阅读说明：本技术 聚丙烯系树脂发泡成型体的制造方法 (Method for producing polypropylene resin foam molded body ) 是由 五味渊正浩 野吕仁一朗 于 2018-09-21 设计创作，主要内容包括：通过将由基础树脂形成的发泡型坯吹塑成型来制造聚丙烯系树脂泡沫成型体的方法,其中：所述基础树脂含有特定混合比例的分支聚丙烯系树脂(A)、直链聚丙烯系树脂(B)和在所述聚丙烯系树脂泡沫成型体的制造过程中回收的回收原料(C),树脂(A)、树脂(B)和回收原料(C)各自的熔体张力和熔体流动速率在特定范围内；树脂(A)的熔点与树脂(B)的熔点之间的差在特定范围内,并且树脂(A)的结晶温度与树脂(B)的结晶温度之间的差在特定范围内。(A method for producing a polypropylene resin foam molded body by blow molding a foamed parison formed of a base resin, wherein: the base resin contains a branched polypropylene-based resin (A), a linear polypropylene-based resin (B) and a recovered raw material (C) recovered in the production process of the polypropylene-based resin foam molded body in a specific mixing ratio, and the melt tension and the melt flow rate of each of the resin (A), the resin (B) and the recovered raw material (C) are within specific ranges; the difference between the melting point of the resin (a) and the melting point of the resin (B) is within a specific range, and the difference between the crystallization temperature of the resin (a) and the crystallization temperature of the resin (B) is within a specific range.)

1. A process for producing a polypropylene-based resin foam molded body, which comprises extruding a foamable molten resin obtained by kneading a base resin and a physical foaming agent through a die to form a foamed parison, and blow molding the foamed parison,

the base resin comprises a branched polypropylene resin (A), a linear polypropylene resin (B) and a recycled raw material (C) recycled in the process of producing the polypropylene resin foamed molded body,

wherein the branched polypropylene-based resin (A) has a melt tension (230 ℃) of more than 100 mN and a melt flow rate (230 ℃, load of 2.16 kg) of 0.1 to 15 g/10 min,

the linear polypropylene-based resin (B) has a melt tension (230 ℃) of less than 30 mN (excluding 0) and a melt flow rate (230 ℃, load of 2.16 kg) of 5 to 25 g/10 min,

the reclaimed raw material (C) has a melt tension (230 ℃) of 5 to 50 mN and a melt flow rate (230 ℃, load of 2.16 kg) of 2 to 50 g/10 min, and

wherein the branched polypropylene-based resin (A) has a melting point T_mA and the melting point T of the linear polypropylene resin (B)_mDifference between B (T)_mA-T_mB) Is between-5 ℃ and 5 ℃,

the crystallization temperature T of the branched polypropylene resin (A)_cA and the crystallization temperature T of the linear polypropylene resin (B)_cDifference between B (T)_cA-T_cB) Is between 0 ℃ and 10 ℃,

the blending amount of the branched polypropylene-based resin (A) in the base resin is 5% by weight or more and less than 20% by weight based on 100% by weight of the base resin, and the blending amount of the recovered raw material (C) in the base resin is more than 65% by weight and 90% by weight or less based on 100% by weight of the base resin, and

the weight ratio (A: B) of the amount of the branched polypropylene-based resin (A) to the amount of the linear polypropylene-based resin (B) blended in the base resin is 80:20 to 40: 60.

2. The method for producing a polypropylene-based resin foam-molded body according to claim 1, wherein the linear polypropylene-based resin (B) has a melt flow rate (230 ℃, a load of 2.16 kg) of 10 to 25 g/10 min.

3. The method for producing a polypropylene resin foamed molding according to claim 1 or 2, wherein the recovered raw material (C) has a melt tension (230 ℃) of 5 mN or more and less than 30 mN.

4. The method for producing a polypropylene-based resin foam-molded body according to any one of claims 1 to 3, wherein the physical blowing agent is an inorganic physical blowing agent.

5. The method for producing a polypropylene-based resin foam molded body according to any one of claims 1 to 4, wherein the foam molded body has 0.10 to 0.35 g/cm³The apparent density of (c).

Technical Field

The present invention relates to a method for producing a polypropylene resin foamed molded article by a foam blow molding technique.

Background

Heretofore, a hollow foamed molded article has been suitably used for an air conditioning duct of an automobile or the like. The foamed blow-molded article is produced, for example, as follows: the base resin and the blowing agent are melted and kneaded in an extruder, and the kneaded substance is extruded from a die to form a foamed parison. Then, the parison is placed in a split mold, and a pressurized gas is blown into the foamed parison to perform blow molding (hereinafter, this molding method is sometimes simply referred to as "foam blow molding").

As a base resin used for an air-conditioning duct or the like made of a foamed blow-molded article, a polypropylene-based resin is often used because it has an excellent balance between heat resistance and rigidity. Further, among polypropylene-based resins, it has been proposed to use a polypropylene-based resin having a high melt tension (hereinafter sometimes referred to as HMS-PP) (patent document 1). HMS-PP has a branched structure in its molecular chain and has excellent extrusion foaming properties. By using HMS-PP, a good foamed molded body having a low apparent density can be obtained.

However, since HMS-PP is expensive, it is desired to reduce the production cost of the foamed molded article. In order to solve this problem, it has been proposed to use, as a base resin, a mixed resin obtained by mixing a branched polypropylene-based resin with a general-purpose linear polypropylene-based resin, and further mixing with a recycled raw material obtained by recycling a foamed molded article (patent document 2). This method makes it possible to reduce the manufacturing cost of the foamed molded body.

Documents of the prior art

[ patent document ]

[ patent document 1] International publication WO99/28111

[ patent document 2] Japanese laid-open publication JP 2004-122488.

Disclosure of Invention

The problems to be solved by the invention are as follows:

however, in recent years, there is a demand for an air conditioning duct for an automobile having a more complicated shape. In blow molding, a parison is held between split molds. At this time, in the portion where the parison is sandwiched between the peripheral edges of the cavity, the opposite inner surfaces of the parison are melt-bonded together to form the pinch-off portion. The outer portion of the pinch-off forms a residual portion called a burr. Finally, burrs are removed to obtain a molded body.

When the shape of the foamed molded article becomes complicated, the amount of burrs increases. Therefore, from the viewpoint of cost reduction, it is desired to recover substantially the entire amount of burrs and reuse them as a raw material for a foamed molded article.

Further, when a branched polypropylene-based resin whose branches are liable to be broken is kneaded with an extruder, the branched chain is broken, resulting in a decrease in melt tension of the resin and deterioration of extrusion foaming properties thereof. In the actual production of a foamed molded body, since a recycled raw material such as flash contains a branched polypropylene-based resin which has been repeatedly kneaded with an extruder, the extrusion foaming property tends to be significantly lowered.

When a large amount of such a recycled raw material having poor extrusion foaming properties is used to produce a foamed molded article having a low apparent density, extrusion foaming properties and blow moldability (hereinafter, these two properties are sometimes referred to as foam blow moldability) deteriorate. Therefore, since excessively large bubbles are generated in the foamed molded article, the inner surface of the molded article becomes rough, and holes are caused to form, so that it is often difficult to produce a good foamed molded article in a stable manner.

An object of the present invention is to provide a method for stably producing a good polypropylene resin foamed molded article having a low apparent density even when a large amount of a recovered raw material is used.

Means for solving the problems:

according to the present invention, there is provided a method for producing a polypropylene resin-based foamed molded article, comprising:

[1] a process for producing a polypropylene-based resin foam molded body, which comprises extruding a foamable molten resin obtained by kneading a base resin and a physical foaming agent through a die to form a foamed parison, and blow molding the foamed parison,

the base resin comprises a branched polypropylene resin (A), a linear polypropylene resin (B) and a recycled raw material (C) recycled in the process of producing the polypropylene resin foamed molded body,

wherein the branched polypropylene-based resin (A) has a melt tension (230 ℃) of more than 100 mN and a melt flow rate (230 ℃, load of 2.16 kg) of 0.1 to 15 g/10 min,

the linear polypropylene-based resin (B) has a melt tension (230 ℃) of less than 30 mN (excluding 0) and a melt flow rate (230 ℃, load of 2.16 kg) of 5 to 25 g/10 min,

the reclaimed raw material (C) has a melt tension (230 ℃) of 5 to 50 mN and a melt flow rate (230 ℃, load of 2.16 kg) of 2 to 50 g/10 min, and

wherein the branched polypropylene-based resin (A) has a melting point T_mA and the melting point T of the linear polypropylene resin (B)_mDifference between B (T)_mA-T_mB) Is between-5 ℃ and 5 ℃,

the crystallization temperature T of the branched polypropylene resin (A)_cA and the crystallization temperature T of the linear polypropylene resin (B)_cDifference between B (T)_cA-T_cB) Is between 0 ℃ and 10 ℃,

the amount of the branched polypropylene-based resin (A) blended in the base resin is 5% by weight or more and less than 20% by weight based on 100% by weight of the base resin, and

the blending amount of the recovered raw material (C) in the base resin is more than 65% by weight and 90% by weight or less based on 100% by weight of the base resin, and

the weight ratio (A: B) of the amount of the branched polypropylene-based resin (A) to the amount of the linear polypropylene-based resin (B) blended in the base resin is 80:20 to 40: 60.

[2] The method for producing a polypropylene-based resin foamed molding body according to the above [1], wherein the linear polypropylene-based resin (B) has a melt flow rate (230 ℃, a load of 2.16 kg) of 10 to 25 g/10 min.

[3] The process for producing a polypropylene resin foamed molding according to the above [1] or [2], wherein the recovered raw material (C) has a melt tension (230 ℃) of 5 mN or more and less than 30 mN.

[4] The method for producing a polypropylene-based resin foamed molding body according to any one of the above [1] to [3], wherein the physical foaming agent is an inorganic physical foaming agent.

[5]According to the above [1]To [4]]The method for producing a polypropylene-based resin foam molded body of any one of, wherein the foam molded body has 0.10 to 0.35 g/cm³The apparent density of (c).

The invention has the following effects:

according to the production method of the present invention, by mixing a specific branched polypropylene-based resin, a specific linear polypropylene-based resin and a specific recycled material at a specific ratio as a base resin, a good polypropylene-based resin foamed molded article having a low apparent density can be stably produced even when a large amount of the recycled material is added.

Drawings

Fig. 1 is an explanatory view showing an example of an apparatus used for carrying out the manufacturing method of the present invention.

Detailed Description

Hereinafter, the method of manufacturing a polypropylene resin foamed molded body of the present invention will be described in detail. In the present invention, a foamable molten resin obtained by kneading raw materials (such as a polypropylene-based resin and the like) and a physical blowing agent is extruded from a die to form a foamed parison. The foamed parison is then blow molded to obtain a polypropylene-based resin foamed molded body (hereinafter, sometimes simply referred to as a foamed molded body).

An example of the method for producing a foamed molded body of the present invention will be described below with reference to the drawings. As shown in fig. 1, a base resin and a physical blowing agent are kneaded in an extruder (not shown) to obtain a foamable molten resin. The molten resin is extruded through a die 2 and introduced between split molds 3, 3 having a desired shape and located right below the die to form a foamed parison 1 (extrusion foaming step). Next, the lower portion of the foamed parison 1 in a softened state is closed by a jig (not shown), and a gas is blown into the foamed parison to increase the internal pressure and expand the foamed parison (a pre-blowing step). Then, by closing the molds 3, the foamed parison 1 is clamped by the molds (clamping step). Then, gas is blown into the hollow portion of the foamed parison 1 held by the mold 3 to press the outer surface of the foamed parison 1 against the inner surface of the mold and form a hollow shape (blow molding step). After cooling, the foam-molded article having burrs is taken out from the mold, and the burrs are removed to obtain a hollow foam-molded article. The waste materials such as burrs and foam molding inferiorities (raw material recovery step) are recovered and reused as recovered raw material (C) to be described later.

Incidentally, the foamed parison shown in fig. 1 is composed of only a foam. However, the foam may be laminated with a non-foamed resin layer and extruded together in the form of a multilayer parison, from which a multilayer molded body can be obtained. Although fig. 1 shows a tubular foamed parison, a sheet-shaped foamed parison may also be used. In the process of the present invention, a hopper (accumulator) is preferably disposed between the extruder and the die 3 or inside the die.

The base resin for forming the foamed parison is obtained by mixing a branched polypropylene-based resin (a), a linear polypropylene-based resin (B), and a recycled raw material (C) at a specific ratio (base resin preparation step). However, in the present invention, other additional component(s) may be added to the base resin.

Next, the branched polypropylene-based resin (a), the linear polypropylene-based resin (B), and the recovered raw material (C) will be described. In the following description, the branched polypropylene-based resin (a) is sometimes referred to as resin (a), and the linear polypropylene-based resin (B) is sometimes referred to as resin (B).

In the present invention, a polypropylene resin is used. Examples of the polypropylene-based resin include a propylene homopolymer and a propylene-based copolymer having 50% by weight or more of a structural unit derived from propylene. Examples of the copolymer include copolymers of propylene and ethylene or α -olefins having 4 or more carbon atoms, such as propylene-ethylene copolymers, propylene-butene copolymers and propylene-ethylene-butene copolymers; propylene-acrylic acid copolymers; and propylene-maleic anhydride copolymers and the like. These copolymers may be any of block copolymers, random copolymers and graft copolymers. In addition, the polypropylene-based resin may include impact polypropylene in which a rubber component such as an ethylene-propylene-diene copolymer is dispersed in a propylene homopolymer or a propylene copolymer (such as a propylene-ethylene random copolymer). The polypropylene-based resin generally has a melting point in the range of about 130 ℃ to 170 ℃.

The resin (a) constituting the base resin of the present invention is a resin having a free-end long-chain branch in the molecular structure of the polypropylene-based resin. Specific examples of the resin (A) include branched homopolypropylene (trade name: WB130, WB135, WB140) manufactured by Borealis AG and branched homopolypropylene resin (trade name: PF814) manufactured by Sun Allomer Co., Ltd.

The branched polypropylene resin (A) has a melt tension of more than 100 mN at 230 ℃. When the melt tension is too low, too large cells and the like may be generated, so that a good foamed molded body may not be obtained. From this viewpoint, the melt tension of the resin (a) is preferably 150 mN or more, more preferably 200 mN or more. On the other hand, the upper limit is preferably 500 mN, more preferably 450 mN. In the present invention, the melt tension at 230 ℃ is referred to as melt tension (230 ℃), and in the following description, the melt tension is sometimes referred to as MT.

The melt flow rate of the resin (A) measured at 230 ℃ under a load of 2.16 kg is from 0.1 to 15 g/10 min. When the melt flow rate is too small, the fluidity of the resin containing the resin (a) at the time of melting may be deteriorated, and thus the extrusion moldability may be lowered. On the other hand, when the melt flow rate is too large, it is difficult to suppress drawdown of the foamed parison, resulting in significant thickness unevenness of the obtained foamed molded article. Therefore, there is a possibility that a good foamed molded body having excellent thickness accuracy cannot be obtained. From this viewpoint, the lower limit of the melt flow rate of the resin (A) is preferably 0.5 g/10 min, more preferably 1 g/10 min. The upper limit is preferably 10 g/10 min, more preferably 5 g/10 min. In the present invention, the melt flow rate measured under the conditions of 230 ℃ and a load of 2.16 kg is also referred to as the melt flow rate (230 ℃, a load of 2.16 kg). In the following description, the melt flow rate is sometimes referred to as MFR.

The resin (A) is preferably homopolypropylene, impact polypropylene or a mixture thereof. Among them, homopolypropylene is more preferable. The resin (A) preferably has a melting point of 155 ℃ to 165 ℃, more preferably 157 ℃ to 162 ℃.

When the resin (A) is homopolypropylene or impact polypropylene, the crystallization temperature thereof tends to have a higher crystallization temperature than that of a linear polypropylene-based resin of the same type having the same melting point because the resin (A) has a branched structure. The crystallization temperature of the resin (A) is about 15 ℃ to 25 ℃ lower than the melting point of the resin (A).

The resin (B) used in the present invention is a resin having a linear molecular chain among the polypropylene-based resins.

The resin (B) has a melt tension (230 ℃) of less than 30 mN (excluding 0). When the linear polypropylene-based resin has a high melt tension, its melt flow rate is also reduced. Therefore, when the melt tension is 30 mN or more, the base resin melted at the time of extrusion tends to generate heat, so that excessively large cells or the like may be generated. As a result, a good foamed molded article may not be obtained. From this viewpoint, the melt tension of the resin (B) is preferably 15 mN or less (excluding 0), and more preferably 10 mN or less (excluding 0).

The resin (B) has a melt flow rate (230 ℃ C., a load of 2.16 kg) of 5 to 25 g/10 min. When the melt flow rate is too small, the flowability of the base resin containing the resin (B) is deteriorated at the time of melting, so that heat is easily generated by shearing in a die, and there is a possibility that extrusion moldability is deteriorated. On the other hand, when the melt flow rate is too large, the foamed parison tends to sag, so that the thickness unevenness of the obtained foamed molded article increases, and there is a possibility that a good foamed molded article having excellent thickness accuracy cannot be obtained. From the above viewpoint, the lower limit thereof is preferably 10 g/10 min, more preferably 12 g/10 min, and the upper limit thereof is preferably 20 g/10 min. When the melt flow rate is from 10 to 25 g/10 minutes, a foamed molded body having a low apparent density can be produced in a more stable manner.

In the present invention, the melting point T of the resin (A)_mMelting Point T of A and resin (B)_mDifference between B (T)_mA-T_mB) Is from-5 ℃ to 5 ℃. When the difference in melting point is within the above range, occurrence of pores and generation of excessively large cells in the foamed molded article can be suppressed even when a large amount of the recovered raw material is used. Albeit for reasons ofIt is not clear, but it is considered that since the difference in melting point between the two resins is small, the compatibility between them is improved, so that both the stretching of the resin during extrusion foaming and the stretching of the resin during blow molding are improved. Therefore, for example, when the resin (A) is homopolypropylene, it is preferable to use one or two or more resins selected from homopolypropylene and impact polypropylene and having a melting point close to that of the resin (A) as the resin (B). From this point of view, the difference (T)_mA-T_mB) The lower limit of (B) is preferably-4 ℃ and the upper limit is preferably 4 ℃.

Further, the crystallization temperature T of the resin (A)_cCrystallization temperature T of A and resin (B)_cDifference between B (T)_cA-T_cB) It must be 0 ℃ to 10 ℃. That is, a linear polypropylene-based resin having a crystallization temperature relatively higher than the melting point thereof is used as the resin (B). When the difference in crystallization temperature is within the above range, the foamed parison has excellent foamability and blow moldability even when a large amount of the recovered raw material is used, and the foamed molded article obtained has a good inner surface state. Although the reason for this is not clear, it is considered that since the crystallization temperature of the resin (B) does not exceed the crystallization temperature of the resin (a) and is close to the crystallization temperature of the resin (a), the growth of cells at the time of foaming is not hindered, and furthermore, the cell walls are rapidly fixed after foaming, thereby achieving early stabilization of the cell structure before blow molding or at an early stage of blow molding. From this point of view, the difference (T)_cA-T_cB) The upper limit of (B) is preferably 9 ℃.

The resin (B) is preferably homopolypropylene, impact polypropylene or a mixture thereof. Among them, homopolypropylene is more preferable.

In the present invention, the resin (B) is a linear polypropylene-based resin having the above-mentioned specific MT and MFR and having specific ranges of differences from the resin (a) in melting point and crystallization temperature. By including such a resin (B) and the resin (a) and the recycled raw material (C) in the base resin, a good polypropylene-based resin product having a low apparent density can be obtained in a stable manner even when the recycled raw material (C) is used in a large amount.

Specific examples of the resin (B) include homopolypropylene (trade name: J105G, J106G) manufactured by Prime Polymer co.

The recycled raw material (C) in the present invention is a resin recycled in the process of producing a polypropylene foamed molded article. That is, the recycled raw material (C) is a waste material generated during various manufacturing steps of the foamed molded article of the present invention. Examples of the waste materials include resin compositions recovered from the kneading step and the extrusion step, burrs generated in the blow molding step, defective products of foamed molded bodies, and the like. After being collected, the waste material may be subjected to an appropriate treatment selected from the group consisting of pulverization, kneading, re-granulation, and a combination thereof, as necessary. In actual production, the recovered raw material (C) contains such a resin (a) and a resin (B) repeatedly kneaded by an extruder a plurality of times.

Therefore, the reclaimed raw material (C) includes a resin containing the resin (a) and the resin (B) kneaded together at least once with an extruder. In addition, when other components such as an olefinic thermoplastic elastomer are added to the base resin, the recovered raw material (C) further contains an olefinic thermoplastic elastomer and the like.

The recovered raw material (C) had a melt tension (230 ℃) of 5 to 50 mN. Usually, the upper limit is 50 mN. However, when the mixing amount of the resin (A) in the base resin is small when a foamed molded article is produced, or when the extrusion temperature is high when a recovered raw material is produced, the upper limit may be less than 30 mN, or even less than 25 mN. On the other hand, when the melt tension is too small, generation of excessively large cells or the like cannot be suppressed, so that there is a possibility that a good foamed molded body having a low apparent density cannot be obtained. From this viewpoint, the lower limit is preferably 10 mN.

The recovered raw material (C) had a melt flow rate (230 ℃ C., a load of 2.16 kg) of 2 to 50 g/10 min. When the melt flow rate is too large, the occurrence of sagging of the foamed parison becomes so significant that the resulting foamed molded body may have an uneven thickness. Therefore, a good foamed molded article may not be obtained. From this viewpoint, the upper limit is preferably 40 g/10 minutes. On the other hand, when the melt flow rate is too small, the molten base resin may generate heat, so that there is a possibility that a good foamed molded body may not be obtained. From this viewpoint, the lower limit is preferably 10 g/10 minutes, more preferably 20 g/10 minutes.

As described above, in the actual production of the foamed molded article, the recovered raw material (C) is repeatedly used. Therefore, the recovered raw material (C) contains polypropylene which has undergone a large heat history during kneading with an extruder. When the number of times of the heat history increases, the cutting of the branch chain of the polypropylene-based resin contained in the recovered raw material (C) proceeds, so that the melt tension of the recovered raw material (C) decreases and the melt flow rate increases. When such recycled raw materials are used, the foam blow moldability is lowered, and it becomes more difficult to obtain a good foam molded body.

However, according to the present invention, by using the reclaimed raw material (C) in combination with the resin (a) and the resin (B) as the base resin, a good foam molded body having excellent foam blow moldability and low apparent density can be obtained even when a reclaimed raw material having a low melt tension is used as the reclaimed raw material (C) or even when a reclaimed raw material having a high melt flow rate is used.

The melt tension can be measured using a measuring device such as Capirograph 1D manufactured by Toyo Seiki Selsakusho, Ltd. First, a nozzle hole having a nozzle diameter of 2.095 mm and a length of 8.0 mm was provided in a cylinder having a cylinder diameter of 9.55 mm and a length of 350 mm. The cylinder and orifice were set at a temperature of 230 ℃. The required amount of polypropylene-based resin sample was charged into a cylinder and held for 4 minutes to form a molten resin of the resin sample. The molten resin was then extruded through the orifice in the form of a strand at a piston speed of 10 mm/min. The wire was placed on a tension detecting pulley having a diameter of 45 mm and wound on a winding roll while increasing the winding speed at a constant winding acceleration, so that the winding speed was increased from 0 m/min to 200 m/min over a period of 4 minutes. As a result of this operation, the wire breaks. The maximum value of the tension immediately before the line breaks is measured. The reason why the period of 4 minutes is employed until the take-up speed reaches 200 m/min from 0 m/min is to suppress thermal deterioration of the resin and to improve the reproducibility of the measured value. The above measurements were performed on ten different samples. From the maximum values of the ten measurements obtained, the maximum three values and the minimum three values were excluded. The arithmetic mean of the remaining four maxima in the middle represents the melt tension (mN) in the process according to the invention.

However, in the above melt tension measuring method, if the resin wire is not broken up to a take-up speed of 200 m/min, the melt tension (mN) is measured by a take-up operation at a constant take-up speed of 200 m/min. More specifically, in the same manner as described above, the molten resin was extruded from the nozzle hole in the form of a strand, and the extruded resin strand was placed on a tension detecting pulley and wound on a winding roll while increasing the winding speed at a constant winding acceleration, so that the winding speed increased from 0 m/min to 200 m/min over a period of 4 minutes. When a take-up speed of 200 m/min was reached, the melt tension data was recorded initially and stopped after 30 seconds. From the tension load curve obtained during the measurement period of 30 seconds, the arithmetic mean (Tave) of the maximum tension (Tmax) and the minimum tension (Tmin) is determined and used as melt tension in the process of the invention. Tmax as used herein is a value obtained by dividing the sum of tension values of peaks detected in the tension load curve by the number of peaks, and Tmin as used herein is a value obtained by dividing the sum of tension values of pits detected in the tension load curve by the number of pits. The above measurement should be performed in such a manner as to prevent bubbles from being included in the strand as much as possible when the molten resin is extruded in a strand form through the orifice.

The Melt Flow Rate (MFR) of the polypropylene-based resin in the present specification means a melt mass flow rate measured by test method A of JIS K7210-1 (2014) using the conditions of a test temperature of 230 ℃ and a load of 2.16 kg.

The melting point in the present specification means a melting peak temperature measured by heat flow type differential scanning calorimetry according to JIS K7121 (1987). As the adjustment of the state of the sample, "the melting temperature is measured after the sample is subjected to a prescribed heat treatment". The cooling rate in the measurement was 10 ℃/min. The heating rate in the melting temperature measurement was 10 ℃/min. When two or more melting peaks occur, the peak top temperature of the melting peak having the largest area represents the melting point.

In the present specification, the crystallization temperature means a crystallization peak temperature determined by heat flow type differential scanning calorimetry based on JIS K7122 (1987). A cooling rate of 10 deg.c/min was used. When two or more crystallization exothermic peaks occur, the peak top temperature of the crystallization peak having the largest area represents the crystallization temperature.

The composition of the base resin used in the present invention will be described below. The amount of the branched polypropylene-based resin (A) to be blended is 5% by weight or more and less than 20% by weight based on 100% by weight of the base resin. When the amount is too large, the manufacturing cost cannot be sufficiently reduced, and the object of the present invention may not be achieved. From this viewpoint, the upper limit of the amount in the base resin is preferably 15% by weight, more preferably 13% by weight. On the other hand, when the amount is too small, the foamability of the base resin may decrease, and a good foamed molded article may not be obtained. From this viewpoint, the lower limit of the blending amount in the base resin is preferably 6% by weight, more preferably 7% by weight.

The blending amount of the recovered raw material (C) in the base resin is more than 65% by weight and not more than 90% by weight based on 100% by weight of the base resin. When the amount is too large, the foamability of the base resin is lowered, and there is a possibility that a good foamed molded article having a low apparent density cannot be obtained. From this viewpoint, the upper limit of the blending amount in the base resin is preferably 87% by weight, more preferably 85% by weight. When the amount is too small, the manufacturing cost cannot be sufficiently reduced, and the object of the present invention may not be achieved. From this viewpoint, the lower limit of the blending amount in the base resin is preferably 70% by weight, more preferably 75% by weight.

In the present invention, the weight ratio (A: B) of the amount of the branched polypropylene-based resin (A) to the amount of the linear polypropylene-based resin (B) is from 80:20 to 40: 60. When the amount of the resin (B) is too small, the production cost may not be sufficiently reduced. When the amount is too large, the foamability of the base resin may be lowered, and a good foamed molded article may not be obtained. From this viewpoint, the ratio (A: B) is preferably 75:25 to 45: 55.

In the present invention, the base resin may incorporate thermoplastic resins (e.g., polyethylene-based resins and polystyrene-based resins), and thermoplastic elastomers (e.g., olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers), as long as the object and effect of the present invention are not adversely affected. In particular, by adding the olefinic thermoplastic elastomer, the impact resistance of the foamed molded article at low temperature can be improved.

Examples of the olefin-based thermoplastic elastomer include a mixture composed of a hard segment composed of a polypropylene-based resin and a soft segment composed of an ethylene-based rubber such as an ethylene-propylene rubber (which may contain a diene component or the like); a block copolymer having a hard segment composed of a polyethylene block and a soft segment composed of an ethylene/α -olefin copolymer block; and ethylene/alpha-olefin copolymers.

As commercially available olefinic thermoplastic elastomers (TPOs), for example, the trade name "thermomun" (manufactured by Mitsubishi Chemical Corporation), the trade name "MILASTOMER" (manufactured by Mitsui Chemicals inc.), the trade name "SUMITOMO TPE" (SUMITOMO Chemical co., Ltd.), the trade name "INFUSE" (Dow Chemical Company), and the trade name "CATALLOY ADFLEX Q100F" (Sun Allomer co., Ltd.) can be mentioned.

The total mixing amount of the thermoplastic elastomer in the base resin may be an appropriate amount necessary to exhibit the above-described effects as long as the object and effects of the present invention are not adversely affected. The total amount is preferably 5 to 25 wt%, more preferably 10 to 20 wt%, and still more preferably 12 to 18 wt%, based on 100 wt% of the base resin. When the reclaimed material (C) contains a thermoplastic elastomer, the amount of the thermoplastic elastomer newly added to the base resin is appropriately adjusted so that the sum of the amount of the thermoplastic elastomer contained in the reclaimed material (C) and the amount of the thermoplastic elastomer newly added to the base resin is within the above-mentioned range. For example, when the reclaimed raw material (C) containing 15% by weight of the thermoplastic elastomer is added to the base resin in an amount of 80% by weight, the thermoplastic elastomer in an amount of 3% by weight should be newly added to the base resin so that the blending amount of the thermoplastic elastomer in the base resin is adjusted to 15% by weight.

In the present invention, a foamable molten resin obtained by kneading a base resin with a physical blowing agent is extruded from a die and foamed to obtain a foamed parison. As physical blowing agents, mention may be made of: organic physical foaming agents, such as aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, isohexane and cyclohexane, chlorinated hydrocarbons such as methyl chloride and ethyl chloride, fluorinated hydrocarbons such as 1,1,1, 2-tetrafluoroethane and 1, 1-difluoroethane, aliphatic ethers such as dimethyl ether, diethyl ether and methylethyl ether, aliphatic alcohols such as methanol and ethanol, and dialkyl carbonates such as dimethyl carbonate and diethyl carbonate; inorganic foaming agents such as carbon dioxide, nitrogen, air and water; and decomposition type chemical foaming agents such as sodium bicarbonate, sodium citrate and azodicarbonamide. These blowing agents may be used as a mixture.

When the foamed parison 1 is formed using an inorganic physical foaming agent, the resin is not plasticized because rapid evaporation of the foaming agent results in rapid completion of foaming, and because the foaming agent hardly or not at all remains in the resin. Therefore, the obtained foamed parison has better blow moldability than a foamed parison obtained by using an organic physical blowing agent.

From the above-mentioned viewpoint, among the above-mentioned foaming agents, an inorganic physical foaming agent is preferably used, more preferably an inorganic physical foaming agent containing carbon dioxide is used, and further preferably a physical foaming agent composed only of carbon dioxide is used.

In the method of the present invention, when a blowing agent containing carbon dioxide is used as the physical blowing agent, the content of carbon dioxide is preferably 20 to 100 mol%, more preferably 50 to 100 mol%, and still more preferably 70 to 100 mol%, based on 100 mol% of the physical blowing agent. When the content of carbon dioxide is within the above range, a foamed molded body having a small cell diameter and a high closed cell content can be obtained.

The mixing amount of the physical blowing agent is preferably 0.05 to 0.8 mol, more preferably 0.1 to 0.5 mol, based on 1 kg of the base resin.

Various additives such as cell control agents, ultraviolet absorbers, infrared reflection agents, flame retardants, fluidity improvers, weather resistance agents, colorants, heat stabilizers, antioxidants, and fillers may be added to the base resin constituting the foamed parison as necessary.

Next, the physical properties of the foamed molded body obtained by the method of the present invention will be described in the order of average thickness, apparent density, and closed cell content.

Average thickness:

the average thickness of the foamed molded article of the present invention varies depending on the shape of the intended foamed molded article, but is usually preferably 1 to 10 mm, more preferably 1.2 to 7 mm, and still more preferably 1.5 to 5 mm. When the average thickness is within the above range, the foamed molded body has an excellent balance between its light weight and mechanical strength.

The average thickness in the present invention is measured as follows. The cross section of the foamed blow-molded body perpendicular to the longitudinal direction was measured at five positions including a position near the midpoint of the longitudinal direction thereof, positions near both ends of the longitudinal direction thereof, and a position near the center between the midpoint and the ends. The thickness of each cross section in the thickness direction was measured at six positions equally spaced from each other in the circumferential direction thereof. The maximum value and the minimum value were excluded from the thickness values at 30 points obtained in this way. The average thickness is the arithmetic mean of the remaining 28 measured thickness values.

Apparent density:

the apparent density of the foamed molded article according to the present invention is not particularly limited, but is preferably 0.10 to 0.35 g/cm³. When the apparent density is within the above range, the foamed molded article has excellent lightweight properties and heat insulating properties which are inherent to the foam, and also can maintain mechanical strength such as compressive stress. In particular, even when it is desired to manufacture a ceramic having a thickness of 0.1 to 0.35 g/cm³The foamed molded article of (3) can be produced in a stable manner even in the case of a foamed molded article having a low apparent density.

In the present invention, the measurement of the apparent density is performed as follows. The apparent density is determined by dividing the weight (g) of the foamed molded article by the volume (cm) of the foamed molded article³) To be determined. The volume of the foamed molded article may beIt is determined by a method (water immersion method) in which a foamed molded body is immersed in water contained in a graduated container to measure the rise of the water level.

Closed cell content:

the closed cell content of the foam-molded article is preferably 60% or more, more preferably 65% or more, and even more preferably 70% or more from the viewpoint of heat insulation and mechanical properties.

In the present invention, the measurement of the closed cell content is performed as follows. A test piece was cut out from the foamed molded article obtained, and Vx was measured by procedure C of ASTM D2856-70 (re-approved in 1976). The closed cell content was calculated by the formula shown below. Those portions in which the cells are crushed should be excluded from the measurement object.

Closed cell content (%) = (Vx-Va (ρ f/ρ s)). times.100/(Va-Va (ρ f/ρ s))

Vx: actual volume of the sample (sum of the volume of the closed cells and the volume of its base resin) (cm)³)

Va: apparent volume (cm) of the sample determined from the external dimensions of the sample³)

ρ f: apparent Density (g/cm) of the sample³)

ρ s: density (g/cm) of base resin of sample³)

The foamed molded article obtained by the present invention is preferably used as, for example, a pipe, a tank, a container and a pallet.

Examples

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

The following are resins used for producing the foamed molded articles in examples and comparative examples. The physical properties of each resin are shown in table 1.

(a) Branched polypropylene resin

Abbreviation "WB 140": "homopolypropylene (trade name: WB 140)" manufactured by Borealis AG "

(b) Linear polypropylene resin

(1) Abbreviation "J106G": homopolypropylene "J106G" manufactured by Prime Polymer co., ltd.

(2) Abbreviation "J105G": homopolypropylene "J105G" manufactured by Prime Polymer co., ltd.

(3) Abbreviation "J700 GP": homopolypropylene "J700 GP" manufactured by Prime Polymer co., ltd.

(4) Abbreviation "J-721 GR": propylene-ethylene random copolymer "J-721 GR" manufactured by Prime Polymer Co., Ltd "

(5) Abbreviation "J226T": propylene-ethylene random copolymer "J226T" manufactured by Prime Polymer co.

TABLE 1

(c) Thermoplastic elastomer

(1) Abbreviation "Q100F": olefinic thermoplastic elastomer (TPO) "Cataroy Adflex Q100F", manufactured by Sun alloy co., ltd.; the melt flow rate was 0.6 g/10 min (230 ℃ C., load of 2.16 kg); the melt tension was 40 mN (230 ℃ C.).

(d) Recovery of raw materials (C)

The branched polypropylene-based resin and the linear polypropylene-based resin shown in table 2 were mixed at a mixing ratio (weight ratio) shown in table 2 to obtain an original polypropylene raw material. To 85 parts by weight of a virgin polypropylene raw material, 15 parts by weight of Q100F (TPO) was mixed, and using the mixed raw material, a foamed molded body 1 was produced under the same conditions as in examples and comparative examples described below.

The foamed molded body 1 was then pulverized, and the pulverized product was supplied to an extruder and kneaded at 230 ℃ to obtain a molten resin. The molten resin was extruded and re-pelletized to obtain a reclaimed raw material (1).

Next, a mixed raw material obtained by mixing 80 wt% of the recovered raw material (1), 17 wt% of the virgin polypropylene raw material, and 3 wt% of Q100F (TPO) was used to produce a foamed molded article 2.

Then, 80 wt% of a recycled raw material (2) obtained by re-granulating the foamed molded body 2 under the same conditions as described above, 17 wt% of a virgin polypropylene raw material, and 3 wt% of Q100F (TPO) were mixed. The mixed raw materials are used to produce a foamed molded body 3.

Next, 80 wt% of the recovered raw material (3) obtained by re-granulating the foamed molded body 3 under the same conditions as described above, 17 wt% of the virgin polypropylene raw material, and 3 wt% of Q100F (TPO) were mixed. The mixed raw materials are used to produce a foamed molded article 4.

As the recycled raw material (C), a recycled raw material (4) obtained by re-granulating the foamed molded body 4 under the same conditions as described above was used. Table 2 shows the melt tension and melt flow rate of each recovered raw material (C).

TABLE 2

*1: for examples 1 and 2

*2: used in example 3

*3: used in example 4

*4: was used in example 5

*5: used in comparative example 1

*6: used in comparative example 2

*7: used in comparative example 3

*8: was used in comparative example 4.

Examples 1 to 5 and comparative examples 1 to 4

A base resin obtained by mixing the resin (A) shown in Table 3-1, the resin (B), the recovered raw material (C) and Q100F (TPO) in the amounts shown in Table 2, and talc (cell control agent) in an amount of 0.6 part by weight based on 100 parts by weight of the base resin were fed into an extruder having an inner diameter of 65 mm and kneaded at 230 ℃ to which carbon dioxide (CO) as a physical blowing agent in the amounts shown in Table 3-2 was injected from the middle part of the extruder₂). The mixture was further kneaded to obtain a foamable molten resin.

The foamable molten resin was then adjusted to the temperature shown in Table 3-2 and charged into a hopper provided on the downstream side of the extruder. Then, the foamable resin melt was extruded in the form of a tube into the atmosphere through an annular lip having a diameter of 75 mm and attached to the tip of an accumulator with an average gap (mm) and a discharge rate (kg/hr) shown in Table 3-2, and foamed to obtain a foamed parison.

Next, after the lower portion of the foamed parison is sandwiched, a preblowing gas is supplied to the hollow portion of the foamed parison, and the foamed parison is expanded. The expanded foamed parison is sandwiched by a two-piece mold disposed just below the die. After completion of the mold clamping, air was blown into the hollow portion inside the foamed parison at a pressure of 0.1 mpa (g) while sucking air from the holes provided in the mold, thereby molding the foamed parison into a shape conforming to the mold. After cooling, the mold is opened and the molded foam with molding flash is removed. Burrs were removed from the foamed molded article to obtain a hollow foamed molded article having a longitudinal length of 740 mm and a maximum circumferential length of 370 mm. Table 4 shows the physical properties and evaluation results of the foamed molded bodies obtained in examples and comparative examples.

TABLE 3-1

TABLE 3-2

TABLE 4

In table 4, the measurement and evaluation of various physical properties of the foamed molded article were carried out as follows.

Apparent density:

the apparent density of the foamed molded article was determined by comparing the weight of the foamed molded article [ g]Divided by the volume of the foamed molded article [ cm ] measured by the water immersion method³]And then obtaining the compound.

Average thickness:

the average thickness of the foamed molded body was measured by the method described previously.

Closed cell content:

test pieces were cut out from the foamed molded body at positions near both ends in the longitudinal direction of the foamed molded body and at positions near the center in the longitudinal direction thereof. Vx was measured for each test piece according to ASTM D2856-70 (procedure C) (re-approved in 1976), and the closed cell content of each test piece was calculated by the above formula. The arithmetic mean of the closed cell contents calculated for the respective test pieces represents the closed cell contents of the foamed molded bodies.

Production of excessively large cells:

the outer surface of the foamed molded body was visually observed to evaluate the generation of excessively large cells according to the following criteria. The term "oversized cells" is intended to mean cells that are significantly larger than the other cells surrounding the cell. The presence of excessively large bubbles leads to deterioration in the appearance of the foamed molded article and reduction in the mechanical strength thereof.

None: no excessively large cells in the outer surface of the foamed molded body;

generating: too large cells are generated on the outer surface of the foamed molded body.

Inner surface state:

the inner surface of the obtained foamed molded body was visually observed to evaluate the inner surface state according to the following criteria. When broken cells exist on the inner surface of the foamed molded body, air passing through the hollow portion of the foamed molded body will generate a significant wind noise.

O: there is no breakage of cells or the like on the inner surface of the foamed molded body;

x: breakage of cells and the like are observed on the inner surface of the foamed molded body.

Formability (stretchability):

the obtained foamed molded article was visually observed to evaluate moldability (stretchability) according to the following criteria. When through holes extending in the thickness direction are present in the foamed molded body, the mechanical strength of the foamed molded body is reduced. In addition, the foamed molded article cannot be used as a pipe.

O: the elongation of the foamed resin is good, so that the foamed molded body has no through-hole extending in the thickness direction;

x: the elongation of the foamed resin is not good, and through holes are formed in the foamed molded body.

Description of reference numerals

1: foamed parison

2: die head

3: a split mold.