Patent Description:
For the bonding of plastic films and sheets in processing of bag-making and sealing, heat-sealing techniques are frequently used, wherein a heating body is pressed on the surface of a heat seal material (hereinafter, occasionally referred to "work"), and faces to be in contact with each other and heat-bonded utilizing heat conduction. The heat-bonding method (heat-sealing) has been commonly used (ASTM F88 established in <NUM>).

The heating methods are classified broadly into (<NUM>) a method of heating the material from both sides simultaneously by a pair of heating bodies utilizing heat conduction (Jaw system), (<NUM>) one side heating which utilizes heat conduction from a surface of the material and is constructed by a heating body only on one side, (<NUM>) a method of local heating near bonding faces (ultrasonic heating, magnetic induction heating, dielectric loss blowing hot air, etc.).

The heat bonding (heat-sealing) utilizes thermoplasticity phenomenon of plastics.

Upon appearance of heat bonding, it enters in a peelable seal zone (interfacial bonding zone) where bonding strength is raised with the elevation of heating temperature at the bonding face. When the heating temperature arrives at a prescribed value or more, the bonding faces become melted into paste state, and after cooled, they are integrated into agglomerate bonding. When the results of measuring specimens at each heating temperature by tensile test are plotted, it can be seen that the heating temperature and heating speed are parameters of heat seal strength (Hishinuma effect), as shown in <FIG>.

In general, the width of interfacial bonding temperature zone is <NUM> - <NUM>. When the heating of bonding faces is adjusted to the boundary temperature zone between interfacial bonding and agglomerate bonding (proper temperature zone), edge cut can be prevented by utilizing peel energy at bonding faces, and properties of each material can be utilized fully. Furthermore, insufficient heating and overheating and depressed to ensure quality of heat seal.

In order to analyze the characteristics of present heating jaw system, using surface temperature of heating body as a parameter, the method of measuring welding face temperature was applied, and temperature response of the sensor was measured at the welding face (bonding face) of a work in laboratory scale. The results are shown in <FIG>.

From the examples shown in <FIG>, relations between the arrived temperature on both sides heating at the same temperature and the heating time are classified into three types of response pattern, i.e. converging equilibrium temperature (Tc), <NUM> % arrival point (Tb), high speed rising region (Ta). The characteristics of the three response pattern types are:.

Today, an appropriate technique to control welding face (bonding face) temperature has not been established in heat bonding techniques, and the heating operation is high speed region is conducted by time control of arrival time.

In order to address peelable seal having a narrow temperature range where the properties of peelable seal appear, high accuracy temperature control and high speed press bonding operation are required, but conventional methods do not satisfy this expectation.

In the present situation, productivity is in preference, and (<NUM>) utilization of high speed rising region (Ta) is conventionally used. However, since high accuracy techniques to control press bonding [<NUM>] time and temperature have not been established, practically, insufficient heating is feared and temperature is set raising about <NUM>. Accordingly, the bonding state tends to be agglomerate bonding which exceeds the boundary temperature region shown in <FIG>, and it makes difficult to regulate to form interfacial bonding which results in easy opening. The solution of this problem is strongly desired worldwide.

On the other hand, the inventor developed a method of setting the temperature of heating body and press bonding time while heat-sealing by mounting temperature sensors on a surface of heating body and between welding faces of test pieces (Patent Document <NUM>), and a method of controlling heat seal temperature by mounting surface temperature sensors in the vicinity of heating source and a surface of heating body (Patent Document <NUM>). Both methods have been patented.

<CIT> discloses a method of heat-sealing using a heat-sealing apparatus which heat-seals a heat seal material (<NUM>) by nipping it between a pair of heating bodies (<NUM>, <NUM>), which comprises: mounting a cover material (<NUM>) on the surface (<NUM>) of at least one of the heating bodies (<NUM>, <NUM>) to be in contact with the heat seal material (<NUM>); attaching a minute temperature sensor (<NUM>) to the surface (<NUM>) of the at least one of the heating bodies (<NUM>, <NUM>); and controlling temperature of welding face by the temperature detected by the minute temperature sensor (<NUM>). The document also discloses a heat-sealing apparatus which nips a heat seal material (<NUM>) between a pair of heating bodies (<NUM>, <NUM>) to heat-seal it, comprising a cover material (<NUM>) is mounted on the surface (<NUM>) of at least one of the heating bodies (<NUM>, <NUM>) to be in contact with the heat seal material (<NUM>); a minute temperature sensor (<NUM>) is attached to the surface (<NUM>) of the at least one of the heating bodies (<NUM>, <NUM>); and an actuating mechanism which moves the heating bodies (<NUM>, <NUM>) forward and backward or a controlling mechanism which controls heating mechanism of the heating bodies, based on the detected result of the minute temperature sensor (<NUM>). The document furthermore discloses a method of heat-sealing using an apparatus which nips a heat seal material (<NUM>) between a heating element (<NUM>) and an anvil (<NUM>) to heat-seal it, which comprises: mounting a cover material (<NUM>) on the surface (<NUM>) of the heating element (<NUM>) to be in contact with the heat seal material (<NUM>); attaching a minute temperature sensor (<NUM>) to the surface (<NUM>) of the heating element(<NUM>); and controlling temperature of welding face by the temperature detected by the minute temperature sensor (<NUM>). In addition, the document discloses a heat-sealing apparatus which nips a heat seal material (<NUM>) between a heating element(<NUM>) and an anvil (<NUM>) to heat seal it, wherein a cover (<NUM>) is mounted on the surface (<NUM>) of the heating element (<NUM>) to be in contact with the heat seal material (<NUM>); and a minute temperature sensor (<NUM>) is attached to the surface of the heating element (<NUM>).

<CIT> discloses a heat seal device and a method for forming a composite heat seal structure in which a linear detachable seal is added to a belt-shaped detachable seal in the longitudinal direction thereof, wherein the heat seal device comprises: a crimping belt conveyance heating part including a pair of belts hung between rollers so as to travel, and heating bodies disposed apart from the belts; and a die roller crimping part including an elastic body roller and a linear roller having, on the circumferential surface thereof, linear projections arranged in the circumferential direction.

<CIT> discloses a joining device (<NUM>) with a first tool half (1a) and with at least one first thin-film sensor (6a) arranged on a surface (2a) of the first tool half (1a), the at least one first thin-film sensor (6a) is set up to detect at least one process parameter value of at least one process parameter during a joining process; and it discloses a joining method in which at least one process parameter value of a process parameter on a surface (2a) of at least a first tool half (1a) is detected by means of at least one first thin-film sensor (6a).

Heretofore, there is a provision against the accuracy of temperature control of heating body (heating bar) (ASTM F2029; <NUM>). The surface temperature of heating body relates multiply to the size and form of the heating body, the position of heating source, heating unevenness of heater, the position of detecting sensor, control speed, mounting method, heat dissipation (heat insulation), etc., and unevenness of heating temperature at heat bonding face is <NUM> or more. Therefore, in order to exhibit essential properties of works (plastic material), it is required to restrain the variation of welding face temperature within <NUM>.

Currently, there is no appropriate control system, and the time limit system is employed where pressing time of heating body is controlled. In the system, the pressing time is set relied on visual inspection of actually produced specimens and tensile test (JIS Z <NUM>, ASTM F88) of a site of the specimens. Necessarily, agglomerate bonding where a constant value of heat bonding (heat seal) strength is gotten is recommended (JIS Z <NUM>).

For the purpose of maintaining stable heat bonding quality, it is expected to develop a technique to control welding face (bonding face) temperature being an essential parameter directly.

Every temperature control methods previously developed by the inventor are to nip a temperature sensor between heat bonding faces of test pieces, and the temperature sensor is incorporated in the product after heat seal. Therefore, in the heat-sealing by a seal machine, the control of temperature is relied on time control based on the data obtained by the preliminary experiment.

While, if heat seal temperature can be traced in a seal machine, more exact temperature control can be done.

An object of the invention is to provide a means capable of controlling exact temperature by measuring the variation of temperature at a specific point in heating system on the side of apparatus relating to heat seal on a real time.

The inventor noticed that the heat flow from heat source to heat seal material relates directly to the temperature of welding face (bonding face). Then, he mounted a minute temperature sensor on the surface of the covering material provided on the surface of heating body, and detected temperature difference depending on heat flow in temperature rise region to succeed is the simulation of temperature response to welding face. The measurement of interface temperature between the covering material and the heat seal material is actually equivalent to the measurement of the surface temperature of the heat seal material.

Explanation of welding face temperature response formula A schematic view of heating jaw system is illustrated in <FIG> indicates a variation of temperature distribution in a work, in the case that heating temperatures of a pair of heating bodies were adjusted to the same.

On the other hand, <FIG> indicates a variation of temperature distribution in the work, in the case that the temperature of only one of the heating bodies was adjusted, but the other was allowed to stand at room temperature.

When a heating body is pressed in a short time, the temperature response of welding face (bonding face) can be dealt with step response.

The definitions of T1, T2, T3 are indicated in <FIG>. Provided that a constant determined by the heat conductivity of material and heat capacity, such as thickness, is denoted k; time constant, and environmental temperature is denoted T3, the welding face temperature response including heating from both sides is expressed by the following formula, as a general formula (see <FIG>).

Wherein Tb is the aforementioned temperature of <NUM> % arrival point, and T1 and T2 are surface temperatures of each heating body. n is expressed by <MAT> and k is k = RC defined by primary delayed electric circuit constructed by resistors and condensers. In the circuit diagram of <FIG>, R = R1 + R3 + r1, C = C3. t represents time.

In the case of both sides heating at the same temperature, T2 = T1, and therefore, temperature response of bonding face results in the response of <FIG> which is determined only by the heat source temperature T2, finally constricts to T2.

When an anvil is rendered at room temperature, T1 = T3, it becomes like primary delayed <FIG>.

n is a factor determined by heat conductivity of the material facing the heat bonding face. Provided that the materials facing are identical, n = <NUM>/<NUM>.

Commonly, although heating is classified into both sides heating and one side heating, they are only different in temperature setting of each heating body. Theoretically, when it understands that both sides heating and one side heating are limiting conditions of setting temperature, practical defects can be dealt systematically.

It is press heating by a pair of metal bodies including heating source, and bonding faces are heated from the surfaces of a work by utilizing heat conduction of the material. It has characteristics that bonding face temperature is equilibrated with the surface temperature of heating bodies without influence of other factors such as environmental temperature by rendering contact face temperatures of the pair of the heating bodies with the material identical.

One side heating is constructed by a heating body on one side and a pressure pad at ordinary temperature without heating function on the other side, heat flow is one side flow passing through bonding faces in proportion to the temperature difference between the surface temperature of the heating body and the pressure pad at ordinary temperature. In an equilibrium state, it is equilibrated around <NUM>/<NUM> of the difference of the surface temperature between the heating side and the pressure receiving side. However, when heating time is lengthened, the surface temperature of the pressure pad is gradually elevated by the heat flow passed through the bonding faces. About <NUM>/<NUM> of the temperature elevation directly concerns the variation of bonding face temperature which gradually rises with heating time, and inhibits appropriate bonding face temperature control. Impulse sealing system belongs to one side heating.

Namely, the present invention provides a method of heat-sealing and a heat-sealing apparatus as defined in the appended claims.

In the heat bonding (heat seal) in situ, transient heating in a high speed region is utilized for the purpose of ensuring productivity. Since instrumentation and control techniques capable of managing the parameter of heating temperature directly have not been completed in the high speed region, management of heating operation relying on time control is not appropriate. The invention capable of controlling the heating temperature directly in the high speed variation region has solved the conventional problems, and has improved the reliability and quality of heat seal techniques, and further, has ensured to achieve ultimate problem of sealing and easy opening.

Film and sheet, which are heat seal materials, are enough to have a heat-sealable layer, and may be formed of single layer or plural layers. The material of the heat-sealable layer may be any material capable of heat-sealing, and in general, it is polyethylene, polypropylene, ethylene copolymers or the like. In addition, not crystallized polyethylene terephthalate and the like are also usable. The thickness of the heat-sealable layer is usually about <NUM> - <NUM>, typically about <NUM> - <NUM>.

The film or sheet composed of plural layers is constructed by laminating two types or more materials in order to improve printability, resistance to breakage, or gas barrier ability, to adjust rigidity of bags, to prevent adhesion of the material in softened state to the heating plate, or the like, and at least, an adhesive layer (sealant) which is the heat-sealable layer, is allocated to one of the surface layers. The material of the surface layer which becomes the outside layer of the bag, is selected from the materials wherein plasticization does not occur in the temperature range where the heating of the adhesive layer is applied.

The thickness of the film or sheet composed of plural layers is usually about <NUM> - <NUM>, typically about <NUM> - <NUM>.

As representative heat seal systems, there are heating jaw system where heating bodies are used, and impulse sealing system where a heating element using as the heating body is pressed and electricity is charged to heating, and the present invention can be applied to both systems.

The heat sealing apparatus of the heating jaw system is fundamentally composed of a pair of heating bodies, their actuating mechanism, and heating mechanism. The heating bodies are fundamentally the same as those of a conventional heat seal apparatus, and the couple of the heating bodies are constructed and arranged so that the heating surfaces are located in parallel, and therefore, upon heat-sealing, pressing is carried out with uniform pressure in the whole area. The heating surface is usually in plane. At least, the width of one heating surface is made only to heat the heat seal portion to be formed on the heat seal material. The other heating surface may be identical, or may be broader than that to be functioned as a pedestal. The material to be used is having a high heat conductivity, such as copper, aluminum, brass or stainless steel.

The working mechanism, that nips or releases the heat seal material by the heating bodies, may be the same as a conventional heat seal apparatus, and the working may be conducted by moving only one heating body or by moving both.

The heating mechanism to heat the heating bodies may also be the same as a conventional heat seal apparatus, and commonly, electricity is used.

A schematic construction (sectional view) of a heat sealing apparatus of heating jaw system to which the invention is applied, is shown in <FIG>. It is constructed by a pair of heating bodies (heating bar) each of which includes a heater <NUM>. Each heating body <NUM>-<NUM>, <NUM>-<NUM> is equipped with a temperature sensor <NUM> which is connected to a temperature controller <NUM>, and temperature is controlled individually. An automatic pressing apparatus <NUM> is attached to at least one of the heating bodies <NUM>, and it acts batchwise motion synchronized with the motion of the body of packaging machine. An air cylinder is used as the automatic pressing apparatus <NUM>, and moves the heating body <NUM>-<NUM>. The work <NUM> is put in and taken out synchronized with the motion of the jaw. Heretofore, the heating body is provided with a Teflon (registered trademark)-impregnated glass wool woven fabric on the surface as a cover, as a measure against burning. To replace it, thin flat Teflon sheet or flat nylon sheet where heat flow is even, is applied as the cover material <NUM>.

A heating pipe <NUM> is embedded between the heater <NUM> and the surface so that heat generation temperature of the surface of heating body becomes even.

Temperature sensors <NUM>-<NUM>, <NUM>-<NUM> are built-in each heating bodies <NUM>-<NUM>,<NUM>-<NUM>, and further, a heating body surface temperature sensor <NUM> and an interface temperature sensor <NUM> attached to the outer face of the cover material <NUM>-<NUM> are provided.

The interface temperature sensor <NUM> is newly introduced by the invention, and only the top portion of the sensor is put on the interface through a minute hole bored into the cover material. The size of the aperture of the hole is to expose the top portion of the sensor to the heat seal material, and usually, is about <NUM> to <NUM>. As a result, only a minute trace of about <NUM> is formed on the heat sealing face.

A mounted state of the sensor is illustrated in <FIG>. Since the heating body <NUM> is made of metal, an insulation film is laid on the heating body <NUM> in order to protect the lead wire of the sensor electrically. The applied insulation film is a polyimide film ("Kapton", du Pont) <NUM>-<NUM> thick.

Alternatively, the interface temperature sensor <NUM> is mounted on the surface of the cover material <NUM> by a stretched very thin mounting film <NUM>, as shown in <FIG> and <FIG>. So that the influence of the mounting film on the heat flow in the cover material can be neglected, the thickness of the mounting film is very thin, such as <NUM> to <NUM>, and preferably one fifth of the cover material or thinner than that. The applied mounting film is also the polyimide film ("Kapton", du Pont) <NUM>-<NUM> thick, and fixed by immobilizing the end of the film using a heat-resistant adhesive tape.

The former is excellent in detectability, but not easy to mount the sensor. Although the latter is slightly inferior in detectability, it is superior in the easy mounting.

The signal of the interface temperature sensor <NUM> is sent to an interface temperature controller <NUM>, and thereby, the automatic pressing apparatus <NUM> is controlled.

As the welding face temperature response of heating jaw system, there are three types, i.e. converging equilibrium temperature (Tc), <NUM> % arrival point (Tb) and high speed rising region (Ta) of transient response, as shown in <FIG>. Among the definitions of three types, at present, the type where temperature value can be dealt directly, is only the equilibrium temperature. Actual heating method to arrive at <NUM> % equilibrium temperature is time control where temperature variation is ≒ <NUM> / <NUM>, and although it is approximate, practical accuracy (<NUM>- <NUM>) can be ensured.

However, today, in order to ensure production per unit time, the high speed rising region where heating time is shorter than the <NUM> % arrival time by one-several-th, is commonly used. Temperature rising characteristics in this region is about <NUM> / s, ≒ <NUM> / <NUM>. In the present time control, the difference from set value in control greatly exceeds the guarantee region of heat bonding properties, and causes defects to have to make too much of agglomeration bonding.

For the utilization of high speed rising region, it is necessary to set a high temperature heating at a temperature <NUM>-<NUM> times higher than the heating temperature of <NUM> % response. (see <FIG>).

Since the temperature of the heating body is set in a temperature zone much higher than the melting point of packaging material, while stopping for a short time, such as <NUM> seconds, the material stayed in the apparatus is melted to adhere to the heating body, etc. to contaminate the apparatus.

In the heating jaw system, as shown in <FIG>, a short heating time (Ta) heating method is usually employed in order to raise production speed, where set temperature of heating bodies is raised to render starting up fast. However, in this process, heating relys on time control, because the temperature variation in transient stage cannot measured directly.

It is desired to develop a control method (simulation) where actual heating temperature is employed as an indication, instead of the time control. The present invention makes possible to solve this problem.

Summary of the development of the invention into the heating jaw system is explained by referring to <FIG>. The surface of heating bodies <NUM>-<NUM>, <NUM>-<NUM> is covered by a cover material <NUM>-<NUM>, <NUM>-<NUM>. A minute interface temperature sensor <NUM> is attached continuously to the surface of either cover material. A welding face temperature sensor <NUM> is provided only at a time of inspecting the response in a laboratory test.

In the invention, welding face temperature response is simulated by noticing that the surface temperature (interface temperature) of the cover material <NUM>-<NUM>, <NUM>-<NUM> (e.g. <NUM> Teflon smooth sheet) of heating bodies descends by the heat flow toward the work. An example of the measurement is shown in <FIG>.

In the measurement, a Teflon smooth sheet or nylon smooth sheet <NUM> - <NUM> in thickness was selected as the cover material <NUM>, and the response of the surface temperature <NUM> of heating body, the contact interface between the cover material and the work <NUM>, and further, the welding face (bonding face) of the work were examined. The graph (a) in <FIG> shows a response of the contact interface temperature sensor <NUM> between the cover material <NUM> and the work <NUM>. The graph (b) shows a response of the welding face temperature sensor <NUM>.

In the measurement of this example, the spaces for measuring the welding face and interface temperature are tens µm. Moreover, a high instrumentation performance capable of measuring <NUM> % response with a resolution ability of <NUM> or less is required. In the measurement, a temperature recording device with a resolution ability of <NUM> was used where a K thermocouple of <NUM> diameter was applied.

Welding face temperature response by surface temperature monitor of cover material since the surface of the cover material before working was exposed to room temperature to radiate heat, the surface temperature of the cover material is indicated a lower value than the surface temperature of heating body. (about <NUM> when controlled at <NUM>) (see <FIG>).

When a work at ordinary temperature comes into contact with the surface of cover material A <NUM>-<NUM> by pressing, the interface temperature sensor <NUM> detects a sharp descending. Then, the interface temperature rises to be asymptotic to the surface temperature of heating body. (see <FIG> graph (a)).

The welding face temperature of the work begins to rise simultaneously, and rises to be asymptotic to the surface temperature of heating body. When the difference between the response of welding face temperature and interface temperature arrives within <NUM>, direct control of welding face (bonding face) temperature becomes possible by employing the interface temperature value as the indication. In this example, an appropriate region is from the vicinity of <NUM>. Since CUT; <NUM> % in this example is in the vicinity of <NUM>, a greater shortening of time can be made than a conventional CUT; <NUM> %, and the effectiveness of the invention can be understood. Detailed explanation is made in a working example (<FIG>).

Although welding face (bonding face) temperature cannot be detected directly in the manufacturing process, the graph (a) in <FIG> can be continuously observed by attaching a minute sensor to the interface. The graphs (a) and (b) occur by the same heat flow phenomenon. Accordingly, by the observation of graph (a), welding face temperature response can be grasped directly. The measuring techniques is the basis of the invention.

The characteristics of heat transfer phenomenon in heat bonding are analyzed by replacing the phenomenon with an electric circuit. The response of the heat flow phenomenon in <FIG> is transferred to an electric circuit, and shown in <FIG>.

In a released condition prior to pressing, provided that heat radiation resistance into atmosphere is denoted R2, and heat transfer resistance of cover material <NUM>-<NUM> is denoted R1, the surface temperature of the cover material <NUM>-<NUM> is expressed as Tf • R2 / (R1 + R2), and therefore, it is lower than the surface temperature of heating body.

When the heating body <NUM> acts jaw motion (switching SW in <FIG>) to conduct press bonding, the heat flow from the heating bodies <NUM>-<NUM>, <NUM>-<NUM> is charged into the heat capacity C3 of welding face through the heat transfer resistance R1 of cover material <NUM>, contact resistance R3 and heat resistance r1 of work <NUM>, welding face temperature is generated by almost primary sending response. In the jaw system, similar heating is also made from the other side, and welding face is asymptotic to the surface temperature of the heating body which is a heat source to equilibrate with Tm.

In the case of heating where the set temperature of the heating body <NUM>-<NUM> is different from the heating body <NUM>-<NUM> (so-called one side heating), one side is at T3 which is room temperature, etc. In this case, heat flow responds to (Tf-T3) and becomes one way from the heating body <NUM>-<NUM> to the heating body <NUM>-<NUM>. Therefore, provided that the surface temperature of heating body <NUM>-<NUM> is not changed by the heat flow, the welding face temperature response is expressed as <MAT>.

The response of interface temperature <NUM> indicates a transient response between thermal resistance R1+R3+r1 and mainly heat capacity C3. As can be seen from an analogous electric circuit, welding face temperature constitutes a part of interface temperature response, and correlated.

Accordingly, it was found that welding face temperature response can be simulated by monitoring the surface temperature response of cover material which can be measured continuously.

The thermal resistance R1 of cover material participates directly the detection of heat flow. When the value increases great, temperature descending becomes sharp. Therefore, the detection sensitivity is high. However, when the thermal resistance is great, the temperature of heat source is raised by the suppression of heat flow, and therefore, undesirable. It is selected so that R1 / (R1 + R3 + rl) is made a rate of <NUM>/<NUM>- <NUM>/<NUM>.

In <FIG>, it is shown a procedure to control welding face temperature in the vicinity of <NUM> of heating time to <NUM>, as an example. From the model data, in the case that the interface temperature of cover material is <NUM> , the welding face temperature becomes <NUM>. Heating operation using temperature as an indication can be conducted by that when the interface temperature detects the set value of T< <NUM> which is obtained by subtracting the delay of the work of heating jaw, pressing is released by the operation of automatic pressing apparatus actuated by the output of the interface temperature controller <NUM>.

Since the model data varies by the change of work, laboratory data for each work are stocked, and referred to them.

In the selection of the heating time around <NUM> or more, it can be seen that since the interface temperature almost agrees with the welding face temperature response, the automatic pressing.

apparatus <NUM> can be operated by the detected temperature signal without referring to the model data.

The selection of the control time zone can be adjusted by the change of the set temperature (T1, T2) of the heating bodies <NUM>-<NUM>, <NUM>-<NUM>.

Most of conventional intermittent motion type packaging machines are driven by one power source, and driving mechanism of the heating jaw is constructed by cam / link. Therefore, in order to control pressing motion by the detection of interface temperature of the invention, it is necessary to provide individual operation units.

Means of adapting the invention to intermittent motion Thereupon, it was devised an application method of the invention to the interval of the intermittent motion.

The periodic speed of the intermittent motion is frequently set by the production schedule on each occasion.

Equivalent effects to the release operation of pressing operation can be gained by adjusting heating body surface temperature so as to arrive at the set temperature at the finish point of the intermittent motion.

The device is characterized by that almost <NUM> % of intermittent motion intervals can conform automatically to heating operation, and unnecessary heating rendered to a high temperature can be prevented. The construction of the method is shown in <FIG>.

As shown in <FIG>, in the packaging machine in situ, it is rare to operate pressing operation independently, and the pressing motion is restricted by the heating time determined by cam /<NUM> ink mechanism to be met the intermittent motion of the machine. High temperature setting more than necessary heating body temperature can be avoided by meeting control temperature with <NUM> % arrival time of intermittent motion.

For example, position signals of <NUM>, <NUM>, <NUM> % in intermittent motion are received from a rotary encoder managing the intermittent motion, an AND logic of interface temperature and set point detecting signal was made.

The AND logic of three signals of the rotary encoder and output of interface temperature device is expressed as a matrix shown in <FIG>.

In the experiment of this example, when <NUM> -<NUM> % and a state of turning the logic of the output of desired control temperature ON were observed, the set values of control temperature of two heating bodies were adjusted so that logic outputs of <NUM> and <NUM> % became a state of ON by repeating increase or decrease several times manually at unit of <NUM>. In a practical production work in situ, an indicator of logic output is attached to the control system, setting is changed manually referring to this, or automatically.

The present invention can be applied to impulse sealing system.

A construction of a conventional impulse sealer is illustrated in <FIG>.

A heating element <NUM> is fixed to a cooling heat radiation material <NUM> through a thermal insulating material <NUM> made of Teflon (registered trademark). The other face of the heating element <NUM> is covered with Teflon material (Teflon impregnated glass wool woven fabric) <NUM>-<NUM> to reduce burning of melted piece of work <NUM>. An anvil <NUM> made of rubber on the other side is also covered with Teflon material (Teflon impregnated glass wool woven fabric) <NUM>-<NUM> to prevent burning of melted piece of work <NUM>.

To the heating element <NUM> of an impulse sealer on the market, a nichrome wire is applied as heating resistor, and heat generation and heating is carried out by applying electricity step wise. Because the heating resistor is a thin plate (about <NUM>), it is characterized by small heat capacity and high speed heating of <NUM> / <NUM>-<NUM>.

Impulse sealing is different from the jaw system where already heated heating bodies are pressed, and heating and pressing are conducted simultaneously by applying impulse-shaped electric voltage. Although the temperature rise of heating element is almost primary delayed response against applied electricity, lamp-shaped input is carried out against work where linear heating is conducted. The time limit system similar to the aforementioned Ta is applied to desired heating temperature control.

In the impulse sealing system, the supply time of electricity is controlled by time limit system using a timer, and the operator controls limiting time by judging the suitability of the bonding state of finished specimens based on tensile test or visual observation at each operation. To ensure quantification is a solving problem. The impulse sealing has a character that since heat capacity of heating element is small, heating properties (speed) varies by the influence of heat load capacity mainly based on the thickness of work.

<FIG> indicates an example of welding face temperature response of an impulse sealer measure by using a "MTMS" kit. As the measuring points, a temperature sensor was attached to each the surface of heating element <NUM>, the space between two sheets of work <NUM> and cover material <NUM>-<NUM> of anvil <NUM> in the impulse sealer of <FIG>, and surface temperature of heating element <NUM>, welding face (bonding face) temperature and the surface temperature of anvil <NUM> (elastic body) were measured respectively.

In the example of measurement, <NUM> V transformed from alternating current <NUM> V power source was applied to the hating element <NUM>. Supplied electric current was <NUM> A, and heat release value was ≒ <NUM> W. Since the temperature in equilibrium state of this apparatus became <NUM> or more, the temperature zone to be applied to heat bonding corresponds to the high speed rising Ta illustrated in <FIG>.

As to the work, the temperature varies as graph (A) in <FIG> which is lamp-shaped heating where temperature rises in straight. Since applied electricity is released at the set time arrived, residual heat in heating element radiates through cooling heat radiation material <NUM> and temperature descends as graph (B). Welding face temperature response becomes the response to linear lamp-shaped input as graph (C).

In this one side heating, (heating temperature - room temperature) / <NUM> + room temperature is the model welding face temperature. In the response zone around <NUM>, the welding face temperature is in the state of one side heating formula (<NUM>). In the one side heating, heat flow is in one-way from heating element <NUM> to anvil <NUM>, and the surface temperature of anvil <NUM> rises as graph (D).

An inflection point (melting point) caused by melting can be seen around <NUM> / <NUM> in the measured data, and heated face is in paste-shaped after <NUM>. The neighborhood of <NUM> is upper limit temperature of heating. Namely, since around <NUM> is the melting point of sealant which is liquefied, the specimen material is expected to be heated to <NUM> - <NUM>. When temperature exceeds the melting point, heat conduction varies to accelerate temperature rising. The utilization of this temperature region causes production of polymer beads, pinholes and edge tear.

The surface temperature of the anvil rises together with start of heating. After heating stops, it continues to rise by the heat inertia, and then, turns to descend by natural cooling.

In the impulse sealing with time limit heating by supplying electricity, temperature at the next start varies upon starting by the heat storage in heating element <NUM> and in anvil <NUM> during repeated operations. By the influence of this, when the same heating time (time of supplying electricity) is controlled exactly, controlled temperature varies within <NUM>. Accordingly, there is a fault in principle in repeating continuous use at an interval of a short tune when cooling has not been completed, that even through exact time limit control is conducted, heating body temperature is not identical. It was found that the time limit control is disqualified.

<FIG> shows an example of temperature drifting induced in repeat operation of a commercial machine by time limit control. From the measured results, <NUM> / <NUM>, <NUM> / <NUM>, <NUM> / <NUM>, <NUM> / <NUM> were obtained. Although the variation of time limit performance within the degree of <NUM>, temperature values were dispersed in a range of <NUM>. The fault of the present state could be grasped clearly.

The response example of <FIG> is in the case that starting temperature of heating element in a commercial machine is room temperature. The response of heating element <NUM> after applied electricity is released, is observed, a time is taken for cooling until room temperature, and drifting occurs. The property is a barrier to repeat operation at a short time interval in the time limit system.

In the invention, in the apparatus of <FIG>, a cover material <NUM> is disposed on heating element <NUM> in the impulse sealer instead of the cover material <NUM>. Actually, a smooth Teflon sheet or smooth nylon sheet <NUM> -<NUM> in thickness is used as the cover material <NUM> instead of a conventional Teflon impregnated glass wool woven fabric. An interface temperature sensor (thermocouple) <NUM> of about <NUM> diameter for the detection of interface temperature is continuously placed on the surface of cover material <NUM> on the side of contact face. A temperature sensor <NUM> of anvil is also continuously put. The welding face temperature detection sensor <NUM> is for the measurement of properties of welding face temperature response, and it is not set in a working machine. A schematic construction to which the invention is applied is shown in <FIG>.

A cascade temperature controller <NUM> is provided which receives the output signals of interface temperature sensor <NUM> and temperature sensor <NUM> of anvil <NUM>, and thereby, the switch of transformer <NUM> sending electricity to heating element <NUM> can be controlled. The structure is shown in <FIG>.

In the system of the invention, when reaching a desired temperature, electric source for heating is released (irrespective of time) to stop heating, and the system is a control method not affected by the initial temperature at starting of heating element <NUM>. The auxiliary operation to change heating time is needless, and the assistance of frequent inspections for bonding state is made minimum.

When the type of product is converted to change the thickness and material of work, temperature rise characteristic varies according to the difference of heat capacity. This directly affects to induce discrepancy in the time limit system.

Heretofore, the suitability of pressing time was judged by the bonding state of finished specimens based on tensile test or visual observation, and the pressing time was controlled relying on a rule of thumb. Temperature was set high so that bonding strength becomes high (melting state), because of being afraid insufficient heating.

A measurement example using the apparatus shown in <FIG> is shown in <FIG>. The result of controlling interface temperature and response value of welding face temperature are enumerated in the graph. By detecting the temperature response of cover material <NUM> and contact face of work <NUM> directly, temperature detection point approaches welding face temperature point to remove the cause of variation. As a result of control, variation of interface temperature becomes <NUM> - <NUM> (<NUM>) and variation of welding face temperature becomes <NUM>-<NUM> (<NUM>).

Because impulse sealing is conducted by one way heating, desired value cannot be controlled directly. Like the example shown in <FIG>, it is important that the results of control are almost the same in every time.

According to the repeat operation of the method of the invention, overheating could be avoided, because the heating of heating element <NUM> was maintained in a proper heating range. Therefore, heat storage in the anvil portion could be minimized.

The temperature variation of anvil is about <NUM> through the repeat of the operation each for about <NUM>.

The welding face temperature of work is determined by the temperature difference between heating element temperature T2 and anvil temperature T1 (see formula (<NUM>)). If anvil temperature T1 varies, welding face temperature is not constant, even controlling heating portion temperature T2 precisely. Practically, the set value of temperature controller <NUM> is corrected with cascade control by the output signal of anvil temperature sensor <NUM> by increasing or decreasing about <NUM>/<NUM> of variation portion of T1 (see <FIG>).

By the invention, welding face temperature can be controlled / managed within <NUM> also in the method of impulse sealing.

The heating time zone which is the subject of the invention is [<NUM>] approximately <NUM> or more.

In order to detect high speed variation in a short time, an instrument capable of dealing with the variation is needed.

For example, the temperature rising speed of the heating element of an impulse sealer was <NUM> - <NUM> / <NUM>. The temperature rising property is <NUM> / s. Namely, the temperature rising variation is <NUM> / <NUM>, <NUM> / <NUM>. Generally, temperature controllers used are of digital type, variation of detecting temperature occurs by the sampling period. By varying the sampling period <NUM>, <NUM>, <NUM>, trial calculation of detecting temperature variation was conducted.

The results of operation are indicated in Table <NUM>. In order to raise accuracy of temperature control, it is necessary to choose a controller having a sampling period of <NUM>-<NUM>. It was found that sampling period of <NUM> is preferred.

In an experiment of practical control system, there is an overrunning of welding face temperature of <NUM> after heating stopped, and it was found that temperature deviation was about <NUM>. This value was the delay of control system, such as switch motion. The deviation is always constant, and can be treated by adding constant set value correction.

Simultaneous achievement of sealing and easy opening was an ultimate solving problem in the heat sealing technique for a long time (presented in the establishment of ASTM F88 in <NUM>).

In the conventional impulse sealing, it was difficult to control welding face temperature response within <NUM>, and selection of agglomerate bonding was the best to be conducted.

By applying the invention, more appropriate temperature control can be carried out, the single linear sealing can be made even by impulse sealing.

By adding a single linear rib to around the center of heating element, a single linear seal (Filigree Seal (<CIT>) capable of both sealing and easy opening simultaneously can be provided.

The single linear seal was developed by the inventor previously, and it has a composite heat seal structure wherein a linear seal is added to a band-shaped seal in the longitudinal direction, and by the linear seal, a step portion formed by folding, such as in a gusset bag, can be ensured sealing.

A construction of a single linear seal unit <NUM> wherein a single linear rib was added to heating element <NUM>, is shown in <FIG>.

In the single linear seal unit <NUM>, a single linear rib (height: <NUM>-<NUM>) to heating element <NUM> is added by the following method.

The performance was examined by using the construction shown in <FIG> and setting practical conditions.

By referring to <FIG> which indicates an example, the following characteristics of the invention were found.

In the impulse sealing, electric voltage in step-shaped is applied to the heating element at each operation, and temperature elevation of the heating element is utilized. Therefore, heating is not step-shaped but lamp-shaped.

Impulse sealing is carried out by one-way heating where one side is heated.

Upon applying the invention to impulse sealing, a method of simulating temperature response of bonding face of work was devised by disposing a cover material <NUM> on the surface of heating element, setting a minute sensor on the surface of cover material <NUM>, and detecting heating flow supplied to work.

Tests were carried out by applying the following conditions to the construction illustrated in <FIG>.

Measured results including inspections of welding face [<NUM>] temperature response, interface temperature and surface temperature of heating element are shown in <FIG>.

When repeat production operation was carried out with cascade control in a short time which corrects variation of anvil temperature, heat flow arrives at anvil to store heat, and temperature of anvil rises. Since the influence of anvil on one-way heating can be defined by the aforementioned formula (<NUM>), variation of anvil temperature can be corrected by continuous watching of anvil temperature.

Claim 1:
A method of heat-sealing using a heat-sealing apparatus which heat-seals a heat seal material (<NUM>) by nipping it between a pair of heating bodies (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>), which comprises mounting a cover material (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) on the surface of at least one of the heating bodies (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) to be in contact with the heat seal material (<NUM>),
characterized in that the method further comprises attaching a minute temperature sensor (<NUM>) to the surface of the cover material (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) on the side to be in contact with the heat seal material, and controlling the temperature of the bonding face of the heat seal material (<NUM>) by the temperature detected by the minute temperature sensor (<NUM>).