Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-03-22
2002-03-12
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...
C521S076000, C521S078000, C521S091000, C521S092000, C521S093000, C521S095000
Reexamination Certificate
active
06355698
ABSTRACT:
TECHNICAL FIELD
The present relates to a substantially anhydrous blowing agent and a process for producing the same.
BACKGROUND ART
Blowing agents, such as azodicarbonamide, have been conventionally utilized extensively for thermoplastic resins, for example, vinyl chloride resins, polyolefin resins (polyethylene resins, polypropylene resins, and the like), ethylene vinyl alcohol resins, rubbers, and the like.
These blowing agents, which are usually finely powdered compounds, have a problem that they aggregate and are solidified with the lapse of time or under load to thereby show impaired flowability in the step of addition to resins to cause hopper clogging, or to thereby have impaired dispersibility into resins. Mitigation of this solidification is desired more and more with the recent trend toward quality improvement in foamed resins and labor saving in the production thereof.
Techniques currently employed for overcoming the above problem include (1) technique of adding inorganic powder particles, such as silica, metal silicate or the like, as a solidification inhibitor to a blowing agent, (2) technique of batchwise drying a blowing agent for a sufficient period to thereby diminish the water contained therein in a slight amount, and the like.
However, use of these techniques has various drawbacks. Namely, technique (1), although effective in solidification prevention in some degree, cannot impart the effect which lasts beyond several months. For application to a blowing agent comprising finer particles, inorganic powder particles should be added in a larger amount. However, the addition of a larger amount of the inorganic powder particles is causative of cell enlargement during foaming, and is hence undesirable in applications where fine cells are required. Technique (2), on the other hand, has significantly reduced productivity because the drying requires much time, resulting in an increased production cost. In addition, technique (2) cannot cope with continuous production. Furthermore, it is difficult to dry and remove the water contained in crystals sufficiently to thereby obtain a substantially anhydrous blowing agent. Also, effects in solidification prevention is limited.
Japanese Published Unexamined Patent Application No. 320432/92 discloses a method of adding a silane coupling agent dissolved in a solvent to azodicarbonamide to thereby improve flowability and dispersibility into resins. However, this method is ineffective in sufficiently preventing solidification.
Furthermore, Japanese Published Unexamined Patent Application No. 295872/96 discloses a method of adding an aluminum coupling agent dissolved in a solvent to a chemically blowing agent to thereby improve flowability and dispersibility into resins. However, this method is also ineffective in sufficiently preventing solidification.
DISCLOSURE OF THE INVENTION
The present inventors made intensive studies in order to eliminate the above problems. As a result, they have-found that a substantially anhydrous blowing agent is obtained by treating a blowing agent with a surface-treating agent capable of removing water from the blowing agent, and optionally by heating it. Furthermore, they found that the blowing agent thus obtained is significantly inhibited from solidification and is exceedingly useful as a blowing agent satisfactory in flowability, dispersibility into resins, and the like, even after the lapse of a prolonged period of time. The present invention has been completed based on these findings.
That is, the present invention relates to a substantially anhydrous blowing agent, especially a substantially anhydrous crystalline azodicarbonamide.
Furthermore, the present invention relates to a substantially anhydrous blowing agent obtained by treating a blowing agent with a surface-treating agent capable of removing water from the blowing agent.
Moreover, the present invention relates to a process for producing a substantially anhydrous blowing agent, which comprises treating a blowing agent with a surface-treating agent capable of removing water from the blowing agent under conditions substantially free of a solvent.
The substantially anhydrous blowing agent of the present invention has been significantly improved especially in unsusceptibility to solidification under load and in unsusceptibility to solidification with the lapse of time. Hence, the substantially anhydrous blowing agent is extremely free from solidification even through long-term storage in a stacked state, and retains for a long time the satisfactory flowability and the satisfactory dispersibility into resins which properties are possessed by the crystalline powder immediately after production.
The foaming performances of the blowing agent of the present invention are equal to those of the conventional blowing agents.
Consequently, as a result that the substantially anhydrous blowing agent of the present invention is provided, the fear that blowing agent products may be solidified under load or with the lapse of time from the production thereof to the use thereof by users is eliminated.
BEST MODE FOR CARRYING OUT THE INVENTION
The blowing agent which can be used in the present invention is selected from conventionally known blowing agents. Examples include azodicarbonamide (ADCA; decomposition temperature: about 200° C.), p,p′-oxybis (benzenesulfonyl hydrazide) (OBSH; decomposition temperature: about 160° C.), dinitropentamethylenetetramine (DPT; decomposition temperature: about 200° C.), p-toluenesulfonyl hydrazide (TSH; decomposition temperature: about 110° C.), benzenesulfonyl hydrazide (BSH; decomposition temperature: about 95° C.), and the like.
The present invention can be advantageously applied especially to blowing agent powders having a decomposition temperature of 100° C. or higher. Particularly, much merit is brought about when the present invention is applied to ADCA, in which solidification has conventionally been a serious problem.
The blowing agent in the present invention is preferably in the form of a powder. Although the particle diameter thereof is not particularly limited, it is generally about 1 to 50 &mgr;m, preferably about 3 to 30 &mgr;m. The term “particle diameter” as used herein means the median size determined with a laser diffraction particle diameter distribution analyzer.
The term “substantially anhydrous” as used herein means to have a water content lower than 0.03% by weight, preferably lower than 0.010% by weight. The water content (% by weight) in crystalline ADCA is herein determined by heating the crystalline ADCA at 110° C. for 2 hours while passing water-free nitrogen gas therethrough, introducing the effluent nitrogen gas into a Karl Fisher's water meter (trade name: MKS-1; manufactured by Kyoto Electronics Manufacturing Co., Ltd.) prevented from suffering water penetration thereinto from the surrounding air to measure the amount of water contained in the nitrogen gas, and converting this water amount into a percentage amount based on the weight of the crystalline ADCA.
The surface-treating agent which can be used in the present invention is one capable of removing water from a blowing agent Examples include compounds having the property of chemically reacting with water and compounds having the property of adsorbing or holding water. Specific examples include coupling agents, organic acid anhydrides, anhydrous inorganic compounds, desiccants, and the like.
Examples of the coupling agents include silane coupling agents, aluminum coupling agents, titanate coupling agents, and the like.
Examples of the silane coupling agents include conventionally known silane coupling agents. Specific examples include methyltrimethoxysilane, &ggr;-aminopropyl-triethoxysilane, N- (&bgr;-aminoethyl) -&ggr;-aminopropyl-trimethoxysilane, N-phenylaminomethyltrimethoxysilane, vinylmethyldiethoxysilane, and the like.
Examples of the aluminum coupling agents include conventionally known aluminum coupling agents. Specific examples include aluminum isopropylate, aluminum ethylate, aluminum tris(ethylacetoacetate), et
Maekawa Tsukasa
Shono Sadafumi
Sumitomo Shigeru
Tachi Yoshifumi
Ueda Nobuyuki
Foelak Morton
Otsuka Chemical Co. Ltd.
Whitham Curtis & Christofferson, PC
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