JPH05239248A - Production of polyolefinic resin foam - Google Patents

Abstract

PURPOSE:To produce a polyolefinic resin foam having excellent dimensional stability and surface smoothness and good appearance and free from age contraction by extrusion molding, using a blowing agent free from the risk of depleting the ozonosphere, without using any special cell shrinkage preventive. CONSTITUTION:This production process is one comprising melt-kneading a polyolefinic/resin with a blowing agent under applied pressure and foaming the obtained expandable mixture by extrusion into a low-pressure zone, wherein the blowing agent comprises a halohydrocarbon containing 1-chloro-1,2,2,2- tetrafluoroethane. The blowing agent comprising a mixture of 30-80wt.% 1- chloro-1,2,2,2-tetrafluoroethane with 70-20wt.% 1-chloro-1,1-difluoriethane or a mixture of 30-80wt.% 1-chloro-1,2,2,2-tetrafluoroethane with 70-20wt.% 1,1- difluoroethane is also provided is also used.

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 polyolefin resin foam by an extrusion foaming method, and more specifically, a polyolefin resin foam having excellent dimensional stability and surface smoothness, good appearance and no shrinkage over time. A method of manufacturing a body.

[0002]

2. Description of the Related Art Generally, as a method for producing a polyolefin resin foam, a chemical foaming method is used in which a resin is kneaded with a pyrolytic chemical foaming agent, molded into a predetermined shape, and then heated and foamed above the decomposition temperature of the foaming agent. A typical method is an extrusion foaming method in which a gas or a volatile liquid having a boiling point below the melting point of a resin such as butane, pentane, or dichlorodifluoromethane is pressed into a molten resin and then discharged into a low pressure region to foam. is there.

In the extrusion foaming method, generally, a polyolefin resin is put into an extruder to be melted, a foaming agent is pressed in from the middle of the extruder, further melt-kneaded, and then extruded and foamed from a die to form a foam. Is getting Blowing agents used in the extrusion foaming method are roughly classified into hydrocarbons and halogenated hydrocarbons.

[0004] Hydrocarbons have a high gas escape rate through the foam film of the foam, so that they tend to easily shrink with time, lack dimensional stability, and require a long aging period after foaming. There is a drawback that.

On the other hand, most of the halogenated hydrocarbons are
While having the same drawbacks as hydrocarbons, dichlorodifluoromethane (CFC-12) and dichlorotetrafluoroethane (CFC-114) have a small dimensional change over time in the resulting foam, and therefore foam for extrusion foaming. Widely used as an agent. However, CFC-12 and CFC-
Since 114 has a large ozone layer depleting power, it has become a major international problem from the viewpoint of global environment protection, and it is moving toward the total abolition as a specific CFC to be regulated.

When a known foaming agent other than CFC-12 and CFC-114 is used, bubble shrinkage after foaming is unavoidable, but conventionally, as a method for solving such a problem, it belongs to surfactants. A method of adding a special shrinkage inhibitor has been proposed. However, most of these shrinkage inhibitors are generally used as lubricants for resins. Therefore, when the shrinkage inhibitor is added together with the polyolefin-based resin from the extruder hopper, the slip is severe and the extrusion fluctuation is caused, so that the extrusion stability is insufficient, and in some cases, the extrusion cannot be performed at all.
In particular, when a crosslinkable polyolefin resin is used, a shrinking agent causes a surging phenomenon (slip fluctuation in extrusion).
In addition to the lack of extrusion stability due to the occurrence of such as, when using a hydroxyl group-containing fatty acid ester or metal soap as a shrinkage-preventing agent, these act as a crosslinking agent or a crosslinking catalyst, which promotes crosslinking gelation, resulting in extrusion molding. Is difficult.

Specific CFCs such as CFC-12 and CFC-114 have been designated as substances subject to total reduction in use or reduction of use in this century, and therefore, hydrogen-containing fluorocarbons and chlorine-free fluorocarbons that are less likely to cause ozone layer depletion. Development is in progress. Among them, for example, monochlorodifluoromethane (HCFC-
22) and monochlorodifluoroethane (HCFC-14
The mixture of 2b) shows promise as an alternative with good foaming properties. However, although these are less likely to damage the ozone layer, they are CFC-12 and CFC-1.
Since the gas escape rate is higher than that of No. 14, bubble shrinkage over time easily occurs due to gas escape without a shrinkage inhibitor,
Not only does it lack dimensional stability, but it requires a long aging period after foaming.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to achieve dimensional stability by the extrusion foaming method without using a foaming agent that does not damage the ozone layer and without using a special anti-foaming agent. And surface smoothness, good appearance, and
An object of the present invention is to provide a method for producing a polyolefin resin foam that does not shrink with time.

As a result of earnest studies, the present inventors have found that 1-chloro-1,2,2,2-tetrafluoroethane (HCF)
(C-124; monochlorotetrafluoroethane) is less likely to destroy the ozone layer, and has a smaller gas permeability coefficient than the polyolefin resin, and the polyolefin resin foam obtained by using this as a foaming agent prevents shrinkage. It was found that there is almost no shrinkage over time, excellent dimensional stability and surface smoothness, uniform and fine cells, and high expansion ratio can be achieved without using an agent.

When HCFC-124 is used alone, the foam molding may be defective due to the size of the foam molded body (size of the hole diameter of the die, etc.).
-Chloro-1,1-difluoroethane (HCFC-14
2b; monochlorodifluoroethane) can be used in an appropriate amount to expand the molding region.

Further, by using HCFC-124 and chlorine-free 1,1-difluoroethane (HFC-152a; difluoroethane), which is chlorine-free and has no danger of depleting the ozone layer, in an appropriate amount, a shrinkage inhibitor can be used. It is possible to obtain a good polyolefin resin foam by the extrusion foaming method without doing so.

HCFC-124 and HCFC-142b,
The combination foaming agent of HCFC-124 and HFC-152a is particularly suitable for producing a foam using a crosslinkable polyolefin resin. The present invention has been completed based on these findings.

[0013]

According to the present invention, a polyolefin resin foam is produced by melt-kneading a polyolefin resin and a foaming agent under pressure, and extruding the resulting foamable mixture into a low pressure region for foaming. In the method, there is provided a method for producing a polyolefin resin foam, which comprises using a halogenated hydrocarbon containing 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124) as a foaming agent. To be done.

According to the present invention, the blowing agent is 1-chloro-1,2,2,2-tetrafluoroethane (HCFC).
-124) 30-80% by weight and 1-chloro-1,1-difluoroethane (HCFC-142b) 70-20% by weight are provided as a mixture.

Further in accordance with the present invention, the blowing agent is 1-chloro-1,2,2,2-tetrafluoroethane (HCF).
Provided is a method for producing a polyolefin resin foam which is a mixture of 30 to 80% by weight of C-124) and 70 to 20% by weight of 1,1-difluoroethane (HFC-152a).

The present invention will be described in detail below. Examples of the polyolefin resin used in the present invention include:
Polyethylene, crosslinkable ethylene copolymer, polypropylene, crosslinkable propylene copolymer, polybutene, polybutadiene, ethylene-propylene copolymer, crosslinkable ethylene-propylene copolymer, ethylene or propylene and α-olefin copolymer , Ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, copolymer of ethylene and acrylic acid derivative, ethylene-vinyl chloride copolymer, ethylene-styrene copolymer and the like. These polyolefin resins can be used alone or in combination of two or more.

If necessary, a bubble nucleating agent, a cross-linking catalyst, an antioxidant, a lubricant, a pigment, an antistatic agent and the like can be appropriately added to the polypropylene resin.

Examples of the bubble nucleating agent include talc, silica, calcium carbonate, calcium stearate, calcium silicate, baking soda and the like. Examples of the crosslinking catalyst include silanol condensation catalysts such as dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, stannous acetate, stannous caprylate, tin naphthenate, zinc caprylate, and zinc stearate. Examples of antioxidants include phenols, organic thioacids, organic phosphoric acids, organic amines, and organic tins.

The shrinkage-preventing agent need not be used, but may be added if desired within a range that does not impair extrusion stability and the like.

HCFC-1 as a blowing agent used in the present invention
As shown in Table 1, 24 (monochlorotetrafluoroethane) is another halogenated hydrocarbon such as CFC-.
12 (dichlorodifluoromethane) and CFC-114
Compared with (dichlorotetrafluoroethane) and the like, the gas permeability coefficient is small and the value is close to that of air, so that the rate at which gas permeates through the bubble membrane and escapes is small. Therefore, HCFC
The polyolefin resin foam using -124 as a foaming agent has almost no cell shrinkage over time and is excellent in dimensional stability.

Since HCFC-124 has a high solubility in polyolefin resin and an appropriate vapor pressure during foaming, it has excellent surface smoothness, has fine and uniform cells, and has a high expansion ratio (density of 0. A foam of 03 g / cm ³ or more) can be easily obtained.

Since HCFC-124 has poor molecular stability as compared with specific CFCs containing no hydrogen (CFC-12, CFC-114), it is easy to decompose and there is little risk of destroying the ozone layer in the sky.

Table 1 shows measured values of gas permeability coefficients of various halogenated hydrocarbons for low density polyethylene films.

[0024]

[Table 1]

Although HCFC-124 can be used alone, it may be appropriately used in combination with other halogenated hydrocarbons having a low risk of ozone layer depletion. However, HC
FC-124 is used in a proportion of 30% by weight or more in the total halogenated hydrocarbon component. If the proportion of HCFC-124 used is too low, the dimensional stability, the effect of preventing bubble shrinkage, and the like are reduced. HCF, among other halogenated hydrocarbons
C-142b and HFC-152a are preferred.

By utilizing the low gas permeability coefficient of HCFC-124, it is possible to prevent bubble shrinkage and
By using 2b together, the vapor pressure is lowered, and as a result,
Low-pressure molding is possible and the molding area can be expanded. And even with a relatively small extruder, HCFC-12
It is possible to easily obtain a large-sized foam body as compared with the case of using only 4 units. In addition, expensive HCFC-124 can be replaced with relatively inexpensive H
The cost can be reduced by diluting with CFC-142b. The preferred ratio of use of both is HCFC
-124 is 30 to 80% by weight, HCFC-142b is 7
It is 0 to 20% by weight. When HCFC-142b exceeds 70% by weight, dimensional stability becomes poor.

Also, HCFC-124 and chlorine-free HF
By using C-152a together, the chlorine content can be further reduced, and ozone layer depletion can be avoided. This combined system can provide a foam having excellent dimensional stability equal to or higher than that of CFC-114 of the specific flon, without adding a shrinkage inhibitor to the crosslinkable polyolefin resin. The preferable ratio of use of both is 3 for HCFC-124.
0-80% by weight, HFC-152a 70-20% by weight
Is. When HFC-152a exceeds 70% by weight, dimensional stability becomes poor.

The blending ratio of the foaming agent used in the present invention is usually 1 with respect to 100 parts by weight of the polyolefin resin.
0 to 35 parts by weight, preferably 15 to 25 parts by weight,
It is appropriately determined according to the required density of the foam.

In the method for foaming a polyolefin resin of the present invention, a mixture of a polyolefin resin and a desired additive is charged into an extruder and melt-kneaded according to a conventional method.
The foaming agent is press-fitted into the extruder through an inlet provided in the barrel of the extruder, the resin and the foaming agent are melt-kneaded under pressure, and then extruded into a low-pressure region from a mold having a predetermined shape to foam.

[0030]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The method of evaluating the characteristics is as follows.

<Extrusion stability> ◎: No discharge fluctuations such as slips: Some discharge fluctuations such as slips, but no problem △: Discharge fluctuations such as slips ×: Large discharge fluctuations such as slips

<Foam moldability> ◎: Beautiful appearance without in-mold foaming ◯: Good foaming appearance △: Slight in-mold foaming (surface roughness) ×: In-mold foaming severely defective appearance

<Dimensional stability> ◎: No dimensional shrinkage or skin shrinkage wrinkles 〇: Slight wrinkles only on the skin △: Dimensional shrinkage and skin shrinkage wrinkles ×: Large dimensional appearance shrinkage × ×: Dimensional appearance shrinkage is more severe

<Maturation period> ◎: None ◯: Within 1 day △: Within 3 days ×: Within 5 days XX: Over 5 days

[Examples 1 to 7] Density 0.925 g / cm
³ , 100 parts by weight of polyethylene having a melt index (MI) of 2.8 at 190 ° C. and 0.2 parts by weight of talc as a cell nucleating agent were mixed into a single extruder having a diameter of 65 mm (L / D = 28). , Melt kneading,
From the foaming agent inlet provided in the center of the extruder, HCFC-
124 (monochlorotetrafluoroethane), HCFC
-22 (monochlorodifluoroethane) and HCFC-
A foaming agent in which 142b (monochlorodifluoroethane) was mixed at the ratios shown in Table 2 was press-fitted at a ratio of about 35 times. Next, the melt-kneaded foamable composition was extruded into the atmosphere from a die attached to the tip of the extruder, and foamed simultaneously with the discharge. The results are shown in Table 2.

[Comparative Examples 1 to 6] HCFC-as a foaming agent
HCFC-22 and HCF shown in Table 2 without using 124
A mixture with C-142b was used and foamed in the same manner as in Examples 1 to 7 with and without the addition of monoglyceride stearate as a shrinkage inhibitor. The results are shown in Table 2.

[0037]

[Table 2]

[Examples 8 to 12] As a crosslinkable polyolefin resin, grafted polyethylene (density 0.92) grafted with 1.5 parts by weight of vinyltrimethoxysilane.
65 g of a mixture of 100 parts by weight of ³ g / cm ³ and MI = 2.8) with 0.2 parts by weight of talc as a cell nucleating agent.
After being supplied to a single extruder (L / D = 28) having a diameter and melt-kneaded, the foaming agents of the combinations shown in Table 3 were blown with a foaming ratio of 35 from the foaming agent injection port provided in the center of the extruder.
It was pressed in at a rate of doubling. Next, the melt-kneaded foamable composition was extruded into the atmosphere from a die attached to the tip of the extruder, and foamed simultaneously with the discharge. The results are shown in Table 3.

[Comparative Examples 7 to 11] For comparison, extrusion foaming was performed in the same manner as in Examples 8 to 12 in the case where stearic acid monoglyceride was blended as a shrinkage inhibitor.
The results are shown in Table 3.

[0040]

[Table 3]

Examples 13 to 22 Low density polyethylene resin (density 0.92 g / cm ³ , MI = 2.0) 100
A single extruder with a 40 mm diameter (L / D = 2) was prepared by blending 0.2 part by weight of talc as a bubble nucleating agent in 1 part by weight.
8) and after melt-kneading, HCFC-124 and HCFC-14 from the blowing agent injection port provided in the center of the extruder.
The foaming agents obtained by mixing 2b in the proportions shown in Table 4 were pressed in an amount (15 to 22 parts by weight) such that the expansion ratio was about 35 times. Next, after re-kneading and cooling, the mixture was extruded into the atmosphere from a die (caliber 4.0 mmφ) attached to the tip of the extruder and foamed simultaneously with discharging. The results are shown in Table 4. Extrusion foaming was carried out in the same manner as above except that extrusion was performed from a die having a diameter of 8.0 mmφ. The results are shown in Table 4.

[Comparative Examples 12 to 15] Examples 13 to 2 except that the type and mixing ratio of the foaming agent were changed as shown in Table 4.
Extrusion foaming was carried out in the same manner as in 2. The results are shown in Table 4.

[0043]

[Table 4]

As is clear from Table 4, HCFC-12
In the case of using 4 alone, molding failure may occur depending on the size to be foam-molded, but by mixing an appropriate amount of HCFC-142b, the region of molding size can be expanded. Also,
By adjusting the mixing ratio of these two types of foaming agents to appropriate values, it is possible to obtain a dimensionally stable, high expansion ratio foamed product that does not cause cell shrinkage similar to the case of using HCFC-124 alone, and a special shrinkage inhibitor. It can be obtained without using.

[Examples 23 to 26, Comparative Example 16] As shown in Table 5, a silylated ethylene polymer (density 0.92 g
/ Cm ³ , MI = 1.5) 100 parts by weight, 0.2 parts by weight of talc as a cell nucleating agent and 0.1 parts by weight of dibutyltin dilaurate as a silanol condensation catalyst are mixed.
Extrusion foaming was performed under the same conditions as in Example 13. The results are shown in Table 5.

[0046]

[Table 5]

As is clear from Table 5, even in silylated ethylene polymers, HCFC-124 and HCFC-1
By using 42b together in an appropriate amount ratio, a good foam can be obtained without the problem of outflow of the retained gelated product.
When a shrinkage inhibitor such as a fatty acid ester compound is added,
Cross-linking reaction with the silyl group causes gelled substance to flow out, resulting in defective molding.

[Examples 27 to 31] Crosslinkable low-density polyethylene (density 0.92 g / cm ³ , MI = 2.0) 10
40 m of a mixture of 0 part by weight, 0.2 part by weight of talc as a bubble nucleating agent and 0.1 part by weight of a silanol crosslinking catalyst.
It is supplied to a single extruder of m diameter (L / D = 28), melted and kneaded, and then the foaming agent of the combination shown in Table 6 is blown from the foaming agent injection port provided in the center of the extruder to have a foaming ratio of about 35 times. The amount (15 to 21 parts by weight) was press-fitted.
Next, after kneading and cooling again, the mixture was extruded into the atmosphere from a die (caliber 4.0 mmφ) attached to the tip of the extruder and foamed simultaneously with discharging. The results are shown in Table 6.

[Comparative Examples 17 to 25] Examples 27 to 3 except that the foaming agent shown in Table 6 and the shrinkage inhibitor were used.
Extrusion foaming was carried out in the same manner as in 1. The results are shown in Table 6.

[0050]

[Table 6]

As is clear from Table 6, HCFC-12
When a mixed foaming agent of 4 and HFC-152a is used, a foam having good extrusion stability and the like and excellent physical properties can be obtained even when crosslinkable polyethylene is used.
Since HFC-152a does not contain chlorine, it has a great effect of preventing ozone layer depletion. HFC-152a is a flammable gas, but it becomes nonflammable when mixed with HCFC-124, so it can be safely used with a slight modification of conventional equipment.

[0052]

According to the present invention, in a method for producing a polyolefin resin foam by an extrusion foaming method, HCFC
By using a halogenated hydrocarbon containing -124 as a blowing agent, dimensional stability and surface can be obtained without using a specific CFC that causes ozone layer depletion and without using a special shrinkage inhibitor. It is possible to provide a polyolefin resin foam having excellent smoothness, good appearance, and no shrinkage over time. Also, HCFC-124 and HCFC
By mixing and using -142b or HFC-152a, it is possible to obtain a good extruded foam while achieving cost reduction and chlorine reduction.

Claims (3)

[Claims] 1. A method for producing a polyolefin resin foam in which a polyolefin resin and a foaming agent are melt-kneaded under pressure, and the resulting foamable mixture is extruded into a low pressure region to foam, and 1-chloro- 1, 2, 2, 2
-A method for producing a polyolefin resin foam, which comprises using a halogenated hydrocarbon containing tetrafluoroethane. 2. A foaming agent is 1-chloro-1,2,2,2-
Tetrafluoroethane 30-80% by weight and 1-chloro-
The method according to claim 1, which is a mixture of 70 to 20% by weight of 1,1-difluoroethane. 3. The foaming agent is 1-chloro-1,2,2,2-
The production method according to claim 1, which is a mixture of 30 to 80% by weight of tetrafluoroethane and 70 to 20% by weight of 1,1-difluoroethane.