JPS6348692B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing multilayer sheets by coextrusion.

In recent years, multilayer sheets have been increasingly manufactured using coextrusion methods, and sheets with multilayer structures that combine two or more types of resin are used for food packaging materials, construction materials, interior materials for automobiles and other vehicles, etc. has been done.

These multilayer sheets are constructed by selecting appropriate resins for each layer depending on the intended use, resulting in various resin combinations. However, because each resin has different thermal properties such as melt viscosity, softening temperature, and melting point, as well as adhesion and tackiness, coextrusion of a multilayer sheet may not be possible depending on the combination.

In other words, if a resin with a high softening temperature and melting point is used for the inner layer of the sheet to be coextruded, and a resin with a lower softening temperature and melting point is used for the outermost layer, the resin in the inner layer will melt at a higher temperature than the resin in the outermost layer. Because of this,
The heat increases the temperature of the resin in the outermost layer, and the resin reaches a temperature higher than the softening temperature of the resin in the outermost layer, and comes into contact with the cooling roll.

Generally, in sheet extrusion molding, when the temperature of the resin in its molten state is high, it becomes sticky and adheres to the cooling roll. The reason for this is that the heat of the molten resin increases the surface temperature of the cooling roll, reducing the ability to cool the resin and causing the surface of the resin to remain at a temperature where it remains sticky forever. In order to solve this problem, it is possible to increase the cooling capacity of the cooling roll so that the surface temperature of the roll is always kept at a temperature at which the outermost layer of resin that comes into contact with it loses its tackiness.However, in normal sheet molding, the resin Since it is extruded at a temperature slightly higher than its softening temperature and melting point, it is possible to cool it with rolls, but if the resin temperature is significantly higher than its softening temperature or melting point, the cooling will not be sufficient and adhesion cannot be prevented.

The present invention provides a method for producing a multilayer sheet that prevents adhesion to a cooling roll even when the resin temperature of the outermost layer is significantly higher than its softening temperature or melting point.

In order to achieve the above objective, the following method was established as a result of intensive study. That is, when the multilayer sheet 2 coextruded from the extrusion die 1 is applied to the cooling roll 3, the synthetic fiber cloth 4 is applied to both or one side of the sheet.
are passed through the roll 3 at the same time as the stacked multilayer sheet 2. The synthetic fiber cloth 4 used for this is a cloth made of fibers made of a resin that has a higher softening temperature and melting point than any resin used for the multilayer sheet 2, and has no adhesive properties with the resin of the outermost layer of the multilayer sheet 2. Further, when only one side of the outermost layer of the multilayer sheet 2 is made of a resin having a low softening temperature and a low melting point, synthetic fiber cloth may be used only on that side.

By doing this, the outermost layer resin, which has been heated to a high temperature due to the high heat of the inner layer resin, is covered with the synthetic fiber cloth 4 and does not come into direct contact with the cooling roll 3, thereby setting the surface temperature of the cooling roll 3. The temperature will no longer rise above that level. In addition, since the synthetic fiber cloth 4 is in contact with the outermost layer of the multilayer sheet 2 at room temperature, it has the effect of cooling the resin, and on the other hand, since it is in contact with the cooling roll 3, an increase in the temperature of the synthetic fiber cloth 4 is prevented. Since the resin itself has a high softening temperature and melting point, it will not melt at the resin temperature of the outermost layer of the multilayer sheet 2, and since it has no adhesive property, it can be easily peeled off and removed after the multilayer sheet 2 has cooled.

In this method, since a long synthetic fiber cloth is continuously supplied, the cloth at room temperature is always in contact with the resin, so that cooling performance is good. On the other hand, in conventional methods, the circumferential surface of the cooling roll is always in contact with the high temperature resin, which causes the temperature of the roll surface to rise, leading to problems such as resin adhesion to the roll.

Example 1 As shown in Figure 2, the inner layer is polypropylene 5 with a thickness of 2 mm, the outer layers are each made of low-density polyethylene 6 with a thickness of 1 mm, and the middle layer between the inner and outer layers is each made with a thickness of 50 μm.
A five-layer sheet with a total thickness of 4.1 mm was coextruded with a layer structure of Adhesive Polymer 7 (a copolymer of polypropylene, ethyl acrylate, and vinyl acetate). At this time, polypropylene is extruded at a resin temperature of 250℃, and low-density polyethylene is extruded at a resin temperature of 190℃, and the outermost layer surface is 215℃.
℃, when nylon cloth (plain weave) was passed through a roll to overlap both sides of the extruded sheet,
Even one hour after the start of the coextrusion work, the roll temperature did not rise, there was no resin adhesion to the rolls, and the nylon cloth could be easily peeled off to produce a multilayer sheet.

Example 2 As shown in FIG. 3, the inner layer was made of low-density polyethylene 6 with a thickness of 2 mm, and both outer layers were made of adhesive polymer 8 (commercial product, trade name: Admer VE-1) with a thickness of 50 μm each.
A three-layer sheet with a total thickness of 2.1 mm was coextruded. At this time, the resin temperature for low density polyethylene is 190℃, and the resin temperature for adhesive polymer is 190℃.
It was extruded at 140°C, and the surface of the outermost layer was 190°C. A sheet was formed using nylon cloth (satin weave) in the same manner as in Example 1, and the desired multilayer sheet was obtained, with no adhesion to the sheet and easy peeling of the nylon cloth.

Example 3 Example 2 was carried out by replacing the adhesive polymer with a commercially available product under the trade name BOND FAST 7B (manufactured by Sumitomo Chemical), and similar good results were obtained.

Comparative Example 1 A sheet with the same structure as in Example 2 was coextruded and passed through a roll without using nylon cloth, resulting in approx.
After 10 minutes, the sheet surface temperature reached 80°C, the outermost resin layer adhered to the roll, and the sheet could not be formed after that.

Conventionally, coextrusion of a multilayer sheet in which a resin with a much lower softening temperature and melting point than the inner layer was arranged in the outermost layer could not be formed into a sheet due to the resin adhering to the cooling roll, but according to the present invention, It has become possible to form sheets using such a combination of resins, expanding the range of types and performance of multilayer sheets. In particular, it has become possible to place a hot melt agent with a low softening temperature and low melting point on the surface as shown in the examples, and it is now possible to easily attach metal foil to the surface of this sheet using a hot press or hot roll. , it has become possible to easily produce building materials and printed circuit boards, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the implementation state of the present invention, FIG. 2 is a sectional view showing the structure of a five-layer sheet according to Example 1 of the present invention, and FIG. 3 is a three-layer sheet according to Examples 2 and 3 of the present invention. FIG. 1 is an extrusion mold, 2 is a multilayer sheet, 3 is a cooling roll, and 4 is a synthetic fiber cloth.

Claims (1)

[Claims] 1 When coextruding a multilayer sheet in which a resin with a low softening temperature and a resin with a high softening temperature are arranged in the outermost layer on at least one side by combining a resin with a low softening temperature and a resin with a high softening temperature, the resin having a softening temperature higher than any of the resins constituting the multilayer is coextruded. In addition, a synthetic fiber cloth whose fibers are made of a resin with a low softening temperature and a non-adhesive resin disposed in the outermost layer is superimposed on the surface of the resin with a low softening temperature of the multilayer sheet and passed through a cooling roll, and then A method for producing a multilayer sheet, characterized by separating a synthetic fiber cloth from the multilayer sheet.