JPS5953854B2 - Surface improvement method for plastic molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the surface of plastic molded products, and particularly to a method of improving the surface of foam molded products.

Conventionally, coating methods such as extrusion coating and paste coating have been used to improve the surface of plastic molded products.

However, with the extrusion coating method, there is a limit to the coating thickness, and it is extremely difficult to coat with a thickness of less than 100 μm.Furthermore, if you try to restart production after discontinuing or discontinuing production, you will have to remove the plastic that has solidified in the extruder. However, it has the disadvantage that extremely complicated work is required.

In addition, in the paste coating method, the plastic to be coated is made into a paste using a solvent and plasticizer, but depending on the type of plastic, it is extremely difficult to select the solvent and plasticizer, although it is a general-purpose surface improvement method. do not have.

Furthermore, when a solvent is used, there are also disadvantages such as deterioration of the working environment. Therefore, the inventors of the present invention have conducted intensive research to invent a surface improvement method that does not have such drawbacks and can be done using simple, efficient, and inexpensive equipment. He completed the present invention by discovering a method for improving the surface of products.

That is, the present invention relates to a method for improving the surface 5 of a plastic molded article by passing the molded article through rolling rolls having a surface temperature such that the molded article does not stick to the rolling rolls.

Furthermore, the present invention provides an even better result by passing the plastic molded product through a roll having a surface temperature that does not stick to the roll while the surface temperature of the plastic molded product is higher than that of the roll. θ surface can be obtained.

In addition, the present invention does not synchronize the roll inlet speed of the plastic molded product with the circumferential speed of the roll and generates slip between the plastic molded product and the roll, thereby improving the plastic surface even further. Molded products can be obtained.

The plastic molded products that can be applied to the present invention are not limited, but examples of the resin include amorphous thermoplastic resins such as vinyl chloride, polystyrene, and polycarbonate, and crystalline thermoplastic resins such as polyethylene, polypropylene, and nylon. These resins may contain organic or inorganic powder or fibrous fillers with or without surface treatment, and as molded products, ordinary molded products, foamed products, etc. Although any molded product is included, foamed molded products are particularly effective as targets for the method of the present invention.

In the present invention, a rolling roll is a roll having grooves or protrusions with a predetermined cross-sectional shape along the circumference of the roll, and is composed of two rotating rolls, top and bottom or left and right, and the plastic molded product is placed between the rolls. A structure that can be pressurized when passing through. Further, the rolling rolls include not only one-stage rolls but also multi-stage rolls, and when the plastic molded product is successively passed through the multi-stage rolls, the surface of the plastic molded product can be rolled in multiple stages without difficulty, which is particularly preferable from the point of view of smoothing the surface. In addition, the surface smoothness of the rolling roll must naturally be sufficient due to its role, and it is used as a processing rolling roll for giving plastic molded products a smooth surface with a center line average roughness of 1μ or less, which will be described later. Use a surface roughness equivalent to 3.2S in the maximum height category specified by JISBO6Ol, and in order to give the molded product a surface with a centerline average roughness of 0.5μ or less,
It is necessary to use a rolling roll with a surface roughness equivalent to 1.6S in terms of the maximum height classification value.

In the present invention, the rolling roll entrance speed of a plastic molded article refers to the speed immediately before the molded article starts contacting the rolling roll. In the present invention, the reason why the surface temperature of the rolling roll is specified to be below the temperature at which the plastic molded product sticks is that if it exceeds this temperature, picking may occur and the surface properties of the molded product may be deteriorated.

This sticking temperature varies depending on the type of plastic, rolling conditions, etc., but is generally between 100° and 150°C. It is advisable to determine this temperature by testing various plastics under actual rolling conditions for molded products. Setting the surface temperature of the plastic molded product higher than the surface temperature of the rolling roll is more effective in improving the surface smoothness of the molded product, but in this case, the surface temperature of the rolling roll is
It is preferable to keep the temperature difference sufficiently low so that the temperature drop on the surface of the molded product can be considerably large.

This is because if the temperature difference is small and the temperature drop on the surface of the molded product due to passing through the rolling rolls is small, the surface of the molded product may become uneven due to uneven cooling, resulting in poor surface properties. Note that if the pressing force that a plastic molded product receives when it passes between rolling rolls is too small, the surface deformation of the plastic molded product will be small; if it is too large, not only the surface but also the inside of the plastic molded product will be deformed. Therefore, it is not preferable, and it is preferably 1 to 20% for general molded products and 1 to 10% for foamed molded products, expressed as the rolling reduction ratio defined below, but it is not limited to this, and depending on the situation. It is best to choose accordingly.

The rolling reduction is the thickness of the plastic molded product before rolling.
, when the thickness after rolling is H2, Pr expressed by the following formula
The surface smoothness of the plastic molded article in the present invention is expressed as a center line average roughness as defined by JISBO6Ol.

This has a measuring length of 1 from the roughness curve in the direction of its center line.
Cut out the part, and set the center line of this cutout part to the X axis,
When the direction of vertical magnification is the y-axis and the roughness curve is expressed as y=f (x), the value of R2 given by the following equation is expressed in μ units. The center line average roughness of the surface of a plastic molded product, which can be generally considered to be a smooth surface, is 0.5 to 1.0.
Therefore, in the present invention, a surface with a center line average roughness of 1 μ or less is referred to as a smooth surface.

Next, examples will be shown.

In this example, a TARYSURF4 type surface roughness meter was used, the cutoff value was 0.8 mm, and the measurement length l = 2.5 m.
The center line average roughness was determined from the roughness curve measured under the conditions of 3 mm per minute and a feed rate of 3 mm per minute.

Example 1 The material was made of 1 part by weight of high-density polyethylene, 1 part by weight of calcium carbonate, and 0.6 part by weight of glass fiber, and had a centerline average roughness of 4.2μ as shown in the curve in Fig. 1, as shown in Fig. 1. If a molded product with a cross-sectional shape is made using a single rolling roll and the surface temperature of the rolling roll is 130°C or higher, the molded product will stick to the roll. A sample with an average roughness of 1.0 μm was obtained.

The measurement results are shown in FIG. R7N'VrIl? To I
i Todoro'1you●'▼'Represents 1-wr-r (the same applies below).

Example 2 Regarding a molded product made of the same material and having the same cross-sectional shape as Example 1,
The surface was processed under the rolling conditions shown in Table 2 to obtain a center line average roughness of 0.5μ. Ta.

The measurement results are shown in FIG. As is clear from this example, when the surface of the plastic molded article was heated to a temperature above the softening point of the plastic molded article and then passed through a rolling roll having a surface temperature below the softening point of the plastic molded article, the product obtained in Example 1 was obtained. It can be seen that a smoother surface can be obtained.

Example 3 Regarding a molded product made of the same material and having the same cross-sectional shape as Example 1,
Surface processing was performed under the rolling conditions shown in Table 3 to obtain a center line average roughness of 0.4μ.

The measurement results are shown in FIG. As is clear from this example, not synchronizing the roll inlet speed of the plastic molded product with the circumferential speed of the roll and generating slip between the plastic molded product and the roll is an effective way to obtain a smoother surface. It turns out that this is an effective method.

As described above, according to the present invention, a smooth surface of a plastic molded product can be produced easily, inexpensively, and efficiently.

Further, the present invention has the advantage that it is possible to improve the surface properties of plastic molded articles and to give them a shape at the same time, and that surface treatments such as embossing can be carried out in one step, and have great practical value.

[Brief explanation of drawings]

Figure] shows an example of the cross-sectional shape of a plastic molded product used in the practice of the present invention.

Claims (1)

[Scope of Claims] 1. A method for improving the surface of a plastic molded article, which comprises passing the plastic molded article through rolling rolls having a surface temperature at which the molded article does not stick to the rolling roll. 2. Claim 1, characterized in that the surface temperature of the plastic molded product is higher than the surface temperature of the rolling roll.
A method for improving the surface of a plastic molded product as described in . 3. Claims 1 or 2, characterized in that the inlet speed of the roll of the plastic molded product and the circumferential speed of the roll are not synchronized, causing slip between the plastic molded product and the roll. The method for improving the surface of plastic molded products described above.