JPS6230218B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for manufacturing a polystyrene resin plate-like foam. More specifically, the present invention relates to a method for producing a polystyrene resin plate-like foam that has good extrusion moldability, is highly foamed, and has high mechanical strength, good dimensional stability, and excellent heat insulation properties. Conventionally, polystyrene resin foam has been widely used as a heat insulating material because it is lightweight, has a high heat insulating effect, can be obtained at a relatively low cost, and is easy to handle and install. Usually 15mm thick
The thick plate-shaped extruded foam described above is widely used as a heat insulating material. When extrusion molding such a relatively thick plate-shaped polystyrene resin foam, there is a method in which the foam immediately after being extruded from a die orifice is passed through a molding device called a guider to form it into a plate of a fixed shape. by. Therefore, the extrusion moldability of the polystyrene resin used has a great influence on the operation of the extruder and the quality of the plate-shaped foam produced. Therefore, in order to produce thick plate-shaped polystyrene resin foams by extrusion molding, conventionally, polystyrene resins with high extrusion moldability, that is, polystyrene resins that are generally used when producing thin sheet-shaped polystyrene foams, have been used. For example, a relatively low molecular weight polystyrene resin with a weight average molecular weight (hereinafter simply referred to as molecular weight) determined by gel permeation chromatography ( ^GPC ) of 20 It is common to use small polystyrene resins. However, when such a low molecular weight polystyrene resin is used, although its extrusion moldability is good, the mechanical strength of the thick plate-shaped foam obtained as a product is low and the dimensional stability is also poor. . Therefore, it is difficult to say that the product has sufficient quality. The present inventors have worked diligently to provide a method for producing a thick plate-like foam that is highly foamed and has excellent mechanical strength, dimensional stability, and heat insulation properties in a well-balanced manner using an extrusion molding method. As a result of research, it was found that even high molecular weight polystyrene resins, which were conventionally unsuitable for obtaining highly foamed plate-like products due to poor extrusion moldability, could be used in the presence of a specific amount of high boiling point solvent. The inventors of the present invention have found that it is possible to easily produce a polystyrene resin foam that exhibits a good extrusion molding method and has the above properties, and has thus arrived at the present invention. It is therefore an object of the present invention to provide a highly expanded polystyrene base material having a foam density of e.g. less than 0.035 g/cm ³ and having excellent mechanical strength, dimensional stability and thermal insulation properties. The purpose of the present invention is to provide a resin foam. Another object of the present invention is to intentionally use a polystyrene resin having a high molecular weight, which is not generally used in the extrusion molding method for thick foams because of its poor extrusion moldability. The object of the present invention is to provide a method for easily producing a thick polystyrene resin foam that satisfies the above-mentioned various performances required as a heat insulating material despite using a high molecular weight polystyrene resin. Further objects of the invention will become apparent from the description below. The objects and advantages of the present invention are that, according to the present invention, a polystyrene resin and a volatile foaming agent are heated and melt-kneaded in an extruder, and then the melt is extruded into a low pressure zone to form a thick plate-shaped foam. In the manufacturing method, a high molecular weight polystyrene resin having a weight average molecular weight determined by gel permeation chromatography (GPC) in the range of 20 × 10 ⁴ to 35 × 10 ⁴ is used as the polystyrene resin. production of a polystyrene resin plate-like foam, characterized in that the high molecular weight polystyrene resin and a volatile blowing agent are heated, melted and kneaded in the presence of a solvent of 2500 to 7000 ppm relative to the resin. achieved by law. The polystyrene resin in the present invention refers to a homopolymer or copolymer containing styrene as the main monomer component, such as polystyrene, high-impact polystyrene, a copolymer of styrene and maleic anhydride, or a copolymer of styrene and acrylonitrile. Copolymer, styrene-butadiene
It is a copolymer of acrylonitrile, etc., and the proportion of the styrene monomer component in the polymer is 50 mol% or more, preferably 80 mol% or more. In addition, as the polystyrene resin of the present invention, a mixture of the above homopolymers or copolymers and other thermoplastic resins may also be used. These polystyrene resins used in the present invention have a molecular weight of 20×10 ⁴ as determined by gel permeation chromatography (GPC).
It is necessary to be in the range of ~35×10 ⁴ . The use of such a polystyrene resin is important in terms of increasing the mechanical strength of the thick plate-shaped foam product and improving the dimensional stability of the extrusion molded product. In general, thick foam plates used as insulation materials are required to have well-balanced mechanical strength in the length, thickness, and width directions (for example, during actual use The compressive strength in the thickness direction, which is a particular problem, is preferably 2.0Kg/cm ² or more) Furthermore, a considerably high degree of precision is required for the dimensional stability of the product (JISA9511
According to, for example (width) 600mm x (thickness) 25mm x
(Length) In the case of a plate-shaped foam with a size of 900 mm, the tolerance for dimensional increase or decrease at room temperature is -2 to 2 in the width direction.
mm, thickness direction -2~1mm and length direction -3~2mm
(within) Polystyrene resins with a molecular weight smaller than 20×10 ⁴ have good fluidity and can be easily extruded, but
The resulting plate-like foam has poor mechanical strength and dimensional stability, making it undesirable as a product. That is,
When using a polystyrene resin with a molecular weight smaller than 20×10 ⁴ , it is extremely difficult to obtain a thick plate-like foam that maintains such a well-balanced mechanical strength, and its dimensional stability is poor. In order to sufficiently satisfy the dimensional stability that is generally inferior and therefore required for the high precision described above, the extruded plate-shaped foam is cured for a considerable period of time before being made into a product. There is a need. However, in some cases, dimensional changes exceeding the allowable range may occur during such curing, necessitating reprocessing, which is extremely disadvantageous from an industrial perspective. On the other hand, polystyrene resins with a molecular weight exceeding 35×10 ⁴ have extremely poor fluidity and cannot be extruded satisfactorily even in the presence of solvents. If a resin based on the resin is used, the object of the present invention cannot be fully achieved. Therefore, the polystyrene resin used in the present invention needs to have a molecular weight of 20×10 ⁴ to 35×10 ⁴ . Among these, those having a molecular weight of 22 x 10 ⁴ to 30 x 10 ⁴ show particularly good extrusion moldability by the method of the present invention, and can be used to form thick plate-shaped invention bodies with excellent mechanical strength and dimensional stability. preferred because it gives In the method of the present invention, it is necessary that a solvent be present during heating, melting, and kneading in an extruder.
Such a solvent is melt-mixed with a high molecular weight polystyrene resin in an extruder and improves the fluidity of the polymer resin in its molten state. The use of such solvents is a feature of the invention. In other words, by using such a solvent, the molecular weight can be reduced to 20×, which could not generally be used in the production of polystyrene resin plate-shaped foams by conventional extrusion molding methods.
For the first time, it became possible to use polystyrene resins with a size of 10 ⁴ to 35 x 10 ⁴ and highly foamed, e.g.
For the first time, a plate-shaped foam is provided which has a foam density of less than 0.035 g/cm ³ and has excellent mechanical strength, dimensional stability or thermal insulation properties. In addition, the use of such a solvent further increases the compatibility between the polystyrene resin and the volatile blowing agent, and therefore, even when a large amount of the volatile blowing agent is used, highly foamed plate-like foam can be obtained without causing the surging phenomenon. It becomes possible to manufacture the body. The solvent used in the present invention preferably has a boiling point of 70°C to 170°C at normal pressure, and is capable of being melt-mixed with the polystyrene resin. For example, styrene monomer,
Ethylbenzene, propylbenzene, toluene,
Examples include xylene and cyclohexane.
Among these, styrene monomer is particularly preferably used. In the present invention, these solvents may be used alone or in combination of two or more. In the present invention, the solvent is
Used in amounts ranging from 2500 to 7000 ppm.
If the amount is less than 2500 ppm, the degree of improvement in extrusion moldability is small and the density is 0.035 (g/cm ³ ).
No highly foamed thick plate product can be obtained. On the other hand, if the amount is more than 7000 ppm, the mechanical strength and dimensional stability of the resulting thick plate-like product will be poor, which is not preferable. In the present invention, various methods are employed to make the solvent present during extrusion molding. For example, the solvent may be injected into the melt in the extruder by means of a pump or the like, or it may be incorporated into the polystyrene resin used as unreacted monomer or as a residue of the reaction medium; There are methods such as adding and mixing it with polystyrene resin. There are various volatile blowing agents that can be used in the present invention, but a mixed blowing agent containing dichlorodifluoromethane as a main component is preferred. In particular, a mixed blowing agent consisting of three components: dichlorodifluoromethane, ethyl chloride, and methyl chloride is preferred. Preferably used. According to the research of the present inventors, by using a mixed blowing agent of dichlorodifluoromethane, ethyl chloride, and methyl chloride as a volatile blowing agent in the method of the present invention, dichlorodifluoromethane is Ethyl chloride and methyl chloride reduce the thermal conductivity and therefore improve the heat insulation properties of the product. Ethyl chloride and methyl chloride improve the fluidity of the foamable molten gel and improve extrusion moldability. It has become clear that among these, ethyl chloride can have the effect of making it possible to increase the amount of mixed blowing agent used. The composition of the mixed blowing agent used in the present invention is that dichlorodifluoromethane accounts for 50 to 70% by weight of the total, and the composition ratio of ethyl chloride and methyl chloride as components other than dichlorodifluoromethane is ethyl chloride. 30-95% by weight and methyl chloride 5-70
% by weight is preferred. The above mixed blowing agent used in the present invention is preferably used in an amount of 8 to 17 parts by weight per 100 parts by weight of the polystyrene resin. If it is less than 8 parts by weight, the resulting thick foam will have a high density, while if it exceeds 17 parts by weight, a surging phenomenon will easily occur during extrusion, making it difficult to obtain a thick foam with a good shape. do not have. According to the present invention, since a solvent is present when the polystyrene resin and the mixed blowing agent are heated and melted and kneaded in an extruder, the compatibility between the blowing agent and the molten gel increases as described above, and therefore a large amount of blowing agents can be used. Therefore, the obtained plate-like foam can be highly foamed with a density of less than 0.035 (g/cm ³ ), and the content of dichlorodifluoromethane in the foam can be increased. Therefore, it is possible to make it into a thick plate shape with excellent heat insulation properties. In addition, the use of a solvent improves the compatibility between the blowing agent and the molten gel.
Compared to the case where the same amount of the same mixed blowing agent is used but a predetermined amount of solvent is not present, the blowing agent is more uniformly dispersed in the molten gel, increasing the foaming effect,
It is therefore possible to obtain a highly foamed slab-like foam. In the present invention, the polystyrene resin is preferably fed into an extruder in the form of pellets and heated and melted. At this time, it is convenient to use a polystyrene resin containing a predetermined amount of solvent. If the extruder does not contain any solvent or contains less than a predetermined amount of solvent, the solvent can be added by pressure using a pump or the like at any point in the extruder, preferably in the mixing zone. In the extruder, the molten material generated by heating and melting gradually advances forward and is mixed with a blowing agent in a mixing zone before reaching a cooling zone. The temperature at which the foamable molten gel mixed with the foaming agent is extruded from the die orifice is within a range where the foamable molten gel exhibits a melt viscosity suitable for foaming. The appropriate temperature range varies depending on the type of polystyrene resin used, the composition and amount of the blowing agent, but generally it is 90℃~
The temperature is 120℃. Moreover, the pressure of the die orifice is generally 50 to 140 Kg/cm ² . The foamable molten gel extruded into the low pressure section through the die orifice is foamed and then passed through a molding device generally called a guider, whereby it is continuously molded into a plate-shaped molded body having a constant cross-sectional area. In the present invention, scraps generated during cutting to finish a plate-shaped foam obtained by extrusion molding into a product can be re-pulverized and used as a raw material. It is preferable that the amount of such scrap be up to about 30% by weight based on the raw material polystyrene resin. In addition, in the present invention, a cell regulator may be added in order to further refine the cells of the plate-shaped foam. Such bubble control agents include, for example, fine powders of inorganic compounds such as talc and clay, or compounds that can generate gas by decomposing or chemically changing at heating temperatures, such as polyvalent carboxylic acids ( citric acid) or an acidic alkali metal salt thereof (eg monosodium citrate) and a carbonate (eg soda carbonate) or bicarbonate (eg soda bicarbonate).
Such a cell control agent is usually used in an amount of 0.05 to 3 parts by weight per 100 parts by weight of the polystyrene resin. Such foam control agents are known per se to those skilled in the art. Japanese Patent Publication No. 44-8731 and Japanese Patent Publication No. 44-19712, which disclose such regulators, are cited herein as references. In addition, additives such as colorants, heat stabilizers, fillers, etc. may be added, if desired, within a range that does not impede the intended purpose of the present invention. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 The molecular weight is 21×10 ⁴ and the volatile components are styrene monomer 2600 ppm and ethylbenzene.
100 parts by weight of polystyrene containing 100 ppm;
and 0.1 part by weight of a foam regulator consisting of an equimolar mixture of monosodium citrate and sodium bicarbonate were fed into an extruder having an inner diameter of 90 mmφ. On the other hand, a mixed blowing agent was injected in an amount of 10 parts by weight per 100 parts by weight of the polystyrene through a blowing agent injection port provided in the extruder. Mixed blowing agent: dichlorodifluoromethane 60% by weight, ethyl chloride
A mixed blowing agent consisting of 20% by weight and 20% by weight of methyl chloride was used. The foamable molten gel uniformly kneaded in the extruder is attached to the outlet of the extruder with a width of 200 mm and a gap of 6 mm.
It was extruded into the atmosphere through a die orifice at 110°C to foam, and then passed through an attached guider to form a thick plate-shaped foam with a cross section of approximately 620 mm in width and approximately 28 mm in thickness. The cross section of this thick plate-shaped foam is 600 mm wide and 25 mm thick.
The specimen was cut and machined to a length of 900 mm and a test piece. The extrusion moldability observed during the above manufacturing process is shown in Table 1 along with various tests. Further, various properties of the obtained test pieces are shown in Table 2. Note that Tables 1 and 2 also show the results of the following Examples and Comparative Examples. Example 2 The molecular weight is 24×10 ⁴ and the styrene monomer is
Using polystyrene containing 3500ppm, the first
The same procedure as in Example 1 was carried out except that the blowing agent shown in the table was used. Example 3 The molecular weight is 26×10 ⁴ and the styrene monomer is
Example 2 was carried out in the same manner as in Example 2, except that polystyrene containing 2300 ppm was used and ethylbenzene was injected into the polystyrene from a solvent injection port provided in the mixing zone of the extruder using a pump at 2700 ppm. Example 4 Styrene monomer with a molecular weight of 30×10 ⁴
Using polystyrene containing 3,500 ppm, toluene is injected into the polystyrene using a 3,000 ppm pump from the solvent injection port provided in the mixing zone of the extruder, and a blowing agent shown in Table 1 is used. was carried out in the same manner as in Example 1. Comparative example 1 Styrene monomer with a molecular weight of 17×10 ⁴
The same procedure as in Example 1 was carried out except that polystyrene containing 1200 ppm was used. Example 2 Styrene monomer with a molecular weight of 26×10 ⁴
The same procedure as in Example 2 was carried out except that polystyrene containing 2300 ppm was used. Comparative Example 3 Styrene monomer 2200ppm and ethylbenzene 3500ppm were added to polystyrene from the solvent injection port.
The same polystyrene as in Example 3 was used and the same conditions as in Example 3 were used, except that the mixture was injected with a pump. Comparative example 4 Styrene monomer with a molecular weight of 36×10 ⁴
Using polystyrene containing 3000 ppm, 2500 ppm of styrene monomer and 2000 ppm of toluene were injected into the polystyrene through the solvent injection port provided in the mixing zone of the extruder using a pump, and the blowing agent shown in Table 1 was used. The rest used is Example 1.
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Claims (1)

[Scope of Claims] 1. A method for producing a thick plate-shaped foam by heating, melting, and kneading a polystyrene resin and a volatile foaming agent in an extruder, and then extruding the melt into a low-pressure zone. As the system resin, a high molecular weight polystyrene resin whose weight average molecular weight as determined by gel permeation chromatography (GPC) is in the range of 20 x 10 ⁴ to 35 x 10 ⁴ is used; 1. A method for producing a polystyrene resin plate-like foam, which comprises heating, melting, and kneading a polystyrene resin and a volatile foaming agent in the presence of a solvent of 2,500 to 7,000 ppm based on the resin. 2. The method according to claim 1, wherein the solvent is a styrene monomer. 3. The method according to claim 1, wherein the volatile blowing agent is a mixed blowing agent consisting of three components: dichlorodifluoromethane, methyl chloride and ethyl chloride.