Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2002-01-18
2003-10-07
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S156000, C428S336000, C428S338000, C428S220000
Reexamination Certificate
active
06630225
ABSTRACT:
BACKGROUND OF THE INVENTION
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an automotive exterior panel having a good appearance and smooth finish and to a method for producing the panel.
Conventional methods for producing hollow molded articles having a smooth appearance disclose a method comprising disposing a parison, which is composed of a noncrystalline resin exhibiting a tensile modulus of 2000 Kg/cm
2
or more at 75° C., between mold halves having mirror-finished cavity surface, closing the mold and closely adhering the parison to the cavity by blowing a pressurizing air into the parison, wherein the parison is adhered to the cavity which is set to a cavity temperature Y° C. falling in the following range:
Y
° C.=(0.96
X
0
−37) to (0.96
X
0
+3)
where X
0
is a temperature at which the tensile modulus of the noncrystalline resin is 2000 Kg/cm
2
(Japanese Patent Application Publication (JP-B) No. 6-22875).
With this method it is impossible to avoid the formation of spot marks or line marks on the external surface of the hollow article of noncrystalline resin. Therefore, when producing an automotive exterior panel whose appearance needs to meet strict requirements, the spot marks and the line marks need to be removed by polishing or wet-sanding the external surface of the blow-molded hollow article of noncrystalline resin prior to the painting of the external surface. Consequently, the number of process steps increases and production costs become higher.
Another prior art method for thermoforming or blow molding a thermoplastic resin, is described in (JP-B No. 1-27849), wherein the gloss of the surface of the molded article is increased by heating selectively and instantly the mold surface to a temperature higher than the thermal deformation temperature of the resin by means of high frequency induction heating.
This method suffers has significant drawback, because it is necessary to use a special molding apparatus equipped with a mold heating device designed for the high frequency induction-heating. Consequently, the production costs become higher.
In (JP-B No. 2-40498), a method comprising blow-molding a molten parison, which has on the surface thereof many minute concavities/convexities having a depth in the range of from 2 to 100 &mgr;m, by means of a mold which is heated to a temperature higher than the crystallization temperature of the resin and the surface of which is mirror-finished to a roughness of 0.5 &mgr;m or less.
The melt fracture is generated on the parison surface so as to create many minute concavities/convexities having a depth in the range of from 2 to 100 &mgr;m. The depth of the minute concavities/convexities are difficult to control, and the resulting article has a certain amount of surface roughness even after painting. However, the control of the melt fracture is difficult and therefore is not suited for mass production.
What is needed is an article that can be produced efficiently and in mass production that has a smooth appearance once painted, suitable for an automobile exterior panel. The process used to create such a panel should eliminate line marks, spot marks, and air marks. The process should allow for mass production and produce a cost-effective product.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above-described problems of conventional technologies. It therefore is an object of the present invention to provide an automotive exterior panel which has excellent mechanical strengths, such as rigidity, and which presents a good appearance, free of coating imperfections such as orange peel, and allow painting without prior polishing or wet-sanding of the external surface of the blow molded hollow article.
Another object of the present invention is to provide a method for producing an automotive exterior panel.
In order to achieve the object, the first automotive exterior panel according to the present invention is an automotive exterior panel which is a blow molded article of a noncrystalline resin exhibiting a tensile modulus of 2000 Kg/cm
2
or more at 75° C. and which is coated with a 15 to 150 &mgr;m thick paint film, wherein the panel to be coated has surface irregularities comprising a surface roughness in the range of from 0.9 to 9.0 &mgr;m and an average peak-to-peak distance in the range of from 10 to 150 &mgr;m.
In order to achieve the object, the second automotive exterior panel according to the present invention is an automotive exterior panel which is a blow molded article of a crystalline resin exhibiting a flexural modulus of 9000 Kg/cm
2
or more at 23° C. and which is coated with a 15 to 150 &mgr;m thick paint film, wherein the panel to be coated has surface irregularities comprising a surface roughness in the range of from 0.9 to 9.0 &mgr;m and an average peak-to-peak distance in the range of from 10 to 150 &mgr;m.
Further, in the second automotive exterior panel, the crystalline resin exhibiting a flexural modulus of 9000 Kg/cm
2
or more at 23° C. may be incorporated with 3% to 35% by weight of an inorganic filler.
Still further, in the second automotive exterior panel, the crystalline resin exhibiting a flexural modulus of 9000 Kg/cm
2
or more at 23° C. is preferably polypropylene.
The first method of the present invention for producing the automotive exterior panel comprises the steps of producing a hollow molded article for automotive exterior panel by blow molding and painting the external face of the hollow molded article for automotive exterior panel, wherein a parison, which is composed of a noncrystalline resin exhibiting a tensile modulus of 2000 Kg/cm
2
or more at 75° C., is disposed between mold halves having minute concavities/convexities such that the surface roughness is in the range of from 0.9 to 9.0 &mgr;m and the average peak-to-peak distance is in the range of from 10 to 150 &mgr;m; the mold is then closed; and thereafter the parison is closely adhered by introducing thereinto a pressurized air to the cavity whose surface temperature is set to Y° C. which falls in the following range:
Y
=(0.96
X+
3) to (0.96
X+
40)
where X is a temperature at which the tensile modulus of the noncrystalline resin is 2000 Kg/cm
2
.
In the first method of the present invention for producing the automotive exterior panel, it is effective to set the cavity surface temperature Z° C., at which a mold opening process is completed for taking out the molded article for automotive exterior panel, to a temperature in the range of Z≦0.9X where X is a temperature at which the tensile modulus of the noncrystalline resin is 2000 Kg/cm
2
.
For clarity and understandability, the variables used for the noncrystalline resin are capital ‘Y’ and capital ‘Z’, while the variables used for the crystalline resin are lower case ‘y’ and lower case ‘z’.
The second method of the present invention for producing the automotive exterior panel comprises the steps of producing a blow molded article for automotive exterior panel by blow molding and coating the external face of the molded article for automotive exterior panel with a 15 to 150 &mgr;m thick paint film, wherein a parison, which is composed of a crystalline resin exhibiting a flexural modulus of 9000 Kg/cm
2
or more at 23° C., is disposed between mold halves having minute concavities/convexities such that the surface roughness is in the range of from 0.9 to 9.0 &mgr;m and the average peak-to-peak distance is in the range of from 10 to 150 &mgr;m; the mold is then closed; and thereafter the parison is closely adhered by introducing therein a pressurized air to the cavity whose surface temperature is raised during the adhesion to y ° C. which falls in the following range:
A<y<
1.07
B
where A is a peak crystallization temperature (° C.) in a Differential Scanning Calorimetry (DSC) curve of the crystalline resin which exhibits a flexural modulus of 9000 Kg/cm
2
or more at 23° C.; and B is a peak fusion temperature (° C.) in a DSC curve of the crystalline resin which exhibits a flexural modulus
Kodaira Tooru
Matsuba Akihiko
Sumi Takehiko
Tamada Teruo
Kyoraku Co. Ltd.
Maine & Asmus
Nordmeyer Patricia L.
Pyon Harold
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