JPH08302056A - Production of flame-retardant foam - Google Patents

Abstract

PURPOSE: To obtain a flame-retardant foam by extrusion foaming, showing excellent flame-retardance, not evolving a harmful halogen-based gas in combustion, and not deteriorating an environment. CONSTITUTION: A thermoplastic resin is melted and blended by a first extruder, further mixed with 3-25 pts.wt. of a blowing agent comprising tetrafluoroethane as an essential component based on 100 pts.wt. of the thermoplastic resin, melted and blended under pressure and sent to a pressurized second extruder 2. A flame-retardant composition composed of neutralized thermally expandable graphite and an ammonium polyphosphate in the ratio of (9:1) to (1:9) in an amount of 5-30 pts.wt. is fed to the second extruder 2. The thermoplastic resin is blended with the flame-retardant compound at 16-25rpm of the number of revolutions of the screw of the second extruder 2 under pressure in a melt state and the prepared foamable mixture is extruded to the atmospheric pressure and foamed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention shows remarkable flame retardancy,
The present invention relates to a method for producing a flame-retardant resin foam excellent in foaming moldability and stability over time by extrusion foaming without generating harmful halogen-based gas during combustion.

[0002]

2. Description of the Related Art Thermoplastic resin foams are used in a wide range of applications such as heat insulating materials and packaging materials because they have excellent chemical stability, excellent heat insulating properties, flexibility and light weight. As a method for producing a thermoplastic resin foam, generally, a resin is kneaded with a pyrolytic chemical foaming agent, and after molding into a predetermined shape,
A chemical foaming method of foaming by heating above the decomposition temperature of the foam, and a low-pressure region after gas or volatile liquid having a boiling point below the melting point of the resin such as butane, pentane, dichlorofluoromethane, etc. is pressed into the molten resin. A typical example is an extrusion foaming method in which the foam is discharged into the foam.

In the extrusion foaming method, generally, a thermoplastic resin is put into an extruder and melted, a foaming agent is injected from the middle of the extruder, and the mixture is melt-kneaded and then extruded and foamed from a die to form a foam. It has gained. As the foaming agent, hydrocarbon type, fluorohydrocarbon type, carbon dioxide gas, nitrogen gas, etc. are used.

Since the above-mentioned thermoplastic resin foam is flammable, it is required to have flame retardancy as its applications are expanded. As a method of making a thermoplastic resin flame-retardant, a method of adding a halogen-containing compound is generally used. The thus flame-retarded material has a high degree of flame retardancy, and the deterioration of the molding processability and the mechanical strength of the molded product are relatively small. However, a large amount of smoke is generated at the time of processing or incineration, which poses a problem of corrosiveness to equipment and harmfulness to human body. In recent years, flame retardation without using a halogen compound has been strongly demanded.

As a flame retardant containing no halogen compound, JP-A-6-25476 describes a flame-retardant polyolefin resin composition obtained by mixing a thermoplastic resin with a two-component system of thermally expandable graphite and ammonium polyphosphate. Has been done.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-mentioned publication, since the thermally expansive graphite obtained by the oxidation treatment with the inorganic acid and the strong oxidant is used as it is without being neutralized, The composition containing this becomes unstable and causes corrosion of machinery during kneading and molding. Further, since the heat-expandable graphite having a large particle size of 80 mesh or more and 99 mesh or less is used, the surface smoothness is deteriorated in the case of extrusion foaming. Therefore, it is not suitable for a method of obtaining a foam by extruding and foaming a thermoplastic resin.

The present invention solves the above-mentioned conventional problems, and it is possible to obtain a flame-retardant resin foam which exhibits remarkable flame retardancy and does not generate a harmful halogen-based gas at the time of combustion by extrusion foaming. An object is to provide a method for producing a flame-retardant resin foam.

[0008]

A method for producing a flame-retardant resin foam according to the present invention as set forth in claim 1, wherein the thermoplastic resin is melt-kneaded in a first extruder, and further 100 parts by weight of the thermoplastic resin is added. On the other hand, a blowing agent 3 containing tetrafluoroethane as an essential component
˜25 parts by weight are added and melt-kneaded under pressure, and this is sent to a second extruder under pressure, and 100 parts by weight of the thermoplastic resin is subjected to neutralization treatment of thermally expandable graphite and ammonium polyphosphate. 5 to 30 parts by weight of the flame-retardant composition having a weight ratio of 9: 1 to 1: 9 is fed to the second extruder,
The above-mentioned thermoplastic resin and flame-retardant composition are melt-kneaded under pressure at a screw rotation speed of the extruder of 16 to 25 rpm, and the resulting foamable mixture is extruded under atmospheric pressure to foam. Is.

The method for producing a flame-retardant resin foam of the present invention according to claim 2 is the method for producing a flame-retardant resin foam according to claim 1, wherein the thermally expansive graphite having a particle size of 150 to 200 mesh is used. Is what you use.

The method for producing a flame-retardant resin foam of the present invention according to claim 3 is:
0.5% weight loss temperature of 95-170 by thermogravimetric analysis
It is characterized in that ammonium polyphosphates having a 2% weight loss temperature of 180 to 220 ° C. are used.

The method for producing a flame-retardant resin foam of the present invention according to claim 4 is the method according to any one of claims 1 to 3, wherein
It is characterized in that the foaming agent contains tetrafluoroethane as an essential component and is a mixture of hydrochlorofluorohydrocarbon or hydrofluorohydrocarbon.

The thermoplastic resin used in the present invention includes:
Ethylene-based monomers, propylene-based monomers, styrene-based monomers, and these and other monomers (for example, vinyltrimethoxysilane, vinyltriethoxysilane, divinylbenzene, acrylonitrile, diallylphthalate, methylmethacrylate, etc. Vinyl-based monomer) polymer, or
These copolymers are mentioned.

Examples of the above polymers or copolymers include polyethylene, polypropylene, styrene, α-methylstyrene, vinyltoluene, chloromethylstyrene, ethylene-propylene copolymer, ethylene-vinyl chloride copolymer, ethylene-acetic acid. Vinyl copolymer, ethylene-1-butene copolymer, ethylene-methyl methacrylate copolymer, ethylene-styrene copolymer, propylene-styrene copolymer, propylene-vinyl chloride copolymer, propylene-vinyl acetate copolymer Coalesce, propylene-1-butene copolymer, propylene-methylmethacrylate copolymer,
Propylene-styrene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-
1-butene copolymers, styrene-methyl methacrylate copolymers and the like can be mentioned. These resins can be used alone or 2
A mixture of more than one type can be used.

Thermally expandable graphite is a conventionally known substance, and powders of natural phosphorous graphite, pyrolytic graphite, quiche graphite and the like are mixed with inorganic acids such as concentrated sulfuric acid, nitric acid and selenate, concentrated nitric acid, perchloric acid, It is a crystalline compound that maintains a layered structure of carbon by treating with a strong oxidant such as permanganate, dichromate, and hydrogen peroxide to form a graphite intercalation compound.

In the present invention, the thermally expansive graphite obtained by the acid treatment as described above is treated with ammonia, an aliphatic lower amine,
It is used after being neutralized with an alkali metal compound, an alkaline earth metal compound, or the like. If it is used without being neutralized, the stability of the composition containing it will be deteriorated, and it will be a cause of corrosion of mechanical devices during kneading and molding.

Examples of the aliphatic lower amine as the neutralizing agent include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine, butylamine and the like. Examples of the alkali metal compound and the alkaline earth metal compound include potassium, calcium, barium,
Hydroxides such as magnesium, oxides, carbonates, sulfates,
Examples thereof include organic acid salts.

The thermally expandable graphite preferably has a particle size of 150 to 200 mesh. If the particle size is smaller than 200 mesh, the degree of expansion of graphite is low, and thus the flame retardancy may be reduced and the desired flame retardancy may not be obtained. Further, if it is larger than 150 mesh, the degree of expansion is large and it is effective in imparting flame retardancy, but the dispersibility is poor when kneading with the resin,
There are problems that the physical properties of the product are deteriorated and that the surface of the foam may be uneven.

Examples of the ammonium polyphosphates used in the present invention include ammonium polyphosphate and melamine-modified ammonium polyphosphate. To improve flame retardance, a 0.5% weight loss temperature of 9% by thermogravimetric analysis is used.
5 to 170 ° C., 2% weight loss temperature is preferably in the range of 180 to 220 ° C.

The above 0.5% and 2% weight loss temperatures are
Using a thermogravimetric analyzer, heating rate 10 ° C / min, flow rate 20
30 mg of 10 mg sample under the condition of air flow of 0 ml / min.
When the temperature is raised from ℃ to 900 ℃, the sample weight is 0.5%
And a temperature that decreases by 2%.

The ammonium polyphosphates are not particularly limited as long as the 5% and 2% weight loss temperatures are within the above ranges, and the ammonium polyphosphate and the melamine-modified ammonium polyphosphate may be used alone or in combination. Absent.

In the present invention, the weight ratio of the thermally expandable graphite and the ammonium polyphosphate is 9: 1 to 1: 9, preferably 8: 2 to 5: 5. This is because if the value is out of this range, there is almost no difference in flame retardancy as compared with the case where each of them is used alone.

The content of the flame retardant mixture of thermally expandable graphite and ammonium polyphosphate in 100 parts by weight of the thermoplastic resin is 5 to 30 parts by weight. Preferably 8-20
Parts by weight. If it exceeds 30 parts by weight, a uniform foam cannot be obtained, and if it is less than 5 parts by weight, sufficient flame retardancy cannot be obtained.

The foamable mixture prepared as described above contains
Flame retardant aids such as hydrated metal oxides such as aluminum hydroxide, magnesium hydroxide and basic magnesium carbonate, shrinkage inhibitors, bubble nucleating agents, antioxidants, lubricants, pigments, electrification, as long as foaming is not hindered. You may mix | blend an inhibitor, a crosslinking catalyst, etc.

As the shrinkage-preventing agent, aliphatic amides having 15 to 22 carbon atoms (stearic acid amide, behenic acid amide,
Stearic acid stearyl amide etc.), and aliphatic alcohols (stearic acid glyceride etc.) are mentioned. Examples of the cell nucleating agent include silica, talc, calcium carbonate, calcium stearate, baking soda and the like. As the antioxidant, antistatic agent, pigment, etc., those which are generally commercially available may be used. Examples of the crosslinking catalyst include dibutyltin laurate, dibutyltin diacetate, dioctyltin dilaurate, stannous acetate, stannous caprylate, tin naphthenate, zinc caprylate, and zinc stearate.

The blowing agent used in the present invention contains tetrafluoroethane as an essential component. Tetrafluoroethane has no ozone depleting effect and has the same foaming characteristics as conventional chlorofluorohydrocarbons, so it is possible to manufacture foams without significantly changing the extrusion foamer that was used in the past. You can If necessary, other components can be mixed with the foaming agent before use. For example, propane, butane, pentane, isopentane, hexane, isohexane, heptane, isoheptane, 2,
Hydrocarbons such as 3-dimethylbutane and cyclopentane,
Halogenated hydrocarbons such as chloromethane and dichloromethane, and hydrochlorofluorohydrocarbons and hydrofluorohydrocarbons are those that are less likely to damage the ozone layer. These can be used by adding one or more kinds to tetrafluoroethane.

As the hydrochlorofluorohydrocarbon,
There are monochlorodifluoromethane, monochlorotetrafluoromethane, and monochlorodifluoroethane, and examples of hydrofluorohydrocarbons include difluoromethane, pentafluoroethane, trifluoroethane, and difluoroethane.

The amount of the foaming agent added is appropriately determined according to the desired expansion ratio, but is usually about 3 to 25 parts by weight per 100 parts by weight of the thermoplastic resin. The blowing agent is 1 at atmospheric pressure
Since it diffuses into the atmosphere in about a week, there is no possibility of generating halogen-based gas upon combustion after it is commercialized.

In the present invention, two extruders, a first extruder and a second extruder, are used. The first extruder is for melting and kneading a thermoplastic resin and for mixing the foaming agent therein, and a normal single screw extruder is used. The second extruder is pressurized so that the foaming agent does not volatilize, and the flame retardant is mixed while rotating the screw at a low speed so as not to give a high shearing force to the flame retardant.

In order to keep the heat-expandable graphite in the above grain size, the first extruder is a single-screw extruder or a twin-screw extruder,
The second extruder is preferably a single screw extruder.

As a foaming method, a thermoplastic resin and a desired additive are charged into a first extruder and melt-kneaded, and a foaming agent containing tetrafluoroethane as an essential component is introduced into an extruder through an injection port in the middle of a barrel. It is pressed in and the foaming agent is kneaded and dissolved in the resin under pressure. The rotation speed of the screw is 35 to 40 rpm. The thermoplastic resin having the foaming agent dissolved therein is fed to the second extruder under pressure so that the foaming agent dissolved in the thermoplastic resin in the first extruder is not volatilized.

The neutralized heat-expandable graphite is mixed with ammonium polyphosphate in a ratio of 9: 1 to 1: 9, and the total weight of ammonium polyphosphate is 100 parts by weight of the thermoplastic resin. It is charged into the second extruder so as to be 5 to 30 parts by weight, and the rotation speed of the screw of the second extruder is set to 16 to 25 rpm, preferably 18 to 20 r.
As the pm, the resin is slowly cooled by gentle kneading and sent out to the mold. After that, when extruded into the atmospheric pressure region from a mold having a predetermined shape provided in the second extruder, foaming occurs.

The reason for doing so is that the raw material and the foaming agent are melted and kneaded in the first extruder, so that the material is subjected to a high shearing force. This is because when the heat-expandable graphite is put into the first extruder, the particle size becomes fine due to the distribution action by the high shearing force, and the particle size distribution spreads toward the finer side, so that the desired flame retardancy cannot be obtained. In other words, when the first extruder is a single-screw extruder or a twin-screw extruder, or the second extruder is a twin-screw extruder, if the thermally expansive graphite is added to these and mixed at a high speed, heat is generated as described above. The particle size of the expandable graphite becomes smaller, and the flame retardancy decreases.

[0033]

The flame-retardant neutralized heat-expandable graphite and ammonium polyphosphate are mixed and used in a weight ratio of 9: 1 to 1: 9, and the rotation speed of the screw of the second extruder is set to 16 Since the flame retardant is mixed while rotating the screw at a low speed so as not to give a high shearing force to the flame retardant at a speed of -25 rpm, remarkable flame retardancy is exhibited. Moreover, even if it burns, it does not generate a halogen-based gas. Further, when the 0.5% weight loss temperature of ammonium polyphosphate is 95 to 170 ° C. and the 2% weight loss temperature is 180 to 220 ° C., more reliable flame retardancy can be obtained.

Since the thermally expandable graphite has been neutralized,
The composition containing it has good stability and does not corrode manufacturing equipment.

[0035]

EXAMPLES Examples of the method for producing a flame-retardant resin foam of the present invention will be described below. FIG. 1 is a schematic view showing a foaming device used in this example. 1 is a first uniaxially arranged laterally
It is an extruder (bore diameter 40 mm, L / D = 32), and the extrusion die 11 is connected to a single-screw second extruder (bore diameter 65 mm, L / D = 28) 2 arranged in the longitudinal direction. From the foaming agent tank 3 via the injection pump 4, the supply pipe 41 is the first
It is connected to the foaming agent inlet 12 of the extruder 1. In addition, another supply pipe 71 connects the pressurizing chamber 5 through the pressurizing pump 7.
The flame retardant supply pipe 61 is connected to the second extruder 2 from the flame retardant feeder 6 installed in the pressurizing chamber 5. 21 is an extrusion die.

The pressure pump 7 applies pressure to the injection pump 4 through the supply pipe 71 to maintain the inside of the first extruder 1 in a pressurized state, and also applies pressure to the pressure chamber 5 to supply the flame retardant supply pipe 61. The inside of the second extruder 2 is maintained under pressure through.

The materials used are as follows: Thermoplastic resin LDPE; low density polyethylene (density 0.91 g / cm
³ , MI = 4.0) GLDPE; crosslinkable low-density polyethylene (the above LDPE
Silane-grafted with a density of 0.91 g / cm ³ ,
MI = 3.9) EVA; ethylene-vinyl acetate copolymer (vinyl acetate content 15%, density 0.92 g / cm ³ , MI = 2.
5) PP; homopolypropylene (density 0.91 g / c
m ³ , MI = 2.5) PS; polystyrene (density 1.95 g / cm ³ ,
MI = 10) Cell nucleating agent Talc; Grain size 200 mesh Thermally expandable graphite p of neutralized thermally expandable graphite and untreated thermally expandable graphite
For H, 1 g of the heat-expandable graphite was put in advance in 100 cm ³ of pure water at 25 ° C., stirred with a stirrer for 5 minutes, and measured with a pH meter. As a result, the pH of the neutralized thermally expandable graphite was
9.5 The pH of untreated thermally expandable graphite was 3.3. Both were subjected to a kneading test using a Labo Plastomill (20 g of thermally expansive graphite was added to 100 parts by weight of low-density polyethylene having a density of 0.91 and a melt index of 4.0), and the untreated product appears to be corroded in the kneading mold. Whitening occurred. Therefore,
Neutralized products were used in Examples and Comparative Examples of the present invention.

Blowing agent HFC-134a; tetrafluoroethane HFC-32; difluoromethane HFC-125; pentafluoroethane HCFC-124; monochlorotetrafluoroethane

(Examples 1 to 7) In FIG. 1, the materials 8 shown in Table 1 other than the heat-expandable graphite and the foaming agent were weighed and mixed in accordance with the formulation, and charged from the hopper 13 of the first extruder 1 and screwed. After melt-kneading at a rotation speed of 40 rpm, a foaming agent having the composition shown in Table 1 was press-fitted at a ratio shown in Table 1 from a foaming agent injection port 12 provided in the central portion of the first extruder 1 to knead and dissolve it. It was pressed into the second extruder 2 from the mold 11.

In order to prevent the dissolved foaming agent from volatilizing, the flame retardant is pressed into the second extruder 2 from the flame retardant feeder 6 in the pressure chamber 5 under pressure, and the screw rotation speed 2
The expandable resin composition that was gently kneaded and cooled at 0 rpm was sent to the extrusion die 21, and extruded into the atmosphere from the die (inner diameter 2.1 mm, outer diameter 4.3 mm) at the tip of the die 21 to have an inner diameter of 11 mm and an outer diameter. A cylindrical foam 9 having a diameter of 21 mm was obtained.

Comparative Examples 1 and 2 Foams were obtained in the same manner as in Example 1 except that the particle size of the thermally expandable graphite was changed as shown in Table 2.

Comparative Examples 3 to 4 Foams were obtained in the same manner as in Example 5 except that the particle size of the thermally expandable graphite was changed as shown in Table 2.

Comparative Examples 5 to 7 The compounding amounts of the respective materials were set as shown in Tables 2 and 3, and extrusion was performed using the conventional single-screw extruder 1 shown in FIG. 2 for foaming. In FIG. 2, 1 is a single-screw extruder (diameter 50 mm, L / D = 32), in which a material 8 other than a foaming agent is charged from a hopper 13 to rotate a screw at a rotation speed 4
The foaming resin composition was melt-kneaded at 0 rpm, a foaming agent was press-fitted from an injection port 12 in the center of the extruder 1, and the kneaded and cooled foamable resin composition was prepared with a die at the tip of a mold 11 (inner diameter 2.1 mm, outer diameter 4.3).
mm) and extruded into the atmosphere, inner diameter 11 mm, outer diameter 21 m
m cylindrical foam 9 was obtained.

(Comparative Examples 8 to 9) The same composition as in Comparative Example 5 was used except that the compounding amounts of the thermally expandable graphite and ammonium polyphosphate were changed as shown in Table 3, and the extruder shown in FIG. 1 was used. A foam was obtained.

(Comparative Examples 10 to 11) The compounding amounts of the respective materials were set as shown in Tables 3 and 4, and the materials were extruded and foamed using the extruder shown in FIG.

Comparative Examples 12 to 13 Foams were obtained using the apparatus shown in FIG. 1 except that tetrafluoroethane was not used as a foaming agent and the materials shown in Table 4 were used.

(Comparative Example 14) A foam was obtained in the same manner as in Example except that the screw rotation speed of the second extruder was changed to 10 rpm.

(Comparative Example 15) A foam was obtained in the same manner as in Example except that the screw rotation speed of the second extruder was 30 rpm.

The foams obtained in the examples and comparative examples were evaluated for flame retardancy and appearance by the following methods. (1) Flame retardance The oxygen index was measured according to JIS D 1201. ◯: Oxygen index of 28 or more ×: Oxygen index of less than 28 (2) Appearance The appearance defect due to unevenness of foaming of the foam was judged by the presence or absence of unevenness. ◯: There is no unevenness of 0.2 mm or more on the surface. X: There is unevenness of 0.2 mm or more on the surface. The above results are shown in Tables 1 and 2.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

[0053]

[Table 4]

As is clear from Tables 1 to 4, since Examples 1 to 7 have the constitution requirements of the present invention, all of them are excellent in flame retardancy and appearance. On the other hand, Comparative Examples 1 to 15 are unsatisfactory in flame retardancy and appearance because any of the constitutional requirements of the present invention is lacking.

[0055]

EFFECTS OF THE INVENTION The method for producing a flame-retardant resin foam of the present invention has the above-mentioned constitution, and therefore has the following effects. In the present invention, the heat-expandable graphite neutralized as a flame retardant and ammonium polyphosphates are mixed and used in a weight ratio of 9: 1 to 1: 9, and the rotation speed of the screw of the second extruder is 16 The flame retardant is mixed while rotating the screw at a low speed so as not to give high shearing force to the flame retardant at ~ 25 rpm, so that it shows remarkable flame retardancy and does not generate harmful halogen-based gas during combustion. Resin foam can be obtained by extrusion foaming. Further, since the heat-expandable graphite is neutralized, the composition containing it has good stability and does not corrode the production equipment. Furthermore, the 0.5% weight loss temperature of ammonium polyphosphates is 95 to 17
When 0 ° C and 2% weight loss temperature are 180 to 220 ° C, more reliable flame retardancy is obtained.

[0056]

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of an extrusion foaming device used in the present invention.

FIG. 2 is a schematic view showing a conventional extrusion foaming device.

[Explanation of symbols]

 1: 1st extruder 2: 2nd extruder 3: Foaming agent tank 4: Injection pump 5: Pressurizing chamber 6: Flame retardant feeder 7: Pressurizing pump 9: Foam 11, 21: Extrusion die 12: Foaming 12 Agent injection port 13: Hopper 41, 71: Supply pipe 61: Flame retardant supply pipe

Claims (4)

[Claims] 1. A thermoplastic resin is melt-kneaded in a first extruder, and 3 to 25 parts by weight of a foaming agent containing tetrafluoroethane as an essential component is added to 100 parts by weight of the thermoplastic resin and the mixture is pressurized. Melted and kneaded with, and sent to a pressurized second extruder, to 100 parts by weight of the thermoplastic resin,
Flame-retardant composition 5 in which the weight ratio of neutralized heat-expandable graphite and ammonium polyphosphate is 9: 1 to 1: 9
To 30 parts by weight are fed to the second extruder, and the thermoplastic resin and the flame-retardant composition are melt-kneaded under pressure at a screw rotation speed of the second extruder of 16 to 25 rpm to obtain a foamable mixture. A method for producing a flame-retardant resin foam, which comprises extruding and foaming under atmospheric pressure. 2. The method for producing a flame-retardant resin foam according to claim 1, wherein the thermally expandable graphite has a particle size of 150 to 200 mesh. 3. A 0.5% weight loss temperature by thermogravimetric analysis of 95 to 1 when added to the neutralized thermally expandable graphite.
The method for producing a flame-retardant resin foam according to claim 1 or 2, wherein ammonium polyphosphates having a temperature of 70 ° C and a 2% weight loss temperature of 180 to 220 ° C are used. 4. The flame-retardant resin foam according to claim 1, wherein the foaming agent contains tetrafluoroethane as an essential component and is a mixture of hydrochlorofluorohydrocarbon or hydrofluorohydrocarbon. Body manufacturing method.