JP2904514B2 - Silicone rubber mold masking material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to molding of a silicone rubber mold, and more particularly to an RTV.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a masking material for preventing the inflow of silicone rubber into a portion of a master where molding is to be avoided when molding using liquid silicone rubber.

(Prior Art) Conventionally, in molding a synthetic resin, a silicone rubber mold formed by molding a master with an RTV liquid silicone rubber has been used.

The silicone rubber mold is used as it is in casting using a liquid resin such as polyurethane resin, and in forming a simple mold for injection molding by casting as shown in FIG. Used as a base type for

That is, in forming a casting mold, first, a master is molded by a silicone mold, then a gypsum mold is formed based on the silicone mold, and finally, a casting mold is obtained by using the gypsum mold to obtain a casting mold. .

When forming a silicone mold based on such a master, masking for preventing the flow of silicone rubber into a portion where mold removal is to be avoided and forming a parting surface is performed in the second step of FIG. Required as shown.

A specific example of masking of the master will be described with reference to FIG. 2. The master 2 fixed on the surface plate 1 is surrounded by a mold 3, and RTV type liquid silicone rubber is poured into the mold 3 and cured to cure the silicone rubber. A mold is formed.

In this case, after the masking material 4 is filled in the undercut portion 2a of the master 2 to form a parting surface, a mold is formed.

FIG. 3 shows an example of a mold handle for the mold on the cavity side and the core side by using a masking material from one master.

First, as shown in Fig. A, a master 5 fixed on a surface plate 1 is surrounded by a mold frame 3 as shown in Fig. B, and then RTV liquid silicone rubber 6 is poured and cured, and a cavity as shown in Fig. C is formed. The side silicone rubber mold 7 is obtained.

Next, as shown in Fig. D, a masking material film 8 having a predetermined thickness corresponding to the thickness is formed on the inner surface of the cavity of the cavity-side silicone rubber mold 7, and as shown in Fig. E, the masking material film is formed on the inner surface of the cavity. After the cavity-side silicone rubber mold 7 on which the film 8 is formed is surrounded by the mold 3, the RTV liquid silicone rubber 6 is poured and cured to form a core-side silicone rubber mold.

As described above, in forming a silicone rubber mold by molding a master using RTV liquid silicone rubber, the use of a masking material is indispensable, and so-called oil clay is conventionally used as the masking material. Was used.

(Problems to be Solved by the Invention) A conventional masking material using an oil clay has a problem in that the curing of the RTV liquid silicone rubber is inhibited or the masking portion is poorly filled.

There are two types of RTV liquid silicone rubber: condensation type and addition reaction type. For molding, addition reaction type without molding shrinkage is used.

However, addition reaction type RTV liquid silicone rubber causes curing inhibition due to catalyst poisons such as sulfur, phosphorus, nitrogen, and tin, and a component that acts as a catalyst poison is often mixed in oil clay to cause curing inhibition.

For this reason, when performing masking using oil clay, it is necessary to apply a barrier coat thereon, but if this is not applied reliably, curing inhibition will still occur.

In addition, since oil clay has poor plastic deformability, it is difficult to completely fill it depending on the shape of holes and dents that require masking, and the effect of air remaining in holes and dents where the masking material is incompletely filled As a result, vacuum defoaming for removing air in the silicone rubber at the time of molding is incomplete, and air bubbles are mixed in the silicone rubber mold, resulting in a failure of good molding.

The present invention eliminates the disadvantages of the prior art as described above,
It was created with the aim of developing an optimal masking material for molding with RTV liquid silicone rubber.

(Means for Solving the Problems) That is, the present invention provides a silicone rubber mold making mask, characterized in that white petrolatum is mixed with α-type hemihydrate gypsum, phlogopite powder and polymethyl methacrylate (PMMA) ultrafine powder. Material.

(Function) The present invention is configured as described above, and the composition constituting the masking material does not contain any component which exceeds the curing inhibition of the addition-reaction type RTV liquid silicone rubber, and the composition has plastic deformation. Since it is excellent in properties and can be completely filled in holes and depressions of any shape, it is possible to extremely smoothly form a silicone rubber mold by molding a master with liquid silicone rubber.

(Example) As a base, white petrolatum was selected as a highly viscous oil component.

Petrolatum is classified into No. 1 to No. 5 in JISK2237 according to the degree of purification. In the present invention, petrolatum, which is the most purified No. 5 white petrolatum, is used.

Α-type gypsum hemihydrate gypsum powder was blended as an aggregate to give petroleum vaseline an appropriate plastic deformation property.

This is selected from the view that it is excellent in water absorption and solidifies due to water absorption and is suitable for forming a masking material.

Alpha-type hemihydrate gypsum is obtained by heating gypsum rough crushed to a particle size of 10 to 80 mm under steam pressure of 2 to 8 atm for 1.5 to 6 hours.
It was dried under normal pressure at 0 to 160 ° C. for 3 to 6 hours, and then ground. The particle size distribution used in the present invention is as shown in Table 3, and the average particle size was less than 200 mesh under 20 mesh. It was a powder of several μm. In addition, the masking material should not cause cracks on the surface during plastic deformation or stickiness when touched by fingers, in addition to plastic deformability. Since various properties were required, such as having to be smooth, phlogopite powder and polymethyl methacrylate (PMMA) ultrafine powder were selected as other compounds.

Since phlogopite powder is in the form of a flat plate, it is expected to have an effect of preventing the occurrence of cracks at the time of plastic deformation.For this purpose, it is preferable that the aspect ratio is high. Mica was selected and its particle size distribution is as shown in Table 1.

PMMA ultrafine powder is usually a very fine powder having a particle size of 0.15 to 2 μm, and is excellent in dispersibility.
As shown in the figure, PMMA ultrafine powder 10
Are considered to be separated from each other and adhered to each other to prevent the plastic deformation property from being lowered by the blending of phlogopite 9.

The properties of the ultrafine PMMA powder used in the present invention are as shown in Table 2, and as can be seen from the table, a large amount of bulk and oil absorption gives the surface smoothness and the property of suppressing stickiness due to finger touch. It was also expected to be done.

Table 4 shows the results of comparing the suitability as a masking material by variously blending each of the above components.

The suitability as a masking material was determined by measuring various properties as shown in the table.The plastic deformability was determined by the rate of increase in deformation when pressed with a load of 500 g with a 10 mm diameter sphere. Is preferably about 20.

A plastic crack is a degree of cracking when plastically deformed. Of course, it is preferable that no crack is generated. Is preferably smooth.

No. 1 to No. 4 are the cases where only α-type hemihydrate gypsum powder was blended with petrolatum, but as this blending amount was increased, only plastic deformability gradually improved, but tackiness Was poor, and the plastic crack and the surface smoothness could not be evaluated.

No. 5 to No. 8 are blended with phlogopite in addition to α-type hemihydrate gypsum.In this case, tackiness is bad, but it is not enough to be able to evaluate prima-plastic cracks and surface smoothness. Did not.

No. 8 to No. 13 are examples of the present invention in which PMMA ultrafine powder is further added to the above-mentioned formulation, and in all examples, tackiness is remarkably improved and some of the properties are unsatisfactory. However, it has become practically usable as a masking material.

In particular, the composition of No. 13 became the most suitable as a masking material in all properties including plastic deformability.

Although not shown in the table, the silicone rubber was also tested for curing inhibition. Toray Silicone Co., Ltd. SH9555 as an addition reaction type RTV liquid silicone rubber was cured while being in contact with the masking material of the above example. No cure inhibition occurred.

(Effects) The present invention has the above-described structure and operation, and does not inhibit curing of silicone rubber as a masking material used in forming a silicone rubber mold by molding a master with liquid silicone rubber. Needless to say, it provides an optimum filling property.

The silicone rubber mold provided by this is effectively used as a mold for casting a liquid synthetic resin or as a master transfer mold when forming a simple mold for injection molding by casting. Has a great effect on

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of an injection molding casting mold, FIG. 2 is a view showing an example of masking at the time of molding of a master, and FIG. 3 is a mold from one master on a cavity side and a core side. FIG. 4 is a view showing an example of the use of a masking material when removing, and FIG. 4 is a view showing the action of ultrafine PMMA powder in the example. 2,5… Master, 4,8… Mask material.

Claims (1)

(57) [Claims] 1. A white petrolatum with α-type hemihydrate gypsum powder, phlogopite powder and polymethyl methacrylate (PMMA)
A silicone rubber mold-making masking material characterized by blending ultrafine powder.