JP5638928B2 - Polypropylene resin for injection foam molding and injection foam molded body thereof - Google Patents

Description

  The present invention relates to a polypropylene resin for injection foam molding and an injection foam molded body using the same.

  Polypropylene resin has good physical properties and moldability, and its use range is rapidly expanding as an environmentally friendly material. In particular, for automotive parts and the like, lightweight and excellent polypropylene-based resin products are provided, and one such product is an injection-foamed molded body of polypropylene-based resin.

  In a polypropylene resin injection-foamed molded article, as a technique for increasing the foam of a polypropylene resin, a resin containing a foaming agent is injection-molded in a mold space that is held so that the mold can be opened, and then the mold is opened. Thus, there is a so-called core back method (moving cavity method) in which the space is expanded to foam the resin (for example, Patent Document 1).

  In general, as a characteristic of a polypropylene resin used for injection foam molding, fluidity for filling a resin in every corner of a mold and foamability for foaming thereafter are required.

  However, since the linear polypropylene resin usually used is crystalline and has low melt tension, the bubble wall is easily broken during bubble growth, and it is difficult to achieve high foaming. Thus, a polypropylene resin having a high melt tension for enabling high foaming has been developed.

  Examples of methods for increasing the melt tension of a polypropylene resin include a method of introducing long chain branching by irradiating a non-crosslinked polypropylene resin with radiation (Patent Document 2), a polypropylene resin, an isoprene monomer, and initiation of radical polymerization. A method for producing a modified polypropylene resin by melt-kneading an agent (Patent Document 3) has been proposed. Certainly, by using these modified polypropylene-based resins, an injection-foamed molded product with a high expansion ratio can be obtained. However, in order to obtain uniform fine bubbles, a certain amount of addition is required. Therefore, the viscosity at the time of melting the resin is excessively increased, the fluidity is deteriorated, and injection foam molding may be difficult.

  In addition, a method of using a polypropylene-based resin that defines a loss tangent together with melt tension for extrusion foaming (Patent Document 4), a method that defines an elongation viscosity characteristic of an insoluble component (Patent Document 5), and the like have been proposed. It is a low melt flow rate resin suitable for extrusion foaming and unsuitable for injection foam molding.

  The present invention has been made in view of the above-described circumstances, and provides a technology that makes it possible to produce a polypropylene-based resin capable of imparting good injection-foaming moldability by addition of a small amount, and an injection-foaming molded body comprising the same. For the purpose.

WO2005 / 026255 JP 2001-226510 A JP-A-9-188774 JP 2009-29900 A JP-A-11-140332

An object of the present invention is to provide a polypropylene-based resin for injection foam molding capable of imparting injection foam moldability with a small amount of addition, and an injection foam molded body using the same.

As a result of intensive studies, the present inventors have found that the above problems can be solved by using a polypropylene resin for injection foam molding characterized by satisfying the following characteristics (a) to (c). The invention has been completed.
(A) The melt flow rate at 230 ° C. is 100 g / 10 min or more.
(B) The loss tangent tan δ, which is the ratio of the storage elastic modulus and loss elastic modulus at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C., is 0.6 or more and 1.8 or less. .
(C) The storage elastic modulus at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C. is 1 × 10 ³ Pa or less.

  That is, this invention consists of the following structures.

1). A polypropylene resin for injection foam molding characterized by satisfying the following characteristics (a) to (c).
(A) The melt flow rate at 230 ° C. is 100 g / 10 min or more.
(B) The loss tangent tan δ, which is the ratio of the storage elastic modulus and loss elastic modulus at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C., is 0.6 or more and 1.8 or less. .
(C) The storage elastic modulus at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C. is 1 × 10 ³ Pa or less.

  2). The polypropylene resin for injection foam molding according to 1), wherein the polypropylene resin for injection foam molding is obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator and a conjugated diene compound.

  3). 1) An injection foam molded article obtained by injection foam molding of a resin composition comprising the polypropylene resin for injection foam molding described in 1) and 2), a linear polypropylene resin, and a foaming agent.

  The polypropylene resin for injection foam molding of the present invention can be imparted with injection foam moldability by adding a small amount.

6 is a graph showing the relationship between the loss tangent (tan δ) of resin used in Example 1 and Comparative Example 1 and angular frequency.

  Embodiments of the present invention will be described below.

  The melt flow rate of the polypropylene resin for injection foam molding used in the present invention has a lower limit exceeding 100 g / 10 minutes, preferably exceeding 150 g / 10 minutes, and more preferably exceeding 200 g / 10 minutes. Yes, the upper limit is 250 g / 10 min or less, preferably 230 g / 10 min or less. When the melt flow rate of the polypropylene resin for injection foam molding is 100 g / 10 min or less, the compatibility with the linear polypropylene resin is insufficient, many voids are generated inside, and the injection foam molding has uniform cells. A body may not be obtained, and when the melt flow rate exceeds 250 g / 10 min, the metering process in injection foam molding may become unstable.

  Here, the melt flow rate (hereinafter sometimes abbreviated as “MFR”) is based on ASTM D-1238, using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho), 230 ° C., 2.16 kg. It refers to a value converted from the amount of resin extruded from a die in a certain time under the load condition into the amount extruded in 10 minutes. The predetermined time is 60 seconds when the melt flow rate is 3.5 g / 10 minutes or more and less than 10 g / 10 minutes, 30 seconds when the melt flow rate is 10 g / 10 minutes or more and less than 25 g / 10 minutes, and 25 g / 10 minutes. When it is 50 g / 10 minutes or less, it is 15 seconds, when it is 50 g / 10 minutes or more and less than 100 g / 10 minutes, it is 5 seconds, and when it is 100 g / 10 minutes or more, it is 3 seconds. If the melt flow rate measured in a certain number of seconds is not in the corresponding range, the measurement is performed again in the number of seconds corresponding to the melt flow rate.

The polypropylene resin for injection foam molding of the present invention has a storage elastic modulus (G ′) and a loss elastic modulus (G ″) at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C. The loss tangent tan δ (G ″ / G ′) as a ratio is 0.6 or more and 1.8 or less, preferably 1.2 or less. The polypropylene resin for injection foam molding of the present invention has a storage elastic modulus of 1 × 10 ³ Pa or less at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C.

  In particular, the melt flow rate of the polypropylene resin for injection foam molding of the present invention exceeds 200 g / min, and 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C. is 0.6 or more and 1.8. A favorable injection-foamed molded product is obtained when it is below.

Here, the angular frequency of 0.1 to 1 rad / s is a so-called low shear region, and the loss tangent tan δ is small in the region, that is, the relatively high storage elastic modulus is advantageous for holding bubbles during foaming. It is thought that. However, a relatively high molecular weight polypropylene resin having a melt flow rate of 30 g / 10 min or less has a high ratio of molecular chains entangled with each other, and the loss tangent tan δ tends to be measured as the melt flow rate decreases. .
However, when the loss tangent tan δ is low because the melt flow rate is low, it cannot be said that the loss tangent tan δ properly represents the melting characteristics suitable for foaming, and is not necessarily sufficient for retaining bubbles in the actual injection foam molding. . That is, in the present invention, a low loss tangent tan δ in a high-flowing polypropylene resin having a melt flow rate exceeding 100 g / 10 min is an index of bubble retention in injection foam molding, and the loss tangent tan δ is 1.8. When the storage elastic modulus exceeds 1 × 10 ³ Pa, bubbles are easily broken and internal voids are generated in the injection foamed molded article.

On the other hand, the lower limit of the loss tangent tan δ is not particularly limited, but when it is less than 0.6, the appearance of the surface of the injection-foamed molded article may be deteriorated. Moreover, when the storage elastic modulus exceeds 1 × 10 ³ Pa, the foam moldability of the resin composition may be impaired.

  Here, the loss tangent tan δ is in a range from a measurement temperature of 200 ° C., a parallel plate interval of 1 mm, an angular frequency of 0.1 rad / s to 100 rad / s using a 25 mmφ parallel plate type jig. Using the measured values of the storage elastic modulus and loss elastic modulus at an angular frequency of 1 rad / s at the time of measurement, the loss elastic modulus is divided by the storage elastic modulus. For the viscoelasticity measurement, for example, a viscoelasticity measuring device manufactured by TA Instruments, ARES, or the like is preferably used.

  Examples of the polypropylene resin for injection foam molding having the physical properties in the present invention include, for example, a method of irradiating a linear polypropylene resin with radiation, a method of melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. And polypropylene resins containing a branched structure or a high molecular weight component obtained by the above-mentioned method. Among these, a polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound is preferable because it does not require expensive equipment and can be manufactured at low cost.

  Examples of the conjugated diene compound used for obtaining the polypropylene resin for injection foam molding of the present invention include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4. -Hexadiene and the like can be mentioned, but these may be used alone or in combination. Among these, butadiene and isoprene are particularly preferable because they are inexpensive and easy to handle and the reaction easily proceeds uniformly.

  The addition amount of the conjugated diene compound used to obtain the polypropylene resin for injection foam molding of the present invention is preferably 0.01 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin, More preferred is 0.05 part by weight or more and 1 part by weight or less. When the addition amount of the conjugated diene compound is less than 0.01 parts by weight, the loss tangent tan δ exceeds 1.8 and the foamability may be insufficient. When the addition amount exceeds 1 part by weight, the melt flow rate is 100 g / It may be 10 minutes or less, and the compatibility with the linear polypropylene resin may be insufficient.

  In the present invention, a monomer copolymerizable with the conjugated diene compound (for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid) , Maleic anhydride, metal acrylate, metal methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, (Methacrylic acid esters such as butyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate) may be used in combination.

  The radical polymerization initiator used to obtain the polypropylene resin for injection foam molding of the present invention generally includes peroxides, azo compounds, etc., but has the ability to extract hydrogen from polypropylene resins and conjugated diene compounds. What has has is preferable, for example, organic peroxides, such as a ketone peroxide, a peroxy ketal, a hydroperoxide, a dialkyl peroxide, a diacyl peroxide, a peroxy dicarbonate, a peroxy ester, are mentioned.

  Among these, those having particularly high hydrogen abstraction ability are preferable, 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, 2,5- Diacyl peroxides such as dimethyl-2,5-di (t-butylperoxy) -3-hexyne and dialkyl peroxides such as benzoyl peroxide Oxide, t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate Peroxyesters such as 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. It is done. These may be used alone or in combination of two or more.

  The addition amount of the radical polymerization initiator used for obtaining the polypropylene resin for injection foam molding of the present invention is preferably 1.5 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. 1.8 parts by weight or more and 5 parts by weight or less is more preferable. When the addition amount of the radical polymerization initiator is less than 1.5 parts by weight, the loss tangent tan δ exceeds 1.8 and the foamability may be insufficient. It may become saturated and not economical.

  Generally, when a linear polypropylene resin is modified so that the loss tangent tan δ is 1.8 or less, the melt flow rate tends to be 100 g / 10 min or less. On the other hand, in the present invention, the amount of radical initiator added is equal to or greater than the amount of conjugated diene compound added, so that the melt flow rate of the modified polypropylene resin exceeds 100 g / 10 min, and the loss tangent It can be adjusted relatively easily so that tan δ is 1.8 or less.

  The linear polypropylene resin used for obtaining the polypropylene resin for injection foam molding of the present invention is a polypropylene resin having a linear molecular structure, specifically, a propylene homopolymer. And a block copolymer and a random copolymer, which are crystalline polymers. As a copolymer of propylene, a copolymer containing propylene in an amount of 75% by weight or more is preferable in that the crystallinity, rigidity, chemical resistance, etc., which are characteristics of the polypropylene resin, are maintained.

  Examples of the α-olefin copolymerizable with propylene include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4- Α-olefins having 2 or 4 to 12 carbon atoms such as dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene, cyclopentene, norbornene, tetracyclo [6,2,11 , 8,13,6] -4-dodecene and the like, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl- Diene such as 1,6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, male Examples thereof include vinyl monomers such as inic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and divinyl benzene. These may be used alone or in combination of two or more. Among these, ethylene and 1-butene are preferable from the viewpoints of improving cold brittleness resistance and low cost.

  In order to obtain the polypropylene resin for injection foam molding of the present invention, the apparatus for reacting the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator includes a roll, a kneader, a Banbury mixer, a Brabender, a uniaxial Examples thereof include kneaders such as an extruder and a biaxial extruder, horizontal agitators such as a biaxial surface renewal device, and a biaxial multi-disc device, and vertical agitators such as a double helical ribbon agitator. Among these, a kneader is preferably used, and an extruder is particularly preferable from the viewpoint of productivity.

  There are no particular restrictions on the order and method of mixing and kneading (stirring) the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator in order to obtain the polypropylene resin for injection foam molding of the present invention. The linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator may be mixed and then melt-kneaded (stirred), or after the polypropylene resin is melt-kneaded (stirred), the conjugated diene compound or the radical initiator may be simultaneously mixed. Alternatively, they may be mixed separately, collectively or divided. The temperature of the kneading (stirring) machine is preferably 130 to 300 ° C. from the viewpoint that the linear polypropylene resin melts and does not thermally decompose. The kneading (stirring) time is generally preferably 1 to 60 minutes.

  In this way, the polypropylene resin for injection foam molding of the present invention can be produced. The shape and size of the polypropylene resin for injection foam molding are not limited, and may be pellets.

  The present invention also relates to an injection foam molded article obtained by injection foam molding of a resin composition comprising the polypropylene resin for injection foam molding of the present invention, a linear polypropylene resin, and a foaming agent.

  The linear polypropylene resin in the present invention preferably has a melt flow rate of 10 g / 10 min to 100 g / 10 min, more preferably 15 g / 10 min to 50 g / 10 min, and a melt tension of preferably 2 cN. Less, more preferably 1 cN or less. When the melt flow rate of the linear polypropylene resin is in the range of 10 g / 10 min or more and 100 g / 10 min or less, when manufacturing an injection foam molded article, a thin portion with a mold cavity clearance of about 1 to 2 mm is used. Also in the molding having, it is possible to fill the mold with the molten resin at a relatively low pressure, and there is a tendency that continuous injection foam molding can be performed. Moreover, if the melt tension is less than 2 cN, an injection foam molded article having a beautiful surface appearance can be obtained.

  Examples of the linear polypropylene resin herein include the same ones as those taken up as the raw linear polypropylene resin used in the production of the polypropylene resin for injection foam molding. Specific examples of the linear polypropylene resin include propylene homopolymer, propylene-ethylene random copolymer, and propylene-ethylene block copolymer.

  The mixing ratio of the polypropylene resin for injection foam molding and the linear polypropylene resin constituting the injection foam molded body of the present invention is preferably a polypropylene resin for injection foam molding when the total of both is 100 parts by weight. Is 5 to 50 parts by weight, more preferably 10 to 30 parts by weight. The linear polypropylene resin is preferably 50 parts by weight or more and 95 parts by weight or less, and more preferably 70 parts by weight or more and 90 parts by weight or less. When the blending ratio is within the above range, an injection foam molded article having uniform fine bubbles and having a foaming ratio of 2 times or more can be provided at low cost. When the blending ratio is out of the above range, for example, when the polypropylene resin for injection foam molding is less than 5 parts by weight, there is a tendency that a foamed molded product having uniform fine bubbles cannot be obtained, and 50 parts by weight is reduced. If it exceeds, there is a tendency that only a molded article having a poor surface appearance can be obtained.

  The foaming agent used in the present invention is not particularly limited as long as it can be usually used for injection foam molding, such as a chemical foaming agent and a physical foaming agent.

  The chemical foaming agent is premixed with the resin and then supplied to an extruder or an injection molding machine, and decomposes in a cylinder to generate a gas such as carbon dioxide. Examples of the chemical foaming agent include inorganic chemical foaming agents such as sodium bicarbonate and ammonium carbonate, and organic chemical foaming agents such as azodicarbonamide and N, N′-dinitrosopentamethylenetetramine. These may be used alone or in combination of two or more.

  A physical foaming agent is injected into a molten resin in a cylinder of an extruder or an injection molding machine as a gaseous or supercritical fluid, dispersed or dissolved, and foamed by being released from pressure after being injected into a mold. It functions as an agent. Physical foaming agents include aliphatic hydrocarbons such as propane and butane, alicyclic hydrocarbons such as cyclobutane and cyclopentane, halogenated hydrocarbons such as chlorodifluoromethane and dichloromethane, nitrogen, carbon dioxide, air, etc. Inorganic gas. These may be used alone or in combination of two or more.

  Among these foaming agents, ordinary extruders and injection molding machines can be used safely, and uniform fine bubbles are easily obtained. As chemical foaming agents, inorganic chemical foaming agents, and as physical foaming agents, nitrogen Inorganic gases such as carbon dioxide and air are preferred. These foaming agents include, for example, foaming aids such as organic acids such as citric acid, talc, and lithium carbonate, in order to stably and uniformly make the bubbles of the injection foam molded article. A nucleating agent such as inorganic fine particles may be added. Usually, the inorganic chemical foaming agent is preferably used as a masterbatch of a polyolefin resin having a concentration of 10 to 50% by weight from the viewpoints of handleability, storage stability, and dispersibility in a polypropylene resin.

  What is necessary is just to set the usage-amount of the foaming agent in this invention suitably by the foaming magnification of the final product, the kind of foaming agent, and the resin temperature at the time of shaping | molding. For example, usually, in the case of an inorganic chemical foaming agent, in 100 parts by weight of the polypropylene resin of the present invention, preferably in the range of 0.5 to 30 parts by weight, more preferably in the range of 1 to 20 parts by weight. Used in. By using the inorganic chemical foaming agent in this range, it is easy to obtain an injection foamed molded article having a foaming ratio of 2 times or more economically and uniform fine bubbles. In the case of a physical foaming agent, it is in the range of 0.05 parts by weight or more and 10 parts by weight or less, preferably 0.1 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. Used to supply.

  In the present invention, if necessary, within the range that does not impair the effects of the present invention, in addition to polypropylene resins that are not within the scope of the present invention, high-density polyethylene resins, high-pressure low-density polyethylene resins, linear low-density polyethylene systems Resins, ethylene-α-olefin copolymers, olefin elastomers, styrene elastomers, and other thermoplastic resins may be mixed.

  In the present invention, if necessary, an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightening agent, a metal soap, as long as the effects of the present invention are not impaired. In combination with stabilizers such as antacid adsorbents, crosslinking agents, chain transfer agents, nucleating agents, plasticizers, lubricants, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents, etc. Also good.

Next, the method of injection foam molding will be specifically described. A known method can be applied to the injection foam molding method itself, and the molding conditions may be appropriately adjusted depending on the melt flow rate of the polypropylene resin, the type of foaming agent, the type of molding machine, or the shape of the mold.
In the case of the polypropylene resin of the present invention, for example, under conditions of a resin temperature of 170 to 250 ° C., a mold temperature of 10 to 100 ° C., a molding cycle of 1 to 120 minutes, an injection speed of 10 to 300 mm / second, an injection pressure of 10 to 200 MPa, and the like. Preferably it is done.
There are various methods for foaming in the mold. Among them, a mold composed of a fixed mold and a movable mold capable of moving forward and backward at an arbitrary position is used. The so-called core back method (moving cavity method), which causes the foam to recede, has a non-foamed layer formed on the surface, and the foamed inner layer tends to be uniform fine bubbles, resulting in an injection foam molded article with excellent lightness. It is preferable because it is easy. In addition, as a method of retracting the movable mold, it may be performed in one step, may be performed in multiple steps including two or more steps, and the reverse speed may be appropriately adjusted.

  In the present invention, by applying a so-called counter pressure method in which a polypropylene resin composition is introduced into a mold while pre-pressing the mold with an inert gas or the like, surface appearance defects due to silver streaks are reduced. Since it can reduce, it is preferable. In this way, the injection foam molded article of the present invention can be obtained.

  The expansion ratio of the injection-foamed molded article of the present invention is preferably 2 to 10 times, more preferably 2.5 to 6 times. If the expansion ratio is less than 2 times, it tends to be difficult to obtain light weight, and if it exceeds 10 times, the rigidity tends to decrease significantly.

By using the polypropylene resin of the present invention, the projected area is reduced. It becomes possible to easily produce an injection foamed molded article of 0.2 m ² or more.
The projected area refers to the area when the injection-foamed molded product is projected onto a surface perpendicular to the moving direction of the mold, and is a numerical value that serves as a reference for calculating the clamping force required during molding.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples.

In the examples and comparative examples, the test methods and criteria used in various evaluation methods are as follows.
(1) Melt flow rate (MFR)
In accordance with ASTM D-1238, using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho), from the amount of resin extruded from a die at a constant time under a load of 2.16 kg at 230 ° C., to the amount extruded in 10 minutes Converted. The fixed time is 60 seconds when the melt flow rate is 3.5 g / 10 minutes or more and less than 10 g / 10 minutes, 30 seconds when the melt flow rate is 10 g / 10 minutes or more and less than 25 g / 10 minutes, and 25 g / 10 minutes or more and 50 g. / 10 minutes or less, 15 seconds, 50 g / 10 minutes or more and less than 100 g / 10 minutes, 5 seconds, and 100 g / 10 minutes or more, 3 seconds.

(2) Melt tension (MT)
Using a capillograph (manufactured by Toyo Seiki Seisakusho) with an attachment for measuring the melt tension, it was lowered at a piston lowering speed of 10 mm / min from a die having a hole with a diameter of 1 mmφ and a length of 10 mm at a resin temperature of 200 ° C. When the strand was taken up at 1 m / min and the take-up speed was increased at 40 m / min ² after stabilization, the take-up load of the pulley with the load cell when it broke was taken as the melt tension. In addition, when the strand did not break, the load at the point where the take-up load of the pulley did not increase even when the take-up speed was increased was taken as the melt tension.

(3) Loss tangent tan δ
A polypropylene resin is hot-pressed at 190 ° C for 5 minutes using a spacer with a thickness of 1.5 mm to produce a 1.5 mm-thick press plate, and punched out with a 25 mmφ punch to obtain a test piece. It was. As a measuring device, a viscoelasticity measuring device ARES made by TA Instruments was used, and a parallel plate type jig of 25 mmφ was attached. A thermostatic chamber was installed to surround the jig, kept at 200 ° C., and after the jig was preheated, the thermostat was opened, a test piece with 25 mmφ was inserted between the parallel plates, the thermostat was closed and preheated for 5 minutes. Later, the parallel plate spacing was compressed to 1 mm. After compression, the thermostat was opened again, the resin protruding from the parallel plate was scraped off with a brass spatula, the thermostat was closed and the temperature was kept again for 5 minutes, and then dynamic viscoelasticity measurement was started.
The measurement was performed in the range of angular frequency from 0.1 rad / s to 100 rad / s, and storage elastic modulus and loss elastic modulus at each angular frequency and loss tangent tan δ were obtained as calculated values. Among these results, the value of loss tangent tan δ at an angular frequency of 1 rad / s was adopted. The amount of strain was 5%, and the measurement was performed in a nitrogen atmosphere.

(4) Injection filling properties When 20 shots were continuously molded, the number of short shots (number of defects) was determined and evaluated according to the following criteria.
○: The number of defects is 0.
X: The number of defects is 1 or more.

(5) measuring the thickness of the foaming magnification injection foam molded article bottom, by dividing the cavity clearance t ₀ in the mold clamped state of the mold of the sites were calculated.

<Production of polypropylene resin for injection foam molding>
A polypropylene resin for injection foam molding was produced under the following production conditions.

Example 1
A mixture of 100 parts by weight of a propylene homopolymer (manufactured by Prime Polymer, J108M) as a linear polypropylene resin with a melt flow rate of 45 g / 10 min, and 3.0 parts by weight of t-butyl peroxyisopropyl carbonate as a radical polymerization initiator Is supplied from a hopper to a 45 mmφ twin-screw extruder (L / D = 40) at 70 kg / hour, melt-kneaded at a cylinder temperature of 200 ° C., and an isoprene monomer as a conjugated diene compound from a press-fitting portion provided in the middle, Feeding at 0.24 parts by weight (a rate of 0.168 kg / hour) using a metering pump, and melt-kneading in the twin-screw extruder, a polypropylene resin pellet for injection foam molding was obtained. Table 1 shows the evaluation of the obtained polypropylene resin for injection foam molding (referred to as A-1). The relationship between the loss tangent (tan δ) of A-1 and the angular frequency is shown in FIG.

(Comparative Example 1)
Pellets were obtained in the same manner as in Example 1 except that the blending amount of t-butyl peroxyisopropyl carbonate was changed to 1.0 part by weight and the supply amount of isoprene was changed to 0.4 part by weight. Table 1 shows the evaluation of the obtained resin (referred to as A-4). The relationship between the loss tangent (tan δ) of A-4 and the angular frequency is shown in FIG.

(Examples 2-3)
<Preparation of polypropylene resin composition>
In the type and composition ratio shown in Table 2, the polypropylene resin for injection foam molding (A-1) synthesized in Example 1 was added to a linear polypropylene resin and a baking soda-based chemical foaming agent masterbatch as a foaming agent ( Erywa Kasei Polyslene EE275F, cracked gas amount 40 ml / g) was dry blended.

  As the linear polypropylene resin, a propylene-ethylene copolymer (manufactured by Prime Polymer, J708UG) having a melt flow rate of 45 g / 10 min and a melt tension of less than 1 cN was used.

<Preparation of injection foam molding>
The temperature is set at 30 ° C after melt-kneading at a cylinder temperature of 200 ° C and a back pressure of 15MPa with an electric injection molding machine (manufactured by Ube Industries Co., Ltd.) having a core back function and a shut-off nozzle with a clamping force of 350t. A box-shaped cavity composed of a fixed mold and a movable mold capable of moving forward and backward (vertical 330 mm × width 230 mm × height 100 mm) (standing wall: tilt 10 °, clearance 3 mm, bottom: clearance t ₀ = 1.5 mm), and filled in a mold having a φ2 pin gate at the center position of the bottom portion at an injection speed of 100 mm / second. After completion of the injection filling, the movable mold was retracted so that the bottom surface portion had a desired thickness (foaming ratio 3 times, 4.5 mm), and the resin in the cavity was foamed. After completion of foaming, the injection foamed molded article was taken out after cooling for 60 seconds. Table 2 shows the evaluation of the obtained injection-foamed molded article.

  Since the polypropylene resin composition for injection foam molding of the present invention is excellent in fluidity, short shots during continuous molding hardly occur and the injection filling property was good. Moreover, the foaming ratio of the bottom face part of the injection foamed molded product was 3 times, and a high foaming ratio was obtained. Even when the addition amount of the polypropylene resin for injection foam molding was reduced, a foaming ratio of 3 times was obtained.

(Comparative Examples 2-3)
<Preparation of injection foam molding>
The obtained blend was subjected to injection foaming in the same manner as in Example 1 to obtain an injection foam molded article. Table 2 shows the evaluation of the obtained injection-foamed molded article.
With the resin of Comparative Example 1, an injection foam molded article having a desired expansion ratio of 3 times could not be obtained due to insufficient foamability of the polypropylene resin. When the amount added was increased, it was possible to foam three times, but only those that deteriorated the appearance of the molded product were obtained.

Claims (2)

A polypropylene resin for injection foam molding characterized by satisfying the following properties (a) to (c) :
A polypropylene resin for injection foam molding, which is obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator and a conjugated diene compound .
(A) The melt flow rate at 230 ° C. is 100 g / 10 min or more.
(B) The loss tangent tan δ, which is the ratio of the storage elastic modulus and loss elastic modulus at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C., is 0.6 or more and 1.8 or less. .
(C) The storage elastic modulus at an angular frequency of 0.1 to 1 rad / s in dynamic viscoelasticity measurement at 200 ° C. is 1 × 10 ³ Pa or less. An injection foam molded article obtained by injection foam molding the resin composition comprising the polypropylene resin for injection foam molding according to claim 1, a linear polypropylene resin, and a foaming agent.