JP2530197B2 - Molding method for plastic rolls - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a plastic roll, in which a cored bar roll is inserted into a mold and a cavity formed between them is filled with molten plastic and molded. The present invention relates to an improved molding method by a core bar roll insert method in which a plastic layer is provided on the peripheral surface of a core bar roll.

2. Description of the Related Art A conventional plastic roll is a core metal roll having a plastic layer formed thereon, and a calender roll or nip roll used when molding a plastic sheet, or a coating composition such as a paint is printed on the plastic sheet,
It is used for a pressing roll used when pressing a printing surface. In particular, as a pressing roll that presses the printing surface, the rubber impression cylinder is too soft, and the roll obtained by compression-molding paper on a metal roll has drawbacks such as maintenance during the pressing operation that mixes with the printing surface and produces a defective product. Yes, there are great expectations for plastic rolls.

As a method of molding this plastic roll, Japanese Patent Laid-Open No.
As described in JP-A-109632, there is known a method of filling and molding molten plastic into a cavity formed between a cored bar roll and a mold.

Problems to be Solved by the Invention However, in this molding method, air is mixed when pouring molten plastic into the cavity, or gas is generated due to melting of the plastic, and molding is performed without sufficient degassing. Therefore, cavities, that is, cavities, are likely to be formed in the plastic layer after molding, and if such cavities are formed, the strength is weakened, and the plastic layer may crack when pressed during use.

Further, the above-mentioned conventional method, by immersing the mold in water,
As it is exposed to air to cool, the outside of the cavity is first cooled and solidified, forming a thin skin. Even if this skin is about several millimeters, the melt inside is not cooled until it solidifies, so the cooling and solidification of the melt progresses with a delay inside the molded product with the outside solidified and fixed volume. However, since only the inside contracts, the contracted amount is not filled up, and the inside becomes negative pressure by a volume corresponding to this, and finally countless bubbles (voids) and large cavities are formed to form nests as described above. Due to the difference in cooling of the molten plastic, it has been difficult to manufacture a plastic roll having a thick molding layer having a thickness of 5 to 10 cm.

Means for Solving the Problems In order to solve the above problems, the present invention inserts a cored bar roll into a mold to form a cavity communicating between the cored bar roll and the mold with the injection part. Then, the cavity is provided with a back pressure means capable of retreating while pressing the molten plastic in a direction opposite to the direction of injecting the molten plastic from the injecting section and cooling it by the flow of the refrigerant, and the molten plastic is introduced from the injecting section to A method for forming a plastic roll, which is characterized by injecting into a cavity against the pressure of the back pressure means, successively filling the cavity with molten plastic by this injection, and cooling and solidifying using the refrigerant. is there.

Action When the molten plastic is injected into the cavity, a back pressure against this injection pressure is applied, so that air is prevented from being mixed in at the time of the injection, and the mixed gas is often degassed. Further, since the molten plastic is cooled by flowing the refrigerant through the back pressure portion, the molten plastic is also cooled from the inside, and the difference from the cooling on the outside can be reduced.

Example Next, an example will be described with reference to FIGS. 1 and 2.

In the figure, reference numerals 1 and 1'indicate split molds, and a cored bar roll 2 is fitted and inserted into a mold formed by assembling these split molds, and a cavity 3 is formed between them, and an injection part 4 communicates with this. Is provided.

5 is a back pressure means, and this back pressure means is the core metal roll 2
A doughnut-shaped back pressure portion 5a having a square cross-section so as to substantially block the cross-section of the cavity 3, and a double-walled tubular portion 5b having one end attached to the entire rear surface thereof. The mounting plate 5c attached to the other end of the section, and a hydraulic device 5d connected to this mounting plate 5c.
5a is formed so as to be able to move forward and backward, and is formed so as to be able to press the molten plastic injected into the cavity, and the back pressure portion is provided with an adjustable hydraulic pressure so as to retract due to the injection pressure that resists the pressing force. There is.

The double-walled cylindrical body 5b has a refrigerant inflow path above and below it,
An outflow passage is formed in communication with the back pressure portion 5a and in communication with a through hole provided in the mounting plate 5c, and a refrigerant such as water flows in from below the back pressure portion 5a and is discharged from above. The molten plastic injected into the cavity through the back pressure portion 5a can be cooled sequentially from its tip side.

 Next, the molding method will be described.

The back pressure part 5a is filled with a refrigerant and is made to flow, for example, polyethylene, polypropylene, nylon,
Fluorine resin and other plastics such as vinylidene difluoride,
Alternatively, when a molten plastic in which a reinforcing material such as carbon fiber is mixed is injected into the cavity 3 from the injection section 4 by an extruder (not shown), the molten plastic is blocked by the back pressure section 5a. When a pressing force is applied by the hydraulic device 5d through the mounting plate 5c and the tubular portion 5b, and the molten plastic is pressed by the pressing force and the injection pressure, air does not enter from the injection part and the back pressure part Since it is cooled from the one close to, the mixed air is expelled to the injection part side. When the molten plastic is pressed so that the gas is expelled in this way, the back pressure by the back pressure part is kept constant at, for example, 20 to 100 Kg / cm ² by the hydraulic device, and if the injection pressure of the molten plastic is raised above this, the back pressure part Is retracted against the pressing force, and the molten plastic is sequentially filled into the cavity while the molten plastic is degassed.

In this way, the molten plastic is filled in the cavities corresponding to the entire circumference of the cored bar roll 2 and is cooled and solidified, but the cooling is carried out directly from the back pressure part or through the cored bar roll or mold cooled from here. It is done and cooled thoroughly. In this way, since the plastic layer is formed on the peripheral surface of the cored bar roll 2, the split molds 1, 1'can be disassembled and the plastic roll can be taken out.

In addition, cooling by immersing the entire mold in water may be used together, and the refrigerant may be air.

Although the plastic roll is completed as described above, the molten plastic is pressed in the process of cooling, is prevented from expanding outward, and is also prevented from contracting inward, so that a strong contracting force is generated. , This becomes the tightening force for the cored bar roll, and it is firmly fixed. This tightening force becomes larger as the crystallinity such as vinylidene difluoride having a relatively high melting point and better crystallinity.

EFFECTS OF THE INVENTION As described above, according to the present invention, since the molten plastic is filled in the cavity while applying the back pressure, the inflow of air can be prevented and the gas mixed in the molten plastic can discharge the gas. . Further, since the cooling is performed by passing the refrigerant through this portion while applying the back pressure, the entire molten plastic is cooled, and the formation of voids and cavities can be prevented. As a result, it is possible to provide a plastic roll having no internal defects, so that even if a large pressing force is applied during its use, it can withstand this and prevent cracks and the like.

[Brief description of drawings]

FIG. 1 is a sectional view of an apparatus for manufacturing a plastic roll by a molding method according to an embodiment of the present invention, showing an initial state of its manufacture, and FIG. 2 shows its finished state. In the figure, 1 and 1'are split molds, 2 is a cored bar roll, 3 is a cavity, and 4 is an injection part.

Claims (1)

(57) [Claims] 1. A core metal roll is inserted into a mold to form a cavity between the core metal roll and the mold, which communicates with an injection part, and a direction in which molten plastic is injected from the injection part into the cavity. Is provided with a back pressure means capable of retreating while pressing the molten plastic in the opposite direction and cooling by circulation of a refrigerant, and injecting molten plastic into the cavity from the injection portion against the pressure of the back pressure means, and sequentially Filling the cavity with molten plastic by injection,
A method for molding a plastic roll, which comprises cooling and solidifying using the above refrigerant.