Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2001-02-28
2004-02-03
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S213000, C428S220000, C428S542600, C428S298100, C428S300700, C264S102000, C264S345000, C264S304000, C264S306000, C264S454000, C264S503000
Reexamination Certificate
active
06686034
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a new process for producing a fiber-reinforced thermoplastic resin molded product, which is suitable for producing automobile parts, electrical appliances, industrial materials, civil engineering materials, commodity products, etc. These products are required to have good outer appearance as well as high mechanical strength and high rigidity.
The present invention also relates to a product such as a tiptoe core for a safety shoe, manufactured by said new process.
BACKGROUND ART
As a process for manufacturing a thermoplastic resin molded product reinforced with fibers, it is known that a sheet of continuous fibers or a chopped glass fiber mat impregnated with a molten thermoplastic resin (hereafter referred to as GMT), is used. GMT is reheat-melted and press-molded after having been cut out in order to adapt it to the shape of an objective product.
However, when GMT is molded, the resulting molded product has deficiency in mechanical strength and outer appearance, due to insufficient impregnation of a thermoplastic resin to glass fibers. Further, when GMT is heat-melted, a phenomenon tends to occur that it expands in a direction of the thickness, which will lower a heat conduction to the inside of the GMT to result in low heat efficiency
In order to solve the problems caused by the insufficient impregnation with the resin, JP-A-7-164439 discloses a molded sheet as a material for a hot stamping molding and a high speed press-molding. Such a molded sheet is prepared by scattering and accumulating fiber-reinforced thermoplastic resin base material, followed by molding it under heat and pressure.
Moreover, JP-A-7-184704 and JP-A-7-11-56410 disclose a tiptoe core for a safety shoe molded by using such a molded sheet mentioned above.
However, the manufacturing process of a molded product disclosed in JP-A-7-164439 requires three heating steps i.e. a step of preparing the fiber-reinforced thermoplastic resin base material, a step of preparing a sheet and a step of re-heating the sheet for press-molding. This process is not preferred from a view point of the energy consumption and causes the heat deterioration of the thermoplastic resin used.
Further, the step of preparing a sheet leads usually to a trim-loss which will lower the yield of the material obtained. Moreover, in the press-molding, a cutting out (a blanking) of the sheet is required in order to adapt the size of the sheet to a mould, wherein a blanking-loss occurs. Such will further lower the work efficiency as well as the production efficiency.
As a result, a tiptoe core for a safety shoe disclosed in JP-A-7-184704 and JP-A-7-11-56410 can manage to satisfy a mechanical strength for L kind and S kind stipulated in Japanese Industrial Standard (JIS) T 8101 (a safety shoes made of leather). However, the molding by using the above mentioned sheet tends to result in the poor productivity and economy.
Under these circumstances, it is an object of the present invention to provide a new process for producing a fiber-reinforced thermoplastic resin molded product with high mechanical strength and no substantial heat deterioration of the resin used, which is attained by an efficient heating without applying shear stress to the fiber-reinforced thermoplastic resin base material.
It is another object of the present invention to provide a fiber-reinforced thermoplastic resin molded product such as a tiptoe core for a safety shoe, produced by said new process.
DISCLOSURE OF THE INVENTION
A process for producing a fiber-reinforced thermoplastic resin molded product of the present invention to accomplish the above objects comprises a step of supplying a base material wherein a fiber-reinforced thermoplastic resin base material in a string form or in a tape form is scattered and accumulated, a step of forming a molten mass wherein a heating gas is passed to said base material accumulated to heat-melt it thereby to form a molten mass, and a molding step of wherein said molten mass is supplied to a mold and then is press-molded to form a molded product.
According to the present invention, the fiber-reinforced thermoplastic resin base material in a string form or in a tape form is scattered and accumulated and a heating gas is passed to openings or gaps among said bulkily accumulated base materials, whereby said base material can be quickly and uniformly heat-melted to form a molten mass. Thus resulting molten mass can be press-molded to produce a molded product with superior mechanical strength attributed to the long residue fibers contained and good outer appearance. Further, in the present invention, after said base material having been produced, the heat-melting of the resin can be one time, whereby the cost of energy consumption will be reduced and the work efficiency will be improved as well as the heat deterioration of the resin will be lowered.
In the present invention, when a bulk density of the fiber-reinforced thermoplastic resin base material in the accumulated state is defined as &rgr;
3
, and a true density of the base material is defined as &rgr;
0
, it is preferred to satisfy the following formula.
{fraction (1/100)}≦&rgr;
1
/&rgr;
0
≦½
When the base material satisfies the above formula, the accumulation of said base material can become properly bulky, whereby heating gas can efficiently pass through the base material and thus the heating can carried out in a short period of time. The above bulk density &rgr;
1
is the density of the base material which is scattered and accumulated randomly as much as possible in a vessel having a inner diameter bigger than the length of the base material. The above true density &rgr;
0
the density (a theoretical density) is the density of the base material itself.
Further, the fiber-reinforced thermoplastic resin base material used in the present invention has preferably the following characteristics of from a) to d).
a) a string form with an average diameter of from 0.1 to 1.5 mm,
b) a reinforcing fiber content of from 15 to 80 vol %,
c) a average length L of from 10 to 50 mm,
d) L/D of from 15 to 100, where D is an average diameter.
When the fiber-reinforced thermoplastic resin base material has the above characteristics, the base material become a fine and a needle-like shape to make the resulting accumulated base material easily voluminous, whereby the heating gas can be smoothly passed through the base material to result in a uniform and rapid heating of the base material.
Further, after passing the heating gas to the accumulated fiber-reinforced thermoplastic resin base material to melt it, it is preferred to press the resulting molten base material to form a molten mass, whereby a time required for the cooling of the molten mass to the solid can be delayed since the surface area of the molten mass can become small.
It is also preferred to prepare the molten mass in such a manner that the average fiber length in the molten mass can retain at least 95% of its original length in the base material, whereby the mechanical strength of the fiber-reinforced thermoplastic resin molded product such as a tiptoe core for a safety shoe can be improved.
It is also preferred to carry out the step of forming the molten mass and the step of forming the molded product in such a manner that the average fiber length in the molded product can retain at least 90% of the original length in the base material, whereby the mechanical strength of the fiber-reinforced thermoplastic resin molded product such as a tiptoe core for a safety shoe can be improved.
It is also preferred to use air and/or inactive gas as the heating gas which is passed through the accumulated fiber-reinforced thermoplastic resin base material. Air is preferably used from the cost saving, and inactive gas such as N
2
, Ar, CO
2
, etc. can reduce the deterioration caused by the oxidation of the thermoplastic resin.
It is also preferred to control the temperature T of the heating gas to pass through the accumulated fiber-reinforced thermoplastic resin base material within the foll
Mizukami Toru
Ozaki Kengo
Tominaga Masahiko
Yokoo Yuji
Asahi Fiber Glass Company Limited
Dixon Merrick
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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