JPH0548776B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a flame-retardant crosslinked polyolefin open cell foam. [Prior art] Cross-linked polyolefin open cell foams developed in recent years are inexpensive and have excellent physical properties such as cushioning properties and sound absorption properties, so they can be used in various applications such as cushioning materials, packing material filters, coating materials, and sound absorption materials. Used for a wide range of purposes. Conventionally, the method for producing open-cell crosslinked polyolefin foams involves partially decomposing the foaming agent and crosslinking agent in the foamable crosslinked polyolefin composition under pressure in a closed mold, and decomposing the remaining foaming agent and crosslinking agent under normal pressure. A method has been proposed in which a closed cell is obtained by decomposing the closed cell, and then the closed cell is destroyed by compressing the obtained closed cell (see: Japanese Patent Publication No. 59-23545 and Japanese Patent Application Laid-open No. 56-146732) Public bulletin). The present applicant also heat-molded a foamable crosslinkable polyolefin composition into a desired shape, heated it under normal pressure to simultaneously decompose the crosslinking agent and the blowing agent, and then generated a foam. Developed a method to make air bubbles open by applying mechanical deformation (Reference: Special Publication 1986-19294)
(Japanese Patent Publication No. 121739/1983). However, polyolefin resins such as polyethylene and polypropylene are extremely flammable and have a high heat of combustion, so polyolefin open cell foams cannot be used for flooring materials, wall materials, materials in aircraft interiors, and the like. On the other hand, a conventional method for producing flame-retardant foam is a method of heating and foaming polyolefin resin with an inorganic filler added (see:
(Japanese Patent Publication No. 60-26500) or a method of heating and foaming a material to which a phosphorus-based or halogen-based flame retardant is added (Reference: Japanese Patent Publication No. 48-9587, Japanese Patent Publication No. 48-9587,
48-29857 and Special Publication No. 58-5930). [Problems to be Solved by the Invention] However, the method of heating and foaming a material to which an inorganic filler or a phosphorus-based, halogen-based, etc. It is difficult to apply. This is because open cells have a larger supply of air that promotes combustion than closed cells, so even if an inorganic filler or flame retardant is added to an open cell at the same rate as the amount added to a closed cell, it will not be enough. It is not possible to provide flame retardant properties and it is not possible to obtain flame retardant open cell bodies. On the other hand, if a large amount of inorganic filler or flame retardant is added, the foaming conditions for an open cell are severe, making it impossible to obtain a satisfactory cell. The present applicant previously impregnated an open-cell polyolefin with a vinyl phosphonate compound in order to overcome the drawbacks of the conventional method and provide a permanently flame-retardant cross-linked open-cell polyolefin. , has developed a method for improving polyolefin open cell foam, which is characterized by irradiating it with an electron beam to produce an insoluble polymer inside and on the surface of the cell, and has already filed a patent application (see: patent application). Showa 63
−172496). However, although it is possible to obtain flame-retardant open-cell polyolefin cells using this method, the problem is that it is uneconomical because it requires the use of large amounts of extremely expensive vinyl phosphonate compounds. Ta. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method for inexpensively producing a permanently flame-retardant crosslinked polyolefin open-cell foam. [Means for Solving the Problems] The method for producing a flame-retardant crosslinked polyolefin open-celled foam of the present invention includes foaming a foamable crosslinkable composition in which a halogenated flame retardant is blended with polyolefin to generate a foam; Next, a step of applying mechanical deformation to connect the cells to obtain a crosslinked polyolefin open cell, impregnating the obtained crosslinked polyolefin open cell with a phosphorus flame retardant, and then irradiating the open cell with an electron beam to It is characterized by a step of producing an insoluble polymer inside and on the surface of the body. [Operation and mode of the invention] That is, the method of the present invention reduces the amount of expensive phosphorus flame retardant used by using a halogen flame retardant and a phosphorus flame retardant together, reduces manufacturing costs, and Excellent flame retardancy can be imparted through the synergistic effect of two types of flame retardants: the halogen-based flame retardant present in the cell membrane and the phosphorus-based flame retardant bonded and attached to the cell surface and the cell surface. It is something. In other words, the ignition combustion prevention and self-extinguishing properties of polyolefin due to the phosphorus flame retardant present on the surface of the cell membrane and the foam surface and the combustion prevention and self-extinguishing properties due to the halogenated flame retardant present in the cell membrane are synergistic. It has excellent flame retardancy. In the present invention, examples of the polyolefin include polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polytetrafluoroethylene, ethylene-propylene copolymer, poly-4-
Methyl-1-pentene, polyvinyl chloride,
Examples include polyvinylidene chloride, polyvinylidene fluoride, and tetrafluoroethylene/ethylene copolymer, and ethylene-vinyl acetate copolymer is particularly preferred in terms of physical properties such as foam recovery and cushioning properties. In the present invention, halogen-based flame retardants include bromine-based and chlorine-based flame retardants, but bromine-based flame retardants are preferred because they have high flame retardancy and do not generate harmful gases. Brominated flame retardants include inorganic flame retardants,
Alternatively, chain hydrocarbon-based, cyclic hydrocarbon-based, or phosphorus-based organic flame retardants can be used, such as ammonium bromide, chlorotetrabromobutane, vinyl bromide, tetrabromo bisphenol A, tetrabromo phthalic anhydride, hexa Examples include bromobenzene, hexabromocyclododecane, bis(bromoethyl ether)tetrabromobisphenol A, and tris(dibromopropyl)phosphate. The amount of the halogen flame retardant added is 10 to 30 parts by weight, preferably 14 to 25 parts by weight, per 100 parts by weight of the resin.
Parts by weight. If the amount added is too small, sufficient flame retardancy cannot be imparted, and the amount of phosphorus flame retardant used cannot be reduced. On the other hand, if it is too large, it will have a negative effect on foaming, so it is not preferable. A method for obtaining a crosslinked polyolefin open cell using the polyolefin and a halogen flame retardant is to foam a foamable crosslinkable composition containing a polyolefin and a halogen flame retardant to form a foam, and then mechanically deform the foam. Any method known in the art can be applied as long as it is a method for obtaining a cross-linked polyolefin open-celled cell by adding . Among these methods, as described in Japanese Patent Publication No. 62-19294 and Japanese Patent Application Laid-open No. 56-121739, a foamable crosslinkable composition is heated and shaped into a desired shape, and then heated and shaped under normal pressure. The effects of the present invention are particularly remarkable in a method in which the crosslinking agent and the blowing agent are simultaneously decomposed by heating to generate foam, and then mechanical deformation is applied to make the foam open. Hereinafter, the method for manufacturing an open cell body according to the present invention will be specifically explained. First, a foaming agent, a crosslinking agent, and if necessary a foaming aid, a filler, and a pigment are added to polyolefin, and the mixture is kneaded using a heated mixing roll or the like. Next, the obtained composition is put into a mold and pressed under pressure according to the type of resin and crosslinking agent.
Heat shaping is carried out at 115-155°C, preferably 120-140°C. In this heat shaping step, maintaining the foamable crosslinkable composition in a gel fraction state of zero is a condition for obtaining an open cell body with an open cell rate of 100% or close to 100%. In addition, in this heat shaping process, a very small amount of foaming agent may initially decompose, and when the shaped product is taken out of the mold, it may expand to about twice its size, but this is far from the concept of foaming. There is no problem with the present invention. The foamable crosslinkable composition shaped as described above is then heated under normal pressure to
The crosslinking agent and the blowing agent are simultaneously decomposed. This foaming/crosslinking process involves, for example, placing the shaped polyolefin composition in a non-airtight, that is, non-sealed mold having a desired cross-sectional shape and dimensions, and heating the metal plate of the mold from the outside. Thus, the composition is indirectly heated. Indirect heating methods include, for example, heating the metal plate by placing a heater in close contact with the outer surface of the metal plate, or providing a heat medium flow path in the metal plate and heating the metal plate using steam, heating oil, etc. using a jacket method. There is. Alternatively, the shaped polyolefin composition is placed in an open/close type mold that is not airtight, and placed in a metal bath or oil bath using Rose alloy, Utsudo alloy, etc.
Direct heating in a salt bath using one or more molten salts such as sodium nitrate, potassium nitrate, potassium nitrite, etc., in a nitrogen stream, or covered with an extensible (or expandable) iron plate, etc. urge After heating for a predetermined time, it is cooled to obtain a foam. The heating temperature is set in the range of 140 to 210°C, preferably 160 to 190°C, depending on the type of polyolefin used. Heating time is preferably 10 to 90 minutes,
More preferably, the time is 20 to 70 minutes. In this way, a cell membrane with a cell membrane that can be easily destroyed by mechanical deformation and a degree of crosslinking (up to about 95% gel fraction) comparable to that of conventional cell foams has been created. can get. Furthermore, in the present invention, the heating in the foaming/crosslinking step can be carried out in two stages, which slows down the foaming and crosslinking conditions and allows the decomposition of the crosslinking agent and the blowing agent to occur more simultaneously in the two stages. be able to. That is, homogeneous heating of the foamable crosslinkable composition is performed, and non-uniformity in heating in the thickness direction of the composition is eliminated, thereby effectively preventing the appearance of local uneven foaming and outgassing phenomena. can be prevented. When heating in the foaming/crosslinking process is performed in two stages as described above, it is effective to set the heating temperature in the second stage to be higher than the heating temperature in the first stage. Heating is performed at 145-180°C, and second-stage heating is performed at 170-210°C. The cell membrane obtained in the above manner (so-called closed cell cell) is then compressed and deformed using, for example, two constant-velocity rolls, so that the cell membrane is destroyed and the cells are communicated to form an open cell cell. is obtained. Countless small needles are provided on the surface of the two constant velocity rolls, or rolls provided with countless small needles are placed before and/or after the two constant velocity rolls, and countless small needles are provided on the surface of the foam. By making a hole,
Communication between air bubbles can be promoted. By this method, open cells of 100% or close to 100% are obtained as measured by the Remington Pariser method (ASTM D1940-62T). The crosslinking agent suitably used in the above-mentioned method for producing open-celled cells is one that has a decomposition temperature higher than the flow initiation temperature of the polyolefin resin, and is decomposed by heating to generate free radicals. Organic peroxides that are radical generators that create crosslinks between or within molecules, such as dicumyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-
Di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butylperoxyhexine, α,α'-bis(t-butylperoxy)diisopropylbenzene, t-butylperoxy There are ketones, t-butyl peroxybenzoate, etc., and blowing agents are chemical blowing agents having a decomposition temperature higher than the melting temperature of polyolefin resins, such as azo compounds such as azodicarbonamide, barium azodicarboxylate, etc. ; Nitroso compounds such as dinitrosopentamethylenetetramine and trinitrosotrimethyltriamine; Hydrazide compounds such as p, p'-oxybisbenzenesulfonyl hydrazide; Sulfonyl semicarbasite compounds p, p'-oxybisbenzene Sulfonyl semicarbazide, toluenesulfonyl semicarbazide, and the like can be suitably used, but the present invention is not limited thereto. Further, a foaming aid can be added depending on the type of foaming agent. Foaming aids include compounds whose main component is urea, metal oxides such as basic zinc carbonate, zinc oxide, and lead oxide, compounds whose main components are salicylic acid, stearic acid, etc., i.e., higher fatty acids or metals of higher fatty acids. There are compounds, etc. Furthermore, for the purpose of improving the physical properties of the compositions used or lowering the cost, we have added compounding agents (fillers) that do not have a significant adverse effect on crosslinking, such as carbon black, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, and Metal oxides such as silicon, carbonates such as magnesium carbonate and calcium carbonate, fiber materials such as pulp, various dyes, pigments, fluorescent substances, and other commonly used rubber compounding agents can be added as necessary. . In the present invention, the open cell ratio of the open cell impregnated with the phosphorus flame retardant is preferably 80% or more,
Particularly preferably 90% or more. An open cell ratio of 80% or less is not preferable because it becomes difficult to impregnate a phosphorus-based flame retardant, such as a vinyl phosphonate compound. In the next step of the present invention, non-halogen phosphoric esters, halogen-containing phosphoric esters, special phosphoric esters, phosphorus-containing polyols, etc. can be used as the phosphorus flame retardant to be impregnated into the open cell. Phonate compounds are particularly preferred because they have excellent flame retardant effects. The vinyl phosphonate compound has the following general formula: (However, a compound represented by x and y≧1) is preferred. In the compound of the above formula, phosphorus P is a flame retardant element and is contained in an amount of about 22.5% by weight. In the present invention, the method for impregnating a polyolefin open cell with a vinyl phosphonate compound first involves adding a vinyl phosphonate compound at a concentration.
It is dissolved in the below-mentioned solvent to a concentration of 10 to 100% by weight, preferably 15 to 75% by weight. In this case, 15
If it is less than 75%, a self-extinguishing foam cannot be obtained, whereas if it exceeds 75%, the viscosity of the solution is high and impregnation efficiency is poor, which is not preferable. Next, the crosslinked polyolefin open cell is impregnated with the solution by immersing the open cell in the solution, or by spraying the open cell with the solution using a sprayer. Next, the open-celled foam impregnated with the above solution is taken out, excess solution is squeezed out, and the foam is sufficiently air-dried or dried under reduced pressure to evaporate the solvent. The impregnation rate is
It can be adjusted by the concentration of the solution and the method of squeezing after impregnation. Examples of the solvent used here include water, acetone, ethanol, methyl ethyl ketone, ethyl acetate, benzene, and tetrahydrofuran. After drying, the foam is irradiated with ionizing radiation under an inert gas atmosphere or under vacuum. As ionizing radiation, gamma rays from Co60 and electron beams from accelerators are conveniently used. For example, by irradiating the foam with a dose of 1 to 20 Mrad at a dose rate of 1.0 to 1.0×10 ⁷ rad/sec at a temperature of preferably 10 to 50°C, an insoluble polymer can be formed inside and on the surface of the foam. give rise to As a result, durable flame retardance can be achieved. The weight increase rate of the foam thus obtained is preferably 5% or more, particularly preferably 10% or more based on the weight of the foam before being impregnated with the phosphorus-based flame retardant, for the effects of the present invention to be significant. It is. The upper limit of the weight increase rate is not particularly limited from an operational point of view, but is preferably 60% or less from an economical point of view. The open cell body obtained by the method of the present invention is
It has excellent flame retardancy and is certified by CFR (Code
It passes the combustibility test applicable to flooring materials, seat cushion materials, etc. as specified in Part 25.853(b) of Title No. 14 (Aeronautics and Space) of the Federal Regulations. The flame-retardant foams obtained can therefore be applied not only in the traditional construction field, but also in the aeronautical and space industries. [Examples] The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to the Examples below. Example 1 100 parts by weight of ethylene-vinyl acetate copolymer (trade name Yucalon EVA-41H, vinyl acetate content 16% by weight, manufactured by Mitsubishi Yuka Corporation), 18 parts by weight of azodicarbonamide, 0.05 parts by weight of activated zinc white. , 0.8 parts by weight of dicumyl peroxide, and 16 parts by weight of a brominated aromatic compound (trade name: Pyrogard SR-600A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was kneaded with a mixing roll at 85°C, The kneaded product was filled into a mold (195 x 380 x 28 mm) in a press heated to 0.degree. C., and heated under pressure for 40 minutes to form a foamable crosslinkable sheet. The gel fraction of the foamable crosslinkable sheet was 0. Next, the obtained foamable crosslinkable sheet was placed in a non-airtight retractable mold (1000 x 500 x 100 mm) that had already been heated to 170°C.
It was heated with steam at 170°C for 60 minutes using a jacket method, and after cooling, it was taken out to obtain a foam. The obtained foam was passed five times between two rolls at a constant velocity set at a roll interval of 20 mm to destroy the cell membrane and to make the cells open. The obtained open cell body had an apparent density of 0.03 g/cm ³ and an open cell ratio of 100.
%, and the bubble diameter was approximately 2 mm. The obtained open-celled foam was cut into six-sided foam sheets of 380 x 80 x 10 mm, and the cut sheets were mixed with a vinyl phosphorus phosphonate compound [Fyrol 76 manufactured by AKZO Chemicals, Inc., USA]. After being impregnated with the solution, the foam was taken out and the methanol was removed by air drying. The thoroughly dried foam was placed in a polyethylene bag, nitrogen was passed through it for 10 minutes, and the bag was sealed. This is placed on a conveyor, and a transformer-rectified electron beam accelerator is used at room temperature.
800Kev, 6mA, 2.1×10 ⁶ rad/sec electron beam
It was irradiated with 10 Mrad. After irradiation, the weight increase rate of the foam was 40.0% based on the weight of the original foam. As a result of conducting the CFR combustion test on the treated foam, it met all requirements and passed. Example 2 A foam was molded in exactly the same manner as in Example 1, except that the concentration of the methanol solution of the vinyl phosphonate compound in Example 1 was changed to 33% by weight, and the vinyl phosphonate compound was molded in the same manner as in Example 1. was impregnated. The weight increase rate of the foam after treatment is
It was 56.5% and passed the CFR combustion test. Comparative Example 1 An open cell was molded under the same conditions as in Example 1, and the CFR combustion test was conducted without impregnating it with a vinyl phosphonate compound, but it failed. Example 3 The number of parts of the brominated aromatic compound (trade name Pyroguard SR600-A) in Example 1 was changed to 20 parts by weight,
Further, the treatment was carried out in exactly the same manner as in Example 1, except that the concentration of the methanol solution of the vinyl phosphonate compound was changed to 15% by weight. The weight increase rate of the foam after treatment was 20.8%, and the
Passed CFR combustion test. Example 4 The treatment was carried out under the same conditions as in Example 1, except that the number of brominated aromatic compounds in Example 1 was changed to 20 parts by weight. The weight increase rate of the foam after treatment was 45.2% and passed the CFR combustion test. Example 5 All conditions were the same as in Example 1 except that the number of blended parts of the brominated aromatic compound in Example 1 was changed to 20 parts by weight, and the concentration of the methanol solution of the vinyl phosphonate compound was changed to 33% by weight. It was treated in exactly the same way. The weight increase rate of the foam after treatment is 59.3
%, and passed the CFR combustion test. Comparative Example 2 An open cell body was molded in exactly the same manner as in Example 1, except that the number of blended parts of the brominated aromatic compound in Example 1 was changed to 20 parts by weight, and the vinyl phosphonate compound was molded. When the CFR was subjected to a combustion test without impregnation, it failed. Comparative Example 3 All treatments were performed under the same conditions as in Example 1, except that the brominated aromatic compound in Example 1 was not added and the concentration of the methanol solution of the vinyl phosphonate compound was changed to 33% by weight. . The weight increase rate of the foam after treatment was 53.3%, and when the CFR combustion test was conducted, it failed. Comparative Example 4 All treatments were performed under the same conditions as in Example 1, except that the brominated aromatic compound in Example 1 was not added and the concentration of the methanol solution of the vinyl phosphonate compound was changed to 75% by weight. . The weight increase rate of the foam after treatment was 80.9%, and it passed the CFR combustion test. Although the treated foam has excellent flame retardancy, it consumes a large amount of vinyl phosphonate compound, which poses an economic problem. Comparative Example 5 Except that 16 parts by weight of the brominated aromatic compound in Example 1 was replaced with 16 parts by weight of red phosphorus (trade name: NOVALETS #120, manufactured by Rin Kagaku Kogyo Co., Ltd.),
Open-cell molding was carried out in exactly the same manner as in Example 1 under the same conditions. The resulting open cell foam was processed without impregnation with a vinyl phosphonate compound.
A combustion test was conducted on the CFR, but it failed. Examples 6 to 10 In Example 1, SAYTEX BT-93 manufactured by SAITECH lnc. was used as the halogen flame retardant,
The number of parts added to the polyolefin composition was changed as shown in Table 1 below, and the impregnation ratio of vinyl phosphonate into the resulting open cells (expressed as the weight increase rate of the cells after polymerization and drying) A flame-retardant open cell was produced in exactly the same manner as in Example 1, except that the conditions were changed as shown in Table 1.

〔Effect of the invention〕

As described above, according to the method of the present invention, a crosslinked polyolefin open cell to which a halogen-based flame retardant is added is obtained, which is then impregnated with a phosphorus-based flame retardant and polymerized for flame retardant treatment. Excellent flame retardancy can be imparted through the synergistic effect of two types of flame retardants: the halogen flame retardant present in the foam and the phosphorus flame retardant bonded and attached to the surface of the cell membrane and the surface of the cell. By using a halogen-based flame retardant and a phosphorus-based flame retardant in combination, the amount of expensive phosphorus-based flame retardant used can be reduced, and manufacturing costs can be reduced. Therefore, according to the method of the present invention, a crosslinked polyolefin open cell having excellent flame retardancy can be produced at low cost. The flame-retardant cross-linked polyolefin open-cell foam produced by the method of the present invention is inexpensive and is used in various fields such as aircraft interior materials, flooring materials, wall materials, cushion materials, adsorbents, and air filters. It is extremely useful as a material for etc.

Claims (1)

[Scope of Claims] 1. A foamable crosslinkable composition containing a halogenated flame retardant blended with polyolefin is foamed to generate cells, and then mechanical deformation is applied to make the cells open to create a crosslinked polyolefin open cell foam. impregnating the obtained crosslinked polyolefin open cell with a phosphorus-based flame retardant, and then irradiating it with an electron beam,
A method for producing a flame-retardant crosslinked polyolefin open cell body, which comprises the step of producing an insoluble polymer inside and on the surface of the open cell body. 2. The method according to claim 1, which uses a foamable crosslinkable composition containing 10 to 30 parts by weight of a halogen flame retardant to 100 parts by weight of polyolefin. 3. The method according to claim 1 or 2, wherein the halogen flame retardant is a bromine flame retardant. 4. The method according to claim 1, wherein the phosphorus flame retardant is a vinyl phosphonate compound.