JP2012197345A - Polypropylenic resin composition for injection foam molding, and injection foam molded body comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection foam molded body which does not have roughened cells even if a chemical blowing agent of a low-temperature decomposition type is used, and has a uniform and fine foam layer.SOLUTION: A polypropylenic resin composition for injection foam molding comprises: 5 to 50 pts.wt of a modified polypropylenic resin (A) whose melt flow rate at 230°C is >30 g/10-min and ≤250 g/10-min, melt tension at 200°C is ≤0.3 cN, and in which the loss tangent tanδ being a ratio of a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad/s in the dynamic viscoelastic measurement at 200°C is ≤6.0; 50 to 95 pts.wt of a linear polypropylenic resin (B) whose melt flow rate at 230°C is ≥15 g/10 min and ≤200 g/10 min, and melt tension is <2 cN; and a chemical blowing agent (C) in which the maximum gas generation temperature in the gas generation amount curve is ≥170°C and ≤200°C, and the maximum point in the curve is one.

Description

  The present invention relates to a polypropylene resin composition for injection foam molding and an injection foam molding 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 resin products are provided, and one of such products is an injection foam molded product of polypropylene resin.

  In the injection foam molding field, as a method of foaming in the mold for the purpose of weight reduction and cost reduction, foaming is performed using a mold composed of a fixed mold and a movable mold that can move forward and backward at any position. There is a so-called core back method (moving cavity method) in which a polypropylene resin composition containing an agent is foamed by retreating a movable mold after completion of injection (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 (melt tension), bubbles are easily broken and foam molding is difficult.

  As a method for increasing the melt tension (melting tension) of a polypropylene resin, for example, a method of introducing long chain branching by irradiating a non-crosslinked polypropylene resin (Patent Document 2), a polypropylene resin and an isoprene monomer There has been proposed a method (Patent Document 3) for producing a modified polypropylene-based resin by melt-kneading a polymer and a radical polymerization initiator. In any method, the melt tension is increased and foam molding is possible, but the fluidity is not sufficient and the viscosity at the time of resin melting is high, so the pressure at the time of injection tends to increase, and as a result, the cylinder at the time of melt kneading We had to set the set temperature to a high temperature.

Conventional chemical foaming agents used for injection foam molding have a relatively high decomposition gas generation temperature, which also causes the cylinder setting temperature to be high. Such chemical foaming agents make the cells of the foamed layer uniform and fine due to the components contained, but on the other hand, many decomposition residues are likely to occur during molding, causing mold contamination.
As a countermeasure, it is possible to use a chemical foaming agent that decomposes at a relatively low temperature with few decomposition residues. However, if such a chemical foaming agent is used at a high cylinder temperature as described above, the inside of the foamed layer may be used. The cell tends to be coarse, that is, the cell tends to become rough, and uniform fine cells tend to be difficult to obtain.

  As described above, in injection foam molding using a low-temperature decomposition type chemical foaming agent, it has been difficult to produce an injection foam molded article in which cell roughening is prevented and the foam layer is uniform and fine.

WO2005 / 026255 JP 2001-226510 A JP-A-9-188774

An object of the present invention is to provide an injection foam molded article in which cell roughening does not occur even when a low temperature decomposition type chemical foaming agent is used, and the foamed layer becomes uniform and fine.

  As a result of intensive studies, the present inventors have found that the melt flow rate exceeds 30 g / 10 minutes and is 250 g / 10 minutes or less, the melt tension at 200 ° C. is 0.3 cN or more, and the dynamic viscoelasticity measurement at 200 ° C. A modified polypropylene resin (A) having a loss tangent tan δ, which is a ratio of a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad / s, of 6.0 or less, and a melt flow rate of 15 g / 10 min to 200 g / 10 minutes or less, the linear polypropylene resin (B) having a melt tension of less than 2 cN, and the maximum gas generation temperature in the gas generation amount curve is 170 ° C. or more and 200 ° C. or less, and there is one maximum point in the curve. The problem can be solved by using a polypropylene resin composition for injection foam molding comprising a chemical foaming agent (C) characterized by Heading, it has led to the completion of the present invention.

  That is, this invention consists of the following structures.

  (1). The melt flow rate at 230 ° C. exceeds 30 g / 10 min to 250 g / 10 min or less, the melt tension at 200 ° C. is 0.3 cN or more, and the angular frequency in dynamic viscoelasticity measurement at 200 ° C. is 1 rad / 5 to 50 parts by weight of the modified polypropylene resin (A) having a loss tangent tan δ which is a ratio of the storage elastic modulus and loss elastic modulus at s of 6.0 or less, and a melt flow rate at 230 ° C. of 15 g. / 10 minutes or more and 200 g / 10 minutes or less, the melt tension is less than 2 cN, linear polypropylene-based resin (B) 50 to 95 parts by weight [the total amount of (A) and (B) is 100 parts by weight], And the maximum gas generation temperature in the gas generation amount curve is 170 ° C. or more and 200 ° C. or less, and the curve contains a chemical foaming agent (C) characterized by having one maximum point. A polypropylene resin composition for injection foam molding.

  (2). The modified polypropylene resin (A) has a melt flow rate at 230 ° C. of more than 50 g / 10 minutes and not more than 250 g / 10 minutes, and is a polypropylene system for injection foam molding according to (1) Resin composition.

  (3). (1) or (2), wherein the modified polypropylene resin (A) is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator and a conjugated diene compound. ) Polypropylene resin composition for injection foam molding.

  (4). An injection foam molded article obtained by injection foam molding of the polypropylene resin composition for injection foam molding according to any one of (1) to (3).

  Since the polypropylene resin composition for injection foam molding of the present invention is excellent in fluidity and foamability, the injection pressure during molding can be lowered. As a result, the cylinder set temperature at the time of molding can be lowered. Even if a low-temperature decomposition type chemical foaming agent with little decomposition residue is used, cell roughening does not occur, and an injection foam molded article having a uniform fine foam layer can be obtained.

It is the gas generation amount curve obtained by heating up the chemical foaming agent used in the Examples at a constant rate, measuring the gas generation amount, and plotting the temperature on the horizontal axis and the gas generation amount on the vertical axis.

  Embodiments of the present invention will be described below.

  The polypropylene resin composition for injection foam molding of the present invention has a melt flow rate of more than 30 g / 10 minutes to 250 g / 10 minutes or less, a melt tension at 200 ° C. of 0.3 cN or more, and an operation at 200 ° C. 5 to 50 parts by weight of a modified polypropylene resin (A) having a loss tangent tan δ of 6.0 or less, which is a ratio of a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement, melt 50 to 95 parts by weight of linear polypropylene resin (B) having a flow rate of 15 g / 10 min or more and 200 g / 10 min or less and a melt tension of less than 2 cN [the total amount of (A) and (B) is 100 parts by weight And the maximum gas generation temperature in the gas generation amount curve is 170 ° C. or more and 200 ° C. or less, and there is one maximum point in the curve. Comprising (C).

  The melt flow rate of the modified polypropylene resin (A) used in the present invention has a lower limit of more than 30 g / 10 minutes, preferably more than 50 g / 10 minutes, and an upper limit of 250 g / 10 minutes or less, preferably It is 100 g / 10 minutes or less. Within this range, the dispersibility of the modified polypropylene resin in the composition is improved, and sufficient foaming properties can be obtained even when the amount of the resin added is small, and the injection pressure and shear during molding are obtained. Since heat generation can be reduced, as a result, the cylinder set temperature during molding can be reduced. If the melt flow rate of the modified polypropylene resin (A) is 30 g / 10 min or less, the flowability may be insufficient and a short shot may occur, and if the melt flow rate exceeds 250 g / 10 min, injection foam molding is performed. The weighing process at 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 modified polypropylene resin (A) used in the present invention has a melt tension at 200 ° C. of 0.3 cN or more, preferably 0.5 cN or more. When the melt tension is less than 0.3 cN in a polypropylene resin having a melt flow rate of more than 30 g / 10 min, foam breakage at the molten resin flow front end during injection foam molding cannot be suppressed, and silver streak occurs. The surface appearance of the foamed molded product may deteriorate.

Here, the melt tension (hereinafter sometimes abbreviated as “MT”) is a capillograph (equipped with a φ10 mm cylinder equipped with an attachment for measuring 1 mmφ and a length of 10 mm, equipped with an attachment for measuring the melt tension. Using Toyo Seiki Seisakusho, 1E), the strand discharged from the die when the piston is lowered at 200 ° C and the piston descending speed is 10mm / min. The load applied to the pulley with a load cell when the strand breaks when the take-up speed is increased at 40 m / min ² after stabilization. If the strand does not break, the melt tension is the load at which the load applied to the pulley with the load cell does not increase even if the take-up speed is increased.

  The modified polypropylene resin (A) used in the present invention has a loss tangent tan δ which is a ratio of a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 200 ° C. of 6. 0 or less, preferably 5.0 or less.

  Here, the angular frequency 1 rad / s is a so-called low shear region, and the loss tangent tan δ is small in that region, that is, the relatively high storage elastic modulus is considered to be advantageous for holding bubbles during foaming. It is done. 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 30 g / 10 min is an index of bubble retention in injection foam molding, and the loss tangent tan δ is 6.0. If it exceeds, bubbles are easily broken, and voids (coarse bubbles with a diameter of 1.5 mm or more generated by bubbles inside the foam) are generated inside the foam, or the thickness of the injection foam molded product is thin. It may become.

  On the other hand, the lower limit of the loss tangent tan δ is not particularly limited, but if it is less than 0.7, the flow mark may be conspicuous on the surface of the injection-foamed molded article, and the surface appearance may deteriorate.

  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 modified polypropylene resin (A) having the physical properties in the present invention include, for example, a method of irradiating a linear polypropylene resin with radiation, a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. Examples thereof include a modified polypropylene resin containing a branched structure or a high molecular weight component obtained by a method.

  Among these, a modified 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 modified polypropylene resin (A) of the present invention include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 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 for obtaining the modified polypropylene resin (A) 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. 0.05 to 2 parts by weight is more preferable. When the addition amount of the conjugated diene compound is less than 0.01 parts by weight, the loss tangent tan δ exceeds 6.0 and the foaming property may be insufficient. When the addition amount exceeds 5 parts by weight, the melt flow rate is 30 g / It may be 10 minutes or less, and fluidity 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 modified polypropylene resin (A) of the present invention generally includes peroxides, azo compounds, etc., but it can extract hydrogen from polypropylene resins and the conjugated diene compounds. Examples thereof include organic peroxides such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydicarbonate, and peroxyester.

  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 amount of radical polymerization initiator used to obtain the modified polypropylene resin (A) of the present invention is 0.05 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. Preferably, 0.2 part by weight or more and 5 parts by weight or less are more preferable. If the addition amount of the radical polymerization initiator is less than 0.05 parts by weight, the loss tangent tan δ exceeds 6.0 and the foaming property 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 6.0 or less, the melt flow rate tends to be 30 g / 10 min or less. In contrast, 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 30 g / 10 min. Can be adjusted relatively easily so that the loss tangent tan δ is 6.0 or less.

  The linear polypropylene resin used for obtaining the modified polypropylene resin (A) of the present invention is a polypropylene resin having a linear molecular structure, specifically, a single weight of propylene. Polymers, block copolymers and random copolymers, including 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 modified polypropylene resin (A) 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 single Examples thereof include kneaders such as a screw extruder, twin screw extruder, a horizontal stirrer such as a biaxial surface renewal machine, a biaxial multi-disc device, and a vertical stirrer such as a double helical ribbon stirrer. Among these, a kneader is preferably used, and an extruder is particularly preferable from the viewpoint of productivity.

  In order to obtain the modified polypropylene resin (A) of the present invention, the order and method of mixing, kneading (stirring) the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator are not particularly limited. 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 modified polypropylene resin (A) of the present invention can be produced. There is no restriction | limiting in the shape and magnitude | size of a modified polypropylene resin (A), A pellet form may be sufficient.

  As the linear polypropylene resin (B) in the present invention, the melt flow rate is 15 g / 10 min or more and 200 g / 10 min or less, preferably 30 g / 10 min or more and 150 g / 10 min or less, the melt tension is preferably less than 2 cN, Preferably it is 1 cN or less. When the melt flow rate of the linear polypropylene resin (B) is within the above range, a relatively low pressure can be obtained even when molding an injection-foamed molded article having a thin portion with a mold cavity clearance of about 1 to 2 mm. Thus, the molten resin can be filled in the mold, and there is a tendency that continuous and stable injection foam molding can be performed. Moreover, if the melt tension is less than 2 cN, an injection-foamed molded article having a beautiful surface appearance that does not generate a flow mark can be obtained.

  Specific examples of the linear propylene resin include a propylene homopolymer, a propylene-ethylene random copolymer, a propylene-ethylene block copolymer, etc. Among them, from the viewpoint of easily imparting impact resistance to an injection foamed molded article. A propylene-ethylene block copolymer is preferred.

  When the mixing ratio of the modified polypropylene resin (A) and the linear polypropylene resin (B) constituting the polypropylene resin composition of the present invention is 100 parts by weight, the modified polypropylene resin ( A) is preferably 5 to 50 parts by weight, more preferably 10 to 45 parts by weight. The linear polypropylene resin (B) is preferably 50 parts by weight or more and 95 parts by weight or less, and more preferably 55 parts by weight or more and 90 parts by weight or less. When the blending ratio is within the above range, it is possible to provide an injection-foamed molded article having a uniform fine surface, a foaming ratio of 2 times or more, and a beautiful surface appearance that does not generate a flow mark at low cost. When the blending ratio is out of the above range, for example, when the modified polypropylene resin (A) is less than 5 parts by weight, there is a tendency that a foamed molded article having uniform fine bubbles cannot be obtained, and 50 parts by weight. If it exceeds 1, there is a tendency that only a molded article having a poor appearance with many flow marks is obtained.

The chemical foaming agent (C) used in the present invention is characterized in that the maximum gas generation temperature in the gas generation amount curve is 170 ° C. or higher and 200 ° C. or lower.
The gas generation amount curve here shows the temperature-decomposition gas generation behavior of the chemical foaming agent, and can be measured by a known method. For example, a chemical foaming agent can be placed in a test tube, the test tube is placed in an oil bath, the temperature is raised at a constant speed, the amount of gas generated is measured, and the temperature indicating the maximum amount of gas generated can be determined. . At this time, the gas generation amount curve as shown in FIG. 1 is obtained by plotting the temperature on the horizontal axis and the gas generation amount on the vertical axis.

  The maximum gas generation temperature here is a temperature indicating the maximum gas generation amount in the gas generation amount curve, and is 170 ° C. or higher and 200 ° C. or lower, preferably 175 ° C. or higher and 195 ° C. or lower. By using the polypropylene resin composition of the present invention, using a chemical foaming agent whose maximum gas generation temperature falls within this range, and setting the cylinder setting temperature at the time of molding to a temperature about the same range, The decomposition of the blowing agent proceeds efficiently. Further, it is possible to hold the gas dissolved in the resin while reducing the melt viscosity of the resin, or until the gas contained in the form of fine bubbles is injected and filled into the cavity. As a result, an injection foam molded article having a uniform fine foam layer is obtained.

  The chemical foaming agent (C) used in the present invention is characterized by having one maximum point in the gas generation amount curve. FIG. 1 illustrates a gas generation amount curve of a chemical foaming agent having one or two maximum points. The gas generation amount curve of a (dotted line) in FIG. 1 is an example of a chemical foaming agent having two maximum points, and the gas generation amount curve of b (solid line) in FIG. 1 has one maximum point. It is an example of a certain chemical foaming agent.

  In general, a chemical foaming agent having two or more maximum points is often a chemical foaming agent containing a large amount of an organic acid such as citric acid, and is likely to cause mold contamination due to a decomposition residue derived from the organic acid. In the present invention, since a chemical foaming agent having only one maximum point in the gas generation amount curve, that is, a chemical foaming agent having a small amount of organic acid such as citric acid, is used, prevention of mold contamination can be expected.

  There is no particular limitation as long as it has such characteristics, but inorganic chemical foaming such as sodium bicarbonate and ammonium carbonate can be used safely with ordinary injection molding machines and uniform fine bubbles are easily obtained. Agents are preferred, and for commercial products, Polyslene EE25C, EE65C manufactured by Eiwa Kasei Kogyo Co., Ltd. can be suitably used.

  When such a foaming agent is used, the cylinder set temperature is usually within 10 ° C, preferably within 5 ° C, or within 30 ° C with respect to the maximum gas generation temperature of the chemical foaming agent used. Preferably, when it is set within a temperature range of 25 ° C. or less, it is easy to obtain an injection foam molded product having uniform fine bubbles. For example, when a chemical foaming agent having a maximum gas generation temperature of 180 ° C. is used, the effect of the present invention can be obtained by setting the cylinder set temperature to 170 ° C. to 210 ° C., preferably 175 ° C. to 205 ° C. It tends to be easy.

  If the set temperature of the cylinder is higher than the above range, the chemical foaming agent will decompose too much, the decomposed gas will coalesce, and there will be many coarse bubbles in the foamed layer, so-called cell roughening tends to occur. . If the set temperature of the cylinder is lower than the above range, the efficiency of gas generation from the foaming agent is poor and it is not economical, and the pressure at the time of injection increases, and molding defects such as short shots tend to occur. It is in.

  The amount of the chemical foaming agent (C) used in the present invention varies depending on the type, concentration in the masterbatch and the desired foaming ratio, but is generally preferably 100 parts by weight of the injection-molded polypropylene resin. It is used in the range of 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight. By using in this range, it is easy to economically obtain an injection foam molded article having a foaming ratio of 2 times or more and uniform fine bubbles.

  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 for injection foam molding of the present invention, molding conditions other than the cylinder set temperature include, for example, 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, and an injection pressure. It is preferable to carry out under conditions such as 10 to 200 MPa.

  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, it is caused by silver streak by using a so-called counter pressure method in which a polypropylene resin composition for injection foam molding is introduced into a mold while pressure is applied in advance in the mold with an inert gas or the like. Since surface appearance defect can be reduced, 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.

  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 thermostat was set up to surround the jig, kept at 200 ° C., and after the jig was preheated, the thermostat was opened, a test piece of 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) 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.

(5) Evaluation of foam layer: A cross section cut in the thickness direction was observed at an arbitrary portion of the injection foam molded article, and the following evaluation was performed with or without bubbles (coarse bubbles) having a diameter of 1 mm or more.
Coarse bubbles of 1 mm or more are not present, and the entire foam layer is uniform and fine.
Coarse bubbles of 1 mm or more exist, and the foam layer is rough.

(6) Injection filling property (injection pressure): In the injection foam molding of this example and comparative example, the following evaluation was performed based on the obtained injection pressure data.
Injection pressure: 70MPa or less ...
Injection pressure: greater than 70 MPa and less than 80 MPa
Injection pressure: Greater than 80MPa

(7) Mold fouling property: In the injection foam molding of this example and comparative example, the surface of the movable mold was observed with the naked eye after 1000 shots, and evaluated as follows depending on whether or not there were contaminated deposits.
There is no contamination on the mold surface ...
There are contaminants on the mold surface ...

(Production example)
A modified polypropylene resin was produced under the following production conditions.

(Production Example A-1)
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 1.0 part 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, Pellets of modified polypropylene resin were obtained by supplying 0.4 parts by weight (rate of 0.28 kg / hour) using a metering pump and melt-kneading in the twin-screw extruder.
Table 1 shows the evaluation of the obtained modified polypropylene resin.

(Production Example A-2)
A modified polypropylene resin was obtained in the same manner as in Production Example A-1, except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 1.4 parts by weight and the supply amount of isoprene was changed to 0.3 parts by weight. It was. Table 1 shows the evaluation of the obtained modified polypropylene resin.

(Production Example A-3)
A modified polypropylene resin was obtained in the same manner as in Production Example A-1, except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 1.4 parts by weight and the supply amount of isoprene was changed to 0.25 parts by weight. It was. Table 1 shows the evaluation of the obtained modified polypropylene resin.

(Production Example A-4)
A modified polypropylene resin was obtained in the same manner as in Production Example A-1, except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 0.6 parts by weight and the supply amount of isoprene was changed to 0.8 parts by weight. It was. Table 1 shows the evaluation of the obtained modified polypropylene resin.

The following were used as the linear polypropylene resin (B) and the chemical foaming agent (C).
(B-1) Propylene-ethylene copolymer having a melt flow rate of 45 g / 10 min and a melt tension of less than 1 cN (manufactured by Prime Polymer, J708UG)
(B-2) Propylene-ethylene copolymer having a melt flow rate of 110 g / 10 min and a melt tension of less than 1 cN (manufactured by Sun Allomer, PMD81M)
(B-3) Propylene-ethylene copolymer having a melt flow rate of 10 g / 10 min and a melt tension of less than 2 cN (Nippon Polypro, BC3L)
(C-1) Baking soda-based chemical foaming agent master batch (Polyslen EE25C manufactured by Eiwa Kasei Co., Ltd., foaming agent concentration 25%, maximum gas generation temperature 180 ° C., the maximum point in the gas generation amount curve is one)
(C-2) Baking soda-based chemical foaming agent master batch (Polyslen EE65C manufactured by Eiwa Kasei Co., Ltd., foaming agent concentration 65%, maximum gas generation temperature 180 ° C., the maximum point in the gas generation amount curve is one)
(C-3) Baking soda-based chemical foaming agent master batch (Polyslen EE275F manufactured by Eiwa Kasei Co., Ltd., foaming agent concentration 27%, maximum gas generation temperature 215 ° C., gas generation amount curve has two maximum points)

(Examples 1-6)
<Preparation of polypropylene resin composition>
The linear polypropylene resin (B) and the chemical foaming agent (C) were mixed and dry blended with the modified polypropylene resin (A) at the types and composition ratios shown in Table 2.

<Preparation of injection foam molding>
An electric injection molding machine (manufactured by Ube Industries Co., Ltd.) with a mold back force of 350t and a core back function is used, the mold has a pinpoint gate, and is a box-shaped cavity with a height of 330mm x width 230mm x height 100mm A mirror-finished product with an internal mirror surface was used.
For the blends in Table 2, after melt-kneading at a cylinder set temperature of 200 ° C. or 220 ° C. and a back pressure of 15 MPa, an initial cavity clearance of 1.3 mm at an injection speed of 100 mm / second and an injection time of 1.2 seconds. The mold was controlled so that the mold surface temperature was controlled at a fixed mold temperature of 50 ° C. and a movable mold of 40 ° C.

  After completion of injection filling, the movable mold was retracted (core back) so as to obtain a desired expansion ratio, and the resin in the cavity was expanded. After cooling for 60 seconds after completion of foaming, the injection foamed molded article was taken out. 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 and foamability, it has good injection filling properties. Moreover, even if the composition ratio of the resin composition was changed, an injection foam molded article having a desired expansion ratio and a uniform and fine foam layer was obtained. Moreover, since the low-temperature decomposition type chemical foaming agent was used, mold contamination after molding was not confirmed.

(Comparative Example 1)
An injection foamed molded article was obtained in the same manner as in Example 1 except that the chemical foaming agent (C-3) having two maximum points was used. Table 2 shows the physical properties of the obtained injection-foamed molded article. Although a desired foamed molded article was obtained, contamination was confirmed on the mold surface after 1000 shots.

(Comparative Example 2)
An injection foam molded article was obtained in the same manner as in Example 1 except that a modified polypropylene resin having a low MFR (A-4) was used. Table 2 shows the physical properties of the obtained injection-foamed molded article. The fluidity was poor and the injection filling property was deteriorated.

(Comparative Example 3)
A modified polypropylene resin having a low MFR (A-4) was used and molding was carried out at a cylinder set temperature of 220 ° C. to obtain an injection foam molded article. The physical property of the obtained injection foaming molding is shown. Only a so-called cell-shaped molded body having coarse bubbles in the foam layer was obtained.

(Comparative Example 4)
An injection-foamed molded article was obtained in the same manner as in Example 1 except that a linear polypropylene resin having a low MFR (B-3) was used. Table 2 shows the physical properties of the obtained injection-foamed molded article. The fluidity was very poor and the injection filling property was deteriorated.

(Comparative Example 5)
An injection foam molded article was obtained in the same manner as in Example 1 except that only the linear polypropylene resin (B-1) was used without using the modified polypropylene resin of the present invention. Table 2 shows the physical properties of the obtained injection-foamed molded article. Since the modified polypropylene resin was not used, the resin composition itself did not have foaming power, and therefore, injection foam molding with a foaming ratio of 2 times or more could not be performed.

Claims (4)

  The melt flow rate at 230 ° C. exceeds 30 g / 10 min to 250 g / 10 min or less, the melt tension at 200 ° C. is 0.3 cN or more, and the angular frequency in dynamic viscoelasticity measurement at 200 ° C. is 1 rad / 5 to 50 parts by weight of the modified polypropylene resin (A) having a loss tangent tan δ which is a ratio of the storage elastic modulus and loss elastic modulus at s of 6.0 or less, and a melt flow rate at 230 ° C. of 15 g. / 10 minutes or more and 200 g / 10 minutes or less, the melt tension is less than 2 cN, linear polypropylene-based resin (B) 50 to 95 parts by weight [the total amount of (A) and (B) is 100 parts by weight], And the maximum gas generation temperature in the gas generation amount curve is 170 ° C. or more and 200 ° C. or less, and the curve contains a chemical foaming agent (C) characterized by having one maximum point. A polypropylene resin composition for injection foam molding.   The polypropylene system for injection foam molding according to claim 1, wherein the modified polypropylene resin (A) has a melt flow rate at 230 ° C. of more than 50 g / 10 minutes and 250 g / 10 minutes or less. Resin composition.   The modified polypropylene resin (A) is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator and a conjugated diene compound. Polypropylene resin composition for injection foam molding. An injection foam molded article obtained by injection foam molding of the polypropylene resin composition for injection foam molding according to any one of claims 1 to 3.

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