Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-06-27
2003-05-27
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S085000, C521S090000, C521S094000, C521S095000, C521S146000
Reexamination Certificate
active
06569912
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an extruded styrene resin foam excellent in environmental compatibility, thermal insulating property and flame retardant property and a method for producing the same.
BACKGROUND ART
A method for continuously producing a foam wherein a styrene resin is heated and melted by means of an extruder or the like, a blowing agent is added thereto, and the resultant mixture is cooled and extruded to a low pressure region is already known (for example, JP-B-31-5393 and JP-B-42-19195) and a method using a flon as a blowing agent is also known (for example, JP-B-41-672 and JP-B-57-7175).
However, from the viewpoint of ozone layer protection, it has been desired to replace flons with others if possible.
As an extruded styrene resin foam using a blowing agent other than flons and a method for producing the foam, JP-A-10-2372 10 discloses an extruded styrene resin foam and a method for producing the foam by using propane, butane or a mixture thereof, or a mixture of these hydrocarbons with methyl chloride, ethyl chloride or a mixture thereof as a blowing agent. Further, the same publication discloses that hexabromocyclododecane or tetrabromobisphenol A is added in an amount of 1 to 3% by weight to a styrene resin and the amounts of blowing agents remaining in the resultant foam are adjusted to not more than 3.5% by weight for propane and to not more than 2.0% by weight for butane so as to meet the flame retardant property prescribed in JIS A 9511.
Further, JP-A-7-53761 discloses a method for producing a polystyrene foam with a relatively thin thickness and flame retardant property using a blowing agent such as propane, butane or a mixture thereof, and a shaped article thereof. The same publication also discloses that the flame retardant property is developed after a long storage period from 1 to 13 weeks and that haloalkylaryl phosphate, ammonium polyphosphate, hexabromocyclododecane, or magnesium hydroxide is used as a flame retardant.
However, in the case of the foam obtained according to the invention disclosed in the above-mentioned JP-A-10-237210 wherein no flon is used, in order to adjust the remaining gas amount of propane or butane to the level as described above, there are problems such as that it is required to limit the amount of propane or butane added in producing a foam and that it is required to subject the obtained foam to a long time storage until the blowing agent is decreased after the production of the foam, which problems result in poor production stability in extrusion foaming and poor productivity.
Further, with the amount of propane or butane in a foam using no flon obtained by the foregoing invention, it is difficult to obtain a foam having high-level thermal insulating property, for example, as required for thermal insulating board No. 3 of extruded polystyrene foam prescribed in JIS A 9511. According to the investigation carried out by the present inventors, in order to obtain a foam having high-level thermal insulating property, it is preferable to allow a saturated hydrocarbon such as propane, butane or the like to remain in a larger amount. For example, though depending upon the foam density, it is supposed that propane is preferable to remain 4% by weight or more and butane is preferable to remain 2.5% by weight or more, especially 3% by weight or more in the case of a foam density within a range of 20 to 35 kg/m
3
. However, in the case where compounds with relatively high flammability such as aliphatic hydrocarbons represented by propane, butane and the like are allowed to remain in large amounts, sometimes the flame retardant property prescribed in JIS A 9511 cannot be satisfied only by using 1 to 3% by weight of hexabromocyclododecane or tetrabromobisphenol A as disclosed in the foregoing invention. In this case, it may be proposed to increase the amount of a flame retardant to be added in order to improve the flame retardant property. However, stable flame retardant property is not easy to obtain only by increasing the amount of a flame retardant. Especially, although the styrene resin, which is a base material of a foam, itself is made flame-retardant, the hydrocarbons evaporated from the foam upon burning are easy to be ignited and hence the problem that suppression of burning tends to be difficult has still been left unsolved. Further, increase in the amount of the flame retardant is likely to lead to deterioration of the formability of the foam and it tends to be difficult to obtain a form product with a satisfactory quality.
Also, in the case of the invention disclosed in the above described JP-A-7-53761, the obtained foam is required to store for a relatively long period and increase of storage cost may be a matter. Further, the invention does not disclose the necessary technique regarding the amount of a blowing agent to be injected to an extruder, the proper amount of a flame retardant to be used and the like, resulting in great difficulty in commercial practice. Moreover, in the working examples of the invention, it is shown that the desired flame retardant property can not be achieved in the case of using a blowing agent composed of 100% by weight of butane or a mixture of butane/propane in 80/20 weight ratio.
As described above, it is extremely difficult to achieve both of high-level thermal insulating property and high-level flame retardant property in the system using saturated hydrocarbons as blowing agents.
In view of such a situation, an object of the present invention is to provide a styrene resin foam having high-level thermal insulating property and at the same time high-level flame retardant property sufficient to meet the flame retardant property prescribed in JIS A 95111 using a blowing agent having a tendency to be highly combustible and to provide a method for producing the foam.
DISCLOSURE OF THE INVENTION
The present inventors have intensively made investigation to solve the above described problems and consequently found that excellent flame retardant property can be achieved by using (A) a halogenated flame retardant and (B) one or more of compounds selected from the group consisting of phosphorus type flame retardants containing nitrogen atom in a molecule, tetrazole compounds, nitrogen-containing compounds having the following general formula 1, nitrogen-containing compounds having the following general formula 2, metal borates, and boron oxides for a styrene resin foam using a hydrocarbon as a blowing agent, in spite of use of a hydrocarbon as a blowing agent, and especially that ignition or combustion of the hydrocarbon evaporated from the foam on burning can be suppressed. More particularly, it has been found that both high-level flame retardant property and high-level thermal insulating property as prescribed in JIS A 9511 can be achieved. Moreover, it has been found that the effect of suppressing the combustion of the hydrocarbon can be further enhanced by using a phosphoric acid ester compound in combination with the foregoing components. It has been also found that the thermal insulating property can be further improved by forming a foam with a specified cell structure by using water as a blowing agent in combination and adding a water absorptive substance such as bentonite together.
That is, the present invention provides the following extruded styrene resin foams and their production methods.
(1) An extruded styrene resin foam obtained by extrusion-foaming of a styrene resin, which contains, as a blowing agent, 100 to 10% by weight of at least one of saturated hydrocarbons having 3 to 5 carbon atoms and 0 to 90% by weight of other blowing agent, based on the total amount of the blowing agent, and contains (A) a halogenated flame retardant and (B) at least one compound selected from the group consisting of phosphorus type flame retardants containing nitrogen atom in a molecule, tetrazole compounds, nitrogen-containing compounds having the following general formula 1, nitrogen-containing compounds having the following general formula 2, metal borates, and boron oxides:
&
Fujiwara Hiroshi
Hirose Fuminobu
Oohara Youichi
Sato Takeshi
Yoshida Toru
Foelak Morton
Kaneka Corporation
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