JPH0618693B2 - Method for drying powder of polyamide synthetic resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for drying a polyamide-based synthetic resin powder or granular material, and more specifically, drying a polyamide-based synthetic resin powder or granular material in a drying tank open to the atmosphere. The present invention relates to a method for drying a polyamide-based synthetic resin powder or granular material that is dried by a heat source.

(Prior Art) Conventionally, as a drying technique of this type, it has been generally accepted that long-time drying is performed at a low temperature in order to prevent oxidation of a material that is proportional to a drying temperature.

That is, since the polyamide-based synthetic resin material targeted by the present invention has an amide group in its molecular chain, it easily binds to oxygen in the air and tends to be oxidized and discolored by the bond. Moreover, the tendency of the oxidative discoloration becomes remarkable in proportion to the increase of the material temperature, and for example, nylon pellets which are the powder particles of the polyamide-based synthetic resin,
In the non-oxidized state, the particles are colorless and transparent, but as the drying temperature rises, the oxidation of the material progresses and changes from yellow to brown, and then changes to black-brown as well as depending on the discoloration density. It also changes the physical properties of the material.

Therefore, in order to avoid the above-mentioned harmful effects due to heating of the material, the low temperature long-time drying method is used as described above.

(Problems to be solved by the invention) However, as described above, a method of widely drying air at a low temperature for a long time at a low temperature is generally known. The production amount is poor for a long time, that is, the processing time and the production amount are not well balanced, and the drying time is long, so the retention time of the pellets in the equipment is inevitably long, and a large capacity that can handle it. Since the above equipment is required, the initial cost becomes high even from the equipment side, and as a result, it is not suitable for productivity.

Then, a drying method using nitrogen as a heating medium has been improved to eliminate the inferiority of productivity as described above, but this method can prevent the oxidation of pellets. Also, as compared with the one using air as the heat transfer medium, the cost is very high, and the nitrogen contained in the apparatus together with the pellets needs to be prevented from being deteriorated in purity due to the inclusion of air. for that purpose,
The nitrogen in the device must be completely isolated from the air outside the device, which is a difficult problem in terms of equipment.

Further, as described above, a vacuum drying method utilizing wall heat transfer without using air or nitrogen as a heat transfer medium is also known, but it is poor in general practical use, and in any case, As described above, the conventional drying technique does not completely satisfy the productivity for drying pellets.

The present invention has been invented in view of the above problems, and an object thereof is to use microwaves as a drying heat source to induce sensible heat of the pellet itself and enable high heat drying in a short time. With the experiment of the dry state, the actual function of the drying temperature and the drying time is grasped, and the coloring limit curve based on the actual function and the drying curve of the target moisture are set,
By maintaining the relative relationship between the drying temperature and the drying time so that the value falls within the allowable limit range indicated by both curves,
It is intended to provide a method for drying a polyamide-based synthetic resin powder granule, which can produce pellets having a low moisture content of, for example, 0.08% or less without oxidative discoloration in a short time.

(Means for Processing Problem) The present invention uses the following means in order to solve the problem. That is, in the drying method in which the drying heat source (F) is provided and the polyamide-based synthetic resin powder or granular material supplied to the drying tank (C) by heating by the heat source (F) is heated and dried in the air, the heat source ( F) is a microwave device that radiates microwaves, and the drying temperature and the drying time are defined by a coloring limit curve (2) and a target moisture drying curve (1) in a real function of the drying temperature and the drying time. The temperature is higher than the drying temperature at the intersection (5), is shorter than the drying time at the intersection (5), is less than or equal to the lower limit time in the coloring limit curve (2), and is equal to or less than the lower limit time in the drying curve (1). It is characterized in that the time is set to be equal to or longer than the lower limit time.

(Operation) In the present invention, when a polyamide-based synthetic resin powder or granular material is heated and dried in air, a microwave device is used as a heat source to radiate microwaves, so that the powder or granular material itself is sensible heat. It is possible to induce high temperature drying in a short time by inducing, and the drying temperature and the drying time at which the high temperature drying is performed, the coloring limit curve based on the actual function of the drying temperature and the drying time, and the target moisture content. To avoid long-term drying at high temperature by setting an allowable limit range that is higher than the drying temperature at the intersection where the drying curve intersects and shorter than the drying time at this intersection, and drying within this setting range. Is.

(Example) A method for drying a polyamide-based synthetic resin powder according to the present invention will be described with reference to an example of the drawings.

First, what is shown in FIG. 1 is a skeleton of a drying apparatus for carrying out the method for drying a polyamide-based synthetic resin powder according to the present invention, wherein the powder (B) is fed through the charging port (A).
Is contained in a drying tank (C), and is stirred by a motor (D) with fins (E), while being heated by a microwave device (that is, a heat source).
(F) A microwave is radiated from (F) to heat and dry the granular material (B) in the drying tank (C), and the drying temperature and the drying time for the heating and drying are described later. Limit curve (2) (4) and target moisture drying curve (1)
(3) The storage tank which is automatically circulated by the operation of a control device (not shown) which controls the drying temperature and the drying time to be within the allowable limits (7) and (8). (G) is discharged to the storage tank (G) and dehumidified air (H) is used for residual heat cooling.
It should be noted that (I) and (J) are sluice valves that restrict the charging and discharging of the powder or granular material (B).

Therefore, the relationship between the drying temperature and the drying time appropriate for achieving the desired value (moisture content of 0.08% or less and yellowness = 0) of the powder or granules (B) dried in the above drying apparatus is shown. The coloring limit curves (2) and (4) and the target moisture drying curves (1) and (3) are preset based on the experimental data.

That is, the coloring limit curves (2) and (4) and the target moisture drying curves (1) and (3) are set on the basis of the actual function of the following experimental results.

First, the initial moisture was adjusted to approximately 1% on 22 mesh stainless steel using a hot air circulation type shelf dryer.
Gram nylon 6 pellets or nylon 66 pellets experimental samples were placed and then dehumidified with dew point of 35 ° C.
The temperature was increased in 5 ° C. intervals between 0 ° C. and 150 ° C., and the water content of the experimental sample at the rising temperature in the 5 ° C. intervals was 0.08% of the water content of the “Karl Fischer” water content measuring instrument.
The drying time is defined as the time required to reach the value of, and the coloring degree is 5 ° C. by using a color difference meter based on the yellowness that cannot be perceived by visually observing the pellet itself. The actual relationship between temperature and time at the coloring allowable limit was obtained by measuring the time required to reach the discoloration limit region, which changes depending on the increase of the drying temperature in the interval.

Then, the drying temperature is set on the horizontal axis, and the time required for the moisture content of the pellets to reach 0.08% is set on the vertical axis, and the coloring limit curve ( 2) and (4) and target moisture drying curves (1) and (3) are as shown in FIG.

A curve (1) shown by a solid line in FIG. 2 is a drying curve of the target water content when nylon 6 pellets are used as the experimental sample, and a solid curve (2) is a coloring limit curve thereof.

The chain double-dashed curve (3) shows a more remarkable oxidation reaction than the nylon 6 as the experimental sample. Nylon 6
6 is a drying curve of the target moisture when the pellets of No. 6 are used, and the two-dot chain line curve (4) shows the coloring limit curve, and the coloring limit curves (2) and (4) and the drying of the target moisture are shown. The intersections (5) and (6) with the curves (1) and (3), respectively.
I have

That is, these intersecting points (5) and (6) are the limit values of the drying time with respect to the drying temperature, and at the drying temperature at the intersecting points (5) and (6), the drying time at the intersecting points (5) and (6) is When the drying time becomes long, the influence of coloring due to air oxidation occurs, and conversely, in the drying time at the intersections (5) and (6), when the drying temperature becomes lower than the drying temperature at the intersections (5) and (6), the target moisture content is increased. It cannot be dried.

Therefore, the drying temperature and the drying time by the microwave device are the drying temperatures at the intersections (5) and (6) of the coloring limit curves (2) and (4) and the target moisture drying curves (1) and (3). At a higher temperature and shorter than the drying time at the intersections (5) and (6), at least the lower limit time in the coloring limit curves (2) and (4), and at the drying curves (1) and (3). ) Is set to a time equal to or longer than the lower limit time.

That is, as indicated by the hatched lines in FIG. 2, the coloring is performed such that the temperature is high in the temperature direction from the intersections (5) and (6) and is short in the time direction from the intersections (5) and (6). The allowable limit range (7) (8) is set so that the time is equal to or less than the lower limit time in the limit curves (2) and (4) and more than the lower limit time in the drying curves (1) and (3).

Therefore, by maintaining the heating by the microwave device at the drying temperature and the drying time within the permissible limit regions (7) and (8), the nylon 6 or the nylon 6 can be obtained.
Polyamide-based synthetic resin powders such as No. 6 and the like, with a water content of 0.08
% Or less, the degree of yellowness becomes 0, and it can be dried in a short time.

The drying curve (1) and the coloring limit curve (2) of nylon 6 are similar to the drying curve (2) and the coloring limit curve (4) of nylon 66, but with respect to the drying temperature. With respect to the intersection point (5), which is the maximum limit of the drying time, the position of the intersection point (6) is on the high temperature side, and the drying time is reduced by that amount. It shows that the oxidation reaction is sensitive to the drying temperature and time.

Incidentally, when drying nylon 6 pellets having an initial water content of 2.6% by the drying device shown in FIG.
When dried at 40 ° C. (9) for 30 minutes (10), the dried pellets were measured by a moisture meter and a color difference meter, and as a result, pellets having a water content of 0.06% and no coloration were obtained. It was.

(Effect of the Invention) In a drying method in which a dry heat source (F) is provided, and the polyamide-based synthetic resin powder or granular material supplied to the drying tank (C) by heating with the heat source (F) is heated and dried in the air, The heat source (F) is a microwave device that radiates microwaves, and the drying temperature and the drying time thereof are the coloring limit curve (2) in the actual function of the drying temperature and the drying time and the drying curve (1) of the target moisture. ) Is higher than the drying temperature at the intersection (5), is shorter than the drying time at the intersection (5), and is less than or equal to the lower limit time in the coloring limit curve (2), and the drying curve ( By setting the time lower than the lower limit time in 1), microwave radiation used as a heat source induces sensible heat in the granular material itself, enabling high-temperature drying in a short time, and drying for a long time as in the past. Due to Since it does not require a drying tank of a certain amount and does not use a heat transfer medium such as nitrogen outside the air, the drying equipment can be extremely simplified and the coloring limit curve and the target moisture drying curve can be obtained. Based on the fact that it can be dried at a high temperature for a short time, the polyamide-based synthetic resin powder is not affected by coloring due to air oxidation, and has a desired moisture content of 0.08% or less in a short time. It has an effect that it can be dried in a colored state.

[Brief description of drawings]

FIG. 1 is a skeleton diagram of a drying apparatus for carrying out the drying method of the present invention, and FIG. 2 is an explanatory diagram showing a relative relationship between a coloring limit curve of the present invention and a target moisture drying curve. (1) …… Target moisture drying curve (2) …… Coloring limit curve (5) …… Intersection (C) …… Drying tank (F) …… Heat source

Claims (1)

[Claims] 1. A drying method comprising a drying heat source (F) and heating and drying a polyamide-based synthetic resin powder or granular material supplied to a drying tank (C) by heating with this heat source (F) in the air. Then, the heat source (F) is a microwave device that radiates microwaves, and the drying temperature and the drying time are
An intersection (5) between the coloring limit curve (2) and the target moisture drying curve (1) in the actual functions of the drying temperature and the drying time.
Higher than the drying temperature of, and shorter than the drying time of the intersection (5), not more than the lower limit time in the coloring limit curve (2) and not less than the lower limit time in the drying curve (1). A method for drying a polyamide-based synthetic resin powder or granular material, characterized in that the time is set.