molded product obtained by heating and molding the polypropylene resin foam according to claim 1. 9. A method of melting and kneading the base resin and the foaming agent according to any one of claims 1 to 3 with an extruder, and then extruding and foaming through a mold attached to a tip of the extruder. A method for producing a polypropylene resin foam.