JP2018162371A - Method for producing polypropylene-based resin black foamed particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamed particle capable of producing an in-mold foamed molded body which has a small gap between granules on a surface of a molded body, has high blackness of the molded body, has uniform color and no color unevenness, and is excellent in appearance, even when a polypropylene-based resin foamed particle is produced in one foaming step.SOLUTION: A polypropylene-based resin foamed particle is produced by a method including a step of impregnating a polypropylene-based resin particle containing a specific amount of cell nucleating agent using carbon black having a specific particle diameter and amount with carbon dioxide as a foaming agent, and discharging the polypropylene-based particle to the atmosphere at 80 degrees or higher and 110 degrees or lower to obtain a polypropylene-based resin foamed particle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing polypropylene resin black expanded particles.

  In-mold foam moldings obtained by filling polypropylene resin foam particles in molds and heat-molding with water vapor are the advantages of in-mold foam moldings, such as shape flexibility, lightness, and heat insulation. have. In addition, compared with in-mold foam moldings using similar synthetic resin foam particles, compared with in-mold foam moldings obtained using polystyrene resin foam particles, chemical resistance, heat resistance, strain recovery after compression The dimensional accuracy, heat resistance, and compressive strength are excellent as compared with an in-mold foam molded article using polyethylene resin expanded particles. Due to these characteristics, in-mold foam molded articles obtained using polypropylene resin foam particles are used in various applications such as heat insulating materials, shock-absorbing packaging materials, automobile interior members, and automobile bumper core materials. In recent years, the application has been further expanded, and a wide variety of products have been developed, and there has been a demand for a molded body quality that has not existed before. Among them, in-mold foam molded products that are used in places where the user can see them, the number of cases in which the appearance is regarded as important is increasing, and the required quality is increasing year by year. In particular, the in-mold foamed molded product may have gaps between the particles of the foamed particles on the surface of the molded product (hereinafter, sometimes referred to as “intergranular”) on the surface of the molded product. Appearance is impaired and surface aesthetics deteriorate. For this reason, in an in-mold foam-molded body that places importance on the appearance, it is desired that the number of intergranular spaces be as small as possible.

  Furthermore, when using an in-mold foam molded article for a member such as an automobile, a black foam molded article is preferred for a portion that enters the human eye, and the color is dark (= high blackness), and the foamed particles are foamed or foamed. There has also been a demand for uniform and uniform color between particles. In addition, the intergranularity on the surface of the molded body becomes more conspicuous due to the black color, and a molded body having a smaller intergranularity is required for the black foamed molded body as compared with an uncolored molded body.

  On the other hand, a steam hole for heating a mold for forming a molded body is not a core vent having a conventional slit, but a conspicuous structure such as a drill hole is required. It is increasing.

  Conventionally, as a foaming agent used in this field, a volatile organic foaming agent has been used since foamed particles with a high expansion ratio can be obtained. However, due to increasing interest in environmental problems, in recent years, inorganic gases such as air, nitrogen, oxygen, carbon dioxide (carbon dioxide) have been used as blowing agents. When inorganic gas is used as a foaming agent, it is difficult to obtain a high magnification in a single foaming process because of its low solubility in polypropylene resin. Then, after impregnating with an inorganic gas and applying an internal pressure, a step of obtaining polypropylene-based resin expanded particles having a higher expansion ratio by heating the expanded particles (sometimes referred to as two-stage expansion) is additionally performed. There is a case.

  Patent Documents 2 to 5 disclose inventions related to polypropylene-based resin foam particles containing inorganic black as a foaming agent and containing carbon black. However, although these documents use inorganic gas as a foaming agent, there is no mention of the relationship between the atmosphere and method during foaming and the appearance quality when obtaining foamed particles in a single foaming process. However, due to recent high quality requirements, it has been found that it is insufficient to make the color between the expanded particles uniform as well as the expanded particles, and to increase the blackness of the in-mold expanded molded article. Moreover, there is no description about the method for obtaining the in-mold foaming molding with few intergranularity.

  Patent Documents 6 to 7 disclose an invention in which foamed particles are released into a specific temperature atmosphere to foam polypropylene resin particles. However, colored foam particles are not assumed, and there is no description about a method for increasing the blackness and obtaining an in-mold foam-molded product with less intergranularity.

JP 2008-106150 A JP 2004-263033 A JP 2008-266478 A JP 2013-35949 A JP 2014-1334 A International Publication No. 2014/136933 JP 2009-221451 A

  The purpose of the present invention is to produce polypropylene resin foam particles in a single foaming process, and even in a mold where steam during heating is difficult to enter during foam molding in the mold, there are few intergranular surfaces on the molded body surface, Provided is a polypropylene-based resin foamed particle that has a high blackness of the entire molded body, a uniform color within the foamed particles and between the foamed particles, no color unevenness, and an in-mold foamed molded product excellent in appearance. There is.

As a result of intensive studies to solve the above problems, the present inventor has found that carbon black having a specific particle size is 2 to 5 parts by weight, and the cell nucleating agent is 0.01 to 0.25 parts by weight. When polypropylene-based resin foamed particles are produced in a single foaming process by using polypropylene-based resin particles containing less than or equal to parts and obtaining polypropylene-based resin foamed particles by releasing them into an atmosphere of 80 ° C or higher and 110 ° C or lower. It is possible to produce polypropylene-based resin foam particles that have a small number of intergranular surfaces on the body surface, high blackness of the molded body, uniform color, no color unevenness, and capable of obtaining an in-mold foam molded body excellent in appearance. The headline and the present invention were completed.
That is, this invention consists of the following structures.

  [1] A production method for obtaining expanded polypropylene resin particles having an expansion ratio of 13 times or more and 28 times or less in a one-stage expansion process, wherein the primary particle diameter is greater than 0 nm and less than or equal to 50 nm with respect to 100 parts by weight of the polypropylene resin. Polypropylene resin particles containing 2 to 5 parts by weight of carbon black and 0.01 to 0.25 parts by weight of a cell nucleating agent are dispersed in an aqueous dispersion medium in a closed container, and a foaming agent is obtained. The polypropylene resin particles impregnated with carbon dioxide and heated to a temperature equal to or higher than the softening temperature of the polypropylene resin particles are discharged into an atmosphere at a pressure lower than the internal pressure of the hermetic container and at 80 ° C. or higher and 110 ° C. or lower. The manufacturing method of a polypropylene resin expanded particle which obtains a polypropylene resin expanded particle by this.

  [2] The method for producing expanded polypropylene resin particles according to [1], wherein the carbon black has a primary particle size of 10 nm to 50 nm.

  [3] Any one of [1] to [2], wherein a hydrophilic compound is contained in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin. The manufacturing method of the polypropylene resin expanded particle of description of claim | item.

  [4] The method for producing expanded polypropylene resin particles according to any one of [1] to [3], wherein the cell nucleating agent is a silicate compound.

  [5] In a molding space in which the expanded particles obtained by the method for producing expanded polypropylene resin particles according to any one of [1] to [4] can be closed by two molds but cannot be sealed. A method for producing a polypropylene resin foamed molded article, wherein the foamed particles are heated with water vapor through water vapor holes arranged in a mold.

  [6] The method for producing a polypropylene resin foam molded article according to [5], wherein the water vapor hole is a mold including a hole having a diameter of 0.5 mm to 2.0 mm.

  According to the polypropylene resin foamed particles obtained by a single foaming process by the production method of the present invention, the intergranular surface on the surface of the molded product is not affected even by a mold in which steam during heating is difficult to enter during foam molding. There can be obtained an in-mold foam-molded body having a small appearance, a high blackness of the molded body, a uniform color within the foamed particles and between the foamed particles and no color unevenness, and an excellent appearance.

It is an example of the DSC curve obtained when the polypropylene resin expanded particles of the present invention are heated at a rate of 10 ° C./min from 40 ° C. to 220 ° C. with a differential scanning calorimeter (DSC). Here, the melting peak calorific value on the low temperature side, which is the amount of heat surrounded by the tangent to the melting start baseline from the maximum point between the melting peak on the low temperature side and the low temperature side peak and the high temperature side peak, is Ql, the high temperature side of the DSC curve Qh is the high-temperature side melting peak calorie, which is the amount of heat surrounded by the tangent line from the maximum point between the melting peak, low-temperature side peak, and high-temperature side peak to the melting end baseline.

  A method for producing expanded polypropylene resin particles according to the present invention is a method for obtaining expanded polypropylene resin particles having an expansion ratio of 13 to 28 times in a single-stage expansion process, and comprises 100 parts by weight of polypropylene resin. And polypropylene resin particles in a closed container containing 2 to 5 parts by weight of carbon black having a primary particle size of 0 nm to 50 nm and a cell nucleating agent of 0.01 to 0.25 parts by weight. The polypropylene resin particles dispersed in an aqueous dispersion medium, impregnated with carbon dioxide as a foaming agent, and heated to a temperature equal to or higher than the softening temperature of the polypropylene resin particles are in a pressure range lower than the internal pressure of the hermetic container and 80 degrees. The polypropylene resin expanded particles are obtained by discharging into an atmosphere of 110 degrees or less.

  The polypropylene resin used as the base resin in the present invention is not particularly limited as long as it contains 50% by weight or more of propylene as the main component of the monomer. For example, propylene homopolymer, olefin-propylene random A copolymer, an olefin-propylene block copolymer, etc. are mentioned. These may be used alone or in combination of two or more.

  The copolymerizable olefin in the polypropylene resin used in the present invention is not particularly limited, and examples thereof include olefins having 2 or 4 carbon atoms. Specifically, ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1- Examples include α-olefins such as heptene, 3-methyl-1-hexene, 1-octene, and 1-decene, and cyclopentene, norbornene, and tetracyclo [6,2,11,8,13,6] -4- Cyclic olefins such as dodecene, dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, etc. Can be mentioned. In addition, these olefins having 2 or 4 or more carbon atoms may be used alone or in combination of two or more.

  Among these, ethylene or α-olefin is preferable and ethylene and 1-butene are most preferable from the viewpoint of availability, economy, and mechanical properties.

The copolymerizable olefin content in the polypropylene resin used in the present invention is preferably 0 to 10% by weight, more preferably 1 to 7% by weight, more preferably 1.5 to 6% by weight. % Or less is more preferable, and 1.5% by weight or more and 5% by weight or less is particularly preferable. When the copolymerizable olefin content in the polypropylene resin is within this range, the resulting polypropylene resin in-mold foam-molded product tends to have good mechanical strength and high dimensional stability at high temperatures.
In the polypropylene resin used in the present invention, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate are further included in the range not impairing the object of the present invention. , Vinyl monomers such as methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and divinyl benzene may be copolymerized.

 Among the above polypropylene resins, ethylene-propylene random copolymer and 1-butene-propylene random copolymer containing ethylene and 1-butene from the viewpoints of good foamability, improved cold brittleness resistance, and low cost. An ethylene-1-butene-propylene random copolymer can be suitably used.

  The melting point of the polypropylene resin used in the present invention is not particularly limited, but is preferably 130 ° C. or higher and 155 ° C. or lower, more preferably 140 ° C. or higher and 151 ° C. or lower. When the melting point of the polypropylene resin is in the above-described range, there is a tendency that an in-mold foam molded article having an excellent balance of dimensional properties, mechanical strength, and surface aesthetics is easily obtained.

  The melting point in the present invention refers to a polypropylene resin or polypropylene resin particles 1 mg to 10 mg heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter DSC, and then The peak temperature of the endothermic peak in the DSC curve obtained when cooling from 220 ° C. to 40 ° C. at a rate of temperature decrease of 10 ° C./min and increasing the temperature from 40 ° C. to 220 ° C. at a rate of temperature increase of 10 ° C./min. is there.

  The melt flow rate (hereinafter sometimes referred to as MFR) of the polypropylene resin used in the present invention is preferably 3.0 g / 10 min or more and 12 g / 10 min or less, more preferably 5.0 g / 10. Min. To 9.0 g / 10 min. When the melt flow rate of the polypropylene-based resin is in the above-described range, there is a tendency that an in-mold foam-molded product with little deformation and excellent surface aesthetics is easily obtained.

  The measurement of MFR in the present invention uses an MFR measuring instrument described in JIS K7210, under conditions of orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 ° C. It is a value when measured by.

  The polypropylene resin used in the present invention can be obtained using a catalyst such as a Ziegler catalyst, a metallocene catalyst, a post metallocene catalyst. When a Ziegler catalyst is used, a polymer having a large Mw / Mn tends to be obtained.

  The polypropylene resin used in the present invention can be adjusted in characteristics such as molecular weight and melt flow rate by oxidative decomposition using an organic peroxide. In order to oxidatively decompose the polypropylene resin, for example, a polypropylene resin added with an organic peroxide can be heated and melted in an extruder.

  Carbon black in the present invention has a primary particle size of more than 0 nm and 50 nm or less. More preferably, it is 10 nm or more and 50 nm or less. When the primary particle size exceeds 50 nm, the blackness of the obtained polypropylene resin-in-mold foam-molded product tends to decrease. Examples of such carbon black include channel black, roller black, disk, gas furnace black, oil furnace black, thermal black, acetylene black, and the like, and one or more of these can be used.

  The primary particle size of carbon black in the present invention was obtained by taking a photograph of a cross section of the cell membrane of the obtained polyolefin-based resin expanded particles magnified 40,000 times with a transmission electron microscope, and the obtained transmission electron micrograph. The particle diameters (Ferre diameter) in the X direction and the Y direction of 50 carbon black primary particles are measured arbitrarily, and the average value is calculated.

  The carbon black content is 2 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. More preferably, it is 2.5 parts by weight or more and 4 parts by weight or less. When content is less than 2 weight part, it exists in the tendency for the blackness of the polypropylene-type resin-in-mold foam-molding body obtained to fall. When content exceeds 5 weight part, it exists in the tendency for the intergranularity of the obtained polypropylene resin-type in-mold foam-molding body to occur easily.

  In the present invention, when producing resin particles containing carbon black, the carbon black is a polypropylene resin as a polyolefin resin in which carbon black is dispersed (hereinafter referred to as “carbon black masterbatch”). It is preferable to melt and knead together. Examples of the polyolefin resin used in the carbon black masterbatch include a polyethylene resin and a polypropylene resin, and a polypropylene resin is preferable. The polypropylene resin used for the carbon black masterbatch is selected from those listed above for the polypropylene resin used in the present invention, and preferably has an MFR of 3.0 g / 10 min or more and 15 g / 10 min or less. Preferably they are 5.0 g / 10min or more and 9.0 g / 10min or less. When the MFR is in this range, the kneading property with the polypropylene resin used in the present invention tends to be improved.

  The carbon black concentration in the carbon black masterbatch is preferably 5% by weight to 60% by weight, and more preferably 20% by weight to 50% by weight. A stabilizer or a lubricant may be added to the carbon black masterbatch.

  The carbon black masterbatch can be produced by melt-kneading a polyolefin resin and carbon black using an extruder, kneader, Banbury mixer, roll, or the like. It is particularly preferable to use an extruder.

  Examples of the cell nucleating agent used in the present invention include inorganic nucleating agents such as feldspar, zeolite, talc, kaolin, mica, calcium stearate, calcium carbonate, silica, titanium oxide, bentonite, and barium sulfate. These may be used alone or in combination of two or more. Among these cell nucleating agents, silicate compounds such as feldspar, zeolite, talc, kaolin and mica are preferable, and talc is more preferable. When a silicate compound is used as the cell nucleating agent, an in-mold foam molded article having high blackness and few intergranularity is easily obtained.

  The content of the cell nucleating agent in the present invention is preferably 0.01 parts by weight or more and 0.25 parts by weight or less, more preferably 0.01 parts by weight with respect to 100 parts by weight of the polypropylene resin. The content is 0.2 parts by weight or less. When the content of the cell nucleating agent is less than 0.01 parts by weight, it is difficult to obtain an in-mold foam-molded product having a uniform color. In addition, there is a risk that the degree cannot be expressed, and intergranularity tends to occur.

  In the method for producing polypropylene resin expanded particles of the present invention, first, polypropylene resin particles are produced.

  Examples of the method for producing the polypropylene resin particles in the present invention include the following methods.

  First, a polypropylene resin, carbon black, a cell nucleating agent, and, if necessary, a mixture of other additives are mixed by a mixing method such as a dry blend method or a master batch method.

  Next, the resulting mixture is melt-kneaded using an extruder, kneader, Banbury mixer (registered trademark), roll, etc., and then chopped using a cutter, pelletizer, etc., to obtain a particle shape, thereby producing a polypropylene system Resin particles are obtained.

  The polypropylene resin particles of the present invention can contain a hydrophilic compound, an antioxidant, an antistatic agent, a flame retardant, and the like as necessary. Such an additive may be preliminarily added to another resin in a high concentration to form a master batch, and this master batch resin may be added to the polypropylene resin. As a resin used for such a masterbatch resin, a polyolefin resin is preferable, and a masterbatch is more preferable with a polypropylene resin.

  In the present invention, when the polypropylene resin particles contain a hydrophilic compound, water in the aqueous dispersion medium also acts as a foaming agent, which contributes to an improvement in the expansion ratio. The hydrophilic compound used in the present invention is a water-absorbing ionic compound such as sulfate, borate or carbonate, or a hydrophilic group such as carboxyl group, hydroxyl group, amino group, sulfo group or polyoxyethylene group in the molecule. A compound containing a functional group or a derivative thereof, including a hydrophilic polymer. Specifically, examples of the compound containing a carboxyl group include lauric acid and sodium laurate, and examples of the compound containing a hydroxyl group include ethylene glycol and glycerin. Other hydrophilic organic compounds include organic compounds having a triazine ring such as melamine (chemical name: 1,3,5-triazine-2,4,6-triamine), isocyanuric acid, and isocyanuric acid condensate. . These may be used alone or in combination of two or more.

    The hydrophilic polymer is a polymer having a water absorption rate of 0.5% by weight or more measured according to ASTM D570, and is a so-called hygroscopic polymer, several times to several times its own weight without dissolving in water. It includes a water-absorbing polymer that absorbs water 100 times and is difficult to dehydrate even under pressure, and a water-soluble polymer that dissolves in water at 15 ° C. or higher.

Specific examples of the hydrophilic polymer include, for example, ethylene-acrylic acid-maleic anhydride terpolymers, carboxylic acid groups of ethylene- (meth) acrylic acid copolymers, alkali metal ions such as sodium ions and potassium ions. Ionomer resins that are neutralized with transition metal ions such as zinc ions and crosslinked between molecules;
Carboxyl group-containing polymers such as ethylene- (meth) acrylic acid copolymers;
Polyamides such as nylon-6, nylon-6,6, copolymer nylon;
Nonionic water-absorbing polymers such as polyethylene glycol and polypropylene glycol;
Polyether-polyolefin resin block copolymer represented by perstat (trade name, manufactured by Sanyo Chemical Co., Ltd.)
Cross-linked polyethylene oxide polymers represented by Aqua Coke (trade name, manufactured by Sumitomo Seika Co., Ltd.) and the like. These may be used alone or in combination of two or more.

  Among these hydrophilic polymers, nonionic water-absorbing polymers and polyether-polyolefin resin block copolymers have relatively good dispersion stability in a pressure-resistant container, and absorb water when added in a relatively small amount. It is preferable because it exhibits its properties.

  Among these hydrophilic compounds, glycerin, polyethylene glycol, polypropylene glycol, and melamine are preferable because the effects of the present invention are great.

  The content of the hydrophilic compound in the polypropylene resin expanded particles of the present invention is preferably 0.01 parts by weight or more and 10 parts by weight or less, and 0.03 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the polypropylene resin. Is more preferable, and 0.05 to 1 part by weight is even more preferable. When the content of the hydrophilic compound is in this range, the expansion ratio is likely to be improved, and the appearance and mechanical properties of the obtained in-mold foam molded product are likely to be good.

  The weight per one polypropylene resin particle in the present invention is preferably 0.2 mg or more and 10 mg or less, and more preferably 0.5 mg or more and 6.0 mg or less. When the weight per polypropylene resin particle is within the above range, the dimensions and filling properties of the obtained in-mold foam-molded product tend to be good.

  Here, the weight per one polypropylene resin particle is the average resin particle weight obtained from 100 particles of randomly selected polypropylene resin particles.

  Usually, the composition and particle weight of the polypropylene resin particles are hardly changed even after the foaming process and the in-mold foam molding process, and the same properties are exhibited even when the foam particles and the in-mold foam molding are remelted.

  In the present invention, polypropylene-based resin expanded particles are produced using the polypropylene-based resin particles thus obtained.

  Carbon dioxide is mainly used as the foaming agent in the present invention. By using carbon dioxide among the inorganic gas foaming agents having a small environmental load, a polypropylene resin in-mold foam molded article having a good appearance can be obtained.

  As the foaming agent used in the present invention, an inorganic gas such as air, nitrogen, oxygen, etc. may be used in combination as long as the quality of the obtained foamed polypropylene resin mold is not impaired. For example, air remaining in a sealed container used for foaming hardly affects the quality of the obtained foamed molded product in a polypropylene resin mold, and may be used in combination.

  In the production method of the present invention, polypropylene resin particles are dispersed in an aqueous dispersion medium in a closed container, impregnated with carbon dioxide as a foaming agent, and heated to a temperature equal to or higher than the softening temperature of the polypropylene resin particles. The particles are released into a pressure range lower than the internal pressure of the sealed container to obtain polypropylene-based resin expanded particles. Such a process may be referred to as a “single-stage foaming process”.

  In one embodiment of the present invention, “more than the softening temperature of polypropylene resin particles” means that the melting point of the polypropylene resin used is −10 ° C. or more. The foaming temperature is not particularly limited, and may be any temperature as long as it is equal to or higher than the softening temperature of the polypropylene resin particles, and is not particularly limited. For example, the melting point of the polypropylene resin used is -10 ° C or higher and melting point + 10 ° C or lower. Is preferred.

  In the present invention, the temperature of the atmosphere to be discharged is heated with water vapor or the like and adjusted to 80 ° C. or higher and 110 ° C. or lower. More preferably, it is 80 degreeC or more and 105 degrees C or less. When the temperature exceeds 110 ° C., high-pressure steam is required, a special device is required to adjust the foaming atmosphere temperature, and the crystallization of the polypropylene resin is slowed down, so that appropriate foamed particles can be formed. There is a risk of not. When the temperature is lower than 80 ° C., color unevenness and intergranularity of the obtained polypropylene resin-in-mold foam-molded product tend to deteriorate.

  The pressure for impregnating the foaming agent in the closed container in the present invention is preferably about 1.5 MPa (gauge pressure) or more and 5.0 MPa or less (gauge pressure), and more preferably about 1.5 MPa (gauge pressure) or more. More preferably, it is 3 MPa or less (gauge pressure). When the foaming pressure is in this range, it is easy to obtain an in-mold foam molded article having a good appearance.

  Specific examples of the “one-stage foaming step” in the method for producing polypropylene-based resin expanded particles in the present invention include the following methods.

  (1) After charging polypropylene-based resin particles, an aqueous dispersion medium, and a dispersing agent as necessary into a sealed container, the inside of the sealed container is evacuated as necessary, and then carbon dioxide as a foaming agent is put into the sealed container. And then heated to a temperature higher than the softening temperature of the polypropylene resin. The amount of carbon dioxide, which is a foaming agent, is adjusted so that the pressure in the sealed container rises to about 1.5 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure) by heating. If necessary, after heating, add carbon dioxide, which is a foaming agent, to adjust to the desired foaming pressure, and further finely adjust the foaming temperature, hold for more than 0 minutes and 120 minutes or less. Then, it is discharged into a pressure region (usually atmospheric pressure) lower than the internal pressure of the sealed container adjusted to 80 ° C. or higher and 110 ° C. or lower with water vapor or the like to obtain polypropylene resin expanded particles.

  Examples of the method of introducing a foaming agent different from the above in the present invention include the following methods.

  (2) A method in which a foaming agent is introduced by charging solid carbon dioxide in the form of dry ice at the same time as charging polypropylene resin particles, an aqueous dispersion medium, and a dispersant as required.

  (3) After charging polypropylene resin particles, aqueous dispersion medium, and dispersing agent, if necessary, in a sealed container, the inside of the sealed container is evacuated and then the softening temperature of the polypropylene resin or higher. A method of introducing a foaming agent while heating to a temperature of.

  (4) In a closed container, polypropylene resin particles, an aqueous dispersion medium, and a dispersant as required are charged, and then, if necessary, the inside of the closed container is evacuated and heated to near the foaming temperature. A method of introducing a blowing agent at this point.

  Examples of the method for increasing the expansion ratio of the expanded polypropylene resin particles include a method for increasing the internal pressure in the sealed container, a method for increasing the pressure release speed, and a method for increasing the temperature in the sealed container before discharge.

  As the aqueous dispersion medium used in the present invention, it is preferable to use only water, but a dispersion medium in which methanol, ethanol, ethylene glycol, glycerin or the like is added to water can also be used.

  The sealed container used in the present invention is not particularly limited, and may be any container that can withstand the pressure in the container and the temperature in the container at the time of producing the expanded particles, and examples thereof include an autoclave type pressure resistant container.

  In the method for producing polypropylene-based expanded particles in the present invention, it is preferable to use a dispersant in the aqueous dispersion medium in order to prevent coalescence of the polypropylene-based resin particles.

  Examples of the dispersant used in the present invention include inorganic dispersants such as tricalcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay.

  These dispersants may be used alone or in combination of two or more.

  In the method for producing polypropylene-based expanded particles in the present invention, it is preferable to use a dispersion aid together with the dispersant.

As an example of the dispersion aid used in the present invention, for example,
Carboxylate types such as N-acyl amino acid salts, alkyl ether carboxylates, acylated peptides;
Sulfonate types such as alkyl sulfonates, n-paraffin sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, sulfosuccinates;
Sulfate ester types such as sulfated oil, alkyl sulfate, alkyl ether sulfate, alkyl amide sulfate, alkyl allyl ether sulfate;
Anionic surfactants such as phosphate ester types such as alkyl phosphates and polyoxyethylene phosphates can be mentioned.

  In addition, as dispersion aids, polyanionic polymer surfactants such as maleic acid copolymer salts and polyacrylates, polystyrene anion salts such as polystyrene sulfonates and naphthalsulfonic acid formalin condensate salts are used. Molecular surfactants can also be used.

  These dispersing aids may be used alone or in combination of two or more.

  Among these, at least one selected from the group consisting of tricalcium phosphate, magnesium triphosphate, barium sulfate or kaolin as a dispersing agent, and n-paraffin sulfonic acid soda and alkylbenzene sulfonic acid as a dispersing aid. It is preferable to use at least one selected in combination.

  The amount of the dispersant and the dispersion aid used in the present invention varies depending on the type and the type and amount of the polypropylene resin particles to be used. Usually, the dispersant is 0.1 weight with respect to 100 parts by weight of the aqueous dispersion medium. It is preferable to blend 3 parts by weight or more and 3 parts by weight or less, and it is preferable to blend 0.001 part by weight or more and 0.1 parts by weight or less of the dispersion aid.

  In order to improve the dispersibility in the aqueous dispersion medium, the polypropylene resin particles are usually preferably used in an amount of 20 to 100 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium.

  The closed cell ratio of the polypropylene resin expanded particles of the present invention is preferably 88% or more, and more preferably 93% or more. When the closed cell ratio of the polypropylene resin foamed particles is less than 88%, internal gas tends to flow out of the foamed particles at the time of in-mold foam molding, and the deformation after molding tends to increase.

  Here, the closed cell ratio is calculated by calculating the closed cell volume of the polypropylene resin expanded particles using an air comparison type hydrometer, and dividing the closed cell volume by the apparent volume separately obtained by the ethanol immersion method. Is the value to be

  The expanded polypropylene resin particles of the present invention are obtained when 5-6 mg of expanded polypropylene resin particles are heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min in measurement by differential scanning calorimetry. It is preferable to have two melting peaks in the DSC curve.

  The expanded polypropylene resin particles of the present invention preferably have a DSC ratio of 10% to 50%, more preferably 15% to 30%. When the DSC ratio is within this range, a polypropylene resin-in-mold foam-molded product having a high surface beauty is easily obtained.

  Here, as shown in FIG. 1, the DSC ratio is the amount of heat surrounded by a tangent line from the melting point on the low temperature side and the maximum point between the low temperature side peak and the high temperature side peak to the melting start baseline. The melting peak calorific value is Ql, and the high temperature side melting peak calorific value is Qh, which is the amount of heat surrounded by the tangent line from the maximum point between the melting peak on the high temperature side of the DSC curve and the low temperature side peak to the high temperature side peak. The ratio of the melting peak on the high temperature side [Qh / (Ql + Qh) × 100] calculated from these.

  Since the DSC ratio changes depending on the temperature and pressure at the time of foaming when producing the polypropylene resin foamed particles, the foamed particles having the desired DSC ratio can be obtained by appropriately adjusting the foaming temperature and the foaming pressure. Can be obtained. In general, the DSC ratio tends to decrease as the foaming temperature and foaming pressure increase, and it depends on the type of polypropylene resin, additive, and type of foaming agent. When the temperature is increased by 1 ° C., the DSC ratio decreases by about 5 to 20%, and when the foaming pressure is increased by 0.1 MPa, the DSC ratio decreases by about 0.5 to 5%.

  The expansion ratio of the polypropylene resin expanded particles obtained by the above production method is 13 times or more and 28 times or less, and more preferably 16 times or more and 24 times or less. When the expansion ratio is less than 13 times, it is not necessary to use the technique of the present invention. When the expansion ratio exceeds 28 times, the mechanical strength of the in-mold foam obtained is weak and the blackness tends to decrease.

  Here, the expansion ratio of the expanded polypropylene resin particles refers to the weight w (g) of expanded polypropylene resin particles, which is then submerged in a graduated cylinder containing ethanol, and the water level rise (submerged method) of the graduated cylinder. The volume v (cm 3) was measured, and the true specific gravity ρb = w / v of the polypropylene resin foamed particles was calculated, and further calculated as the ratio (ρr / ρb) with the density ρr of the polypropylene resin particles before foaming. Value.

  The average cell diameter of the expanded polypropylene resin particles of the present invention is preferably from 100 μm to 500 μm, and more preferably from 120 μm to 400 μm. When the average cell diameter of the expanded polypropylene resin particles is within the range, the appearance of the obtained expanded foam in the polypropylene resin mold tends to be good.

  Here, the average bubble diameter is a value measured as follows.

  In an image obtained by microscopic observation of the cut surface of the foamed particle, a straight line passing through substantially the center of the foamed particle is drawn, and the foamed particle is determined from the number of bubbles n passing through the straight line and the intersection of the straight line and the surface of the foamed particle The diameter L (μm) is read and obtained by the equation (1).

Average bubble diameter (μm) = L / n (1)
The method for producing an in-mold foam molded body from the foamed particles according to the present invention includes filling a polypropylene resin foamed particle in a mold that can be closed but cannot be sealed, and heating with steam or the like to mutually connect the foamed particles. This is a method of forming by heating and fusing, forming according to the mold, cooling with a coolant such as water and taking out, and obtaining an in-mold foam molded article.

  It is preferable that the polypropylene-based resin expanded particles apply a pressure equal to or higher than the atmospheric pressure inside the expanded particles before in-mold foam molding. In-mold foam molding using foam particles to which pressure equal to or higher than the atmospheric pressure is applied to the inside of the foam particles makes it easy to obtain a polypropylene resin in-mold foam molded article having no intergranularity and a beautiful surface and little deformation. Although there is no restriction | limiting in particular in the method of providing the pressure more than atmospheric pressure inside a foamed particle, For example, a pressure can be provided inside a foamed particle by methods, such as the conventionally known internal pressure provision method and the compression filling method.

  In the internal pressure application method, a polypropylene resin expanded particle is previously held under pressure of an inorganic gas to apply an internal pressure of atmospheric pressure or higher to the expanded particle, and the expanded particle to which the internal pressure is applied can be closed but is not sealed. Fill the molding space such as a mold.

  The internal pressure is preferably from 0.12 MPa (absolute pressure) to 0.40 MPa (absolute pressure), more preferably from 0.14 MPa (absolute pressure) to 0.30 MPa (absolute pressure). When the internal pressure of the polypropylene resin expanded particles is within the above range, it tends to be easy to obtain an in-mold expanded molded article having a beautiful appearance. As the inorganic gas used for applying the internal pressure, air, nitrogen, helium, neon, argon, carbon dioxide or the like can be used. These gases may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  In the compression filling method, polypropylene resin foam particles are compressed in a compression tank using a pressurized gas, preferably to a bulk density of 1.25 to 3 times the bulk density of the foam particles before filling, more preferably before filling. The foamed particles are compressed to a bulk density of 1.5 to 2.2 times the bulk density, and the compressed foamed particles are filled in a molding space such as a mold that can be closed but not sealed.

  When the compression ratio is within the above range, it tends to be easy to obtain an in-mold foam molded article having a beautiful appearance.

  As the pressurized gas used for the compression, air, nitrogen, helium, neon, argon, carbon dioxide or the like can be used. These gases may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  After filling polypropylene resin expanded particles into a mold or the like by the above method, heating is performed for about 3 to 50 seconds at a heating water vapor pressure of about 0.15 to 0.4 MPa (G) using water vapor or the like as a heating medium. After molding with time and fusing the polypropylene resin foamed particles, the mold is cooled by water cooling, and then the mold is opened to obtain a foam in a polypropylene resin mold.

  In addition, when heating using water vapor | steam, it is preferable to raise pressure over the time for about 5 to 30 seconds until it sets it as the target heating water vapor pressure.

  When water vapor is used for in-mold foam molding, the mold to be used does not allow the foam particles to pass through, but water vapor holes that allow air or water vapor to pass therethrough are disposed, and the foam particles in the mold are heated. Since foaming is performed in the mold by in-mold foam molding, the shape of the water vapor holes is also transferred to the surface of the in-mold foam molded body.

  As the water vapor hole, it is easy to secure the air flow rate, so it is slit type (slit width of about 0.5 mm to 2.0 mm, about 3 to 8 slits) or lotus root type (hole diameter of about 0.5 mm to 2.0 mm). In general, the core vent (about 5 to 15 mm in diameter) having a number of holes of about 5 to 25 is arranged in the mold, but for the purpose of making the water vapor holes transferred to the surface of the in-mold foamed body inconspicuous. In some cases, a mold having a drill hole is used. When the drill hole is disposed as a water vapor hole, the amount of air flow is reduced, and water vapor during heating is less likely to enter the mold.

  In particular, in the foamed particles obtained by the production method of the present invention, even when using a mold in which water vapor does not easily enter into a mold including a drill hole as a water vapor hole, there are few intergranular surfaces on the surface of the molded body, and blackness Can be suitably used because an in-mold foam molded article can be obtained.

  Although it will not specifically limit if the diameter of the drill hole arrange | positioned at a metal mold | die is a diameter which does not let foam | bubble particle | grains pass but air and water vapor | steam, 0.5 mm or more and 2.0 mm or less are preferable. When in this range, the in-mold foam moldability is hardly impaired, and the shape of the transferred water vapor holes tends to be inconspicuous.

  Next, although the polypropylene resin expanded particle of this invention and its manufacturing method are demonstrated in detail, giving an Example and a comparative example, it is not limited to these.

In the examples and comparative examples, the substances used were as follows, but were used without any particular purification.
○ Polypropylene resin (commercially available or resin manufacturer's sample)
Polypropylene resin 1: ethylene-propylene random copolymer [MFR = 7.5 g / 10 min, melting point 146.1 ° C.]
Polypropylene resin 2: ethylene-propylene random copolymer [MFR = 7.0 g / 10 min, melting point 150.6 ° C.]
Polypropylene resin 3: ethylene-1-butene-propylene random copolymer [MFR = 6.7 g / 10 min, melting point 143.0 ° C.]
Carbon black Carbon blacks A, B, and C were used as carbon black master batches containing 40% by weight of carbon black A, B, and C, respectively, in a polypropylene resin (MFR = 7.5 g / 10 minutes). In Table 1, the average particle system of carbon black in the obtained expanded particles is also shown.
○ Other additives, glycerin [manufactured by Lion Corporation, purified glycerin D]
-Polyethylene glycol [Lion Corporation, average molecular weight 300]
・ Talc [manufactured by Hayashi Kasei Co., Ltd., Talcan powder PK-S]

The evaluation methods implemented in the examples and comparative examples will be described.
<Particle size of carbon black>
The photograph which expanded the cross section of the cell membrane of the obtained polyolefin resin expanded particle 40,000 times with the transmission electron microscope was image | photographed. In the obtained transmission electron micrograph, arbitrarily measure the particle diameter (Ferre diameter) in the X direction and Y direction for 50 carbon black primary particles, respectively, calculate the average value, did.

<Measurement of expansion ratio>
The obtained expanded polypropylene resin particles were dried at 60 ° C. for 2 hours and allowed to stand in a room at a temperature of 23 ° C. and a humidity of 50% for 1 hour, and then the weight w (g) was measured. The volume v (cm3) was measured, and the true specific gravity ρb = w ÷ v of the expanded particles was calculated.
Then, the expansion ratio = ρr ÷ ρb was calculated from the ratio with the density ρr of the polyethylene resin particles before foaming.

<DSC ratio of expanded particles>
Obtained when 5-6 mg of polypropylene resin expanded particles are heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min using a differential scanning calorimeter [DSC6200 type, manufactured by Seiko Instruments Inc.] The DSC curve (illustrated in FIG. 1) has two peaks, and was calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side of the melting peak by the following equation.
DSC ratio = Qh / (Ql + Qh) × 100

<Blackness of the entire in-mold foam molding>
The surface of the obtained in-mold foam molded body (300 mm × 400 mm surface formed from a mold surface in which water vapor holes described later are drill holes) is scanned by a printer complex machine (iR-ADV C5035, manufactured by Canon Inc.). RGB analysis was carried out using image processing software (DIBAS32) for the entire range of the 300 mm × 400 mm surface of the obtained image.
About the mode value (measured value) of the total RGB of the obtained molded body surface, black 0 (100%), white 255 (0%) are used as a reference, and the numerical value is converted into blackness by the following formula to obtain the following reference. Judged.
Blackness (%) of in-mold foam molded product = (255−measured value) / 255 × 100
○: Blackness is 88% or more (high blackness)
X: Blackness is less than 88%

<Color unevenness of in-mold foam molding>
In the evaluation of “the blackness of the entire in-mold foam molding”, the in-mold foam molding was visually observed and evaluated according to the following criteria.
○: The black color of the in-mold foam molding is uniform, and there is almost no unevenness in the color within the foam particles and between the foam particles. ×: The black color of the in-mold foam molding is uneven, and grayish parts are scattered. No evaluation due to low blackness

<Granularity of in-mold foam molding>
The surface of the obtained in-mold foam molding was visually observed and evaluated according to the following criteria.
○: Almost no intergranularity is found Δ: Small intergranularity is scattered ×: Many small intergranularities exist or large interstitial intergranularity exists

Example 1
[Production of polypropylene resin particles]
Polypropylene resin A is used as the polypropylene resin, and 4 parts by weight of carbon black A, 0.2 part by weight of glycerin, and 0.05 part by weight of talc as a cell nucleating agent with respect to 100 parts by weight of polypropylene resin. And dry blended. The dry blended mixture was melt-kneaded at a resin temperature of 220 ° C. using a twin-screw extruder [manufactured by Toshiba Machine Co., Ltd., TEM26-SX], and the extruded strand was water-cooled in a 2 m long water tank. Cut to produce polypropylene resin particles (1.2 mg / grain).

[Production of polypropylene resin single-stage expanded particles]
In a pressure-resistant autoclave having a capacity of 10 L, 100 parts by weight (2.4 kg) of the obtained polypropylene resin particles, 200 parts by weight of water, and tribasic calcium phosphate as a poorly water-soluble inorganic compound [manufactured by Taihei Chemical Industry Co., Ltd.] 5 parts by weight, sodium alkyl sulfonate (sodium n-paraffin sulfonate) as a surfactant (0.03 parts by weight, manufactured by Kao Corporation, Latemuru PS), and carbon dioxide as a foaming agent under stirring 5 parts by weight were added.

  The autoclave contents were heated and heated to a foaming temperature of 152.0 ° C. shown in Table 1. Thereafter, carbon dioxide as a foaming agent was additionally injected, and the internal pressure of the autoclave was increased to the foaming pressure of 2.8 MPa described in Table 1. After maintaining at the foaming temperature and foaming pressure for 30 minutes, the valve at the bottom of the autoclave is opened, and the autoclave contents are discharged into an atmosphere adjusted to 95 ° C. with water vapor through an opening orifice (1 hole) having a diameter of 3.6 mm. Thus, expanded polypropylene resin particles were obtained.

  About the obtained polypropylene resin foamed particles, the expansion ratio and DSC ratio were measured. The results are shown in Table 1.

[Production of foamed molded product in polypropylene resin mold]
The obtained expanded particles were washed with an aqueous hydrochloric acid solution having a pH of 1, followed by water for 30 seconds each, and dried at 75 ° C. The foamed foam particles after washing are put into a pressure-resistant container, impregnated with pressurized air, and expanded in advance to have a foamed particle internal pressure of 0.20 MPa (absolute pressure). X Filled in a 50 mm thick mold. The inside of the mold chamber was heated with water vapor for 10 seconds. Thereafter, the exhaust valve was closed and heated with water vapor for 18 seconds (main heating step), thereby further expanding the expanded particles and fusing the expanded particles together. The set pressure in this heating step was 0.30 MPa (gauge pressure), and the holding time at the set pressure was 12 seconds out of the heating time of 18 seconds. Subsequently, water vapor was exhausted, and the inside of the mold and the surface of the molded body were cooled with water, and then the molded body was taken out to obtain a polypropylene resin foam molded body. As for the water vapor hole of the mold, one surface of 300 mm × 400 mm has a 1 mm diameter drill hole arranged at intervals of 9 mm vertically and horizontally, and the other five surfaces have a diameter of 10 mm having six 1 mm wide slits in the vertical direction. A mold having core vents arranged at intervals of 24 mm was used.

  The obtained in-mold foam molded product was allowed to stand at 23 ° C. for 2 hours, then cured at 75 ° C. for 16 hours, and then allowed to stand in a room at 23 ° C. for 4 hours. Evaluation was carried out. The results are shown in Table 1.

(Examples 2 to 10, Comparative Examples 1 to 9)
In [Preparation of polypropylene resin particles], the types and mixing amounts of the polypropylene resin and additives were changed as shown in Table 1, and in [Preparation of polypropylene resin foam particles], the foaming agent, foaming temperature, foaming pressure were changed. Except that the release atmosphere temperature was changed as shown in Table 1, polypropylene resin particles, polypropylene resin expanded particles, and a polypropylene resin in-mold foam molded article were produced in the same manner as in Example 1.

  Table 1 shows the evaluation results of the obtained polypropylene resin foamed particles and the polypropylene resin in-mold foam molded product.

(Reference Example 1)
Using the expanded particles prepared in Comparative Example 3, in [Preparation of foamed molded product in polypropylene resin mold], a core vent having a diameter of 10 mm having six 1 mm wide slits in the vertical direction on all six surfaces of the water vapor holes. Except using the metal mold | die arrange | positioned at a space | interval of 24 mm, the polypropylene resin resin in-mold foam molding was produced by operation similar to Example 1. The shape of the water vapor holes was transferred to the entire surface, and although the water vapor holes were conspicuous, there was obtained an in-mold foam molded product having a small intergranularity, a high blackness, and a uniform color.

  As can be seen from Examples 1 to 10, when the polypropylene resin expanded particles obtained by the production method of the present invention are used, even when using a mold in which steam during heating is difficult to enter during in-mold foam molding. An in-mold foam-molded product having a small intergranularity, high blackness, and uniform color can be obtained. On the other hand, as in Comparative Example 1, when the foaming atmosphere temperature is low, the blackness is high, but the color unevenness evaluation and the intergranular evaluation are inferior. When the cell nucleating agent was not added as in Comparative Example 6, the blackness was high and the intergranular evaluation was excellent, but the color unevenness evaluation was inferior. As in Comparative Examples 2 and 7, when the carbon black amount is within the range of the present invention and the carbon black particle size is large, when the carbon black amount is small, the intergranular evaluation is excellent, but the blackness evaluation is inferior. When the carbon black content is increased as in Comparative Examples 3, 4, and 6, when the amount of talc as the cell nucleating agent is large, the blackness evaluation and color unevenness evaluation are excellent, but the intergranular evaluation is inferior. I understand. When the expansion ratio of the expanded particles is high as in Comparative Examples 8 and 9, when nitrogen is used as the foaming agent, the blackness evaluation and the intergranular evaluation are inferior.

Claims (6)

  A production method for obtaining expanded polypropylene resin particles having an expansion ratio of 13 times or more and 28 times or less in a one-stage foaming process, wherein carbon black having a primary particle size of greater than 0 nm and less than 50 nm is obtained with respect to 100 parts by weight of the polypropylene resin. Polypropylene resin particles containing 2 parts by weight or more and 5 parts by weight or less and a cell nucleating agent of 0.01 parts by weight or more and 0.25 parts by weight or less are dispersed in an aqueous dispersion medium in a closed container, and carbon dioxide is used as a foaming agent. And releasing the polypropylene resin particles heated to a temperature equal to or higher than the softening temperature of the polypropylene resin particles into a pressure range lower than the internal pressure of the hermetic container and in an atmosphere of 80 degrees to 110 degrees. A method for producing expanded polypropylene resin particles, which obtains expanded resin particles.   The method for producing expanded polypropylene resin particles according to claim 1, wherein the carbon black has a primary particle size of 10 nm to 50 nm.   The polypropylene resin foam according to any one of claims 1 to 2, comprising a hydrophilic compound in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin. Particle production method.   The method for producing expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the cell nucleating agent is a silicate compound.   The foamed particles obtained by the method for producing polypropylene-based resin foamed particles according to any one of claims 1 to 4 are filled in a molding space that can be closed but cannot be sealed by two molds, A method for producing a polypropylene resin foamed molded article, wherein the foamed particles are heated with water vapor through water vapor holes arranged in a mold.   The method for producing a polypropylene resin foam molded article according to claim 5, wherein the water vapor hole is a mold including a drill hole having a diameter of 0.5 mm or more and 2.0 mm or less.

Images