JPH07195508A - Method for forming crystalline polyethylene terephthalate sheet - Google Patents

Abstract

(57) [Summary] [Structure] A method of molding a crystalline polyethylene terephthalate sheet, which comprises heating a molded product A to a glass transition point or more after molding into a predetermined shape and before trimming into individual molded products. Annealed and then individual molded product A
I try to trim it. [Effect] If there is a deviation between the shape of the molded product by the heat mold during molding and the shape of the molded product after cooling by the cooling mold, correct it by heating annealing, restore it to the shape at the time of heat molding, and shape after heat shrinkage. The change can be suppressed. It is suitable as a molding process for molded products that require dimensional accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a crystalline polyethylene terephthalate sheet, and more particularly, it is improved so that a molded product after molding does not change due to heating.

[0002]

2. Description of the Related Art As a conventional sheet forming apparatus, there is an oven 50 for heating and softening a sheet S as shown in FIG. 6, and a press platen 51, 52 in a forming zone has about 160. The heat-molding dies 53 and 54 heated to ˜180 ° C. and the cooling dies 55 and 56 cooled to about 20 to 50 ° C. were fixed in pairs. The arrangement is an oven 50, heat-molding dies 53, 5
4, the cooling molds 55 and 56 were arranged in this order. The sheet S was formed at these locations by a forming device that can be conveyed by a sheet feeding chain.

Regarding the forming method, the sheet S is heated and softened by the oven 50 to a temperature before the crystallization is promoted, and is conveyed to the heat forming molds 53 and 54 which are the next forming zones. . Therefore, after heat-molding with the heat-molding dies 53 and 54 until sufficient crystallization, the mold is once released, and the molded product molded with the heat-molding dies 53 and 54 is cooled in the next zone. It is conveyed to the molds 55 and 56, and the molded product 60 is cooled and molded there by the cooling molds 55 and 56. By repeating this, sheet softening heating, crystallization heating molding, and cooling molding were carried out to obtain a heat-resistant crystallized molded article.

However, when the molded product molded by the heat molding molds 53, 54 is conveyed to the cooling molds 55, 56 in the next zone, the molded product 60 is affected by the variation in the feed amount of the conveying device.
Shifts from the cooling dies 55 and 56 of the cooling dies 55 and 56, respectively, and is pressed by the cooling dies 55 and 56 with the positional shift of the shift amount d, so that the molded product is shifted. Was there. If the mold is misaligned, there is a drawback that a molded product having no heat resistance and capable of deforming is formed. In addition to variations in the feed, since the heat-softened molded product is conveyed to the cooling mold, there is a drawback that it causes positional deviation due to inertia during conveyance (especially during deep drawing).

The mold deviation is shown in FIGS. 6 to 8. If explained in order, the mold deviation occurs when the positional deviation of the deviation amount d occurs as shown in FIG. 6, and FIG. The edge line R '(heat molding line) when molded with a mold is doubled with the line R by cooling molding, resulting in mold deviation. FIG. 7 shows that in the case of a molded product with a collar L, the molded product 60 molded by the cooling mold 56 having the flange molding portion L'remembers the shape 60 'molded by the heat molding mold. If you put such a molded product in the oven during cooking,
In particular, a large deformation (heat shrinkage) occurs at the part, and the memorized molding edge line remains and the appearance becomes bad.

This phenomenon varies to some extent depending on the heating temperature and time during cooking and the like, but it is extremely difficult to control especially in the case of a molded container product that requires dimensional accuracy to fit the lid after cooking. there were. Further, it has been difficult to manage the above-mentioned deformation phenomenon at the production site because it is difficult to determine the occurrence of the deformation phenomenon unless it is actually heated and used.

That is, with respect to the positional deviation, a sample is taken out on the production line, it is judged by actually heating it in a microwave oven, the defective portion is estimated to judge whether it is acceptable or not. The sex is low. Also, for heat shrinkage, a usage test is conducted in the market, and the outer diameter dimension of the molded product is determined by the data, but if the market conditions change,
It is necessary to change the size, and it is necessary to prepare various sizes of the same product. It is demanded by the industry that the products can be manufactured with the same dimensions at the production site, and that the dimensions are not changed even if the heating temperature changes in the market.

The above-mentioned drawbacks of the molded article which does not have heat resistance and is easily deformed are peculiar when a crystalline polyethylene terephthalate sheet is used as a sheet molding object, and have been a serious problem in molding. More specifically, a molded article having heat resistance made of a polyethylene terephthalate sheet, when heated in a microwave oven,
It has the property of returning to the shape it had when crystallized.
Therefore, when the molded product A molded by the heat molding mold is molded by the cooling mold while the position is changed, the shape becomes that at the time of the cold molding, and the shape is trimmed as it is. For the time being, the part of the collar a is uniform as shown in Fig. 9- (1), but the collar shape a'at the time of heat molding is latent, and it is heated at 220 ° C for about 30 minutes when used after trimming. Then, in order to return to the shape molded by the heat-molding die, especially the flange portion is shown in FIG.
As shown in (2), it changes the most and becomes biased, which makes the product value unattractive.

It is an object of the present invention to provide a molding treatment method capable of obtaining a molded product which is free from the above-mentioned mold deviation and deformation of a crystalline polyethylene terephthalate sheet.

[0010]

As a method of forming a sheet of crystalline polyethylene terephthalate which can solve the above problems and achieve the object of the present invention, a method of forming a crystalline polyethylene terephthalate sheet by heating and softening the sheet, It is characterized in that after the sheet is formed into a predetermined shape, it is annealed by heating until the molded product reaches a glass transition point or higher before trimming into individual molded products, and then trimmed into individual molded products.

[0011]

According to the above-described molding method of the present invention, after the molded product having a predetermined shape is formed, the molded product is annealed by heating until the molded product reaches the glass transition point or above before trimming. Even if there is a shape deviation from the above, it is possible to correct this and return the molded product to the shape at the time of heat molding.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described first with reference to the cases shown in FIGS. The crystalline polyethylene terephthalate sheet S, which is a forming material, is formed into a predetermined shape by the heating forming dies 13 and 14 provided on the upper and lower platens 11 and 12 while being heated through the oven 10, and the next cooling die is formed. The molded product A is cooled at 15 and 16. After cooling, it is sent to a trimming process in the conventional case, but in the case of the present invention, it is sent to an annealing device 18 by a constant temperature bath having a heater 17, in which the molded product A has a glass transition point ( It is heated up to about 75 ° C or higher.

After that, natural cooling is performed, and a manual or automatic trimming process is performed to trim each individual molded product A or when a plurality of molded products for each shot are simultaneously molded. In some cases, the number of shots may be trimmed once, and the next trimming may be performed. When the annealing chamber 18 is used as the constant temperature bath as described above, in order to raise the temperature of the molded article A to the glass transition point or higher, the atmosphere in the bath is required to be heated at 100 ° C. for a heating time of 8 seconds. The temperature and the sheet surface temperature are as follows when the heating time is 8 seconds.

[0014]

[Table 1]

When an annealing apparatus using a hot plate contact method is used instead of the constant temperature oven method, in order to bring the temperature of the molded article A to the glass transition point or higher, heating for 8 seconds requires a hot plate temperature of 220 ° C. or higher. is necessary. As a result of the annealing treatment, the total shrinkage amount was 2.5% before annealing, and the variation was 1.6, but the shrinkage amount was 1.0% and the variation was 0.1 after annealing at 180 ° C. or higher. Stable up to. The shrinkage rate of the molded product after 30 minutes at the annealing temperature and the heating temperature of 220 ° C. is as shown in Table 2 below. This shrinkage rate table is calculated from the average value of the dimensions measured at four locations around the molded product after trimming and before heating, from the average value of the dimensions of the same location after annealing.

[0016]

[Table 2]

In practice, the annealing treatment may be carried out by providing an annealing device at a stage where the feeding chain clamp is removed after the molding process, or by performing a shot cut and then performing the annealing treatment. All of these are performed before the trimming into individual molded products. Next, in order to observe the variation of the dimension L due to the presence or absence of annealing in the flange portion of the container having the most shape deviation between the heat molding using the heat molding die and the cooling molding using the cooling die as the molded article, a collar as shown in FIG. The following table shows the results of measuring the dimensions before heating at 1 to 8 parts of the part and the flange size of the same part after heating at 220 ° C. for the molded product for 30 minutes for the molded product with different annealing temperature and without annealing. Shown in 3.

[0018]

[Table 3]

The width L of the collar portion after trimming the unannealed molded container and heating it at 220 ° C. for 30 minutes has a large difference R between the maximum value and the minimum value and a large standard deviation σ. There is. The width of the flange portion after heating the annealed molded container and heating at 220 ° C. for 30 minutes was small, R was small, and the standard deviation σ was the same as before heating, and became uniform.

FIG. 2 illustrates the annealing effect of the above-described method of the present invention. Even if there is a latent mark A ′ formed by the heat-molding die on the molded article A before annealing as shown in FIG. After annealing, as in 2- (2), the latent molded shape of the heat-molding die becomes visible and the shape returns. Therefore, after trimming, even if it is heated in an oven, the shape of the collar portion L is stable with a normal and non-biased shape as shown in FIG. 2- (3).

In the above description of the embodiments, it is assumed that the crystalline polyethylene terephthalate sheet is molded by using a pair of heat-molding dies and cooling dies separately to perform the annealing process in the subsequent process. However, in the modified embodiment shown in FIGS. 4 and 5, instead of the molding die 2, the cooling die 3 is traversed to the molding zone in the direction perpendicular to the flow direction of the sheet S, and the molding is performed. Cooling molding is carried out without transferring the molded product A after the heat molding by the molds 1 and 2, which will be described in more detail below.

First, FIG. 4 shows a molding apparatus viewed from the sheet discharge side. The sheet S is heated by an oven and conveyed to a molding zone portion, and a molding die 1 with a plug is formed in the molding zone portion.
2 shows a state in which the molding die 2 for heat molding and the molding die 2 are press-molded. The molding die 2 for heat molding is heated by the heater 4, and the cooling die 3 is cooled by the cooling plate 5. The forming die 2 for heat forming and the cooling die 3 are fixed in parallel by a traverse plate 6, and the traverse plate 6 is pressed by each die.
As a result, the sheet S moves in the sheet width direction which is a direction perpendicular to the flow direction. A servo motor 7 is attached to the plate 6 and is used for driving the plate 6.

The molds 2, 3 and the plate 6 are attached to the lower platen 12. A molding die 1 using a plug is attached to the upper platen 11, and the molding method can be arbitrarily selected depending on the shape of the molded product, such as plug assist and match mold. Since the molding die 1 using the plug is vacuum-molded in the molding die 2 using the cavity, the molding die 1 is airtight so as to prevent vacuum leakage, and it is not particularly necessary to raise the die temperature.

However, if necessary, the temperature may be raised or the heater may be pushed in. A sheet chain clamp 8 shown at the center of the molding apparatus is an apparatus that holds the end portion of the sheet and conveys the sheet. The sheet S is pressed by the molding die 2 for heat molding and the molding die 1 by the plug, and when the crystallization heating is sufficient, the press is released, but the molded article A is crystallized, but still softened. It is in a state where it is easily deformed. Molded product A that has softened after heat molding
In order to cool, the traverse plate 6 moves, the molding die 2 moves to the position of the chain line in FIG. 4 (left in the figure), and the cooling die 3 matches the molding die 1 with the plug and can repress. To move. FIG. 5 shows a state in which the cooling die 3 is being repressed from the front.

After that, the cooling mold 3 and the plug-molding mold 1 are released, and the cooled molded product A is conveyed to the annealing device 18 in the next zone shown in FIG. Can be finished. By repeating this operation,
We are trying to continuously obtain molded products with good heat resistance.
Reference numerals 20 and 30 in the figure denote cylinder mechanisms. The sheet S may be a non-foamed or foamed crystalline polyethylene terephthalate sheet.

In the above-described embodiment, unlike the previous embodiment, one pair of molding dies and one cooling mold are not used, and one of the molding dies is shared during cooling, so that the dimensional stability is higher, and therefore annealing is performed. It can be further stabilized by treatment. In this embodiment, the cooling mold 3 is connected to the molding mold 2 for heat molding, but the cooling mold 3 may be traversed individually at different timings.

If a heating / cooling mold is required for both the pair of molding dies 1 and 2 as a range that can be deformed in practice, a traverse plate is attached to both platens 11 and 12 to traverse them. Good.

[0028]

As described above, according to the present invention, after the sheet is formed into a predetermined shape, the sheet is annealed by heating until it reaches the glass transition point or above before trimming into individual molded articles. , Even if there is a deviation between the shape when heated by the heat molding die and the shape after cooling by the cooling die, it can be restored to the shape at the time of heat molding by annealing by heating, and the shape deviation can be corrected. .

Therefore, in the case of a container-molded product with a collar, there is no problem that the collar shape is biased, and when the molded product is trimmed into individual molded products, it is heated in a microwave oven or the like when the contents are cooked, for example. Also, the change due to heat shrinkage, which is a problem of the crystalline polyethylene terephthalate sheet molded product, can be suppressed, and the manufacturing control becomes easy.

Therefore, it is extremely suitable as a method for forming a lid-fitted container molded product which requires particularly dimensional accuracy, and a molded product having a high commercial value can be provided.

[Brief description of drawings]

FIG. 1 is a schematic sectional view.

FIG. 2 (1) to (3) are a plan view and a side view showing a change in shape of a molded product.

3 (1) and (2) are a plan view and a cross-sectional view showing a measurement point.

FIG. 4 is a side view showing a molding side of a modified example.

FIG. 5 is a front view of a modification example of the above.

FIG. 6 is a schematic sectional view of a conventional example.

FIG. 7 is a schematic cross-sectional view showing a shape deviation of a conventional example.

FIG. 8 is a plan view showing a shape deviation of a conventional example.

9A and 9B are a plan view and a side view showing a shape deviation of a conventional example.

[Explanation of symbols]

 1 Mold for plug 2 Mold for heat molding 3 Cooling mold 6 Traverse plate A Molded product S sheet

[Procedure amendment]

[Submission date] June 30, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

3 is a plan view and a sectional view showing the measurement point.

Claims (1)

[Claims] 1. A method for forming a crystalline polyethylene terephthalate sheet by heating and softening the sheet, which is formed by forming the sheet into a predetermined shape and then heating the formed article before trimming into individual shaped articles until the molded article reaches a glass transition point or higher. A method for forming a crystalline polyethylene terephthalate sheet, which comprises performing annealing and then trimming the individual formed articles.