JPH0321643A - Foamable resin composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a foamable resin composition suitable for injection molding with fine foaming to prevent sink marks, and in particular to a styrene resin composition with improved foaming state. The present invention relates to a foamable resin composition of the type.

[Prior Art] For example, in injection molding of structural members such as housings and chassis of OA equipment, the resin in the mold heat-shrinks during cooling, causing depressions called sink marks and uneven shrinkage in the molded product. In order to prevent warping, etc., we use the so-called low-foaming injection molding method, in which foamable resin containing a foaming agent is injection-molded and slightly foamed internally during molding, and closed molding that is pressurized with a gas in advance. A so-called gas counter molding method or the like is used, in which a foamed molded article surrounded by an unfoamed outer shell is obtained by injecting foam into a mold cavity of a shape and releasing the pressure in the mold cavity after injection. The main purpose of these is to prevent the occurrence of sink marks by utilizing the expansion of the resin due to foaming, albeit slightly.

By the way, in the above-mentioned injection molding, if the bubbles are expanded to a large extent, the air bubbles will be exposed on the surface of the molded product, which will not only impair the appearance of the molded product, but also reduce the mechanical strength of the molded product. In particular, in the gas counter molding method, the main purpose is to obtain an unfoamed layer with a smooth surface, so spoiling the appearance due to air bubbles is a fatal defect. For this reason, a foamable resin composition used for injection molding that involves microfoaming is usually adjusted so that foaming is performed relatively slowly.

Conventionally, as a foamable resin composition used for injection molding accompanied by micro-foaming, one in which a foaming agent mixed with sodium citrate and sodium bicarbonate is blended with a styrene resin is known (Japanese Patent Application Laid-Open No. 1983-1999). No. 89743). This is intended to achieve a fine and uniform internal foaming state by foaming the foaming agent in two stages, so to speak, without foaming the foaming agent rapidly at once.

Additionally, azodicarbonamide (hereinafter referred to as rADcAJ) is known as a general foaming agent, although it has not been specifically developed for injection molding that involves microfoaming (Japanese Patent Laid-Open No. 47-26406). ).

[Problems to be Solved by the Invention] However, conventional styrene-based foamable resin compositions containing a blowing agent consisting of sodium citrate and sodium bicarbonate do not produce air bubbles on the surface due to injection molding accompanied by microfoaming. Although it is possible to obtain a molded article with internal foaming that is not exposed, foaming cannot be achieved unless a relatively large amount of blowing agent is added, and there is a problem that the amount of blowing agent consumed is large. Furthermore, the foamed state obtained cannot be said to be sufficiently fine. If the bubbles are not fine enough, the distribution of the bubbles tends to be uneven, and especially if the wall thickness of the molded product is uneven, the thin-walled areas will not foam sufficiently, making it difficult to achieve a reliable sink prevention effect. Otherwise, the problem arises that the strength of the molded product tends to be uneven.

On the other hand, ADCA is certainly a suitable blowing agent for polyolefins, and is good for large foams such as insulation materials, but when used in injection molding of styrenic resins, which involves fine foaming, The foaming is too rapid and it is difficult to achieve fine and uniform internal foaming or foaming in thin walls.

[Means for Solving the Problems] To explain the means taken in the present invention to solve the above problems, in the present invention, azodicarbonamide 1
A method is taken in which a blowing agent in which 2 to 8 parts by weight of sodium citrate and sodium bicarbonate are each added to 0 parts by weight is blended into the styrene resin.

The present invention will be further explained.

ADCA used in the present invention has the following structural formula.

00 The blowing agent used in the present invention is the above-mentioned ADCA plus sodium citrate and sodium bicarbonate.

The mixing ratio thereof is 2 to 8 parts by weight per 10 parts by weight of ADCA, preferably 4 to 6 parts by weight per 10 parts by weight of ADCA.

If the ratio of ADCA is too low, foaming tends to be insufficient, whereas if it is too high, rapid foaming tends to occur.

Sodium citrate may be monosodium citrate or trisodium citrate, but trisodium citrate is preferred because it is easier to obtain a finer foamed state and does not cause the yellow-brown coloring that tends to occur when using monosodium citrate. .

The foamable resin composition according to the present invention is a composition in which a blowing agent consisting of the above-mentioned ADCA, sodium citrate, and sodium bicarbonate is blended with a styrene resin.

The blending ratio of the blowing agent and styrene resin in the present invention is as follows:
Foaming agent 0.1 to 5 per 100 parts by weight of styrene resin
It is preferably 0.1 to 1.0 parts by weight, particularly 0.1 to 1.0 parts by weight. If the amount of foaming agent added is too small, it will be difficult to foam, whereas if it is too large, excessive foaming will occur and the appearance will be easily impaired.

The styrene-based resin used in the present invention includes not only general bar-pass polystyrene but also polymers containing styrene such as high-impact polystyrene, acrylonitrile-styrene copolymers, ABS resins, etc., as long as they can be injection molded. It may also be a polymer.

In addition to the above-mentioned foaming agent and styrene resin, the resin composition of the present invention may contain a foaming aid such as CaO, a foaming inhibitor such as a fatty acid ester, a lubricant, a softener, a pigment, and the like.

In the present invention, the styrenic resin and the blowing agent are preferably blended by a masterbatch method. This masterbatch is manufactured by using a stylinone resin, which is the same type as the stylinone resin that constitutes the resin composition of the present invention, as a supported polymer, and at a high concentration of about 5-25% by weight and 47% by weight. : It can be produced by adding and mixing the above-mentioned blowing agent.

The conditions for performing injection molding with fine foaming using the resin composition of the present invention are almost the same as conventional ones. That is, the injection temperature is 180''-250°C, the injection LL force 1 length 40
”-80 kg/cm2, back pressure is 10-30
kl4/c:lll'culm L0.

1 action] Figure 1? J., is a graph showing the decomposition behavior of a blowing agent. In the figure, the curve (1) is 8 i')
In the present invention, in which one part of each of sodium succinic acid and sodium DI acid was added (the foaming agent used, the curve (2) is A D C: A double part (!) enoic acid 1
・The foaming agent used in the present invention, in which one bundle of Lyso-da and Soda Carbonate is added, the bent cotton of (3) is ADCA A,
A German blowing agent, curve (4), is a blowing agent made by combining 100ml of monosodic acid and 300ml of sodium carbonate.Measurements were made using a famous foaming agent (10ml of monoliquid paraffin), The temperature was increased at 2°C/min.The blowing agent was added in an amount of 1g each.

As is clear from Fig. 1, the blowing agent used in the present invention generates more gas on the low temperature side than the blowing agent (3). It generates gas more slowly than the valve foaming agent (4).In addition, the total amount of gas generated is 7 liters more than the foaming agent (4). The blowing agent according to the present invention is called l:tr.
Regardless of the names of the blowing agents in (3) and (4), the gas generation characteristics of these two sources are not defined as the pure gas generation characteristics. No. It is clear (not necessarily) that the two sides are suppressing each other's gas generation in some way, and it can be inferred that the two are suppressing each other's gas generation. Then, such a slow decomposition movement that transitioned to {3'' in temperature measurement is
It is considered to be particularly suitable for steel-based resins.

[Example] Example 1 Three types of high, inbaku1, borisdine1/n were molded. Resin 2.1 (slightly foamy) injection molding was carried out to form plate-shaped molded products each having a thickness of 5 f!@class 0).

Hii゛7 Baku1 Borisug) As a non-Boristi! Copolymerization of 2-nd polybutadiene at a ratio of 95:2:4.8 (monomer weight ratio of 2 or less) (resin A), and copolymerization of polystyrene and polyptadiene at a ratio of 92:8. (Resin B) Polystyrene and polybutadiene were combined in a ratio of 94.5:5.5 (Resin C). The thickness of the plate-shaped molded product is 7, 5, 3, 2.5, and 2mm. It was classified as a kind.

The blowing agent was (Blowing Agent I) obtained by adding J parts of monosodium citrate and sodium bicarbonate to the ADCA double air section.

The above blowing agent contains polystyrene as a carrier polymer, and 2
The masterbatch is 0%, and the amount of blowing agent added is 0.24.
This master badge was supplied to an injection molding machine together with the resin to be molded, and molding was performed so as to achieve the same weight percentage.

Regarding the obtained plate-shaped molded product, "C', foam size, average cell diameter, diameter distribution,
,Ta.

The results are not shown in Tables E to Table 3. *i: 2. Resin C
Figure Δ2 shows the constant foam state of the plate-shaped molded product with a thickness of 3 mm.

The molding was performed at an injection temperature of 220°C and an injection pressure of 60kg/cn.
17 at a back pressure of 20 kg/cL12.

Example 2 The blowing agent was 2 parts by weight of ADCA, 1 part by weight each of HLC and 1-lysodium bicarbonate added to 2 parts by weight of (foaming agent II): In the same manner, the foaming ratio, average cell diameter, cell diameter distribution, and cell density were each measured.

The results are shown in Tables 1-3. In addition, resin C″r-molded 2
Figure 3 shows the foamed state of a plate-shaped molded product with a thickness of 3 mm.

Comparative Example 1 Resin 8 was molded with resin 7, foamed shavings made by whitening equal parts by weight of monosodium citric acid and sodium bicarbonate (foaming agent n+
) and the injection temperature was 220° C. to 230° C. The same procedure as in Example 1 was used to mold plate-shaped molded products with thicknesses of 3 and 2 mm. We attempted to measure the expansion ratio, average cell diameter, cell diameter distribution, and cell density of the obtained plate-shaped molded product, but despite adding the same amount of foaming agent (■) as in Examples 1 and 2, There was no foaming, so these measurements were not possible.

The results are shown in Table 1.

Comparative Example 2 Resin A was made in the same manner as in Example 1, except that ADCA alone as a blowing agent (Blowing Agent IV) was used and the proportion of the blowing agent in the resin to be molded was 0.18%. , 5 and 3 am, thicknesses 7, 5, 3, 2 for resins B and C.
, 5 and 2 mm plate-shaped molded products were molded.

Regarding the obtained plate-shaped molded product, the expansion ratio, average cell diameter,
Cell diameter distribution and cell density were each measured.

The results are shown in Tables 1 to 3. Further, the foamed state of a plate-shaped molded product molded from resin C and having a thickness of 3 au++ is shown in FIG.

[Effects of the Invention] The present invention is as explained below, and since sufficiently small bubbles can be formed in extrusion molding accompanied by microfoaming, the effect of preventing sinkage due to foaming is reliable. Also, the mechanical strength of the molded product is less likely to be uneven.

[Brief explanation of drawings]

Figure 1 is a graph showing the decomposition characteristics of blowing agents, Figure 2 (,j
Figure 3 is a diagram showing a 3 mm thick plate-shaped molded product molded with 4J resin C in Example 1 (1 state, and FIG. 3 is a diagram showing Example 21.
Figure 4 shows the air bubbles in a plate-shaped molded product with a thickness of 3111+11 molded with Resin C in Comparative Example 2. It is a figure showing a state.

Claims (1)

[Claims] 1) A foamable resin composition characterized in that a foaming agent containing 2 to 8 parts by weight of sodium citrate and sodium bicarbonate each added to 10 parts by weight of azodicarbonamide is blended into a styrene resin.