JP2010037367A - Polyolefin resin foam and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin resin foam which has a high expansion ratio, e.g. 35 times or larger, has small cells, is excellent in cell dispersibility and has small heat conductivity, and to provide a production method thereof. <P>SOLUTION: The production method of the polyolefin resin foam comprises carrying out melt-extrusion and foaming of a mixture using an extruder equipped with a multi-hole die having 50-5,000 openings of 0.1-10 mm in diameter, provided that the mixture is obtained by adding a foaming agent comprising carbon dioxide in a liquefied or supercritical state to a linear polyolefin resin composition containing 0.3-1.5 mass% porous microgranules. The mixture is extruded under the atmosphere at a discharge amount V of 0.05-0.45 kg/hr per opening of the die and at a proximal resin pressure of 7-20 MPa at the opening of the die. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyolefin resin foam having a high expansion ratio and excellent thermal conductivity, and a method for producing the same.

  Conventionally, in order to obtain a foam of thermoplastic resin such as polyolefin, it is known to foam using a chemical foaming agent or a hydrocarbon foaming agent, or by adding water or liquefied carbon dioxide to vaporize it. ing. It is also known that an organic balloon is added to form a foam cell with the balloon.

For example, in Patent Document 1, a thermoplastic resin and a balloon made of a resin are mixed at a volume ratio of 80:20 to 15:85 to form a mixture, and the mixture is mixed with carbon dioxide at a temperature lower than the melting point of the thermoplastic resin and the balloon. By dissolving a supercritical fluid such as carbon under a predetermined pressure and reducing the pressure of the mixture in which the supercritical fluid is dissolved, the density is 0.2 g / cm ³ or less, and the shrinkage after the production is 3% or less. It is disclosed to produce a foam that is

  Patent Document 2 discloses that ultrahigh molecular weight polyolefin having an intrinsic viscosity [η] of 10 to 40 dl / g is 8 to 40% by weight, and polyolefin 92 to 60 having an intrinsic viscosity [η] of 0.1 to 5 dl / g. A linear polyolefin foam composed of a linear polyolefin having a weight percent, a crystallinity of 45% or more, and an intrinsic viscosity [η] of 1 to 15 dl / g is disclosed. In this case, it is described that it is possible to use an inorganic fine powder that acts as a foam nucleating agent.

As the inorganic fine powder, talc, calcium carbonate, clay, magnesium oxide, zinc oxide, glass beads, glass powder, titanium oxide, carbon black, anhydrous silica and the like are used. Of these, talc, calcium carbonate, titanium oxide, and anhydrous silica are preferred. The particle size of the inorganic fine powder needs to be 50 μm or less, preferably 10 μm or less, more preferably 5 μm or less. In particular, if an inorganic fine powder having a particle size of 50 μm or less is used, It describes that the surface appearance is good.
In addition, the amount of inorganic fine powder added in Patent Document 2 is 0.01 to 40 parts by weight, preferably 0.05 to 100 parts by weight with respect to 100 parts by weight of the linear polyolefin in order to improve the surface appearance. It is described that it is in the range of 20 parts by weight, more preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight.

JP 2005-104998 A JP 2001-146530 A

  Depending on the application, polyolefin resin foam is used as a heat insulating material, but in addition to low thermal conductivity, the foam is lighter or the thickness of the foam is increased by weight reduction. Although it is desirable to increase the thermal resistance value, for that purpose, it is desired that the foam has as high a magnification as possible. On the other hand, it is difficult to increase the expansion ratio of polyolefin resin, and as described in Patent Document 1 and Patent Document 2 described above, it is about 2 to 3 times at most. Conventionally, in the case of a non-crosslinked polyolefin resin, foaming is performed. It was not easy to make the magnification 30 times or more, further 32 times or more, and preferably 35 times or more.

  That is, in Patent Document 1, a supercritical fluid and a resin balloon are used as a material for foaming a thermoplastic resin, and this balloon is removed by extraction with a supercritical fluid in a later process and used as a cell forming material for a foam. ing. For this reason, in order to form a large number of foam cells with the balloon, it is necessary to include a large amount of the balloon. For example, when the amount of the balloon is 15% by mass or more, the dispersibility of the balloon in the resin is reduced. As a result, the foam had problems that not only foamed cells became non-uniform and contained many voids, but also the foaming ratio was low and the thermal performance was sufficient. In addition, a large amount of supercritical fluid is required to extract the resin machine balloon, which increases the processing cost.

  In Patent Document 2, when foaming a linear polyolefin resin with carbon dioxide in a supercritical state, as described above, as a foam nucleating agent, talc, calcium carbonate, It describes that 0.01 to 40 parts by weight of an inorganic fine powder such as titanium oxide or anhydrous silica is added to 100 parts by weight of a linear polyolefin. However, Patent Document 2 does not describe that the foaming ratio can be increased by adding these inorganic fine powders, and the foaming ratio of the disclosed polyolefin resin foam is doubled in Example 1, In Example 2, it is as small as 3 times.

  The object of the present invention is a foam having a high expansion ratio, for example, a foam of 30 times or more, further 32 times or more, and preferably 35 times or more, and the cells of the foam are small and the dispersibility of the cells is improved. An object of the present invention is to provide a polyolefin resin foam having excellent thermal conductivity and a method for producing the same.

  As a result of diligent research to achieve the above object, the present inventors have found that when a foam is obtained from a composition containing a polyolefin resin, a specific amount of microporous particles is contained as the composition containing the polyolefin resin. It is quite unexpected that conventional additives are used and the addition of liquefied or supercritical carbon dioxide as a blowing agent is foamed under specific conditions using an extruder. For example, it was found that a foam having an expansion ratio of 30 times or more, further 32 times or more, and particularly 35 times or more was obtained.

The present invention is based on such knowledge and has the following gist.
1. An additive in which a foaming agent composed of carbon dioxide in a liquefied or supercritical state is added to a linear polyolefin resin composition containing 0.3 to 1.5% by mass of fine porous particles, Is an extruder having a multi-hole die having a numerical aperture of 50 to 5000, and a discharge amount V per opening of the die is 0.05 to 0.45 kg / hour, A method for producing a polyolefin resin foam, characterized by melt-extrusion in the atmosphere and foaming under the condition that the resin pressure at the die opening is 7-20 MPa.
2. The method for producing a polyolefin resin resin foam according to claim 1, wherein the microporous granular material has a bulk specific gravity of 0.1 to 1.0 g / cc.
3. 3. The method for producing a polyolefin resin foam according to 1 or 2 above, wherein the microporous particles have an average particle diameter of 10 to 80 μm.
4). 4. The method for producing a polyolefin resin foam according to any one of 1 to 3 above, wherein the microporous granular material is a vitreous spherical hollow body.
5). The polyolefin resin foam according to any one of 1 to 4 above, wherein 4 to 20 parts by mass of the carbon dioxide is mixed with respect to 100 parts by mass of a total amount of the linear polyolefin resin and the microporous granular material. Manufacturing method.
6). 1 to 5 above, wherein the linear polyolefin resin is a polypropylene resin in which the relationship between the melt tension (MT) at 230 ° C. and the melt flow rate (MFR) at 230 ° C. satisfies the following formula (A): The manufacturing method of the polyolefin resin foam in any one of.
Log (MT)> − 1.33 Log (MFR) +1.2 (A)

7. The relationship between the melt tension (MT) at 230 ° C. and the melt flow rate (MFR) at 230 ° C. includes a linear polypropylene resin that satisfies the following formula (A), and the foam has a small amount A polyolefin resin foam containing spherical fragments, having an expansion ratio of 30 to 45 times, and an average cell diameter of the foam of 200 to 350 μm.

Log (MT)> − 1.33 Log (MFR) +1.2 (A)

8). 9. The polyolefin resin foam according to 8 above, wherein the expansion ratio is 1.2 to 1.8 times that of a foam that does not include a microporous granular material and / or a fragment thereof.

Log (MT)> − 1.33 Log (MFR) +1.2 (A)

  According to the present invention, a foam with a high expansion ratio, for example, a foam of 30 times or more, further 32 times or more, particularly 35 times or more, and the cells of the foam are small and the cell uniformity is excellent. In addition, a polyolefin resin foam having low thermal conductivity and a method for producing the same are provided.

  The reason why the present invention provides a polyolefin resin foam having an extremely high expansion ratio and excellent properties as described above is not necessarily clear, but is presumed as follows.

  The foam of the present invention includes a microporous granule, but is characterized by including at least a fragment shape that does not retain the original shape of the microporous granule. In particular, the microporous particles are considered to be destroyed by the above specific temperature conditions, discharge amount, and resin pressure in the die, and the reason for this is not clear, but this makes the expansion ratio more than the volume added with microporous particles. It seems that it is increasing.

  In the present invention, a linear polyolefin resin composition is used. The polyolefin resin includes a polyolefin homopolymer or a polyolefin copolymer. In addition, the term “linear” as used herein refers to an aggregate of polymers obtained by polymerizing each molecular chain of the olefin polymer into a substantially single string that is not branched and has a linear structure. That means. Since this linear polymer does not have a cross-linked structure using a method such as chemical cross-linking or electron beam cross-linking or a graft structure such as long-chain branching, production and quality control are relatively easy, Also suitable for repeated thermal histories that are received in the process of re-pelletizing and the like applied at the time of recycling, since the molecular structure hardly deteriorates.

  In the present invention, the polyolefin resin is preferably a polypropylene resin (hereinafter referred to as polypropylene resin A). The polypropylene resin A preferably has a melt tension of 5 to 30 g at 230 ° C., more preferably 6.5 to 20 g, and most preferably 7.5 to 10 g. If the melt tension value is less than 5 g, cell breakage is likely to occur at the time of foaming, which is not preferable, and if it exceeds 30 g, sufficient cell growth is not performed at the time of foaming, which is not preferable.

In the polypropylene resin A, the relationship between the melt flow rate (MFR) at 230 ° C. and the melt tension (MT) at 230 ° C. preferably satisfies the following formula (A). MFR is calculated | required by the method according to ASTM-D1238 here.

Log (MT)> -1.33 Log (MFR) + 1.2 (A)

When the polypropylene resin A does not satisfy the above formula (A) in the relationship between the above-described melt tension and MFR, the melt fluidity of the resin becomes too poor with respect to the increase in melt tension. It is not preferable because a problem such as a very high resin pressure occurs or it may be difficult to obtain a high-magnification foam because sufficient elongation of the cell membrane cannot be obtained at the time of foaming. In particular, the value on the left side in the above formula (A) is preferably 0.5 to 3 larger than the value on the right side, particularly preferably 0.5 to 2 larger.

  The polyolefin resin composition in the present invention may contain a polypropylene resin other than the polypropylene resin A (hereinafter referred to as polypropylene resin B). Examples of the polypropylene resin B include a propylene homopolymer, a copolymer mainly composed of propylene and an α-olefin other than propylene copolymerizable with the propylene, a polypropylene resin, and a polyethylene resin, for example. And a mixture with a polyolefin resin other than a polypropylene resin. These polyolefin resins may be used alone or in combination of two or more.

  As the polypropylene resin B, among them, the extrusion foamability and the performance of the resulting foam are excellent, so that a propylene polymer having a relatively large molecular weight or a copolymer mainly composed of propylene and ethylene is used. Alternatively, a mixed resin of a polypropylene resin and a polyethylene resin is preferably used.

  The α-olefin other than propylene copolymerizable with the polypropylene is not particularly limited, and examples thereof include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1 -Heptene, 1-octene, etc. are mentioned. These α-olefins other than propylene may be used alone or in combination of two or more.

  When the polyolefin resin composition in the present invention contains a polypropylene resin B other than the polypropylene resin A, the polypropylene resin B is preferably not more than 200 parts by mass, particularly preferably not more than 200 parts by mass of the polypropylene resin A. Is preferably 100 parts by mass or less. When the content of the polypropylene resin B exceeds 100 parts by mass, the influence of the polypropylene resin B on the foaming property is increased, and in some cases, the possibility of inhibiting the foaming property is large, which is not preferable. Further, when a mixed resin of a polypropylene resin and a polyethylene resin is used as the polypropylene resin B, it is not particularly limited, but the content of the polypropylene resin in the mixed resin is 40 to 100% by weight. It is preferable that it is 60 to 100 weight%. When the content of the polypropylene resin in the mixed resin is less than 40% by weight, the mechanical strength and heat resistance of the obtained foam may be insufficient.

The fine porous particles contained in the polyolefin resin composition in the present invention are fine particles having pores such as a hollow shape or a porous shape, and the bulk specific gravity is preferably 0.1 to 1.0 g / cm. ^3, more preferably 0.1 to 0.8 g / cm ^3, in particular 0.1 to 0.5 g / cm ³ there is preferably. The average particle diameter is preferably 100 μm or less, more preferably 10 to 80 μm, and particularly preferably 50 to 70 μm. The material is not particularly limited, such as inorganic materials such as glassy and ceramics, woody materials, and organic materials, but is preferably an inorganic material and preferably has a low water content. Of these, shirasu balloons and glassy microspherical hollow bodies are preferred.

  Here, the average particle diameter is defined by an average particle diameter measured by a 50% diameter of the weight cumulative particle size distribution, and is measured by, for example, a dry sieving method or a laser method.

  In the present invention, the microporous granular material is preferably used in a composition containing a linear polyolefin resin in an amount of 0.3 to 1.5 parts by mass, more preferably 0.4 to 1.3 parts by mass. The The amount of microporous particles used greatly affects the foaming ratio of the foam. When the amount used is small, the foaming ratio is 1.2 to 1.2 compared to the foam without the addition of microporous particles. If the foam does not swell 1.8 times and is too large, the foam does not expand to the following expansion ratio as in the case of the foam to which the microporous granular material is not added.

In the present invention, when a polyolefin resin foam is produced, a linear polyolefin resin and a microporous sphere are sufficiently uniformly mixed. The resulting polyolefin resin composition is made into a molten state and then added with liquefied or supercritical carbon dioxide as a foaming agent. The amount of carbon dioxide added is preferably 4 to 20 parts by mass, more preferably 5 to 15 parts by mass, when the total amount of the linear polyolefin resin and the microporous granule is 100 parts by mass. Is preferred. If the amount of carbon dioxide added is small, the cell will be enlarged and the heat insulation property will be impaired or the expansion ratio will be reduced. Conversely, if it is too large, voids will be generated due to carbon dioxide that does not melt into the resin. Appearance will be significantly impaired. The addition amount (mass%) of carbon dioxide (CO ₂ ) is obtained by the following formula.

Carbon dioxide addition amount (% by mass) = Carbon dioxide supply amount (kg / hr)
/ Extruder total discharge (kg / hr) x 100

In the polyolefin resin composition used in the present invention, one or more of the following various additives may be added as necessary within the range not impairing the object of the present invention. Phenol, phosphorus, amine, sulfur and other antioxidants (anti-aging agents); heat stabilizers; light stabilizers; UV absorbers; phosphorus, nitrogen, halogen, antimony and other flame retardants; Lubricant ;; Metal harm preventive agent; Antistatic agent; Filler; Colorant; Cell nucleating agent;

  The cell nucleating agent is not particularly limited, but talc, calcium carbonate, clay, kaolin, mica, magnesium oxide, zinc oxide, carbon black, glass, quartz, silica, alumina, nobicularite, hydrated alumina, Examples thereof include iron, iron oxide, silicon dioxide, and titanium oxide.

  The crystal nucleating agent is not particularly limited, but generally includes a rosin-based crystal nucleating agent, a sorbitol-based crystal nucleating agent, and a phosphate ester-based crystal nucleating agent. The rosin-based crystal nucleating agent is not particularly limited as long as it is a rosin-based resin, and examples thereof include dibenzylidene sorbitol (DBS) manufactured by Shin Nippon Rika Co., Ltd. The phosphoric acid ester salt nucleating agent is not particularly limited, and examples thereof include NA-11 manufactured by Asahi Denka Kogyo Co., Ltd. These crystal nucleating agents may be used alone or in combination.

  In the present invention, the foam is produced from the polyolefin resin composition by using an extruder having a die attached to the tip and having a foaming mechanism. A mixture obtained by adding carbon dioxide to a polyolefin resin composition is discharged into the atmosphere at a melt extrusion temperature of preferably 160 to 250 ° C., and a resin pressure (pressure loss) immediately near the die opening is preferably 7 to 20 MPa. Let Here, the immediate vicinity of the die opening means the resin immediately before entering the die opening. As a specific example, the resin flow path between the tip of the extruder connected to the die and the die opening. Say.

  If the melt extrusion temperature is less than 160 ° C., the dissolution and diffusion of carbon dioxide in the resin is poor, and if it exceeds 250 ° C., deterioration such as molecular chain breakage due to heat of the polypropylene-based resin is not preferable. In particular, the melt extrusion temperature is preferably 170 to 240 ° C.

  Furthermore, the resin temperature immediately before the resin enters the die opening is preferably 170 to 200 ° C. If it is lower than 170 ° C., it is not preferable because sufficient elongation cannot be given to the resin. On the other hand, when the temperature exceeds 200 ° C., it cannot be cooled and solidified immediately after foaming, and thus heat shrinks. The die mold temperature is preferably 175 to 190 ° C, more preferably 180 to 185 ° C.

  Further, in the present invention, the pressure loss in the immediate vicinity of the die in the extruder is 7 to 20 MPa, and when the pressure loss is less than 7 MPa, carbon dioxide dissolved in the polyolefin resin composition is inside the extruder. Further, vaporization is likely to occur inside the die, and foaming occurs inside the apparatus, resulting in cell foaming, excessive growth, a decrease in expansion ratio, and a significant decrease in appearance. When the pressure loss exceeds 20 MPa, large shearing is likely to be applied to the cell during cell formation in foaming, and cell foaming and cell structure non-uniformity are likely to occur, and the resin solidifies before the resin is fully stretched. Therefore, the cells cannot be sufficiently grown, and as a result, the expansion ratio is not increased, which is not preferable. Such imperfect cell structure is a major obstacle to exhibiting sufficient appearance and thermal performance as a foam. The pressure loss is preferably 7.5 to 20 MPa, more preferably 8 to 15 MPa.

  The die in the extruder used in the present invention has an opening (hole) diameter of the die of 0.1 to 10 mm, preferably 0.5 in terms of appearance of the molded product after foaming and ease of shape adjustment. ~ 3mm. If the diameter is less than 0.1 mm, the strand diameter of the foam structure is too small, and it is easy to tear at the time of take-off, and if it exceeds 10 mm, the strand diameter is too large, the resin pressure is too low, or immediately after foaming It is not preferable because it becomes difficult to cool down and heat shrinks, making post-molding difficult to achieve smoothness. The depth of the die is preferably 0.1 to 50 mm, and a plurality of openings are preferably provided on the front surface of the die.

Moreover, the number of openings (holes) of the die in the extruder used in the present invention is 50 to 5000, and preferably a multi-hole type die having 100 to 3000, and the discharge amount V in one opening (hole) of the die is 0. It needs to be 0.05 to 0.45 kg / hr. The discharge amount V (kg / hr) per one hole opening of the die is obtained by the following equation.

Discharge rate per die opening V (kg / hr)
= Extruder total discharge (kg / hr) / Number of dies opened

Adjustment of the discharge amount V per die opening to the above range increases the screw rotation speed of the extruder; increases the pitch between the screw threads of the extruder; deepens the groove between the screw threads of the extruder; Can be performed.

  When the discharge amount V (kg / hr) per die opening is less than 0.05, not only the productivity is inferior, but also the foaming ratio is lowered, the heat insulating performance is inferior, and the pressure suitable for foaming at the die part. It is difficult to maintain the loss, and it is difficult to obtain a foam having a sufficient magnification. On the other hand, if the discharge amount V (kg / hr) exceeds 0.45, the resin is solidified before the resin is sufficiently stretched, so that the cell cannot be sufficiently grown. As a result, the expansion ratio is not increased and the appearance is also improved. It is not preferable because it is damaged, and cell foaming is likely to occur. Not only cannot a sufficient heat insulating performance be obtained, but also the foamed shape cannot be maintained, but it is not preferable. In particular, the discharge amount V (kg / hr) is preferably 0.06 to 0.3.

  The total extrusion discharge amount is preferably 1 to 1000 kg / hr, although it depends on the specifications of the extruder. In an actual production machine type having a relatively large screw diameter, 20 to 1000 kg / hr is preferable. On the other hand, the total extrusion discharge rate is preferably about 15 kg / hr to 50 kg / hr for a laboratory type with a relatively small screw diameter. Especially, in order to make the open cell ratio in the foamed material 60% or more, the total extrusion discharge rate is more preferably 20 to 50 kg / hr in the laboratory type, and 180 to 1000 kg / hr in the actual production machine type. Is more preferable.

  If the total extrusion discharge amount is too large, the expansion ratio is preferably high, but if the temperature of the foamed resin is not sufficiently controlled, cell foaming tends to occur and sufficient heat insulation performance cannot be obtained. In addition, the foamed shape may not be maintained. On the contrary, if the total extrusion discharge amount is too small, not only the productivity is inferior, but also the heat insulation performance is inferior, and it becomes difficult to maintain a pressure loss suitable for foaming at the die part, and a foam with sufficient magnification can be obtained. You may not get it.

  For the extruder to be used, the screw diameter (D) is preferably 40 to 80 mm, and the L / D when the screw length is L is preferably 15 to 40, and the two screws are connected in series. A tandem type extruder constructed on the basis of combination is preferable. By using the tandem type, the pressure loss condition and the discharge amount of the die part suitable for foaming can be controlled independently by the number of rotations of each screw, which is suitable for the production of a foam. The shape of the die to be used is not limited, but the number, shape, and thickness of the openings are preferably designed so that the pressure loss per opening is preferably 7 to 20 MPa. Selection of the die satisfying such conditions can favorably obtain a foam exhibiting sufficient thermal performance.

However, the extruder used in the present invention is not limited to the tandem type, and a foam with a high expansion ratio and a good appearance can be obtained if sufficient temperature control is possible even with a single type.
When a tandem type extruder is used, there is an advantage that it is easy to increase the magnification because the resin temperature can be controlled sufficiently, but it is difficult to balance the injection amount of the first stage and the second stage, and the work becomes complicated, Furthermore, there is a disadvantage that the apparatus becomes expensive.

  On the other hand, when a single type extruder is used, the work is simple and the cost of the equipment is low, but if sufficient resin temperature control is not possible, the extrusion capacity cannot be fully exhibited or the foaming ratio becomes high. There is also a disadvantage that the appearance is impaired.

  Furthermore, as a specific example of the method for producing a foam of the present invention, the above-mentioned polyolefin resin composition is, for example, an extruder equipped with a liquid or supercritical carbon dioxide supply line from a carbon dioxide supply machine in the middle of a cylinder barrel. When is used, it is performed as follows. That is, the foamable polyolefin resin composition is heated to a predetermined temperature and uniformly melted and kneaded, and then supplied together with a predetermined amount of carbon dioxide from the supply line of the extruder and extruded into a sheet or board shape. By doing so, a foam is manufactured.

  Furthermore, if necessary, in order to adjust the form of the foam, the shape and the size may be adjusted using a cutting machine, a sandwiching conveyor, or the like. Also, if necessary, for example, an aluminum sheet, a non-woven fabric, a sheet-like material such as Taniyama leather may be bonded to one or both sides of the foam as a face material, mechanical strength, heat resistance, flame resistance, Various performances such as antistatic may be imparted.

  Depending on the linear polyolefin resin used, the foam of the present invention can have an expansion ratio of 30 times or more, preferably 32 times or more, more preferably 35 to 45 times. Is possible. If the value is less than 30 times, the weight and raw material cost cost are excessively increased in order to develop sufficient member thermal performance.

  In the present invention, as described above, a polyolefin resin composition containing microporous particles is used. However, in the obtained polyolefin resin foam, the microporous particles used remain almost intact. It will be included in a more crushed form. This is presumed that the microporous granule is broken in the process of melt foaming by the extruder under the above specific temperature conditions, discharge amount, and resin pressure in the die. Although the reason is not clear, it is considered that the expansion ratio is increased beyond the volume of the microporous granular material added.

  The polyolefin resin foam of the present invention has the above-described high expansion ratio and an average cell diameter of preferably 350 μm or less, and more preferably 100 to 350 μm, in order to develop excellent thermal performance. The average cell diameter here is determined by cutting the obtained foam into test pieces, observing the cross-sectional area with an SEM, and taking the average value.

  In addition, the polyolefin resin foam of the present invention has a thermal conductivity measured in accordance with JIS-A1412, preferably 20 to 45 mW / mK, particularly preferably 20 to 40 mW / mK, and suitable heat insulation properties. Have.

  In order to describe the present invention more specifically, examples will be given below, but the present invention should not be construed as being limited to these examples.

Examples 1-8, Comparative Examples 1-11
The polypropylene resin A includes a polypropylene resin (Prime Polymer Co., Ltd.) having an MFR at 230 ° C. of 3.3 (g / 10 min) and a melt tension at 230 ° C. of 7.6 g. As a stabilizer, Irganox A polypropylene resin composition containing 5000 ppm of a mixture of 1010 and Irgaphos 168 (Ciba Specialty Chemicals Co., Ltd.) and containing various components shown in Tables 1 and 2 in various contents as microporous particles was obtained. . Each component was sufficiently mixed by dry blending with a Henschel mixer so as to have a uniform composition.

  In addition, in Examples 1-5, 7, and 8 and Comparative Examples 2 and 7-11 as a microporous granular material, a shirasu balloon (manufactured by Marunaka Shiratosha) shown in Table 1 was used, and in Example 6, Using foamed perlite (trade name of Mitsui Kinzoku Mining Co., Ltd .: RocaHelp), Comparative Examples 3 to 6 are solid fine powders that are not fine porous particles, and Comparative Example 1 does not contain fine porous particles. The resin composition was performed alone.

  For each of the above polypropylene resin compositions, a tandem type in which a carbon dioxide supply line from a supercritical carbon dioxide supply machine (CO2-3 manufactured by Kawata Co., Ltd.) is attached to the first stage and a die 1 is attached to the tip of the second stage. Using a single screw extruder (KGT-50-65 manufactured by Kawata), extrusion foam molding was performed under the conditions shown in Tables 1 and 2.

  In Comparative Examples 7 to 11, extrusion was performed under the production conditions where the discharge amount V per opening of the die was 0.05 to 0.45 kg / hr, or the resin pressure at the opening of the die was not 7 to 20 MP.

  About the polypropylene resin foam obtained in Examples and Comparative Examples, (1) foam density, (2) average cell diameter, (3) foaming ratio, (4) thermal conductivity, (5) foaming ratio , And (5) discharge amount were evaluated by the following methods, and are shown in Table 1 and Table 2, respectively.

Further, the polypropylene resin foam obtained in Example 1 was observed with an electron microscope (manufactured by Shimadzu Corporation, trade name: Superscan 220), and a micrograph (magnification 50 times) is shown in FIG.

(1) Foam density: The foam is cut into a rectangular test piece of 20 cm × 20 cm × 2.5 cm, the weight and length of each side are accurately measured, and the foam density is calculated by the following formula. Calculated.

Foam density (g / cm ³ ) = foam weight (g) / foam volume (cm ³ )

(2) Average cell diameter: The obtained foam was cut into a rectangular test piece having the same dimensions as described above, and its cross-sectional area was observed at a magnification of 50 times using a SEM superscan 220 manufactured by Shimadzu Corporation. The average cell diameter of approximately 10 to 20 cells was calculated.

(3) expansion ratio: Polypropylene resin of resin density 910 kg / ^{m 3} from the product density calculated in (1) to calculate the expansion ratio by the following equation.

Foaming ratio (times) = 910 / foam density (g / cm ³ )

(4) Thermal conductivity: In accordance with JISA-1412, the obtained foam was cut into rectangular test pieces having the same dimensions as described above, and a thermal conductivity measuring device HC-074 manufactured by Eihiro Seiki Co., Ltd. was used. The thermal conductivity was measured.

(5) Discharge amount: The foam was extruded and produced continuously for 1 hour under each condition, and the total weight of the obtained foam was weighed to obtain the discharge amount.

  The shape of the polyolefin resin extruded foam of the present invention is arbitrary such as a sheet shape, a rod shape, a cylinder shape, a block shape and the like since it has substantially no cross-linked structure. For example, in the case of a sheet form, the extruded foam can be secondarily formed by vacuum forming, pressure forming, matched die, or the like to obtain a second formed body such as a tray or a container. As its application, it can be widely used for automobile parts, general consumables such as stationery, and packaging cushioning.

The microscope picture of the polypropylene resin foam manufactured in Example 1 is shown.

Claims (8)

  An additive in which a foaming agent composed of carbon dioxide in a liquefied or supercritical state is added to a linear polyolefin resin composition containing 0.3 to 1.5% by mass of fine porous particles, Is an extruder having a multi-hole die having a numerical aperture of 50 to 5000, and a discharge amount V per opening of the die is 0.05 to 0.45 kg / hour, A method for producing a polyolefin resin foam, characterized by melt-extrusion in the atmosphere and foaming under the condition that the resin pressure at the die opening is 7-20 MPa.   The method for producing a polyolefin resin resin foam according to claim 1, wherein the microporous granular material has a bulk specific gravity of 0.1 to 1.0 g / cc.   The method for producing a polyolefin resin foam according to claim 1 or 2, wherein the microporous granular material has an average particle diameter of 10 to 80 µm.   The method for producing a polyolefin resin foam according to any one of claims 1 to 3, wherein the microporous granular material is a vitreous spherical hollow body.   The polyolefin resin foam according to any one of claims 1 to 4, wherein the carbon dioxide is added in an amount of 4 to 20 parts by mass with respect to 100 parts by mass of a total amount of the linear polyolefin resin and the microporous granular material. Body manufacturing method. The linear polyolefin resin is a polypropylene resin in which the relationship between the melt tension (MT) at 230 ° C and the melt flow rate (MFR) at 230 ° C satisfies the following formula (A): 6. The method for producing a polyolefin resin foam according to any one of 5 above.
Log (MT)> − 1.33 Log (MFR) +1.2 (A) A linear polypropylene resin satisfying the following formula (A) in which the relationship between the melt tension (MT) at 230 ° C. and the melt flow rate (MFR) at 230 ° C. is 100 parts by mass of the polypropylene resin. On the other hand, it contains 0.3 to 1.5 parts by mass of microporous granular material and / or fragments thereof, and the expansion ratio is 30 to 45 times, and the average cell diameter of the foam is 200 to 350 μm. A featured polyolefin resin foam.

Log (MT)> − 1.33 Log (MFR) +1.2 (A)   9. The polyolefin resin foam according to claim 8, wherein the expansion ratio is 1.2 to 1.8 times that of a foam that does not include a microporous granule and / or a fragment thereof.