JPS6241972B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a foamable composition capable of producing a highly foamed molded article and a method for producing a foamed molded article from the composition. ``Prior art'' Highly foamed thermoplastic resin with closed cells is
It has excellent insulation properties, and PVC resin foam in particular has excellent flame retardancy, chemical resistance, and mechanical strength, and is used as insulation for various cold storage tanks, cooling gas insulation, and construction insulation. It has come to be used. Polyvinyl chloride resin foams can be manufactured by extrusion molding, injection molding, or other methods in which polyvinyl chloride resin containing a foaming agent is foamed at the same time as the molding process, or by pressurizing the foamable resin in a mold. A method is known in which the pressure is removed after thermal decomposition of a blowing agent heated to . In addition, as a special method, there is a method in which a solvent and liquefied butane are mixed with vinyl chloride resin and a filler to foam, for example, Japanese Patent Nos. 615762 and 897788,
It is known from the same No. 929418. However, it is difficult to obtain foams as high as 10 to 50 times with these foaming methods. Due to strict selection of methods, foaming was limited to about 16 to 17 times. Even if molded under severe conditions, the resulting molded product will have poor expansion ratio, bubble distribution, dimensional stability, etc., and will be far from being a molded product with commercial value.In other words, it will not be possible to stably produce the desired molded product. Currently, molded products cannot be manufactured in bulk, and as a result, the yield of molded products based on raw materials is extremely low. ``Problems that the invention seeks to solve'' The inventors of the present invention conducted intensive studies to produce a molded product with fine and uniform cells, good dimensional stability, and high expansion ratio, and discovered that vinyl chloride resin It was discovered that by including acrylonitrile in a resin composition consisting of an organic solvent and a blowing agent, it is possible to produce a highly foamed molded product with an extremely fine and uniform cell structure and excellent compressive strength as well as dimensional stability. Furthermore, by adding acrylonitrile, even if an amount of inorganic filler equal to or more than that of the vinyl chloride resin is added to the composition, the phenomenon called so-called outgassing does not occur at all, and it is extremely easy and stable. The present invention was completed by discovering that it is possible to produce a highly foamed molded product with good dimensional stability and having uniform cells similar to those of vinyl chloride resin. That is, the object of the present invention is to provide a foamable composition capable of producing a highly foamed molded product having a fine, uniform cell structure, good dimensional stability, and excellent compressive strength, and a foamed molded product using the same. To provide a manufacturing method. "Means for Solving the Problems" The gist of the present invention is, firstly, a foamable composition comprising a vinyl chloride resin, an organic solvent, a blowing agent, and acrylonitrile; In the method of producing a foamed molded product by heating and molding the composition in a closed mold and then removing it from the mold, the foamable composition comprises a vinyl chloride resin, an organic solvent,
The foaming agent and acrylonitrile are kneaded together, and the foaming composition is heated slowly in the sealed mold so that the temperature difference between each part of the foaming composition is small during heating. The present invention relates to a method for producing a foamed molded article, which comprises heating to a temperature at which the vinyl chloride resin gels and above a temperature at which it decomposes or vaporizes. To explain the present invention in more detail, the vinyl chloride resin that can be used in the composition of the present invention is not particularly limited, and includes homopolymers of vinyl chloride or vinylidene chloride, as well as monomers thereof. Examples include copolymers with monomers copolymerizable with ethylene, propylene, vinyl acetate, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, styrene, and the like. Among these, vinyl chloride homopolymers or copolymers of vinyl acetate and vinyl chloride homopolymers are preferably used because they are miscible with fillers and can provide flame-retardant molded products. Furthermore, in view of the method of manufacturing foamed molded products, the vinyl chloride resin is preferably in powder form, and in particular, in the case of vinyl chloride resin, it is most preferably a paste resin having an average particle size of 3 μm or less. Inorganic fillers that can be used in the composition of the present invention include carbonates, sulfates, silicates, oxides, or hydroxides of calcium, magnesium, aluminum, etc., talc, bentonite, clay, glass fiber, asbestos, etc. There are various fillers used as fillers for thermoplastic resins, and one or more of these may be used as a mixture. The particle size distribution of these fillers is 1 mm or less,
In other words, it is better to have a value of 20 meshes or more,
Preferably, those that pass through a 60 mesh sieve are used. In the composition of the present invention, an appropriate amount of fine particles having a value of 200 mesh or more and particles having a value of 200 mesh or less are preferably mixed in consideration of the expansion ratio, desired physical properties of the foamed molded product, etc. It is often used. The mixing ratio of the inorganic filler to the vinyl chloride resin is not particularly limited, and it can be added in large amounts up to 900 parts by weight per 100 parts by weight of the vinyl chloride resin. In the case of resin, 200 to 100 parts by weight of resin component
A content of 900 parts by weight, particularly preferably from 400 to 800 parts by weight, is preferable from the viewpoints of physical properties of the foam molded product, imparting flame retardance, and economical efficiency. The organic solvent that is one of the components of the composition of the present invention should be selected depending on the type of vinyl chloride resin used, and the organic solvent does not need to completely dissolve the vinyl chloride resin; Any solvent may be used as long as it partially dissolves or swells the resin, and in short, it only needs to be compatible with the vinyl chloride resin or inorganic filler during kneading. However, it is preferable that the solvent does not decompose during kneading or hot molding, and that it can be easily removed from the molded product once molded.
Suitable examples of the organic solvent include aromatic compounds having a boiling point of about 70 to 150°C, such as benzene, toluene, xylene, and chlorobenzene.Other examples include ethylene chloride, trichloroethane, and carbon tetrachloride. In the case of vinyl chloride resins, it is most preferred to use toluene or a mixture of toluene and xylene. The proportion of organic solvent to be used is not particularly restricted, but from the viewpoint of kneading properties and economic efficiency, it is 30 parts by weight per 100 parts by weight of vinyl chloride resin or a mixture of it and filler (hereinafter referred to as "base material"). ~80 parts by weight, preferably 40-70 parts by weight is suitable. As the amount of solvent becomes less than 30 parts by weight, it becomes difficult to uniformly mix the components of the composition without the presence of a plasticizer, and if it is used in an amount of 80 parts by weight or more, the foamability during heating increases. Although it has the advantage of being able to uniformly heat the composition and reduce the temperature difference between different parts of the composition, it can also cause the bubbles in the foam molded product to become rough and require a huge amount of money to recover the solvent. There is a tendency for there to be many disadvantages. As the blowing agent, any of thermally decomposable organic blowing agents, inorganic blowing agents, and volatile blowing agents can be used. For example, organic blowing agents include azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, N,N'-dinitroso-N,N'-dimethylterephthalamide, benzene-1,3-disulfohydrazide, and terephthalamide. Examples include azide. Examples of inorganic blowing agents include thermally decomposed blowing agents that generate a large amount of gas of 150 c.c. or more per gram, such as sodium bicarbonate and ammonium chloride. Further examples include blowing agents that are gaseous at room temperature (20° C.), such as liquefied propane, methyl ether, methane dichloride difluoride, and butane. These blowing agents may be used alone or in combination. In the composition of the present invention, it is particularly preferable to use a sensible heat blowing agent such as N,N'-dinitrosopentamethylenetetramine;
Optimally, a mixture of N'-dinitrosopentamethylenetetramine and other blowing agents such as azodicarbonamide or sodium bicarbonate is used. The ratio of the former to the total foaming agent is
It is preferably in the range of 30 to 90% by weight, particularly 40 to 80% by weight. By using bicarbonate of soda, the cells in the foamed molded product become finer and more uniform. Therefore, the amount of the foaming agent added is appropriately selected from the range of 2 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the base material. Acrylonitrile, which is an essential component of the composition of the present invention, can be used in an amount of up to 10 parts by weight, preferably in a range of 2 to 5 parts by weight, based on 100 parts by weight of the base material. Even if a large amount is used, the compressive strength of the molded article does not increase proportionally as the amount used increases. Although it is unclear what the reason is, foamed molded products manufactured from compositions containing nitrile compounds have been found to have improved physical properties such as compressive strength by uniformly dispersing the foaming agent gas in the composition. It has had a huge impact. In addition to the above-mentioned essential components, the foamable composition of the present invention includes an auxiliary agent for adjusting the decomposition temperature of the foaming agent, an ultraviolet absorber, a heat stabilizer, an antioxidant, an organic filler,
Dyes and pigments can be added as necessary. To produce a foamed molded product from the composition of the present invention, first a vinyl chloride resin, an organic solvent, a blowing agent,
Acrylonitrile or an inorganic filler and, if necessary, a foaming aid and the like are mixed uniformly. As a method of mixing these components, they are uniformly mixed at room temperature using a super mixer, a crusher, a Banbury mixer, a kneader, or the like. In the method of the present invention, it is particularly preferable to knead in a kneader for at least about 10 minutes, preferably 30 to 80 minutes. Of course, if a volatile blowing agent is used as one of the components, a closed kneader is preferably used. When kneading all ingredients,
The inorganic filler and acrylonitrile are kneaded together with an organic solvent if necessary, and then the vinyl chloride resin, blowing agent, organic solvent, etc. are kneaded to make the cells in the foam molded product dense. This is preferable because it has a uniform effect. The uniformly kneaded foamable composition is transferred into a mold using a transfer device such as a screw extruder or a rotary pump, and after the mold is sealed, heating is started. Further, the foamable composition may be transferred to a mold by press-fitting the foamable composition into a closed mold. It is preferable that the amount of filling into the mold completely fills the space within the mold.
By doing this, it is possible to reduce the temperature difference between different parts of the foamable composition in the mold during heating, and also to prevent the separation of foaming gas in the mold, so that the foamable composition itself It also doesn't foam. The mold is not particularly limited as long as it is sealed and can be heated easily, but in the method of the present invention, it is possible to use a transfer molding device and a mold similar to the transfer molding mold that are commonly used for molding thermosetting resins. These molds are the most popular in that they have advantages such as high mold clamping pressure, no leakage of foaming gas from the mold, and can easily produce molded products with excellent dimensional stability. used for convenience. The mold is usually heated using electricity, a heating medium such as oil, or steam, and is carried out by a nichrome wire or piping attached to the mold or press plate. The speed of heating must be determined by taking into account the size of the mold cavity, i.e. the thickness and width of the foamable composition, and the temperature difference at each location of the foamable composition in the mold will increase during heating. It is preferable not to make it too large. In short, it is preferable to raise the temperature at a rate that does not create a large temperature difference, that is, a temperature gradient, between the center of the foamable composition and the temperature of the composition in contact with the mold. It is preferable to maintain the temperature difference within 15°C, preferably within 10°C.
Therefore, the temperature of the foamable composition needs to be at least higher than the temperature at which the foaming agent decomposes or vaporizes, and heated to a temperature at which the vinyl chloride resin gels. If the blowing agent has a slow decomposition rate, it is desirable to maintain the blowing agent at a temperature at or above the gelling temperature until the blowing agent is completely decomposed. The upper limit of the temperature of the foamable composition may be a temperature at which the vinyl chloride resin does not decompose, but it usually depends on the type of vinyl chloride resin,
It is best to decide based on the type of blowing agent, etc., and the temperature is 200℃.
Thereafter, the temperature can be increased preferably to a range of 150 to 180°C, particularly 160 to 170°C. Of course, the temperature increase of the foamable composition is not limited to the above-mentioned temperature increase method, and the temperature can also be increased intermittently or in stages. After the foamable composition has sufficiently gelled and the foaming agent has been decomposed or vaporized, heating is stopped and the mold is quickly cooled with the mold closed. The cooling method may be any method such as air cooling or water cooling, but it is preferable to cool by passing cooling water through the piping used for steam heating, and there is no problem even if the cooling is supercooled to below room temperature. When the foamable composition cooled in the mold is depressurized and the mold is opened, the foaming composition usually expands 2 to 5 times as much as the pressure is removed, thereby forming a foamed molded product. When the wall thickness of a molded product is large, although the surface has solidified, the inside of the molded product is often not yet sufficiently cooled. It solidifies without major changes and becomes a good foam molded product. The foamed molded product obtained by the method of the present invention is further heated in an oven maintained at 80 to 120°C, preferably 90 to 110°C, so that the foamed molded product itself becomes 2 to 10 times larger than the foamable composition. It undergoes secondary foaming and expands to 4 to 50 times the volume. The time for holding in the oven depends on the wall thickness of the foam molded product, but if the foam molded product has a wall thickness of about 100 mm, it is usually 30 minutes or more, preferably 50 to 70 minutes. If the inside of the foam molded product is not yet sufficiently cooled, it will be advantageous for secondary foaming, and the cell structure will be uniform, and the heating time will be shorter than when the inside is completely cooled. be done. "Effects of the Invention" The present invention has the following particularly remarkable effects, and its industrial utility value is extremely large. 1. The foamable composition of the present invention provides a highly foamed product with a dense and uniform cell structure that cannot be obtained from conventional compositions, and although it is not clear what effect acrylonitrile has,
Even if 9 times as much inorganic filler is added to the vinyl chloride resin, there will be no outgassing phenomenon during foaming, and there will be no large shrinkage after foaming, making it possible to mold foam molded products with good dimensional stability. be able to. 2 If acrylonitrile is not used, the foam molded product recovered waste (pulverized reuse, hereinafter referred to as R-resin) generated from the secondary processing of the foam molded product is ) could not be mixed, but by using a small amount of acrylonitrile, R-
It has been found that resin can be used without losing the entire amount of the base material, and it is also possible to manufacture good foam molded products extremely easily, which is extremely advantageous economically. . 3. Foamed molded products obtained from the composition of the present invention exhibit extremely high compressive strength compared to products that do not use acrylonitrile, and have a closed cell structure, making them excellent as buoyancy materials, heat insulating materials, and electrical insulating materials. Highly useful. Although a plasticizer can be added to the composition of the present invention to produce a soft foam, it is better to produce a hard, highly foamed molded product without using a plasticizer. It is advantageous because it imparts quasi-nonflammable properties, and has a wide range of uses as a heat insulating material for various cold storage tanks or as a heat insulating material for buildings. "Examples" Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 and Comparative Example 1 Vinyl chloride paste resin (base material) 800 g, dinitrosopentamethylenetetramine (DPT) 54
g, 12 g of azodicarbonamide (ADCA), 32 g of urea foaming aid, 10 g of calcium-zinc stabilizer (Ca-Zn stabilizer), 440 g of toluene, and 32 g of acrylonitrile were placed in a kneader at 20°C.
The mixture was kneaded for about 1 hour. The obtained composition was transferred to a transfer molding mold (inner volume 250 mm x 250 mm x 15 mm) using a screw-type transfer machine, the mold was clamped to prevent foaming gas from leaking, and 8 kg/kg was transferred to the piping provided in the mold. The temperature was slowly raised to 160° C. over 30 minutes while controlling the steam having a pressure of cm ² and maintained at this temperature for 10 minutes. Thereafter, cooling water was passed through the piping of the mold to cool it down to room temperature for 30 minutes, and the mold was depressurized to obtain a foamed molded product. The foamed molded product expanded approximately 2.8 times as soon as the mold was opened. This foamed molded product was further left in an oven heated to 100° C. for 1 hour to allow it to foam freely, and then removed from the oven. The total foaming ratio at this time is 16
It was more than double that, and the apparent specific gravity was 0.0923. The cells in the obtained secondary foamed molded product have a diameter of about 1.5 to 2 mm and are uniformly dispersed, and the compressive strength at 8 points of the molded product has a maximum value of 8.82 Kg/cm ² and a minimum value of 8.36 Kg/cm 2 .
^cm2 , and the average was 8.52Kg/ ^cm2 . For comparison, a secondary foam molded product was obtained in the same manner as in Example 1 except that acrylonitrile was not used. The cells in the secondary foamed molded product had a size of 2 mm to 5 mm, and were larger toward the center, and the wall thickness between the cells was also larger. The apparent specific gravity of the foam is
It was 0.132. In addition, in Comparative Example 1, the compressive strength at 8 points of the secondary foam with an increased amount of blowing agent and an apparent specific gravity similar to that of Example 1 was 9.3 Kg/cm 2 at the maximum and 9.3 Kg/cm ² at the minimum.
3.6Kg/cm ² , and an average of 6.1Kg/cm ² , which was significantly lower than that of Example 1.

[Table] Example 2 Vinyl chloride paste resin 120g, R-resin
280g (base material), DPT24g, ADCA8g, urea foaming aid 16g, Ca-Zn stabilizer, toluene 220g
g and 12 g of acrylonitrile were uniformly kneaded and placed in a mold smaller than that used in Example 1 to obtain a secondary foam molded product in the same manner as in Example 1. The molded product had an apparent specific gravity of 0.0677, was foamed more than 21 times, and had a uniform cell structure with a diameter of 2 to 3 mm. Example 3 Talc 276g, calcium carbonate 180g in kneader
g, asbestos powder 54g and acrylonitrile 36g
g was charged and mixed uniformly for 10 minutes, then 100 g of toluene was added and mixed for an additional 10 minutes. Then 300g of vinyl chloride paste resin, R-resin
90g of toluene, 395g of toluene, 36g of DPT, and a urea-based foaming aid were added and thoroughly kneaded uniformly. The kneaded composition was transferred to a smaller mold than that used in Example 1, and then a secondary foam molded article was produced in substantially the same manner as in Example 1. The apparent specific gravity of the obtained molded product was 0.135, and it was a uniform highly foamed molded product having a cell structure with a diameter of about 2 to 3 mm. Example 4 DPT18 instead of DPT36g in Example 3
A secondary foam was produced in the same manner as in Example 3, except that 18 g of sodium bicarbonate was used. The foam had an apparent specific gravity of 0.101, an expansion ratio of 22 times or more, and was a highly foamed molded product having a dense, uniform cell structure with a diameter of about 1 mm. Example 5 A secondary foam molded product was obtained in the same manner as in Example 3, except that 40 g of commercially available nitrile rubber was dissolved in toluene and added instead of 36 g of acrylonitrile. The foamed product had an apparent specific gravity of 0.140 and a cell structure with a diameter of about 3 mm.

Claims (1)

[Scope of Claims] 1. A foamable composition comprising a vinyl chloride resin, an organic solvent, a blowing agent, and acrylonitrile. 2. The foamable composition according to claim 1, which contains an inorganic filler. 3. Claim 1 or 2, characterized in that the vinyl chloride resin is a vinyl chloride resin.
The foamable composition described in . 4. The foamable composition according to claim 1 or 2, wherein the foaming agents are dinitrisopentamethylenetetramine, azodicarbonamide, or sodium bicarbonate. 5. A method of manufacturing a foam molded article by heating and molding a foamable composition in a closed mold and then removing it from the mold, wherein the foamable composition contains a vinyl chloride resin, an organic solvent, a blowing agent, and acrylonitrile. The foaming composition is kneaded and heated in the sealed mold slowly so that the temperature difference between each part of the foamable composition during heating is small, and the temperature at which the foaming agent decomposes or vaporizes is maintained. A method for producing a foamed molded product, which is as above and further comprises heating to a temperature at which the vinyl chloride resin gels. 6. The method for producing a foamed molded article according to claim 5, which is a foamable composition obtained by kneading an inorganic filler. 7. The method for producing a foamed molded article according to claim 6, wherein the foamable composition is obtained by kneading an inorganic filler with acrylonitrile and kneading this with other components. 8. The method for producing a foamed molded product according to claim 5, 6 or 7, wherein the kneading is carried out using a kneader. 9. A method for producing a foamed molded article according to claim 5, 6, or 7, which comprises heating the foamable composition so that the temperature difference at each location is within 15°C. .