JP3318866B2 - How to measure the thermal welding temperature of plastics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a "welding temperature" necessary for setting a heating temperature for each material in a heat sealing operation which is often performed for sealing and bag making of a sheet-like plastic by pressurizing and heating. To provide an easy measurement method

[0002]

2. Description of the Related Art In a packaging material, a container is sealed using a sheet-like plastic or a sheet-like material is laminated to form a bag. It also has the purpose of preventing gas and microorganisms from entering and exiting because of its reliability. The reliability of the thermal welding characteristics of plastic materials themselves is extremely high, and the “welding temperature” of each material (including each lot) is easy. If it can be accurately grasped, high reliability of heat welding can be achieved, but there is no simple measurement method of `` welding temperature ''. In the past, in order to obtain a reliable state of welding, production of actual equipment was suspended for a long time, Sealing and heat-sealing tests are performed using a large amount of materials and hands using actual materials, and welded samples obtained under a wide range of operating conditions are determined by indirect inspections based on tensile tests and observations specified by JIS.

[0003]

There are the following problems to reliably measure the temperature of the thermocompression bonding surface. (1) A method for measuring the temperature of a minute portion (2) High-speed recording of a minute temperature change (3) Heat capacity (4) Control of heating slightly larger than the heat of fusion (5) Method of processing collected data to minimize measurement disturbance

[0004]

In the present invention, the "welding temperature" is determined by the following means. (1) A fine sensor is sandwiched between the welding surfaces, and a change in the welding surface temperature is automatically stored or recorded at a high speed. (2) Heating In a temperature zone, a sheet-like material having a uniform thickness with a minimal change in heat conduction characteristics is closely adhered to the surface of the plastic to be heated to restrict the heating flow. (3) Heating is sequentially increased in time ( 4) The obtained welding surface temperature rise value is divided at regular intervals, and the difference between the data at the base point is obtained from the data immediately after each time interval. The same calculation is performed for the entire measurement range, and the time of the welding surface temperature is calculated. Approximately differentiating the change to obtain a “welding surface temperature rise rate value” (5) The “welding surface temperature rise value” is calculated in the same time section as above.
Further, a difference calculation is performed, an approximate second derivative is performed, a change in the welding surface temperature is replaced with a plus value or a minus value, the influence of the variation in the heating rate is minimized, and the inflection point detection sensitivity is mathematically enhanced. (6) From the result of the approximate second derivative, assume that the temperature at which the value is significantly increased is referred to as “welding temperature”. (7) ± 1 to 5 around the “welding temperature” obtained above
Perform pressure bonding heating in the heating temperature range of ℃, correct the “welding temperature” obtained above, and determine the practical “welding temperature” from observation of the welding surface.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 1 (the scale of each part is varied for easy understanding of the form). The plastic to be heated is a heat sealant layer (1). And the heat sealant layers (1) and (1 ') and the substrates (2) and (2') each showing a composite of (1 ') and the substrates (2) and (2'). The thickness is several tens of μm. The welding surface temperature sensor (4) is installed so as to be sandwiched between the welding surfaces of the heat sealant layers (1) and (1 ′),
The temperature is converted into a voltage signal, connected to a recorder (6), and used for data analysis. The heating blocks (5) and (5 ') have substantially the same temperature, which is higher than the estimated temperature of thermal welding of the plastic to be heated. Adjusted to
An operating mechanism (not shown) allows the pressurization and release of the plastic to be heated. On the surface of the plastic to be heated, heat flow control materials (3) and (3 ') for controlling the amount of heating are provided. The data obtained by the recorder (6) is mathematically analyzed to determine the welding start temperature.

[Example]

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Temperature sensor (4) for the welding surface shown in FIG.
Since the detection of the melting phenomenon becomes ambiguous when the heat capacity of the sensor is large, it is necessary to use a bare thermocouple or thermistor of 50 μm or less barely. Heat flow control materials (3), (3 ′) Uses a Teflon (registered trademark) sheet or paper that does not cause thermal denaturation in the test heating temperature range. The amount of heating flow control is determined in consideration of the set temperature of the heating blocks (5) and (5 '). However, the temperature recorder (6) that adjusts the thickness and the number of sheets so that the heating rate in the analysis time section is 0.5 to several degrees Celsius can set the analysis time section to about 0.1 to 1 second. Selecting a device having a response speed A description will be given of an example of determining the “welding temperature” with reference to FIG. 2. FIG. 2 (a) shows heat such as melting in a heating temperature zone heated by a heating block adjusted to a constant temperature. Note the temperature of the crimping surface of the material that does not cause denaturation The first derivative result (8) and the second derivative result (9) of the temporal data (7) are shown. Each of the differential values shows a phenomenon approaching 0. Figure 2 (b) has a heat sealant layer The softening start zone (10) and the melting start zone (11) are observed in the change in temperature rise, which is a heating record of the composite material, but it is difficult to read a fine temperature value. Set a 1 second section,
Figure 2 shows the approximate first derivative (12) converted to a bar graph by calculating the change between plots and enlarging the display scale.
The approximate first derivative (12) shown in (c) is further calculated for each section,
Obtain the approximate second derivative result (13) From the approximate second derivative (13), it is possible to detect that the heat conductivity has significantly increased at the inflection point (14). The inflection point (14) is a liquid from a solid or a viscous body. Esti- mated point,
In the present invention, this point is referred to as “welding temperature”, and the inflection point (14) is used as a starting point.
(B) is combined to determine the “welding temperature” T _{M The} purpose of approximating the second derivative of the measured data is to minimize the effect of the variation in the heating temperature gradient. Determining the accuracy under high-speed measurement is actually difficult, so as a complementary method, use a heating block that has been precisely temperature-controlled to within ± 5 ° C of the “welding temperature” obtained. By doing so, it is possible to determine the corrected practical "welding temperature"

[0007]

[Effect of the Invention] Actual "welding temperature" of plastic materials
(1) Fine-grained "welding temperature" of each material (including lot) can be easily grasped. (2) Sealant of material with unknown "welding temperature" can be obtained. Easy qualification (3) Easy heating and compression conditions for actual plastic materials
Can be used reliably and at low cost. (4) Can be used as a universal quality assurance index of heat sealing technology. (5) Can have the function of "CCP" in the heat sealing process required by "HACCP".

[Brief description of the drawings]

FIG. 1 is an outline of a method for measuring a “welding temperature” of the present invention.

FIG. 2 Outline of the method for determining the “welding temperature” of the invention

[Explanation of symbols]

1, 1 'heat sealant layer 2, 2' base material 3,
3 'heat flow control material 4 temperature sensor 5 heating block 6 temperature recorder 7 time data 8 primary differential result 9 secondary differential result 10 softening start point 11 melting start point 12 approximate primary differential result 13 approximate secondary differential result 1
4 Inflection point

Claims (1)

(57) [Claims] 1. The actual welding temperature is determined by the following method. (1) A fine sensor is sandwiched between the welding surfaces, and the change in the welding surface temperature is automatically stored or recorded at a high speed. A sheet-like material having a uniform thickness with a minimal change in conduction characteristics is adhered to the surface of the plastic to be heated, and the heating flow is restricted. (3) Heating is performed in ascending order over time. (4) Obtained The welding surface rise temperature value is divided at regular intervals, and the same calculation is performed for the entire measurement range in which the difference between the data at the base point and the data after one in each time section is calculated, and the approximate differential of the time change of the welding surface temperature is calculated. (5) The “welding surface temperature rise value” is obtained in the same time section as above.
Further, a difference calculation is performed, an approximate second derivative is performed, a change in the welding surface temperature is replaced with a plus value or a minus value, the influence of the variation in the heating rate is minimized, and the inflection point detection sensitivity is mathematically enhanced. (6) From the result of the approximate second derivative, assume that the temperature at which the value is significantly increased is referred to as “welding temperature”. (7) ± 1 to 5 around the “welding temperature” obtained above
Perform pressure bonding heating in the heating temperature range of ℃, correct the “welding temperature” obtained above, and determine the practical “welding temperature” from observation of the welding surface.