Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-22
2004-07-27
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S044000, C523S500000, C523S513000
Reexamination Certificate
active
06767971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a molding composition suitable for production of sound absorbing interior automotive parts, heat insulating materials, sound absorbing materials for a soundproof chamber, sound absorbers of air conditioners, fiber-reinforced plastics (hereinafter “FRP”), constructional materials, and the like.
2. Description of the Related Art
Cores or soundproofing materials of automobile interior materials, sound absorbing materials for a soundproof chamber, sound absorbers of air conditioners, FRP, constructional materials, and the like are produced from molding compounds mainly comprising fiber, a urea formaldehyde resin, a melamine formaldehyde resin or a phenolic resin and an amine curing agent to secure sufficient strength (see, for example, JP-A-57-55962 and JP-A-7-1666). However, the urea formaldehyde resin and the like produce formaldehyde on forming and curing or thermal reaction, and the amine curing agent has the problem of smell.
In order to eliminate generation of formaldehyde and/or to improve the smell, a cured resin comprising an epoxy compound and a carboxylic acid or an anhydride thereof has been proposed as disclosed in JP-A-63-221169 and JP-A-5-31362. However, this combination requires a relatively high curing temperature. Many molded parts obtained from an unsaturated polyester combined with a radical generator are known, but most of them need a curing aid, such as styrene. Although they do not generate formaldehyde, the problem of smell remains unsolved. Molding compounds comprising a diallyl phthalate prepolymer and an unsaturated polyester are also known (see JP-A-5-169475). However, the diallyl phthalate prepolymer has a low iodine value and fails to achieve a high crosslinking density so that the resulting molded article has insufficient strength.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a molded article having sufficient strength for practical use and improved safety and smell.
Another object of the present invention is to provide a molding composition suitable for producing such a molded article.
The present invention relates to a molding composition comprising (A) a fibrous material, (B) a crystalline unsaturated polyester, (C) a non-crystalline unsaturated polyester, and (D) a radical generator. The invention also relates to a molded article obtained by molding the molding composition.
The molding composition according to the invention provides a molded article with sufficient strength for practical use and free from the problems of formaldehyde generation and smell.
DETAILED DESCRIPTION OF THE INVENTION
A combined use of a crystalline unsaturated polyester (B) and a non-crystalline unsaturated polyester (C) reduces the respective softening points of the unsaturated polyesters. That is, each unsaturated polyester has a lower melt viscosity when used in combination than when used alone. Use of a radical generator (D) makes the molding composition cure without using a crosslinking assistant such as styrene that may cause the problems of smell and safety. As a result, not only are solved the problems of formaldehyde generation and smell, but the molding composition can cure in low temperature to provide a molded article equal or superior in strength to the conventional molding compositions comprising a urea formaldehyde resin, a phenolic resin, etc.
Reduction of curing temperature of a molding material and/or increase of curing rate could be achieved by combining an unsaturated polyester having a reduced melt viscosity and a radical generator having a moderate half-life temperature. In this case, however, reduction of melt viscosity of an unsaturated polyester merely by reduction of molecular weight results in reduction of strength of the resulting molded article due to the remaining low-molecular weight components such as monomers. In the present invention, by using a mixture of a crystalline unsaturated polyester and a non-crystalline unsaturated polyester, the melting point and the softening point of both the unsaturated polyester resins in thermal forming can be decreased. Therefore, the molding composition has a lowered melt viscosity without increasing low-molecular weight components so that is can be cured in lower temperature and/or at an increased curing rate to provide a molded article with enhanced strength.
While the details are unclear, it is generally said that a crystalline polyester is hard and brittle, while a non-crystalline polyester is tough. In the present invention the crystalline unsaturated polyester and the non-crystalline unsaturated polyester are combined to make an eutectic mixture, which is cured to provide a molded article with higher toughness than obtained with either one of them.
The term “crystalline unsaturated polyester” as used herein means a polyester having a clear endothermic peak indicative of a melting point in analysis with a differential scanning calorimeter (hereinafter “DSC”). The term “non-crystalline unsaturated polyester” as used herein denotes a polyester having no clear endothermic peak indicative of a melting point but an endothermic peak indicative of a glass transition point in analysis with a DSC. Whether an endothermic peak is indicative of a melting point or a glass transition point can easily be distinguished from the fact that the former remains while the latter disappears in second-scanning.
The crystalline unsaturated polyester as component (B) preferably has a melting point of 60° C. or higher so as not to aggregate at room temperature irrespective of the kind of an additive. The crystalline unsaturated polyester preferably has a lower melting point than 180° C., particularly lower than 150° C., so that it may cure sufficiently in a short molding time.
It is preferred for the non-crystalline unsaturated polyester as component (C) to have a softening point of 80° C. or higher and lower than 200° C., particularly lower than 150° C., and/or a glass transition point of 40° C. or higher and lower than 100° C., particularly lower than 90° C. The preference for the softening point and/or the glass transition point is based on the same reasons as for the melting point of the crystalline unsaturated polyester.
The difference between the melting point of the crystalline unsaturated polyester and the softening point of the non-crystalline unsaturated polyester is preferably 50° C. or smaller, particularly 40° C. or smaller, in order to easily form a eutectic mixture. Where two or more kinds of crystalline unsaturated polyesters and/or two or more kinds of non-crystalline unsaturated polyesters are used, it is preferred that the difference between the melting point of one of the crystalline unsaturated polyesters and the softening point of one of the non-crystalline unsaturated polyesters be within 50° C.
The crystalline unsaturated polyester and the non-crystalline unsaturated polyester can separately be ground to the respective desired particle sizes, followed by mixing up. Alternatively, mixing either in a powdered state or in a molten state may be followed by grinding to a desired particle size.
The crystalline or non-crystalline unsaturated polyesters are not particularly limited as long as they have an addition polymerizable unsaturated bond. For example, non-linear unsaturated polyesters comprising a monomer with tri- or higher functionality can be used. Polyester-polyamide which is obtained by modifying with a small amount (preferably 10 mol or less per 100 mol of a carboxylic acid component) of an amino-containing monomer is also employable as far as it has an addition polymerizable unsaturated bond.
The monomers providing the crystalline or non-crystalline unsaturated polyester are not particularly limited and include known di- or higher polyhydric alcohol components and known di- or higher polybasic carboxylic acid components, inclusive of their anhydrides, esters, etc. The di- or higher polyhydric alcohol components and the di- or higher polybasic carboxylic acid components are preferably use
Kawabe Kuniyasu
Yamaguchi Takashi
Kao Corporation
Short Patricia A.
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