JPS6210176B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laminated resin sheet having voids inside. In other words, the present invention relates to resin sheets that are bonded together so that a large number of voids are formed on the bonded surfaces.

It is already known to bond two sheets together to create a resin sheet containing a number of voids therein. For example, one sheet of polyethylene is bent to create a sheet with many hemispherical protrusions, air is stored in the hemispherical protrusions, and the sheet is bonded to another sheet, leaving a void inside the hemispherical protrusions. This is what was left as. The laminated sheets made in this way are widely used as cushion materials.

However, such laminated sheets have drawbacks. The drawback is that if the sheet forming the protrusion is torn, the cushioning properties will be reduced and the product will become unsuitable for use. Also,
The problem is that it takes time and effort to form the protrusions and bond them together. Therefore, there was a need to improve these shortcomings.

The inventor prepared two resin sheets having a large number of peaks 1 and valleys 2, as shown in FIG.
A laminated resin sheet as shown in FIG. 2 was made. When pasting together, the surfaces on which peaks 1 and valleys 2 are formed face each other, and the two sheets are overlapped with the extending directions of the peaks and valleys intersecting each other, and the two sheets are stacked at the place where the peaks and valleys contact each other. A and b were adhered to form a bonded sheet. The thus obtained bonded sheet has voids between the valleys 2 of sheet a and the valleys 2 of sheet b.
When the cushioning properties of this laminated sheet were examined, it was found that it exhibited good cushioning properties. Therefore, the inventor tried to come up with an efficient manufacturing method for making such a laminated sheet.

The inventor decided to make the above-mentioned sheets a and b by first making cylindrical sheets, extruding and crushing them into flat shapes, and pasting them together, instead of making them separately. In this case, the die used to make the cylindrical sheet was formed with a large number of peaks or valleys along the circumferential direction in the inner die, and the inner die was extruded while rotating. Then, the peaks and valleys are formed to extend spirally on the inner surface of the cylindrical sheet, and when these are crushed and flattened, the extending directions of the peaks intersect with each other between the opposing inner surfaces, resulting in a bonded sheet. We have found that it is convenient to do so. This invention was made based on such knowledge.

This invention extrudes thermoplastic resin softened by heating from a die with an annular gap,
In a method for manufacturing a cylindrical molded body, a large number of peaks or valleys are formed along the circumferential direction on the wall surface of an inner mold that constitutes an annular gap, and while the inner mold is rotated around the axis of the annular gap. A laminated resin sheet with internal voids, characterized by extruding a resin, flattening the extruded cylindrical molded body, gluing or fusing the peaks on the inner surface, and leaving voids in the valleys of the inner surface. This relates to a manufacturing method.

The main points of this inventive method are explained below based on the drawings. As already mentioned, FIG. 2 is a partially cutaway perspective view of a bonded resin sheet that is the object of the method of this invention. FIG. 3 is a partially cutaway perspective view schematically showing the main points of the method of this invention. FIG. 4 is a diagram showing details of the cap used in the method of this invention.

In FIG. 3, reference numeral 11 is a die attached to the tip of the extruder. The cap 11 has an outer mold 12 and an inner mold 1.
3, and an annular gap 14 is provided between the outer mold 12 and the inner mold 13. A thermoplastic resin heated and softened in an extruder is extruded from the annular gap 14, and a cylindrical molded body 15 is formed. Inner mold 1
A large number of ridges or valleys 16 are formed along the circumferential direction on the wall surface of 3. Therefore, the cylindrical molded body 1
Valleys or peaks are formed on the inner surface of the mold 5 at locations corresponding to the peaks or valleys 16 of the inner mold 13, and the peaks extend as protrusions 17.

The thermoplastic resin is extruded from the die 11 at a speed indicated by the arrow x. At this time, the inner mold 13 is rotated at a constant speed indicated by the arrow y. Therefore, the cylindrical molded body 15
The protrusion 17 is twisted on the inner surface and extends in a spiral shape. In this way, the cylindrical molded body 1
5 is provided with a spiral protrusion 17 on the inner surface. While the inner surface of the cylindrical molded body 15 is still softened, it is pressed from the outside by a pair of rolls 18 to flatten it.

When it is flattened, the protrusions 17 are formed in a spiral shape on the inner surface, so between the inner surfaces facing each other,
The extending directions of the protrusions 17 intersect with each other. Therefore, when the flat body is further pressed, the ridges on the inner surface of the flat body come into contact with each other at their tips. At this time, if the inner surface of the resin is still in a softened state, the protrusions fuse together between the contact points, and a bonded sheet is obtained there. In this laminated sheet, gaps are left between the valleys on the opposing inner surfaces. In this way, a laminated resin sheet with gaps between the inner laminated surfaces is obtained.

In the above explanation, the inner mold 13 is rotated at the speed of the arrow y, but if only the inner mold 13 is rotated, the cylindrical molded body 15 is likely to be twisted during the extrusion process. To prevent this, it is preferable to rotate the outer mold 12 in the direction opposite to the arrow y. That is, the outer mold 12
When rotated at the speed of arrow z, the cylindrical molded body 1
Since 5 itself is not twisted, it is extruded straight. The rotational speed z of the outer mold 12 is preferably such that the linear velocity of rotation on the wall surface of the outer mold 12 is equal to the linear velocity of rotation on the wall surface of the inner mold 13.

Various thermoplastic resins can be used in the method of this invention. The main resins that can be used are polyvinyl chloride, polyethylene, polypropylene, polystyrene, polyester, etc. Although the method of this invention is intended for a laminated sheet in which the resin does not contain a foaming agent and is therefore not composed of a foam, it also includes cases where the sheet is made of a foam. When the sheet is made of foam, the resulting laminated sheet has even better cushioning properties. In particular, when a soft resin is used as the resin and it is made into a closed-cell foam, a sheet with extremely excellent cushioning properties can be obtained.

When the resin is made into a foam, the cells in the foam are elongated in the direction in which the protrusions 17 extend, and therefore the orientation of the resin molecules in the direction in which the protrusions 17 extend is clearly shown. Is recognized. Therefore, in the case of foam, the direction in which the bubbles are stretched is
This will differ between the facing laminated sheets.

As the blowing agent to be added when forming a foam, various known blowing agents can be used. Foaming agents can be broadly divided into those that are gaseous at room temperature;
There are three types: those that are liquid at room temperature and easily volatilize, and those that are solid at room temperature and decompose and generate gas when heated, and any of these can be used in the method of this invention. . As blowing agents that are gaseous at room temperature, nitrogen, carbon dioxide, propane, butane, etc. can be used, and as easily volatile liquids,
Aliphatic hydrocarbons such as pentane, hexane, petroleum ether, halogenated hydrocarbons such as methylene chloride, trichloromonofluoroethane, trichlorotrifluoroethane can be used, and as decomposable solid compounds, Azo compounds such as azodicarbonamide can be used.

The method of the invention requires rotating a portion of the wall surface of the inner mold, particularly the wall surface around the tip of the inner mold forming the annular gap. Attempts to rotate parts of the base are already known for achieving other purposes. For example, when forming a non-foamed cylindrical film using the extrusion inflation method and winding the formed film into a roll, a part of the cap is rotated to improve the packaging appearance of the wound film. It is known to do. In more detail,
The extruded film has local thickness differences, so if the extruded film is wound as is, the thicker parts of the film will overlap in one place and the outer diameter of the rolled product will be uneven. , it has been proposed and known to rotate the tip of the die that forms the extrusion slit.

However, in the above-mentioned known method, the base to be rotated is provided with an annular gap of substantially equal width, and a large number of ridges or valleys curved in the circumferential direction are formed on the wall surface constituting the gap. It is not something that has been specifically established. Furthermore, the purpose of rotation is to improve the packaging appearance of the wound film, and is not to create peaks or valleys or to change the direction in which the peaks or valleys extend. Further, in the known method, the rotation is extremely slow, and it takes approximately 10 to 20 minutes to rotate the cap once. However, in the method of this invention, the rotation is fast, and the rotation is about three times in less than one minute.

Although FIG. 3 shows a case where no ridges or valleys are formed along the circumferential direction on the wall surface near the tip of the outer mold 12, ridges or valleys may also be formed on the wall surface of the outer mold 12. . If peaks or valleys are also formed on the wall surface of the outer mold 12, a bonded sheet with protrusions formed on the outer surface can also be obtained. This laminated sheet has peaks and valleys on the outer surface, so when used as a cushion material, the surface can be prevented from coming into close contact with other objects. This is advantageous because it exhibits good cushioning properties.

The rotating portion of the cap is the wall surface of the resin passage located near the tip of the cap. The rotating wall surface is provided with a large number of peaks or valleys that bend along the circumferential direction. This peak or valley extends from the tip of the cap to the back of the cap. The direction in which it extends is
It may coincide with the axial direction of the annular gap, but it may also be slightly inclined. It is desirable that the direction of inclination roughly corresponds to the direction in which the resin travels as a result of the combination of the extrusion speed of the die and the rotational speed of the die.

The ridges or valleys provided on the wall surface of the resin passage of the cap can also be viewed as mere kerfs. The kerf provided in the inner mold is a valley when viewed from the mouthpiece itself, and the portion other than the kerf is a ridge. The mountains or valleys are
It is determined appropriately depending on the thickness of the resin sheet to be obtained. As shown in Figure 2, 1 before bonding.
Taking two sheets and explaining their relationship is as follows. First, let T be the thickness of the sheet at the bottom of the valley, q be the difference in height between peaks and valleys, and P be the distance between the peaks of adjacent peaks, then q should be within the range of 0.5 to 5 times T. Yes, P should be within the range of 2 to 10 times T. Among these, it is preferable that q be in the range of 1 to 3 times as much as T, and that P be in the range of 3 to 8 times as much as T.

The rotational speed of the die changes in accordance with the advancing speed of the resin within the die due to extrusion. In other words, the rotational speed is
Make it bigger accordingly. In this case, the relationship between the rotational speed of the cap and the advancing speed of the resin can be considered as follows. In FIG. 3, among the angles formed by the rotational linear velocity y of the inner mold 13 and the advancing speed x of the resin in the extrusion direction, if the angle α is used as a reference as shown in the figure, then y/x=tanα. Become. Similarly, among the angles formed by the rotational linear velocity z of the outer mold and the extrusion direction velocity x of the resin, if the angle β is taken as a reference as shown, z/x=tanβ. Therefore, taking into consideration that y and z rotate in opposite directions, the larger the sum of the angles α and β, the larger the ratio of the rotational speed to the extrusion speed. In particular, if the values of angle α and angle β are both
At 45 degrees, the effect of rotational speed should be most pronounced.

However, in reality, this is not always the case, and the rotational speed at which the influence of rotation becomes noticeable varies somewhat depending on the resin. For example, in the case of polyethylene and polystyrene, when this is made into a foam, the sum of the angle α and the angle β is 20 or more.
The effect of rotation was most pronounced when within 60 degrees.

In order to bond the inner surfaces of the cylindrical molded body 15 together, it is convenient to do as follows. The cylindrical molded body 15 extruded by the method shown in FIG. 3 is cooled from the outside. Then, the surface of the cylindrical molded body facing outward is first cooled. However, the inner surface of the cylindrical molded body is still softened due to the delay in cooling. Therefore, when the cylindrical molded body is crushed to make it flat, the outer surface is not deformed because it is cooled, but the inner surface is in a softened state and is fused together and becomes one body. At this time, the degree of flatness is adjusted so that the inner valleys do not become fused together. In this way, it is possible to bond them together while leaving a gap.

In addition, in order to form a bonded body, it is also possible to first form a cylindrical molded body, then apply an adhesive to the inner surface of the molded body, and adhere the peaks on the inner surface to each other to form a bonded body. In this case, the cylindrical molded body may be slightly heated. For bonding, it is preferable to use a pair of rolls and to allow continuous passage between the rolls with a gap between the rolls just such that the ridges on the inner surface are in contact with each other.

According to the method of this invention, a ridge or valley bent in the circumferential direction is provided on the inner mold wall surface at the tip of the die, and the tip of the die is rotated, thereby crushing the obtained cylindrical molded body and flattening it. By simply applying light pressure from the outside, the protrusions intersecting on the inner surface can be bonded or fused together. Therefore, according to the method of the present invention, laminated resin sheets having internal voids can be manufactured easily and continuously. Moreover, since the thus obtained bonded sheet has the extending directions of the protrusions intersecting each other inside, it is difficult to tear along one valley. In particular, as the tip of the cap rotates, the resin molecules become oriented in the direction in which the protrusions extend, so even if the sheet is made from foam, the laminated sheet will not tear easily. It is becoming. Moreover, since the sheet has voids inside, it is suitable as a cushion material. In particular, when a foamable resin is used, the cushioning action of the bubbles is further added, making the laminated sheet even more excellent as a cushioning material. The method of the invention thus provides various advantages.

Next, an example of the method of this invention will be specifically explained with reference to Examples. In the following, parts simply mean parts by weight.

Example 1 Using low density polyethylene as the resin, the resin
After mixing 100 parts with 1 part of talc (bubble control agent), this mixture was heated at a rate of 15 kg for 1 hour with a diameter of 40 mm.
It was fed to a φ extruder. The temperature of the resin inside the extruder
The resin was heated to 180°C to melt it, and 12 parts of butane (a blowing agent) was press-fitted in the middle of the extruder, and the resin was cooled to 110°C at the tip of the extruder and extruded from the die.

The cap shown in FIG. 4 was used.
In Figure 4, Figure A is a front view of the die with the extrusion end clearly visible, Figure B is a cross-sectional view taken along the Ro-Ro line in Figure A, and Figure C is a partially cutaway view of Figure A. This is an enlarged view.
The die was provided with an annular gap 14 between an outer mold 12 and an inner mold 13, from which the resin was extruded. Further, the inner mold 13 was provided with a hole 19 in the center thereof which communicated with the outside air. Annular gap 14
When viewed from the extrusion end surface, protrusions were formed as if 33 isosceles triangular kerfs 16 were formed at equal intervals on the wall surface of the inner die 13. Describing the dimensions of the gap, the diameter of the annular gap 14 is approximately 60 mm, the width W is 0.4 mm, the gap between the grooves M is 2.3 mm, the base N of the groove 16 is 3.4 mm, and the height H is 3.0 mm. And so.

While rotating the outer mold 12 and inner mold 13 of this cap in opposite directions at a rate of 6 revolutions per minute,
The resin was extruded. The resin took on a cylindrical shape and foamed as it exited the cap, increasing its thickness and significantly increasing its diameter. In this case, in order to increase the diameter and adjust the amount of gas contained within the cylindrical molded body,
Air was introduced through hole 19. The tip of the cylindrical molded product thus extruded was pinched between a pair of pinch rolls to make it flat, and the gap between the last rolls was set to 3 mm.
While the inner surface of the molded body was still in a softened state, the tips of the protrusions on the inner surface were fused together, leaving a gap between the valleys on the inner surface.

The foam sheet thus obtained has a density of 0.035
g/ ^cm3 , the seat width is 453mm, and the maximum internal
It had a gap of 7.0 mm and had excellent cushioning properties.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a conventional chevron-shaped resin sheet. FIG. 2 is a partially cutaway perspective view of a bonded resin sheet that is an object of the present invention. FIG. 3 is a schematic perspective view showing the main parts of the method of this invention. FIG. 4 is a diagram showing details of the cap used in the method of this invention.

Claims (1)

[Claims] 1. In a method for manufacturing a cylindrical molded body by extruding a thermoplastic resin softened by heating from a die having an annular gap, the wall surface of the inner mold forming the annular gap First, a large number of peaks or valleys are formed along the circumferential direction, the resin is extruded while the inner mold is rotated around the axis of the annular gap, and the extruded cylindrical molded body is flattened so that the peaks on the inner surface are separated from each other. A method for manufacturing a laminated resin sheet having internal voids, which is characterized by adhering or fusing and leaving voids in the valleys on the inner surface. 2. The method according to claim 1, characterized in that a foaming agent is included in the resin and the resin is foamed simultaneously with extrusion. 3 The linear velocity of rotation on the wall of the annular gap is
The inner mold is rotated so as to be equal to the advancing speed of the resin in the annular gap,
A method according to claim 1 or 2. 4. In a method for producing a cylindrical molded body by extruding a thermoplastic resin softened by heating from a die having an annular gap, a wall surface of an inner mold constituting the annular gap is filled in the circumferential direction. The inner mold is rotated around the axis of the annular gap, and the outer mold is rotated in the opposite direction around the axis of the annular gap to extrude the resin, forming an extruded cylindrical shape. A method for producing a laminated resin sheet having internal voids, which is characterized by flattening a molded product and bonding or fusing the peaks on the inner surface to each other, leaving voids in the valleys on the inner surface. 5. The method according to claim 4, characterized in that a foaming agent is included in the resin and the resin is foamed simultaneously with extrusion. 6 The linear velocity of rotation on the wall of the annular gap is
The method according to claim 4 or 5, characterized in that the inner mold and the outer mold are rotated so as to be equal to the advancing speed of the resin in the annular gap.