Method for manufacturing a foamed blow-molded article, and the foamed blow-molded article

Abstract

To provide a method for manufacturing a foam blow molding excellent in cold impact resistance, rigidity and surface flatness, and the foam blow molding.SOLUTION: In a method for manufacturing a foam blow molding, the method includes blow molding a foamed parison formed by foaming a mixed resin of a polyolefin-based resin (A) and an olefin-based thermoplastic elastomer (B), wherein the polyolefin-based resin (A) consists of branched homopolypropylene (a1) and linear block polypropylene (a2), and a mass ratio of branched homopolypropylene (a1) to linear block polypropylene (a2) [(a1):(a2) ] is 50:50 to 93:7, and the olefin thermoplastic elastomer (B) is a hydrogenated product of a triblock copolymer consisting of a crystalline olefin polymer block and a conjugated diene compound polymer block. In the mixed resin, an amount of the olefin thermoplastic elastomer (B) based on 100 pts.mass of the polyolefin-based resin (A) is 20 pts.mass or more and 40 pts.mass or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a foamed blow-molded article, and to a foamed blow-molded article. [Background technology]

[0002] A foam blow-molded article is known, which is formed by shaping a foam parison formed from a foamable resin melt containing a base resin. Among the foam blow-molded articles, hollow molded articles using a polyolefin resin as the base resin have been used in various applications, such as air conditioning ducts (hereinafter referred to as "ducts") in automobiles, etc., from the viewpoint of light weight, etc.

[0003] In recent years, there has been a demand for foamed blow-molded articles that have improved cold impact resistance while maintaining or improving their light weight. Cold impact resistance refers to the impact resistance of a foamed blow-molded article at low temperatures. Patent Documents 1 and 2 disclose a technique for adding an elastomer to a polypropylene resin to improve the cold impact resistance of a foamed blow-molded article. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 059112 [Patent Document 2] Japanese Patent Application Publication No. 2018-141031 Summary of the Invention [Problem to be solved by the invention]

[0005] The techniques disclosed in Patent Documents 1 and 2 leave room for improvement in terms of cold impact resistance and rigidity of the foamed blow-molded article. Furthermore, the techniques of Patent Documents 1 and 2 leave room for improvement in terms of improving the surface smoothness (hereinafter, unless otherwise specified, simply referred to as surface smoothness) of the inner peripheral surface of the foamed blow-molded article when the foamed blow-molded article is a hollow molded article.

[0006] An object of the present invention is to provide a method for producing a blow-molded foam having excellent cold impact resistance, rigidity and surface smoothness, and to provide the blow-molded foam. [Means for solving the problem]

[0007] The present invention is summarized as follows: (1) to (5).

[0008] (1) A method for producing a foamed blow-molded article, comprising a step of blow-molding a foamed parison obtained by foaming a mixed resin of a polyolefin-based resin (A) and an olefin-based thermoplastic elastomer (B), the polyolefin resin (A) comprises a branched homopolypropylene (a1) and a linear block polypropylene (a2), and the mass ratio of the branched homopolypropylene (a1) to the linear block polypropylene (a2) [(a1):(a2)] is 50:50 to 93:7; the olefin-based thermoplastic elastomer (B) is a hydrogenated triblock copolymer consisting of a crystalline olefin polymer block and a conjugated diene compound polymer block, The method for producing a foamed blow-molded article, wherein the mixed resin contains the olefin-based thermoplastic elastomer (B) in an amount of 20 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the polyolefin-based resin (A). (2) The melting point of the olefin-based thermoplastic elastomer (B) is 80°C or higher and 100°C or lower. A method for producing the foamed blow-molded article according to (1) above. (3) The linear block polypropylene (a2) has a flexural modulus of 1000 MPa or more and 1500 MPa or less. A method for producing the foamed blow-molded article according to (1) or (2) above. (4) The melt flow rate of the olefin-based thermoplastic elastomer (B) (at 230°C under a load of 2.16 kg) is 1 g / 10 min or more and 10 g / 10 min or less. A method for producing the foamed blow-molded article according to (1) or (2) above. (5) A foamed blow molded article of a mixed resin of a polyolefin resin (A) and an olefin thermoplastic elastomer (B), the polyolefin resin (A) comprises a branched homopolypropylene (a1) and a linear block polypropylene (a2), and the mass ratio of the branched homopolypropylene (a1) to the linear block polypropylene (a2) [(a1):(a2)] is 50:50 to 93:7; the olefin-based thermoplastic elastomer (B) is a hydrogenated triblock copolymer consisting of a crystalline olefin polymer block and a conjugated diene compound polymer block, The foamed blow-molded article, wherein the blending amount of the olefin-based thermoplastic elastomer (B) per 100 parts by mass of the polyolefin-based resin (A) is 20 parts by mass or more and 40 parts by mass or less. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for producing a blow-molded foam having excellent cold impact resistance, rigidity, and surface smoothness, and to provide the blow-molded foam. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in the following order: 1. A method for producing a foamed blow-molded article, and 2. A foamed blow-molded article. Note that the present invention is not limited to the embodiments and the like described below.

[0011] [1. Manufacturing method of foam blow molded product] The manufacturing method according to the present invention is a manufacturing method for a foamed blow-molded article including a blow molding step. The following continues to explain one embodiment of the manufacturing method for a foamed blow-molded article according to the present invention.

[0012] [1-1 Manufacturing method details] (Extrusion foaming process) Inside the extruder, the mixed resin and the blowing agent are kneaded to obtain a foamable resin melt. The obtained foamable resin melt is extruded from a die connected to the extruder. A circular die is usually used as the die. A molding die is arranged directly below the die, and the foamable resin melt is extruded into the molding die. At this time, a foam parison is formed. The molding die has a desired internal shape depending on the molded product to be obtained. The molding die is usually a split mold.

[0013] (Pre-blow process) The foam parison is in a softened state immediately after the extrusion foaming process. The bottom of the softened foam parison is closed using a pinch or the like, and gas is blown into the foam parison to increase the internal pressure of the foam parison. This causes the foam parison to expand. During or after the pre-blowing process, the foam parison is clamped in a mold.

[0014] (Blow molding process) The blow molding process is a process in which a foamed parison formed by foaming a base resin is sandwiched between a mold and gas is blown into the foamed parison. At this time, the outer surface of the foamed parison is pressed against the inner surface of the mold, and the foamed parison is shaped into a hollow shape. This produces a foamed blow-molded article. As the foamed blow-molded article, for example, a hollow molded article can be obtained. In the method for producing a foamed blow-molded article, it is preferable to provide an accumulator between the extruder and the die or at the die.

[0015] (Mixed resin composition) The mixed resin for forming the foamable resin melt is a mixed resin of a polyolefin resin (A) and an olefin thermoplastic elastomer (B).

[0016] (Polyolefin resin) The polyolefin resin (A) is a resin composition containing a branched homopolypropylene (a1) and a linear block polypropylene (a2).

[0017] (branched homopolypropylene) The branched homopolypropylene (a1) is a homopolypropylene having a branched structure in its molecular structure. An example of the branched structure is a branched portion in the molecular structure, a long-chain structural portion, and a structural portion having a free end. The branched structure can be confirmed by high-temperature GPC-MALS measurement or the like.

[0018] The melt flow rate of the branched homopolypropylene (a1) measured at 230°C under a load of 2.16 kg is preferably 0.1 g / 10 min to 15 g / 10 min. If the melt flow rate is within the above range, the resin has excellent fluidity when melted, and drawdown of the foamed parison is further suppressed. From this perspective, the melt flow rate of the branched homopolypropylene (a1) is preferably 0.5 g / 10 min to 10 g / 10 min, and more preferably 1 g / 10 min to 5 g / 10 min. The melt flow rate (MFR) of the resin can be measured by a known method, for example, based on JIS K7210-1:2014 (Test Method A).

[0019] From the viewpoint of foamability in foam blow molding, the melt tension of the branched homopolypropylene (a1) at 230°C is preferably 5 cN to 50 cN, and more preferably 10 cN to 45 cN. The melt tension (MT) of the branched homopolypropylene (a1) can be measured by a known method, for example, using a Capilograph 1D manufactured by Toyo Seiki Seisaku-sho, Ltd.

[0020] The melting point of the branched homopolypropylene (a1) is preferably 155 to 165° C., more preferably 157 to 162° C. The melting point can be measured in accordance with JIS K7121:2012 in the same manner as the melting point of the olefin-based thermoplastic elastomer (B) described below.

[0021] Since the branched homopolypropylene (a1) has excellent foamability, the polyolefin resin (A) containing the branched homopolypropylene (a1) can easily produce a foamed blow-molded article having excellent lightness and surface smoothness. Specific examples of the branched homopolypropylene (a1) include those commercially available as HMS-polypropylene and UMS-polypropylene. Other examples of the branched homopolypropylene (a1) include branched homopolypropylenes manufactured by Borealis (trade names: WB130, WB135, WB140) and branched homopolypropylene resin manufactured by SunAllomer (trade name: PF814).

[0022] (Linear block polypropylene) Linear block polypropylene (a2) is a block polypropylene with a linear molecular structure. Examples of block polypropylene include a polymerization mixture obtained by polymerizing ethylene and one or more C3-C10 α-olefins (α-olefins having 3 to 10 carbon atoms) in the presence of a propylene polymer. These include impact-resistant polypropylene polymers as defined in JIS K6921-1, and are generally commercially available as block polypropylenes. However, the examples of block polypropylenes shown here are merely examples and are not intended to exclude other examples. Specifically, block polypropylenes include propylene-ethylene block copolymers. More specifically, propylene-ethylene block copolymers include block copolymers containing a crystalline propylene block and an ethylene-propylene random block.

[0023] (Flexural modulus of linear block polypropylene) The flexural modulus of the linear block polypropylene (a2) is preferably 1000 MPa or more and 1500 MPa or less. When the flexural modulus of the linear block polypropylene (a2) is 1000 MPa or more, the rigidity of the foamed blow-molded article can be more effectively improved and the cushioning properties of the foamed blow-molded article can be ensured. From this viewpoint, the flexural modulus of the linear block polypropylene (a2) is more preferably 1100 MPa or more and 1400 MPa or less.

[0024] (Measurement of flexural modulus) The flexural modulus of the linear block polypropylene (a2) can be measured in accordance with JIS K7171:2016.

[0025] Although the flexural modulus of the linear block polypropylene (a2) resin itself is generally smaller than that of the branched homopolypropylene (a1), the inclusion of the linear block polypropylene (a2) in the polyolefin resin (A) in addition to the branched homopolypropylene (a1) improves the rigidity of the foamed blow-molded article. Furthermore, the inclusion of the linear block polypropylene (a2) in the polyolefin resin (A) facilitates the production of foamed blow-molded articles with good lightness and excellent surface smoothness.

[0026] The linear block polypropylene (a2) preferably has a melt flow rate of 1 g / 10 min to 40 g / 10 min, measured at 230°C under a load of 2.16 kg. If the melt flow rate is within the above range, the mixed resin will have excellent fluidity when melted. From this perspective, the melt flow rate of the linear block polypropylene (a2) is preferably 2 g / 10 min to 35 g / 10 min. The melt flow rate (MFR) of the resin can be measured by a known method, for example, based on JIS K7210-1:2014 (Test Method A).

[0027] The melting point of the linear block polypropylene (a2) is preferably 155 to 169° C. The melting point can be measured in accordance with JIS K7121:2012 in the same manner as the melting point of the olefin-based thermoplastic elastomer (B) described below.

[0028] (Mass ratio [(a1):(a2)]) In the mixed resin, the mass ratio [(a1):(a2)] of the branched homopolypropylene (a1) to the linear block polypropylene (a2) is preferably 50:50 to 93:7. When the mass ratio [(a1):(a2)] is within the above-mentioned range, the blend ratio of the branched homopolypropylene (a1) in the polyolefin resin (A) is at least half. When the mass ratio [(a1):(a2)] is within the above-mentioned range, the foamability of the mixed resin is improved, resulting in improved surface smoothness and improved rigidity and cold impact resistance of the foamed blow-molded article. To further enhance this effect, the mass ratio [(a1):(a2)] is preferably 80:20 to 90:10.

[0029] (olefin-based thermoplastic elastomer) The olefin-based thermoplastic elastomer (B) is a hydrogenated product of a triblock copolymer consisting of a hard segment of a crystalline olefin polymer block and a soft segment of a conjugated diene compound polymer block. The triblock copolymer is preferably a block copolymer having a so-called ABA structure (sandwich type). In this case, it is preferable that the A blocks at both ends of the block copolymer having the ABA structure are polymer blocks of a crystalline olefin, and the B block sandwiched between the A blocks is a polymer block of a conjugated diene compound. When the olefin-based thermoplastic elastomer (B) is a hydrogenated product of a block copolymer having the above structure, it is possible to achieve the effects of improving impact resistance and surface smoothness without inhibiting foamability.

[0030] Examples of the crystalline olefin polymer include ethylene polymers, etc. Examples of the conjugated diene compound polymer include ethylene and butylene polymers, as well as polymers of 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc.

[0031] Specific examples of the olefin-based thermoplastic elastomer (B) include hydrogenated triblock copolymers in which both end blocks are ethylene polymer blocks and the central block is a 1,3-butadiene polymer block. Examples of the olefin-based thermoplastic elastomer (B) after hydrogenation include a block copolymer of crystalline olefin, ethylene butylene, and crystalline olefin.

[0032] (Melting point of olefin-based thermoplastic elastomer) The melting point of the olefin-based thermoplastic elastomer (B) is preferably 80°C or higher and 110°C or lower. If the melting point of the olefin-based thermoplastic elastomer (B) is within the above range, it will have excellent foamability. From this viewpoint, the melting point of the olefin-based thermoplastic elastomer (B) is more preferably 85°C or higher and 105°C or lower, and even more preferably 90°C or higher and 100°C or lower.

[0033] (Method for measuring melting point) The melting point of the olefin-based thermoplastic elastomer (B) can be determined as the melting peak temperature measured by heat flux differential scanning calorimetry as described in JIS K7121:2012. The specimen conditioning method used is "(2) Measurement of melting temperature after a certain heat treatment," with heating and cooling rates of 10°C / min. If multiple melting peaks appear on the DSC curve, the melting point is determined as the apex temperature of the melting peak with the largest area.

[0034] (Flexural modulus of olefin-based thermoplastic elastomer) The upper limit of the flexural modulus of the olefinic thermoplastic elastomer (B) is preferably 50 MPa. The lower limit of the flexural modulus of the olefinic thermoplastic elastomer (B) is preferably approximately 1 MPa. That is, the flexural modulus of the olefinic thermoplastic elastomer (B) is preferably 1 MPa or more and 50 MPa or less. When the flexural modulus of the olefinic thermoplastic elastomer (B) is within the above-mentioned range, it becomes easier to obtain the effect of further improving the cold impact resistance of the foamed blow-molded article. From the viewpoint of further enhancing this effect, the flexural modulus of the olefinic thermoplastic elastomer (B) is more preferably 3 MPa or more and 30 MPa or less, and even more preferably 5 MPa or more and 25 MPa or less.

[0035] (Measurement of flexural modulus) The flexural modulus of the olefin-based thermoplastic elastomer (B) can be measured in accordance with JIS K7171:2016.

[0036] (Melt flow rate (MFR) of olefin thermoplastic elastomer) The MFR (230°C, load 2.16 kg) of the olefinic thermoplastic elastomer (B) is preferably 1 g / 10 min or more and 10 g / 10 min or less, more preferably 1.5 g / 10 min or more and 5 g / 10 min or less.

[0037] (MFR measurement) The MFR (g / 10 min (230°C)) of the olefin-based thermoplastic elastomer (B) can be determined, for example, based on JIS K7210-1:2014 (Test Method A). The measurement conditions used were 230°C and a load of 2.16 kg.

[0038] (Mixing ratio of each component of mixed resin) In the mixed resin, the blending amount of the olefin-based thermoplastic elastomer (B) per 100 parts by mass of the polyolefin-based resin (A) is 20 parts by mass or more and 40 parts by mass or less. When the blending amount of the olefin-based thermoplastic elastomer (B) per 100 parts by mass of the polyolefin-based resin (A) is within the above range, it becomes easy to achieve both the impact resistance and surface smoothness required of a foamed blow-molded article. From the above viewpoints, the blending amount of the olefin-based thermoplastic elastomer (B) is preferably 22 parts by mass or more and 35 parts by mass or less, more preferably 23 parts by mass or more and 30 parts by mass or less.

[0039] (Other additives in mixed resins) When producing a foam blow-molded article, the mixed resin and the foaming agent are kneaded together as described above. Examples of physical foaming agents include the following:

[0040] (foaming agent) Examples of blowing agents include organic physical blowing agents such as aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and cyclohexane, chlorinated hydrocarbons such as methyl chloride and ethyl chloride, fluorohydrocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane, aliphatic ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, aliphatic alcohols such as methyl alcohol and ethyl alcohol, and dialkyl carbonates such as dimethyl carbonate and diethyl carbonate, inorganic physical blowing agents such as carbon dioxide, nitrogen, air, and water, and chemical blowing agents such as sodium bicarbonate, sodium citrate, and azodicarbonamide. These blowing agents may be used alone or in combination.

[0041] When a foam parison is formed using an inorganic physical foaming agent, foaming is completed early, and little or no foaming agent remains in the resin, preventing plasticization of the resin and preventing drawdown. As a result, a foam parison is obtained that has superior blow moldability compared to one obtained using an organic physical foaming agent. From this perspective, among the foaming agents described above, inorganic physical foaming agents are preferred, inorganic physical foaming agents containing carbon dioxide are more preferred, and physical foaming agents consisting solely of carbon dioxide are even more preferred.

[0042] In the present invention, when a blowing agent containing carbon dioxide is used as the physical blowing agent, the carbon dioxide is preferably blended in an amount of 20 to 100 mol %, more preferably 50 to 100 mol %, and even more preferably 70 to 100 mol %, relative to 100 mol % of the physical blowing agent. When the carbon dioxide content is within the above range, a foamed blow-molded article having a small cell diameter and a high closed cell content can be easily obtained.

[0043] The amount of the physical foaming agent added is preferably 0.05 to 0.8 mol, and more preferably 0.1 to 0.5 mol, per 1 kg of the mixed resin.

[0044] (Other resins) The mixed resin may contain other resins different from the polyolefin resin (A) and the olefin thermoplastic elastomer (B) to the extent that the intended effects of the present invention are not impaired. Examples of such other resins include thermoplastic resins such as polystyrene resins and polyolefin resins other than the polyolefin resin (A), and thermoplastic elastomers (TPEs) other than the olefin thermoplastic elastomer (B). Furthermore, biomass polyolefin resins, ASR-derived polyolefin resins, and mass-balance polyolefin resins may also be used as polyolefin resins other than the polyolefin resin (A). The amount of such other resins is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the total of the polyolefin resin (A) and the olefin thermoplastic elastomer (B).

[0045] (Various additives) When producing a foamed blow-molded article, various additives may be added to the mixed resin in addition to the above-mentioned blowing agent. Examples of additives include flame retardants, flow control agents, UV absorbers, conductivity imparting agents, antistatic agents, colorants, heat stabilizers, antioxidants, inorganic fillers, and pigments. The amount of the additives added is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the total of the polyolefin resin (A) and the olefin thermoplastic elastomer (B).

[0046] Carbon black may be added to the mixed resin as an additive. The content of carbon black in the mixed resin is preferably 0.1 to 2 parts by mass, more preferably 0.3 to 1 part by mass, per 100 parts by mass of the total of the polyolefin resin (A) and the olefin thermoplastic elastomer (B). Examples of carbon black include gas furnace black, oil furnace black, acetylene black, channel black, roller black, thermal black, and ketjen black. When recycled raw materials containing carbon black are used as part of the raw materials in producing a foamed blow-molded article, the total carbon black content of the mixed resin includes the carbon black in the recycled raw materials.

[0047] (Use of recycled materials) When producing the foam blow-molded article of the present invention, defective molded articles with burrs or dimensional deviations may occur. These burrs and defective molded articles can be used as recycled raw materials. The recycled raw materials preferably contain a polyolefin resin (A) and an olefin-based thermoplastic elastomer (B). In the method for producing a foam blow-molded article of the present invention, a foamable resin melt containing the recycled raw materials is formed, and the foam blow-molded article is formed from the foamable resin melt. When the recycled raw material containing the polyolefin resin (A) and the olefin-based thermoplastic elastomer (B) is used as part of the raw materials for forming the foamable resin melt, the blending amounts of the polyolefin resin (A) and the olefin-based thermoplastic elastomer (B) in the mixed resin constituting the foam blow-molded article are determined as values ​​including the polyolefin resin (A) and the olefin-based thermoplastic elastomer (B) contained in the recycled raw materials.

[0048] [1-2 Effects of manufacturing method for blow-molded foam] Foamed blow-molded articles using polypropylene-based resins are particularly excellent in terms of heat resistance and light weight, and can be suitably employed, for example, in applications such as ducts mounted on vehicles such as automobiles. In recent years, there has been a demand for foamed blow-molded articles that are suitably used in such applications with improved cold impact resistance.

[0049] However, adding an elastomer to a polypropylene resin to improve the cold impact resistance of a foamed blow-molded article increases the risk of a decrease in the rigidity of the foamed blow-molded article.When a foamed blow-molded article is used as a duct, the decrease in rigidity of the foamed blow-molded article may cause the foamed blow-molded article forming the duct to bend slightly inward due to the negative pressure inside the duct when a gas such as air passes through the duct.

[0050] Furthermore, when a foamed blow-molded article is formed into a hollow shape and used as a duct, there is a strong demand for improving the surface smoothness of the inner surface of the foamed blow-molded article from the viewpoint of suppressing the air resistance of the duct and suppressing ventilation noise (wind noise).

[0051] According to the method for producing a foamed blow-molded article of the present invention, a specific polypropylene resin (polyolefin resin (A)) and a specific elastomer (olefin thermoplastic elastomer (B)) are used in specific ranges, thereby making it possible to obtain a foamed blow-molded article that is excellent in both cold impact resistance and rigidity. Furthermore, by using the specific elastomer, the foamability of the polypropylene resin is not significantly hindered, and the risk of adversely affecting surface smoothness can be reduced.

[0052] Furthermore, by using not only branched homopolypropylene but also linear polypropylene blocks in a specific range as the polypropylene-based resin, the risk of a decrease in rigidity due to the use of an elastomer can be reduced, and a foamed blow-molded article with excellent rigidity can be obtained.

[0053] Furthermore, foamed blow-molded articles are required to have various apparent densities depending on various conditions such as applications, etc. According to the method for producing a foamed blow-molded article of the present invention, a specific polypropylene resin and a specific elastomer are used in specific ranges, so that foamed blow-molded articles with excellent surface smoothness (excellent inner surface smoothness) can be obtained under various apparent density conditions.

[0054] Next, the foamed blow molded article according to the present invention will be described.

[0055] [2. Foam blow molded body] [2-1 Structure of foam blow molded body] The foamed blow-molded article according to the present invention is a foamed molded article made of a mixed resin of a polyolefin resin (A) and an olefin thermoplastic elastomer (B).

[0056] The foamed blow-molded article according to the present invention can be obtained by the above-described method for producing a foamed blow-molded article. That is, the foamed blow-molded article can be obtained by carrying out the extrusion foaming step, the blow-blowing step, the blow molding step, and the like, as described in the above section 1. Method for producing a foamed blow-molded article. Note that each step is the same as described in the above section [1. Method for producing a foamed blow-molded article], and therefore a description thereof will be omitted.

[0057] The polyolefin resin (A) blended into the mixed resin used in the foamed blow-molded article of the present invention contains a branched homopolypropylene (a1) and a linear block polypropylene (a2) in a predetermined mass ratio [(a1):(a2)]. The structures and physical properties (such as flexural modulus) of the branched homopolypropylene (a1) and the linear block polypropylene (a2), as well as the mass ratio [(a1):(a2)], are the same as those described in [1. Method for producing foamed blow-molded article], and therefore further explanation is omitted. Biomass-derived polypropylene and mass-balance polypropylene can be used as the polyolefin resin (A).

[0058] Furthermore, the structure and physical properties (melting point, etc.) of the olefin thermoplastic elastomer (B) blended into the mixed resin used for the foamed blow-molded article, and the blending amount of the olefin thermoplastic elastomer (B) per 100 parts by mass of the polyolefin resin (A) in the mixed resin are the same as those described in [1. Manufacturing method for foamed blow-molded article], and therefore further explanation will be omitted.

[0059] (Shape of foam blow molded body) The shape of the foamed blow-molded article is not particularly limited, but if it is a hollow molded article, it becomes easy to use the foamed blow-molded article as an air-conditioning duct provided in a vehicle or the like, for example.

[0060] (closed cell ratio) From the viewpoint of improving the appearance, the closed cell ratio of the foamed blow molded article is preferably 65% ​​or more, and more preferably 70% or more.

[0061] (Measurement of closed cell ratio) Test pieces measuring 25 mm x 25 mm x the thickness of the flat portion are prepared by cutting the foamed blow-molded article from the approximately flat portion. A number of test pieces are stacked so that the total thickness is as close to 20 mm as possible to prepare the test piece for measurement. Next, the true volume Vx of the test piece is measured using a Toshiba Beckman air comparison hydrometer Model 930 or similar, in accordance with Procedure C of ASTM-D2856-70, and the closed cell content S (%) is calculated using the following formula (Equation (1)). The above measurement is performed using five test pieces, and the arithmetic average value is the closed cell content of the foamed blow-molded article.

[0062]

number

[0063] however, Vx: The true volume (cm) of the test piece measured by the above method 3 ) which corresponds to the sum of the volume of the resin constituting the foamed blow molded body and the total volume of the closed cell portion in the test piece, Va: Apparent volume (cm) of the test specimen calculated from the outer dimensions of the test specimen used in the measurement 3 ), W: total mass (g) of the test specimens used in the measurement, and ρ: Density of the resin constituting the foamed blow molded product (g / cm 3 ), is.

[0064] (Apparent density) The apparent density of the foam blow molded product is 100 kg / m 3 More than 450kg / m 3 By having the above apparent density, it is possible to stably obtain a molded article that is lightweight and has appropriate rigidity. From the viewpoint of the balance between lightness, rigidity, and cushioning properties, the apparent density of the foamed blow molded article is preferably 120 kg / m or less. 3 More than 400kg / m 3 It is preferable that the saturation is 130 kg / m or less. 3 More than 350kg / m 3 More preferably, it is 150 kg / m or less. 3 More than 250kg / m 3 It is even more preferable that:

[0065] (Measurement of apparent density) For a total of three vertical cross sections in the longitudinal direction of the foam blow molding, near the longitudinal center and both ends, select four equally spaced locations on the circumferential flat portion of each vertical cross section, and measure the area of ​​approximately 10 cm2 in plan view. 2 Then, for each test piece, its mass Wi [g] is calculated as the volume Vi [cm 3 The apparent density (Wi / Vi) of each test piece was calculated by dividing the result by [Wi / Vi] and converting the unit, and the arithmetic mean of these values ​​was taken as the apparent density (D).

[0066] (Flexural modulus of foam blow molded body) The flexural modulus (MPa) of the foamed blow-molded article is preferably 140 MPa or more and 250 MPa or less. When the flexural modulus of the foamed blow-molded article is within the above range, sufficient rigidity can be easily ensured. From the viewpoint of further enhancing this effect, the flexural modulus of the foamed blow-molded article is more preferably 150 MPa or more and 200 MPa or less.

[0067] (Measurement of flexural modulus of foam blow molded body) The flexural modulus of the foamed blow-molded article can be determined by cutting a sample from a flat portion of the foamed blow-molded article and measuring the flexural modulus of the sample piece in accordance with JIS K7171:2016.

[0068] [2-2 Effects of foam blow molding] As explained above in [1. Manufacturing method for foamed blow-molded article], the foamed blow-molded article of the present invention is a foamed molded article of a mixed resin in which a specific polypropylene resin (polyolefin resin (A)) and a specific elastomer (olefin thermoplastic elastomer (B)) are blended in a specific range, and therefore has excellent both cold impact resistance and rigidity. Furthermore, the use of the specific elastomer in the foamed blow-molded article does not significantly inhibit the foamability of the polypropylene resin, and can suppress the risk of adversely affecting surface smoothness.

[0069] Furthermore, the foamed blow-molded article of the present invention uses not only branched homopolypropylene but also linear polypropylene blocks in combination within a specific range as the polypropylene-based resin, thereby suppressing the risk of a decrease in rigidity due to the use of an elastomer, and has excellent rigidity.

[0070] Furthermore, foamed blow-molded articles are required to have various apparent densities depending on various conditions such as applications, etc. In the foamed blow-molded article of the present invention, a specific polypropylene resin and a specific elastomer are used in specific ranges, and foamed blow-molded articles with excellent surface smoothness can be obtained even when the apparent density of the foamed blow-molded article is set to various values.

[0071] The above-mentioned cold impact resistance of the foamed blow molded article can be determined by the following (-10°C ball drop test).

[0072] (-10℃ drop ball test (1.5m, 1kg)) The foamed blow-molded article was conditioned by being left in an atmosphere of -10°C for 24 hours, and the conditioned foamed blow-molded article was placed on a test bench with the flat part facing up, and a 1 kg iron ball was dropped onto the flat part from 1.5 m above. The damage to the foamed blow-molded article was then observed. The less damage there was to the foamed blow-molded article (including no damage), the better its cold impact resistance.

[0073] In addition, if the force is applied to a location other than the flat portion when the iron ball hits the foamed blow-molded body and the foamed blow-molded body is damaged, it is preferable to perform the above-mentioned -10°C ball drop test again.

[0074] Next, a more detailed explanation will be given using examples. [Example]

[0075] (Resin preparation) The polyolefin resins and elastomers shown in Table 1 were prepared. Regarding the polyolefin resins, branched homopolypropylene (a1), linear block polypropylene (a2), and linear homopolypropylene were prepared. Table 1 also shows the physical properties (MFR (g / 10 min (230°C, load 2.16 kg)) and flexural modulus (MPa)) of the prepared polyolefin resins and elastomers.

[0076] The MFR (g / 10 min (230°C, load 2.16 kg)) and flexural modulus (MPa) of the polyolefin resin and elastomer can be determined using the same methods as those described above for the polyolefin resin (A) and olefin thermoplastic elastomer (B). The melting points (°C) of the branched homopolypropylene (a1) and elastomer described below are determined using the same method as described above for the olefin thermoplastic elastomer (B). The crystallization temperatures (°C) of the branched homopolypropylene (a1) and elastomer are measured using a heat flux differential scanning calorimeter in accordance with JIS K 7121:1987. When multiple crystallization peaks appear in a differential scanning calorimetry (DSC) curve, the peak temperature of the highest crystallization peak is taken as the crystallization temperature.

[0077] As the branched homopolypropylene (a1), a product manufactured by Borealis under the trade name "WB140" was prepared (melt tension (230°C): 36 cN, melting point 159°C, crystallization temperature 129°C). In Tables 2 and 3, the prepared branched homopolypropylene is abbreviated as WB140.

[0078] As the linear block polypropylene (a2), those shown as L-PP1 to L-PP3 in Table 1 were prepared.

[0079] L-PP1 is a copolymer of propylene and ethylene (propylene-ethylene copolymer) (manufactured by Japan Polypropylene Corporation, trade name "Novatec (trademark) PP (model number BC03GS)"). The propylene-ethylene copolymer of L-PP1 is a copolymer produced by a Ziegler catalyst (MFR is 30 g / 10 min).

[0080] L-PP2 is a polypropylene block copolymer manufactured by Japan Polypropylene Corporation under the trade name "Novatec PP (Model No. BC6DRF)" (MFR is 2.5 g / 10 min).

[0081] L-PP3 is a propylene block copolymer (manufactured by SunAllomer Co., Ltd., trade name "Qualia (trademark) (model number CM688A)") containing an ethylene-α-olefin copolymer (MFR 15 g / 10 min). The MFR of the propylene block copolymer in L-PP3 is 9.5 g / 10 min.

[0082] In Tables 2 and 3, the linear block polypropylenes shown as L-PP1, L-PP2, and L-PP3 are abbreviated as BC03GS, BC6DRF, and CM688A, respectively.

[0083] The linear homopolypropylene was prepared under the trade name "Prime Polypro (trademark) (model number J106G)" manufactured by Prime Polymer Co., Ltd. In Table 3, the prepared linear homopolypropylene is abbreviated as J106G.

[0084] As the elastomers, olefin-based elastomers shown in EL1 to EL4 and styrene-based elastomer shown in EL5 were prepared.

[0085] EL1 is a hydrogenated triblock copolymer consisting of a crystalline olefin polymer block and a polymer block of a conjugated diene compound. EL1 was prepared as a hydrogenated block copolymer (manufactured by JSR Corporation under the trade name "Dynaron (trademark) 6200P"), in which both end blocks were ethylene polymer blocks and the central block was a polymer block of a conjugated diene compound (block copolymer containing 30% by mass of ethylene-derived components, 70% by mass of 1,3-butadiene-derived components, a hydrogenation rate (hydrogenation rate) of 98% or more, a melting point of 97°C, and a crystallization temperature of 64°C). EL1 corresponds to the olefin-based thermoplastic elastomer (B).

[0086] EL2 is a metallocene-based propylene-ethylene copolymer (manufactured by ExxonMobil Corporation, trade name "Vistamax™ 6202," melting point 102°C). EL3 is RPTO (Reactor TPO (Thermoplastic Olefinic Elastomer)) (manufactured by Basell Corporation, trade name "Catalloy (model number Q100F)," melting point 143°C, crystallization temperature 96°C). RPTO is a propylene-based random block copolymer sequentially polymerized using a Ziegler catalyst. EL4 is an ethylene-butene block copolymer (manufactured by Mitsui Chemicals, Inc., trade name "Tafmer™ (model number DF605)," melting point 50°C or less).

[0087] EL5 is a hydrogenated styrene-based thermoplastic elastomer (manufactured by Asahi Kasei Corporation under the trade name "Tuftec (trademark)" (model number H1041)) in which the double bonds of a block copolymer made of styrene and butadiene are hydrogenated.

[0088] In Tables 2 and 3, the elastomers shown in EL1, EL2, EL3, EL4 and EL5 are abbreviated as 6200P, 6202, Q100F, DF605 and H1041, respectively.

[0089] [Table 1]

[0090] Examples 1 to 5, Comparative Examples 1 to 9 (Extrusion foaming process) The types and blending amounts (mass%) of polyolefin resin, elastomer, and additives shown in Table 2 (Examples 1 to 5) and Table 3 (Comparative Examples 1 to 9) were fed into an extruder with a 65 mm diameter, melted and kneaded to form a resin melt. Carbon dioxide (CO2) was then injected into the extruder as a foaming agent, and the mixture was further kneaded to form a foamable resin melt. The foamable resin melt was filled into an accumulator connected to the extruder. The foamable resin melt was then extruded into a normal pressure range through an annular die located at the tip of the accumulator at a foaming temperature of 170°C and foamed to form a cylindrical foam parison.

[0091] (Pre-blow process) A two-piece mold was placed directly below the annular die as a molding tool, and the cylindrical foam parison formed in the extrusion foaming process was placed between the molds. After the opening of the foam parison was closed below the mold using a pinch, pre-blow air was blown into the foam parison, and the two-piece mold was closed to sandwich the foam parison between the molds.

[0092] (Blow molding process) By blowing air from a blow pin into the interior of the foamed parison sandwiched between the molds and suctioning through holes in the molds to reduce the pressure in the space between the outer surface of the foamed parison and the inner surface of the mold, the outer surface of the foamed parison was pressed against the inner surface of the mold, and the foamed parison was formed into a shape corresponding to the inner surface of the mold. After shaping and cooling, the molds were opened to remove the molded body, and flash and pockets were removed. This resulted in a foamed blow-molded body. The obtained foamed blow-molded body was hollow and shaped like a duct with a roughly rectangular cross-section, a maximum length of 650 mm, and a maximum width of 180 mm.

[0093] The descriptions (abbreviations) of the types of polyolefin resins and elastomers ("Type" column) shown in Tables 2 and 3 correspond to the types of polyolefin resins and elastomers shown in Table 1. In Tables 2 and 3, the numerical values ​​shown in the columns immediately below the descriptions of the types of polyolefin resins correspond to the blending ratios (mass%) of the branched polypropylene and linear polypropylene in the polyolefin resin, where the total of the branched polypropylene and linear polypropylene in the polyolefin resin is taken as 100. Furthermore, the numerical values ​​shown in the columns immediately below the descriptions of the types of elastomers correspond to the blending amount (parts by mass) of the elastomer per 100 parts by mass of the polyolefin resin.

[0094] Furthermore, the mixed resin contained 0.9 parts by mass of carbon black and 2 parts by mass of talc as additives per 100 parts by mass of the polyolefin resin (A) and the olefin thermoplastic elastomer (B). These additives were added as a carbon black masterbatch (45% masterbatch (MB)) and a talc masterbatch (20% masterbatch (MB)). The carbon black masterbatch was manufactured by B&Tech Corporation under the trade name "PP Black Master Batch, BT920F-JSJ." The talc masterbatch was manufactured by Matsumura Sangyo Kaisha under the trade name "Hifiller #12" (talc concentration 20% by mass, median diameter 7.5 μm). Talc can function as a cell adjuster.

[0095] The amount (mol / kg) of the blowing agent injected is as shown in Tables 2 and 3. The amount (mol / kg) of the blowing agent injected shown in Tables 2 and 3 is the amount (mol / kg) per 1 kg of the mixed resin of the polyolefin resin and the elastomer.

[0096] (Physical properties of foam blow molded products) The physical properties of the foamed blow-molded articles obtained in Examples 1 to 5 and Comparative Examples 1 to 9 were as follows: apparent density (kg / m 3 The thickness (mm), closed cell ratio (%), and flexural modulus (MPa) were measured. The results are shown in Tables 2 and 3.

[0097] The apparent density, closed cell content, and flexural modulus of the foamed blow-molded article are measured by the methods described above.

[0098] (Thickness of foam blow molded product) The thickness of a foamed blow-molded article indicates the average thickness of the foamed blow-molded article, and is a value measured by the following method. Vertical cross sections were obtained in the longitudinal direction of the foamed blow-molded article at five locations: the longitudinal center, both longitudinal ends, and an intermediate location between the center and both ends. The thickness (wall thickness) of the foamed blow-molded article was measured at six locations equally spaced circumferentially on each vertical cross section, and the arithmetic mean value of the thicknesses at 28 locations, excluding the maximum and minimum values, from the 30 thickness measurements obtained was used as the average thickness of the foamed blow-molded article.

[0099] (Evaluation of foam blow molded products) The foamed blow-molded articles obtained in Examples 1 to 5 and Comparative Examples 1 to 9 were evaluated for cold impact resistance and surface smoothness. The results are shown in Tables 2 and 3.

[0100] (Cold impact resistance) The cold impact resistance of the foamed blow molded articles was evaluated by conducting a -10°C ball drop test (1.5 m, 1 kg).

[0101] (-10℃ drop ball test (1.5m, 1kg)) The foamed blow-molded article was conditioned by placing it in an atmosphere of -10°C for 24 hours. The conditioned foamed blow-molded article was placed on a test bench with the flat part facing up, and a 1 kg iron ball was dropped onto the flat part from 1.5 m above, and damage to the foamed blow-molded article was observed. The ball drop test was conducted five times. If the flat part of the foamed blow-molded article that was hit by the ball (flat part) bent and force was applied to a part other than the flat part (a part outside the flat part), causing damage to the foamed blow-molded article, this was not counted as a number of ball drop tests, and the ball drop test was conducted again. Based on the results of the ball drop test, the cold impact resistance of the foamed blow-molded article was evaluated according to the following criteria.

[0102] ◎ (Very good): The foam blow molded article does not crack. ◯ (Good): Cracks were observed in the foam blow molded product, but no scattering of fragments was observed. × (bad): The foamed blow molded article was cracked, and scattered pieces of the broken foamed blow molded article were observed.

[0103] For each of the Examples and Comparative Examples, 10 samples were prepared as foamed blow-molded articles for the -10°C ball drop test, and the cold impact resistance of the foamed blow-molded articles was evaluated using each sample. The number of samples that achieved an evaluation result of ⊚ or ◯ (number of good samples) was counted. The results are shown in Tables 2 and 3.

[0104] (Evaluation of surface smoothness) The surface smoothness of a foamed blow-molded article refers to the smoothness of the inner surface of the foamed blow-molded article. The surface smoothness of the foamed blow-molded article was measured by cutting out a flat portion of the foamed blow-molded article and visually observing the inner surface of the foamed blow-molded article in that flat portion. The surface smoothness of the foamed blow-molded article was measured according to the following criteria.

[0105] ○ (Good): When the inner surface of the foam blow molded body is visually inspected, the number of uneven areas where the difference in height between adjacent uneven areas (the difference between the bottom position of the concave part and the tip position of the convex part) is 1 mm or more is within 100 cm of the inner surface. 2 There is no more than one per area (including cases where no irregularities are found on the inner surface) × (Poor): When the inner surface of the foam blow molded article is visually inspected, there are no irregularities formed within 100 cm of the inner surface where the difference in height between adjacent irregularities (the difference between the bottom position of a concave portion and the top position of a convex portion) is 1 mm or more. 2 There are two or more locations per area.

[0106] In Tables 2 and 3, the surface smoothness column lists the number of locations where irregularities were recognized in addition to the above evaluation results. For example, in the foamed blow-molded articles obtained in Examples 1 to 5, the number of locations where irregularities were formed was 0 (i.e., no irregularities were recognized on the inner surface).

[0107] It was confirmed that in Examples 1 to 5, foamed blow-molded articles excellent in cold impact resistance and surface smoothness were obtained, as shown in Table 2. It was also confirmed that the flexural modulus of the foamed blow-molded articles had a value corresponding to the rigidity generally required for applications such as ducts.

[0108] In Comparative Examples 1 and 2, the blending ratio of polyolefin resin and elastomer in the mixed resin was changed compared to Example 2, and as shown in Table 3, the impact resistance and surface smoothness required for the foamed blow molded article were not achieved at the same time.

[0109] In Comparative Examples 3 to 6, the type of elastomer was changed compared to Example 1, etc., and as shown in Table 3, the impact resistance and surface smoothness required for the foamed blow molded article were not both achieved.

[0110] In Comparative Examples 7 and 8, the blending amount of linear block polypropylene (a) was changed compared to Example 1 etc., and the impact resistance and surface smoothness required for the foamed blow-molded article were not compatible, as shown in Table 3. Furthermore, in Comparative Examples 7 and 8, as shown in Table 3, the flexural modulus values ​​were lower than those of Examples 1 to 5, and the rigidity of the foamed blow-molded article was insufficient.

[0111] In Comparative Example 9, the linear block polypropylene used in Example 1 was changed to a linear homopolypropylene, and as shown in Table 3, the impact resistance and surface smoothness required for the foamed blow molded product were not both achieved.

[0112] [Table 2]

[0113] [Table 3]

[0114] The manufacturing method and the embodiment of the present invention described above are merely examples, and the present invention is not limited to these.

[0115] Based on the above description of this specification, the present invention may employ the following configurations [E1] to [E8]. [E1] A method for producing a foamed blow-molded article, comprising a step of blow-molding a foamed parison obtained by foaming a mixed resin of a polyolefin-based resin (A) and an olefin-based thermoplastic elastomer (B), the polyolefin resin (A) comprises a branched homopolypropylene (a1) and a linear block polypropylene (a2), and the mass ratio of the branched homopolypropylene (a1) to the linear block polypropylene (a2) [(a1):(a2)] is 50:50 to 93:7; the olefin-based thermoplastic elastomer (B) is a hydrogenated triblock copolymer consisting of a crystalline olefin polymer block and a conjugated diene compound polymer block, The method for producing a foamed blow-molded article, wherein the mixed resin contains the olefin-based thermoplastic elastomer (B) in an amount of 20 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the polyolefin-based resin (A). [E2] The melting point of the olefin-based thermoplastic elastomer (B) is 80°C or higher and 100°C or lower. A method for producing the foamed blow-molded article according to [E1] above. [E3] The linear block polypropylene (a2) has a flexural modulus of 1000 MPa or more and 1500 MPa or less. A method for producing a foamed blow-molded article according to any one of [E1] and [E2] above. [E4] The melt flow rate of the olefin-based thermoplastic elastomer (B) (at 230°C under a load of 2.16 kg) is 1 g / 10 min or more and 10 g / 10 min or less. A method for producing a foamed blow-molded article according to any one of the above [E1] to [E3]. [E5] A foamed blow-molded article of a mixed resin of a polyolefin resin (A) and an olefin thermoplastic elastomer (B), the polyolefin resin (A) blended into the mixed resin comprises a branched homopolypropylene (a1) and a linear block polypropylene (a2), and the mass ratio of the branched homopolypropylene (a1) to the linear block polypropylene (a2) [(a1):(a2)] is 50:50 to 93:7; the olefin-based thermoplastic elastomer (B) blended in the mixed resin is a hydrogenated triblock copolymer consisting of a crystalline olefin polymer block and a conjugated diene compound polymer block, The foamed blow-molded article, wherein the blending amount of the olefin-based thermoplastic elastomer (B) per 100 parts by mass of the polyolefin-based resin (A) is 20 parts by mass or more and 40 parts by mass or less. [E6] The melting point of the olefin-based thermoplastic elastomer (B) is 80°C or higher and 100°C or lower. The foamed blow-molded article according to [E5] above. [E7] The linear block polypropylene (a2) has a flexural modulus of 1000 MPa or more and 1500 MPa or less. The foamed blow-molded article according to [E5] or [E6] above. [E8] The melt flow rate of the olefin-based thermoplastic elastomer (B) (at 230°C under a load of 2.16 kg) is 1 g / 10 min or more and 10 g / 10 min or less. The foam blow-molded article according to any one of [E5] to [E7] above.

Claims

1. A method for producing a foamed blow-molded article, comprising a step of blow-molding a foamed parison obtained by foaming a mixed resin of a polyolefin-based resin (A) and an olefin-based thermoplastic elastomer (B), the polyolefin resin (A) comprises a branched homopolypropylene (a1) and a linear block polypropylene (a2), and the mass ratio of the branched homopolypropylene (a1) to the linear block polypropylene (a2) [(a1):(a2)] is 50:50 to 93:7; the olefin-based thermoplastic elastomer (B) is a hydrogenated triblock copolymer comprising a crystalline olefin polymer block and a conjugated diene compound polymer block, In the mixed resin, the amount of the olefin-based thermoplastic elastomer (B) blended per 100 parts by mass of the polyolefin-based resin (A) is 20 parts by mass or more and 40 parts by mass or less.

2. The melting point of the olefin-based thermoplastic elastomer (B) is 80°C or higher and 100°C or lower. A method for producing the foamed blow-molded article according to claim 1.

3. The flexural modulus of the linear block polypropylene (a2) is 1000 MPa or more and 1500 MPa or less. A method for producing the foamed blow-molded article according to claim 1 or 2.

4. The olefin-based thermoplastic elastomer (B) has a melt flow rate (230°C, load 2.16 kg) of 1 g / 10 min or more and 10 g / 10 min or less. A method for producing the foamed blow-molded article according to claim 1 or 2.

5. A foamed blow-molded article of a mixed resin of a polyolefin-based resin (A) and an olefin-based thermoplastic elastomer (B), the polyolefin resin (A) comprises a branched homopolypropylene (a1) and a linear block polypropylene (a2), and the mass ratio of the branched homopolypropylene (a1) to the linear block polypropylene (a2) [(a1):(a2)] is 50:50 to 93:7; the olefin-based thermoplastic elastomer (B) is a hydrogenated triblock copolymer comprising a crystalline olefin polymer block and a conjugated diene compound polymer block, In the mixed resin, the blending amount of the olefin-based thermoplastic elastomer (B) per 100 parts by mass of the polyolefin-based resin (A) is 20 parts by mass or more and 40 parts by mass or less.

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