Method of blow molding a parison against an insert having a groove filled with adhesive

A method of producing a blow molded product. The method includes preparing a tubular part having a groove at a portion that is to be embedded in a body portion. The groove is formed in a peripheral edge portion of a hole in a manner so as to surround the hole. A thermoplastic filler is filled in the groove over the entire area of the groove. The tubular part is then set in a blow mold as an insert. A parison is then expanded within the mold while the temperature is maintained at a level higher than the softening temperature of the filler.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved method of producing a blow molded 
product including a blow molded body portion and a tubular part embedded 
in the body portion by insertion, the tubular part having a hole 
communicating with an internal space of the body portion. This method is 
suited, for example, for forming an engine intake pipe. The description 
will hereinafter be made, taking this pipe as an example of blow molded 
product. 
2. Prior Art 
Among pipes of the type described, there is the type of pipe which is 
connected to another pipe at other portion than its opposite ends (that 
is, its peripheral wall). In this case, a tubular part such as a nipple 
must be embedded in the peripheral wall of the pipe. 
Where the pipe has a relatively simple configuration, the pipe and the 
nipple can be integrally blow molded. However, when the pipe has a 
complicated configuration having a three-dimensionally bent portion or the 
like, or depending on the position of embedding of the nipple, the nipple, 
in some cases, can not be blow molded together with the intake pipe. 
In this case, the pipe has been blow molded in the following manner. 
First, a nipple is prepared, and this nipple is set, as an insert, in a 
blow mold. Then, a parison for forming a body portion of the pipe is 
inserted into the mold, and the air is blown into the parison to expand 
the parison into contact with the surface of the cavity. At this time, the 
material of the parison partially envelops the nipple, so that the nipple 
is embedded in the body portion of the pipe. 
In the above blow molding, where the molding materials for the body portion 
of the pipe and the nipple are both a polyolefin-type resin such as PP, 
the body portion and the nipple can be fusingly bonded together, so that a 
relatively good airtightness between the two can be assured. The reason is 
considered to be that because of a relatively low melting temperature of 
PP or the like and of a wide temperature range of the molding, the bonding 
surfaces of the two are sufficiently fused at the time of the blow 
molding, and are connected together. 
However, where the blow molding is effected using a so-called such as 
polyamide, the melting temperature of such material is high, and also a 
temperature range of the blow molding is narrow, so that airtightness can 
not be assured between the body portion and the nipple. 
SUMMARY OF THE INVENTION 
It is an object of this invention to overcome the above problem of the 
prior art. 
According to the present invention, there is provided a method of producing 
a blow molded product, which comprises the steps of: 
(a) preparing a tubular part which has a groove at that portion thereof to 
be embedded in a body portion, said groove being formed in a peripheral 
edge portion of a hole in surrounding relation to the hole, and a 
thermoplastic filler being filled in the groove over an entire area of the 
groove; 
(b) setting the tubular part, as an insert, in a blow mold; and 
(c) expanding a parison within the mold while maintaining a temperature 
higher than a softening temperature of the filler. 
In the above blow molded product, since the filler is interposed between 
the body portion and the tubular part, airtightness is assured between the 
two. 
It can be considered to use, as the filler, the type having fluidity at 
room temperature (e.g., a cold-setting type (two-part type) adhesive or a 
dry-type adhesive). However, (1) there is a possibility that after the 
tubular part is set in the mold, the filler may flow into the mold, so 
that the cavity surface is contaminated to damage the design of the 
product. Therefore, the filler on the cavity surface must be removed, and 
time and labor are required for the maintenance. (2) Also, when the 
adhesive of the above type is used, the timing of filling the adhesive in 
the groove of the tubular part is limited to the time immediately before 
setting the tubular part in the mold, in connection with the setting or 
curing time of the adhesive. Therefore, the blow molding is limited. 
On the other hand, when the thermoplastic type filler is used as in the 
present invention, (1) the filler itself will not change its nature before 
the heat is applied thereto, and therefore the timing of filling the 
filler in the tubular part is not particularly limited, thus improving the 
operability of the blow molding. 
(2) Further, the thermoplastic type filler comes to have fluidity when heat 
is applied to the filler after the tubular part is set in the mold. At 
this time, the parison is expanded, and the filler has already been 
covered by the material of the parison. Therefore, the filler hardly flows 
into the cavity surface. 
Thus, in the present invention, the operability of the blow molding of the 
blow molded product (in which the filler is interposed between the body 
portion and the tubular part to maintain the airtightness between the two) 
is enhanced.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
The invention will now be described in further detail with reference to a 
method of producing an intake pipe 1 for a vehicle shown in FIG. 1 by way 
of example. 
The pipe 1 is to be mounted around an engine, and therefore in view of heat 
resistance, a body portion 3 and tubular parts 10 and 20 are made of 
polyamide. A bellows portion 5 absorbs vibrations, etc. 
The production method of this embodiment comprises (1) a step of preparing 
the tubular parts 10 and 20, (2) a setting step, (3) a blowing step, (4) a 
mold release step, and (5) a punching step. 
(1) STEP FOR PREING THE TUBULAR TS 10 AND 20 
One of the tubular parts is a valve mounting member 10. FIG. 2 is a 
cross-sectional view of the valve mounting member 10, and FIG. 3 is a 
bottom end view thereof. The valve mounting member 10 has two through 
holes 11 and 19. A valve is inserted into the greater-diameter hole 11, 
and the smaller-diameter hole 19 is a threaded hole for fixing the valve. 
At the lower surface of the valve mounting member 10, a groove 13 is 
formed in the peripheral edge portion of the hole 11, and surrounds the 
hole 11. A filler 15 is filled in the groove 13 over the entire area of 
the groove 13. The filler 15 is a hot-melt type adhesive for polyamide 
(specifically, this adhesive is "MT MELT" (tradename) marketed by Mitsui 
Toatsu K. K. and has a melting temperature of 142.5.degree. C.). The 
filler 15 has a softening temperature lower than the temperature within 
the mold used at the later blowing step. The filler 15 may not have the 
ability of adhesively bonding the valve mounting member 10 and the body 
portion 3 together (that is, the ability of effecting 
polyamido-to-polyamido bonding). 
The filler 15 does not possess fluidity at room temperature. In this 
embodiment, after the valve mounting member 10 is injection molded, the 
filler 15 is filled in the groove 13. Of course, the filler 15 only need 
to be filled in the groove 13 before the next step, that is, the setting 
step (2). 
A flange 17 is formed on the lower edge of the valve mounting member 10. As 
shown in FIG. 8, the flange 17 is embedded in the material of the body 
portion 3 so as to provide an undercut. 
The other of the tubular parts is a nipple 20. FIG. 4 is a longitudinal 
cross-sectional view of the nipple 20, and FIG. 5 is an end view thereof. 
The nipple 20 is formed by injection molding a base portion 23 of a resin, 
using a central tube 21 of metal as an insert. Of course, the nipple 20 
can be made entirely of a resin. Reference numeral 22 denotes a hole or 
bore, and reference numeral 27 denotes a flange. 
The base portion 23 has a groove 25 disposed in surrounding relation to the 
central tube 21. A thermoplastic filler 15 is also filled in the groove 
25, as is the case with the valve mounting member 10. 
(2) SETTING STEP 
In this step, the tubular members 10 and 20 prepared in the preceding step 
are set in a blow mold 30. 
As shown in FIG. 6, the valve mounting member 10 is set, as an insert, in 
the mold 30. The showing of holder means such a set pin is omitted. 
Reference character P denotes a parison. As shown in the drawings, part of 
the mold 30 is inserted into the through holes 11 and 19 so that the 
material of the parison P may not be introduced into the holes 11 and 19. 
Although the filler 15 is slightly elevated in temperature by the mold 30, 
it will not reach the softening temperature, and therefore the filler is 
retained in the groove 13. Therefore, the filler 15 will not flow into the 
mold, thus preventing the filler 15 from contaminating a cavity surface 31 
of the mold. 
As shown in FIG. 7, the nipple 20 is set, as an insert, in the mold 30. The 
filler 15 of the nipple 20 will not flow into the mold, as is the case 
with the valve mounting member 10. 
(3) BLOWING STEP 
In this step, the air is blown into the parison P to expand it. By doing 
so, the material of the parison P is brought into contact with the cavity 
surface 31 as indicated in dots-and-dash lines in FIGS. 6 and 7. At the 
same time, the material of the parison P covers the flanges 17 and 27 
formed respectively on the tubular members 10 and 20, thereby ensuring 
that the tubular members 10 and 20 may not be disengaged from the body 
portion 3. 
This step is carried out in a plastic condition of the parison P, that is, 
at temperatures above the melting temperature of the parison P. Therefore, 
when the material of the parison P comes to cover the tubular members 10 
and 20, its heat is applied to the fillers 15 to soften them. Then, the 
parison P is expanded to compress the fillers 15, so that the fillers 15 
are deformed to fully fill in the grooves 13 and 25, with no space 
remaining therein. As a result, the airtightness between the body portion 
3 and the tubular members 10 and 20 is assured. Particularly, in this 
embodiment, since the hot-melt type adhesive is used as the filler 15, the 
strength of connection between the two is enhanced. 
(4) MOLD RELEASE STEP 
In this step, when the workpiece within the mold 30 is cooled to a 
predetermined temperature, the mold is opened, and the workpiece is 
removed from the mold. 
(5) PUNCHING STEP 
In the workpiece obtained in the preceding step, the holes 11 and 22 are 
closed by the material of the parison P as indicated by dots-and-dash 
lines in FIGS. 6 and 7. Therefore, in this step, those portions of the 
parison P respectively closing the holes 11 and 22 are punched (see FIGS. 
8 and 9). 
Thus, the finished product is obtained. 
In the above embodiment, with respect to the tubular parts 10 and 20 to be 
inserted, the molding material of those portions thereof to be joined to 
the body portion 3 is the same as the molding material of the body portion 
3. Of course, the molding material of the insert is not particularly 
limited, and for example, the central tube 21 of the nipple 20 may be 
embedded directly in the body portion 3. In this case, a flange is formed 
on the lower edge of the central tube 21, and a groove is formed in this 
flange in surrounding relation to the hole 22. 
The tubular members may have a closed bottom.