JPH0911318A - Foamed polypropylene resin and production thereof - Google Patents

Abstract

PURPOSE: To provide a method for continuously producing a foamed polypropylene resin which has a high expansion ratio, good mechanical properties including heat resistance, thermal insulation, rigidity, and impact resistance, and a smooth skin layer on the surface, and further provide a plate-shaped foamed polypropylene resin having these properties. CONSTITUTION: The temperature of an expandable molten polypropylene resin containing a foaming agent is adjusted to be lower by 0-25 deg.C than the melting point of the polypropylene resin in an extruder, the molten resin is extruded from the nozzle of the extruder under high pressure, the extruded resin which is plasticized in a foaming process is molded in a molding mold in which the temperature of the surface of a resin passage is adjusted at the crystallization temperature of the polypropylene resin or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin foam and a method for producing the same. More specifically, a method for producing a polypropylene resin foam having a high expansion ratio, excellent mechanical properties such as heat resistance and heat insulation, rigidity, and impact resistance, and having a smooth skin layer on its surface, The present invention also relates to a plate-shaped polypropylene-based resin foam obtained by the manufacturing method and suitable for use as a building material such as a heat insulating material and a packaging material such as a cushioning material.

[0002]

2. Description of the Related Art Conventionally, as one of the methods for producing a thermoplastic resin foam, a thermoplastic resin is melted in an extruder, and a foaming agent is kneaded and kept at a high pressure, and then the extruder is extruded under a low pressure. An extrusion foam molding method is widely used in which a material is extruded to foam and then molded.

Amorphous resins such as polystyrene are often used in the extrusion foam molding method. The reason is that the amorphous resin generally has a wide temperature range of foaming suitability and can be easily foamed because the temperature change of viscosity is gentle in a molten state, and the amorphous resin is extruded from a die to be foamed. At some stage, the foams can be fused together relatively easily.
For example, it can be easily integrated into a plate shape.

However, in recent years, there has been a great demand for improving the quality of foams, particularly heat resistance and impact resistance, and the foam of an amorphous resin such as polystyrene is inferior in heat resistance. As a foam capable of meeting these requirements, a foam of a polyolefin resin has been studied.

Among the above-mentioned polyolefin resins, polypropylene is a resin which has excellent heat resistance and impact resistance and can meet the above requirements, but has a relatively high crystallinity,
There is a problem that viscoelasticity changes greatly even with a slight temperature change, the temperature range suitable for foaming is extremely narrow, and it is difficult to obtain a good foam.

Further, conventionally, development of a method for producing a sheet-shaped or plate-shaped foamed body made of a polyolefin resin has been advanced.

[0007] For example, Japanese Patent Publication No. 51-14540 discloses a mold (base) attached to the tip of an extruder and having a narrow gap at the outlet to improve the fluidity of a foamable resin melt. Adjust the temperature so that it can be held, and further mold (base)
A method for producing a polyolefin resin foam by a device in which a molding device having a resin passage and a cooling device is continuously provided at the tip is described. In this method, a pressure state is induced in the resin passage by a resistance generated by a foam body advancing in parallel resin passages provided inside the molding apparatus, and the polyolefin resin is pressurized under the pressure state. The heated melt is foamed and cooled and molded.

However, in the above method, when a foamable resin melt, that is, a polypropylene resin melt containing a foaming agent, is foamed under the above-mentioned pressure state, the viscosity of the resin in the melted state is low, and therefore the flattened air bubbles And foaming occurs, and a foam having a high expansion ratio cannot be obtained. Further, in the above method, the die temperature is set to a temperature at which the foamable resin melt can maintain fluidity, but excellent surface properties,
In particular, when a foam having a smooth skin layer and a high expansion ratio is to be produced, the cell structure inside the foam can be prevented by simply setting the die temperature to a temperature at which fluidity is maintained. There is a problem that the resin temperature at the time of extrusion must be controlled accurately because it cannot be maintained in a good state without breakage.

Further, in JP-A-4-363227, a non-crosslinked polypropylene resin and a foaming agent are melt-kneaded in an extruder and extruded into an accumulator, and the melt-kneaded product is extruded from the accumulator. A method of foaming and molding is described.

However, in the above method, since the accumulator is used, the melt-kneaded product cannot be continuously extruded and foamed, so that a foam of the same quality cannot be continuously produced. There's a problem.

[0011]

In view of the above-mentioned prior art, the present inventors have found that a polypropylene resin foam, which is a crystalline resin, has a density of about 0.1 g / cm ³ or less and a thickness of 10 mm. As a result of repeated intensive research on a method for producing a plate-shaped polypropylene resin foam, which is more than a certain degree, the foamable melt of the polypropylene resin containing the foaming agent was adjusted to a specific temperature in the extruder. By extruding the foamable melt at a high pressure and molding it with a molding die whose temperature is controlled to be equal to or lower than the crystallization temperature of the resin, a smooth skin layer is provided on the surface, and a flattened internal cell structure is obtained. The inventors have found that a good state of no bubble breakage is maintained, that the foaming ratio is high, and in particular that a plate-shaped foam can be continuously and easily manufactured, and the present invention has been completed.

[0012]

That is, according to the present invention, the temperature of a foamable melt of a polypropylene resin containing a foaming agent in an extruder is 0 to 25 ° C. lower than the melting point of the polypropylene resin. And extruding the expandable melt at a high pressure from the die of an extruder, and then extruding the extrudate in a plastic state in the foaming process, the passage surface of the extrudate being equal to or lower than the crystallization temperature of the polypropylene resin. The present invention relates to a method for producing a polypropylene-based resin foam, which is characterized in that it is molded with a molding die whose temperature is adjusted to the above.

The present invention also relates to the above-mentioned manufacturing method, wherein the molding die has a passage of an extrudate in which the area of the hole on the inner surface side is gradually made larger than the area of the hole on the outer surface side.

Furthermore, the present invention relates to a plate-shaped polypropylene resin foam having a smooth skin layer on the surface obtained by the above-mentioned production method.

[0015]

Functions and Examples As described above, the method for producing a polypropylene resin foam of the present invention is such that the temperature of the expandable melt of the polypropylene resin containing the foaming agent is set to the melting point of the polypropylene resin in the extruder. The temperature is adjusted to 0 to 25 ° C. lower than that, and the foamable melt is extruded from the die of the extruder at a high pressure, and the extruded plastic extrudate in the foaming process is It is characterized in that it is molded by a molding die whose temperature is controlled to be equal to or lower than the crystallization temperature of the polypropylene resin.

According to the production method of the present invention, first, the temperature of the foamable melt comprising the polypropylene resin and the foaming agent is adjusted to a temperature lower than the melting point of the polypropylene resin used by a specific temperature. Unlike in the case where only the temperature of the die is set to a temperature at which the fluidity of the resin is maintained, the viscoelasticity of the foamable melt reaches a region sufficient to hold the cell walls. In addition, the surface is crystallized more smoothly by cooling during molding. In this way, it is adjusted to a specific temperature,
Since the extrudate of the expandable melt extruded at high pressure is molded with a molding die that has a temperature below the crystallization temperature of the polypropylene resin used, the molded product is sufficiently cooled, and especially the surface of the molded product is Crystallization is sufficiently promoted, and a smooth skin layer can be formed on the surface of the obtained foam.

In the present specification, the crystallization temperature of the resin means a differential scanning calorimeter (DSC20 manufactured by Seiko Denshi Kogyo KK) according to the differential scanning calorimetry.
0) in a nitrogen atmosphere at a heating rate of 10 ° C./min.
It refers to the crystallization peak temperature detected during the process of heating and melting the resin to 00 ° C. and then cooling it to room temperature at a cooling rate of 10 ° C./min.

In the present specification, the melting point of the resin is detected in the process of heating the resin cooled in the same manner as in the measurement of the crystallization temperature up to 200 ° C. at a temperature rising rate of 10 ° C./min. The melting peak temperature.

Further, in the present specification, the skin layer means a surface layer portion which is not foamed or slightly foamed.

Typical examples of the polypropylene resin used in the present invention include propylene homopolymer,
Block or random copolymers of propylene with up to 50% by weight of other olefins, polypropylene with 50
Up to 50% by weight of other polyolefins or graft copolymers with aromatic vinyl polymers, polypropylene and 50
Examples thereof include a mixture with other polyolefins or aromatic vinyl polymers in an amount of up to wt%, a mixture of polypropylene and a halogen-containing polymer, and these can be used alone or in admixture of two or more.

Examples of the polyolefin include high density, low density or linear low density polyethylene, poly-1.
-Butene, polyisobutylene, polymethylpentene and the like.

Examples of the aromatic vinyl polymer include styrene, α-methylstyrene, ethylstyrene,
Examples thereof include polymers composed of styrene-based monomers such as halogenated styrene and polymers composed of the styrene-based monomer and other monomers.

Examples of the halogen-containing polymer include polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polyperfluoroalkoxyalkene and polychloro. Examples thereof include trifluoroethylene, polytrifluoroethylene, fluorinated ethylene-propylene copolymer, ethylene-chlorotrifluoroethylene copolymer and the like. It should be noted that these halogen-containing polymers are preferably mixed in an amount of 0.01 to 10 parts with respect to 100 parts of polypropylene (parts by weight, the same applies hereinafter). Further, among these halogen-containing polymers,
Polytetrafluoroethylene is particularly preferably used because the effect of improving the viscoelasticity and crystallization of the polypropylene resin is remarkably high.

Examples of the foaming agent used in the present invention include evaporative foaming agents and decomposable foaming agents.

As typical examples of the evaporative blowing agent, for example, chlorodifluoromethane, dichlorodifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, 2-chloro-1,1,1,2- Tetrafluoroethane, 1,1,1-trifluoro-2-chloroethane,
1,1-dichloro-1-fluoroethane, 1-chloro-
1,1-difluoroethane, difluoroethane, 1,
1,2-trifluoroethane, 1,1,1-trifluoroethane, 1,1,2,2-tetrafluoroethane,
1,1,1,2-tetrafluoroethane, octafluoropropane, 1,1,1-trifluoropropane, 2,
2-difluoropropane, methyl chloride, halogenated hydrocarbons such as ethyl chloride; methane, ethane, propane, n
-Butane, i-butane, n-pentane, i-pentane,
Examples include lower aliphatic hydrocarbons such as neopentane, n-hexane, cyclohexane, and n-heptane; inorganic substances such as carbon dioxide, water, and nitrogen. These can be used alone or in combination of two or more. .

As typical examples of the decomposition type foaming agent, for example, azodicarbonamide, azobisisobutyronitrile, diazoaminobenzene, N, N'-dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazide, benzenesulfonylhydrazide. And so on,
These may be used alone or in combination of two or more.

Among these foaming agents, lower fats having 3 to 5 carbon atoms have excellent solubility in polypropylene resin and have a vapor pressure suitable for giving a desired foaming ratio to the obtained foam. Group hydrocarbons are particularly preferably used.

The amount of the foaming agent used varies depending on the type of polypropylene resin and the type of the foaming agent. If it is too small, the foaming ability is insufficient and a foam having a desired expansion ratio can be obtained. Therefore, it is desirable to adjust to 2 parts or more, preferably 5 parts or more, relative to 100 parts of the polypropylene resin, and when it is too much, the foamable melt In that case, since the foaming agent is not uniformly dispersed in the polypropylene-based resin and is difficult to dissolve, it tends to be difficult to obtain a foam in a uniform foamed state. 30 parts or less, preferably 2 parts
It is desirable to adjust the amount to 5 parts or less, more preferably 15 parts or less.

Further, in the present invention, inorganic fine powders such as talc, calcium silicate and silica, and higher fatty acid metals such as sodium stearate, calcium stearate, magnesium stearate and potassium stearate, to the extent that the object is not impaired. A foam control agent such as a salt, a mixture of sodium hydrogen carbonate and citric acid; an additive such as a stabilizer such as dibasic lead stearate, octyl tin maleate, epoxidized soybean oil, and a hindered phenolic antioxidant, It can be appropriately blended with the polypropylene resin, and additives such as these bubble regulators and stabilizers are
Each can be used alone or in combination of two or more.

Further, in order to further improve the dispersibility of the additives such as the cell regulator and the stabilizer in the polypropylene resin, for example, blend oil may be used.

In the production method of the present invention, first, the compounding amounts of the polypropylene resin and the foaming agent, and other additives as necessary are appropriately adjusted, and then these are heated in an extruder to be melt-kneaded, A polypropylene-based resin foamable melt containing a foaming agent.

The extruder is not particularly limited and, for example, a single-screw extruder, a multi-screw extruder, a tandem extruder or the like can be used.

In the present invention, the method of incorporating the blowing agent into the polypropylene resin is not particularly limited,
For example, a method of melt-kneading a polypropylene-based resin in an extruder and then press-in a foaming agent from the middle of the extruder, or a method of impregnating or mixing a polypropylene-based resin with a foaming agent in advance and then introducing the same into an extruder are adopted. You can

Next, in the extruder, the temperature of the foamable melt is 0 to more than the melting point of the polypropylene resin used.
The temperature is adjusted to a low temperature of 25 ° C., and the expandable melt is extruded from the die of the extruder into the low pressure region at a high pressure of, for example, about 20 to 40 atm.

In the present invention, the temperature of the foamable melt is 0 to 25 ° C. higher than the melting point of the polypropylene resin used.
One of the major characteristics is that the temperature is controlled to be lower by ℃.

The temperature of the expandable melt in the extruder is
When it is higher than the melting point of the polypropylene resin used, the viscoelasticity of the extrudate in the plastic state in the foaming process, in which the expandable melt is extruded from the die of the extruder, is sufficient to hold the cell walls. It does not reach a certain area and breaks bubbles. On the other hand, when the temperature of the expandable melt in the extruder is lower than the melting point of the polypropylene resin used by more than 25 ° C., the expandable melt is crystallized in the extruder or When the expandable melt is extruded, the polypropylene resin is solidified and clogged, the extruded state is not stable, and the desired good foam cannot be obtained. Therefore, in the present invention, the temperature of the foamable melt in the extruder is adjusted to a temperature 0 to 25 ° C. lower than the melting point of the polypropylene resin used. Further, in order to smoothly crystallize the surface by cooling during molding, the temperature of the expandable melt is lower than the melting point of the polypropylene-based resin within the range of maintaining its fluidity. Preferably, if the temperature of the expandable melt is adjusted to a too low temperature, the solidification occurs until the growth of bubbles inside is sufficiently promoted, and it becomes difficult to obtain a foam having a desired expansion ratio and thickness. Considering that there is a possibility that the temperature of the foamable melt is 5 to 20 higher than the melting point of the polypropylene resin.
It is preferable to adjust the temperature lower by 0 ° C.

Further, in the present invention, it is possible to extrude the foamable melt adjusted to a temperature 0 to 25 ° C. lower than the melting point of the polypropylene resin used, from the die at the tip of the extruder. The product exhibits a freezing point lowering action and a crystallization inhibiting action due to the high-pressure melting of the foaming agent from the extruder to the die, and is constantly subjected to mechanical force by the extruder screw. Based on the above, it is considered that the foamable melt can maintain fluidity without solidifying or crystallizing.

Next, the extrudate extruded from the die of the extruder is molded with a molding die in which the passage surface of the extrudate is adjusted to a temperature not higher than the crystallization temperature of the polypropylene resin used.

In the present invention, one of the major features is that the passage surface of the extruded product of the molding die is adjusted to a temperature not higher than the crystallization temperature of the polypropylene resin used, and molding is carried out with such a molding die. is there.

If the passage surface of the extruded product of the molding die is higher than the crystallization temperature of the polypropylene resin used, the surface of the molded product cannot be crystallized.
A smooth skin layer is not formed on the surface of the foam, and due to insufficient cooling, the surface of the foam is fused to the molding die, and peeling or foam breakage occurs, so that the desired good foam can be obtained. I can't. Therefore, in the present invention, the extrudate is molded with a molding die whose passage surface is adjusted to a temperature not higher than the crystallization temperature of the polypropylene resin used. In addition, since the foam is cooled more sufficiently to promote crystallization of the surface of the molded product, and a smooth and excellent skin layer can be formed, the extruded product of the molding die can be passed through. The road surface is 30 to 10 higher than the crystallization temperature of polypropylene resin.
It is preferable to adjust the temperature to 0 ° C. lower, and more preferable to adjust the temperature to 55 to 85 ° C. lower than the crystallization temperature.

Further, an extrusion foam molding apparatus that can be used in the method for producing the polypropylene resin foam of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic explanatory view showing an embodiment of an extrusion foam molding apparatus used in the manufacturing method of the present invention.

In FIG. 1, reference numeral 1 denotes a single screw type extruder, and only the tip portion thereof is shown.
2 is an adapter for connecting the extruder 1 and the base 3. A resin passage is provided inside the adapter 2 and the base 3, and the tip portion 3a of the base 3 has a width of usually about 50 to 70 mm, and a thickness of about 5 mm, especially about 1 to 5 mm. It has a structure that can be adjusted.

In the present invention, in the extruder 1, the temperature of the foamable melt is adjusted to a temperature 0 to 25 ° C. lower than the melting point of the polypropylene resin used, and the temperature of the adapter 2 and the die 3 is adjusted. High pressure is extruded from the die 3 to the low pressure area through the resin passage inside, but when the foamable melt is obtained,
Since the resin mixture is usually heated so that the polypropylene resin is in a molten state, the foamable melt may be cooled in order to adjust the temperature of the foamable melt to the predetermined temperature.

As a cooling method for adjusting the foamable melt to the above-mentioned predetermined temperature, for example, the extruder 1 is adjusted to a desired temperature, and particularly in the vicinity of the end of the extruder 1 connected to the adapter 2. There is a method of adjusting the temperature of the foamable melt by adjusting the temperature.

The temperature of the foamable melt in the extruder 1 is measured by, for example, a thermocouple projecting in the resin passage inside the adapter 2 in FIG.

Next, the extrudate extruded from the die 3 at high pressure reaches the molding die 4 attached to the tip of the die 3. The molding die 4 is connected to the die 3, and the heat transfer in the connecting portion affects the temperature control of the die 4 and the die 3 to each other, so that the area of the connecting portion is as small as possible. It is preferable that the structure is as follows. In addition, it is preferable that such a connecting portion does not have a step that deteriorates the surface property of the obtained foam.

In the present invention, the extrudate in the plastic state in the foaming process extruded from the die 3 is the passage 5 of the extrudate.
It is introduced into the molding die 4 through the molding and is molded. In the molding die 4, the passage surfaces 5a and 5b of the extrudate are adjusted to a temperature not higher than the crystallization temperature of the polypropylene resin. .

Passage surfaces 5a, 5 of the extrudate of the molding die 4
In order to adjust the temperature of b to the specific temperature, a fine hole 6 is provided inside the molding die 4 which is extremely close to the passage surfaces 5a, 5b of the extrudate, and a refrigerant is circulated in the fine hole 6, for example. Good. As the refrigerant, for example, water, oil, air or the like can be used. Since the pores 6 are provided at positions extremely close to the passage surfaces 5a and 5b of the extrudate of the molding die 4, in the present invention, the temperature of the refrigerant in the pores 6 is set to the passage surface of the extrudate. It can be defined as a temperature of 5a, 5b.

Further, in order to reduce the frictional resistance between the molding die 4 and the molded article inside the molding die 4 and further improve the surface properties of the obtained foam, for example, a substance having a small frictional resistance such as polytetrafluoroethylene. Is preferably coated on the passage surfaces 5a and 5b of the extrudate of the molding die 4.

Further, according to the present invention, the extruded product in the plastic state in the foaming process can be contacted and molded without giving a great resistance, and the high foaming can be achieved without causing the flattening of cells and the breaking of bubbles. From the viewpoint that a foam having a magnification and having a smooth skin layer on the surface is more likely to be obtained, as shown in FIG. 1, in the molding die 4, the area of the holes on the inner surface side is on the outer surface side. It is preferable to have the passage 5 of the extrudate that is gradually larger than the area of the holes.

By adjusting the size of the opening angle of the passage 5 of the extrudate of the molding die 4, for example, the passage 5 of the extrudate of the molding die 4 has a hole on the inner surface side having an area of the outer surface side. It can be gradually larger than the area of the holes.

The opening angle of the passage 5 of the extrudate of the molding die 4 will be described with reference to the drawings.

FIG. 2 is an enlarged schematic explanatory view of a connecting portion between the die 3 and the molding die 4 of the extrusion foam molding apparatus shown in FIG. In FIG. 2, α and β are opening angles of the passage surfaces 5a and 5b of the extrudate, respectively, with respect to the direction in which the extrudate shown by the arrow A is extruded. In order to further reduce the resistance of the extrudate on the passage surfaces 5a and 5b and further improve the surface property of the obtained foam, the opening angles α and β are each 10 ° or more, especially 1.
It is preferable to adjust it so that it is 5 ° or more, and the resin of the surface layer of the obtained foam is stretched more smoothly,
In order to provide the surface of the foam body with excellent smoothness without unevenness, it is not more than 35 °, especially 30
It is preferable to adjust it so that it is not more than °.

Although FIG. 2 shows the molding die 4 having opening angles α and β in the vertical direction from the outer surface side to the inner surface side, in the present invention, such a vertical direction is used. Instead, it is possible to use a molding die having an opening angle in the left-right direction from the outer surface side to the inner surface side thereof, or it is possible to use a molding die having an opening angle in both the vertical and horizontal directions.

As described above, for example, FIGS.
By using the extrusion foam molding apparatus as shown in (3), the plate-shaped foam of the present invention having a smooth skin layer on the surface and having a high expansion ratio can be easily obtained.

The density of the polypropylene resin foam thus obtained by extrusion foam molding may be appropriately adjusted depending on the purpose of use of the foam, but is usually 0.01-.
0.1g / cm ³ about, inter alia, 0.02 to 0.06
It is preferable to set it to about g / cm ³ . Further, the thickness of the polypropylene-based resin foam may be appropriately adjusted depending on the purpose of use of the foam, but is usually 5 to 5
It is preferably about 0 mm, especially about 10 to 30 mm.

As described above, according to the production method of the present invention, a skin having a high expansion ratio, excellent mechanical properties such as heat resistance and heat insulating property, rigidity and impact resistance and having a smooth surface is formed. It is possible to continuously and easily obtain, for example, a plate-shaped polypropylene resin foam having a layer and excellent surface properties. Further, since such a foam has excellent properties as described above, it can be suitably used as a building material such as a heat insulating material or a packaging material such as a cushioning material.

Next, the polypropylene resin foam of the present invention and the method for producing the same will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 The extrusion foam molding apparatus shown in FIGS. 1 and 2 was used.
The extruder 1 is a tandem extruder composed of an extruder I having a diameter of 65 mm and an extruder II having a diameter of 90 mm, and the outer surface side of the extrudate 5 of the molding die 4 (contact side with the die 3). Has a width of 62 mm and a thickness of 2 mm, and the shape of the inner surface side (non-contact side with the die 3) of the extrudate passage 5 of the molding die 4 is a width of 62 mm and a thickness of 20 mm. The opening angles α and β are each 21.4 °.

First, homopolypropylene (PF-814 manufactured by Highmont Co., melting point 162 ° C., crystallization temperature 128 ° C.,
Hereinafter, 100 parts of PF-814) is blended oil (Super Ease manufactured by Koshigaya Chemical Co., Ltd.) 0.
After adding 05 parts and mixing with a ribbon blender, 0.1 part of a powder mixture of sodium hydrogen carbonate and citric acid (Cerbon SG / K manufactured by Eiwa Kasei Co., Ltd.) was added and mixed again with a ribbon blender. Was fed to extruder I.

Next, the mixture fed to the extruder I was mixed with 23
The mixture is heated to 0 ° C. to be melt-kneaded, and isorich butane (i-butane 85% by weight and n
-Mixture with 15% by weight of butane) PF-814 10
It was pressed at a pressure of 60 atm at a ratio of 7 parts to 0 parts and kneaded to obtain a foamable melt.

Then, the cylinder temperature of the extruder II is adjusted to cool the foamable melt to 157 ° C. (The temperature of the foamable melt is projected in the resin passage inside the adapter 2 in FIG. (Measured with a thermocouple) and supplied to a base whose temperature was adjusted to 150 ° C. Then, the foamable melt is extruded from the die at 30 atm, and the extruded plastic extrudate in the foaming process is passed through the pores through the refrigerant (water) at 60 ° C. to form the passage surface 5a of the extrudate. 5b was molded with a molding die 4 whose temperature was adjusted to 60 ° C. to obtain a plate-shaped good polypropylene resin foam having a smooth skin layer on the surface.

The surface properties of the obtained foam were examined according to the following method. Table 1 shows the results.

(Surface property) The surface of the obtained foam was visually observed and evaluated based on the following evaluation criteria.

A: No bubble breakage or peeling was observed, there were no irregularities, and a smooth skin layer was formed on the surface. B: Bubble breakage and peeling were observed, and the surface was slightly uneven, and a smooth skin layer was not partially formed. C: Blasting and peeling were remarkable, the surface had large irregularities, and the skin layer was not formed.

Example 2 The same as Example 1 except that the temperature of the refrigerant was changed to 70 ° C. and the passage surface of the extruded product of the molding die was adjusted to 70 ° C. in Example 1. A good plate-shaped polypropylene resin foam having a smooth skin layer was obtained.

The surface properties of the obtained foam were examined in the same manner as in Example 1. Table 1 shows the results.

Example 3 In the same manner as in Example 1 except that the foamable melt was cooled to 146 ° C., a good plate-shaped polypropylene resin foam having a plate-like surface having a smooth skin layer was prepared. I got it.

The surface properties of the obtained foam were examined in the same manner as in Example 1. Table 1 shows the results.

Example 4 The same as Example 3 except that the temperature of the refrigerant was changed to 70 ° C. and the temperature of the passage surface of the extruded product of the molding die was adjusted to 70 ° C. in Example 3. A good plate-shaped polypropylene resin foam having a smooth skin layer was obtained.

The surface properties of the obtained foam were examined in the same manner as in Example 1. Table 1 shows the results.

Example 5 In Example 1, ethylene- was used instead of PF-814.
Propylene block copolymer (SD- manufactured by Highmont Co., Ltd.
613, ethylene content about 3% by weight, melting point 160 ° C., crystallization temperature 128 ° C., hereinafter referred to as SD-613),
Good plate-like polypropylene resin foam having a smooth skin layer on the surface in the same manner as in Example 1 except that the foamable melt was cooled to 155 ° C. and supplied to a die adjusted to 160 ° C. I got it.

The surface properties of the obtained foam were examined in the same manner as in Example 1. Table 1 shows the results.

Example 6 The same as Example 5 except that the temperature of the refrigerant was changed to 70 ° C. and the passage surface of the extrudate of the molding die was adjusted to 70 ° C. in Example 5. A good plate-shaped polypropylene resin foam having a smooth skin layer was obtained.

The surface properties of the obtained foam were examined in the same manner as in Example 1. Table 1 shows the results.

The foams obtained in Examples 1 to 6 were
All of them have sufficient heat resistance and heat insulation properties as heat insulating materials and cushioning materials,
It had rigidity and impact resistance.

Comparative Example 1 In Example 1, except that the temperature of the refrigerant was changed to 140 ° C. and the passage surface of the extruded product of the molding die was adjusted to 140 ° C.
Extrusion foaming or molding was carried out in the same manner as in Example 1.

However, the extruded product in the plastic state in the foaming process is fused to the molding die at the stage of molding to cause peeling on the surface of the foam, and the foam obtained is in a corrugated state. It was not molded into a shape.

Comparative Example 2 Extrusion foaming or molding was performed in the same manner as in Example 1 except that the expandable melt was cooled to 170 ° C.

However, the foamable melt was violently broken as soon as it was extruded from the die, and a good foam could not be molded.

Comparative Example 3 Extrusion foaming or molding was performed in the same manner as in Example 1 except that the expandable melt was cooled to 132 ° C.

However, at the stage of extruding the foamable melt from the die, clogging of the foamable melt occurs at the tip of the die, stable extrusion cannot be performed, and a foam cannot be molded. It was

Comparative Example 4 In Example 5, except that the temperature of the refrigerant was changed to 140 ° C. and the passage surface of the extruded product of the molding die was adjusted to 140 ° C.
Extrusion foaming or molding was performed in the same manner as in Example 5.

However, the extruded product in the plastic state in the foaming process is fused to the molding die at the molding stage to cause peeling on the surface of the foam, and the foam obtained is in a corrugated state. It could not be molded into a shape.

Comparative Example 5 Extrusion foaming or molding was performed in the same manner as in Example 5 except that the foamable melt was cooled to 170 ° C.

However, the foamable melt was violently broken as soon as it was extruded from the die, and a good foam could not be molded.

Comparative Example 6 Extrusion foaming or molding was carried out in the same manner as in Example 5 except that the expandable melt was cooled to 132 ° C. However, the step of extruding the expandable melt from the die Then, the foamable melt was clogged at the tip portion of the die, stable extrusion was not performed, and the foam could not be molded.

Table 1 also shows the density and thickness of the foam.

Table 1 also shows the type of polypropylene resin used, the temperature of the expandable melt, the temperature of the refrigerant, and the temperature of the passage surface of the extrudate of the molding die.

Further, in Comparative Examples 1, 2, 4 and 5, the results of evaluating the surface properties of the foams in the same manner as in Example 1 are also shown in Table 1.

[0092]

[Table 1]

From the results shown in Table 1, the foams obtained in Examples 1 to 6 have a thickness of about 15 to 19 mm and a density of about 0.04 to 0.06 g / cm ³ , that is, About 17
It can be seen that it has a high expansion ratio of up to 26 times, has no bubble breakage or peeling on its surface, and has a surface property with a smooth skin layer formed, which is extremely excellent.

[0094]

According to the manufacturing method of the present invention, a smooth skin layer having a high expansion ratio, excellent heat resistance and heat insulation, mechanical properties such as rigidity and impact resistance, and a smooth surface is formed. It is possible to continuously and easily obtain, for example, a plate-shaped polypropylene resin foam having excellent surface properties.

Since the plate-like foam of the present invention obtained by the above-mentioned manufacturing method has excellent properties as described above, it can be used as a building material such as a heat insulating material or a packaging material such as a cushioning material. It can be used preferably.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing one embodiment of an extrusion foam molding apparatus used in a method for producing a polypropylene resin foam of the present invention.

FIG. 2 is an enlarged schematic explanatory view of a connecting portion between a die and a molding die of the extrusion foam molding apparatus shown in FIG.

[Explanation of symbols]

 1 Extruder 3 Base 4 Molds 5a, 5b Passage surface of extrudate

Claims (3)

[Claims] 1. The temperature of a foamable melt of a polypropylene-based resin containing a foaming agent is adjusted to a temperature 0 to 25 ° C. lower than the melting point of the polypropylene-based resin in an extruder to obtain the foamable melt. After extruding from the extruder die at high pressure,
A polypropylene-based resin foam, characterized in that the extruded product in a plastic state in the foaming process is extruded with a molding die whose passage surface is adjusted to a temperature not higher than the crystallization temperature of the polypropylene-based resin. Manufacturing method. 2. The method for producing a polypropylene-based resin foam according to claim 1, wherein the molding die has an extrudate passage in which the area of the holes on the inner surface side is gradually made larger than the area of the holes on the outer surface side. 3. A plate-like polypropylene-based resin foam having a smooth skin layer on the surface obtained by the method according to claim 1.