JPH10139914A - Thermoplastic resin foam and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermoplastic resin foam being safe in respect of labor hygienics and environmental hygienics and having a high expansion ratio, a high closed-cell rate and improved appearance by mixing an expandable resin composition containing a thermoplastic resin, a dialkyl carbonate and a physical blowing agent under high-temperature high-pressure conditions and expanding the mixture by extrusion into a low-pressure zone. SOLUTION: 100 pts.wt. thermoplastic resin is mixed with 0.5-10 pts.wt. alkyl carbonate with a 1-4C alkyl and 1-50 pts.wt. at least one physical blowing agent selected among inorganic gases, hydrocarbons and fluorohydrocarbons to obtain an expandable resin composition. A melt obtained by kneading the mixture at 100-250 deg.C is injected into an extruder and expanded by extrusion through an expansion device such as a slit die into a low-pressure zone to obtain the thermoplastic resin foam having a mean cell diameter of 0.1-3mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermoplastic resin foam and a method for producing the same.

[0002]

2. Description of the Related Art At present, for example, when an extruded alkenyl aromatic resin foam is produced, a method using a physical foaming agent utilizing volume expansion due to a phase change from a liquid phase or a solid phase to a gas phase is mainly used. Has become. The physical foaming agent used here not only becomes foaming energy, but also exhibits a plasticizing function in the resin kneading step, and also has a function of adjusting the bubble size and controlling the growth rate of the bubbles in the foaming step. The inclusion in the cells of the manufactured foam has a great effect on the performance of the foam, especially on the thermal conductivity which governs the heat insulation. For this reason, the selection of such a physical foaming agent has been a major research issue when developing the extrusion foaming technology.

[0003] Conventionally, in the production of extruded alkenyl aromatic resin foams, as a sub-foaming agent, it has a plasticizing function in the extrusion system, reduces the melt viscosity of the resin, and expands to the extent that foam molding is possible. Chlorine-containing compounds such as methyl chloride and ethyl chloride which lower the temperature of the molten resin are used (Japanese Patent Publication No.
672).

[0004] However, from the viewpoint of occupational health, the working environment of methyl chloride and ethyl chloride is required to be preserved in a manufacturing plant. Therefore, from the use of chlorine-containing compounds such as methyl chloride and ethyl chloride,
There is a demand for an alternative to a foaming agent that is easy to handle on equipment.

[0005] In recent years, from the viewpoint of protection of the ozone layer, which has been sought out in recent years, the use of blowing agents such as inorganic gas, hydrocarbons, and fluorocarbons, which have a low risk of destroying the ozone layer, has been studied. JP-A-51-7068, JP-B-51-46536, JP-B-5-15735 and the like.

However, when these foaming agents are used alone, the plasticizing effect is not sufficiently exhibited, the foam molding temperature is increased, and the resulting foam has poor surface properties and a closed cell ratio. Tend to be low. Also,
Since most of these foaming agents have low solubility in alkenyl aromatic resins such as polystyrene resins, it is difficult to obtain a foam having a high expansion ratio by using these alone. Therefore, from various viewpoints, at present, a foam having few problems and having a high expansion ratio and a high closed cell ratio has not been obtained.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and uses a foaming agent having high safety in occupational hygiene and environmental hygiene to achieve a high expansion ratio and a high closed cell rate. It is an object of the present invention to provide a thermoplastic resin foam having a beautiful appearance and a method for producing the same.

[0008]

The present invention provides a foamable resin composition comprising a thermoplastic resin, a dialkyl carbonate (dialkyl carbonate) and a physical foaming agent (a physical foaming agent other than the dialkyl carbonate). Thermoplastic resin foam obtained by foaming a product, and a thermoplastic resin,
The present invention relates to a method for producing a thermoplastic resin foam, which comprises mixing a foamable resin composition containing a dialkyl carbonate and a physical foaming agent at a high temperature and a high pressure, and extruding the mixture in a low pressure range to foam.

[0009]

According to the method for producing a thermoplastic resin foam of the present invention, a foamable resin composition containing a thermoplastic resin, a dialkyl carbonate and a physical foaming agent is mixed at a high temperature and a high pressure. Thereafter, by extruding and foaming in a low pressure range, a thermoplastic resin foam can be produced.

The thermoplastic resin foam of the present invention uses a foaming agent having high safety in occupational health and environmental health, has a high expansion ratio, a high closed cell rate, and has a beautiful appearance. However, the reason why a foam having such excellent properties was obtained is based on repeated studies to solve the problems of the prior art.

That is, as a result of intensive studies conducted by the present inventors, a small amount of a dialkyl carbonate, which is not regulated in terms of occupational health and environmental health, is added to a thermoplastic resin, whereby a resin containing a chlorine-containing compound is added. The same effect as the plasticizing effect is obtained, it is possible to lower the molten resin temperature to the extent that foam molding is possible, and by using such a dialkyl carbonate and a physical foaming agent in combination, It has been found that a thermoplastic resin foam having a high expansion ratio and a high closed cell ratio and a beautiful appearance can be obtained.

The study of the plasticizing effect of the dialkyl carbonate as described above is based on the background art relating to the melt shear viscosity of the resin as described below.

In the extrusion foaming of an alkenyl aromatic resin, which is an example of a thermoplastic resin, generally, a volatile foaming agent is injected under pressure into a molten alkenyl aromatic resin, mixed under high pressure, and mixed with a die of an extruder. A method of extruding into the atmosphere, expanding rapidly, and foaming is adopted. On this occasion,
Due to the plasticizing effect of the volatile blowing agent, the extrusion temperature can be set lower than the melting temperature of the alkenyl aromatic resin. In addition, the foam film quickly solidifies and fixes due to the cooling effect of the volatile foaming agent due to the heat of vaporization during extrusion foaming.
The destruction of air bubbles can be prevented, and a foam having a high expansion ratio can be stably obtained.

FIG. 1A shows the relationship between the amount of methyl chloride added to 100 parts by weight of polystyrene and the melt shear viscosity of the polystyrene to which the methyl chloride was added (resin temperature: 170 ° C., shear rate: 122 s ⁻¹ ). A graph showing the relationship and FIG. 1B show the amount of ethyl chloride added to 100 parts by weight of polystyrene and the melt shear viscosity of the polystyrene to which the ethyl chloride was added (resin temperature: 170 ° C., shear rate: 1).
22s ^-1 ) is a graph showing the relationship.

As is apparent from FIGS. 1A and 1B, methyl chloride or ethyl chloride, which is usually used in the production of extruded polystyrene resin foam, is mixed with, for example, 4 parts by weight or more based on 100 parts by weight of polystyrene. It can be seen that when added, the melt shear viscosity is reduced by half compared to polystyrene alone.

Therefore, the present inventors have conducted various studies on substances which, when added to an alkenyl aromatic resin, sufficiently exhibit a plasticizing effect on the alkenyl aromatic resin and can be suitably used as a foaming agent. . as a result,
When the same amount of dialkyl carbonate as the methyl chloride or ethyl chloride is added to the alkenyl aromatic resin, a greater plasticizing effect may be exhibited than when the methyl chloride or ethyl chloride is added. Was found.

FIG. 1C shows the amount of dimethyl carbonate added to 100 parts by weight of polystyrene and the melt shear viscosity of the polystyrene to which the dimethyl carbonate was added (resin temperature: 170 ° C., shear rate: 122 s ⁻¹ ). 4 shows a graph representing the relationship with.

As is apparent from FIG. 1, when the same amount of dimethyl carbonate as methyl chloride or ethyl chloride is added, the melt shear viscosity of polystyrene is further reduced.

As described above, the use of a dialkyl carbonate is one of the major features of the present invention, and the combined use of the dialkyl carbonate and a physical foaming agent is also a major feature of the present invention. is there.

The thermoplastic resin used in the present invention is not particularly limited as long as it can be foamed.

Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene; polymethyl methacrylate; polyvinyl chloride; polyvinyl fluoride; ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene-diene. Copolymers of olefins and other monomers such as copolymers; ABS resins; alkenyl aromatic resins; copolymers having an alkenyl aromatic monomer content of 50% by weight or more;
Polyamides such as nylon, 66-nylon and 12-nylon; polyesters such as polyethylene terephthalate and polybutylene terephthalate; bisphenol A
Polycarbonate; polyphenylene oxide; polyacetal; polyphenylene sulfide, and the like. These can be used alone or as a mixture of two or more. Among these, alkenyl aromatic resins are particularly preferred because they are remarkably susceptible to the plasticizing effect of dialkyl carbonate described below.

Representative examples of the alkenyl aromatic resin include, for example, styrene; methyl such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene and trimethylstyrene. Styrene; chlorostyrene such as α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, trichlorostyrene; o-bromostyrene, m-bromostyrene, p-bromo Bromostyrene such as styrene, dibromostyrene and tribromostyrene; fluorostyrene such as o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, difluorostyrene and trifluorostyrene; o-nitrostyrene, m-nitros Nitrostyrenes such as len, p-nitrostyrene, dinitrostyrene and trinitrostyrene; vinylphenols such as o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene and trihydroxystyrene; o-divinylbenzene, p -Divinylbenzene such as divinylbenzene; o-diisopropenylbenzene,
homopolymers of alkenyl aromatic monomers such as diisopropenylbenzene such as m-diisopropenylbenzene, copolymers of two or more of the alkenyl aromatic monomers, methyl methacrylate, acrylonitrile, butadiene and the alkenyl aromatic monomers And the like, and copolymers with a copolymerizable monomer, and the like, and these can be used alone or in combination of two or more. Among these, polystyrene is particularly frequently used because of its low cost.

The dialkyl carbonate used in the present invention is, for example, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, di-isopropyl carbonate, di-n-carbonate, since it has a great effect of plasticizing a thermoplastic resin. Preferred examples include dialkyl carbonates having 1 to 4 carbon atoms in the alkyl group, such as -butyl carbonate, diisobutyl carbonate, disec-butyl carbonate, di-t-butyl carbonate, and the like. These can be used in combination. Among these, at least one selected from dimethyl carbonate and diethyl carbonate is particularly preferable because of its high solubility in a thermoplastic resin.

In order to sufficiently exhibit the effect of plasticizing the thermoplastic resin, the amount of the dialkyl carbonate should be 0.5 parts by weight or more, preferably 2 parts by weight or more based on 100 parts by weight of the thermoplastic resin. In order to sufficiently dissolve and uniformly disperse the dialkyl carbonate in the thermoplastic resin, the amount is preferably 10 parts by weight or less, especially 8 parts by weight or less based on 100 parts by weight of the thermoplastic resin. Is preferred.

Preferred examples of the physical foaming agent used in the present invention include inorganic gases, hydrocarbons, and fluorinated hydrocarbons from the viewpoint of high occupational safety and low possibility of destruction of the ozone layer. Is done.

Examples of the inorganic gas include a single gas such as carbon dioxide, nitrogen, air, water, neon, argon, and helium, and a mixed gas thereof.

Examples of the hydrocarbon include methane,
Ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane and the like can be mentioned.

Examples of the fluorinated hydrocarbon include fluoromethane, difluoromethane (HFC-32), trifluoromethane (HFC-23), perfluoromethane, 1-fluoroethane, 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoroethane (HFC-134a), pentafluoroethane, perfluoroethane, 2,2-difluoropropane, 1,1, Fluorocarbons such as 1-trifluoropropane, perfluoropropane, perfluorobutane, perfluorocyclobutane; chlorodifluoromethane (HCFC-22), 1,1-dichloro-1-fluoroethane (HCFC-142b), 1,1-dichloro-
2,2,2-trifluoroethane (HCFC-12
3) and chlorofluorocarbons such as 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124).

These physical foaming agents can be used alone or in combination.
Although more than one species can be used in combination, among these, inorganic gas, hydrocarbon and fluorocarbon that do not contain chlorine atoms in the molecule are particularly high in terms of safety with respect to destruction of the ozone layer. Particularly preferred.

The amount of the physical type foaming agent is selected from the group consisting of thermoplastic resin 100 and 100 to obtain a foam having a high expansion ratio.
1 part by weight or more, preferably 3 parts by weight or more based on parts by weight.
In order to improve the heat insulating property by preventing the bubbles from being broken, the amount is preferably 50 parts by weight or less, more preferably 40 parts by weight or less based on 100 parts by weight of the thermoplastic resin.

Further, in the present invention, if necessary, an antioxidant, a metal deactivator, a phosphorus-based stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent enhancer are used as long as the object of the present invention is not impaired. Stabilizers such as whitening agents, metal soaps, antacid adsorbents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments,
Generally used additives such as a flame retardant and an antistatic agent may be appropriately added to the foamable resin composition.

The thermoplastic resin foam of the present invention can be produced by a known extrusion foaming method. That is, for example, a foamable resin composition prepared by adjusting a predetermined amount of a thermoplastic resin and, if necessary, an additive, heating and kneading them, and then adding or press-fitting a dialkyl carbonate and a physical foaming agent thereto. Mix things under high temperature and pressure,
Then, the foam is extruded into a low pressure region and foamed to obtain the foam of the present invention.

There are no particular restrictions on the heating temperature, melt-kneading time and melt-kneading means when the foamable resin composition is heated and melt-kneaded. The heating temperature may be at least the temperature at which the thermoplastic resin melts, usually about 100 to 250 ° C. The melt-kneading time cannot be determined unequivocally because it differs depending on the extrusion amount per unit time, the melt-kneading means, etc., but usually, the time required for the thermoplastic resin and the additive to be uniformly dispersed is selected. It is. As the melt-kneading means, for example, a screw type extruder can be used, but there is no particular limitation as long as it is used in ordinary extrusion foaming.

The dialkyl carbonate and the physical foaming agent may be simultaneously added or press-fitted into the heat-melt kneaded material at the same time, or may be added or press-fitted in divided portions. However, the present invention is not limited by the method of adding or injecting the dialkyl carbonate and the physical foaming agent.

The pressure at which the dialkyl carbonate and the physical foaming agent are pressed into the heat-melt kneaded material is not particularly limited, and may be higher than the internal pressure of the extruder because it is pressed into the extruder. I just need.

The heat-melt kneaded material into which the dialkyl carbonate and the physical foaming agent have been added or press-fitted is then
For example, through a commonly used foaming device such as a slit die, for example, extrusion to a low pressure region such as under atmospheric pressure,
Foamed.

Thus, according to the method for producing a thermoplastic resin foam of the present invention, a thermoplastic resin foam mainly composed of cells having an average cell diameter of about 0.1 to 3 mm, which can meet the demand for excellent heat insulating properties. Can be obtained. The average cell diameter is represented by the average value of the diameters of all cells contained in a cross section 5 cm ² crossing the foam extrusion direction. In the case of a foam having a bimodal foam distribution, the size of large and small cells is measured for each of large and small cells, and the average value of the diameter of each large and small cell is shown.

The thermoplastic resin foam of the present invention has a high expansion ratio, a high closed cell ratio, a suitable average cell diameter, and a beautiful appearance. For example, various heat insulating materials, various cushioning materials, and various displays It can be suitably used as a plate, various floating plates and the like.

[0039]

Next, the thermoplastic resin foam of the present invention and the method for producing the same will be described in more detail with reference to Examples. However, the present invention is not limited to only these Examples.

Examples 1 to 8 Polystyrene resin (manufactured by Nippon Steel Chemical Co., Ltd., trade name: Estyrene G-17, melt index (MI): 3.
1) To 100 parts by weight, 0.1 part by weight of talc as a nucleating agent and 3.0 parts by weight of hexabromocyclododecane as a flame retardant were mixed for 15 minutes using a ribbon blender. A tandem extruder (first stage extruder cylinder diameter: 40 mmφ, second stage extruder cylinder diameter:
50 mmφ) and melted at 210 ° C. in the first-stage extruder. Then, through a pressure inlet provided in the latter half of the cylinder of the first-stage extruder, dialkyl carbonate as a foaming agent and The physical foaming agent shown was press-fitted and kneaded in the amount shown in Table 1 and cooled in a second-stage extruder so that the resin temperature became 110 ° C., and the orifice became 3 mmφ.
It was extruded from a × 25 mm circular die to obtain a round bar-shaped polystyrene resin foam.

The expansion ratio, closed cell ratio and average cell diameter of the obtained round rod-shaped foam were measured in accordance with the following methods, and the appearance was visually evaluated based on the following evaluation criteria. Table 1 shows the results.

(1) Expansion ratio The approximate density of the polystyrene resin is set to 1.05 (g / g).
cm ³ ), the formula: expansion ratio (times) = 1.05 / density of foam (g / c)
m ³ ).

The density of the foam is calculated from the weight of the foam and the volume obtained by the submersion method.

(2) Closed cell rate The closed cell rate is measured according to ASTM D-2856 using a multi bikinometer (product name, manufactured by Yuasa Ionics Co., Ltd.).

(3) Average cell diameter The longitudinal section of the foam was photographed with a scanning electron microscope (manufactured by Hitachi, Ltd., product number: S450) at a magnification of 30 times, and the obtained photograph was dry-copied. Copied on the machine.

Next, in the copy paper of the obtained photograph,
The air bubbles were painted with black ink and subjected to a primary treatment. Next, using the primary-processed copy paper, the diameter of each bubble was measured with an image processing device (manufactured by Pierce Co., Ltd., product number: PIASII), and the diameter of all the bubbles in a vertical cross section of 5 cm ² of the foam was measured. The average value was determined and defined as the average bubble diameter (mm).

(4) Evaluation Criteria for Appearance A: A foam having very good appearance without cross-sections of unfoamed resin blocks and voids and without wrinkles or protrusions on the surface. ：: A foam having a good appearance, although a small amount of unfoamed resin mass or void is present in the cross section, or wrinkles or protrusions are slightly present on the surface. ×: A foam having a poor appearance in which an unfoamed resin mass and voids are present in the cross section and wrinkles and protrusions are present on the surface.

Comparative Examples 1 to 3 Round bar-shaped polystyrene resin foams were obtained in the same manner as in Examples 1 to 8, except that only the physical foaming agents shown in Table 1 were used and no dialkyl carbonate was used.

The properties of the obtained round rod-shaped foam were measured in Examples 1 to 4.
The examination was performed in the same manner as in Example 8. Table 1 shows the results.

[0050]

[Table 1]

From the results shown in Table 1, the foams obtained in Examples 1 to 8 all have a high expansion ratio and a high closed cell ratio, and have an average cell diameter of 0.14 to 0.22 mm. It can be understood that the foam is a foam having a beautiful appearance while being able to meet the demand for excellent heat insulating properties.

[0052]

The thermoplastic resin foam obtained by the production method of the present invention has high safety in occupational health and environmental health, has a high expansion ratio, a high closed cell rate, and a suitable average cell diameter. In addition, the appearance is beautiful.

Therefore, the thermoplastic resin foam of the present invention can be suitably used as, for example, various heat insulating materials, various cushioning materials, various display plates, various floating plates, and the like.

[Brief description of the drawings]

1 is a graph showing the relationship between the amount of methyl chloride added to 100 parts by weight of polystyrene and the melt shear viscosity of polystyrene to which the methyl chloride is added, and FIG. 1B is a graph showing the relation between B and 100 parts by weight of polystyrene. 4 is a graph showing the relationship between the amount of ethyl chloride and the melt shear viscosity of polystyrene to which the ethyl chloride has been added, wherein C is polystyrene 10;
5 is a graph showing the relationship between the amount of dimethyl carbonate added to 0 parts by weight and the melt shear viscosity of polystyrene to which dimethyl carbonate has been added.

Claims (6)

[Claims] 1. A thermoplastic resin foam obtained by foaming a foamable resin composition containing a thermoplastic resin, a dialkyl carbonate and a physical foaming agent. 2. The thermoplastic resin foam according to claim 1, wherein the thermoplastic resin is an alkenyl aromatic resin. 3. The thermoplastic resin foam according to claim 1, wherein the dialkyl carbonate is a dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms. 4. The physical foaming agent is at least one of an inorganic gas, a hydrocarbon and a fluorinated hydrocarbon.
Or a thermoplastic resin foam according to item 3. 5. An amount of the dialkyl carbonate is 0.5 to 10 parts by weight based on 100 parts by weight of the thermoplastic resin,
5. The thermoplastic resin foam according to claim 1, wherein the amount of the physical foaming agent is 1 to 50 parts by weight based on 100 parts by weight of the thermoplastic resin. 6. A thermoplastic resin comprising: a foamable resin composition containing a thermoplastic resin, a dialkyl carbonate and a physical foaming agent, mixed at a high temperature and a high pressure, and extruded in a low pressure range to foam. Manufacturing method of resin foam.