JP2003327732A - Polypropylene resin foamed sheet, and molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene resin foamed sheet which is lightweight, has post-formability, heat-resistant rigidity, and heat insulating properties by using a polypropylene resin having a specified strain hardening rate at a specified strain rate, and a molded product having a variety of shapes obtained from the sheet. <P>SOLUTION: The polypropylene resin foamed sheet has a strain hardening rate η<SB>e</SB>/(3η) (wherein η<SB>e</SB>is elongational viscosity; and η is shear viscosity) at a strain rate of 100 sec<SP>-1</SP>of a polypropylene resin of ≥1.5. The sheet has a density of 0.091-0.45 g/cm<SP>3</SP>and a thickness of 0.5-10 mm. The sheet has a closed- cell ratio of ≥60%. The sheet uses a modified polypropylene resin modified by the reaction of a polypropylene resin with an isoprene monomer and a radical polymerization initiator, and the molded product is obtained by thermoforming the above sheet. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene resin foam sheet and a molded article thereof.

[0002]

2. Description of the Related Art Generally, a foamed sheet made of a thermoplastic resin is light in weight and has good heat insulating properties and buffering properties against external stress.
Since a molded product can be easily obtained by heating secondary molding such as vacuum molding, it is widely used mainly for polystyrene resins and polyethylene resins as cushioning materials, food containers, heat insulating materials, automotive parts, etc. ing.

However, the polystyrene-based resin foamed sheet, which is widely used for food containers and the like, has the drawback of poor heat resistance and oil resistance due to the properties of the polystyrene-based resin as a base material.

On the other hand, polypropylene resins are expected to be the next generation of foaming resins because they are excellent in heat resistance and oil resistance. Since it is extremely difficult to obtain a foam by extruding and foaming a linear polypropylene resin itself, in recent years, a branched structure has been introduced into the polypropylene resin (for example, Japanese Patent No. 2521388) to extrude and foam. Have been developed to obtain foams. It is said that such a resin has a large melt tension (size of strain hardening during extensional deformation), so that the bubble film is not easily broken when the bubble grows and the bubble shape can be maintained.

A conventional method for producing an extruded foamed sheet made of a thermoplastic resin is to melt a resin in an extruder, knead the obtained melt and a foaming agent under high temperature and high pressure, and then lower the mixture through a circular die. A foamed sheet is manufactured by extruding mandrel into the area. It is generally said that a polypropylene resin capable of forming a foamed sheet by such a method has a high melt tension.
A polypropylene-based resin in which the polypropylene-based resin is melted in a melt indexer, and the melted polypropylene-based resin is extruded into a strand shape and taken out, and the take-up speed (drawdown property) when the strand breaks is 60 m / min or less. (Patent No. 2898469) has been proposed, but the strain rate at the time of drawdown measurement is extremely small, and it greatly deviates from the strain rate at the time of foam molding. It is hard to say that it is a measurement method. It is difficult to properly express the extrusion foaming suitability of the resin by the index of drawdown property.

When manufacturing an extruded foam sheet, a circular die is often used because it has an advantage of eliminating and reducing pressure unevenness during foaming and easily obtaining a wide foam sheet.

The strain rate when the mixture of the polypropylene resin and the foaming agent is extruded from the circular die is about 50 to 1000 sec ^-1 . No study has been made on the magnitude of strain hardening in a high strain rate region where actual extrusion foam molding is performed.

The present invention uses a polypropylene-based resin having a specific strain hardening rate at a specific strain rate, so that the polypropylene-based resin foam sheet which is lightweight and is excellent in secondary moldability, heat resistance and heat insulation, and The purpose of the present invention is to provide molded articles of various shapes with the sheet.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, changed the type of polypropylene resin used for extrusion foaming and the magnitude of strain hardening at each strain rate. As a result of studying the above, the present invention has been achieved. That is, in the present invention, the strain hardening rate η _e / (3η) of the polypropylene resin at a strain rate of 100 sec ⁻¹ (where η _e represents extensional viscosity and η represents shear viscosity).
Of 1.5 or more, the polypropylene resin foam sheet (claim 1), and the strain hardening rate η _e / (3η) of polypropylene resin at a strain rate of 100 sec ⁻¹ is 3.0 or more. The polypropylene-based resin foam sheet according to claim 1 (claim 2), the density is 0.091 to 0.45 g / cm ³ , and the thickness is 0.5 to 10.
The polypropylene-based resin foam sheet according to claims 1 and 2 (claim 3), wherein the closed cell ratio is 60% or more. The foamed sheet (claim 4), wherein the polypropylene resin is a modified polypropylene resin obtained by modifying the polypropylene resin by reacting with an isoprene monomer and a radical polymerization initiator. 4 to the polypropylene-based resin foamed sheet (claim 5), and the polypropylene-based resin foamed sheet according to claims 1 to 5 formed by thermoforming (claim 6).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene-based resin foam sheet of the present invention has a strain hardening rate of 100 sec ^-1 of 1.
It is obtained by extruding and foaming 5 or more polypropylene resins. Examples of the polypropylene resin used in the present invention include propylene homopolymers, block copolymers and random copolymers, and crystalline polymers. As the propylene copolymer, those containing 75 parts by weight or more of propylene, particularly 90 parts by weight or more, are the crystallinity which is a characteristic of polypropylene resin,
It is preferable in that rigidity, chemical resistance and the like are maintained. Examples of the copolymerizable α-olefin include ethylene, butene-1, isobutene, pentene-1,3-methyl-butene-1, hexene-1,4-methyl-pentene-1,3.
4-Dimethyl-butene-1, heptene-1, 3-methyl-hexene-1, octene-1, decene-1 and other α-olefins having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, 1,4,5 , 8-dimethano-1,
Cyclic olefins such as 2,3,4,4a, 8,8a-6-octahydronaphthalene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-
Diene such as hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate,
One or more of acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, vinyl monomers such as styrene, methylstyrene, vinyltoluene, divinylbenzene, etc. Is mentioned. Of these, ethylene and butene-1 are preferable because they are inexpensive.

Examples of such a polypropylene resin include, for example, a method of irradiating a linear polypropylene resin with radiation, or a method of melting and mixing a linear polypropylene resin, a radical polymerization initiator, and a monomer. Produced using polypropylene resin containing branched structure or high molecular weight component, polypropylene resin with higher rigidity and heat resistance by adding molecular structure and solid structure control technology, and metallocene catalyst system Propylene containing a specific amount of α, ω-dienes
Examples include α, ω-diene-based copolymers. Among these, a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator and a monomer is preferable because it can be produced at a low cost. Examples of the polypropylene resin used for the modified polypropylene resin include the above polypropylene resins.

As the above-mentioned monomer, for example, styrene monomer, isoprene monomer and 1,3-butadiene monomer are preferable, and these may be used alone or in combination. Among these, the isoprene monomer is particularly preferable because it is inexpensive, easy to handle, and the reaction is likely to proceed uniformly.

The amount of the monomer added is preferably 0.05 to 20 parts by weight, and 0.1 to 10 parts by weight, based on 100 parts by weight of the polypropylene resin, from the viewpoint of reaction efficiency in melt kneading. preferable.

Monomers copolymerizable with the above monomers, such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, Acrylic acid metal salts, methacrylic acid metal salts, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylic acid esters such as stearyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid 2-ethylhexyl acid, methacrylic acid esters such as stearyl methacrylate, and the like may be used in combination.

The radical polymerization initiator generally includes peroxides and azo compounds. In order for the graft reaction to occur between the polypropylene resin and the monomer (polymer consisting of) or the polypropylene resin,
What has a so-called hydrogen abstraction capability is required, and generally, organic peroxides such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydicarbonate, and peroxyester can be mentioned. . Of these, those having a particularly high hydrogen abstraction ability are preferable, and for example, 1,1-bis (t-butylperoxy)
3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl 4,4-bis (t-butylperoxy) valerate,
Peroxyketals such as 2,2-bis (t-butylperoxy) butane, dicumyl peroxide, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, diacyl peroxides such as benzoyl peroxide, t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy 3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5di (benzoylperoxy) Hexane,
One or more of peroxyesters such as t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate may be used.

The amount of the radical polymerization initiator added is 0.05 to 100 parts by weight of the polypropylene resin.
10 parts by weight, particularly 0.1 to 2 parts by weight is preferable from the viewpoint of preventing the melt viscosity of the modified polypropylene resin from excessively decreasing and being economical.

As a device for reacting the polypropylene resin, the isoprene monomer and the radical polymerization initiator, a kneader such as a roll, a co-kneader, a Banbury mixer, a Brabender, a single screw extruder or a twin screw extruder, A biaxial surface renewing machine, a biaxial multi-disc device or other horizontal type agitator, a double helical ribbon agitator or other vertical type agitator, etc. may be mentioned. Of these, an extruder is particularly preferable in terms of productivity.

The order and method of mixing and kneading (stirring) the polypropylene resin, the isoprene monomer and the radical polymerization initiator are not particularly limited. The polypropylene resin, the isoprene monomer and the radical polymerization initiator may be mixed and then melt-kneaded (stirred), or the polypropylene resin may be melt-kneaded (stirred) and then the isoprene monomer or the radical initiator may be added. You may mix simultaneously or separately. When they are mixed simultaneously or separately, they may be mixed all at once or may be mixed separately. The temperature of the kneading (stirring) machine is preferably 130 to 400 ° C. because the polypropylene resin melts and is not thermally decomposed. The time is generally 1 to 60 minutes. It is preferable to produce the modified polypropylene resin in this way. If necessary, the polypropylene-based resin may be an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an optical brightener, a metallic soap, as long as the effects of the present invention are not impaired. , Additives such as stabilizers such as antacid adsorbents, crosslinking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents, etc. Good.

In the present invention, the strain hardening rate is a value measured by the following method.

The strain hardening rate is an index of the strain hardening property of a resin and is defined by η _e / (3η) (where η _e is a steady value of elongational viscosity and η is a steady value of shear viscosity). It Strain hardening refers to the property that the elongational viscosity increases as the strain increases. For the strain rate, see The Journal of Rheological Society of Japan, vol. 11, p. 13-23.

In the method of measuring elongational viscosity by pulling a resin sample molded in a rod shape or a strip shape in a molten state, when a resin having no strain hardening property is measured, as the sample is stretched (the strain is increased. As the value of extensional viscosity increases, it approaches 3η and reaches a steady value. On the other hand, in the case of a resin having a strain hardening property, the value of extensional viscosity rises greatly from 3η as the strain increases, and then reaches a steady value. It is for these reasons that η _e / (3η) is an index of strain hardening.

That is, η _e / of a resin having no strain hardening property
(3 η) is 1 or less, and η _{e of the} strain-hardening resin is
/ (3η) is larger than 1, and the higher the strain hardenability, the larger the value.

In the conventional measurement of elongational viscosity of polypropylene resin, the strain rate is measured only in the strain rate range of less than 5 sec ^{-1, which} is largely deviated from the strain rate range of the actual extrusion foaming. However, the present inventors have found that the extensional viscosity of the polypropylene-based resin in the strain rate range during actual extrusion foaming can be measured by the following method.

The pressure loss of the molten resin is measured with a capillary rheometer equipped with a short die and a long die having the same diameter. According to the following equation (1), the pressure loss p ₀ of the die having a virtual length of ₀ is calculated.

[0024]

[Equation 1] Where p ₁ is the pressure loss measured with the long die, p ₂ is the pressure loss measured with the short die, L ₁ is the length of the long die, L ₂
Is the short die length. Shear viscosity and shear rate can be determined using a capillary rheometer.

The extensional viscosity η _e and the strain rate ε'are calculated by the following equations (2) and (3).

[0026]

[Equation 2]

[0027]

[Equation 3] n is a power low index and is defined by the following equation (4).

[0028]

[Equation 4] γ'is the shear rate, η is the shear viscosity, and c is a constant.

Measured by such a method is a steady value of extensional viscosity. Therefore, the strain hardening rate can be calculated from η _e and η obtained by this method.

In the present specification, the strain hardening rate is a value measured by the following method.

After measuring the extensional viscosity and the shear viscosity of the resin at 230 ° C. by the above-mentioned method, the relation between the shear rate and the shear viscosity is approximated by the least square method by the equation (5) to obtain a and p, and the strain rate and The relationship between extensional viscosities is approximated by Eq.

[0032]

[Equation 5]

[0033]

[Equation 6] Of ε '= 100 sec ^-1 , γ' = 100 sec
^The ratio η _e / (3η) to 3η in ⁻¹ is defined as the strain hardening rate in the present invention. That is, the strain hardening rate can be calculated by the equation (7).

[0034]

[Equation 7] When a foamed sheet is made of a resin having strain hardening property,
It is considered that a uniform bubble structure can be obtained because the thinned portion of the bubble film has larger resistance during bubble growth and suppresses explosive bubble growth.

The strain rate of the resin used in the present invention is 100.
The strain hardening rate at sec ⁻¹ is 1.5 or more, and the strain hardening rate is preferably 3.0 or more in order to obtain a foamed sheet having a more uniform and fine cell structure. The strain hardening rate can be adjusted by the molecular weight distribution of the resin and the degree of long-chain branching, and in the case of a modified polypropylene resin, the amount of radical initiator or monomer added during modification.

If the strain hardening rate is less than 1.5, the closed cell rate of the foamed sheet will decrease to 50% or less.

For the foamed sheet made of polypropylene resin in the present invention, for example, after the foaming agent is pressed into the molten polypropylene resin, the foaming sheet is adjusted to the optimum foaming temperature in the extruder and extruded from the die to the low pressure region. Can be manufactured by. As the extruder, a tandem type extruder in which two single-screw extruders are vertically connected, a twin-screw extruder in which a gear pump is attached to the tip, and the like can be used.

In the case of a tandem type extruder, the resin is melted and the molten resin and the foaming agent are kneaded in the first extruder, and in the subsequent extruder, the mixture of the molten resin and the foaming agent is heated to a temperature range suitable for extrusion foaming. The purpose is to cool.

In the case of a twin-screw extruder having a gear pump at the tip, the resin and the foaming agent are mixed more uniformly. Further, when the gear pump is attached, the extrusion pressure and the discharge amount are stable, so that stable extrusion can be realized.
Since the melt-kneading and the cooling can be performed at the same time, the space can be saved as compared with the tandem type extruder.

As the cell regulator (foam nucleating agent), an inorganic substance such as a thermal decomposition type chemical foaming agent or talc can be used as the cell regulator.

The thermal decomposition type chemical foaming agent is classified into an endothermic type chemical foaming agent and an exothermic type chemical foaming agent. There is an endothermic chemical foaming agent alone or in combination with a weak acid. Examples of the inorganic carbon dioxide generator include carbonates or bicarbonates of alkali metals or alkaline earth metals, as well as ammonium carbonate and ammonium bicarbonate. Further, these may be a mixture of two or more kinds.

As weak acids, oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, itaconic acid, citraconic acid, adipic acid, formic acid, acetic acid, propionic acid, butyric acid,
Stearic acid, oleic acid, caprylic acid, enanthic acid,
Organic acids such as caproic acid, valeric acid, lactic acid, tartaric acid, citric acid, phthalic acid, benzoic acid, benzenesulfonic acid, toluenesulfonic acid, chloroacetic acid, diglycolic acid, inorganic acids such as boric acid and acidic acids such as potassium potassium tartrate Examples thereof include salts, and citric acid is preferably used from the viewpoint of improving the performance of the chemical foaming agent. The weak acid may be a mixture of two or more kinds. Examples of the exothermic chemical foaming agent include azodicarbonamide, azobisformamide, azobisisobutyronitrile, N, N'-dinitropentatetramine and the like, and azodicarbonamide is preferable from the viewpoint of controlling the decomposition temperature. In addition, when a nitrogen atom-containing bubble control agent is used, there is a coloring problem such that the foamed sheet becomes yellowish.

Among the above-mentioned foam control agents, a combination of sodium bicarbonate and citric acid is preferable.

Although a powdery or masterbatch type air-conditioning agent is available, a masterbatch is preferred from the viewpoint of easy handling.

In the present invention, preferred volatile type blowing agents include, for example, inorganic gases such as water, carbon dioxide and nitrogen. Two or more of these inorganic gases may be used in combination. In addition, aliphatic hydrocarbons such as propane, butane, isobutane, pentane, hexane, heptane, alicyclic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane, chlorodifluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane Halogenated hydrocarbons such as trichlorofluoromethane, chloroethane, dichlorotrifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane and perfluorocyclobutane can also be used. Inorganic gas and these aliphatic hydrocarbons, alicyclic hydrocarbons, and halogen-based hydrocarbons may be used in combination. Aliphatic hydrocarbons,
Compared with alicyclic hydrocarbons and halogen-based hydrocarbons, inorganic gas has a lower solubility in polypropylene-based resin, so the number of nucleation during foaming tends to increase, so inorganic gas is used. It is preferable.

The amount of the foaming agent added is selected depending on the type of the foaming agent and the target expansion ratio, but generally 0.1 to 20 parts by weight is preferable with respect to 100 parts by weight of the resin.

In order to obtain a desired cell structure, the foamed sheet of the present invention may be subjected to, for example, extrusion foaming to promote surface cooling of the foamed sheet by blowing air, or at the time of mandrel molding. Alternatively, stretching may be performed by changing the take-up speed or the mandrel diameter.

The density of the foamed sheet in the present invention is preferably 0.091 to 0.45 g / cm ³ , and more preferably 0.120 to 0.320 g / cm ³ . If it is less than 0.091 g / cm ^3, the rigidity of the foamed sheet will be low, and the rigidity of the molded product of the foamed sheet will also be low. When the density of the foamed sheet is more than 0.45 g / cm ³ , the heat insulation of the molded product is low and the cost is high, which is not preferable.

The number of cells in the thickness direction of the foamed sheet in the present invention is preferably 5 to 100. More preferably, it is 10 to 60. If the number of cells in the thickness direction of the foamed sheet is less than 5, it is possible to mold a shallow container such as a tray, but mold a container or bowl container with a complicated shape having a partition inside the container. You cannot do it. When the number of cells in the thickness direction of the foamed sheet is more than 100, the time required for the secondary molding becomes long, the molding cycle becomes worse, and the economy is deteriorated, which is not preferable.

The closed cell rate of the foamed sheet in the present invention is preferably 60% or more. More preferably 70
% Or more, particularly preferably 80% or more. If the closed cell content of the foamed sheet is less than 60%, the rigidity of the molded article will be reduced, and the mold determination during secondary molding will be unfavorable.

Further, since the foamed sheet of the present invention is excellent in hot moldability such as plug molding, vacuum molding and pressure molding, it is possible to obtain a molded article having a small thickness unevenness and a beautiful appearance.

Examples of heat molding include plug molding, matched mold molding, straight molding, drape molding,
Methods include plug assist molding, plug assist reverse draw molding, air slip molding, snap back molding, reverse draw molding, free drawing molding, plug and ridge molding, and ridge molding.

In the heat molding, the foamed sheet is preheated and then molded. However, the density, thickness, and closed cell ratio may change due to secondary foaming of the foamed sheet during preheating. is there.

In the foamed sheet of the present invention, a non-foamed layer made of a thermoplastic resin is formed on one surface or both surfaces of the foamed sheet for the purpose of improving surface properties, rigidity and heat moldability. Good.

As the thermoplastic resin, polystyrene resin, modified polyphenylene ether resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin, polybutylene terephthalate, polyamide resin, polyarylate resin, polyimide resin, Polyether sulfone resin, polysulfone resin, polyester resin, acrylic resin, polyvinyl chloride resin, polycarbonate resin, etc. can be used. These may be used alone or in combination of two or more, and polypropylene resin is preferable from the viewpoint of adhesiveness to the foamed sheet.

The method for forming the non-foamed layer is not particularly limited, and it may be formed by preparing a foamed sheet and then laminating a non-foamed film prepared separately by heating or using an adhesive. Directly on the foam sheet
It may be formed by extruding a non-foamed film from a die and laminating it. As the non-foamed film, a biaxially oriented polypropylene resin film is particularly preferable from the viewpoint of rigidity and gloss.

The foamed sheet or molded product of the present invention can be used as a cushioning material for fruit packaging trays of apples, pears and the like, food containers, heat insulating materials, automobile members such as automobile ceiling materials and the like. In particular, it can be suitably used as a food container such as curry, omelet rice, pasta, and dashimaki, a lunch box container having a partition portion, and a deep cup container.
These foods can be heat-treated as they are in a microwave oven or the like.

[0058]

EXAMPLES Next, the present invention will be explained based on Examples and Comparative Examples, but the present invention is not limited to such Examples.

The following polypropylene resins were used in the examples and comparative examples.

PP-1: propylene homopolymer (linear homopolypropylene, melt index 4 g / 10 minutes)
As a radical generator, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane was added in an amount of 0.5 part by weight, and a ribbon blender was used to prepare
The mixture was stirred for one minute. This mixture was manufactured by Nippon Steel Works, Ltd., twin-screw extruder (TEX44) (the twin-screw extruder is a twin-screw type in the same direction, and the hole diameter of the cylinder is 44 mmφ).
And the maximum screw effective length (L / D) was 38) was supplied at a supply rate of 50 kg / hr from the hopper, and 0.25 kg of isoprene monomer was introduced from the introduction part provided on the way using a metering pump. / Hr at a rate (a ratio of 0.5 parts by weight to 100 parts by weight of propylene homopolymer), extruded into a strand, and the strand is water-cooled and then shredded to obtain a modified polypropylene resin. Obtained.

PP-2: Commercially available high melt tension polypropylene (Profax PF-814, manufactured by Sun Allomer Co., Ltd.) The density, the closed cell rate and the number of cells in the thickness direction of the obtained foamed sheet were measured by the following methods. 1) Measurement of strain hardening rate A capillograph manufactured by Toyo Seiki Co., L = 20 mm, D =
The barrel and die were set to 230 ° C when a 1 mm die (this is called a long die) was attached, and when a die with L = 1 mm and D = 1 mm (this was called a short die) was attached. Then, the pellets were fed and melted, and simultaneously extruded to measure the pressure loss in the shear rate range of 20 to 2000 sec ⁻¹ . From the pressure loss, the pressure loss p ₀ of the die having a virtual length of 0 was calculated by the following formula (8).

[0062]

[Equation 8] Here the pressure drop measured with the long die, is the pressure drop measured with the short die, is the long die length, and is the short die length. The extensional viscosity and strain rate were calculated by the following equations (9) and (10).

[0063]

[Equation 9]

[0064]

[Equation 10] n is the power law index and is defined by the following equation (11).

[0065]

[Equation 11] γ'is the shear rate, η is the shear viscosity, and c is a constant.

The relationship between the shear rate and the shear viscosity is approximated by the equation (12) by the method of least squares to obtain a and p, and the relationship between the strain rate and the extension viscosity is approximated by the equation (13) by the method of least squares and b. And q. Η _{e when the} strain hardening rate is ε ′ = 100 sec ⁻¹
Of η _{e with} respect to 3 η at γ ′ = 100 sec ⁻¹
/ (3η), that is, calculated by the equation (14).

[0067]

[Equation 12]

[0068]

[Equation 13]

[0069]

[Numerical equation 14] The characteristics of the obtained resin are shown in Table 1. 2) Measurement of density of foamed sheet Measurement was performed according to JIS-K6767. 3) Measurement of closed cell rate of foamed sheet Measurement was performed by an air pycnometer according to the method described in ASTM D-2856. 4) Molding method and mold A bowl-shaped (FIG. 1) molded product is obtained by plug-assisted vacuum molding for a continuous molding test using a continuous molding machine so that at least the foamed sheet surface becomes the inner surface. Get
The touch was evaluated according to the following criteria. Figure 1 shows the bowl-shaped body
In (A) and (B), each dimension of a to c is a: 16.
It is 0 mm, b: 80 mm, and c: 80 mm.

FIG. 1 (A) is a plan view of the molded body, and FIG. 1 (B) is a side view of the molded body.

The practical rigidity of the obtained molded product was evaluated according to the following criteria by the following method. Pour hot water of about 90 ° C. into the molded body, and after 30 seconds, lift the mouth of the bowl container with both hands. ⊚: The mouth of the molded body is rigid and firm without bending. ◯: The mouth of the molded body is slightly bent, but has rigidity, and there is no problem in practical use. X: The mouth of the molded body was largely bent and lacked in rigidity, so that the hot water of the content was likely to spill. (Examples 1 and 2) A linear homopolypropylene having PP-1, 2 and MI = 5 was used, and a resin composition having a composition ratio shown in Table 1 and a chemical foaming agent as a foam control agent (Hydrocease manufactured by Boehringer). Roll HK-70, 0.3 part) was mixed with stirring with a ribbon blender to prepare a mixture of 65 mm uniaxial-
It is charged into a 90 mm single-screw tandem type extruder, the 65 mm single-screw extruder is set to 210 ° C., the resin composition is melted in the 65 mm single-screw extruder, and then isorich butane (Mitsui Chemicals Co., Ltd.) is used as a foaming agent. 80 wt% isobutane,
90 parts by press-fitting 2 parts of normal butane (20 wt% ratio)
m The single-screw extruder is set to 163 ° C., the resin composition and the isorich butane mixture are cooled, and then the mixture is extruded into a cylindrical shape from a 75 mmφ circular die under atmospheric pressure to foam and cut through a 200 mmφ cooling cylinder. , Width 6
A 40 mm foam sheet was obtained. A bowl-shaped molded body was obtained from the obtained foamed sheet by the above-described molding method. The results are shown in Table 2. (Examples 3 and 4) Resin compositions having the composition ratios shown in Table 1 were prepared. Twin screw extruder with gear pump attached at the tip (57mmφ, L / D = 40, 190-200 ° C setting)
Is used to inject 0.5 part by weight of carbon dioxide into the extruder with respect to 100 parts by weight of the polypropylene resin composition,
Extruding at a rate of 100 kg / hr from a 170 ° C circular die (150 mmφ, gap 0.9 mm), stretching a tubular foam and cutting it open to a thickness of 2 m.
A foamed sheet having a width of m and a width of 640 mm was obtained. A bowl-shaped molded body was obtained from the obtained foamed sheet by the above-described molding method. The results are shown in Table 2. (Comparative Example 1) A resin composition having a composition ratio shown in Table 1 was prepared. A foamed sheet was obtained by the same method as in Example 1. A bowl-shaped molded body was obtained by the method described above. However, with respect to the cup mold, the side portion of the molded body was avoided by stretching during molding, and a proper molded body could not be obtained. The results are shown in Table 2.

[0072]

[Table 1]

[0073]

[Table 2]

[Brief description of drawings]

FIG. 1 shows a bowl-shaped molded body molded from the polypropylene resin foam sheet of the present invention. (A) is a plane explanatory view of the bowl-shaped molded body. (B) is a side view of the bowl-shaped molded body.

According to the present invention, it is possible to obtain a lightweight foamed sheet excellent in heat resistance and heat insulation and molded articles having various shapes.

Claims (6)

[Claims] 1. A strain rate of polypropylene resin is 100.
Strain hardening rate at sec ^-1 η _e / (3η) (where η _e represents extensional viscosity and η represents shear viscosity)
Is 1.5 or more, a polypropylene-based resin foam sheet. 2. The strain rate of polypropylene resin is 100.
The polypropylene-based resin foam sheet according to claim ^1, wherein the strain hardening rate η _e / (3η) at sec ⁻¹ is 3.0 or more. 3. A density of 0.091 to 0.45 g / c
The polypropylene-based resin foam sheet according to claim 1 or 2, wherein m ³ and thickness are 0.5 to 10 mm. 4. The polypropylene-based resin foam sheet according to claim 1, wherein the closed cell ratio is 60% or more. 5. The modified polypropylene-based resin, wherein the polypropylene-based resin is a modified polypropylene-based resin modified by a reaction of the polypropylene-based resin with an isoprene monomer and a radical polymerization initiator. Polypropylene resin foam sheet. 6. A molded product obtained by thermoforming the polypropylene-based resin foam sheet according to claim 1.