JP3289973B2 - Melamine resin molded article joining method - Google Patents

Abstract

PURPOSE:To bond molded products of melamine resin with high bonding force even at high ambient temperatures. CONSTITUTION:Molded products 1, 2 are made with an epoxu-modified melamine resin molding material. After heat treatment at 100-150 deg.C for 3-10hr, one molded product 1 is press fitted into a hole for press fitting formed in the other molded product 2. Since the molded product of the epoxy-modified melamine resin is highly flexible and tough and has a low modulus of elasticity, molded products can be bonded together with a high bonding force by the press fitting without causing breaking. The molded product of the epoxy-modified melamine resin molding material shrinks by heat treatment. The molded product without large shrinkage even at high ambient temperatures can control the reduction of press fitting strengthis without raising a creep phenomenon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining melamine resin molded articles by press-fitting.

[0002]

2. Description of the Related Art Melamine resin molded products are mainly used for electric parts and wiring devices. In general, when joining parts of a molded article made of a resin molded article, it is common to engage them by a snap method or to fit them by press fitting. However, a melamine resin molded product is a thermosetting resin, and therefore has low flexibility and inferior toughness, has a high elastic modulus, and is liable to be cracked or chipped. It is difficult to join by snap method or press fit.

On the other hand, a molded article molded from an epoxy-modified melamine resin molding material has high flexibility, high toughness, and low elastic modulus. Therefore, molded products molded from epoxy-modified melamine resin molding materials are less likely to crack or chip even when pressed, and should be joined together with high joining strength by press-fitting, as with thermoplastic resin molded products. Have been found by the applicant to be possible.

As described above, by using a molded article molded from an epoxy-modified melamine resin molding material, the molded articles can be joined together by press-fitting in the same manner as a molded article of a thermoplastic resin. The same high joining strength as that of the product can be obtained.

[0005]

However, 10 to 30 ° C.
Although bonding can be performed with such a high bonding strength at such a normal temperature, there is a problem that the bonding strength is significantly reduced in an atmosphere at a high temperature of about 130 ° C. to 150 ° C. This is considered to be due to the fact that, for example, in the case of a thermoplastic resin molded article, the press-fitting strength of the molded article is widened and enlarged by creep due to heat, so that the press-fit strength is reduced and the bonding strength is reduced. Similarly, it is considered that this is due to the expansion of the press-fit hole due to the creep phenomenon.

The present invention has been made in view of the above points, and has as its object to provide a method for joining melamine resin molded articles which can be joined with a high joining force even in a high-temperature atmosphere. is there.

[0007]

The method for joining melamine resin molded articles according to the present invention comprises heating a plurality of molded articles formed of an epoxy-modified melamine resin molding material at a temperature of 100 to 150 ° C. for 3 to 10 hours. After performing the above process, the other molded product is joined by press-fitting the other molded product into a press-fit hole formed in one molded product.

Hereinafter, the present invention will be described in detail. By modifying the melamine resin with epoxy, it is possible to increase flexibility, increase toughness, and decrease elastic modulus. The present invention, by using a molded article molded with such an epoxy-modified melamine resin molding material having a low elastic modulus,
The joining can be performed by press-fitting.

The epoxy-modified melamine resin is not particularly limited, and for example, those described in Japanese Patent Application No. 62-142102 provided by the present applicant can be used. That is, this epoxy-modified melamine resin can be produced by reacting melamine with a glycidyl compound as an epoxy compound as a primary reaction, and then reacting this reactant with formaldehyde as a secondary reaction. Examples of the glycidyl compound include ethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol glycidyl ether, neopentyl glycol diglycidyl ether, 1,6 hexanediol glycidyl ether, trimethylolpropane polyglycidyl ether, and polyethylene glycol diglycidyl ether. Can be used.

Here, it is desirable to set conditions so that the primary reaction is performed at a temperature of about 80 to 100 ° C. for about 10 to 150 minutes, and the secondary reaction is performed at a temperature of about 70 to 90 ° C. at a temperature of 5 to 120 ° C. It is desirable to set the condition so that the operation is performed for about a minute. The amount of each component in the above reaction is represented by the following formula, where M is the number of moles of melamine, G is the number of moles of the glycidyl compound, and F is the number of moles of formaldehyde. The molar ratio of the glycidyl compound to melamine is G / M = 0.01 to 5.8 It is desirable to set the range so that the molar ratio of formaldehyde to the difference in the number of moles of melamine and the glycidyl compound is F / | M−G | = 0.5 to 4.0. When the molar ratio of the glycidyl compound to melamine is less than 0.01, the modification by the glycidyl compound is insufficient, and the effect of increasing the flexibility of the melamine resin and improving the toughness cannot be sufficiently obtained. When the molar ratio exceeds 5.8, the amount of the glycidyl compound in the reaction system becomes too large, so that it is easy to gel by the action of amine, and similarly, the effect of improving the flexibility of the melamine resin and improving the toughness is sufficient. Can not get to. Generally, the mole number M of melamine is set to be larger than the mole number G of the glycidyl compound. Further, if the molar ratio of formaldehyde to the difference in the number of moles of melamine and the glycidyl compound is less than 0.5, the amount of formaldehyde is insufficient and the melamine resin cannot be sufficiently cured, and the molar ratio is 4. If it exceeds 0, the amount of formaldehyde becomes excessive and the crosslink density of the melamine resin becomes too high, so that the effect of increasing the flexibility of the melamine resin and improving the toughness cannot be sufficiently obtained.

The epoxy-modified melamine resin obtained by the above reaction is mixed with an organic base material such as pulp, wood flour or paper, or an inorganic base material such as asbestos, mica or glass fiber, and a releasing agent or curing agent. An epoxy-modified melamine resin molding material can be prepared by mixing other components such as an agent. Then, the molding material can be subjected to injection molding, compression molding or the like to produce a molded product.

Thus, in forming a molded article by molding the above epoxy-modified melamine resin molding material, of a pair of molded articles 1 and 2 joined as shown in FIG.
One of the molded products 1 is provided with a press-fitting hole 3 and the other molded product 2 is provided with a press-fitting protrusion 4. The inner diameter of the press-fitting hole 3 is formed smaller than the outer diameter of the press-fitting protrusion 4. By press-fitting the press-fitting projections 4 into the press-fitting holes 3 to join the pair of molded products 1 and 2 as shown in FIG. Can be done. Since the molded article molded from the epoxy-modified melamine resin molding material has high flexibility and high toughness and a low elastic modulus, the inner diameter of the press-fit hole 3 and the size of the press-fit projection 4 are smaller than those of other thermosetting resins. Even if the press-fit margin, which is the difference from the outer diameter, is increased, no crack or chipping occurs, and the molded articles can be joined with high joining strength by increasing the press-fit margin. The press-fit margin depends on the size of the molded product, etc.
It is preferable to set the distance in a range of about 5 mm to 0.3 mm. As shown in FIGS. 1 and 2, when the press-fitting hole 3 is formed as a round hole and the press-fitting protrusion 4 is formed as a round bar, the press-fit margin D is determined from the outer diameter r of the press-fitting protrusion 4 to the inner diameter of the press-fitting hole 3. A value obtained by subtracting R, that is, D = r-R (r> R). FIG.
When the press-fit hole 3 is formed as a round hole and the press-fit protrusion 4 is formed as a square bar (square section), the press-fit margin D is defined as the diagonal length L of the press-fit protrusion 4 as the outer diameter. Numerical value obtained by subtracting the inner diameter R of the press-fit hole 3 from this L, that is, D = LR
(L> R). If the press-fitting margin is smaller than 0.05 mm, it is difficult to obtain a high joining strength by press-fitting, and if the press-fitting margin is larger than 0.3 mm, breakage such as cracking or chipping may occur at the time of press-fitting, which is not preferable.

In the present invention, as described above, the molded article 1
Before the press-fit projections 4 of the molded product 3 are pressed into the press-fit holes 3 of the molded products 3, the molded products 1 and 2 are heated at 100 to 150 ° C. for 3 to 10 hours. By press-fitting the press-fit projections 4 into the press-fit holes 3 after the heat treatment in this manner, it is possible to suppress a decrease in the strength of the press-fit even in a high-temperature atmosphere of about 130 to 150 ° C. and to suppress a decrease in the bonding strength. You can do it. When heat treatment is applied to the molded products 1 and 2 made of the epoxy-modified melamine resin molding material, the molded products undergo dimensional changes and shrink, but once shrinked in this way, they do not significantly shrink even if heated again. Therefore, once the molded products 1 and 2 made of the epoxy-modified melamine resin molding material are heat-treated and shrunk once, the press-fit projections 4 are pressed into the press-fit holes 3 and the molded products 1 and 2 are formed.
After joining, the molded articles 1, 2
The creep phenomenon does not occur, and the press-fitting strength of the press-fitting projection 4 into the press-fitting hole 3 can be suppressed from being reduced, so that the joining strength by press-fitting can be kept high even in a high-temperature atmosphere. Incidentally, since the molded article of the thermoplastic resin does not shrink even when subjected to the heat treatment, the effect of maintaining the bonding strength in a high temperature atmosphere by the heat treatment cannot be obtained.

The heat treatment conditions for the molded articles 1 and 2 made of the epoxy-modified melamine resin molding material are 100 as described above.
3 to 10 hours at 150 ° C.,
If the heat treatment is performed at a temperature of 150 ° C. or more for 10 hours or more, the molded article cannot be obtained if the heat treatment is performed at 150 ° C. or more for 10 hours or more. This is not preferable because there is a possibility that the strength of the steels 1 and 2 is reduced due to thermal deterioration. Heat treatment conditions are 12
About 6 to 8 hours at 0 ° C is preferable. The standard of the degree of this heat treatment is that the dimensions of the molded products 1 and 2 are 0.4
It is generally preferred that the value be minus about 0.9%. The effect can be obtained only by performing the heat treatment on one of the molded products 1 and 2, but it is preferable to perform the heat treatment on both. Also, the operation of press-fitting the press-fitting projections 4 into the press-fit holes 3 may be performed after the heat treatment of the molded products 1 and 2 is performed while the molded products 1 and 2 are still hot. May be performed after cooling to room temperature (room temperature).

[0015]

The present invention will now be illustrated by examples. (Example) 1500 g of melamine, 750 g of polyethylene glycol diglycidyl ether and 1430 g of water were charged into a 5-liter three-necked flask, and the temperature was raised to 9 g.
The reaction was carried out at a temperature of 5 ° C. for 45 minutes. Next is 40%
After injecting 1935 g of formalin, raise the temperature to 85 ° C
For 35 minutes to obtain a melamine resin syrup modified with a glycidyl compound. In this formulation, G / M = 0.12 and F / (M−G) = 2.4
6.

After drying the melamine resin syrup, take 70 parts by weight, add 30 parts by weight of pulp powder, 0.2 parts by weight of phthalic anhydride as a hardener, and 0.6 parts by weight of zinc stearate as a release agent. The mixture was mixed to obtain an epoxy-modified melamine resin molding material. Using this epoxy-modified melamine resin molding material, 165 ° C., 90
Injection molding under the condition of 100 kgf / cm ² of mold clamping pressure for ² seconds, a molded product 1 in which a press-fit hole 3 is formed as a round hole as shown in FIG. 2
Was molded. Here, the molded article 1 has a press-fit hole 3 having an inner diameter R =
The molded product 2 is formed to have an outer diameter r of the press-fitting protrusion 4 of 0.01 mm, 0.05 mm,
Three types were formed so as to be 0.15 mm.

Next, each of the molded products 1 and 2 is placed in a thermostatic drier, heated at 120 ° C. for 6 hours to perform a pre-treatment, and then the press-fitting projection 4 is inserted into the press-fitting hole 3 with a maximum press-fit of 10 kgf. The molded products 1 and 2 were joined by press fitting to a press fitting depth of 10 mm in depth. (Comparative Example 1) Using the molded products 1 and 2 molded in the example, the molded products 1 and 2 were joined in the same manner as in the example without performing pretreatment by heating.

Comparative Example 2 Molded products 1 and 2 were injection molded using polybutylene terephthalate (PBT: containing 30% glass fiber) in the same manner as in the example.
Were joined in the same manner as in the example without performing pretreatment by heating. Both of the molded products 1 and 2 joined in Example and Comparative Examples 1 and 2 were fixed, and the maximum load when the press-fitting protrusion 4 was pulled out from the press-fitting hole 3 at a speed of 2 mm / min was measured as the separation strength. At this time, the separation strength was measured in a normal temperature (room temperature) atmosphere, and the separation strength was measured in a high temperature atmosphere at 130 ° C. The results are shown in the following table.

[0019]

[Table 1]

As can be seen from the results in the table, it is confirmed that the molded article of the epoxy-modified melamine resin can obtain the same high level of peel strength at room temperature as the molded article of PBT which is a thermoplastic resin. The molded product of PBT (Comparative Example 2) has a peel strength of 1/10 in a high temperature atmosphere.
In the case of Comparative Example 1 in which the pretreatment by heating was not performed even with a molded article of an epoxy-modified melamine resin, the peel strength in a high-temperature atmosphere was greatly reduced. It is confirmed that the decrease in bonding strength in a high-temperature atmosphere can be suppressed.

[0021]

As described above, according to the present invention, a plurality of molded articles molded from the epoxy-modified melamine resin molding material are joined by press-fitting the other molded article into a press-fitting hole formed in one molded article. Therefore, a molded article molded from the epoxy-modified melamine resin molding material has high flexibility and high toughness, and has a low elastic modulus. It is possible to join molded products with high joining strength by taking a large press-fitting margin, and a plurality of molded products molded with an epoxy-modified melamine resin molding material can be formed in a range of 100 to 100.
Since the above-mentioned press-fitting is performed after performing the heating at a temperature of 150 ° C. for 3 to 10 hours, the molded product shrinks due to a dimensional change due to the heating, and greatly shrinks even in a high-temperature atmosphere. As a result, the molded article does not cause creep phenomenon and can suppress the decrease in the press-fit strength, and the joining strength by the press-fit can be kept high even in a high-temperature atmosphere.

[Brief description of the drawings]

FIG. 1 shows an example of the present invention, in which (a) is an exploded perspective view and (b) is a cross-sectional view.

FIG. 2 is a sectional view showing dimensions of a press-fitting hole and a press-fitting rod according to the first embodiment.

3A and 3B show another example of the present invention, in which FIG. 3A is an exploded perspective view, and FIG. 3B is a schematic view showing dimensions of a press-fit hole and a press-fit rod.

[Explanation of symbols]

 Reference Signs List 1 Molded product 2 Molded product 3 Press-in hole 4 Press-in protrusion

Claims (1)

(57) [Claims] 1. A method of molding a plurality of molded articles made of an epoxy-modified melamine resin molding material at a temperature of 100 to 150 ° C.
A method for joining a melamine resin molded article, comprising: after performing a heating treatment for 10 to 10 hours, and then press-fitting the other molded article into a press-fit hole formed in one molded article.