JP2001279012A - Expansion-molded product having improved dimensional stability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a container for storing mechanical and electrical parts to which ultrahigh dimensional stability is required and a delivery box most suitable as a tray for an industrial robot, etc., and the like. SOLUTION: This expansion-molded product is composed of a styrenic resin foam having 0.4-0.05 bulk specific gravity, contains a residual foaming agent therein in an amount of <=3 wt.% based on the weight thereof, has -0.5 to 0% rate of dimensional change as compared with the previous state when left in an oven at 50 deg.C for 100 days and has dimensional stability. The styrenic-base resin of the foam preferably contains a polyolefin resin having a low molecular weight in an amount of 0.1-10 pts.wt. and a styrene resin having a low molecular weight in an amount of 1-30 pts.wt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a styrene-based resin foam molded article having a small dimensional shrinkage over a long period of time and excellent dimensional stability. The present invention also relates to a foam molded article having flame retardancy of 26 or more in an oxygen index value in a combustion test defined by JIS-K-7201, in addition to excellent dimensional stability. The foamed molded article according to the present invention further includes a container for storing mechanical parts, electric parts, and the like that require a high degree of flame retardancy and dimensional stability, and a tray for a robot used in an assembly line by an industrial robot. The present invention can provide an optimum return box and the like.

[0002]

2. Description of the Related Art In an assembly line in which an industrial robot is used, a returnable box (tray) or the like on which parts are placed includes:
Recently, for example, a foamed product of a styrene-based resin has been used, but this type of foamed product is required to have a much higher dimensional stability than ever before due to the nature of its use. . This is because when assembling a machine or the like using an industrial robot, it is necessary to extremely accurately position components handled by the robot. If the dimensional change occurs in the foam molded product (tray) on which the parts are placed, and the position of the parts placed on this tray deviates even slightly from the predetermined position, the industrial robot cannot cope with this positional deviation. As a result, a desired operation cannot be performed, and as a result, a stop of the production line or a defective assembly occurs. Therefore, to prevent these troubles beforehand,
It is important how to reduce the dimensional change of the foam molded article.

[0003] On the other hand, several proposals and attempts have been made with respect to the dimensional stability of foamed styrene resin products. Japanese Patent Publication No. 111181/1986 discloses that a foamed polystyrene molded article is heated at normal pressure or reduced pressure for several hours or more to equilibrate a blowing agent gas pressure in the molded article with atmospheric pressure, thereby obtaining a dimension of the molded article. The present invention discloses a method for stabilizing the size of expanded polystyrene, which comprises forcibly shrinking the foamed polystyrene to the vicinity of a desired size. According to the contents of this publication, the molded article obtained is molded in air at 45 to 70 ° C. after molding.
It is necessary to leave the mixture at room temperature for 2 to 24 hours at room temperature or 65 ° C. under reduced pressure. However, assuming a case where this method is actually used in a production factory, in order to perform these dryings, a new drying facility must be created and molded articles must be sequentially put into the equipment, which makes the work complicated. is there. Further, as a foaming agent for foamed polystyrene, flammable gases such as butane and pentane are usually used, but since these foamed gases escape during the heating and drying, the drying equipment has a high explosion-proof property. Needed. Therefore, introduction of the drying equipment requires huge equipment costs and is not practical. JP-A-61-207448 discloses a copolymer comprising an aromatic vinyl monomer and a polyfunctional monomer copolymerizable therewith and having a gel content of 30% by weight or more. A united foam molded product (expansion ratio 3 to 15 times) is disclosed. In this publication, as the evaluation of the dimensional stability performance, the dimensional change rate on the 7th day after molding and the change rate of the molded article on the 90th day after molding are obtained, and the dimensional change rate over time is represented by the difference between the two. . Therefore, the observation period of the change with time is 90-7 = 83 days, and the room temperature (19 to 20 ° C.)
Only the dimensional change data during this period is taken. However, when a foamed molded product is usually used as a tray for a robot, its use period is as long as one year or more, and it is particularly important to evaluate the long-term dimensional stability of the foamed molded product over time. However, this publication does not provide evaluation data over a longer period than the above period. Japanese Patent Publication No. 4-38222 discloses that, after heating polyethylene-styrene copolymer resin containing an easily volatile foaming agent, pre-foamed foamed particles are allowed to stand at room temperature for 2 to 14 days, and then filled in a mold. Heat molding to obtain a foam molded product, 40-60 ° C
A production method for aging the foamed molded product at a temperature of 4 hours or more, preferably 8 hours or more. In this publication, since polyethylene-styrene copolymer resin is used,
It is stated that the foaming agent and the solvent remaining in the foamed molded product easily escape and the dimensions of the foamed molded product are stabilized. But,
In this publication, a method is employed in which the pre-expanded particles are allowed to stand for 2 to 14 days (one week in Examples), and it is necessary to age the molded article in a drying chamber. Usually, the maturation period of the pre-expanded particles is about 8 hours to 1 day, but leaving for one week (example) after pre-expansion as in the method of Japanese Patent Publication No. 4-38222 requires a special hopper. In this case, the pre-expanded particles are stored as they are in the (air-permeable bag for storing the pre-expanded particles) for one week, during which time the hopper cannot be used, which is extremely inefficient in production. In addition, in order to dry the molded product, there is a problem that special equipment is required as in the case of Japanese Patent Publication No. 61-11183. Furthermore, this Tokuhei 4-3
In the evaluation of dimensional stability described in Japanese Patent No. 8222, data of 6 months storage at room temperature is shown.
The dimensional change rate during this period is 0.5 to 1.2% (Example)
Therefore, it is not suitable for the field where precise dimensional stability is required, such as a robot tray.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a stable size which does not undergo aging over a long period of time without aging in a drying chamber or using a special resin composition as shown in the above prior art. The point is to obtain a foam molded product to be retained. Heretofore, it has been vaguely known that a styrene-based resin foam molded article has a small dimensional change rate when the amount of a foaming agent and a foaming aid contained in the molded article is small. However, it was unclear how much the amount of the dimensional change would be reduced. Further, in order to evaluate the degree of dimensional change over time, it is necessary to take measurement data of the dimensional change rate over as long a period as possible. These tests are for evaluating the dimensional stability in a short period of one year, and do not describe an evaluation test for measuring the dimensional change rate over a longer period. For this reason, when the foam molded article is actually used as a robot tray for a long period of time (one year or more), it has not been confirmed how much dimensional stability performance can be maintained as it is. Furthermore, recently, these trays may require a high degree of flame retardancy due to safety concerns.
In general, a molded article made of an expandable styrene resin is a combustible material, and therefore, there is a risk of ignition or fire due to sparks, heat, or the like in an assembly line, and its use has naturally been limited. Therefore, the present inventors have conducted intensive studies to achieve the above object. As a result, first, 1) the correlation between the amount of the foaming agent and the amount of the foaming aid in the molded article and the dimensional change rate was clarified, and thereby, it was possible to obtain a foam molded article having improved dimensional stability. I found it. The present inventors have also studied 2) a method for simply measuring the dimensional change over time over a long period of time, and by limiting the range of the dimensional change over time of the foam molded article based on the method, the conventional method has been proposed. It has been found that a styrene-based resin foam molded product that is optimal for robot trays and the like that maintains high dimensional accuracy for a long time can be obtained.

[0005]

That is, the present inventors have found that the dimensional change rate of a foamed molded product obtained from expandable styrene resin particles, the amount of the foaming agent and the foaming agent remaining in the molded product. The close relationship with the amount of auxiliaries is as follows. When the amount of the foaming agent (or foaming agent and foaming aid) remaining in the foamed molded product exceeds 3% by weight in the foamed styrene resin having a bulk specific gravity of 0.4 to 0.05. Shows that the dimensional change rate (degree of dimensional shrinkage) of the molded product is -0.1 in one year even at room temperature compared to before the standing.
While the value is as high as 6% to -0.8%, when the amount of the blowing agent is 3% by weight or less, the dimensional change rate can be as low as -0.3% to 0%. It is. In addition, the inventors of the present invention have conducted a test for accelerating the aging of foamed styrenic resin molded articles, and found that the value of the dimensional change rate of the foamed molded article when the foamed molded article was left in an oven at 50 ° C. for about one month. Finds that the same foam molded article is substantially equal to or equivalent to the value of the dimensional change rate of the foam molded article when left at room temperature for one year (see Examples below).
Therefore, the degree of time-dependent dimensional change of the foamed molded article when left at room temperature for 3 years is evaluated by substituting the measured value of the dimensional change rate when the foamed molded article is left in an oven at 50 ° C. for 100 days. I came to the conclusion that I can. Therefore, in order to obtain the desired foam molded article in the present invention, the dimensional change rate when left in an oven at 50 ° C. for 100 days due to a reduction in the content of the foaming agent or the like is −0. Any material having dimensional stability of 5% to 0% may be used. Therefore, the present invention relates to a foamed molded article made of a styrene resin foam having a bulk specific gravity of 0.4 to 0.05, and a foaming agent (or a foaming agent and a foaming aid) remaining in the molded article. Is not more than 3% by weight based on the weight of the foamed molded article, and when the foamed molded article is left in an oven at 50 ° C. for 100 days, the dimensional change rate of the foamed molded article is as follows: -0.5 compared to
% To 0%, with improved dimensional stability. The preferred blowing agent is pentane or butane. In addition, the foamed molded article of the present invention is preferably prepared by adding a low-molecular-weight polyolefin resin to the styrene-based base resin in an amount of 0.1% based on the total amount of the base resin.
It is a foam molded product containing 1 to 10 parts by weight. In this case, the low molecular weight polyolefin resin has a weight average molecular weight of 5
A low molecular weight polyethylene of from 00 to 10,000,
It is desirable that the melting point is 100 to 130 ° C.
Further, among the foamed molded articles of the present invention, those containing a low molecular weight styrene resin having a weight average molecular weight of 500 to 100,000 in an amount of 1 to 30 parts by weight based on the total amount of the styrene base resin are preferable. The present invention also provides a foam molded article having improved flame retardancy, more specifically, hexabromocyclododecane, tetrabromocyclooctane, tetrabromobisphenol A or a diallyl ether thereof as a flame retardant. The present invention relates to a foam-molded article characterized in that it contains 0.5 to 20 parts by weight, based on the total amount of a styrene-based base resin, of an organic bromine-based flame retardant comprising one or more selected optional combinations. In this specification, the term "styrene-based base resin" means not only a main resin component (base resin) such as a styrene-based resin and a styrene-based resin blend or copolymer, but also other than a foaming agent. And various additives, modifiers and auxiliaries as necessary.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The (volatile) blowing agents used in the present invention include, for example, propane, butane, n-pentane,
Aliphatic hydrocarbons such as isopentane and hexane, or
Halogenated hydrocarbons such as methyl chloride and freon are used. These volatile blowing agents may be used alone,
Moreover, you may use it in combination of 2 or more types. However, aliphatic hydrocarbons that do not easily cause environmental destruction are preferably used. Butane or pentane is more preferably used, and pentane is most preferably used, in view of the fact that the residual amount of the blowing agent in the case of a foam molded article is small. When aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, and isomers thereof are used alone or in combination, an aromatic hydrocarbon such as toluene, xylene or ethylbenzene, or butyl acetate or the like is used. Solvents such as esters, known and commonly used solvents such as toluene, ketone and acetone can also be used in small amounts as foaming aids. The total amount of the foaming agent and the foaming aid (hereinafter sometimes abbreviated as the amount of the foaming agent) added to the styrene-based base resin which is the raw material of the foam molded article having dimensional stability of the present invention is defined as In order to reduce the amount of the foaming agent remaining in the foamed molded product to 3% by weight or less, it is desirable that the amount is smaller than the amount added to the base resin of the conventional general foamed molded product. Therefore, the amount will usually be in the range of 1 to 6 parts by weight based on the weight of the styrene base resin particles. From the viewpoint that a smaller amount is suitable, the amount of the blowing agent is preferably about 1 to 4.5 parts by weight, and more preferably about 1 to 3.5 parts by weight. When the aging time after the pre-expansion of the expandable styrenic resin particles is set in a normal range (8 hours to 1 day), and when the general expandable styrenic resin particles are used, the expanded molded article In order to suppress the amount of the foaming agent or the total amount of the foaming agent and the foaming auxiliary therein to 3% by weight or less, the amount of the foaming agent added is generally 3.5% by weight based on the weight of the expandable styrene resin particles.
The following settings are usually required: However, 3.
When a foaming agent amount of 5% by weight or less is used, the foaming time is extremely long when a foamed product having a desired bulk specific gravity of 0.1 to 0.05 is obtained at a relatively high foaming ratio. It is not practical. Therefore, in an attempt, a low-molecular-weight polyolefin resin was mixed into a styrene-based resin as a base material.
As a result, the low-molecular-weight polyolefin resin has an effect of enabling to obtain a foam molded article having a desired expansion ratio even with a low foaming agent amount, and at the same time, an effect of efficiently dissipating the foaming agent from the foamed resin particles. Has been found to significantly contribute to the improvement of dimensional stability. When 0.1 to 10 parts by weight of the low molecular weight polyolefin resin is added based on the total amount of the styrene base resin, a desired expansion ratio can be obtained even with a foaming styrene resin having a low foaming agent amount of 3.5 wt% or less. It is possible to obtain a foamed molded product, and since the blowing agent quickly escapes from the pre-expanded particles after the pre-expansion,
A foam molded article having a foaming agent amount of 3.0% by weight or less can be obtained within a general aging time. As the low-molecular-weight polyolefin resin, low-molecular-weight polypropylene, polyethylene or a mixture thereof can be used, and in particular, the weight-average molecular weight is 500 to 10,000 and the melting point is 100 to 1
Low molecular weight polyethylene at 30 ° C. is preferred. The addition amount of the low molecular weight polyolefin resin is 0.1 to 10 parts by weight, for example, 0.5 to 10 parts by weight, preferably 0.3 part by weight based on the total amount of the styrene-based base resin. To 3 parts by weight. If the amount is less than 0.1 part by weight, the effect of mixing the low-molecular-weight polyolefin resin cannot be obtained as expected, and if it exceeds 10 parts by weight, the fusion of the molded article is extremely reduced. This is not preferred. Accordingly, a preferred embodiment of the present invention is a low-molecular-weight polyolefin resin, preferably a low-molecular-weight polyethylene resin having a weight-average molecular weight of 500 to 10,000 and a melting point of 100 to 130 ° C, a styrene-based base resin. 0.1 to 1 based on the total amount of
The above foam molded article characterized by containing 0 parts by weight.

Further, when a low-molecular-weight styrene resin is added to the styrene-based base resin in addition to the addition of the low-molecular-weight polyolefin, the addition of the low-molecular-weight polyolefin synergistically improves the expansion ratio. It was found that there was an action to dissipate the foaming agent. Further, the addition of the low molecular weight styrene resin may be replaced by the addition of the low molecular weight polyolefin. By using a low-molecular-weight styrene resin, a foamed molded article having a desired expansion ratio can be obtained even with expanded styrene-based resin particles having a low foaming agent amount of 3.5% by weight or less. Since the blowing agent quickly escapes from the particles, the amount of the blowing agent becomes 3.0% by weight or less within a general aging time. The low molecular weight styrene resin may have a weight average molecular weight of 500 to 1
00000, preferably 5000 to 100000 are used. The addition amount of the low molecular weight styrene resin is 1 to 30 parts by weight, preferably 3 to 10 parts by weight based on the total amount of the styrene resin as the base resin.
If the amount is less than 1 part by weight, the effect of the above-mentioned addition is hardly observed. If the amount exceeds 30 parts by weight, the strength of the foamed molded article is extremely lowered, which is not preferable. Therefore, a preferred embodiment of the present invention is that the weight average molecular weight is 500 to 10
The foam-molded article according to the above, wherein the low-molecular-weight styrene resin having a molecular weight of 0000 is contained in an amount of 1 to 30 parts by weight based on the total amount of the styrene-based base resin.

Further, the present inventors have obtained a foamed molded article having a high flame retardancy, that is, an oxygen index of 26 or more in a combustion test defined by JIS-K-7201, in addition to the dimensional stability described above. Was investigated, and it was found that a foamed molded article having flame retardancy can be obtained by adding a specific organic bromine-based flame retardant. Therefore, the present invention is selected from the group consisting of hexabromocyclododecane, tetrabromocyclooctane, tetrabromobisphenol A, and diallyl ether thereof as a flame retardant for the styrene-based base resin of a foam molded article having dimensional stability. The present invention also relates to the above foam molded article, characterized in that the foam molded article contains an organic bromine-based flame retardant composed of one or two or more optional combinations based on the total amount of the styrene-based base resin. . Flame retardants that can be used in the present invention, in addition to those described above, pentabromomonochlorocyclohexane, brominated polystyrene, brominated aromatic triazine compounds, especially 2,2
4,6- (Tris-2,4,6-tribromophenoxy) -1,3,5-triazine or the like may be used alone or in combination of two or more.
3-dimethyl-2,3-diphenyl butane, 3,4-dimethyl-3,4-diphenyl hexane, dicumyl peroxide, Sb ₂ O ₃ and the like. Of the above flame retardants, hexabromocyclododecane is preferable, and it is also preferable to use 2,3-dimethyl-2,3-diphenylbutane as a flame retardant auxiliary. The amount of the flame retardant and the flame retardant auxiliary added to the styrene-based base resin is 0.5 to 20 parts by weight, preferably 0.3 to 10 parts by weight, based on the total amount of the styrene-based base resin, Particularly preferably 0.5 to 7 parts by weight, and the flame retardant aid is 0.1 to 2.0 parts by weight, preferably 0.2 to 1.0 part by weight. This is not preferable because the physical properties of the foamed molded article deteriorate. Incidentally, as a raw material of the expanded molded article of the present invention, when producing expandable polystyrene resin particles containing a flame retardant, the addition of a flame retardant and a flame retardant auxiliary, during polymerization,
For example, it may be added at the initial stage of suspension polymerization or when a certain degree of polymerization conversion has been reached.Flame retardant such as dispersing a flame retardant and a flame retardant auxiliary together with expandable resin particles in an extruder. This is performed by performing a chemical conversion treatment. In the case of the present invention, in particular, even if a flame retardant or the like is added at the time of extrusion processing, the properties of the obtained expandable resin particles are not impaired, and they work effectively. The foam molded article of the above aspect of the present invention has an oxygen index value of 26 depending on the flame retardant contained therein.
As it can secure the above high flame retardancy, it has self-extinguishing properties, so it burns temporarily when exposed to flame, but it is extinguished naturally when the flame is removed, so it can be used safely. . These flame-retardant foamed molded products having good dimensional stability are used for containers for storing mechanical parts, electric parts, etc., and for robots that have been difficult to use in places where fires are conventionally used. It is most suitable for use as a tray for a secondary battery manufacturing process in addition to a tray.

The styrenic resin serving as a base resin in the foam molded article having dimensional stability of the present invention is not limited to a homopolymer of a styrenic monomer, but may be a copolymer (a) with another monomer ( Styrene-based monomer in a proportion of 50% by weight or more). The styrenic monomers include substituted styrenes such as α-methylstyrene, ethylstyrene, p-chlorostyrene, etc., in addition to styrene alone.
Further, the other monomer of the copolymer, methyl methacrylate, methyl acrylate, butyl methacrylate,
Examples thereof include (meth) acrylates such as butyl acrylate, and vinyl monomers such as acrylonitrile, vinyl toluene, and vinyl carbazole. These may be used alone or in combination of two or more. Therefore, as the styrene resin used in the present invention,
Other than polystyrene, poly α-methylstyrene, poly p-
In addition to polysubstituted styrene such as chlorostyrene, a copolymer of styrene and substituted styrene (for example, α-methylstyrene), a copolymer of styrene and a vinyl monomer (for example, acrylonitrile), and the like can be given. . More preferred styrene resins include polystyrene, polystyrene-butadiene copolymer, polystyrene-maleic anhydride copolymer, polystyrene-acrylonitrile copolymer, styrene graft copolymer, and the like.
Further, it may be selected from a copolymer with a styrene-maleimide derivative, a styrene-acrylate copolymer, a styrene-methacrylate copolymer, and a styrene copolymer such as a styrene-acryl or methacrylic acid copolymer. It is possible. More preferred are α-methylstyrene-styrene copolymer, α-methylstyrene-acrylonitrile copolymer and styrene-α-methylstyrene-acrylonitrile terpolymer. Where α
-Methylstyrene or the total amount of styrene and α-methylstyrene must be at least 50 parts by weight based on 100 parts by weight of the total resin. Also, as the styrene resin,
Usually, a weight average molecular weight of 150,000 to 500,000
0, more preferably 200,0 weight average molecular weight
A high molecular weight styrenic resin having a number of from 00 to 300,000 is used, but it is also possible to partially blend a lower molecular weight styrenic resin as described above. The styrene-based resin includes, in addition to the above-mentioned polyolefin resin, a resin in which another resin such as a polyphenylene ether-based resin is blended in an amount of 50% by weight or less.

[0010] The styrene resin is not limited to a styrene resin newly synthesized by suspension polymerization.
A styrene-based resin regenerated by recycling (recycling) a styrene-based resin foam or the like is used. It is preferable to use the regenerated styrene resin as a raw material for the expandable styrene resin particles from the viewpoint of resource reuse and environmental protection. Therefore, in recent years, the use of recycled styrenic resins is rapidly advancing. In the regenerated styrenic resin, the styrenic resin and the styrenic resin foam which were distributed and used in the market were recovered, and then the foam was reduced in volume by melting or the like, and then recovered. The styrene-based resin is finely pulverized by cutting, and the pulverized material is put into an extruder and extruded to obtain pelletized styrene-based resin particles (so-called regenerated pellets). In a production plant for expandable styrene resin particles,
Off-grade expandable styrenic resin particles produced during the production process, that is, having a particle size of less than 0.5 mm or a particle size of 2
recover foamable styrene-based resin particles outside the required quality that are not suitable for general use of styrene-based resin foam exceeding
By extruding this, the regenerated pellets obtained are also regenerated styrene resin,
It can be used for the styrene base resin in the present invention.

The above-mentioned styrenic base resin is generally produced by suspension polymerization of a styrenic monomer or the like in an aqueous medium. These suspension polymerizations are carried out in an aqueous suspension system containing a radical polymerization initiator, a dispersant and a dispersing aid. Examples of the radical polymerization initiator include polymerization initiators used in general radical polymerization, for example, organic peroxides such as benzoyl peroxide, butyl perbenzoate, t-butyl peroxybenzoate, and azobisisobutyro. An azo compound such as nitrile is exemplified. In addition, examples of the dispersant to be used include poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium phosphate, and hydroxyapatite, and organic polymer compounds such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose. Further, as the dispersing aid used in combination with the above dispersant, dodecyl phenyl oxide disulfonate, sodium dodecyl benzene sulfonate, anionic surfactants such as sodium α-olefin sulfonate, polyoxyethylene alkyl ether, Nonionic surfactants such as polyoxyethylene octyl phenol ether are exemplified.

The styrenic base resin used for the dimensionally stable foam molded article of the present invention may optionally contain a plasticizer (for example, DOP, DOA, DB, etc.) for improving the expansion ratio.
P, coconut oil, palm oil, stearic acid, etc.), inorganic or organic nucleating agents (for example, talc, bentonite,
Ethylene bisstearic acid amide, zinc stearate, etc.), a cell forming agent, a coloring agent, a lubricant, an antistatic agent and the like can be added in appropriate amounts. These chemicals are appropriately selected and used from those conventionally used in expandable styrene resin particles, and are added in the step of extruding the styrene base resin or the step of impregnating the blowing agent.

Except for the case where off-grade expandable styrene resin particles already containing a blowing agent are used as a raw material, the styrene resin particles are usually impregnated with a blowing agent. Therefore, the above-mentioned suspension-polymerized styrene-based base resin is formed into a particle form or a pellet form by extrusion molding, and an expandable styrene-based resin particle is produced by impregnating it with a foaming agent. That is, expandable styrene resin particles produced by extrusion are usually obtained by, for example, three methods. 1) Styrene-based resin particles (extruded pellets) in the form of pellets are produced by extrusion molding of a styrene-based resin. In this case, additives such as the above-described flame retardant are also added to the styrene-based resin, The resulting extruded pellets are dispersed in an aqueous suspension system, and a foaming agent is press-fitted into the dispersion system, and then appropriately heated to impregnate the extruded pellets, thereby forming a foamable styrene system in a pellet form. How to make resin particles. 2) A system in which the styrene-based base resin is melt-kneaded in the extruder during the process of extruding the styrene-based base resin in the extruder to melt-knead the styrene-based base resin in a molding machine. A method for producing foamable styrene-based resin particles in the form of pellets by adding a foaming agent therein to impregnate and adding an additive such as the above-described flame retardant to the styrene-based base resin at the time of extrusion molding. 3) When using off-grade expandable styrenic resin particles as a raw material, knead them alone or in combination with another resin such as styrene, or with an additive such as the above-mentioned flame retardant in an extruder, A method of producing foamable styrene resin particles in the form of pellets by subsequent extrusion.

The foamable styrenic resin particles or pellets thus produced are usually subjected to a sufficient drying treatment using a drier or the like, and then separated into particles having a predetermined particle size by a sieving machine. Next, a blending agent such as a lubricant and an antistatic agent is mixed with the separated expandable styrene resin particles or pellets, and then sealed and packed in a drum or the like. Thus, the stored expandable styrene resin particles or pellets are pre-expanded to any apparent specific gravity as necessary, and then, according to a conventional method, the pre-expanded particles are filled in a mold such as a mold, and steam is discharged. By heat-foaming using, the pre-expanded particles are fused to each other to produce a foam molded article (foam) having dimensional stability of a desired shape (dimension).

[0015]

The present invention will be described in more detail with reference to the following examples, but these examples are not intended to limit the present invention.

Examples 1 to 4 and Comparative Examples 1 to 3 1800 g of ion-exchanged water was charged into an autoclave having a content of 5 liters equipped with a Fiddler-type stirrer, and 5.4 g of tricalcium phosphate and sodium dodecylbenzenesulfonate were added to each other. 0.05g was added and mixed well and stirred. To the system, 1800 gr (100 parts by weight) of a styrene monomer, 5.4 gr of benzoyl peroxide and 1.8 gr of t-butylperoxybenzoate as a polymerization initiator were added, and the temperature was raised to 90 ° C. while stirring. The polymerization was allowed to proceed for a period of time to produce polystyrene particles. After completion of the polymerization, n-pentane as a blowing agent was press-fitted into the autoclave in an amount shown in Table 1 below, and the system was heated to 120 ° C. and maintained for 6 hours to convert the blowing agent into polystyrene. The particles were impregnated. After this treatment, the polymerization reaction system was cooled to room temperature, and the formed expandable styrene resin particles were taken out of the vessel, and trilime phosphate adhering to the particle surfaces was removed by acid washing. Thereafter, water adhering to the particle surface was removed through a centrifugal separation or drying step, and particles having a particle diameter of 0.7 to 1.0 mm were separated by sieving. After aging these particles at room temperature for 5 days, they were prefoamed with steam at 101 ° C. to a bulk magnification of 10 times (bulk specific gravity of 0.1). After the obtained pre-expanded particles were aged at room temperature for 24 hours, they were charged into a molding die of an automatic molding machine and heated at a pressure (gauge pressure) of 0.7 kg / cm ^{2 for} 8 seconds.
A 30 × 30 × 5 cm foam molded product produced by water-cooling and allowing the mold to cool was taken out and used as a sample for dimension measurement.

After molding, the amount of the foaming agent contained in the molded article is 1
A part of the foamed molded product on the day is taken, its weight is measured, it is kept in an oven at 150 ° C. for 1 hour, and then its weight is measured again. ]. Similarly, the amount of the foaming agent contained in the expandable styrene-based resin particles before molding was also measured by taking a part of the expandable styrene-based resin particles before prefoaming and measuring the weight by 150. The temperature was kept in an oven at a temperature of 1 ° C. for 1 hour, and then the weight was measured again.

(Equation 1) The results are shown in Table 1.

[Table 1] Next, in order to evaluate the dimensional stability performance of the foam molded article, the relationship between the amount of the foaming agent contained in the foam molded article and the dimensional change rate of the molded article with time was examined. As described below, the rate of dimensional change over time of the foamed molded product is expressed by the following [Formula-2] or
It was determined according to [Equation-4]. Regarding the foamed molded article, first, the dimensional change rate of the molded article on the first day after molding was calculated based on the following [Equation-2], and this value was used as a reference value before leaving. The dimensional change rate of the foamed molded article at room temperature was determined from the difference between the dimensional change rate with respect to the mold at the time when the molded article was left at room temperature for a predetermined number of days and the above-mentioned reference value, according to the following [Equation 3]. The dimensional change rate of the foamed molded article when left in an oven at 50 ° C. is calculated according to the following [Equation-4].
It was determined from the difference between the dimensional change rate with respect to the mold at the time when it was left for a predetermined number of days in a 50 ° C. oven and the reference value. Even if the dimensional change rate of the foamed molded product on the first day after molding is large, it is not a problem since the change rate may be considered in advance in the mold design stage. On the other hand, the dimensional change rate with time is desirably as small as possible.

(Equation 2)

(Equation 3)

(Equation 4)

The dimensional change rate of the foam molded article over time when the samples of Example 1 and Comparative Example 1 were left at room temperature and the dimensional change rate over time of the foam molded article when left in an oven at 50 ° C. are graphs. And FIGS. 1 and 2 respectively.
It was shown to. In the graph shown in FIG. 1, the dimensional change rate of the foamed molded article after about one year of standing at room temperature was − in the sample of Example 1 in which the amount of the foaming agent contained in the foamed molded article was 1.2% by weight. Although it is 0.2% or less, in the sample of Comparative Example 1 in which the amount of the foaming agent contained in the foam molded article is 3.5% by weight, the dimensional change rate of the foam molded article is about -0.7%. It turns out that it is very large. In the graph shown in FIG. 2, in the sample of Example 1 in which the amount of the foaming agent contained in the foam molded article is 1.2% by weight, the foam molding on the 100th day when left in an oven at 50 ° C. The dimensional change of the product is about -0.2%
However, the amount of the foaming agent contained in the foam molded article is 3.5
In the sample of Comparative Example-1 which is% by weight, a remarkable dimensional shrinkage of about -1% was observed in the dimensional change of the foam molded article. Also, from the graph shown in FIG. 1 and the graph shown in FIG.
It is clear that the value of the dimensional change of the foamed article for about one month when left in an oven at ℃ C substantially corresponds to or corresponds to the dimensional change of the foamed article for about one year when left at room temperature. is there. Therefore, it is estimated that leaving the foamed molded article in the oven at 50 ° C. for 100 days is equivalent to leaving the foamed molded article at room temperature for about 3 years. The degree of dimensional change over time of the foamed molded article when left at room temperature for 3 years can be evaluated based on the actually measured value of the dimensional change rate. In addition, the amount of the foaming agent in the foamed molded product and 50 ° C.
The relationship between the dimensional change rate of the foam molded article when left in an oven for 100 days is shown on the basis of the data of the samples of Examples -1 to 4 and Comparative Examples -1 to 3 shown in Table 1. And shown in FIG. According to the graph shown in FIG. 3, when the amount of the foaming agent contained in the foamed molded product exceeds 3% by weight, the dimensional change rate of the foamed molded product when left in an oven at 50 ° C. for 100 days increases, It can be seen that the product shrank significantly.

Example-5 100 parts by weight of styrene resin particles already containing 4% by weight of n-pentane as a blowing agent, and a weight average molecular weight of 100
0, 1 part by weight of polyethylene wax having a melting point of 111 ° C. is put into an extruder, which is melted by heating, kneaded with a screw, extruded in the form of a strand, and then cut by a rotary pelletizer. Thus, foamed resin pellets containing a foaming agent were obtained. The pellets were prefoamed in the same manner as in Example 1, and then foamed and evaluated. Example-6 In Example-5, the weight average molecular weight was 300 at the time of extrusion.
0 and the same procedure as in Example-5 except that 2 parts by weight of polyethylene wax having a melting point of 128 ° C. was added. Example-7 In Example-5, a weight average molecular weight of 100 was obtained at the time of extrusion.
Example 5 was repeated except that 1 part by weight of polyethylene wax having a melting point of 111 ° C. and 1 part by weight of a low-molecular-weight styrene resin having a weight average molecular weight of 50,000 were added. Example-8 In Example-5, the weight-average molecular weight at the time of extrusion was 100.
0, the same as Example-5 except that 1 part by weight of a polyethylene wax having a melting point of 111 ° C., 5 parts by weight of a low-molecular-weight styrene resin having a weight average molecular weight of 50,000, and 10 parts by weight of hexabromocyclododecane as a flame retardant were added. I went to.

Comparative Example 4 The procedure of Example 5 was repeated except that no polyethylene wax was added. Comparative Example-5 The same procedure was performed as in Example-5, except that the bulk specific gravity of the foam molded article was changed to 0.04. Comparative Example-6 Example 5 was repeated except that 100 parts by weight of styrene resin particles already containing 5% by weight of n-pentane were used as the blowing agent. The results for Examples 5 to 8 and Comparative Examples 4 and 6 are summarized in Table 2.

[Table 2]

1) Comparison of Example-5 and Example-6 with Comparative Example-4 shows that the addition of polyethylene wax reduces the amount of the blowing agent in the foam molded article.
When the amount of the foaming agent in the foamed molded product exceeds 3% by weight, the dimensional change of the foamed molded product after 100 days of standing in an oven at 50 ° C. also becomes large. 2) When a styrene resin having a lower molecular weight than that of Example-7 was further added, the amount of the foaming agent in the foamed molded article was further decreased, and the dimensional change rate of the foamed molded article after 100 days of standing in an oven at 50 ° C. was also reduced. is decreasing. 3) Example-8 is an example in which a flame retardant was added to Example-7. The foam molded article of this example is JIS-K-7201.
In the combustion test specified in, the dimensional change of the foamed molded article after 100 days of standing in a 50 ° C. oven is small while the oxygen index value is 26 or more. 4) Comparative Example-5 has a bulk specific gravity of 0.04 (expansion ratio 25 times)
When the specific gravity is reduced, even if the amount of the foaming agent in the foamed molded product is 3% by weight or less, the foamed product is left in an oven at 50 ° C.
It can be seen that the dimensional change of the foam molded article on the day is large. 5) In Comparative Example-6, the amount of the foaming agent in the foam molded article was 3% by weight.
However, the dimensional change after 100 days of leaving the foam molded article in a 50 ° C. oven was large.

[0022]

As described above, according to the present invention, it is possible to obtain a molded article having stable dimensions which is not affected by aging over a long period of time without aging in a drying chamber or using a special resin composition. According to the present invention, the dimensional change when the foamed molded article is left at room temperature for about 3 years is -0.1 as compared with before the standing.
A foam molded article having excellent dimensional stability of 5% to 0% is obtained. Therefore, the foam molded article of the present invention is most suitable for containers for storing mechanical parts, electric parts, and the like that require extremely high dimensional stability, and for robot trays used in assembly lines by industrial robots. Can be used for applications such as boxes. Further, the foamed molded article of the present invention containing a specific flame retardant is also JIS-K-720.
It is an excellent foam molded article having a high flame retardancy of 26 or more in the oxygen index value in the combustion test specified in 1. Therefore, the foamed molded article of the present invention can secure a high degree of flame retardancy and has self-extinguishing properties, so that it burns temporarily when exposed to a flame, but is extinguished naturally when the flame is removed and used safely. It is possible to do. These molded articles having flame retardancy and good dimensional stability are most suitable for trays for the secondary battery manufacturing process in addition to the above-mentioned applications.

[Brief description of the drawings]

FIG. 1 shows Example-1 when left at room temperature for one year.
7 is a graph showing the relationship between the number of days at room temperature and the dimensional change rate of each of the foamed molded products of Comparative Example 1 and Comparative Example-1.

FIG. 2 is a graph showing the relationship between the number of days aged at 50 ° C. and the dimensional change rate of each of the foamed molded products of Example-1 and Comparative Example-1 when left in an oven at 50 ° C. for 100 days. It is.

FIG. 3 shows the amount of blowing agent contained in a foamed molded product and 50%.
It is a graph which shows the relationship with the dimensional change rate of the said molded article when left for 100 days in the oven of ° C.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C08L 25/04 C08L 25/04 // (C08L 25/04 (C08L 25/04 23:00) 23:00) (C08L 25/04 (C08L 25/04 23:04) 23:04) F-term (reference) 4F074 AA17 AA24 AA32 AB01 AB03 AD02 AD12 AG10 BA34 BA39 CA24 DA24 DA33 4J002 BB032 BB122 BC031 BC061 BC071 BC081 BC091 BC111 BC113 EB017 EB0EB EB067 EB067 EU186 FB133 FD136 FD327

Claims (5)

[Claims] 1. A foam molded article comprising a styrene resin foam having a bulk specific gravity of 0.4 to 0.05, wherein the amount of a foaming agent remaining in the molded article is based on the weight of the foam molded article. And the dimensional change of the foamed molded product when left in an oven at 50 ° C. for 100 days is from −0.5% to 0 % Foam molded article having improved dimensional stability. 2. The foam molded article according to claim 1, wherein the low-molecular-weight polyolefin resin contains 0.1 to 10 parts by weight based on the total amount of the styrene-based base resin. 3. The low molecular weight polyolefin resin,
The foam molded article according to claim 2, wherein the molded article is a low molecular weight polyethylene having a weight average molecular weight of 500 to 10,000 and a melting point of 100 to 130 ° C. 4. A weight-average molecular weight of 500 to 100,000
The foamed molded article according to claim 1, wherein the low molecular weight styrene resin is contained in an amount of 1 to 30 parts by weight based on the total amount of the styrene base resin. 5. An organic bromine compound comprising one or an arbitrary combination of two or more selected from the group consisting of hexabromocyclododecane, tetrabromocyclooctane, tetrabromobisphenol A and diallyl ether thereof as a flame retardant. The foamed molded article according to any one of claims 1 to 4, wherein the flame retardant is contained in an amount of 0.5 to 20 parts by weight based on the total amount of the styrene-based base resin.