JP5143625B2 - Melamine resin tableware - Google Patents

Description

  The present invention relates to melamine-based resin tableware, and more particularly to a melamine-based resin tableware that is formed by compression-molding a melamine-based resin and then heat-treated at a specific temperature for a specific time.

Conventionally, melamine-based resin molding materials containing fillers such as α-cellulose (wood pulp) are excellent in heat resistance, solvent resistance, abrasion resistance, electrical insulation, etc. It is used in various fields such as tableware such as tea bowls, trays, bowls, etc., decorative plates in desks, chests, box boxes, etc. and electrical equipment parts such as connectors, converters, switchboards, and insulators.
In general, melamine-based resins are heat-molded at a pressure much higher than the volatile pressure of volatile substances such as formaldehyde, so that volatile components are enclosed in the molded product during molding, and the molded product maintains its internal pressure when heated. It is taken out as it is and becomes a product. For this reason, strict regulations on formaldehyde elution are provided in Ministry of Health and Welfare Notification No. 370 for tableware made from formaldehyde. In addition, a thermosetting resin such as a melamine-based resin is filled in the mold while the molten resin is cured, so that internal stress is liable to stay partially due to the shape of the mold. However, there is a tendency that the phenomenon that stress is released by external factors such as heat is likely to occur.

Conventionally, plastic tableware was generally recognized to be used at 100 ° C. or lower, but in recent years, resins having high heat resistance such as polybutylene terephthalate, polyethersulfone, polyethylene naphthalate and polyphenylene sulfide have been used. Table products such as tableware developed using these resins have been provided, and products that can be used in an environment of 100 ° C. or higher have also appeared. Taking advantage of these circumstances, the use environment of melamine resin tableware has recently been used in a temperature atmosphere exceeding 100 ° C., and elution of formaldehyde has become a problem in use at normal temperature. Due to the background, there is a concern that formaldehyde may be eluted when used in a high-temperature atmosphere.
However, as described above, since it was outside the range of common sense to use at high temperatures in the past, formaldehyde elution in such a situation has never been a problem.
In Patent Document 1, it is possible to perform reheating treatment after forming a thermosetting resin such as a melamine resin into a tableware shape so as to shrink it to the vicinity of the time point when the elongation of the change curve of the dimensional shrinkage rate slows down. It is disclosed. However, it is described that the heat treatment requires heat treatment for 72 hours at 120 ° C. and 48 hours at 130 ° C. at the time when the shrinkage rate decreases, specifically, shrinkage to 1.4%. Only. However, Patent Document 1 discusses tableware shrinkage, but does not describe any formaldehyde elution amount of the tableware.

JP 2004-321523 A

  An object of the present invention is to provide a safer melamine resin tableware by gradually decreasing the eluted formaldehyde of melamine resin tableware used in a high temperature atmosphere.

As a result of diligent study on the gradual decrease of the eluted formaldehyde of the melamine resin tableware, the present inventor, after compression-molding the melamine resin, by heat-treating the obtained melamine resin tableware at a specific temperature for a specific time The present invention was completed by finding that a built-in volatile substance in the tableware immediately after molding is volatilized and that the internal stress of the tableware is released, so that a safer and higher quality product can be obtained.
That is, the present invention is characterized by being subjected to heat treatment for 15 to 20 hours at a temperature of less than 110 to 120 ° C. or for 5 to 20 hours at a temperature of 120 to 140 ° C. after compression molding of a melamine-based resin. The melamine resin tableware is characterized in that the heat treatment temperature is 120 to 140 ° C.

  According to the present invention, it is possible to provide a safer and higher quality melamine-based resin tableware with gradually decreasing eluted formaldehyde.

Hereinafter, embodiments of the present invention will be described in detail.
Melamine resin, the raw material for melamine tableware, is produced by the condensation of methylolmelamine produced by reacting melamine and formaldehyde with an alkali catalyst. The uncured resin is filled with α-cellulose (wood pulp) and other hardeners. A kneading agent and the like are added, dried, and a coloring agent is added and pulverized to obtain a melamine resin molding material.
In the present invention, the melamine-based resin is a melamine / formaldehyde resin obtained by reacting melamine and formaldehyde (hereinafter sometimes abbreviated as “melamine resin”); melamine, formaldehyde and melamine capable of cocondensing with these. Mention may be made of melamine / formaldehyde-based cocondensation resins (hereinafter sometimes abbreviated as “melamine cocondensation resins”) obtained by reacting the components for cocondensation.

Examples of the melamine co-condensation component include ureas such as urea, thiourea and ethylene urea; guanamines such as benzoguanamine, acetoguanamine, formguanamine, phenylacetoguanamine and CTU guanamine; and guanidine, dicyandiamide and paratoluenesulfone. Other amino compounds such as amides; phenols such as phenol, cresol, xylenol, ethylphenol, butylphenol, bisphenol A; and the like can be used, and these components may be used in combination.
The melamine resin or melamine cocondensation resin is reacted with about 1 to 3 moles of formaldehyde with respect to 1 mole of melamine alone or the total amount of melamine and the melamine cocondensation component.

There are various molding methods such as a compression molding method, a transfer molding method, an injection molding method, etc., and melamine resin tableware is molded by a compression molding method in which heat and pressure are applied. That is, the melamine-based resin molding material is placed in a mold heated to 160 to 170 ° C., and is generally molded by pressing to 150 to 200 kgf / cm ² by a compression molding machine. The obtained molded product becomes a molded product such as tableware through a finishing process such as deburring.
As for plastic tableware, standard standards for materials of synthetic resin utensils or containers and packaging have been established based on the Food Sanitation Law (December 28, 1959, Ministry of Health and Welfare Notification No. 370). The standard is defined in “Synthetic resin appliances or containers and packaging using formaldehyde as a raw material”, and the national safety standard regarding the amount of formaldehyde eluted is regulated to “4 μg / ml or less”.

In response to this, the Japan Plastics Daily Products Industrial Association, an industry group, has established voluntary standards that are stricter than national standards, and regulates the amount of formaldehyde elution to be 2 μg / ml or less, providing products that customers can feel at ease. want to be.
In the present invention, for the melamine-based resin tableware assumed to be used in a high-temperature atmosphere, the heating of the formaldehyde eluate collection operation is performed under the conditions of 60 ° C. and 130 ° C., respectively, for three specimens as molded. Holding for 30 minutes, the elution amount of formaldehyde was measured, and the average value was obtained. The results are as shown in Table 1 below, and it was found that the higher the operating temperature environment, the higher the amount of formaldehyde eluted, as reported in known literature.

The measurement of the amount of formaldehyde in the table is in accordance with sanitary test standards, and the eluate of the elution test when used at a temperature exceeding 100 ° C is obtained by adding 95 ° C water to the sample at a rate of ² ml / cm ^2. And heated at 130 ° C. for 30 minutes. When using at a temperature not exceeding 100 ° C., water was added to the specimen at a rate of ² ml / cm ² and heated at 60 ° C. for 30 minutes.

Therefore, the present invention shows the results of measuring the amount of elution of formaldehyde with respect to specimens that were previously heat-treated at various temperatures for various times with tableware products molded from melamine-based resin molding materials, and are shown in the examples described later. Even when used under a high temperature atmosphere based on the results, it was possible to obtain tableware with less formaldehyde elution and higher safety.
In the heat treatment of the present invention, the treatment temperature is required to be 110 to 140 ° C., preferably 120 to 140 ° C. If the heat treatment temperature is less than 110 ° C., the amount of elution of formaldehyde decreases, and if the heat treatment temperature exceeds 140 ° C., the melamine resin may be decomposed, which is not preferable.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Example 1]
[Sample preparation]
The molding conditions of the sample used for the formaldehyde dissolution test are as follows.
Molded product: outer diameter 13.4 cm × height 5.8 cm mold surface temperature: concave mold; 175 ° C. (bottom part of measuring part)
Convex mold: 167 ° C, (measurement section top surface)
Materials used: Nicarette MC (trade name), manufactured by Nippon Carbide Industries Co., Ltd.
Preheating temperature: 120 ° C
Molding conditions: Molding material preheat molding
Molding pressure: 140 kgf / cm ²
Curing time: 50 seconds Heat treatment temperature of the molded wrinkles is 110, 120, 130, 140 ° C., and the heat treatment time is 5 hours, 10 hours, 15 hours, 20 hours, 25 hours at each temperature. The amount of formaldehyde eluted from each heat-treated soot was measured by adding hot water at 95 ° C. at a rate of ² ml / cm ² to the specimen and holding at 130 ° C. for 30 minutes each to measure the amount of formaldehyde eluted.
The obtained specimen is shown in Table 2.

The measurement of the amount of formaldehyde eluted from the obtained specimen was carried out by the following operation. Standard solutions, reagents, and HPLC operating conditions used for the operation are as follows.

The measurement results of the elution amount of formaldehyde from three specimens (No1 to No3) are shown in Table 5 below, and the results are shown in FIG.
From the above results, the molded melamine-based resin tableware is subjected to a heat treatment at a temperature of less than 110 to 120 ° C. for 15 to 20 hours, or at a temperature of 120 to 140 ° C. for 5 to 20 hours. Even in the use below, the elution amount of formaldehyde could be suppressed to 1.18 μg / ml or less.

[Example 2]
[Sample preparation]
The molding conditions of the sample used for the bending strength test based on JIS-K-6911 are as follows.
Molded product: a plate having a length of 120 mm, a width of 50 mm, and a thickness of 4 mm (for the bending strength test, this plate was divided into five equal parts so as to form a test piece having a length of 120 mm, a width of 10 mm, and a thickness of 4 mm).
Mold surface temperature: convex mold; 161 ° C
Concave mold; 160 ° C
Materials used: Nicarette MC (trade name), manufactured by Nippon Carbide Industries Co., Ltd.
Preheating temperature: 120 ° C
Molding conditions: Molding material preheat molding
Molding pressure: 20.6 MPa
Curing time: 160 seconds The molded specimen is divided into 5 equal parts, the heat treatment temperatures are 110, 120, 130, and 140 ° C., and the treatment times are 5 hours, 10 hours, 15 hours, 20 hours, and 25 at each temperature. A heat treatment was performed for a time, and a bending strength test was performed on each heat-treated specimen.

The obtained specimens are shown in Table 6 below.
The bending strength test of the obtained specimen was performed based on JIS-K-6911.

The results of the bending strength test are shown in Table 7 below.

FIG. 2 shows the relationship between the bending strength and the heat treatment time, with the bending strength on the vertical axis and the processing time on the horizontal axis for each processing temperature, and an approximate curve obtained by the least square method.
Bending strength tends to decrease in any temperature range by long-time heat treatment.
Moreover, the tendency that bending strength has fallen large around 15 to 25 hours in all is seen.
The inflection points of this approximate curve are obtained as follows, and in any case, inflection points exist at 10 to 20 hours.
110 ° C .: 11.3 hours 120 ° C .: 11.3 hours 130 ° C .: 16.7 hours 140 ° C .: 17.8 hours From the above results, applying heat treatment for more than 20 hours leads to a decrease in strength. This is not preferable because it may not fulfill its function.
In addition, when the treatment time is less than 5 hours, the amount of formaldehyde eluted does not decrease, and even when heat treatment is performed for more than 20 hours, the amount of formaldehyde eluted is constant and the effect is not improved.
From the above, the heat treatment time in the present invention needs to be 5 to 20 hours.

  The heat treatment technique according to the present invention is used for gradually reducing the amount of formaldehyde eluted in the field of melamine resin tableware such as dishes, teacups, trays, and bowls.

FIG. 1 is a graph showing the relationship between heat treatment time, temperature and formaldehyde elution amount. FIG. 2 is a diagram showing the relationship between heat treatment time, temperature and strength.

Claims (2)

  After compression molding of melamine-based resin, heat treatment is performed at a temperature of less than 110-120 ° C. for 15-20 hours, or at a temperature of 120-140 ° C. for 5-20 hours. Tableware.   The melamine resin tableware according to claim 1, wherein the heat treatment temperature is 120 to 140 ° C.