JP5422246B2 - Foam blow molded article and method for producing the same - Google Patents

Description

  The present invention relates to a foamed blow molded article and a method for producing the same.

Foam blow molding is performed by extruding a thermoplastic resin to which a foaming agent has been added as a parison into the atmosphere and then sandwiching it with a split mold (see, for example, Patent Document 1).
In addition, as a foamed blow molded product obtained by such a method, a product mainly composed of a polypropylene resin having predetermined physical properties is known (for example, see Patent Document 2).

  However, in these foam blow-molded products, when opened to the atmosphere, the cell cell of the parison is rapidly expanded to increase the size of the bubbles, and in some cases, there is a possibility of causing bubble breakage.

On the other hand, a method for reducing the diameter of the bubble cell while maintaining a high expansion ratio has been studied.
For example, the foam duct shape | molded by the foam blow molding which added the supercritical fluid as a foaming agent is mentioned (for example, refer patent document 3).

JP-A 63-309434 Japanese Patent No. 3745960 JP 2005-241157 A

  However, in the foam duct described in Patent Document 3 in which the bubble cell is miniaturized, the diameter of the bubble cell is miniaturized, but variation in the size of the diameter is recognized. For this reason, such a foam duct cannot be said to have sufficient surface smoothness.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a foamed blow molded article having a uniform cell size cell, lightweight, and having high surface smoothness, and a method for producing the same. To do.

  The inventors of the present invention have intensively studied to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by using the following configuration, and have completed the present invention.

That is, the present invention provides (1) a foamed blow molded article comprising a wall portion formed by blow molding a thermoplastic resin mixed with a foaming agent, wherein the wall portion includes a plurality of closed cells. The closed cell structure has a closed cell ratio of 70% or more, and the bubble cell has a flat shape in a direction perpendicular to the thickness direction of the wall portion. The average bubble diameter is 56 μm or more and less than 300 μm, the center line average roughness Ra of the outer surface of the wall is less than 9.0 μm, and the standard deviation of the bubble diameter of the bubble cell in the thickness direction of the wall is 47 μm It exists in the following foam blow molded object.

The present invention resides in (2) the foamed blow molded article according to the above (1), wherein the expansion ratio of the wall portion is 2.0 times or more.
The present invention resides in (3) the foamed blow molded article according to the above (1) or (2), wherein the thermoplastic resin is a polyolefin resin.

The present invention resides in the foamed blow molded article according to the above ( 3 ), wherein ( 4 ) the polyolefin resin is a propylene homopolymer having a long chain branched structure.

This invention exists in the foam blow molding as described in any one of said (1)-( 4 ) whose standard deviation of the bubble diameter of the bubble cell in the thickness direction of a (5 ) wall part is less than 30 micrometers.

  This invention exists in the foaming blow molded object as described in any one of said (1)-(5) which is an air-conditioning duct for vehicles (6).

The present invention (7) In the method of the onset bubble blow molded article, the thermoplastic resin was added to the blowing agent, a mixing step of the mixing to the mixed resin in an extruder, the mandrel and the die outer cylinder A storage step for storing the mixed resin in a cylindrical space between the two, a extrusion step for extruding the parison between the split molds at an extrusion speed of 700 kg / hour or more from the die slit using a ring-shaped piston, and a parison between the split molds And a molding step in which blow molding is performed by blowing air in the range of 0.05 to 0.15 MPa into the parison, and a wall portion of the obtained foamed blow molded article includes a plurality of bubble cells. The closed cell structure has a closed cell ratio of 70% or more, and the bubble cell has a flat shape in a direction perpendicular to the thickness direction of the wall portion. Average bubble diameter of bubble cell There is less than 300μm above 56 .mu.m, the standard deviation of the cell diameter of the foamed cells in the thickness direction of the wall portion lies in der Ru manufacturing method of the foamed blow molded article below 47 [mu] m.

  The present invention resides in (8) the method for producing a foamed blow molded article according to the above (7), wherein the thermoplastic resin is a polyolefin resin and the foaming agent is in a supercritical state.

The present invention resides in (9) the method for producing a foamed blow molded article according to the above (7) or (8) using a foaming agent comprising nitrogen .

The foamed blow molded article of the present invention has a closed cell structure including a plurality of bubble cells and a wall portion with a foaming ratio within a predetermined range, thereby reducing the weight, and in the thickness direction of the wall portion. By setting the standard deviation of the bubble diameter of the bubble cell within a predetermined range, it is possible to have a bubble cell having a uniform size, and the center line average roughness Ra of the outer surface of the wall portion is set to a predetermined value. By setting it as this range, it can be set as the thing whose surface smoothness is high.
For this reason, when the said foaming blow molded object is used for the air conditioning duct for vehicles, for example, the frictional resistance with respect to distribution | circulation air is low, and ventilation efficiency will also improve. Thereby, the pressure loss of air-conditioning air is reduced, and the occurrence of condensation on the outside of the duct wall surface is reduced.
In addition, when used for a panel with a skin, the welding strength of the reinforcing rib formed inside the panel wall surface and the welding strength of the skin stuck to the outside of the panel wall surface are improved, and the rigidity and appearance are also excellent. Become.

  Since the foamed blow molded article is excellent in flexibility when the thermoplastic resin is made of a polyolefin resin, impact resistance is improved. The polyolefin resin is more preferably a propylene homopolymer having a long chain branched structure. In this case, it becomes easy to foam and a bubble cell is made more uniform.

  When the foamed blow molded article has an average cell diameter of the bubble cells in the thickness direction of the wall portion of less than 300 μm, the surface smoothness becomes more excellent. The average cell diameter is more preferably less than 100 μm.

According to the method for producing a blow-molded foam of the present invention, the size of the bubble cell is homogenized by storing the mixed resin at a predetermined position, and extruded at a predetermined extrusion speed using a ring-shaped piston. Thus, blow molding is performed in a state where the size of the bubble cell is maintained.
Thereby, according to the manufacturing method of the said foam blow molding, the foam blow molding which has a cell with a uniform magnitude | size, is lightweight, and the surface smoothness is high is obtained. In addition, a bubble cell is refined | miniaturized more by using the foaming agent which is a supercritical fluid.

  In the method for producing a foamed blow molded article, the cell size is more uniform when the extrusion speed of the parison in the extrusion process is 700 kg / hour or more.

FIG. 1 is a perspective view showing a first embodiment of a blow-molded foam according to the present invention. FIG. 2 is a flowchart of the method for producing a foamed blow molded article according to the present invention. FIG. 3 is a partial cross-sectional view showing an extrusion head used in the method for producing a blow-molded foam according to the present invention. FIG. 4 is a cross-sectional view showing a blow molding aspect in the method for producing a foamed blow molded article according to the present invention. FIG. 5 is a perspective view showing a second embodiment of the blow-molded foam according to the present invention. 6 is a cross-sectional view of the foamed blow molded article shown in FIG. FIG. 7 is an enlarged photograph of the wall surface cross section of the sample in Example 1 using a CCD camera. FIG. 8 is an enlarged photograph of the wall surface cross section of the sample in Comparative Example 1 using a CCD camera. FIG. 9 is a partial cross-sectional view showing a conventional extrusion head.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[First Embodiment]
As a first embodiment, a case where the foamed blow molded article according to the present invention is used as an air conditioning duct will be described.
FIG. 1 is a perspective view showing a first embodiment of a blow-molded foam according to the present invention.
As shown in FIG. 1, a foamed blow molded article (hereinafter also referred to as “air conditioning duct”) 1 according to the present embodiment is formed from a wall portion formed by blow molding a thermoplastic resin mixed with a foaming agent. It comprises a main body part 11, an air inflow part 13 provided at one end of the main body part 11, and an air outflow part 12 provided at the other end of the main body part 11. The blow molding will be described later. Moreover, the air outflow part 12 cuts off the part closed by the post-process after blow molding, and is made into the open state.

The air conditioning duct 1 has a hollow structure with a rectangular cross section. That is, the cross section of the main body 11 has a hollow structure surrounded by the wall.
Therefore, the air-conditioning duct 1 can distribute the air-conditioned air through the hollow portion.

In the air-conditioning duct 1, the main body 11 is smoothly curved, and the air-conditioning air that has flowed in from the air inflow portion 13 is sent from the air outflow portion 12 that faces the L-shaped direction with respect to the direction in which the air-conditioning air has flowed. It performs the function of draining.
For example, in an air conditioning duct for a vehicle, the air inflow portion 13 is connected to an air conditioner unit, and air conditioned air supplied from the air conditioner unit is circulated through the hollow portion and discharged from the air outflow portion 12 disposed at a desired position. be able to.

The wall portion has a closed cell structure including a plurality of bubble cells. Here, the closed cell structure is a structure having a plurality of bubble cells, and means a structure having at least a closed cell ratio of 70% or more.
In the air-conditioning duct 1, the wall portion has a closed cell structure, so that the surface smoothness is excellent, and the appearance, particularly in the air-conditioning duct, has the advantages of improving the blowing efficiency and reducing the occurrence of condensation.

The bubble cell preferably has an average bubble diameter in the thickness direction of the wall portion of less than 300 μm, and more preferably less than 100 μm. Here, the average bubble diameter means an average value of the maximum diameters of the respective bubbles in the thickness direction of the wall portion.
When the average cell diameter is 300 μm or more, the surface roughness tends to be large and the surface smoothness tends to be inferior compared with the case where the average cell diameter is in the above range.

In the air conditioning duct 1, the average wall thickness is preferably 3.5 mm or less.
When the average thickness exceeds 3.5 mm, the air flow path is reduced and the air blowing efficiency tends to be inferior as compared with the case where the average thickness is within the above range.

In the air conditioning duct 1, the center line average roughness Ra of the outer surface of the wall portion is less than 9.0 μm, and preferably less than 6.0 μm. Here, the center line average roughness Ra is a value measured according to JIS B0601.
By setting the centerline average roughness to less than 9.0 μm, the surface smoothness is excellent, and there is an advantage that appearance is improved, especially in an air-conditioning duct, air blowing efficiency is improved and condensation is reduced.

In the air conditioning duct 1, the standard deviation of the bubble diameter of the bubble cell in the thickness direction of the wall portion is less than 40 μm. Here, the standard deviation of the bubble diameter indicates the homogeneity of the bubble cell diameter, and the smaller the standard deviation, the more uniform the cell diameter.
If the standard deviation of the bubble diameter exceeds 40 μm, the variation in the bubble cell diameter tends to be large and the surface smoothness and appearance tend to be inferior. The standard deviation of the bubble diameter is more preferably less than 30 μm.

The air conditioning duct 1 has a wall foaming ratio of 2.0 times or more. Here, the expansion ratio is a value obtained by dividing the density of the thermoplastic resin used for foam blow molding by the apparent density of the wall surface of the foam blow molded article.
If the expansion ratio is less than 2.0, a lightweight foamed blow molded product cannot be obtained.

A foamed blow molded article (air conditioning duct) 1 according to the present embodiment is obtained by blow molding a thermoplastic resin mixed with a foaming agent.
Examples of such thermoplastic resins include polyolefin resins such as polyethylene resins and polypropylene resins. Since the polyolefin resin is excellent in flexibility, the impact resistance of the foamed blow body is improved.
Among these, the thermoplastic resin preferably has a propylene unit, and specific examples thereof include a propylene homopolymer, an ethylene-propylene block copolymer, and an ethylene-propylene random copolymer.
Further, among these, a propylene homopolymer having a long chain branched structure is particularly preferable. In this case, since melt tension becomes high, it becomes easy to foam and a bubble cell is made more uniform.

  The propylene homopolymer having a long chain branched structure is preferably a propylene homopolymer having a weight average branching index of 0.9 or less. The weight average branching index g ′ is represented by V1 / V2, where V1 is the intrinsic viscosity of the branched polyolefin and V2 is the intrinsic viscosity of the linear polyolefin having the same weight average molecular weight as the branched polyolefin.

  The thermoplastic resin is preferably a polypropylene resin having a melt tension at 230 ° C. in the range of 30 to 350 mN. Here, melt tension means melt tension. When the melt tension is within the above range, the foaming polypropylene resin exhibits strain-hardening properties, and a high foaming ratio can be obtained.

The thermoplastic resin preferably has a melt flow rate (MFR) of 1 to 10 at 230 ° C. Here, MFR is a value measured according to JIS K-7210.
If the MFR is less than 1, it tends to be difficult to increase the extrusion speed as compared with the case where the MFR is in the above range. If the MFR exceeds 10, the MFR is in the above range. In comparison, blow molding tends to be difficult due to the occurrence of drawdown or the like.

  It is preferable to add a styrene elastomer and / or low density polyethylene to the thermoplastic resin. When a styrene elastomer or low density polyethylene is added, the impact strength at low temperature of the foamed blow molded article is improved.

Although it does not specifically limit as a styrene-type elastomer, What is necessary is just an elastomer which has a styrene unit to which hydrogen was added in the molecule | numerator. Examples thereof include hydrogenated elastomers such as styrene-ethylene / butylene-styrene block copolymers, styrene-ethylene / propylene-styrene block copolymers, and styrene-butadiene random copolymers.
The blending ratio of the styrene elastomer is preferably in the range of less than 40 wt% with respect to the thermoplastic resin.
In addition, the content of styrene in the styrene-based elastomer is preferably less than 30 wt%, more preferably less than 20 wt%, from the viewpoint of impact strength at low temperatures.

As the low density polyethylene, those having a density of 0.91 g / cm ³ or less are suitably used from the viewpoint of impact strength at low temperatures. In particular, it is preferable to use linear ultra-low density polyethylene polymerized by a metallocene catalyst.
The blending ratio of the low density polyethylene is preferably in the range of less than 40 wt% with respect to the thermoplastic resin.

The thermoplastic resin is foamed using a foaming agent before blow molding.
Examples of such foaming agents include inorganic foaming agents such as air, carbon dioxide gas, nitrogen gas, and water, or organic foaming agents such as butane, pentane, hexane, dichloromethane, and dichloroethane.
Among these, it is preferable to use air, carbon dioxide gas or nitrogen gas as the foaming agent. In this case, since tangible materials can be prevented from being mixed in, deterioration in durability and the like is suppressed.

  Moreover, it is preferable to use a supercritical fluid as the foaming method. That is, it is preferable that carbon dioxide gas or nitrogen gas is in a supercritical state to foam the mixed resin. In this case, air bubbles can be uniformly and reliably formed.

  In addition to the styrene-based elastomer, the low-density polyethylene, and the foaming agent, a nucleating agent, a coloring agent, and the like may be added to the thermoplastic resin.

The air-conditioning duct 1 (foamed blow molded article) according to the present embodiment has a closed cell structure including a plurality of bubble cells and a wall portion with a foaming ratio within a predetermined range, thereby reducing weight. By setting the standard deviation of the bubble diameter of the bubble cell in the thickness direction of the wall portion within a predetermined range, it is possible to have a bubble cell of a uniform size, and the center line of the outer surface of the wall portion By setting the average roughness Ra within a predetermined range, the surface can be highly smooth.
Further, the air conditioning duct 1 has a low frictional resistance against the circulating air, and the air blowing efficiency is improved. Thereby, the pressure loss of air-conditioning air is reduced, and the occurrence of condensation on the outside of the duct wall surface is reduced.

Next, the manufacturing method of the foaming blow molded object of this invention is demonstrated.
FIG. 2 is a flowchart of the method for producing a foamed blow molded article according to the present invention.
As shown in FIG. 2, the manufacturing method of the foam blow molded body according to the present embodiment includes a mixing step S1 in which a thermoplastic resin is added to a foaming agent and mixed with an extruder to obtain a mixed resin, and the mandrel and the outside of the die. A storage step S2 for storing the mixed resin in a cylindrical space between the cylinder, an extrusion step S3 for extruding the parison from the die slit using a ring-shaped piston, and clamping the parison between the divided molds. And a molding step S4 for performing blow molding by blowing air.

According to the method for producing a foamed blow molded article according to the present embodiment, blow molding is performed while maintaining the size of the bubble cell by extruding at a predetermined extrusion speed using a ring-shaped piston.
Thereby, according to the manufacturing method of the said foam blow molding, the foam blow molding which has a cell with a uniform magnitude | size, is lightweight, and the surface smoothness is high is obtained.

Hereinafter, each step will be described in more detail.
(Mixing process)
The mixing step S1 is a step in which a thermoplastic resin is added to the foaming agent and mixed with an extruder to obtain a mixed resin. In addition, a well-known thing is used suitably for an extruder.
Moreover, in the manufacturing method of the foam blow molding which concerns on this embodiment, the polyolefin resin mentioned above is used as a thermoplastic resin, and a foaming agent is used as a supercritical state. By using a foaming agent that is a supercritical fluid, the bubble cell is further refined.

Here, the foaming agent is preferably carbon dioxide gas or nitrogen gas. These can be brought into a supercritical state under relatively mild conditions.
Specifically, the conditions for using carbon dioxide gas as a supercritical fluid are a critical temperature of 31 ° C. and a critical pressure of 7.4 MPa or higher, and the conditions for using nitrogen gas as a supercritical fluid are the critical temperature 149.1. The critical pressure is 3.4 MPa or higher.

  And a mixed resin is obtained by foaming polyolefin resin using a supercritical fluid. At this time, as described above, a styrene elastomer and / or low density polyethylene may be added to the polyolefin.

(Storage process)
Storage process S2 is a process of storing mixed resin in the cylindrical space between the mandrel and the die outer cylinder. Such a storage process is performed using an extrusion head.

FIG. 3 is a partial cross-sectional view showing an extrusion head used in the method for producing a blow-molded foam according to the present invention.
As shown in FIG. 3, the extrusion head 20 includes a die outer cylinder 28, a mandrel 27 disposed substantially at the center of the die outer cylinder 28, a cylindrical space 29 between the die outer cylinder 28 and the mandrel 27, A ring-shaped piston 22 for pushing the mixed resin stored in the cylindrical space 29 downward, and a die slit 21 for discharging the resin are provided.

In the storage step S <b> 2, the mixed resin extruded by an extruder (not shown) travels around the mandrel 27 and falls into the cylindrical space 29 between the mandrel 27 and the die outer cylinder 28 and is stored.
At this time, the amount of resin to be stored is preferably 5 to 40 liters.

  In the method for producing a blow-molded foam according to the present embodiment, since the mixed resin is stored in the cylindrical space 9, the size of the bubble cells is homogenized while the mixed resin is stored. It will be.

(Extrusion process)
Extrusion process S3 is a process of extruding a parison from a die slit using a ring-shaped piston. That is, after a predetermined amount of resin is stored in the cylindrical space 29, the parison (not shown) is discharged from the die slit 21 by pushing the ring-shaped piston 22 downward.

In the method for producing a blow-molded foam according to the present embodiment, since the ring-shaped piston 22 pushes the parison in the die (in-die accumulator method), the distance of the die slit 21 can be shortened. The extrusion speed can also be increased. For this reason, the state of a bubble cell can be maintained.
Incidentally, since the conventional extrusion head shown in FIG. 9 is a method of extruding a parison with an accumulator 35 outside the die (external die accumulator method), the distance between the die slits becomes long and the extrusion speed cannot be increased. .
In addition, it is preferable that the extrusion speed | rate of the parison at this time is 700 kg / hour or more. In this case, a foamed blow molded article having higher surface smoothness can be obtained. The in-die accumulator used in the present invention has an injection rate of 200 cm ³ / sec or more, preferably 500 cm ³ / sec or more.

(Molding process)
The molding step S4 is a step of performing blow molding by clamping the parison between the divided molds and blowing air into the parison.

FIG. 4 is a cross-sectional view showing a blow molding aspect in the method for producing a foamed blow molded article according to the present invention.
As shown in FIG. 4, the cylindrical parison 32 is extruded between the split molds 33 from a die slit (not shown). Then, the mold is clamped by the split mold 33 so that the parison 32 is sandwiched from both sides.

Thereafter, air is blown into the parison 32 for blow molding.
At this time, the pressure for blowing air is preferably 0.05 to 0.15 MPa from the viewpoint of maintaining the shape of the bubble cell.

Thus, a foamed blow molded product is obtained.
According to the method for producing a blow-molded foam according to this embodiment, the size of the bubble cells is homogenized by storing the mixed resin at a predetermined position, and the ring-shaped piston is used at a predetermined extrusion speed. By extruding, blow molding is performed in a state where the size of the bubble cell is maintained.
As a result, a foamed blow-molded article having a uniform size cell, light weight and high surface smoothness can be obtained.

[Second Embodiment]
As a second embodiment, a case where the foamed blow molded article according to the present invention is used as a panel with a skin will be described.
FIG. 5 is a perspective view showing a second embodiment of the blow-molded foam according to the present invention.
As shown in FIG. 5, the foamed blow molded article (hereinafter also referred to as “panel with skin”) 3 according to this embodiment is a wall portion formed by blow molding a thermoplastic resin mixed with a foaming agent. It has a structure having a hollow double wall structure made of and having a skin material 4 adhered to one surface of a base body 2 made of a wall portion. The skin material 4 is integrally attached simultaneously with the blow molding of the wall in the molding process.

6 is a cross-sectional view of the foamed blow molded article shown in FIG.
As shown in FIG. 6, in the panel 3 with the skin, the base body 2 made of a wall portion has a hollow double wall structure having a hollow portion 5, and a plurality of reinforcing ribs 6 are defined so as to partition the hollow portion 5. Is provided. Such reinforcing ribs 6 improve the strength in the vertical direction.

The reinforcing rib 6 is formed so as to fold the wall portion of the parison by pressing against the side surface of the parison with a projecting slide core from one direction when the parison is clamped in the molding process.
Therefore, in the manufacture of the panel with the skin, the skin material 4 is adhered and the reinforcing ribs 6 are simultaneously formed in the molding process.

In addition, since the said wall part is synonymous with the wall part in the foam blow molding which concerns on 1st Embodiment mentioned above, and a structure and a physical property are also the same, description is abbreviate | omitted.
Moreover, the manufacturing method of the foam blow molded object which concerns on 2nd Embodiment is the same as the manufacturing method of the foam blow molded object which concerns on 1st Embodiment except a formation process differing as mentioned above.

The panel with skin 3 (foamed blow molded article) according to the present embodiment has a closed cell structure including a plurality of bubble cells in the wall portion, and the wall portion has a foaming ratio within a predetermined range, thereby reducing weight. By setting the standard deviation of the bubble diameter of the bubble cell in the thickness direction of the wall portion within a predetermined range, it is possible to have a bubble cell of a uniform size, and the center of the outer surface of the wall portion By setting the line average roughness Ra within a predetermined range, the surface smoothness can be high.
Further, the welding strength of the reinforcing ribs formed on the inside of the panel wall surface and the welding strength of the skin adhered on the outside of the panel wall surface are improved, and the rigidity and appearance are also excellent.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
70 wt% propylene homopolymer (thermoplastic resin, manufactured by Sun Allomer, trade name: PF814) having a long chain branched structure with an MFR of 3.0 g / min at 230 ° C. and an MFR of 0.5 g / min at 230 ° C. 30 wt% of a crystalline ethylene-propylene block copolymer (Novatech PP EC9, manufactured by Nippon Polychem Co., Ltd.) to make a mixture, 96 parts by weight of this mixture and 3 parts of talc MB (masterbatch) as a nucleating agent Part by weight and 1 part by weight of black MB (masterbatch) as a colorant were mixed. The density of the mixed resin was 0.91 g / cm ³ .
Then, carbon dioxide in a supercritical state was added as a foaming agent and foamed to obtain a mixed resin. After mixing this with an extruder, the mixed resin is stored in a cylindrical space between the mandrel and the die outer cylinder using the extrusion head shown in FIG. 3, and 1500 kg using a ring-shaped piston (in-die accumulator). A cylindrical parison is extruded between the split molds shown in FIG. 4 at a speed of / hour, and after mold clamping, blown air is blown into the parison at a pressure of 0.1 MPa after mold clamping. Got. The MFR is measured with a test load of 2.16 kg according to JIS K-7210.

(Example 2)
Sample B was obtained in the same manner as in Example 1 except that the extrusion speed was 750 kg / hour.

(Example 3)
Sample C was obtained in the same manner as in Example 1 except that nitrogen gas was used instead of carbon dioxide gas.

Example 4
Sample D was obtained in the same manner as in Example 1 except that nitrogen gas was used instead of carbon dioxide gas and the extrusion rate was 700 kg / hour.

(Example 5)
Sample E was obtained in the same manner as in Example 1 except that nitrogen gas was used instead of carbon dioxide gas and the extrusion rate was 600 kg / hour.

(Example 6)
Sample F was obtained in the same manner as in Example 1 except that the extrusion speed was 600 kg / hour.

(Comparative Example 1)
Instead of the extrusion head shown in FIG. 3, a conventional extrusion head shown in FIG. 9 was used. That is, the mixed resin mixed by the extruder was supplied from a horizontal accumulator cylinder (external die accumulator) provided outside the die head to the crosshead using a plunger, and extruded as a cylindrical parison from the die slit. The extrusion speed was 450 kg / hour.
A sample G was obtained in the same manner as Example 1 except for these.

(Comparative Example 2)
Sample H was obtained in the same manner as in Comparative Example 1 except that nitrogen gas was used instead of carbon dioxide gas.

(Comparative Example 3)
Sample I was obtained in the same manner as in Comparative Example 1 except that the extrusion speed was 300 kg / hour.

The physical properties of Samples A to I obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated as follows. Samples A to I were cut with a microtome (RM2145, manufactured by LEICA) at a relatively flat portion at both ends and the center in the longitudinal direction, and a cut cross section was photographed with a CCD camera (Keyence VH-630).
1. Average wall thickness (mm)
The thickness of each of the three points obtained by photographing samples A to I with a CCD camera was measured from the photograph, and the average value of each value was obtained by calculation.
2. Foaming ratio The foaming ratio was calculated by dividing the density of the mixed resin used in samples A to I by the apparent density of the wall surfaces of the corresponding samples A to I.
3. Average bubble diameter (μm)
For each of the three points obtained by photographing the samples A to I with a CCD camera, the size in the thickness direction of the bubble diameter at five equally spaced points from the outside in the thickness direction of the wall surface was measured from the photograph, and the average value was obtained by calculation.
4). Centerline average roughness (Ra) (μm)
The center average roughness of samples A to I was measured using a surface roughness measuring instrument (Surfcom 470A manufactured by Tokyo Seimitsu Co., Ltd.) according to JIS B0601. The measurement site | part of the surface roughness of a foam blow molded object measured the outer five points of the wall surface of a foam blow molded object, and the inner five points of the wall surface, and made it the average value.
5. Standard deviation of bubble diameter (μm)
The standard deviation was obtained by calculation from the values of the bubble diameter in the thickness direction at a total of 15 points measured when calculating the average bubble diameter.
The results obtained from these evaluations are shown in Table 1.

[Table 1]

Samples A to F of Examples 1 to 6 can be extruded as a parison in a short time by using an in-die accumulator having a high injection rate. As a result, the standard deviation of the bubble diameter of the bubble cell is small. A foamed blow molded article having a high surface smoothness (small variation in bubble diameter distribution) could be obtained.
It was also found that the cell diameter can be made smaller by using supercritical nitrogen as the foaming agent.

  On the other hand, in Samples G to I of Comparative Examples 1 to 3, variation occurred in the bubble diameter distribution of the bubble cells. This means that when an off-die accumulator is used, the molten thermoplastic resin stored in the cylinder is pushed out by changing the direction of flow by 90 degrees at the crosshead during extrusion, and is provided outside the die. This is presumably because the pressure loss of the extruded thermoplastic resin increases because the distance from the cylinder to the die slit extruded as a parison is relatively long.

Next, the effects of Samples A to I obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated as follows.
1. Photo A comparatively flat portion at the center in the longitudinal direction of Samples A and G obtained in Example 1 and Comparative Example 1 was cut out with a microtome (LEICA RM2145), and the cut cross section was taken with a CCD camera (Keyence VH-6300). I took a picture.
A photograph of Sample A obtained in Example 1 is shown in FIG. 7, and a photograph of Sample G in Comparative Example 1 is shown in FIG.
2. Peel strength (gf)
A non-woven fabric (hereinafter referred to as “packing”) (thickness 3 mm, width 10 mm) with a double-sided tape attached to each test piece cut out from Samples A to I, and one end face of the packing was adhered to the test piece. The tensile tester was attached to the other end face.
Then, the other end face of the packing was pulled with a tensile tester so as to be folded back to the one end face side, and the peel strength at that time was measured. The packing used was a nonwoven fabric / acrylic adhesive material (double-sided tape # 5782 for interior member fixation manufactured by Sekisui Chemical Co., Ltd.) having an adhesive strength of 18.6 N / 25 mm according to JIS Z0237 (180 ° peeling method). 300 mm / min.
The obtained results are shown in Table 2.
3. Appearance The appearance of Samples A to I was visually evaluated according to the following criteria.
○: The surface is smooth and has a uniform appearance. Δ: The surface is relatively smooth but the appearance is inferior. ×: The surface irregularities are clearly visible and the appearance is inferior. Is shown in Table 2.

[Table 2]

Samples A to F of Examples 1 to 6 of the present invention were superior in peel strength to samples G to I of Comparative Examples 1 to 3. Thereby, it can be said that the foamed blow molded article of the present invention is excellent in smoothness.
From these, according to the present invention, it was confirmed that a foamed blow-molded article having a uniform cell size, light weight and high surface smoothness can be obtained.

  The foamed blow molded article according to the present invention can be applied to vehicle interior materials and the like in addition to vehicle air conditioning ducts and skin panels. The foam blow molded article contributes to weight reduction of the vehicle without deteriorating various physical properties as a plastic part.

1. Air conditioning duct (foamed blow molded product)
2 ... Base 3 ... Panel with skin (foamed blow molded product)
DESCRIPTION OF SYMBOLS 4 ... Skin material 5 ... Hollow part 6 ... Reinforcement rib 11 ... Main-body part 12 ... Air outflow part 13 ... Air inflow part 20 ... Extrusion head 21 ... Die slit 22 ... Ring-shaped piston 27 ... Mandrel 28 ... Die outer cylinder 29 ... Cylindrical space 32 ... Parison 33 ... Split mold 35 ... Accumulator S1 ... Mixing process S2 ... Storage process S3 ... Extrusion process S4 ... Molding process

Claims (9)

In the foamed blow molded article comprising a wall portion formed by blow molding a thermoplastic resin mixed with a foaming agent,
The wall is a closed cell structure including a plurality of bubble cells,
The closed cell structure has a closed cell ratio of 70% or more,
The bubble cell has a flat shape in a direction perpendicular to the thickness direction of the wall,
The average cell diameter of the cell in the thickness direction of the wall is 56 μm or more and less than 300 μm,
A foamed blow molded article having a center line average roughness Ra of the outer surface of the wall portion of less than 9.0 μm, and a standard deviation of the bubble diameter of the bubble cell in the thickness direction of the wall portion being 47 μm or less .   The foam blow molded article according to claim 1, wherein the expansion ratio of the wall portion is 2.0 times or more. The foamed blow molded article according to claim 1 or 2, wherein the thermoplastic resin is made of a polyolefin resin. The foamed blow molded article according to claim 3 , wherein the polyolefin resin is a propylene homopolymer having a long-chain branched structure. Foamed blow molded article according to any one of claims 1 to 4 Standard deviation of cell diameter is less than 30μm of the foamed cells in the thickness direction of the front Kikabe portion.   It is a vehicle air-conditioning duct, The foaming blow molded object as described in any one of Claims 1-5. A method of manufacturing a foamed blow molded article,
Adding a thermoplastic resin to the foaming agent and mixing with an extruder to make a mixed resin;
A storage step of storing the mixed resin in a cylindrical space between the mandrel and the die outer cylinder;
An extrusion process for extruding the parison between the split molds at an extrusion speed of 700 kg / hour or more from the die slit using a ring-shaped piston;
A forming step of performing blow molding by blowing air in a range of 0.05~0.15MPa the parison clamping between the split molds, into said parison,
Equipped with a,
The wall portion of the obtained foamed blow molded article has a closed cell structure including a plurality of cell cells,
The closed cell structure has a closed cell ratio of 70% or more,
The bubble cell has a flat shape in a direction perpendicular to the thickness direction of the wall,
The average cell diameter of the cell in the thickness direction of the wall is 56 μm or more and less than 300 μm,
A method for producing a foamed blow molded article, wherein the standard deviation of the bubble diameter of the bubble cell in the thickness direction of the wall portion is 47 μm or less .   The method for producing a blow-molded foam according to claim 7, wherein the thermoplastic resin is a polyolefin resin, and the foaming agent is in a supercritical state. The manufacturing method of the foam blow molding of Claim 7 or 8 using the foaming agent which consists of nitrogen .

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