JPH03167236A - Flame-retardant polystyrene resin foam and its production - Google Patents

Abstract

PURPOSE:To obtain the title foam excelling in flame retardancy, showing self- extinguishing properties even when ignited and not dripping even in contact with a flame by incorporating a specified thermally expansible graphite in the foam. CONSTITUTION:A thermally expansible graphite prepared by coating graphite with a film-forming resin (e.g. acrylonitrile/butadiene copolymer) is incorporated in such an amount that the content of the graphite is 5-50wt.% and the content of the film-forming resin is 0.2-25wt.%.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a polystyrene resin foam with improved flame retardancy, and the polystyrene resin foam of the present invention can be used as a heat insulating material, a building material, a cushioning material, etc. suitable for use.

[Conventional technology]

Polystyrene resin foam has traditionally been used in various fields such as building materials due to its excellent properties and workability.The manufacturing method involves extruding polystyrene resin and a volatile foaming agent at high temperatures. A method of producing a foam by mixing under high pressure and extruding the resulting mixture through a nozzle attached to the tip of an extruder in a relatively low-temperature, low-pressure zone, and foaming it, or when carrying out suspension polymerization of monomers. A method is known in which a volatile blowing agent is added at the initial stage of polymerization or when a certain degree of polymerization conversion has been reached to obtain expandable resin particles, and then a foaming treatment is performed to form a foam. However, various problems have been pointed out with the foams produced in this way, and in particular, from the viewpoint of preventing disasters caused by fires in recent years, there has been a demand for improvement, particularly in terms of resistance to combustion. To solve this problem, we added antimony trioxide to the foam.
It is also well known to add inorganic flame retardants such as aluminum hydroxide and borates, and organic flame retardants such as halogen derivatives of aromatic hydrocarbon compounds or non-aromatic hydrocarbon compounds. Further, as another means of achieving this objective, US Pat. No. 3,574,644 proposes a method of increasing flame retardance by adding thermally expandable graphite. [Problems to be Solved by the Invention] The conventional methods described above cannot be said to have a sufficient flame retardant effect on polystyrene resin foams, and in order to obtain the desired flame retardancy, it is necessary to add flame retardants. The amount added becomes extremely large, and as a result, the physical properties of the foam deteriorate, and some problems have been recognized from an economic standpoint. In addition, inorganic flame retardants are incompatible with polymers, which reduces foaming properties, the manufacturing process becomes complicated in order to uniformly disperse flame retardants, or organic flame retardants are low-molecular compounds. In some cases, manufacturing problems have also been pointed out, such as the foam particles scattering or escaping during the process, worsening the working environment. In addition, thermally expandable graphite is known to be used as a flame retardant by taking advantage of its property of rapidly expanding when it comes in contact with flame. Because they contain sulfuric acid, they are acidic,
Therefore, when foaming polystyrene-based resin to which it is added, it may corrode metal manufacturing equipment, and when cutting the resulting foam, it may corrode the cutter blade. On the other hand, since thermally expandable graphite exhibits acidity, in order to improve the stability of latex, emulsion, etc. to which it is added, the method described in U.S. Pat. However, according to the experimental results of the present inventors, in the case of neutralization with ammonia, the ammonium sulfate that appears to be generated by neutralization causes the expandable polystyrene resin beads to be heated with steam etc., foamed, and fused. It was found that the problem could not be solved because it decomposed due to the heat generated and, as a result, it could not maintain neutrality. The present invention aims to overcome the above problems and provide a polystyrene resin foam with excellent flame retardancy and a method for producing the same.

[Means to solve the problem]

The present inventors have conducted various studies on polystyrene resin foam with excellent flame retardancy, and found that by adding and blending a specific thermally expandable graphite, an excellent flame retardant foam without the above-mentioned problems can be obtained. It was discovered that a polystyrene resin foam having flammability can be obtained, and the present invention was completed. That is, in the present invention, thermally expandable graphite coated with a film-forming resin is prepared such that the graphite content is 5 to 50% by weight and the film-forming resin content is 0.2 to 25% by weight. This article focuses on the flame-retardant polystyrene resin foam containing the material and its manufacturing method. The present invention will be explained in detail below. Examples of the polystyrene resin used as a raw material for the polystyrene resin foam used in the present invention include polymers of monomers such as styrene, α-methylstyrene, dimethylstyrene, ethylstyrene, chlorostyrene, promostyrene, and vinyltoluene, and polymers of these monomers. Copolymers of monomers or these monomers with butadiene, acrylonitrile, methyl methacrylate, isoprene, vinyl chloride,
Examples include copolymers with vinyl monomers such as imptylene. Further, these polystyrene resins may be mixed with other resins such as polyolefins.

In addition, the blowing agent is usually an easily volatile organic compound having a boiling point lower than the softening temperature of the polystyrene resin, such as aliphatic hydrocarbons, aliphatic halogenated hydrocarbons, aliphatic ketones, and aliphatic esters. Polystyrene.
At a ratio of 1 to 30 parts by weight per 100 parts by weight of the system resin,
More preferably, it is customary to impregnate at a ratio of 3 to 8 parts by weight. The raw material graphite for the thermally expandable graphite used in the present invention is not particularly limited, and those used in the production of normal thermally expandable graphite, such as natural graphite, pyrolytic graphite, and kitsch graphite, can be used. The thermally expandable graphite used in the present invention is
The raw graphite is treated with an acid, for example, brought into contact with a mixture of 98% concentrated sulfuric acid and 60% hydrogen peroxide at a temperature of 45°C or less for 10 to 30 minutes, and then the graphite after the acid treatment is washed with water, filtered, and dried. After that, it is coated with a film-forming resin.

The thermally expandable graphite of the present invention desirably has a degree of expansion of 50 to 250 −/g when rapidly heated at 1000° C. for 10 seconds from the viewpoint of exhibiting a flame retardant effect. The "degree of expansion" in the present invention means that a 150cc quartz beaker that has been heated in an electric furnace maintained at 1000°C for 10 minutes or more is taken out of the furnace, and immediately 0.5g of thermally expandable graphite is used.
quickly placed in the same furnace maintained at <1000°C, held there for 10 seconds, and then taken out of the furnace.
Volume/weight ratio of expanded graphite after natural cooling (unit: ml
/g).

The degree of expansion of thermally expandable graphite generally depends on the particle size of the thermally expandable graphite, and when the particle size is finer than about 80 mesh, the degree of expansion tends to be small, and when it is finer than 150 mesh, the degree of expansion is extremely low. As a result, the flame retardant effect is significantly reduced. On the other hand, if the particle size is about 20 to 30 mesh, it is not preferable because uniform addition becomes difficult when added to polystyrene resin. Therefore, the particle size of the thermally expandable graphite used in the present invention is from 30 to 120
A mesh material is preferable, and a material classified into about 40 to 100 mesh is most preferable. The particle size of thermally expandable graphite usually depends on the particle size of the raw material graphite used to manufacture it, so the particle size may be adjusted using the raw material. Alternatively, the expanded graphite may be crushed and classified. You can.

The thermally expandable graphite used in the present invention is produced by treating the raw material graphite with an acid as described above, and then treating the free sulfuric acid with one or more basic compounds selected from ammonia, alkali metal compounds, and alkali metal earth compounds. It is preferable that the Preferred neutralizing agents include caustic soda, caustic potash, calcium hydroxide, and magnesium hydroxide.
It is desirable that the alkali metal or alkaline earth metal is contained in the form of sulfate through the neutralization treatment, but a portion may also be present in the form of excess hydroxide or carbonate. Neutralization treatment is carried out by treating the raw graphite with an acid, and then mixing it with an aqueous solution of caustic soda, an aqueous calcium hydroxide solution, etc., and bringing it into contact with it after or during the water washing process. As for the degree of neutralization, the pn of the lm% aqueous dispersion of thermally expandable graphite after treatment is 4.5 to 9.
It is preferable that the degree of The pH is measured by adding 1 g of thermally expandable graphite to be measured into 99 g of deionized water, stirring for 10 minutes, and then using a pH electrode. Note that the deionized water used for this measurement has a pH of 5.5.
-7.0 is used.

Examples of film-forming resins that coat thermally expandable graphite include acrylonitriloptadiene copolymer, styrene-
butadiene copolymer, ethylene-vinyl acetate copolymer,
Examples include polyvinyl acetate resin, polyvinyl chloride resin, polyacrylate resin, and mixtures thereof. For modification, some of the monomers of these resins may be chemically modified, second and third components may be copolymerized, or additives such as plasticizers may be added. Among these, acrylonitrile looptadiene copolymer with an acrylonitrile content of 15 to 50% by weight, and a styrene content of 20 to 50% by weight.
A styrene-butadiene copolymer having a content of 30% by weight and an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20 to 80% by weight are preferred.

These polymeric substances are used as an aqueous emulsified dispersion emulsified with an anionic or nonionic surfactant, and those having a solid content concentration of 1 to 50% are suitable. Also,
This emulsified dispersion is neutral to alkaline, especially pH 7 to 11.
is suitable. These polymeric materials are commonly used as coatings for surface modification, as binders, and as adhesives in industrial products manufactured as latinx or emulsions; The product can also be adjusted to a desired concentration and pH before use.

Other examples of film-forming resins include synthetic water-soluble polymeric substances or natural water-soluble polymeric substances, such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid Na salt,
In addition to carboxymethyl cellulose Na salt, carboxymethyl starch Na salt, alginate Na salt, hydroxyethyl cellulose, hydroxybrobyl cellulose, methyl cellulose, ethyl cellulose, milk casein protein,
Examples include water-soluble derivatives of natural products such as glue, gelatin, mannan, gum arabic, guar gum, and chitin, which may be used alone or in mixtures. These water-soluble polymer substances are usually used as an aqueous solution of about 0.1 to 10% depending on the solubility, but neutral to alkaline, particularly pH 7 to 1 l is preferable. The coating amount of the film-forming resin is 1 to 25% by weight, preferably 4 to 20% by weight of the coated thermally expandable graphite. t
In order to prevent corrosion of C-type equipment, it is necessary that the surface of thermally expandable graphite is almost completely covered, and if the amount of film-forming resin is less than 1% by weight, the thermally expandable graphite A nearly complete coating may not be achieved or the coating may be destroyed during the foaming or shaping process. On the other hand, if the coating amount exceeds 25% by weight, prosocing of the coated graphite may occur, making it difficult to uniformly disperse the graphite into the foam.

The thermally expandable graphite can be coated by adding the above-mentioned film-forming resin as an emulsified dispersion or aqueous solution to the thermally expandable graphite by a method such as spraying, and then drying it, or by stirring both together with a blender or the like. One method is to mix and then dry. If the coating amount of the film-forming resin is small, the thermally expandable graphite is added to an emulsified dispersion or an aqueous solution of the film-forming resin, and then separated and recovered.
You can also dry it. When the film-forming resin is used as an emulsified dispersion, it is advantageous for handling to adjust the solid content concentration to about 5-25%, and when it is used as an aqueous solution, it is adjusted to about 0.1-2%.

When coating by spraying, the amount of film-forming resin coated may be adjusted by repeating addition and drying to form a multilayer coating of thermally expandable graphite. Drying is preferably carried out so that the loss on drying at 105° C. is approximately 0.5 to 2%. As drying progresses, the thermally expandable graphite is bound by the resin content, and the apparent particle size may increase, so in this case, it is ground to the desired particle size using a commonly used dry grinder. On the other hand, if the particle size of the thermally expandable graphite before coating is fine, this may be utilized to increase the apparent particle size.

The flame-retardant polystyrene resin foam of the present invention contains thermally expandable graphite coated with a film-forming resin as described above. It contains so that If it is less than 5% by weight, the flame retardance will be insufficient, and if it exceeds 50% by weight, the properties of the polystyrene resin foam will deteriorate, which is not preferable. To produce such a polystyrene resin foam, a foaming agent and thermally expandable graphite coated with the above-mentioned film-forming resin (hereinafter abbreviated as coated thermally expandable graphite) are added to the polystyrene resin. The materials are mixed and foamed, and methods for adding the foaming agent and thermally expandable graphite and for foaming the resin include the so-called bead foaming method or extrusion foaming method. According to the bead foaming method, for example, polystyrene resin beads are impregnated with a foaming agent in advance, and after the beads are pre-foamed to a desired size, a spreading liquid such as a polymer compound emulsion is sprayed onto the beads. The coated thermally expandable graphite is fixed and dried at a temperature of about 25 to 60°C, then filled into a mold for shaping, and heated and foamed with steam or the like at about 110 to 130°C to produce a foam. Alternatively, before impregnating the foaming agent, a spreading liquid may be applied to the polystyrene resin beads to fix the coated thermally expandable graphite, and then the beads may be impregnated with the foaming agent and foamed.

The spreading liquid is preferably used in such a proportion that the solid content in the liquid is 5 to 20% by weight of the thermally expandable graphite to be fixed.

Note that a polymer compound emulsion containing the same type of resin as the film-forming resin that coats the thermally expandable graphite can be used as the spreading liquid; however, in this case, the film-forming resin in the foam is It is preferable that the content is in the range of 0.2 to 25% by weight.

In the case of extrusion foaming, for example, a polystyrene resin, a blowing agent, and coated thermally expandable graphite are supplied to an extruder, and after kneading them at high temperature and high pressure, the resulting mixture is passed through an extruder at a relatively low temperature and under low pressure. The foam is manufactured by extrusion from the tip nozzle. Note that, depending on the case, the foaming agent may be impregnated into the resin in advance, or the foaming agent may be press-injected into the molten resin through an injection port provided at an appropriate location in the extruder. In addition to the coated thermally expandable graphite, in addition to conventionally known organic flame retardants such as tris(2-chloroethyl) phosphate and tris(2,3-dibromobrobyl) phosphate, metal oxides, An inorganic flame retardant such as antimony trioxide may also be added.

[Effects and operations of the invention]

The polystyrene resin foam of the present invention has high flame retardancy,
Even if ignited, it has self-extinguishing properties. In addition, it not only has the advantage that there is no dripping (hereinafter referred to as "drip") caused by melting of the resin when it comes into contact with flames, but also has the advantage of reducing the generation of "soot" that is seen when polystyrene resin is burned. be.

Although it has not yet been elucidated how these effects are produced, it is believed that when the added thermally expandable graphite comes into contact with flame, it expands thermally, resulting in bulky expanded graphite with a large specific surface area. It seems to be working effectively. Furthermore, the polystyrene resin foam of the present invention does not corrode the cutter blade during cutting. This is because the thermally expandable graphite is coated with a film-forming resin.
This is presumed to be because the release of corrosive adhering sulfuric acid or its salts is suppressed. The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In addition, in Examples and Comparative Examples, "parts" is "!Amount parts".
%” indicates “% by weight”. Examples 1 to 4, Comparative Examples 1 to 3 <Preparation of coated thermally expandable graphite> Natural flaky graphite produced in Canada (particle size: 36 mesh to 80 mesh) with fixed carbon content of 90% and ash content of 8% was treated with acid. Then, the free sulfuric acid content was neutralized with caustic soda, calcium hydroxide, or ammonia to obtain thermally expandable graphite (hereinafter abbreviated as EG) shown in Table 1. 50 parts of the above EC was placed in a household stainless steel bowl with a capacity of approximately 2 liters, and while stirring the contents thoroughly with a spatula, a predetermined amount of the treatment solution containing the film-forming strong resin shown in Table 2 was added as shown in Table 2. ．． After adding and mixing the processing liquid,
The contents were transferred to a stainless steel vat and dried for 2 to 4 hours in a dryer maintained at 105°C. During drying, the contents of the vat were stirred once every 20 minutes. After crushing the dried product for a few seconds with a household crusher, it is divided into 36 meshes and 80
The mixture was classified between mensch to obtain thermally expandable graphite (hereinafter abbreviated as CG) coated with a film-forming resin shown in Table 2.

Table 1: Approximately 13 parts of commercially available polystyrene expandable beads (Kanebuchi Chemical Industry Co., Ltd. special product "Kanepal GMJ, average particle size 1.2 an)" containing about 5% by weight of C, ~C, hydrocarbons as a blowing agent were added. , diameter 20 with 32 mesh wire mesh on the bottom
Place the beads in a cylindrical container with a height of 205cm and heat them with steam at about 100°C for 2 minutes to achieve a pre-expansion ratio of 25 times.Then, the pre-expanded beads are left at 25°C for one day and night to dry. I did. Next, 11 parts of the dried and aged pre-expanded beads were mixed with a commercially available latex (manufactured by Nippon Zeon, SBR Latex rNippol LX-11) as a spreading liquid.
0J) whose concentration and pH were adjusted to a solid content of 10% by weight and a pH of 9, the CG shown in Table 2 was fixed in the amount of M (parts) shown in Table 3. For fixation, the spreading solution was sprayed onto the pre-foamed beads using air spray, and while stirring, CG was added little by little with a spatula, uniformly added while stirring, and then left at 25°C for one day and night. Next, 11 parts of pre-foamed beads to which CG was fixed were mixed into 14 parts.
The mixture was filled into a 5s+sxg4 open x 40mm foaming mold, and the mold was placed in a pressure cooker and heated at about 120°C for 2 minutes to cause foaming. After heating, the pressure cooker was opened, the mold was cooled to about 50°C, the mold was taken out, the foam was removed from the mold, and the foam was cooled to room temperature. Note that Comparative Example 1 is an example in which CG was not added, and Comparative Examples 2 and 3 are examples in which EC was used. After the foam obtained as described above was left in a constant temperature room at 25°C for about 24 hours, the skin of the foam was cut off and then cut into test pieces, which were subjected to combustion tests and corrosion tests. I did. Combustion test> A sample piece in the shape of a 130 mm x 10 a+m x 5-garden was cut out, and the oxygen index was measured in accordance with JISK-7201. Also, separately 120s + sX30 open X30
A test piece in the shape of a gam was cut out, the corner part was brought into contact with a flame, and the presence or absence of resin dripping and the appearance of smoke were visually observed. The test results are summarized in Table 3. Corrosion test> The foam produced by the above method was tested using a commercially available cutter knife (
Using an NT cutter L500 model manufactured by Nippon Transfer Paper, perform cutting operations 15 times in the long side direction so that the total contact distance between the knife blade and the foam corresponds to 1950 mm, and then cut the knife blade into the foam. After removing it from the container, it was left as it was at room temperature for one day and night, and the surface condition was observed. On the other hand, the surface of commercially available soft iron L-sized nails was washed with methanol, dried, and then inserted into a part of the foam, 5 nails per foam, left at room temperature for 3 days, and then removed to remove the surface. I observed the condition. The results are summarized in Table 3. The evaluation criteria are as follows. Items whose metal surface is almost the same as before the test Items where there is slight change (corrosion, dirt) on the metal surface ± Items where corrosion or rust is observed on approximately 1/2 of the metal surface
10. Corrosion and rust observed on the entire metal surface ++Example 5 Mitsubishi Monsanto Kasei special polystyrene resin "Dialex HH-102-307RJ (softening point 101℃,
32 parts of MFR3g/10min) and 8 parts of CG were placed in the chamber of a Brabender plasticorder, kneaded for 2 minutes at a set temperature of 190°C, and after the kneaded mixture was taken out, it was hot pressed at 190°C for 10 minutes. 0 wam
It was made into a sheet with a thickness of . This sheet 1 2 0++v
After cutting to +X 60mmX 1a+m, 60
The sheet was brought into contact with 0 ml of n-hexane and heated at 68°C for 2 hours to impregnate the foaming agent, and then air-dried at 25°C to obtain a foaming agent-impregnated sheet. Cut this sheet to approximately 3cm
Expandable beads with a shape of mX2s+sX1sua were obtained.
Next, a polystyrene resin foam was obtained using a foaming mold in the same manner as in Example 1. After this foam was left in a constant temperature room at 25°C for about 24 hours, the skin of the foam was cut off and cut into test pieces, and a combustion test and a corrosion test were conducted in the same manner as in Example 1. Ta. The measurement results are summarized in Table 3. As shown in Table 3, the polystyrene resin foam produced by the method of the present invention is free from corrosion of the cutter blade when cutting the foam. Furthermore, based on the oxygen index value, it is clear that not only does it have excellent flame retardancy, but there is no dripping, and it also produces very little soot, which is generated when ordinary polystyrene resins are burned when exposed to flame. ．．

Claims (3)

[Claims] (1) Heat-expandable graphite coated with a film-forming resin is contained such that the graphite content is 5 to 50% by weight and the film-forming resin content is 0.2 to 25% by weight. Flame-retardant polystyrene resin foam. (2) Polystyrene resin is coated with a film-forming resin, and thermally expandable graphite with a coating amount of 1 to 25% by weight of the resin and a foaming agent are added to the polystyrene resin foam. A method for producing a flame-retardant polystyrene resin foam, which comprises adding, mixing and foaming so that the content is 50% by weight. (3) The film-forming resin is selected from the group consisting of acrylonitrile-butadiene copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl acetate resin, polyvinyl chloride resin, and polyacrylate resin. The flame-retardant polystyrene resin foam according to claim 1 or the flame-retardant polystyrene resin foam according to claim 2, characterized in that the flame-retardant polystyrene resin foam is at least one type of water-soluble polymer substance or a water-soluble polymer substance. How the body is manufactured.