1. Field of the Invention
The present invention relates to a method of forming a marking portion such as a mark, a number, an own name (ordered characters or a figure), or the like on the surface of a golf ball through use of an electrostatic copying machine, a printer, or a like machine.
2. Description of the Related Art
The surface of a golf ball bears a marking portion such as a mark, a number, an own name, and the like. Conventionally, the marking portion is formed on the golf ball surface primarily by a transfer printing method or a pad printing method. In the transfer printing method, a transfer foil which has been formed on transfer paper through printing is transferred onto a marking-portion forming surface of the golf ball through application of heat and pressure. In the pad printing method, a marking portion is formed by applying ink on the surface of a golf ball through use of a stamp.
According to the transfer printing method, a large number of identical marks and numbers are printed on transfer paper, and these printed marks and numbers are continuously transferred onto golf balls. According to the pad printing method, a marking portion is formed by applying ink on each of a large number of golf balls through use of a stamp. Accordingly, these methods can efficiently print an identical marking portion on a large number of golf balls, but are not suited for printing different markings, for example, different own names, on golf balls in small lots. The above-mentioned conventional methods are technically difficult to print a photographic image onto a golf ball.
By contrast, Japanese Patent Publication No. JP-B-1991-34480 discloses a method suited for printing different markings on golf balls in small lots. According to this method, through use of an electrostatic copying machine, characters, a symbol, a figure, or the like is printed onto a copying substrate in the form of a reverse toner image, and then the copying substrate is applied onto a transparent resin layer formed on a marking-portion forming surface of a golf ball through application of heat and pressure, to thereby transfer the toner image onto the marking-portion forming surface.
However, the method of Japanese Patent Publication No. JP-B-1991-34480 has involved the following drawbacks (A) to (D). Regarding characteristics of markings formed by this method, a marking portion in the form of a transferred full-color toner image has been inferior to a marking portion in the form of a transferred monochromatic toner image in mechanical strength and fixation.
(A) The method of Japanese Patent Publication No. JP-B-1991-34480 has sometimes resulted in defective markings due to poor adhesion of a toner image onto the marking-portion forming surface of a golf ball. According to studies conducted by the present inventors, this is caused by the following: PA1 (B) In the method of Japanese Patent Publication No. JP-B-1991-34480, a marking portion on a golf ball, particularly, in the form of a transferred color toner image has exhibited poor endurance to impact applied thereto and has been easily damaged by impact. PA1 (C) In the method of Japanese Patent Publication No. JP-B-1991-34480, when a copying substrate is pressed under a strong pressure against a golf ball in order to obtain a good fit between the marking-portion forming surface of the golf ball and the copying substrate for the purpose of solving the above problem (2), a toner image slips due to the applied pressure, resulting in a distorted transferred toner image. PA1 (D) In the method of Japanese Patent Publication No. JP-B-1991-34480, in order to solve the above problem (2), an attempt to use a polypropylene sheet, which is soft and extendable, as a copying substrate has involved the following problem. The thickness of a copying substrate is preferably 20 .mu.m to 80 .mu.m in view of thermal conduction during transfer, whereas an electrostatic copying machine is designed to receive sheets having a thickness of approximately 100 .mu.m. Thus, a polypropylene sheet having a thickness of 20 .mu.m to 80 .mu.m is not suited for use as a copying substrate. Also, a sheet on which a toner image is to be formed by an electrostatic copying machine must have a predetermined range of volume resistivity. However, the volume resistivity of a polypropylene sheet does not fall in the range. Thus, even when a polypropylene sheet having a thickness of approximately 100 .mu.m is used as a copying substrate, a good toner image is not obtained. Further, a polypropylene sheet having a thickness of approximately 100 .mu.m is usually manufactured without orientation. Since a nonorientation polypropylene sheet contracts and deforms when heated, the nonorientation polypropylene sheet passing through an electronic copying machine curls due to contraction and deformation caused by heat of a fixation roller section, disabling the machine operation.
(1) In an electrostatic copying machine, generally, copying paper onto which a toner image has been transferred from a drum is passed through a pair of fixing rollers so that the toner image is fixed on the copying paper. In this fixing step, silicone oil is fed onto the surface of a fixing roller which comes in contact with the toner image, in order to prevent the toner image from directly contacting the fixing roller surface. Thus, a small amount of silicone oil usually adheres to the surface of the toner image formed on the copying paper. According to the method of Japanese Patent Publication No. JP-B-1991-34480, a toner image which has been copied onto a copying substrate by means of an electrostatic copying machine is directly transferred onto a golf ball, so that a small amount of silicone oil is present between the marking-portion forming surface of the golf ball and the transferred toner image. As a result, the silicone oil impairs adhesion of the toner image to the marking-portion forming surface of the golf ball. PA2 (2) In a method where a toner image formed on a copying substrate is transferred onto the surface of a golf ball, the copying substrate is preferably soft and extendable so as to closely fit onto the dimpled marking-portion forming surface of a golf ball. However, if a copying substrate is so soft and extendable, it will not pass through an electrostatic copying machine. Accordingly, in the method of Japanese Patent Publication No. JP-B-1991-34480, a copying substrate must be hard enough to pass through an electrostatic copying machine. However, such a copying substrate does not closely fit onto the marking-portion forming surface of a golf ball due to dimples formed thereon, resulting in formation of a slight gap between a toner image and the marking-portion forming surface of the golf ball. Again, such a gap impairs adhesion of the toner image to the marking-portion forming surface of the golf ball.