JPH0363487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heating a thermoplastic resin sheet. More specifically, when a sheet such as a uniaxially stretched or biaxially stretched thermoplastic resin sheet is used as a material, it is heated by an indirect heating method, and a molded product is manufactured by a vacuum forming method and/or a pressure forming method. This invention relates to an improvement in the method of heating a material sheet.

A method of manufacturing a molded article by a vacuum forming method and/or a pressure forming method by intermittently feeding a thermoplastic resin sheet to a molding machine in which a heating section, a molding section, and a molded product punching section are sequentially arranged, includes: It has been known for a long time. Such indirect heating method (synonymous with radiant heating method) adopted in conventional technology
Examples include those described in Japanese Patent Publication No. 41-16394. According to this method, the heating section is divided into three compartments, and the resin sheet to be molded is preheated in three stages. However, when heating a resin sheet to be molded using this method, the thickness of the resin sheet to be molded must be substantially uniform, and there are restrictions on the molding materials that can be used. That is, if the thickness is uneven, the thick part will take longer to heat up because the heat capacity of this part is larger than the thin part, and the thin part will be heated in a shorter time because the heat capacity of this part is smaller than the thick part. This is because the thin portions that are heated quickly are stretched by the heat shrinkage tension of the sheet and become thinner and thinner, and the thicker portions become thicker and thicker.

Furthermore, a heating method using a device described in Japanese Utility Model Publication No. 48-27250 has also been proposed. This method is
Molding methods that do not intermittently feed and mold the resin sheet to be molded have practical value, but when heating the resin sheet for 2 to 3 shots or more while intermittently transporting the resin sheet to be molded, it is difficult to maintain the temperature. There are disadvantages in that automatic adjustment is difficult and considerable skill is required for temperature adjustment.

In addition, Japanese Utility Model Publication No. 56-3126 proposes a heating method that eliminates the drawbacks of the above-mentioned heating methods, but it is still insufficient and has the disadvantage that temperature control still requires skill.

In view of this situation, the inventors of the present invention have conducted intensive studies to provide a method for heating thermoplastic resin sheets that can be easily heated even by inexperienced persons, and as a result, they have completed the present invention. .

The object of the present invention is to use a sheet such as a uniaxially stretched or biaxially stretched thermoplastic resin sheet as a material, heat it using an indirect heating method (radiation heating method), and then perform vacuum forming and/or pressure forming. An object of the present invention is to provide a method for heating a material sheet when manufacturing a molded article by a method.

However, the gist of the present invention is that in the heating section of a thermoplastic resin sheet molding machine in which a heating section, a molding section, and a molded product punching section are sequentially arranged, ) is heated by indirect heating method, only one of the upper side or the lower side, or both the upper side and the lower side of the forming sheet transferred in the heating section, is parallel to the direction of transfer of the sheet to be formed. One or more heaters are arranged to form multiple rows in the direction of and/or at right angles, and the next ()
Formula, namely Q=F(a,x,y)・σ・(THij+273.16) ⁴ …() [In formula (), Q is the amount of radiant heat at one point on the sheet to be formed (cal/sec/cm ² ) ;F(a, x,
y) means F(a, x, y) = F'(a, x, y)・ε...(), and in formula (), F'(a, x, y) is the distance between each heater and the molded object. It means the view factor determined by the relative positional relationship with the sheet, and ε means ε=ε ₁・ε ₂ ...(). In formula (), ε ₁ is the radiation capacity of the heater, and ε ₂ means the radiant heat absorption capacity of the sheet to be formed; σ means the Stefan-Boltzmann constant; THij is the heater (i, j is the It means the temperature (unit: °C) at the j-th position. ] A method for heating a thermoplastic resin sheet, characterized by setting a heater and adjusting the amount of radiant heat calculated by the following, to a desired value.

In the present invention, thermoplastic resin sheets include styrene resin sheets, vinyl chloride resin sheets,
Typical examples include olefin resin sheets, but other examples include polycarbonate sheets, polyamide sheets, and polyester sheets. These sheets may be stretched or unstretched sheets.

Hereinafter, the present invention will be explained in detail based on the drawings, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

FIG. 1 is a schematic side view showing an example of a state in which a sheet to be formed is heated and a molded product is manufactured by the method of the present invention, FIG. 2 is a perspective view showing an example of calculating a view factor, and FIG. FIG. 3 is a plan view showing an example of arrangement of heaters and an example of heater temperature, and FIG. 4 is a schematic diagram showing a temperature control mechanism of a molding machine suitable for industrial use.

In the figure, 1 is a roll of sheet 2 to be formed, 3
is a guide roll, 4 is an adjustment roll, 5 is a thickness gauge,
6 and 36 are upper heating furnace walls, 7 and 37 are upper heaters, 8 is a lower heating furnace wall, 9 is a lower heater, 10 is a mold, 11 is a mold frame, 1
2 is a face plate, 13 is a hot plate, 14 is a heater, and 15 is a molded product before punching. 21 is a heater, 2
2 is the central part of the heater surface, 23 is the sheet to be formed,
A is the point where the perpendicular line hanging down from the central part 22 of the heater surface of the heater 21 onto the sheet to be formed intersects with the sheet to be formed, and P is the direction x cm parallel to the conveyance direction of the sheet to be formed from point A, and the direction perpendicular to the direction of conveyance of the sheet to be formed. A is a point y cm away from point A, and a indicates the distance from the center 22 of the heater surface to point A. 41 is a start switch, 42 is a timer, 43 is a thickness gauge, 44 is a thickness distribution variation detector, 45 is a temperature distribution calculation device, 46 is a heater temperature adjustment device, and 47 is a heater. The arrows in FIGS. 1 to 3 indicate the direction of conveyance of the sheet to be formed.

The method of the present invention is utilized in a molding machine for molding a thermoplastic resin sheet in which a heating section, a molding section, and a molded product punching section are sequentially arranged. The thermoplastic resin sheet to be molded (sheet to be molded) is a long one, which is heated according to the method of the present invention, and then in the molding section, by a vacuum molding method, a pressure molding method, or a combination thereof. It is molded into the desired molded product. When using the method of the present invention, a molded product can be manufactured (molded) while heating the sheet to be molded using an indirect heating method and transporting the sheet intermittently and continuously. Intermittent and continuous means that a molded product is produced by repeatedly transporting a long sheet to be formed in a fixed length intermittently, and one molded product is produced for each molding shot. This does not mean a method of preparing a sheet material and manufacturing a molded product.

When using the method of the present invention, the sheet to be formed is heated in the heating section using an indirect heating method. The heating part is
The sheet to be formed is placed in a heating furnace, heated for one forming shot or several formed shots, and then transferred. In order to do this, a heater may be installed in the heating section.

The heater may be installed either above or below the sheet to be formed, or both above and below the sheet to be formed. FIG. 1 shows an example in which the rollers are installed both above and below the sheet to be formed 2 being transferred.

Examples of the heater include rectangular or rectangular magnetic heaters, aluminum cast heaters of similar shapes, quartz tube heaters, etc. Among them, rectangular heaters are preferred. It is preferable to arrange a plurality of these in the heating furnace. When arranging heaters, it is preferable to combine a plurality of heaters of the same type, but it is also possible to combine a plurality of heaters of different types. When the heaters are arranged on both the upper side and the lower side of the sheet to be formed, the heaters arranged on the upper side and the heaters arranged on the lower side may be of different types. FIG. 1 shows an example in which the upper heater 7 is a rectangular magnetic heater and the lower heater 9 is a cast aluminum heater, and a plurality of these are combined.

It is preferable to arrange the heaters so that one or more heaters form multiple rows in parallel or perpendicular to the direction of conveyance of the sheet to be formed. . When the length of the heater is long, one heater forms one row, and when the length of the heater is small, a plurality of heaters form one row.

When installing heaters on both the upper and lower sides of the sheet to be formed, the direction of the rows of heaters should be
The upper and lower sides may be installed in the same direction, or they may be installed so as to cross each other.

When heating the sheet to be formed in the heating section, if heaters are placed both above and below the sheet to be formed, and the temperature is controlled by these heaters, the central part of the sheet to be formed in the heating furnace is receives radiant heat from more heaters than the surrounding area. Therefore, the temperature of the central portion of the sheet to be heated after heating for a certain period of time is higher than that of the peripheral portion. If a sheet to be formed having such an uneven temperature distribution is sent to the next forming section and formed there into a desired molded article, the resulting molded article will have an uneven thickness, which is not preferable.

According to experiments conducted by the present inventors, it has been found that the above drawbacks can be eliminated when heating is performed under conditions in which the amount of heat (Q) radiated to each point on the surface of the sheet to be formed is maintained at a substantially constant value.

In other words, the following equation () for each point on the surface of the sheet to be formed, Q=F(a,x,y)・σ・(THij+273.16) ⁴ ...() Radiant heat amount (cal/sec/cm ² ) at one point (p) above; F(a,
x, y) means F(a, x, y)=F'(a, x, y)・ε...(), and in formula (), F'(a, x, y) is the relationship between each heater and A view factor determined by the relative positional relationship a, x, y with the sheet to be formed and the geometrical shapes of the sheet to be formed and the heater, where a is the vertical direction from the heater onto the sheet to be formed. The distance (cm) to the point (A) where the perpendicular line intersects with the sheet to be formed, x is the distance (cm) in the direction parallel to the direction of conveyance of the sheet to be formed from point A to p on the sheet to be formed,
Similarly, y is the distance (cm) in the direction perpendicular to the conveying direction of the sheet to be formed, and ε is ε=ε ₁・ε ₂ ...() In the formula (), ε ₁ is the radiation power of the heater, and ε ₂
is the radiant heat absorption capacity of the sheet to be formed; σ is the Stefan-Boltzmann constant; THij is the heater (i, j is the j-th heater in the direction parallel to the direction of conveyance of the sheet to be formed, and the i-th heater in the perpendicular direction temperature (unit: °C). ] The temperature may be adjusted while setting the heater so that the amount of radiant heat calculated by is a desired value.

The radiation efficiency ε ₁ of the heater is determined by the material and temperature of the surface of the heater, and can be determined by actual measurement. The radiant heat absorption capacity ε ₂ of the sheet is determined by the type of resin, thickness, etc. of the sheet to be molded, and can be determined by actual measurement. Once ε ₁ and ε ₂ are determined, ε in the above equation () is determined.

The view factor (also called the shape angle factor or angular relationship) F' (a, x, y) in equation () above is determined by the type of heater, the shape of the heater, the arrangement of the heater, the heater and the sheet to be formed. It is a coefficient determined by the distance from

Now, rectangular magnetic heaters are arranged in the heating furnace in 13 rows only above the sheet to be formed, in a direction perpendicular to the direction of conveyance of the sheet to be formed (referred to as the i direction), as shown in the plan view in Figure 3. However, a case will be explained in which they are arranged in seven rows in a direction parallel to the sheet transport direction (referred to as the j direction).

Sk,l (k=1
~13,l=1~7), and the total amount of heat radiated from each heater to this virtual point is Qk,l(k
= 1 to 13, l = 1 to 7), the total amount of radiant heat
Qk, l is Qk, l=σ・{ ₁₃ 〓 ⁱ⁼¹ ₇ 〓 〓 ^j=1 F(i, j, k, l)・(THij+273.16) ⁴ }…(
) (k=1 to 13, l=1 to 7). In order to uniformly heat the sheet to be heated, set Qk,l=(k=1~13,l=1~7)=const() in equation (), and set THij(i=1 ~13,j=
By solving the simultaneous equations for 1 to 7), the temperature of each heater can be determined.

ε ₁ , ε ₂ , F' (a, x, y), etc. are determined by actual measurement or calculation, and the amount of radiant heat added to each point on the surface of the sheet to be formed is a predetermined value based on formula (). An example of determining the temperature conditions for each heater to achieve the following is shown in FIG. In FIG. 3, the units of numerical values are degrees Celsius.

By setting this temperature condition in the upper heater of the heating furnace, it is possible to very easily determine the appropriate conditions for heating the sheet to be formed when using the same device.

If the thickness of the sheet to be formed is uneven,
It is preferable to control the temperature by a temperature control mechanism shown schematically in FIG.

That is, as shown in figure 5 in Fig. 1, a thickness gauge for measuring the thickness of the sheet to be formed is installed before the sheet to be formed enters the heating section, and the thickness of the sheet to be formed is thereby measured. . Although the thickness of the sheet to be formed may be measured at all times, it is preferable to measure it at regular intervals, and a timer 42 is used for this purpose.
is preferably connected to the thickness gauge 43. The thickness of the sheet to be formed is measured by the thickness gauge 43 at multiple points at certain positions in the direction perpendicular to the direction in which the sheet to be formed is transported, with a constant interval. The measured value is sent to the thickness distribution variation detection device 44, and if the thickness distribution variation tolerance range input in advance is exceeded, a signal is sent to the heater temperature adjustment device 46 via the temperature distribution calculation device 45. , by turning on and off the heater 47, adjusting the voltage applied to the heater, etc., it is possible to correct non-uniform heating caused by non-uniform thickness.

In this case, the virtual point Sk on the surface of the sheet to be formed,
Total radiant heat amount Q′k,l after correction based on thickness distribution in l (k=1 to 13, l=1 to 7)
From the above (), Q'k,l=Qk,l×DSk,l/DS...() (k=1~13,l=1~7) [In formula (), DSk,l is the The thickness of the sheet to be formed at each point at the position where the thickness is measured using the sheet thickness gauge is DSk,l (k=1~
13, means the average thickness of the sheet to be formed at the positions of l=1 to 7). ].

Solving the equation in this equation (), we get Q′k,l
The temperature of each heater can be determined by substituting this value into Qk,l in the above equation ().

The present invention has the following special and remarkable effects, and its industrial utility value is extremely large.

(1) When using the method of the present invention, when manufacturing a molding machine, the type, size, shape, location, arrangement method, etc. of the heater to be installed in the heating furnace of the heating section, and the radiation efficiency of such heaters, etc. Since it is known in advance, the view factor can be calculated. Further, the radiant heat absorption ability of the sheet to be formed is also determined in advance depending on the type, thickness, etc. of the sheet to be formed mainly by the molding machine. Based on these calculated values and measured values, the heater temperature is
THij can be calculated. Based on this calculated value, the heater capacity can be appropriately set. In this way, when using a molding machine in which appropriate heaters are set and arranged in advance, it is extremely easy to properly heat the sheet to be formed.

(2) The method of the present invention can be extremely easily applied to the heating method using the heating section of an existing molding machine. In other words, confirm the type, size, shape, arrangement position, arrangement method, radiation efficiency, etc. of the heater in the heating section of the existing molding machine, calculate the view factor,
The type, thickness, radiation absorption capacity, etc. of the sheet to be formed are also confirmed, and based on these, the heater temperature THij for keeping Q in the above equation () constant can be calculated. By appropriately setting the heating conditions based on this calculated value, the heating temperature can be adjusted to an appropriate heating temperature very easily.

(3) Even if the thickness of the sheet to be formed is uneven, the method of the present invention makes it easy to modify the heating method according to the thickness, and it is extremely easy to produce molded products with less uneven thickness and high commercial value. can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a schematic side view showing an example of a state in which a sheet to be formed is heated and a molded product is manufactured by the method of the present invention; FIG. 2 is a perspective view showing an example of calculating a view factor; FIG. 3 is a plan view showing an example of arrangement of heaters and an example of heater temperature, and FIG. 4 is a schematic diagram showing a temperature control mechanism of a molding machine suitable for industrial use. In the figure, 1 is a sheet to be formed, 2 is a roll,
3 is a guide roll, 4 is an adjustment roll, 5 is a thickness gauge, 6 and 36 are upper heating furnace walls, 7 and 37
are the upper heater, 8 is the lower furnace wall, and 9 is the upper heater, respectively.
is a lower heater, 10 is a mold, 11 is a mold frame, 12 is a face plate, 13 is a hot plate, 14 is a heater,
15 shows a molded product before punching. 21 is a heater, 22 is a central part of the heater surface, 23 is a sheet to be formed, 41 is a starting switch, 42 is a timer, 4
3 is a thickness gauge, 44 is a thickness distribution variation detector, 45 is a temperature distribution/arithmetic device, 46 is a heater temperature adjustment device, and 47 is a heater. The arrows in FIGS. 1 to 3 indicate the direction of conveyance of the sheet to be formed.

Claims (1)

[Claims] 1. A thermoplastic resin sheet to be molded (sheet to be molded) is indirectly heated in a heating part of a molding machine for molding a thermoplastic resin sheet in which a heating part, a molding part, and a molded product punching part are sequentially arranged. When heating using this method,
On only one of the upper side or the lower side, or on both the upper side and the lower side, of the forming sheet being transported through the heating section, in a direction parallel to and/or perpendicular to the direction of transport of the sheet to be formed. , one or more heaters are arranged to form multiple rows, and each point on the surface of the sheet to be formed is calculated by the following equation (), that is, Q=F(a,x,y)・σ・(THij+ 273.16) ⁴ ...() [In formula (), Q is the amount of radiant heat at one point on the sheet to be formed (cal/sec/cm ² ); F(a, x,
y) means F(a, x, y) = F'(a, x, y)・ε...(), and in formula (), F'(a, x, y) is the distance between each heater and the molded object. ε means the view factor determined by the relative positional relationship with the sheet and the geometric shape of the sheet to be formed and the heater, ε means ε=ε ₁・ε ₂ ...(), () In the formula, ε ₁ means the radiation capacity of the heater, ε ₂ means the radiant heat absorption capacity of the sheet to be formed; σ means the Stefan-Boltzmann constant, THij is the heater (i, j are the transfer rate of the sheet to be formed) (means the i-th position in the direction perpendicular to the direction and the j-th position in the parallel direction) (unit: °C). ] A method for heating a thermoplastic resin sheet, which comprises setting a heater and adjusting the amount of radiant heat calculated by the above to a desired value. 2. Scope of claims characterized in that the thickness of the sheet to be formed is measured before the sheet to be formed is transferred to a heating section, and the amount of radiant heat applied to each part of the sheet to be heated is adjusted based on the measurement results. The method for heating a thermoplastic resin sheet according to item 1.