JPH03167237A - Production of flame-retardant polystyrene resin foam - 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 binding a thermally expansible graphite with expansible PS resin beads pre-expanded under specified conditions with a film-forming resin and expanding the beads. CONSTITUTION:A thermally expansible graphite is bound with expansible PS resin (e.g. PS) beads pre-expanded to 5-95% of the maximum expansion ratio at the pre-expansion temperature with a film-forming resin (e.g. acrylonitrile/ butadiene copolymer) in an amount 0.05-1 time by weight as much as the graphite so that the graphite is contained in an amount of 7-50wt.% in the PS resin foam, and the beads are expanded.

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 processability.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 low-pressure zone at a relatively low temperature and foaming it, or when carrying out suspension polymerization of monomers. A known method is to obtain foamable resin particles by adding a volatile blowing agent at the initial stage of polymerization or when a certain degree of polymerization conversion has been reached, and then performing a foaming treatment to form a foam. However, various problems have been pointed out with foams manufactured in this way, especially from the perspective of preventing disasters caused by fires in recent years.
In particular, improvements have been requested in terms of resistance to combustion.
To solve this problem, we added inorganic flame retardants such as antimony dioxide, aluminum hydroxide, and borate to the foam.
It is also well known to add organic flame retardants such as halogen derivatives of aromatic hydrocarbon compounds or non-aromatic hydrocarbon compounds. Further, as another means for achieving this objective, US Pat. No. 3,574,644 proposes a method of increasing flame retardance by adding thermally expandable graphite. [Problem to be solved by the invention a) The conventional methods described above cannot be said to have a sufficient flame retardant effect on polystyrene resin foams, and it is necessary to use flame retardants to obtain the desired flame retardancy. The amount of additive added becomes extremely large, and as a result, the physical properties of the foam deteriorate, and there are some problems from an economic standpoint. In addition, inorganic flame retardants are incompatible with polymers, reducing foaming properties, complicating the manufacturing process to allow the flame retardant to break down evenly, or organic flame retardants being low-molecular compounds. If there is,
Manufacturing problems have also been pointed out, such as these particles scattering or breaking during foam molding, worsening the working environment. The present invention aims to provide a method for producing a polystyrene resin foam that is easy to implement and has better flame retardancy. [Means for Solving the Problems] The present inventors have conducted various studies on methods for manufacturing polystyrene resin foams with excellent flame retardancy. As a result, the present inventors have developed a method for producing polystyrene resin foams with excellent flame retardancy. The inventors have discovered that by blending these materials, it is possible to obtain a polystyrene-based resin foam that is free from the above-mentioned problems and has excellent flame retardancy, leading to the completion of the present invention. That is, the present invention has a maximum expansion ratio of 5 at the pre-foaming temperature.
Thermal expandable graphite is added to expandable polystyrene resin beads pre-foamed to ~95% so that the graphite is contained in the polystyrene resin foam at 0% to 0%. The gist of this invention is a method for producing a flame-retardant polystyrene resin foam, which is characterized by spreading the beads with .05 to 1 times the weight of a film-forming resin and foaming the beads. The present invention will be explained in detail below. The expandable polystyrene resin beads used in the present invention are made by impregnating a suspension polymer of polystyrene resin with a blowing agent such as propane, butane, or chlorofluorocarbon. It is used. In addition, polystyrene resins include polymers of monomers such as styrene, α-methylstyrene, dimethylstyrene, ethylstyrene, chlorostyrene, promostyrene, and vinyltoluene, and copolymers of these monomers or copolymers of these monomers. Further examples include copolymers with vinyl monomers such as putadiene, acrylonitrile, methyl methacrylate, isobrene, vinyl chloride, and isobutylene. 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. It is customary to impregnate 100 parts by weight of the polystyrene resin in an amount of 1 to 30 parts by weight, more preferably 3 to 8 parts by weight.

Preliminary foaming of the expandable polystyrene resin beads in the present invention is carried out by heating with steam or the like according to a conventional method. The expansion ratio of expandable polystyrene resin beads increases with the passage of heating time, reaches a maximum value, and then gradually decreases. The maximum expansion ratio in the present invention refers to this maximum value, and is determined by measuring the expansion ratio that changes depending on the heating time at the temperature at which preliminary foaming is performed.

To measure the maximum expansion ratio, for example, heat at 100°C for a
It can be determined by measuring the filling volume of beads at 2 minutes, 4 minutes, 6 minutes, 8 minutes, 10 minutes, and 12 minutes, and dividing by the filling volume of beads before heating.

In addition, the filling volume is usually 60 mm or less since the expandable polystyrene resin beads have a diameter of about 2 mm or less.
It can be easily measured by filling a cylinder with a diameter of about mm or more and reading the filling height.

In the present invention, it is necessary to pre-foam the expandable polystyrene resin beads to 5 to 95% of the maximum expansion ratio at a desired pre-foaming temperature. Pre-foaming ratio is
If the maximum expansion ratio at the pre-foaming temperature is less than 5%, thermally expandable graphite cannot be spread enough to provide sufficient flame retardancy, and uniform dispersion is difficult. If it exceeds %, the beads will not be sufficiently fused together during the main foaming process, resulting in a decrease in the strength of the final product, which is not preferable.

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 Quiche graphite, can be used. The thermally expandable graphite used in the present invention is produced by contacting raw graphite with a mixture of 98% concentrated sulfuric acid and 60% hydrogen peroxide for 10 to 30 minutes at 45°C or lower, and then washing the acid-treated graphite with water. It is produced by filtering, separating and drying. The thermally expandable graphite used in the present invention desirably has a degree of expansion of 50 to 250 ml/g when rapidly heated at 1000 t for 10 seconds from the viewpoint of exhibiting a flame retardant effect.

The "degree of expansion" in the present invention refers to 150 m
i! Take out the quartz beaker from the furnace and immediately add thermally expandable graphite. 5 g, quickly put it into the same furnace maintained at <1000℃, kept it that way for 10 seconds, took it out of the furnace, and after cooling naturally, the volume/weight ratio of expanded graphite (unit: m1/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 approximately 8o 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, when the particle size is about 20 to 30 mesh, miscibility with the expandable polystyrene resin beads becomes insufficient, making it difficult to uniformly disperse the thermally expandable graphite in the foam. Therefore, the particle size of the thermally expandable graphite used in the present invention is 3.
0 to 120 mesh is preferable, and 40 to 10 mesh is preferable.
The most preferred is one classified to about 0 mesh.

The thermally expandable graphite used in the present invention is produced by treating raw 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 alkaline earth metal compounds. It is preferable that the Preferred neutralizing agents include caustic soda, caustic potash, calcium hydroxide, and magnesium hydroxide. Although it is desirable that the alkali metal or alkaline earth metal is contained in the form of sulfate through the neutralization treatment, 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, it is preferable that 98 of a 1% by weight aqueous dispersion of thermally expandable graphite is about 4.5 to 9. pH is 99 for 1g of thermally expandable graphite
g of deionized water and stirred for 10 min, then measured by a pH electrode. Note that the deionized water used in this measurement has a pH within the range of 5.5 to 7.0.

In the present invention, it is necessary that thermally expandable graphite be contained in the polystyrene resin foam, which is the target product, in a range of 7 to 50% by weight. Thermal expandable graphite content is 7
If it is less than 50% by weight, flame retardation is insufficient, and if it is less than 50% by weight.
If the amount exceeds 100%, the flame retardant effect corresponding to the amount added cannot be expected, and the properties of the polystyrene resin foam will deteriorate, which is not preferable. A particularly preferable range is 15 to 40% heavy crab.
It is. Polystyrene resin beads pre-foamed with thermally expandable graphite (hereinafter abbreviated as pre-foamed beads). ) Film-forming resins used as spreading agents include polymeric substances such as acrylonitrile-butadiene copolymers, styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, polyvinyl acetate resins, etc. , polyvinyl chloride resins, polyacrylate resins and mixtures thereof. For modification, some of the monomers of these resins may be chemically modified, some of the second and third monomers may be copolymerized, or additives such as plasticizers may be added. Among these, the acrylonitrile content is 15~
50m! Preferred examples include an acrylonitrile-butadiene copolymer containing 1% of styrene, a styrene-butadiene copolymer containing 20 to 30% by weight of styrene, and an ethylene-vinyl acetate copolymer having a vinyl acetate content of from 20 to 80% by weight. These polymeric substances are used as emulsifying dispersions that are emulsified with anionic or nonionic surfactants, and the solid content concentration is 1 to 5.
0% is preferred. It is also possible to use industrial products produced as latexes or emulsions used as coating agents for surface modification, binders, and adhesives.

Further examples of the film-forming resin 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, carpoxymethyl starch Na salt, algin fiNaF, hydroxyethyl cellulose, hydroxypubiru cellulose, medyl cellulose, and ethyl cellulose, milk casein protein, glue, gelatin, mannan, gum arabic, guar gum, chitin, etc. Examples include water-soluble mF forms of natural products,
These may be used alone or in mixtures. These water-soluble polymeric substances usually have a 0.0-. 1-1
Although it is used as an approximately 0% aqueous solution, it may be alkaline or acidic for the purpose of improving solubility.

In the present invention, the amount of film-forming resin used as a spreading agent needs to be 0.05 to 1 times the weight of thermally expandable graphite. If the amount of the spreading agent is less than 0.05 times by weight, the spreading of thermally expandable graphite may be insufficient, while if it exceeds 1 times by weight, the fluidity of the pre-foamed beads may be impaired or the main foaming During this process, the pre-foamed beads may not be sufficiently fused together, resulting in a decrease in the strength of the final molded product.

Furthermore, what is the total amount of thermally expandable graphite and film-forming resin?
! In flammable polystyrene resin foam, 85% or less,
The content is preferably 75% by weight or less. If the content exceeds 85% by weight, when foaming and molding pre-expanded beads spread with thermally expandable graphite, the beads may become insufficiently fused together.

The following methods can be used to spread thermally expandable graphite onto pre-expanded beads.

(a) While stirring the pre-foamed beads, add a spreading agent to the pre-foamed beads, for example, at a solid content of 0. Adding an aqueous dispersion of a resin composition such as Latesox prepared to 1 to 50% by weight, preferably 0.5 to 10% by weight, by a method such as spraying, and further adding a predetermined amount of thermally expandable graphite. Mix, 25~
A method of drying at a temperature of about 60°C.

Mt.) Mix a predetermined amount of pre-expanded beads and thermally expandable graphite,
A method in which the spreading agent prepared as described above is sprayed onto the mixture while stirring, and then dried.

(C) A method of mixing the spreading agent prepared as described above and a predetermined amount of thermally expandable graphite, adding this mixture to pre-foamed beads while stirring the beads, and then drying.

In addition, in the above method (al), a spreading agent is added to the pre-foamed beads by spraying or the like, and after drying to some extent to form a film of the spreading agent on the surface of the pre-foamed beads, thermally expandable graphite is added. By repeating this operation,
It is possible to increase the star with the addition of thermally expanded graphite.

The method for producing polystyrene resin foam by molding pre-expanded beads spread with thermally expandable graphite is to fill a pre-expanded mold with the pre-expanded beads in a predetermined amount in a mold according to a conventional method, and heat the beads at a temperature of about 110 to 130°C. This is done by heating with steam or the like. At this time, separately pre-foamed beads may be additionally mixed.

In addition to thermally expandable graphite, in addition to conventionally known organic flame retardants such as tris(2-chloroethyl) phosphate and tris(2,3-dibromoprobyl) phosphate, metal oxides, An inorganic flame retardant such as antimony oxide may also be added.

[Effects and operations of the invention] The polystyrene resin foam obtained by the method of the invention has the following properties:
It is highly flame retardant and has self-extinguishing properties even if it ignites. In addition, it not only has the advantage that there is no dripping (hereinafter referred to as "drip") caused by the melting of the resin when it comes into contact with flame, but also the "drip" that occurs when polystyrene resin is burned.
This has the advantage of reducing the generation of soot.

Although it is not yet clear how these effects are produced, it is believed that the bulky expanded graphite with a large specific surface area, which is generated by thermal expansion of added thermally expandable graphite when it comes into contact with flame, is effective. It is thought that this is working. Hereinafter, the present invention will be explained in more detail with reference to 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, "part" means "part by weight" and "%" means "% by weight".
” is shown.

Examples 1 to 8, Comparative Examples 1 to 5 <Thermally expandable graphite> Natural flaky graphite produced in Canada (particle size: 36 mesh to 80 mesh) with a fixed carbon content of 90% and an ash content of 8% was acid-treated. , J thermally expandable graphites A and B shown in Table 1 whose sulfuric acid content was neutralized with caustic soda or calcium hydroxide were used.

Table 1 Spreading agents> Spreading agents (A), (C), (C), and (II) shown in Table 2 after adjusting the solid content concentration and pH of the commercially available emulsions and water-soluble resin aqueous solutions shown below. )It was used.

SBR: Nippon Zeon SBR latex, rNi
ppol LX-110J EVA: Manufactured by Hoechst Gokai■ EVA emulsion "Movinyl 181EJ PVA: Manufactured by Nippon Synthetic Chemical Industry ■" Gohsenol NH-
1 8 SJ CMC-Na: “Celogen 3HJ” manufactured by Daiichi Kogyo Seiyaku ■
Production of foam from an aqueous solution> Commercially available expandable polystyrene beads containing about 5% by weight of C3 to C6 hydrocarbons as a blowing agent [Kanebuchi Chemical Industry Co., Ltd.]
manufactured by Kanepal GMJ, average particle size 1.2mm (
(hereinafter abbreviated as GM) and product name "Kanepal GT", average particle size 0.9 mm (hereinafter abbreviated as GT)] on the bottom.
The mixture was placed in a cylindrical container with a diameter of 20 aa and a height of 20 cm and has a 2-mesh wire mesh, and heated with steam at about 100° C. The expansion ratio was measured every 2 minutes after the start of heating to determine the maximum expansion ratio. In the measurement, the expansion ratio was measured after pre-foamed beads were heated for a predetermined period of time and left overnight at 25° C. to dry and mature. GM's maximum foaming ratio is 45 times, GT
The maximum expansion ratio was 40 times.

Pre-foamed beads in which 13 parts of GM or GT were heated in the same manner as above for the time shown in Table 3 were dried and aged in the same manner as above, and the amounts shown in Table 3 were weighed. The thermally expandable graphite shown in Table 3 was spread using the spreading agent shown in Table 3. The spreading operation involves spraying a spreading agent onto the pre-foamed beads.
While stirring, thermally expandable graphite was added little by little to the mixture, and the mixture was stirred in a oven so that the thermally expandable graphite was evenly spread on the pre-foamed beads.The mixture was then spread in a stainless steel container and heated at 30°C. I left it for 6 hours under ventilation, stirring occasionally with a spatula. In addition, in examples other than Examples 1 and 3, the amount of thermally expandable graphite and spreading agent used was divided into n (n is an integer),
The spraying of the spreading agent and the addition of thermally expandable graphite were carried out in n steps, and at that time, after the addition of thermally expandable graphite, the mixture was heated at 30°C under blowing air.
The operation of leaving it for 6 hours was repeated.

Next, 14 pre-expanded beads spread with thermally expandable graphite were added.
A foaming mold of 5 questions x 84 questions x 400111+ was filled with the amount shown in Table 3, and the mold was placed in a pressure cooker at approximately 120°C.
It was heated for 2 minutes to obtain a polystyrene resin foam. After heating, the pressure cooker was opened, the mold was cooled to approximately 50°C, the mold was taken out, the foam was removed from the mold, and the foam was cooled to room temperature. In addition, Comparative Example 1 is an example in which thermally expandable graphite was not added, Comparative Examples 2 and 3 are examples in which the pre-expansion ratio of the expandable polystyrene resin beads is outside the range of the pre-expansion ratio of the present invention, and Comparative Example 4 is an example in which the pre-expansion ratio of the expandable polystyrene resin beads is outside the range of the pre-expansion ratio of the present invention. This is an example in which the proportion of the spreading agent used is outside the range specified by the present invention. Approximately 24 kg of the polystyrene foam obtained as described above
After being left in a constant temperature room at 25°C for an hour, the skin of the foam was cut off and then cut into test pieces, which were subjected to a combustion test, measured for tensile strength, and measured the content of thermally expandable graphite in the foam. Measurements were made. In addition, the state of fusion of the pre-foamed beads in the foam was confirmed.

<Combustion test> A test piece in the shape of 130 mm x 10 mta x 5 strokes was cut out, and the oxygen index was measured in accordance with JISK-7201. Also, separately 120m+++X30
A test piece having a shape of +smx 30 mm was cut out and the corner portion 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.

Measurement of tensile strength> A test piece in the shape of 120III+×10III1×51III was cut out, and the tensile strength was measured in accordance with JISK-6767. The measurement results are summarized in Table 3.

Measurement of thermally expandable graphite content> Approximately 2 (lue
Cut out a test piece of X30s+sX30+m,
The content of thermally expandable graphite was measured by treating it with concentrated sulfuric acid and hydrogen peroxide according to the [sample pretreatment] method described in Section 4 of JISK-0101.The measurement results are shown in Table 3. I will show you a summary. Checking the fusion state> Cut the foam with a sharp cutter, visually observe the cut surface of the foam, and if the cut surface is the same as that of Comparative Example 1, it is considered that the fusion is good, and there are no voids on the cut surface. If this was observed, it was determined that the adhesion was poor.

In addition, a test piece with a shape of 20 questions x 30 a + m x 60 questions was cut out, and the test piece was held at both ends and gradually bent to break, and the state of break was compared with that of Comparative Example 1. A case similar to that of Comparative Example 1 is considered to be good fusion, and a case where it is clearly recognized that beads are not sufficiently fused together on the fractured surface, or a case where fractures occur from several places is considered poor fusion. did. The observation results are shown in Table 3.

As shown in Table 3, the polystyrene resin foam produced by the method of the present invention not only has excellent flame retardancy based on the oxygen index value, but also has no dripping and is resistant to flame contact. It can be seen that there is very little soot, which is generated when ordinary polystyrene resin is burned. In addition, although the tensile strength of the foam molded product is affected by the density of the foamed molded product, a value close to that of the blank (Comparative Example 1) was obtained, indicating that it is within a sufficient range for practical use. ．． Furthermore, in the foaming process of thermally expandable graphite spread beads,
Thermally expandable graphite may peel off due to elution of the spreading agent, dissipation of the blowing agent, and changes in the foamed shape of the pre-foamed beads due to steam heating, but according to the present invention, the foam of the thermally expandable graphite It is possible to maintain a high yield rate. For example, in Comparative Example 2, the pre-expanding ratio of the foamed resin beads was so small that during the main foaming, the shape of the pre-expanded beads changed significantly, and it is thought that the thermally expandable graphite peeled off due to this shape change. It will be done.

In addition, when the preliminary expansion ratio of the expandable resin beads is larger than the range specified in the present invention (Comparative Example 3), the resulting foam has poor fusion properties and similar strength, and if a large amount of spreading agent is used ( In Comparative Example 4), the fluidity of the pre-foamed beads is poor and the resulting foam has poor fusion properties.

Claims (2)

[Claims] (1) 5 to 95% of the maximum expansion ratio at the pre-foaming temperature
Heat-expandable graphite is added to expandable polystyrene resin beads that have been pre-foamed into polystyrene resin foam.
A flame-retardant polystyrene resin characterized by being spread with a film-forming resin in an amount of 0.05 to 1 times the weight of the thermally expandable graphite so that the bead is foamed so as to contain up to 50% by weight. Method of manufacturing foam. (2) In the method according to claim 1, the film-forming resin is an acrylonitrile-butadiene copolymer,
Styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl acetate resin, polyvinyl chloride resin,
and at least one selected from the group consisting of polyacrylate resin or a water-soluble polymer substance.