JPH06246761A - Manufacture of lid skin of air bag for vehicle - Google Patents

Abstract

PURPOSE:To obtain a method for manufacturing an air bag lid skin having elongation characteristics, tear properties of a high level and reduced in thickness and weight by setting high polymerization degree of base vinyl chloride resin. CONSTITUTION:A powder molding material in which plasticizer, stabilizer, fluidization agent, etc., are mixed with base vinyl chloride resin having 1500-2500 of mean polymerization degree is cast in a mold heated to a predetermined temperature, and excess material fusion-bonded to a mold surface is discharged out of the mold. Then, a fusion-bonded layer is heat treated from its rear surface, the mold is then cooled, and it is released from the mold to obtain powder slush molded skin. Thus, a method for manufacturing a lid skin of an air bag for a vehicle having 250% or more of elongation according to JIS K6723 is obtained. (5/100)X+35 >=Y>=70 (in the formula, Y is a weight of plasticizer per 100 pts.wt. of the base vinyl chloride resin, and X is mean polymerization degree of the base vinyl chloride resin.)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lid skin of an airbag mounted on an automobile instrument panel.

[0002]

2. Description of the Related Art As is well known, the powder slush molding method is a mold in which a powder molding material obtained by mixing a plasticizer, a stabilizer, a fluidizing agent and the like in a base vinyl chloride resin is heated to a predetermined temperature. It is a method for molding a skin material, which comprises a step of cooling the molding die and releasing it after the excess material is discharged to the outside of the die after the material is melted in the die layer after being melted in the die surface.

The powder slush molding method is characterized in that it is capable of forming a deep-drawing shape and that a surface shape such as a thread pattern different from its surrounding can be formed at a predetermined position. , Has been widely used for molding pad skin materials for automobile instrument panels.

By the way, there is a tendency that the instrument panel is increasingly equipped with an airbag as a safety measure in the event of a collision on the assist side recently.

The airbag mechanism operates a starting device to inflate and deploy the airbag with high-pressure gas or the like when more than a predetermined energy is applied at the time of collision of a vehicle. At this time, a skin material or urethane is used. It is an important problem from the viewpoint of safety such as eye protection to prevent the lid component material of the airbag from scattering.

Particularly, since the lid of an airbag is exposed to direct sunlight, there is a concern that the elongation rate may decrease due to light or heat.

On the other hand, with respect to pad skins for automobile instrument panels, in addition to demands for weight reduction, demands for durability and the like are becoming stronger and stronger, and the thicknesses are made thinner while keeping strength such as tear strength at a high level. Is desired.

Therefore, it is conceivable to use a resin having a high degree of polymerization as the base vinyl chloride resin, but the powder slush molding method, which is superior as a molding method for pad skins for instrument panels for automobiles, is Since it is a different construction method, there is a great limitation on heat melting of the powder molding material, and it has not been put to practical use.

The average degree of polymerization of the base vinyl chloride resin of the commercially available powder molding materials (3 kinds) investigated and analyzed by the present inventors is as follows.
780 to 860, and Fujiwara et al.'S report “Molding Technology for Powder Slash Instrument Panel” (Automotive Technology, 4
0, No. 5,74 (1989)), the range of PVC degree of polymerization is 700-1000.

Further, regarding the prior art examples found in the patents applied for, the average degree of polymerization of the base vinyl chloride resin disclosed in the examples of JP-B-63-54019 is 800 and 1050, and the comparative examples Regarding the above, an example in which the degree of polymerization of the base vinyl chloride resin is 2350 is shown, but the elongation is 80%, which is significantly inferior to the elongations of 350 to 400% shown in the examples, and is practically used. It cannot be used, and in other Comparative Examples, the meltability and the surface smoothness are inferior. These low elongation and poor surface smoothness are considered to be due to poor melting and incomplete melting.

In JP-A-63-74146, the average degree of polymerization of vinyl chloride resin is in the range of 400 to 1500,
Although the range of 500 to 1200 is particularly preferable, the vinyl chloride resin disclosed in the examples has an average degree of polymerization of 500 to 1050.

An embodiment of Japanese Patent Laid-Open No. 2-138355,
Also in the comparative example, the average degree of polymerization of the base vinyl chloride resin is 800, and in the examples of JP-A-2-112913, the average degree of polymerization of the base vinyl chloride resin is 700 and 800.

[0013]

On the other hand, the characteristics of the skin material,
In particular, the elongation property and the tear property are superior when the average polymerization degree of the base vinyl chloride resin is higher, and the improvement of these properties has an advantage that the thickness can be further reduced.

However, as described above, the vinyl chloride resin is easily deteriorated by heat and the molding temperature is limited. Therefore, the heat melting property is limited, and the average degree of polymerization of the base vinyl chloride resin of the powder molding material is limited. There was a problem that it could not be raised.

The present inventors have made an average polymerization of the base vinyl chloride resin by, for example, increasing the composition of the powder molding material, increasing the thickness of the molding die to increase the heat capacity, and using copper as a backup to improve the thermal conductivity. Various studies have been conducted on measures to increase the degree of polymerization, and the technical prospect has already been obtained that the average degree of polymerization can be increased to 1300 by extending the conventional knowledge.

Furthermore, the present invention has been accomplished by earnestly researching a new method for increasing the average degree of polymerization of the base vinyl chloride resin, such as observing the heat melting behavior in detail.

Thus, the object of the present invention is to have a high level of elongation property and tear property by setting the degree of polymerization of the base vinyl chloride resin high.
The purpose of this is to provide a method for manufacturing an air bag grid skin that can be made thin and lightweight.

[0018]

The present invention provides a powder molding material comprising a base vinyl chloride resin having an average degree of polymerization of 1500 to 2500 and a plasticizer, a stabilizer, a fluidizing agent, etc. It is put into a mold heated to a temperature, the excess material deposited on the mold surface is discharged out of the mold, then heat-treated from the back surface of the welding layer, and then the mold is cooled to remove the desired material. Characterized by obtaining a powder slush molded skin.

When the average degree of polymerization of the base vinyl chloride resin is less than 1500, the effect of improving the characteristics is small,
On the other hand, if it exceeds 2,500, thermal fusion becomes incomplete, and it becomes difficult to obtain practical properties.

A more preferable range of the average degree of polymerization is 170.
It is 0-2200. If the average particle size of the base vinyl chloride resin is too large, the meltability will be poor, and if it is too small, the fluidity of the powder will be poor.
The range of 0 μm is preferable.

The amount of plasticizer is related to the hardness of the molded product,
It affects the heat melting property and the fluidity of the powder. If the amount of the plasticizer per 100 parts by weight of the base vinyl chloride resin is too small, the heat melting property becomes poor, and if it is too large, the fluidity of the powder becomes poor. The range represented by the following general formula is a useful range, and more preferably 70 to 110 parts by weight.

(5/100) X + 35 ≧ Y ≧ 70 (In the formula, Y represents the weight of the amount of the plasticizer per 100 parts by weight of the base vinyl chloride resin, and X represents the average degree of polymerization of the base vinyl chloride resin.) As a heat treatment method for the back surface of the welding layer, a method using hot air,
Infrared irradiation is a practical method.

Further, as a characteristic of the powder slush molded skin, it is necessary that it is sufficiently melted, and the elongation rate according to JIS K6723 is 250% or more, excluding the influence of the surface shape such as drawing depth, and further, It is preferably 300% or more.

[0024]

[Function] In the heat melting in powder slush molding, the powder molding material in contact with the molding die is melted, the heat is transferred to the next powder through the melting layer, and the powder is melted. Melting progresses in the form of heat being transferred to and melting.

When the average degree of polymerization of the base vinyl chloride resin is increased, when the molten layer has a certain thickness, the amount of heat transferred decreases, and the melting of the powder becomes insufficient. The behavior is such that the thermal conductivity decreases and it becomes more difficult to melt.

The decrease in thermal conductivity caused by the insufficient melting has a larger effect than expected on the thermal melting of the powder molding material having a high average degree of polymerization of the base vinyl chloride resin.

That is, the decrease in the heat melting property of the powder molding material having a high average degree of polymerization of the base vinyl chloride resin is caused by the decrease in the heat melting property caused by the high average degree of polymerization of the base vinyl chloride resin. There are parts that are directly related and parts that are indirectly related through the phenomenon of decreased thermal conductivity.By providing a means to compensate for this decreased thermal conductivity, the degree of polymerization of the base vinyl chloride resin is significantly increased. It has been found that it is possible to achieve the present invention.

[0028]

【Example】

<Example 1> -Preparation of powder molding material 100 parts by weight of a base vinyl chloride resin having an average degree of polymerization of 1700 (average particle diameter 130 μm) was added to Supermixer [(Ltd.)
Kawata] and epoxidized soybean oil 5 with stirring
4 parts by weight of a metal-based stabilizer and 3 parts by weight of a paste-like colorant dispersed in 1 part by weight are sequentially added, and subsequently 80 parts by weight of a trimellitate plasticizer are sequentially added. Continue stirring and start cooling when the temperature of the contents reaches 120 ° C. When the temperature of the contents falls below 50 ° C, the fluidizing agent [average particle size is 1 μm
Pasty vinyl chloride resin (average degree of polymerization 1500)]
10 parts by weight were added and mixed to obtain a powder molding material.

Powder slush molding A nickel electroforming mold (100 × 200 × 20 m) having a thickness of 3 mm
(box of m) is heated to 230 ° C. on a hot plate, a powder molding material is charged, and after 10 seconds, unwelded powder is discharged. Further, the molding die was continuously heated on the hot plate for 40 seconds. At this time, hot air at 320 ° C. was blown on the back surface of the welding layer (the surface not in contact with the mold) for 10 seconds, and after 40 seconds, the nickel electroforming mold was put into water and cooled to remove the mold. -Evaluation of powder slush molded product The following evaluation was carried out, and the results are shown in Table 1. The powder was almost completely melted and the elongation was 430%, which was a sufficiently high level.

Evaluation Test Items Meltability of the back surface (surface not in contact with the mold): visually evaluated and melted ◯ Somewhat insufficient melting Δ Incomplete melting × Tensile strength and elongation of molded product: JIS K6723
Compliant with. Tear strength of molded product: JIS K6723
Compliant with. Residual elongation rate after light resistance test (sunshine weather meter black panel temperature 83 ° C. × 1000 Hr no rainfall): conforming to JIS K6723. Residual elongation after heat resistance test (120 ° C. × 400 Hr constant temperature bath): According to JIS K6723.

Example 2 Example 1 was repeated except that a base vinyl chloride resin having an average degree of polymerization of 2200 was used. As a result of the molding test, it was almost completely melted and the elongation rate was 430%, which was a sufficiently high level.

Comparative Example 1 The procedure of Example 1 was repeated except that a base vinyl chloride resin having an average degree of polymerization of 800 was used. As a result of the molding test, although it was completely melted, the elongation rate was 250%, which was not a high level.

Comparative Example 2 The same procedure as in Example 1 was carried out, but the back surface of the molten layer was not blown with hot air. Molding test results,
Incomplete melting and low elongation 73 in the case of Example
%Met.

Comparative Example 3 Comparative Example 2 was followed except that the nickel electroforming mold heating temperature was 280 ° C. As a result of the molding test, melting was incomplete, and the surface in contact with the mold was thermally deteriorated and discolored remarkably.

Comparative Example 4 The procedure of Example 1 was repeated except that the base vinyl chloride resin having a degree of polymerization of 3000 was used. As a result of the molding test, the melt was incomplete, which is expected to have an elongation of 100% or less.

[0036]

[Table 1]

[0037]

As described above, according to the method of the present invention, a method for easily molding a powder molding material having a high degree of polymerization of a base vinyl chloride resin was found, and a high level of elongation property and tear property was realized. Made possible. Also, the residual elongation after heat and light resistance was improved.

Therefore, there is an effect that it is possible to provide a thin and lightweight air bag grid skin.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area B29L 31:58 4F

Claims (2)

[Claims] 1. An elongation rate according to JIS K6723 by powder-slush molding a powder molding material having an average degree of polymerization of a base vinyl chloride resin of 1500 to 2500 and a plasticizer amount within a range represented by the following general formula. Is 250
% Or more, a method for manufacturing a lid skin in an automobile airbag. (5/100) X + 35 ≧ Y ≧ 70 (In the formula, Y represents the weight of the amount of the plasticizer per 100 parts by weight of the base vinyl chloride resin, and X represents the average degree of polymerization of the base vinyl chloride resin.) 2. A molding die obtained by heating a powder molding material obtained by mixing a base vinyl chloride resin having an average degree of polymerization of 1500 to 2500 with a plasticizer, a stabilizer, a fluidizing agent and the like to a predetermined mold temperature. A lid for an automobile airbag, which is characterized in that after being charged and welded to the mold surface, excess material is discharged out of the mold, then the back surface of the welding layer is heat-treated, and then the mold is cooled and demolded. Method of manufacturing epidermis.