JPH0257491B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a polystyrene foam;
Specifically, the present invention relates to a method for producing a polystyrene foam having fine cells. [Prior art] In a synthetic resin foam, if the bubbles are large,
Since the appearance of the foam is damaged, the cells are made finer by adding large amounts of inorganic powder such as talc as a nucleating agent, or by adding decomposable organic foaming agents such as amide compounds. . Furthermore, in the production method of polyolefin foam, it has been proposed to add a specific amount of a substance with a specific melting point, such as barium stearin, to polyolefin resin in order to make the cells finer (Japanese Patent Publication No. 59-23341). ). [Problems to be solved] However, if a large amount of nucleating agent is used, black spots may occur in the foam sheet, probably because the inorganic powder is not uniformly dispersed, and fish-like spots may appear on the surface of the foam sheet. spots and phenomena occur,
There was a defect that spoiled the appearance of the foam sheet. On the other hand, if the amount of nucleating agent used is reduced in order to improve the appearance, the bubbles will become larger and the closed cell ratio will decrease, which will increase the brittleness of the foam sheet and, as a result, the cushioning properties of the foam sheet will decrease. Deteriorate. Therefore, it has not been possible to achieve both the appearance, brittleness, and cushioning properties of a foam sheet. In addition, in the method using a decomposable organic blowing agent, as the extruder is continuously operated, decomposed organic matter may adhere to the screen attached to the tip of the extruder or to the lip portion with a narrow gap of the subsequent molding die.
Not only does the appearance of the foam sheet gradually become rough due to discoloration caused by decomposition products, but the extruder must be shut down and cleaned every 3 to 10 days, resulting in poor workability. It was hot. In addition, in the method for producing polyolefin foam described above, the melt viscosity of polyolefin resin is significantly lower than that of polystyrene resins, etc., and it changes significantly depending on the temperature. Not only is it difficult;
Since the air bubbles tend to become open cells and are distributed unevenly, it is difficult to obtain a foam sheet that is smooth and has good appearance, cushioning properties, and insulation and heat retention properties, and requires careful operations, making work management complicated. It had the disadvantage of being. Due to its properties, polyolefin resin has
Although there is no increase in brittleness, rigidity,
Due to their low strength, polyolefin foams naturally have the disadvantage of limiting their uses. The present invention has been made in order to solve the above-mentioned conventional problems, and its purpose is to provide a method for manufacturing polystyrene foam that has high rigidity and strength and can make the cells finer. It is about providing. [Means and effects for solving the problems] The present invention provides a method for producing a polystyrene foam by mixing a polystyrene resin and a volatile blowing agent in an extruder and extruding the mixture. The above-mentioned conventional problems are solved by adding and mixing a masterbatch in which at least one of an inorganic powder and a divalent or trivalent metal salt of a higher fatty acid is melt-mixed with a polystyrene resin in advance. The present invention will be explained in detail below. The polystyrene resin used in the present invention is a homopolymer of various styrene monomers such as styrene, α-methylstyrene, paramethylstyrene,
Examples include copolymers and copolymers of monomers copolymerizable with the styrene monomers.
Examples of copolymerizable monomers include methacrylates or acrylates having 1 to 18 carbon atoms such as methyl methacrylate and butyl acrylate, acrylic monomers such as acrylonitrile, olefinic monomers such as butadiene, and unsaturated acids such as maleic anhydride or their esters. Can be mentioned. Among these, polystyrene resin and paramethylstyrene resin are preferred because they have high rigidity and strength, and the latter has better heat resistance. These styrene resins can be appropriately selected with a degree of polymerization depending on the intended use, and may be used in combination with other resins such as SBR resins and acrylic resins. Further, volatile blowing agents used in the present invention include aliphatic hydrocarbons such as propane, butane, and pentane, and halogenated hydrocarbons such as dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, and methylene chloride. , those with a boiling point of 40°C or less are generally used. The above volatile foaming agent is press-mixed into the pressurized molten polystyrene resin in an extruder. The amount of the volatile blowing agent used can be arbitrarily changed depending on the expansion ratio of the foam, the use, etc. Such a volatile foaming agent does not decompose in the extruder and expands during extrusion to foam the polystyrene resin, so there is no problem such as coloring of the foamed sheet due to decomposition products. In the present invention, when producing a polystyrene foam by the method described above, the polystyrene resin contains inorganic powder and at least one divalent or trivalent metal salt of a higher fatty acid at a high concentration as a nucleating agent. By adding and mixing masterbatch, the bubbles are made finer. The masterbatch contains 2 to 40 parts by weight of inorganic powder and at least 1 type of divalent or trivalent metal salt of higher fatty acid per 100 parts by weight of polystyrene resin.
~10 parts by weight is preferred. If the amount of inorganic powder is less than 2 parts by weight, it will not be possible to make the bubbles finer.
If the amount exceeds 1 part by weight, poor dispersion of the inorganic powder will occur; if the amount of divalent or trivalent metal salts of higher fatty acids is less than 1 part by weight, it will not be possible to make bubbles fine; if it exceeds 10 parts by weight, it will be used excessively. Not economical. Various inorganic powders can be used, such as talc, kaolin, calcium carbonate, barium sulfate, etc., but talc is preferred from the viewpoint of fine bubble formation, cost, etc. Further, as the higher fatty acid, a saturated fatty acid or an unsaturated fatty acid having 10 to 30 carbon atoms is used. If the number of carbon atoms is less than 10, it is difficult to obtain fine bubbles when used in combination with the inorganic powder, and if the number of carbon atoms exceeds 30, it is expensive and therefore undesirable. Higher fatty acids include capric acid, lauric acid, myristic acid,
Palmitic acid, oleic acid, linoleic acid, ricinoleic acid, linolenic acid, stearic acid, dihydroxystearic acid, behenic acid, erucic acid, cerotic acid, montanic acid, and the like. In addition, examples of divalent or trivalent metal salts include calcium salts, aluminum salts, barium salts, magnesium salts, zinc salts, and strontium salts, and among them, calcium salts, aluminum salts, and barium salts are more effective for miniaturization. It is. The divalent and trivalent metal salts of the higher fatty acids mentioned above can be used alone or in combination of two or more. It is sufficient as long as it contains it. The masterbatch is obtained by melt-mixing under heating and pressure conditions using equipment such as a kneader and an extruder. When the masterbatch thus obtained is added and mixed with a polystyrene resin and extruded and foamed, even finer cells can be obtained even if the concentration of the inorganic powder or the like is increased. The amount of masterbatch added can be selected as appropriate, but
It is preferable to add and mix the masterbatch with the polystyrene resin so that the amount of the inorganic powder is 0.2 to 1.0 parts by weight, preferably 0.3 to 0.7 parts by weight, based on 100 parts by weight of the polystyrene resin. If it is less than 0.2 part by weight, the bubbles will not be made fine enough, and the feeding of the raw material into the extruder will become unstable, making it impossible to perform a stable extrusion operation. On the other hand, if the amount exceeds 1.0 parts by weight, it is difficult to mix uniformly with the polystyrene resin, and the inorganic powder adheres as a lump to a part of the resin pellet, causing black spots on the foam sheet, which is not preferable. Regarding divalent and trivalent metal salts of higher fatty acids, for 100 parts by weight of polystyrene resin,
It is preferable to add and mix the masterbatch to the polystyrene resin in an amount of 0.01 to 0.2 parts by weight, preferably 0.02 to 0.1 parts by weight. If it is less than 0.01 parts by weight, the bubbles cannot be made sufficiently fine, and if the amount is less than 0.2 parts by weight,
If the amount exceeds 1 part by weight, the amount used is excessive and is not economical, and it may also adhere to the tip of the mold and cause streaks on the sheet surface. In particular, the amount of the inorganic powder and the divalent or trivalent metal salt of the higher fatty acid used is within the above range, but the ratio of the inorganic powder to the divalent or trivalent metal salt of the higher fatty acid is 2:1. When using a master batch with a ratio of ~25:1, bubbles can be effectively refined. If the ratio of the inorganic powder is less than 2:1, the bubbles will be rough, and if the ratio is more than 25:1, the inorganic powder will not be sufficiently dispersed. The effects of the above-mentioned inorganic powders and divalent and trivalent metal salts of higher fatty acids are not clear, but their combined use in polystyrene resins, which have a high melt viscosity and a small change in viscosity due to temperature, improves extrusion. Coupled with the large shear stress caused by the screws in the machine, not only the inorganic powder and divalent and trivalent metal salts of higher fatty acids are uniformly dispersed, but also the divalent and trivalent metals of higher fatty acids are dispersed. The salt melts and liquefies in the molten polystyrene resin, preventing the agglomeration of the inorganic powder, so each individual particle of the inorganic powder effectively functions as a bubble nucleating agent, forming fine bubbles. It is assumed that. In addition, by using inorganic powder and divalent or trivalent metal salts of higher fatty acids within the above range,
Since the extrusion pressure is high at the melt outlet end of the mold, internal foaming is prevented, and it is presumed that fine bubbles are efficiently formed. The masterbatch is used to make the inorganic powder etc. have a predetermined concentration in the extruder that produces the foam.
Polystyrene resin or a mixture of polystyrene resin and inorganic powder or divalent or trivalent metal salts of higher fatty acids is mixed and extruded and foamed. The present invention can use one or more extruders. In the latter case, the masterbatch is manufactured using one extruder, and the obtained masterbatch is continuously fed to another extruder that is supplied with polystyrene resin, inorganic powder, etc., thereby producing the foam. Production may also be carried out continuously. Then, a volatile blowing agent is press-injected into the polystyrene resin etc. melted and mixed in the extruder through a blowing agent inlet provided in the cylinder, mixed with the molten polystyrene resin etc., and the blowing agent is released into the atmosphere or into a reduced pressure section. A molten polystyrene-based resin, etc. containing , is extruded and foamed. At this time, by changing the shape of the mold, rod-shaped, sheet-shaped, and tube-shaped foams can be continuously obtained. In addition, spreading agents commonly used in the production of foams,
The use of lubricants, antioxidants, flame retardants, colorants, etc. is optional. [Example] Examples of the present invention will be described below in comparison with comparative examples. Examples 1 to 7 and Comparative Examples 1 to 7 100 parts by weight of polystyrene resin (M1-2.2),
Inorganic powder and metal salts of higher fatty acids in the added parts shown in Table 1 were mixed in a tumbler, and the mixture was fed into an extruder through a hopper (diameter 40 mm) at a rate of 50 kg/hr.
The mixture was heated to 240°C to melt and mix. Next, the molten mixture was extruded through a nozzle, cooled with water, and then cut to form a masterbatch with a diameter of 2 mm.
Kneaded pellets having a length of 2 mm were prepared and designated as pellets A to F. Next, these pellets, polystyrene resin (M1 = 2.2) and inorganic powder were mixed in the proportions shown in Table 2, and the pellets were heated at 70 m
Kg/hr, heated to 220℃, melted and mixed, and added 2.5Kg/hr of butane as a volatile blowing agent through the blowing agent inlet installed in the cylinder.
and mixed with the molten resin and the like. Next, it was cooled to 160°C in the extruder, extruded into the atmosphere through a circular mold (diameter 100 mm, lip gap 0.7) attached to the tip, foamed, and then taken in a sheet form using a 410 mm diameter mandrel (Example 1). ~7). As a comparative example, the above polystyrene resin, talc as an inorganic powder, and calcium laurate as a divalent and trivalent metal salt of higher fatty acids were mixed in a tumbler in the proportions shown in Table 2 without using pellets. It was extruded and foamed using an extruder under the same conditions as above, and then it was made into a sheet and collected (Comparative Examples 1 and 2). In addition, inorganic powder and polystyrene resin were mixed in the proportions shown in Table 2, extruded into the air under the same conditions, foamed, and then collected in the form of a sheet (Comparative Examples 3 to 5). Furthermore, as another comparative example,
In the blending of polystyrene resin with inorganic powder and metal salt of higher fatty acid, as shown in Table 2, there were cases where excessive inorganic powder was used (Comparative Example 6) and cases where excessive amount of metal salt of higher fatty acid was used (Comparative Example 7) was similarly performed. The foam sheet has a thickness of 2 ± 0.2 mm and a basis weight of 180
It was adjusted to ±5 g/m ² . Table 2 shows the performance of the obtained foam sheet. Note that the amounts added and the ratios in Tables 1 and 2 indicate parts by weight. In Table 1, La-Ca is calcium laurate, St-Ba is barium stearate,
St-Mg represents magnesium stearate, St-Al represents aluminum stearate, and La-Zn represents zinc laurate. Further, in Table 2, PS resin indicates polystyrene resin, and total T/FA indicates the overall ratio of talc to divalent and trivalent metal salts of higher fatty acids.

【table】

【table】

[Table] As is clear from Table 2, the invention of the present application is
Since inorganic powder and divalent or trivalent metal salts of higher fatty acids were used together, the number of cells was large even when the amount of inorganic powder was increased, and the closed cells of the foamed sheet were dense and had a good appearance. Furthermore, since a master batch was used, the results were better than those in which inorganic powder and divalent and trivalent metal salts of higher fatty acids were added all at once. On the other hand, in Comparative Examples 1 and 2, in which inorganic powder and higher fatty acid metal salt were added at once, air bubbles were lower than in Examples 1 and 2, which had the types and proportions of inorganic powder and higher fatty acid metal salt. There were few. In addition, Comparative Examples 3 to 5 using only inorganic powder
However, as the amount of inorganic powder increases, the number of cells increases and the closed cells tend to become finer.However, at 0.4 parts by weight, only a sheet with a small number of cells and a rough appearance can be obtained; When the temperature was exceeded, black spots appeared, which appeared to be due to poor dispersion of the inorganic powder. Further, in Comparative Examples 6 and 7, in which inorganic powder and higher fatty acid metal salt were used in excess, black spots and lines appeared. [Effects of the Invention] The present invention combines inorganic powder and divalent and trivalent metal salts of higher fatty acids to polystyrene resin,
It is melt-extruded and foamed, and the melt viscosity of polystyrene resin is high and the viscosity changes little due to temperature.
Perhaps because the trivalent metal salt is uniformly dispersed and the individual particles of the inorganic powder are finely dispersed so that they each function effectively as a cell nucleating agent, fine closed cells with a good appearance and no black spots are formed. A foam having a large number of . In particular, since a masterbatch containing highly concentrated inorganic powder and divalent and trivalent metal salts of higher fatty acids is used, the effect is great. In addition, polystyrene resin, which has high rigidity and strength, is used as the resin material, and fine closed cells are evenly distributed, so a foam with low brittleness and good cushioning, heat insulation and heat retention properties can be obtained. That is, it is possible to provide a polystyrene foam having excellent properties that is compatible with appearance and cushioning properties. Furthermore, since the extrusion pressure is high, internal foaming is prevented and a foam with good smoothness can be obtained. Furthermore, since we use a volatile foaming agent that is difficult to thermally decompose, the foam will not be colored by decomposition products, so the appearance of the foam will not be impaired, and the decomposition products will not discolor the lip of the mold, etc. Because it does not adhere to the surface, there is no need for complicated cleaning work, and it can be operated continuously for a long period of time, resulting in good workability. Since the foam obtained by the present invention has excellent properties as described above, it can be used in a wide variety of applications such as food containers and fruit trays.

Claims (1)

[Claims] 1. A method for manufacturing a foam by press-mixing a volatile foaming agent into a molten polystyrene resin in an extruder and extruding the polystyrene resin, in which a highly concentrated inorganic powder is added to the polystyrene resin. A method for producing a polystyrene foam, which comprises adding and mixing a masterbatch in which at least one divalent or trivalent metal salt of a higher fatty acid is melt-mixed in advance to a polystyrene resin. 2 The master batch is made of polystyrene resin 100
Production of the polystyrene foam according to claim 1, which comprises 2 to 40 parts by weight of an inorganic powder and 1 to 10 parts by weight of at least one divalent or trivalent metal salt of a higher fatty acid. Method. 3 Add a masterbatch to the polystyrene resin so that the inorganic powder is 0.2 to 1.0 parts by weight and at least one divalent or trivalent metal salt of higher fatty acid is 0.01 to 0.2 parts by weight, based on 100 parts by weight of the polystyrene resin. A method for producing a polystyrene foam according to claim 1 or 2, wherein the polystyrene foam is added and mixed. 4. The ratio of inorganic powder to at least one divalent or trivalent metal salt of higher fatty acid is 2:1 to 25:1.
Claims 1 to 3 in which a masterbatch is added to and mixed with polystyrene resin so that
A method for producing a polystyrene foam according to any one of Items 1 to 3. 5. The method for producing a polystyrene foam according to any one of claims 1 to 4, wherein the inorganic powder is talc. 6. The method for producing a polystyrene foam according to any one of claims 1 to 5, wherein the divalent or trivalent metal salt is a calcium salt, an aluminum salt, a barium salt, a magnesium salt, or a zinc salt. 7 Claims 1 to 6 in which the higher fatty acid is a saturated or unsaturated fatty acid having 10 to 30 carbon atoms
A method for producing a polystyrene foam according to any one of Items 1 to 3.