JPS63193940A - Sheet molding compound having low specific gravity - Google Patents

Abstract

PURPOSE:To obtain the titled compound giving a molded article having excellent paintability, by dispersing short fibers at the core part of a sheet and dispersing glass microballoons in a manner that the content of the balloons in one surface layer is lower than the content in the other surface layer. CONSTITUTION:The objective sheet molding compound (SMC) having low specific gravity contains glass microballoons 2 and is produced by dispersing short fibers 3 (e.g. glass fiber, ceramic fiber, etc.) at the core part of a sheet made of a resin 1 (e.g. unsaturated polyester resin). The content of the glass microballoons in one of the surface layers is made to be zero or lower than the content of the baloons 2 in the other surface layer. A molded article of the SMC having excellent paintability can be produced without causing cracking of the product and preventing the concentration of the glass balloons at a surface by molding the SMC facing the surface layer with low balloon content upward.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to sheet molding compounds containing glass microballoons.

[Conventional technology]

Recently, passenger car engine hoods and exterior parts such as rear and
Two-piece sheet molding compound (SMC) parts are now being used for the quarter upper, #-7, rear deck lid, hood, etc. Among them, the inner panel contains a low specific gravity 8M that contains glass micro balloons as a filler to reduce weight.
C is used.

Conventionally, this low specific gravity SMC is mixed by a pipe 11 as shown in FIG. The glass micro balloons are thoroughly mixed with the resin 13 containing calcium carbonate etc. supplied into the resin 12 using the stirring blade 14. Next, the mixed resin is conveyed through a pipe 15 to a relay tank 16, where the thickener is sufficiently mixed with a stirring blade 18 to form a resin mixture 17. Next, this resin mixture 17 is divided into two parts and sent to the SMC impregnating device through pipes 19 and 19a.
The doctor blades 20 and 20a are applied onto the polyethylene films 23b and 23C that have come out of the polyethylene film rolls 23 and 23a. Next, one glass roving 21 is cut into a length of about 25 m with a cutter 22, and the cut short glass fibers are sandwiched between sheet-like resin mixtures on polyethylene films 23b and 23C, and then cut with a compression roller 24. It is manufactured by compressing and impregnating the resin sheet, winding the formed resin sheet around a roller 26, aging it at a constant temperature, and making it have a constant viscosity. The low specific gravity SMC manufactured as described above is shown in Figure 4 (a
), short glass fibers 3 are dispersed in the center of the sheet, and glass microballoons 2 are dispersed throughout the resin 1.

[Problem that the invention seeks to solve]

However, with low specific gravity SMC in which glass microballoons are mixed into the resin as described above, the viscosity of the resin temporarily decreases due to heat during molding, and the glass microballoons have a low specific gravity. ), the glass microballoon 2 moves upward. At this time, since the short glass fibers 3 are dispersed in the center of the SMC, the glass microballoon 2 below the short glass fibers 3 is
Even if it rises, the short glass fibers 3 touch the short glass fibers 3 and do not go any further upwards, but the glass microballoons 2 above the short glass fibers 3 rise and gather near the surface. When such a molded product is painted, as shown in Figure 4(C), the glass microballoons 2a that have broken due to the shear force during flow are included in the glass microballoons 2 that have gathered near the surface. During paint baking, the gas in the broken glass micro balloon 2a expands due to the heat of about 140 degrees Celsius and breaks through the paint film 4, causing paint defects 4a called wrinkles on the paint film 4. There is a problem with this.

The present invention is intended to solve the above-mentioned problems, and aims to provide a low specific gravity SMC that provides a commercial quality surface with excellent paintability after molding.

[Means for solving problems]

The low specific gravity sheet molding compound of the present invention is
In a low specific gravity sheet molding compound that contains glass microballoons and has short fibers dispersed in the center of the sheet, the content of glass microballoons in one of the surface layers is zero or less than the content in the other surface layer. It is characterized by:

In the present invention, as described above, glass microballoons are distributed in the SMC so that the content of glass microballoons in one surface layer is zero or less than that in the other surface layer. The proportion of the microballoons may be appropriately determined depending on the strength of the glass microballoons, the amount mixed into the entire SMC, and the like. Furthermore, although the content of glass microballoons in one surface layer is reduced to zero, this does not mean that the amount of glass microballoons mixed into the entire low specific gravity SMC is reduced.

The amount of the glass microballoons to be mixed into the entire SMC may be appropriately determined depending on the specific gravity of the target low specific gravity 8MC, the strength of the SMC molded body, the strength of the glass microballoons to be mixed, etc.

The glass microballoon used in the present invention is a low specific gravity SM
A glass microballoon commonly used for C can be used, and its size may be, for example, 50 to 100 μm in diameter (average diameter 70 μm).

Further, the resin used in the SMC of the present invention can be a resin normally used in SMC, and examples thereof include unsaturated polyester resin, epoxy resin, and the like.

The short fibers to be dispersed can be short fibers normally used in SMC, such as glass fibers, ceramic fibers, metal fibers, polymer fibers, and the like.

[For production]

When the low specific gravity SMC of the present invention is molded with the surface layer containing zero or less glass microballoons than the other surface layer facing upward, the viscosity of the resin temporarily decreases due to the heat during molding. , the glass microballoon rises due to buoyancy, but even if the glass microballoon below the short fibers dispersed in the center of the sheet rises, it does not rise any further and falls into contact with the short fibers. There are no or only a few glass microballoons on the short fibers, so even if they rise, they do not gather near the surface. Since there are no or very few microballoons, no or almost no coating defects occur.

〔Example〕

The present invention will be explained by way of one embodiment with reference to the drawings.

First, as shown in FIG.
Resins 13 and 13a containing a filler such as calcium carbonate are supplied to mixing tanks 12 and 12a by la. Therefore, glass micro balloons are added to the resins 13 and 13a, and the resins are thoroughly mixed using stirring blades 14 and 14+L, respectively. At this time, the resin 13 for the lower layer of the glass microballoon was 75%.

Add 25 inches of resin 13a for the upper layer.

Next, the mixed resin is passed through pipes 15 and 15a, respectively.
Then, a thickener made of acidic magnesium oxide is added to the relay tanks 16 and 16a, and mixed thoroughly with stirring blades 18 and 18a, respectively, to obtain resin mixtures 17 and 17a. In addition, magnesium hydroxide etc. may be used as a thickener.

Next, the resin mixture 17 is supplied through the pipe 19 to the lower layer doctor blade 20 of the 8Mc impregnating device, while the resin mixture 17a containing less glass microballoons is supplied through the pipe 19a to the upper layer doctor blade 20a, and each polyethylene Film rolls 23 and 2
Polyethylene films 23b and 23 coming out from 3a
Apply on C.

Short fibers obtained by cutting the glass roving 21 to about 25 vaa with a cutter 22 are made into polyethylene fibers A/A23 b
.

The short fibers are sandwiched between the resin mixture 17.17b coated on 23C and compressed with a compression roller to impregnate the short fibers with resin.Then, both surfaces are coated with polyethylene film 23b,
Wrap the resin sheet covered with 23C around the roll 25,
It is aged at a constant temperature and thickened with magnesium oxide to reach the desired viscosity. A cross-sectional view of the low specific gravity SMC thus obtained is shown in Fig. 1←). In the figure, 1 is resin;
2 represents a microballoon, and 3 represents a short fiber. Low specific gravity S
The short fibers 3 are dispersed in the center of the MC, and the content of the glass microballoons 2 is smaller in the upper layer than in the lower layer. When this low specific gravity SMC is molded with the side containing less glass microballoons facing up, the molding specific viscosity temporarily decreases and the glass microballoons 2 with lower specific gravity become more buoyant, as shown in Figure 1). However, the glass microballoon 2 below the short fibers 3 dispersed in the center of the sheet
Even if they rise, they stop at the short fibers 3 and do not collect on the surface, and since the amount of glass microballoons 2 on the short fibers 3 is small, they hardly collect on the surface. Although this low specific weight SMC was baked and painted, there were few glass microballoons near the surface, and when mixing 4.
Because the content was low, it did not break easily, so there were almost no broken glass microballoons on the surface, and almost no coating defects called waki occurred on the painted surface.

Furthermore, when the low specific gravity SMC in which the content of glass microballoons in the upper layer was reduced to zero was coated after molding, no coating defects occurred.

〔Effect of the invention〕

As mentioned above, in the low specific gravity 8MC of the present invention, the content of glass microballoons in one surface layer is zero or lower than that in the other surface layer, so a molded product with zero or less glass microballoons on one surface is As a result, the surface becomes flatter and there are no or almost no broken glass microballoons, so even if baked-on paint is applied, there will be no or almost no paint defects called waki on the painted surface, compared to conventional methods. It can also be applied to outer panels that require high surface quality, which was not previously used.

[Brief explanation of the drawing]

FIG. 1 (i!L) is a cross-sectional view of a main part of a low specific gravity SMC according to an embodiment of the present invention, and FIG. Figure 2 is an explanatory diagram of the manufacturing process of a low specific gravity SMC according to an embodiment of the present invention, Figure 3 is an illustration of the manufacturing process of a conventional low specific gravity SMC, and Figure 4 (a) is an illustration of the main points of a conventional low specific gravity SMC. Partial sectional view, 4th
Figure (b) is a sectional view of the main part of a conventional molded low specific gravity SMC,
FIG. 4(C) shows a sectional view of a main part of a conventional coated low specific gravity 8MC molded body. In the figure, 1...Resin 2...Crow micro balloon 3...Short fiber Patent applicant Toyota Motor Corporation Fig. 1 3...Short ix, m Fig. 2

Claims (1)

[Claims] In a low specific gravity sheet molding compound that contains glass microballoons and has short fibers dispersed in the center of the sheet, the content of glass microballoons in one of the surface layers is zero or less than the content in the other surface layer. A low specific gravity sheet molding compound featuring: