JPS61108525A - Manufacture of thermoplastic resin foam - Google Patents

Abstract

PURPOSE:To improve the cushioning characteristics due to the local change of packing of fine foam strands and consequently extends the field of application of the strands by a method wherein the relationship of the diameter and interval of the extrusion holes of a mouth piece to the extent of free expansion ratio from the extrusion hole is specified and further the relationship of the extrusion speed and taking-up speed to the diameter and interval of the extrusion holes and the extent of free expansion ratio is specified. CONSTITUTION:A large number of extrusion holes 51 with the hole diameter of Dmm is regularly arranged on the resin discharging surface of a mouth piece 5 provided at the tip of an extruder 1. A mouth piece 5 provided at the tip of an extruder l consists of a sheet-like body, or the resin discharging surface of which a large number of extrusion holes 51 with the hole diameter of Dmm is provided at regular intervals L so as to realize a similar shape scaled-down from the sectional shape of foams. The interval L of the arrangement of the extrusion holes is determined by the attached formula (1). In this case, the extent of free expansion ratio of a fine foam strand freely extruded from the extrusion hole of the mouth piece. The thermoplastic resin kneaded with foaming agent in the extruder 1 is extruded from the extrusion holes 51 of the mouth piece 5 in the form of fine strands and led in a shaping device 6 and finally taken off by a puller 7. In this case, the fine foam strands 8 are taken off at the extrusion rate or take-off speed (v), which is controlled so as to satisfy the attached formula (2), in which V represents the extrusion speed of the fine foam strand freely extruded from the extrusion hole.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing thermoplastic resin foams having different filling rates (densities) of foam strips in the thickness direction by extrusion molding.

[Prior Art] A thermoplastic resin foam manufactured by an extrusion foam molding method is a method in which a large number of naturally plastic resin foam strips that are undulated in the longitudinal direction are fused or adhered at the contact portions to form strips. Some have a structure in which they are concentrated while forming irregularly shaped voids between them, and are used as various core materials, cushioning materials, thermal insulation materials for buildings, etc. Publication No.).

In addition, as a method for producing thermoplastic and resin foams, a foam molding device is installed in front of the mouthpiece of an extruder by drilling a large number of small holes on the inner surface that communicate with an exhaust device, and the resin in this device is There is a method of foaming while performing vacuum suction through small holes (Japanese Patent Publication No. 18779/1983).

[Problem to be Solved by the Invention 1] However, the thermoplastic resin foams described in Utility Model Publication No. 57-38254 and Utility Model Publication No. 57-47283 are all The material is also uniform, and its use as a cushioning material, etc. is limited.

In addition, the method described in Japanese Patent Publication No. 36-18779 is a method for manufacturing a foam whose inside is homogeneously foamed, and although vacuum suction using a foam molding device is effective in making the surface smooth and beautiful, this method However, it was not possible to produce foams with different densities in the thickness direction, that is, different filling rates.

The present invention solves these problems and attempts to produce a thermoplastic resin foam with partially different filling ratios of foamed strips, good cushioning properties, and a wide range of uses using an extrusion foaming method. be.

[Means for Solving the Problems] The present invention provides a method of extruding a thermoplastic resin containing a blowing agent from an extruder to produce a thermoplastic resin foam. At intervals of 0.9D/”Tr ≦L ≦3,6D fl (however,
D represents the diameter of the extrusion hole, and R represents the expansion ratio when the thermoplastic resin is freely foamed through the extrusion hole. same as below.

) After forming a large number of R foam strips by extruding the thermoplastic resin from a nozzle with a large number of extrusion holes arranged on the fat discharge surface of the skewer, immediately introducing these foam strips into a shaping device, While at least one side of the foam strip is vacuum-suctioned inside the shaping device, the take-up speed V is within the range shown below: 0.54 VD (rπ/L) ≦v ≦1.26 V
D ((π/L) (where v ku ■, ■ represents the extrusion speed of the foamed strips when freely extruded from the extrusion hole.) This is the manufacturing method.

The method of the present invention will be explained with reference to the drawings.

FIG. 1 is a side view showing an embodiment of the method of the present invention.

In this figure, 1 is an extruder, 2 is a resin supply hopper, 3 is a foaming agent injection pump, 4 is a foaming agent tank, 5 is a mouthpiece attached to the tip of the extruder 1, 6 is a shaping device, and 7 8 shows the drawing machine and 8 shows the extruded foam strips.

As shown enlarged in FIG. 2, the cap 5 has a hole diameter of Dmm.
A large number of extrusion holes 51 are regularly arranged on the resin discharge surface, and the holes are spaced so that the envelope shape of the extrusion holes 51, that is, the cross-sectional shape of the foam to be manufactured, has a similar shape that is linear. It consists of a plate-shaped body separated by

The arrangement interval of the extrusion holes 51 is 0.9[) 4π≦L≦3.6[) (π (However, R is the free foaming ratio of the foamed strips when freely extruded from the extrusion holes of the die. ).

As shown in FIG. 3, the shaping device 6 forms a shaping portion by arranging a rotating belt 61 so as to have a cross-sectional shape slightly larger than the outer contour connecting the outermost rows of extrusion holes 51, for example. A large number of pores or 111162 are perforated in the upper surface of the belt 61.

Further, a vacuum suction mechanism is disposed adjacent to these pores or slits 62. As shown in an enlarged view in FIG. 4, the reduced pressure suction mechanism includes a suction box 64 in which a large number of small holes 63 are provided on a surface close to the pores or slits 62, and a suction box 64 provided inside on the other surface of this box. Intake duct 6 installed in communication
5, and the other end of the intake duct 65 is connected to a vacuum suction pump or the like, and the vacuum suction is carried out through the small hole 63.

In addition to such a rotary belt, the rough shaping device 6 may be used, for example, by combining a plurality of rolls 66, 67 in a grid pattern as shown in FIG. It is also possible to use a plate in which shaped parts are formed by arranging the plates vertically and horizontally. Even in such a forming device 6 consisting of rolls 66 and fixed plates, a large number of pores or slits 63 are bored on the outer peripheral surface of some of the rolls or on the surface of one of the fixed plates, and these pores Alternatively, the inside is configured to be vacuum-suctioned from the slit by a vacuum suction mechanism.

In the present invention, extrusion t! The thermoplastic resin kneaded with the foaming agent in the die 11 is extruded into strips through the extrusion hole 51 of the die 5, introduced into the shaping device 6, and taken off at a take-off 417.

Here, the extrusion amount or take-up speed of the foamed strip 8 is adjusted so that the following range 0.54 VD < (π/l-)≦V≦ 1.26
VD (fl/L) (However, v<V, and V is 1 freely from the extrusion hole.
It represents the extrusion speed of the foam strips during extrusion. ) is picked up at a picking speed V.

The foamed strips 8 thus extruded and foamed travel through the forming device 6 while meandering and bending, and are sucked under reduced pressure from one side within the shaping device 6, and at the same time, contact portions with adjacent foamed strips 8. are fused to each other to produce a thermoplastic resin foam having the same shape as the inner surface of the shaping device 6 but with the filling rate of the foamed strips 8 varying in the thickness direction.

In the present invention, if the arrangement interval of the extrusion holes 51 of the nozzle 5 is less than 0.9 [π], the foamed strips 8 will not meander and bend sufficiently, resulting in a foam with a high filling rate. On the other hand, if the array spacing exceeds 3.6D (π), the mutual fusion of the foamed strips 8 becomes poor, making it impossible to obtain the desired cross-sectional shape, which is not desirable.

On the other hand, the take-up speed V of the foam strips 8 is 0.54VD (Fπ/
L) If the foam strips 8 are smaller, the foam strips 8 may become clogged in the forming device 6 and become impossible to remove, or the surface of the foam may become bagged, spoiling the appearance, or the apparent foaming ratio may be reduced. may be lower than the foaming ratio of the R foam strips 8.

Furthermore, if the take-up speed V exceeds 1.26 VD ((π/L)), the foamed strips 8 may not meander at all, resulting in incomplete fusion of the foamed strips 8 with each other.

Examples of the thermoplastic resin used in the present invention include homopolymers such as polyethylene, polypropylene, polybutene, polystyrene, polyvinyl chloride, and polymethyl methacrylate, and monomers copolymerizable with monomers of these polymers. copolymers with polymers, or mixtures of homopolymers or copolymers thereof are used.

Gases or volatile liquids used as blowing agents include those with a boiling point of 60'C or less, such as propane, butane,
Dichlorodifluoromethane, dichlorotetrafluoroethane, etc. are preferably used. Further, the blowing agent may be used by impregnating the thermoplastic resin in advance.

In the present invention, a cell regulator, a colorant, a stabilizer, an antistatic agent, a filler, a plasticizer, etc. may be added to the resin as necessary.

Extrusion 811 is not particularly limited as long as the blowing agent is sufficiently melted and mixed with the resin and the temperature of the resin can be controlled, but a type in which the blowing agent is press-fitted from the middle of the barrel is preferably used.

(Function) In the present invention, the diameter and interval of the extrusion holes of the nozzle are set in the above range in relation to the free expansion ratio from the extrusion hole, and the relationship between the extrusion speed and the withdrawal speed is set to the diameter of the extrusion hole of the nozzle,
By setting the spacing and the free expansion ratio from the extrusion holes within the above-mentioned specific ranges, and by vacuum suctioning the inside of the extrusion device from at least one side of the inner surface using a vacuum suction mechanism, it is possible to The extruded foamed strips bend in a nearly meandering manner within the shaping device, and are vacuum-suctioned from one direction, making the arrangement spacing coarser and denser, changing in that direction to become bulkier, and the contact portions of the foamed strips melting into each other. A thermoplastic resin foam is produced which has an apparent expansion ratio greater than the expansion ratio of the resin and in which the filling rate of the foamed strips changes continuously in the thickness direction.

(Example) Extruder diameter: 50mm, barrel length: 1,500mm
Plate body thermoplastic resin arranged in the 0th row: Low density polyethylene (Sumi Rikisen L40
2, MI: 3,5, density: 0.922) 100
Contains 0.5 parts by weight of talc powder.

The blowing agent dichlorotetrafluoroethane was injected at a ratio of 25 parts by weight per 100 parts by weight of low density polyethylene from the blowing agent injection port located 150IllIll from the resin supply port of the extruder. 'Molding temperature: 100-150℃ from the extruder's resin supply port to the foaming agent injection port, 110℃ from the foaming agent injection port to the tip of the extrusion tip, and 100℃ from the die.
Each maintained at ℃.

Foaming ratio (R): 35 times Extrusion speed (V): 10111/min Shaping device and pulling machine Two wheels 850IIIm, length 1,
000mm belt type pulling machine. The belt placed above is made of 40-mesh stainless steel mesh, and a vacuum suction device is built in close to the inside. The belt placed below is made of rubber.

A vacuum suction device is a suction box with a large number of small holes on one side and an intake duct attached to the other side, and the intake duct is connected to a vacuum suction pump.

Under the above conditions, the foamed strips extruded from the nozzle were collected under vacuum suction using a vacuum suction pump while changing the withdrawal speed. The appearance and foaming state of the obtained foam were observed, and the filling rate of the foam strips was measured, and the results shown in the following table were obtained.

(Margin below) (Note) The filling rate of the foam strips is 17'2 thick.

[Effects of the Invention] As is clear from the above description, the method of the present invention uses a die having a large number of extrusion holes, and uses a forming device to form a large number of foamed strips extruded from the die. Since the foam is formed into a desired shape by mutual fusion by serpentine bending while vacuum suction is applied from the direction, it is possible to produce a foam that is bulkier and has a larger apparent expansion ratio than conventional foams, as well as being thicker. By changing the filling rate of the foam strips in the horizontal direction, a foam with good cushioning properties can be produced.

Further, it can be manufactured in one simple process, which has the advantage of not only high productivity but also low equipment costs.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the method of the present invention, FIG. 2 is an enlarged perspective view of the base used in this actual M embodiment, and FIG.
FIG. 4 is an enlarged perspective view of a vacuum suction mechanism, and FIG. 5 is a perspective view of another example of the shaping device. 1......Extrusion rock 5......Clip 6......Formation device 7...・・・・・・・・・Take-up machine 8・・・・・・・・・・・・For foam strips Applicant Sekisui Chemical Co., Ltd. Representative Yasutori Fujinuma 221 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) When extruding a thermoplastic resin containing a blowing agent from an extruder to produce a thermoplastic resin foam, the extruder is attached to the tip of the extruder, and the array interval L is 0.9D√R≦L≦ within the range shown below. 3.6D√R (However, D represents the diameter of the extrusion hole, and R represents the expansion ratio when the thermoplastic resin is freely foamed from the extrusion hole.) A large number of extrusion holes were arranged on the resin discharge surface. After extruding the thermoplastic resin from the die to form a large number of foamed strips, the foamed strips are immediately introduced into a forming device, and at least one side of the foamed strips is depressurized inside the forming device. 0.54VD (√R/L) ≦v≦1.26VD (√R/
L) (where v<V, D is the diameter of the extrusion hole, R is the expansion ratio when the thermoplastic resin is freely foamed from the extrusion hole, and V
represents the extrusion speed of the foam strip when extruded freely from the extrusion hole. ) A method for producing a thermoplastic resin foam, characterized by taking off.