JPH06210697A - Interfacial instability evaluation method in molding process of multilayer resin body - Google Patents

Abstract

(57) [Summary] [Objective] To provide a method for evaluating interface instability in a molding process of a multilayer resin body, which enables quantitative evaluation based on scientific calculation. [Structure] A method applied to a molding process of a multilayer resin body made of a thermoplastic resin, in which a multilayer resin flow analysis is performed based on respective data such as flow path shape data, resin physical property data, molding condition data, The state quantities such as velocity, pressure, temperature, etc. of each resin 1, 2, 3 are obtained, and the maximum shear stress at the resin interface is obtained from the shear stress distribution obtained from the flow velocity distribution of each resin 1, 2, 3 The instability at the resin interface is evaluated by comparing the maximum shear stress with the critical shear stress that causes the melt fracture, which was previously obtained by experiments.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating interfacial instability in a molding process of a multilayer resin body, and in particular, it is applied to a system for analyzing a multilayer resin flow which flows through the same flow path after a plurality of kinds of resins merge. To be done.

[0002]

2. Description of the Related Art In the process of molding a multilayer resin body,
The flow of each resin is very complicated because plural kinds of resins flow in the same flow path in parallel at the same time.

That is, at the interface between resins having different resin characteristics (viscosity, etc.), the shear stress distribution is determined by the resin characteristics and molding conditions. Then, when the critical shear stress of the resin is exceeded, melt fracture (melt fracture) occurs, resulting in the appearance of a wood grain pattern on the resin body.

For these reasons, it is necessary to prevent the shear stress at the resin interface from becoming larger than the critical shear stress. Then, in order to eliminate this unstable phenomenon, in the past, molding was performed once under a predetermined initial condition, and thereafter, while finely adjusting the flow rate, temperature, etc., by the experience and intuition of a skilled person,
Molding was repeated many times until this unstable phenomenon disappeared. In addition, new adjustment was required from the beginning each time the constituent resin changed.

[0005]

As described above, the prior art is as follows.
It is necessary to perform molding many times based on the experience and intuition of an expert, and quantitative evaluation based on scientific calculation has not been performed. Therefore, a lot of man-hours are required before molding, and it is difficult to optimally design the flow path.

The present invention was devised to solve the above problems, and an object thereof is to provide an interface instability evaluation method in a molding process of a multilayer resin body which enables quantitative evaluation based on scientific calculation. To provide.

[0007]

In order to solve the above-mentioned problems, an interface instability evaluation method in a molding process of a multi-layer resin body according to the present invention includes various data such as channel shape data, resin physical property data and molding condition data. By performing a multi-layer resin flow analysis based on, to determine the state quantities such as velocity, pressure, temperature, etc. of each resin, determine the maximum shear stress at the resin interface in the shear stress distribution obtained from the flow velocity distribution of each resin, The instability at the resin interface is evaluated by comparing the obtained maximum shear stress with the critical shear stress that causes the melt fracture, which was previously obtained by an experiment.

[0008]

[Function] In the molding process of a multi-layer resin body in which a plurality of resins simultaneously flow in the same flow path, a multi-layer resin flow analysis is performed based on each data such as flow path shape data, resin physical property data, molding condition data, and the speed of each resin , State quantities such as pressure and temperature are calculated. Then, the maximum shear stress at the resin interface is obtained from the shear stress distribution obtained from the flow velocity distribution of each resin, and the molding conditions such as the flow rate and the temperature and the flow path are evaluated by the obtained maximum shear stress. That is, since the shear stress (critical shear stress) that causes the melt fracture is obtained in advance for each resin and each combination of the resins by experiments, the flow path, molding conditions, and resin characteristics are input, and the multilayer resin flow analysis is performed. By performing it, it is possible to know whether or not melt fracture has occurred. Then, the flow path and the molding conditions within the allowable range can be known depending on the presence or absence of the melt fracture, so that the design of the flow path in which the interface instability does not occur and the molding conditions can be set.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of a resin merging portion of a molding die (hereinafter, simply referred to as a die) of a multilayer resin body to which the interface instability evaluation method of the present invention is applied.

This die is a feed block die generally used for coextrusion, and in this embodiment, it is 3
A layer feedblock is shown.

That is, the resin inlets 1, 2, 3 divided into three by the two adjusting blades 51, 52 for adjusting the flow velocity of the resin forming each layer, and the resin inlets 1, 1.
Resin merging portion 7 where the resin that has flowed in through 2 and 3 merges
And an outlet 4 for taking out the multi-layer resin body 14 formed of three layers by the joined resins, and the pins 61 and 62 are formed in the resin joining portion 7 so as to face the upper and lower positions thereof.
Are arranged.

The adjusting blades 51 and 52 are provided with support shafts 511 and 5 respectively.
It is configured to be rotatable by 21, and by finely adjusting the vertical rotation angle in FIG.
It is possible to adjust (relatively adjust) the flow velocity of each of the resins 1, 2, and 3.

The pins 61 and 62 have the shape shown in FIG. 2 (a). That is, each resin that has flowed into the resin merging portion 7 has a roll shape in order to press it to a predetermined thickness, and concave cutouts 611 and 612 are formed in a part of the outer peripheral surface of the central portion thereof. It is a thing. The notches 611 and 612 are formed in the pins 61 and 62 in order to make the thickness of each layer of the coextruded multilayer resin body 14 substantially uniform.

That is, when the pins 61 and 62 do not have such cutouts 611 and 612, the thickness of each resin when passing through the resin merging portion 7 is substantially uniform as shown in FIG. 3 (a). Become. However, due to the difference in viscosity when passing through the resin joining portion 7, the multilayer resin body 14 after extrusion is
Is in the state shown in FIG. That is, regarding the middle layer 12, when the viscosity of the middle resin is high, when viewed from the extrusion side, the central portion has a non-uniform thickness that bulges from the left and right side portions.

Therefore, in order to eliminate the depression at the center,
Recessed cutouts 611, 612 are formed in a part of the outer peripheral surface of each pin 61, 62 (the central portion when viewed from the extrusion side), and each resin 11, 12, 13 passes through the resin confluence portion 7. 4a, as shown in FIG.
The central portions of the layers 1 and 13 are bulged in a convex shape.
As a result, the multilayer resin body 14 after extrusion becomes a layer having a uniform thickness as seen from the extrusion side, as shown in FIG. 4B.

However, the notches 61 are formed on the pins 61 and 62, respectively.
In the case where the multilayer resin body 14 after extrusion is in a state opposite to the state shown in FIG. 6
Let 1, 62 be the shape shown in FIG.

Next, a method for evaluating the interface instability of a multilayer resin body molded by using the mold having the above construction will be described.

The interface instability evaluation method of the present invention uses, as input data, flow path shape data, resin physical property data, and molding condition data created by a mesh generator.

Here, the resin physical property data refers to the viscosity, density and thermal characteristics (thermal conductivity, specific heat, etc.) of a plurality of resins, and the molding condition data refers to the flow rate, injection resin temperature, mold temperature distribution. It is data such as.

A multi-layer resin flow analysis is performed based on these data. By solving a partial differential equation modeled by a motion equation, a continuity equation, and an energy equation for each resin in the flow process by the finite element method, Resin speed,
Obtain the state quantities such as pressure and temperature. At this time, regarding the interface of the resin, the boundary condition is that each resin does not cross the interface, and the force in the normal direction of the interface is zero. The equation of motion, continuity equation, energy equation,
Each equation such as a partial differential equation is a general equation used in conventional resin flow analysis.

Under these conditions, in the mold structure shown in FIG. 1, the three kinds of resins 11, 12, and 13 that have flowed in from the resin inlets 1, 2, and 3 are mixed with each other at the resin confluence portion 7. It will flow without. As a result, a flow velocity distribution as shown in FIG. 6 (the velocity becomes higher as the viscosity becomes lower) is formed at the interface between the resins 11, 12, and 13. From this flow velocity distribution, the shear stress distribution shown in FIG. 7 is obtained. Is formed.

Then, the maximum shear stress is obtained from the shear stress distribution shown in FIG. 7, and a series of calculations is completed.

After that, the instability at the resin interface is evaluated by comparing the obtained maximum shear stress with the critical shear stress τc that causes the melt fracture, which is previously obtained by an experiment. That is, when the maximum shear stress exceeds the critical shear stress τc, it can be predicted that an unstable phenomenon due to melt fracture will occur at that portion.

Based on this prediction, if the flow channel is designed such that the maximum shear stress obtained is below the critical shear stress τc or if the molding conditions are determined, a stable multilayer resin body free from melt fracture can be obtained. It can be molded.

[0026]

The interface instability evaluation method in the molding process of a multilayer resin body according to the present invention is performed by performing a multilayer resin flow analysis based on each data such as flow path shape data, resin physical property data and molding condition data. , The velocity, pressure, temperature, etc. of each resin, the maximum shear stress at the resin interface is calculated from the shear stress distribution obtained from the flow velocity distribution of each resin, and the maximum shear stress thus obtained and the experimentally obtained in advance Since the instability at the resin interface was evaluated by comparing with the critical shear stress that causes melt fracture, the design of the flow channel or the determination of molding conditions that does not cause instability phenomena such as melt fracture. There is an effect that it becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a structure of a resin merging portion of a multilayer film molding die to which an interface instability evaluation method of the present invention is applied.

FIG. 2 is a perspective view showing the shape of a pin.

FIG. 3 is a front view showing a change in thickness of each co-extruded resin layer during and after extrusion.

FIG. 4 is a front view showing a change in thickness of each co-extruded resin layer during and after extrusion.

FIG. 5 is a front view showing a layer structure of a multilayer resin body.

FIG. 6 is a graph showing an example of a velocity distribution of a multilayer resin.

FIG. 7 is a graph showing an example of shear stress distribution of a multilayer resin.

[Explanation of symbols]

 1,2,3 Resin inflow port 7 Resin merging part 11,12,13 Resin 14 Multi-layer resin body 61,62 pin

Claims (1)

[Claims] 1. A method applied to a molding process of a multilayer resin body made of a thermoplastic resin, wherein a multilayer resin flow analysis is performed based on respective data such as flow path shape data, resin physical property data, molding condition data and the like. According to, the speed, pressure, temperature, etc. of each resin is obtained, and the maximum shear stress at the resin interface is obtained from the shear stress distribution obtained from the flow velocity distribution of each resin. An interface instability evaluation method in a molding process of a multilayer resin body, which comprises evaluating the instability at a resin interface by comparing with the obtained critical shear stress causing the melt fracture.