JP2001301002A - Producing method for olefinic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for substituting inorganic gas such as air in a short time without damaging the surface of a foam for foaming agent gas which is not simply substituted for air by only being allowed to stand in the atmosphere and remains in the foam for a long period. SOLUTION: Inorganic gas such as air is substituted for foaming agent gas remaining in the inside of a foam by compressing the foam in the direction of thickness so that the void content of a closed cell becomes 10-60% after a plastic resin foam having 40-90% void content of the closed cell is obtained by an extrusion foaming method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin foam which facilitates replacement of a residual blowing agent gas with an inorganic gas.

[0002]

2. Description of the Related Art As a method for producing a long plate or sheet foam, an extrusion foaming method in which a thermoplastic resin is melt-kneaded with a foaming agent in an extruder and then extruded under a low pressure to foam is widely used. Used. In the foam obtained by the above-mentioned extrusion foaming method, the foaming agent gas used for foaming remains for a while after production, but propane as a foaming agent,
When a combustible foaming agent such as butane, pentane or hexane is used, the foaming agent remaining in the foam before the residual foaming agent gas in the foam is replaced with a nonflammable gas such as air. There is a danger that the gas may ignite due to static sparks or the like, and the manufacturer cannot ship the product to ensure safety until the residual foam gas in the foam is replaced with air or the like.

In the case of a thin sheet-like foam, it is possible to replace the residual blowing agent gas with air in a relatively short time only by leaving the foam in the air after production. When the wall thickness is large, there is a problem that the residual foaming agent gas is not easily replaced with air, and it takes several months or more for it to be left in the atmosphere and completely replaced with air.

[0004] As a method of shortening the time for replacing the foaming agent gas remaining in the foam with a nonflammable inorganic gas such as air, a method of forming a large number of small holes in the foam, or a method of forming the small holes. After that, there is a method of performing replacement by compressing with a roll or the like (Japanese Patent Laid-Open No. 4-307227). But,
When small holes are formed, the appearance is impaired because holes are opened in the foam surface, and especially when the foam is used for heat insulating material, the water absorption increases, and the heat insulating property is deteriorated by absorbing moisture. There's a problem. Further, in this method, since the transfer speed of the foam by the pinch roll is as slow as 5 to 30 mm / sec, the effect of promoting the replacement of the residual foaming agent with the inorganic gas by the communication of the cell membrane cannot be obtained.

[0005] As another method for making the cell membrane open, a method of compressing a crosslinked polyolefin resin foam with a roll or the like (for example, Japanese Patent Publication No. 59-23545, Japanese Patent Application Laid-Open No.
No. 191027). However, in order to make the cell membrane open by compression, it is necessary to form a cell membrane that easily breaks by heating the molded body by the batch foaming method and adjusting the decomposition rate of the crosslinking agent and the foaming agent. Therefore, it was difficult to make the non-crosslinked olefin-based resin foam into communication only by compression by the continuous extrusion method.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above points, and is intended to reduce the blowing agent gas remaining in a foam using polyolefin as a base resin in a very short time to a nonflammable form such as air. It is an object of the present invention to provide a method for replacing a residual foaming agent gas in a resin foam plate with an inorganic gas, which can be replaced with a water-soluble inorganic gas.

[0007]

According to the method of the present invention, a method for replacing a residual foaming agent gas in a resin foam with an inorganic gas uses a flammable gas as a foaming agent and a closed cell rate of 40 to 40 by an extrusion foaming method.
After obtaining a 90% plate-shaped resin foam, the foam is compressed in the thickness direction so that the closed cell ratio becomes 10 to 60%, thereby replacing the foam gas remaining in the foam with an inorganic gas. It is characterized by doing.

In the present invention, the polyolefin resin as the base resin of the foam includes polyethylene such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, and polypropylene. , Polybutene, ethylene-propylene block copolymer, ethylene-propylene random copolymer, ethylene-butene random copolymer, ethylene-butene-propylene random copolymer, and the like. These resins can be appropriately mixed and used.
Also, 70% by weight or less of the whole resin, more preferably 50% by weight.
If it is at most 40% by weight, more preferably at most 40% by weight, a polystyrene-based resin such as polystyrene or high-impact polystyrene can be mixed. Further, when a polystyrene resin is mixed, the content is preferably 20% by weight or less, more preferably 10% by weight, based on the total resin in order to increase the compatibility.
If it is less than the weight percentage, a hydrogenated styrene-butadiene block copolymer can be mixed.

The method of the present invention is preferably applied to a foam in which a combustible blowing agent gas remains, but can also be applied to other foams in which a non-flammable volatile blowing agent gas remains. As the flammable foaming agent, for example, propane, n-
Examples thereof include aliphatic hydrocarbons such as butane, i-butane, pentane, and hexane; cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane; and halogenated hydrocarbons such as chlorodifluoroethane, difluoroethane, methyl chloride, and ethyl chloride. Examples of other nonflammable volatile blowing agent gases include halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoromethane, tetrafluoroethane, dichlorotetrafluoroethane, and methylene chloride.

In the present invention, a foam control agent may be further added to the melt-kneaded product of the resin and the foaming agent. Examples of the cell regulator include inorganic powders such as talc and silica, acidic salts of polycarboxylic acids, and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate.

The foam used in the present invention is obtained by an extrusion foaming method in which a resin and a foaming agent are melt-kneaded in an extruder, and the melt-kneaded product is extruded under a low pressure through a die attached to the extruder tip to foam. Can be The closed cell rate of the foam after extrusion foaming (measured by a method according to ASTM-D-2856) is 40 to 90%, preferably 50 to 90%.
It must be 80%, more preferably 50-70%. If the closed cell ratio is less than 40%, a foam having a sufficiently large cross-sectional area cannot be obtained, and if it exceeds 90%, communication after the subsequent compression step does not reach a sufficient level. In order to obtain a resin foam having a closed cell rate of 40 to 90% after extrusion foaming, it can be controlled by the amount of the foaming agent added, the foaming temperature, the resin composition, or the like. In general, by increasing the amount of the foaming agent added or increasing the foaming temperature from the usual level, the closed cell rate of the resin foam after extrusion foaming can be reduced. For example, after adding 27 to 31 parts by weight of a foaming agent consisting of 30 to 60% by weight of i-butane and 70 to 40% by weight of i-pentane or n-pentane per 100 parts by weight of high-density polyethylene, and then melt-kneading in an extruder, By extruding and foaming at a temperature of 139 to 141 ° C., a foam having a closed cell ratio of 60 to 80% can be obtained.

The resin foam having the closed cell ratio adjusted to 40 to 90% after extrusion foaming is cooled and solidified (the temperature at the center of the foam falls below the softening temperature of the resin). Press and compress in the thickness direction. By compression, the closed cell ratio of the foam is 10 to 60%, preferably 10 to 60%.
４０40%. If the closed cell ratio is less than 10%, the thickness recovery rate after compression does not reach a satisfactory level (90% or more), and if it exceeds 60%, the effect of promoting the replacement of the residual blowing agent gas with the inorganic gas is sufficient. Can not be obtained. The compression ratio of the foam is preferably set to 50 to 95% in order to sufficiently communicate the cell membrane and to improve the recoverability in the thickness direction. In order to enhance the effect of breaking and communicating the foam film of the foam, it is preferable that the transfer speed of the foam taken between the pinch rolls is 5 to 100 m / min. If the transfer speed is lower than this range, communication becomes insufficient. If the transfer speed is high, compression becomes uneven or slippage occurs between the foam and the pinch roll. A pinch roll embossed on the roll surface can be used to improve the biteability of the foam between the pinch rolls and prevent slippage. Further, instead of the pinch roll, it is also possible to press and compress by a press device. In this case, the compression time required for releasing from the start of pressurization is within 5 seconds, and the speed of compressing the foam is 2 cm / It is preferable to set it to seconds or longer. On the other hand, when compression is performed by pressurizing with a pinch roll, the foam can be efficiently communicated in a very short time, so that it is more preferably used than compression by a press device. Since the foam after compression is excellent in elasticity and restoring property, the thickness of the compressed foam is restored to almost the original thickness when the pressure is released. Although some residual strain is generated after the compression, this has an effect of improving the heat insulating performance of the foam plate by reducing the diameter of the bubbles in the thickness direction and increasing the density. Further, as a characteristic of the foam after compression, under the compression conditions of the present invention, since no pores or cracks are generated on the foam surface, it is possible to avoid deterioration of the heat insulating performance due to absorption of moisture which is observed when the foam is perforated. Since a series of these processes is usually performed in the atmosphere, the blowing agent gas in the foam is replaced with air, but the process may be performed in an inorganic gas atmosphere other than air. Examples of the inorganic gas other than air include carbon dioxide, nitrogen, oxygen, argon, and neon, and it is preferable to use inexpensive carbon dioxide or nitrogen.
Hereinafter, the present invention will be described based on examples.

[0013]

Example 1 100 parts by weight of high density polyethylene
50% by weight of i-butane and 50% by weight of i-pentane.
29 parts by weight of a foaming agent and 0.1 g of talc as a cell regulator.
After adding by weight and melt-kneading in the extruder, the temperature of the kneaded material
Extrusion dies (taper angle: 10 °, open at 140 ° C)
3 through the mouth shape width: 60 mm, thickness: 1.6 mm)
Thickness by extrusion foaming at a discharge rate of 00 kg / hour
A 25 mm foam having a width of 300 mm was obtained. Of this foam
The closed cell rate is determined by the air pycnometer method (ASTM-D-
When measured according to 2856), it was 72%.
The closed cell ratio is calculated from each position divided into 5 equal parts in the width direction of the foam.
Cut out in the thickness direction (sample size: 20 mm
X 20 mm x thickness 25 mm) and measure the average of those values.
Average values were used. This foam is compressed by a pinch roll
(Compression rate: α, thickness before compression: D ₁, Compressed thickness: D
_TwoWhere α = (D₁-D_Two) / D₁× 100
Compression at 90% transfer speed of 20 m / min.
Measurement was carried out after standing for 2 hours in a constant temperature room controlled at 3 ° C.
However, it recovers to a thickness of 95% before compression and has a good appearance.
A foam having a closed cell ratio of 39% was obtained. This foam 2
Aged in a constant temperature room at 3 ° C, 3 days after 1 day
, 1 week, 1 month after measuring the concentration of residual blowing agent gas
did. For measurement of residual gas concentration, the center of the foam is in the entire thickness direction
After sealing in a glass bottle,
Gas released from the foam by heating and melting
Was measured and calculated by gas chromatography. Measurement
The results are shown in Table 1. Note that the residual gas concentration
If the detection limit is less than (10 ppm), "Not detected" is indicated.
did. The residual amount of the blowing agent gas in the foam is represented by the following symbol.
It was expressed by. : Gas is not detected. Δ: Gas is detected but below the lower combustion limit. ×: Gas remaining above the lower limit of combustion remains.

[0014]

Example 2 The resin composition was 80% by weight of high-density polyethylene, 20% by weight of polystyrene, and
The same treatment as in Example 1 was performed except that the foaming temperature was 138 ° C. and 26 parts by weight per 0 parts by weight. Table 1 shows the results.

[0015]

Example 3 The same processing as in Example 1 was performed except that compression was performed using a press device instead of the pinch roll. During the compression, the compression time from the start of pressurizing the foam to the release thereof was 1 second, and the speed of compressing the foam was 10 cm / sec. Table 1 shows the results.

[0016]

Comparative Example 1 A foamed board extruded and foamed under the same conditions as in Example 1 was placed in a constant temperature room at 23 ° C. without compression, and aged to measure the residual foaming agent concentration. One month later, the measurement showed that the value was equal to or higher than the lower combustion limit concentration.
Table 1 shows the results.

[0017]

COMPARATIVE EXAMPLE 2 Extrusion foaming was carried out at 34 parts by weight per 100 parts by weight of the resin and at a foaming temperature of 144 ° C. in Example 1, and the cross-sectional area with a closed cell ratio of 23% was small (thickness: 15 mm). , 170 mm in width) only a foam was obtained. Table 1 shows the results.

[0018]

Comparative Example 3 The amount of the foaming agent added was 2 per 100 parts by weight of the resin.
The same treatment as in Example 1 was performed except that the foaming temperature was 139 ° C. and 3 parts by weight. Table 1 shows the results.

[0019]

COMPARATIVE EXAMPLE 4 Extrusion foaming was carried out at a foaming agent addition amount of 29 parts by weight per 100 parts by weight of resin and at a foaming temperature of 142 ° C. to obtain a foam having a closed cell ratio of 43%. The foam was compressed at a compression ratio of 98%, and the closed cell ratio was measured. As a result, it was 3%, and the recovery in the thickness direction at the point of time 2 hours after the compression was 82%. Table 1 shows the results.

[0020]

Comparative Example 5 The same processing as in Example 1 was performed except that the compression ratio was set to 30%. Table 1 shows the results.

[0021]

Comparative Example 6 The transfer speed of the foam by the pinch roll was 2
The same processing as in Example 1 was performed except that the flow rate was set to m / min. Table 1 shows the results.

[0022]

Comparative Example 7 The transfer speed of the foam by the pinch roll was 1
The same treatment as in Example 1 was performed except that the speed was 20 m / min. As a result, slippage occurred between the foam and the pinch roll, and compression was not possible. Table 1 shows the results.

[0023]

[Table 1]

[0024]

According to the method of the present invention, the closed cell ratio is 10
By reducing to about 60%, it becomes possible to replace the blowing agent gas remaining in the olefin-based resin foam with air or the like in a short period of time. When the foaming agent is a flammable gas, the time required to reduce the residual gas concentration in the foam to the combustion lower limit or less can be significantly reduced as compared with the case where the foaming agent is left alone in the atmosphere. Furthermore, since the present invention does not damage the foam surface, the time required for replacing the residual foaming agent with air can be reduced without deteriorating the heat insulating performance of the foam and without impairing the appearance of the foam.

Continued on the front page F term (reference) 4F074 AA16 AA17 AA18 AA19 AA20 AA24 BA35 BA36 BA37 BA38 BA39 BA40 BA44 BA47 BA53 BA54 BA55 CA22 CC03Z CC34Z CD01 DA12 4F207 AA03 AB02 AG20 KA01 KA11 KW21

Claims (3)

[Claims] 1. A flaky resin having a closed cell ratio of 40 to 90% is obtained by an extrusion foaming method using a flammable gas as a foaming agent. A method for producing an olefin-based resin foam, characterized in that the foam is compressed in the thickness direction. 2. The method for producing an olefin resin foam according to claim 1, wherein the olefin resin foam is compressed by pressing with a pinch roll or a press device. 3. The method for producing an olefin resin foam according to claim 2, wherein the transfer speed of the foam by the pinch roll is 5 to 100 m / min.