JPH08302055A - Production of thermoplastic resin foam - Google Patents

Abstract

PURPOSE: To produce a thermoplastic resin foam by using a halogenated hydrocarbon not containing a chlorine atom as a blowing agent, having no fear of destroying an ozone layer, excellent in dimensional stability, foaming moldability, surface smoothness, etc. CONSTITUTION: A thermoplastic resin is mixed with a nonspecified fluorocarbon mixture comprising 30-70wt.% of 1,1,1,2-tetrafluoroethane (HFC-134a), 15-35wt.% of 1,1-difluoromethane (HFC-324 and 15-35wt.% of 1,1,1,2,2,-pentafluoroethane (HFC-125) as a blowing agent and foamed to give the objective thermoplastic resin foam.

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 thermoplastic resin foam, and more specifically, the use of non-specific CFCs as a foaming agent prevents the ozone layer from being destroyed and causes no shrinkage of the thermoplastic resin. The present invention relates to a method for producing a foam. According to the production method of the present invention, it is possible to provide a foam having excellent dimensional stability as well as a conventional foam and excellent foam moldability and surface smoothness.

[0002]

2. Description of the Related Art Generally, a method for producing a foam of a thermoplastic resin is as follows: (1) a chemical in which a pyrolytic foaming agent is kneaded into a thermoplastic resin and heated to a temperature above the decomposition temperature of the foaming agent to foam. Foaming method and (2) thermoplastic resin with methanol, butane, pentane, dichlorodifluoromethane (C
FC-12), dichlorotetrafluoroethane (CFC)
A typical example 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 -114) is melted and kneaded under pressure, and then discharged into a low pressure region to foam.
In the extrusion foaming method, generally, a thermoplastic resin such as a polyolefin resin is put into an extruder to be melted, a foaming agent is press-fitted in the middle of the extruder, melt-kneaded, and then extruded and foamed in a low pressure region. There is. In the extrusion foaming method, when hydrocarbons are used as a foaming agent, the rate of gas escape through the foamed film of the foamed body is high, and therefore, after the foamed body is foamed, it is easy to cause cell shrinkage and lack dimensional stability. Therefore, a long aging period is required after foam molding. Many of the halogenated hydrocarbons have the drawback that bubble shrinkage with time tends to occur, like the hydrocarbons.

On the other hand, among halogenated hydrocarbons, CFCs such as CFC-12 and CFC-114 have been conventionally used as a foaming agent because they do not cause cell shrinkage. Contains a chlorine atom in its molecule, so it may destroy the ozone layer after being released into the atmosphere. Therefore, CFCs have been proposed as a specific CFC internationally from the viewpoint of global environment protection. Therefore, in order to eliminate the risk of ozone layer depletion, research has been conducted on a method for producing a thermoplastic resin foam using non-specific CFC as a foaming agent. For example, monochlorodifluoromethane (HCFC-
22), 1-chloro-1,1-difluoroethane (HC
Since FC-142b) or a mixture thereof has a good foaming property, it is known that specific freon can be substituted in the extrusion foaming method of polyolefin resin. However, since these non-specific CFCs have a higher gas escape rate than the specific CFCs, they tend to cause cell shrinkage over time, lack dimensional stability of the foam, and require a long aging period after foaming. It has the drawback of Moreover, although these compounds are non-specific CFCs, they contain chlorine atoms, and thus there is a risk of ozone layer depletion.

Japanese Unexamined Patent Publication (Kokai) No. 6-345892 discloses a method for producing a polyolefin resin foam, in which 1-chloro-1,1,2,2-tetrafluoroethane (HCFC) is used.
-124) 40-80 wt%, 1,1,1,2-tetrafluoroethane (HFC-134a) 10-50 wt%, and 1,1-difluoromethane (HFC-32) 1
A method of using a blowing agent consisting of 0-40% by weight is disclosed. According to this manufacturing method, as the foaming agent, HFC-134a having a small gas permeability through the cell membrane but having a low expansion ratio, HFC-32 having a large gas permeability but having a high expansion ratio, and a mixed foaming agent By using HCFC-124, which has non-combustibility and is excellent in foamability, mixed at a specific ratio, it is possible to obtain a foam in which dimensional change due to cell shrinkage or expansion over time is suppressed. However, although HCFC-124 is not a specific CFC, it is a halogenated hydrocarbon containing a chlorine atom, and therefore there is a risk of ozone layer depletion.

[0005]

The object of the present invention is to use halogenated hydrocarbons containing no chlorine atom as a foaming agent so that there is no danger of ozone layer destruction, dimensional stability, foam moldability and surface. It is intended to provide a method for producing a thermoplastic resin foam having excellent smoothness and the like. The present inventors have conducted extensive studies to overcome the problems of the prior art, and as a halogenated hydrocarbon, in a method for producing a thermoplastic resin foam using a halogenated hydrocarbon as a foaming agent, None containing chlorine atom 1,1,
1,2-tetrafluoroethane (HFC-134a),
1,1-difluoromethane (HFC-32), and 1,
1,1,2,2-Pentafluoroethane (HFC-12
By using 5) in combination at a specific ratio, there is no danger of ozone layer depletion, excellent dimensional stability and appearance,
It was found that a foam having good foaming stability can be obtained.
The present invention has been completed based on these findings.

[0006]

According to the present invention, 30 to 70% by weight of 1,1,1,2-tetrafluoroethane (HFC-134a) as a foaming agent is added to a thermoplastic resin,
1,1-Difluoromethane (HFC-32) 15-35
A thermoplastic resin foam characterized by kneading and foaming a non-specific CFC mixture containing 15 to 35% by weight of 1,1,1,2,2-pentafluoroethane (HFC-125). A method of manufacturing the same is provided. Hereinafter, the present invention will be described in detail.

The thermoplastic resin used in the present invention is a polymer or copolymer of a thermoplastic hydrocarbon, such as polyethylene, polypropylene, styrene, α-methylstyrene, vinyltoluene, chloromethylstyrene, ethylene. -Propylene copolymer, ethylene-acrylic acid copolymer, ethylene-styrene copolymer, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, ethylene-1-butene copolymer, ethylene-methyl Methacrylate copolymer, propylene-acrylic acid copolymer, propylene-styrene copolymer, propylene-
Vinyl chloride copolymer, propylene-vinyl acetate copolymer, propylene-1-butene copolymer, propylene-methyl methacrylate copolymer, styrene-acrylic acid copolymer, styrene-vinyl chloride copolymer, styrene-
Vinyl acetate copolymer, styrene-1-butene copolymer,
A styrene-methylmethacrylate copolymer etc. can be mentioned. Among these thermoplastic resins, polyolefin resins such as polyethylene, ethylene copolymers, polypropylene, propylene copolymers, or a mixture of two or more thereof are preferable. These resins can be used alone or in combination of two or more. Further, these resins may be cross-linked after being graft-polymerized with a vinyl-based monomer such as vinylmethoxysilane, divinylbenzene, acrylonitrile, diallylphthalate.

In the present invention, depending on the purpose, a bubble nucleating agent (silica, talc, calcium carbonate, calcium stearate, baking soda, etc.), an antistatic agent, an antioxidant,
Stabilizers, pigments, crosslinking catalysts (dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, stannous acetate, stannous caprylate, tin naphthenate, zinc caprylate, zinc stearate, etc.), surface modifiers (Stearic acid amide, stearic acid stearyl amide, glycerol stearate, etc.), flame retardants and the like can be appropriately used as necessary.

In the present invention, as the foaming agent, 1, 1, 1,
2-tetrafluoroethane (HFC-134a), 1,
1-difluoromethane (HFC-32), and 1,1,
1,2,2-Pentafluoroethane (HFC-125)
It has the greatest feature in that it is used in combination at a specific ratio. 1,1,1,2-Tetrafluoroethane (HFC-134a) or 1,1,1,2,2-as a foaming agent
When pentafluoroethane (HFC-125) is used alone, since the gas permeability coefficient of the foaming agent for the thermoplastic resin is smaller than the gas permeability coefficient of air, after foaming,
The foam begins to expand and then returns to its original volume in 1-2 days. Therefore, the dimensional accuracy with respect to the final product is different between the case of processing immediately after manufacturing and the case of processing after 1 to 2 days. Moreover, HFC-134a and HFC-
All of 125 have low solubility in a thermoplastic resin, and it is difficult to increase the expansion ratio. On the other hand, when 1,1-difluoromethane (HFC-32) is used alone as the foaming agent, the foaming agent shrinks after foaming because the gas permeability coefficient of the foaming agent to the thermoplastic resin is larger than that of air. And then return to the original volume in about 3 to 5 days. Therefore, the dimensional accuracy with respect to the final product differs depending on whether the processing is performed within 2 days immediately after manufacturing or after 3 to 5 days. Moreover, HFC-32
Requires an explosion-proof facility because there is a combustion range. However, since HFC-32 has high solubility in a thermoplastic resin, it is possible to increase the expansion ratio.

Therefore, by combining these halogenated hydrocarbons having different gas permeability and foaming ratio, the gas permeability of the foaming agent is brought close to that of air,
At the same time, it may be possible to optimize the expansion ratio. However, 1,1,1,2-tetrafluoroethane (HFC
-134a) is not flammable, but it has 1,1-
It was found that the addition of difluoromethane (HFC-32) in an amount of 5% by weight or more makes the material flammable. On the other hand, 1,1,
1,2,2-Pentafluoroethane (HFC-125)
Has a gas permeability coefficient smaller than that of HFC-134a and has a low solubility in a thermoplastic resin, but has a high non-combustibility.
Therefore, HFC-134a, HFC-32 and HFC-1
It has been found that the combination with 25 in specific proportions gives a non-flammable mixture. In the present invention, by using these three types of HFCs in combination at a specific ratio as a foaming agent, the gas permeability as a foaming agent is brought close to the gas permeability of air, and the volume expansion of the foam immediately after foaming. While suppressing shrinkage and shrinkage, achieving a high expansion ratio, and
Nonflammability and ozone layer nondestructiveness can be imparted.

The gas permeability of the blowing agent used in the present invention is
Depending on the type of thermoplastic resin, it may differ a little
30-70% by weight of 1,2-tetrafluoroethane (HFC-134a), 1,1-difluoromethane (HFC
-32) is used in a proportion of 15 to 35% by weight and 1,1,1,2,2-pentafluoroethane (HFC-125) in a proportion of 15 to 35% by weight.
It is possible to obtain a thermoplastic resin foam which has no fear of ozone layer destruction and is excellent in foamability, dimensional stability, appearance (surface smoothness) and the like. The blowing agent of the present invention has a desired expansion ratio within a range of usually 1 to 35 parts by weight, preferably 5 to 25 parts by weight, and more preferably 10 to 20 parts by weight with respect to 100 parts by weight of the thermoplastic resin. According to the above, it can be used in an appropriate amount.

The thermoplastic resin foam can be obtained by kneading a foaming agent in a thermoplastic resin and foaming. Specifically, a mixture of a thermoplastic resin and a desired additive is charged into an extruder and melt-kneaded, while a foaming agent is pressed into the extruder through an injection port provided in an extruder barrel, Melt and knead the thermoplastic resin and the foaming agent under pressure, then extruded from the mold of a predetermined shape into the low pressure region,
The foaming agent is vaporized to foam the thermoplastic resin. More specifically, as shown in FIG. 1, a raw material 1 is put into a hopper 2 of an extruder and kneaded with a screw 3 of the extruder. On the other hand, the foaming agent is injected from the foaming agent tank 6 through the foaming agent injection pump 5 and the foaming agent injection port 4 into the extruder. Furthermore,
The foamable composition kneaded by the screw 3 of the extruder is cooled by the cooling mold 7 and extruded from the nozzle 8 into the low pressure region (in air). Extruded foamable composition,
The foaming agent is foamed to form a foam 10. The foam 10 is taken up by the take-off machine 9.

[0013]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The evaluation criteria of physical properties are as follows. (1) Non-combustibility of foaming agent ○: Non-combustibility ×: Combustibility (2) Dimensional changes over time (expansion is +, contraction is-sign) ○: No change △: Restored within 3 days ×: 1 week As above, (3) Surface smoothness ○: Good △: Slightly bad (surface fluffing, etc.) ×: Poor (surface fluffy) (4) Foaming ratio ○: 27.0 to 28.5 times △: 26.0 26.9 times ×: 25.9 times or less (5) Ozone layer non-destructive ◯: No ozone layer destructive possibility ×: Ozone layer destructive possibility

[Examples 1 to 7] First, 100 parts by weight of the thermoplastic resin was mixed with the foaming agent (mixed HFCs) shown in Table 1, a thermoplastic resin, a cell nucleating agent and a crosslinking catalyst.
Premixing additive components, diameter 40mm, L / D = 3
It was fed to a No. 6 single-screw extruder, and these mixtures were melt-kneaded in the first half of the barrel of the extruder. Next, based on the gas generation amount of the foaming agent, the foaming ratio of the obtained foam is theoretically 27.5.
The foaming agent was press-fitted from the center of the extruder barrel so as to double the pressure. After further kneading in the latter half of the barrel, it is cooled to the optimum foaming temperature with the barrel tip and the die and extruded from the die at the tip of the die with a diameter of 1.5 mm to give a cylindrical foam with a foaming ratio of 27.5 times. Obtained. Table 1 shows the evaluation results.

[0015]

[Table 1]

(* 1) LDPE: Density 0.19 g / cm
³ , low-density polyethylene with MI = 4.0 (* 2) GLDPE: Silane-grafted LDPE (0.1 part by weight of vinylmethoxysilane, 0.1 part by weight of dicumyl peroxide, based on 100 parts by weight of LDPE) And 0.1 part by weight of antioxidant, 33 mmL /
In a twin-screw extruder with D = 26, the feed section was set at 120 degrees, and the rest was set at 200 degrees, and it was extruded into a strand shape,
Pellets having a diameter of 3 mm and a length of 5 mm). (* 3) EVA: Density 0.94 g / cm ³ , MI = 2.
5, ethylene-vinyl acetate copolymer having a vinyl acetate content of 15% (* 4) PP: density 0.91 g / cm ³ , MI = 1.5
Polypropylene (* 5) PS: polystyrene with a density of 1.05 g / cm ³ , MI = 10 (* 6) Cell nucleating agent: talc (particle size 300 mesh) (* 7) Cross-linking catalyst: dibutyltin dilaurate (* 8) HFC -134a: 1,1,1,2-tetrafluoroethane (* 9) HFC-32: 1,1-difluoromethane (* 10) HFC-125: 1,1,1,2,2-pentafluoroethane

[Comparative Examples 1 to 7] A foaming composition (Comparative Examples 1 to 6) in which the compounding ratio of the foaming agent was changed by the compounding formulation of the foaming agent, the thermoplastic resin, and the cell nucleating agent shown in Table 2. A foam was obtained in the same manner as in Example, except that a foamable composition (Comparative Example 7) containing HCFC-124 containing chlorine atoms was prepared in an extruder. Table 2 shows the evaluation results.

[0018]

[Table 2] (* 1) to (* 10): Same as footnote in Table 1 (* 11) HFC-124: 1-chloro-1,1,2,
2-tetrafluoroethane

[0019]

According to the production method of the present invention, a thermoplastic resin foam excellent in dimensional stability and surface smoothness is obtained by using a foaming agent composed of a non-specific chlorofluorocarbon mixture which does not cause ozone layer depletion. be able to. This foam can be used in a wide range of applications as, for example, a cushion material, an inner layer material, a heat insulating material, and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an extrusion foaming machine used in a manufacturing method of the present invention.

[Explanation of symbols]

 1. Raw materials and additives 2. Hopper 3. Screw 4. Foaming agent inlet 5. Foaming agent injection pump 6. Foaming agent tank 7. Cooling die 8. Nozzle 9. Collection machine 10. Foam

Claims (1)

[Claims] 1. A thermoplastic resin containing 1,
1,1,2-tetrafluoroethane (HFC-134
a) 30 to 70% by weight, 1,1-difluoromethane (H
FC-32) 15-35% by weight, and 1,1,1,2,
2-pentafluoroethane (HFC-125) 15-3
A method for producing a thermoplastic resin foam, which comprises kneading and foaming a non-specific freon mixture containing 5% by weight.