JP2896832B2 - Mold for extruded thermoplastic resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for extruded thermoplastic resin foam, and more particularly to a molten resin in a flow path in the mold for extruded foam and a material of a surface of the mold in contact with the molten resin.

[0002]

2. Description of the Related Art As a material for a mold for extruded thermoplastic resin foam, S45C or S55C containing iron as a main component and SCM-4 or SCM-3 containing a small amount of chromium as an alloy are used. Examples of surface treatment materials for the surface of the mold in contact with the molten resin in the mold include chrome plating, Teflon coating, electroless nickel plating, and the like. However, these surface treatment materials have the following problems. (1) In the case of chromium plating or electroless nickel plating, since the sliding property with the molten resin is not good, heat is generated at the tip end of the mold outlet, which causes quality deterioration. Further, the additive builds up at the tip end of the mold outlet and adheres to the tip portion, and a line is generated on the product surface. (2) In the case of Teflon coating, although the sliding property with the molten resin is good, the abrasion resistance is not good. Therefore, when used for a long period of time, the surface treating agent peels off and lines are formed on the product surface.

[0003]

The present inventor has conducted various studies to improve the above problems, and as a result, has found that the contact angle between the surface material of the mold for the thermoplastic resin extruded foam and the molten resin, and the resin flow. By solving the above problems by selecting the surface roughness of the road and the narrowing ratio of the flow path in the mold within a specific range, it was found that a foam having improved quality was obtained, and the present invention was completed. An object of the present invention is to provide a mold for a thermoplastic resin extruded foam that can maintain appropriate sliding properties.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a mold having a surface having a contact angle with the molten resin of at least 45 mm from the exit of the mold at least 5 mm from the exit of the mold. Mold of material, surface roughness of resin channel is 6.3S
The following is a mold for a thermoplastic resin extruded foam having a narrowing ratio of a channel in the mold of 3 to 40, and the thermoplastic resin is a polystyrene resin, a polyethylene resin, a polypropylene resin, a polyphenylene oxide resin. The mold for a thermoplastic resin extruded foam described above, which is a resin, a polyester-based resin, a copolymer of these resins, or a mixed resin.

In the present invention, a method for measuring a contact angle with a molten resin is performed by the following method. Measuring instrument used: Contact angle measuring instrument (goniometer type) manufactured by Elma Inc. One polystyrene particle (about 0.014 g) is placed on a metal piece 3 mm × 20 mm × 50 mm, and heated at 160 ° C. and 15 HR (for polystyrene) After heating, the contact angle between the metal and the molten resin is measured by a contact angle measuring device. The narrowing ratio of the mold flow channel in the present invention is a value represented by the following equation.

[0006]

(Equation 1)

Next, the present invention will be described in detail. The thermoplastic resin extruded foam in the present invention is obtained by melting and kneading a thermoplastic resin and a foaming agent in an extruder, and extruding the mixture into the atmosphere.As the thermoplastic resin, polystyrene resin, polyethylene Resins, polypropylene resins, polyphenylene oxide resins and polyester resins, and copolymers or mixed resins of these resins. Any foaming agent may be used as long as it is conventionally used as a foaming agent for this type of extruded foam.
For example, normal butane, isobutane or a mixture thereof, propane or the like, or a fluorochloro-substituted hydrocarbon or a halogenated hydrocarbon is used. Further, a nucleating agent such as talc or the like, if necessary, may be added to control foaming.

The extruder is not particularly limited, and the molten thermoplastic resin composition containing a foaming agent is extruded into the atmosphere from a mold at the tip of the extruder and foams at the same time. In the present invention, it is necessary that the contact angle of the mold surface material of the extruder in contact with the molten resin is 45 to 65 °, and by satisfying this condition, the appropriate slip property of the extruded thermoplastic resin foam is obtained. Can be maintained. When the contact angle is out of this range, if the contact angle is less than 45 °, the sliding property is not good, so that the head pressure tends to increase, and heat is generated near the exit of the mold, resulting in a rough appearance. On the other hand, when the contact angle exceeds 65 °, the slipperiness is too good to maintain the pressure at the tip of the mold, which tends to cause uneven thickness. In addition, since this material was not durable, long-term continuous operation could not be performed. The contact angle here is 5 m before the die exit in the present invention.
m, but 5 mm before this mold exit
Means up to a position of 5 mm along the flow path surface of the molten resin from the tip end of the mold outlet. The reason for defining the contact angle as 5 mm before the mold exit in the present invention is that the length is less than this. The reason for this is that the mold outlet is difficult to manufacture, and the processing accuracy cannot be improved. Regarding the range of the narrowing-down ratio for obtaining an appropriate foaming area, if it is less than 3, internal foaming occurs at the tip end of the mold outlet, and the quality deteriorates. On the other hand, if it exceeds 40, surface unevenness occurs when the ejection amount is high.

By the way, the result of measuring the contact angle of the surface material of a conventionally used mold is as follows. Contact angle measuring method: 3 mm x 20 m with surface treatment using a contact angle measuring device (goniometer type) manufactured by Elma Corporation
One particle of thermoplastic resin is placed on a metal piece of mx 50 mm,
After heating with a heating gear oven, the contact angle between the metal and the molten resin is measured with a contact angle measuring device. The heating conditions were 15 HR at 160 ° C. for polystyrene and 15 HR at 120 ° C. for LDPE. Table 1 shows the results of the contact angle measurement results.

[0010]

[Table 1]

In the present invention, it is essential that the surface roughness of the resin flow path is 6.3 S or less and the narrowing ratio of the flow path in the mold is 3 to 40. The reason why the surface roughness of the flow channel is set to 6.3S or less is that if the surface roughness exceeds 6.3S, the resistance is increased due to the surface being too rough even if the sliding property of the material is good, resulting in poor appearance. The narrowing ratio of the mold flow path is defined by the above-described equation (1). If the narrowing ratio exceeds 40, surface unevenness occurs when the discharge amount is high. Internal foaming occurs at the tip of the mold outlet, and the quality of the product deteriorates. The shape of the slit of the mold in the present invention is not particularly limited, and may be any of an annular shape and a plate shape.

FIG. 1 is an explanatory view of a mold according to the present invention, and FIG. 2 is an explanatory view of another mold according to the present invention. In FIG. 1, a mold 1
Has a flow path 2 of a molten resin, and the molten resin passes through the flow path 2 and is foamed and extruded in an annular shape from a mold outlet 3. Portions having the characteristics defined in the present invention are hatched portions. FIG. 2 is an explanatory view of a mold used for extruding and foaming into a plate shape. Portions having characteristics specified in the present invention are hatched portions.

[0013]

Next, the present invention will be described by way of examples. Examples 1 to 3 and Comparative Examples 1 to 5 Foams obtained using an extrusion die having the conditions of the present invention and foams obtained using an extrusion die lacking the conditions of the present invention Are as shown in Tables 2 and 3.

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

As described above, the present invention relates to a mold for a thermoplastic resin extruded foam, which is at least 5 m in front of the mold outlet on the mold flow path surface in contact with the molten resin in the mold flow path.
Until m, the contact angle with the molten resin was 45 to 65 °, the surface roughness of the resin flow path was 6.3S or less, and the narrowing ratio of the flow path in the mold was 3 to 40. Thus, 1) heat generation at the tip of the mold is small. 2) The die swell is small. 3) There are few lines on the product surface. And the like.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold according to the present invention.

FIG. 2 is a sectional perspective view of another mold shape according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 extruder 2 flow path 3 mold outlet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-287338 (JP, A) JP-A-57-105324 (JP, A) JP-A-63-95929 (JP, A) JP-A-1- 281916 (JP, A) JP-A-4-131219 (JP, A) JP-B-46-10675 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 47/00-47 / 96

Claims (2)

(57) [Claims] 1. A mold having a surface material having a contact angle with the molten resin of 45 to 65 ° at least from the mold outlet to 5 mm in front of the mold flow path surface in contact with the molten resin. A mold for extruded thermoplastic resin having a surface roughness of 6.3S or less and a narrowing ratio of a channel in the mold of 3 to 40. 2. The method according to claim 1, wherein the thermoplastic resin is a polystyrene resin, a polyethylene resin, a polypropylene resin, a polyphenylene oxide resin, a polyester resin, a copolymer of these resins, or a mixed resin. The mold for extruded thermoplastic resin foam according to the above.