JP2000351153A - Method for molding biaxially drawn polyethylene terephthalate sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding biaxially drawn polyethylene terephthalate sheet by a low molding pressure being similar to an ordinary hot plate air-pressure molding without requiring high air-pressure molding pressure. SOLUTION: A sheet obtd. by draw orientation and crystallization of a polyethylene terephthalate resin with draw ratios of at least 2.5 times in the longitudinal direction and at least 2 times in the transverse direction and degree of crystallization of 38-50% is molded under a condition where (a) a relation between sheet heating time X (sec) and sheet heating temp. Y is Y>=220-1.5X or Y>=238-1.5X and X>=1 and (b) air-pressure molding pressure is 3.0-6.0 kg/cm2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a biaxially stretched polyethylene terephthalate sheet.

[0002]

2. Description of the Related Art Conventionally, it has been extremely difficult in industrial production to form a physically very tough biaxially stretched polyethylene terephthalate (hereinafter abbreviated as PET) sheet by hot plate press forming or press forming. However, Japanese Patent Publication No. 62-183
No. 39 discloses a molding temperature (T) = 220 to 2 at the time of molding.
45 ° C, molding pressure (P) ≧ [30+ (220-T) /
2] A solution for pressure forming under the condition of kg / cm ² is shown. However, under these conditions, molding can be performed by applying a very high compressed air molding pressure of about 20 to 40 kg / cm ^{2 at} the actual molding pressure.

[0003]

The above-mentioned biaxially stretched PET
In the sheet forming method, about 20 to 40 kg / cm
^Since a very high compressed air forming pressure of 2 is required, special production equipment is required, and it has not been put to practical use in the field of low-cost one-way containers and the like. An object of the present invention is to eliminate the need for such a high compressed air forming pressure of 3.0 to 3.0.
An object of the present invention is to provide a method for forming a biaxially stretched PET sheet at a low forming pressure of 4.5 kg / cm ^{2, which} is as low as ordinary hot platen pressure forming.

[0004]

In order to solve the above-mentioned problems, in the present invention, a stretch ratio obtained by stretching and crystallizing a polyethylene terephthalate resin is 2.5 times or more in a machine direction and 2 or more in a machine direction. The sheet having a degree of crystallinity of 38% or more and 50% or less is (a) the relation between the sheet heating time X (second) and the sheet heating temperature Y (° C.) is Y ≧ 220-1. 5XX X ≧ 1 (b) The compressed air forming pressure is 3.0 kg / cm ² or more, 6.0
The molding was performed under the condition of kg / cm ² or less.

It is particularly preferable that Y ≧ 238−1.5X.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a hot platen pressure forming apparatus used in the forming method of the present invention. This apparatus is a commonly used sheet heating type air pressure forming apparatus by hot plate contact. As shown in FIG.
The sheet S is intermittently fed in the direction of the arrow. The molding die 10 is provided with a plurality of cavities 11, and a plurality of supply / exhaust holes 12 are provided on the inner surface of the cavities 11. On the other hand, the hot platen 20 is also provided with a large number of air supply / exhaust holes 22 opened on the surface 21 thereof.

At the time of forming the sheet S, as shown in FIG. 1B, the sheet S is brought into close contact with the hot platen 20 by evacuation from the air supply / exhaust holes 22 of the hot platen 20 and heated by the heater 23. At this time, a pressurized gas may be supplied from the supply / exhaust hole 12 of the molding cavity 11 to assist the adhesion action. Next, as shown in FIG. 1C, a pressurized gas is supplied from a supply / exhaust hole 22 of the hot platen 20, and the softened sheet S is pressed against the cavity 11 of the forming die 10 to form the sheet. At this time, the formability can be enhanced by evacuating the air from the supply / exhaust hole 12 of the cavity 11. Finally, as shown in FIG. 1D, the pressurized gas is discharged from the supply / exhaust hole 12 of the cavity 11 and the mold is released.

As described above, the heating method of the sheet S requires uniform heating of the entire sheet, and therefore the direct heating method using a hot plate is most suitable. In the indirect heating method, uneven heating of the sheet is liable to occur, and in an extreme case, a portion under-heated may be broken during molding.

It is important that the molding is performed under the conditions selected from the range of the following formula. That is, the relationship between the sheet heating time X (second) and the sheet heating temperature Y (° C.) is Y ≧ 220−1.5X X ≧ 1 As long as molding is performed within the range of this condition, the compressed air molding pressure is at least 3.0 kg /. Molding can be performed sufficiently with a pressure as low as ² cm ² . The molded product obtained by this molding method is heat-resistant (deformation starts at 100 ° C. or higher, but does not significantly deform even in a high temperature range, and does not melt or have holes even at a high temperature of 230 ° C.), and is transparent. It has excellent properties such as strength, tensile strength, impact strength, gas barrier properties, and fragrance retention. If the conditions of the sheet heating temperature and the sheet heating time are out of the above ranges, the molding cannot be performed sufficiently, and the reproducibility of the detailed shape becomes insufficient.

An excellent molded product can be obtained by molding under the conditions selected from the following formulas. That is, the relationship between the sheet heating time X (second) and the sheet heating temperature Y (° C.) is Y ≧ 238−1.5X X ≧ 1 As long as molding is performed within the range of this condition, the compressed air molding pressure is at least 3.0 kg /. Molding can be performed sufficiently with a pressure as low as ² cm ² . Furthermore, when molded under this condition range, as shown in the examples described later, the volume change rate when the molded article is immersed in a silicone oil bath heated to 160 ° C. for 20 minutes is 10%.
%, And a molded article having extremely excellent heat resistance can be obtained. This molded product exhibits excellent properties such as transparency, tensile strength, impact strength, gas barrier properties, and fragrance retention. If the conditions of the sheet heating temperature and the sheet heating time are out of the above-mentioned ranges, the molding can be performed, but the heat resistance of the molded article is greatly reduced.

In the above-mentioned molding method, the molding time can be about several seconds as in the case of molding a general-purpose resin sheet. Even if the molding time is extremely long, the cost is high but no great effect is obtained. . In addition, compressed air forming pressure is 3kg
If it is less than / cm ² , molding cannot be performed sufficiently. There is no problem in increasing the compressed air forming pressure, but if it is higher than 6 kg / cm ² , air leakage and the like at the time of molding are likely to occur. It is not preferable.

The PET resin used in the present invention is a homopolymer and a copolymer (for example, a resin containing at least 85 mol% of PET units) which does not impair the characteristics of PET.
This is biaxially oriented and crystallized by a known method for producing a biaxially stretched crystallized polyester film to form a film into a sheet. If the crystallinity of the stretched and crystallized PET sheet (including the film) is less than 38%, the heat resistance will be poor, and if it exceeds 50%, the material will have poor elongation and will not be molded, which is not preferable. The crystallinity is derived based on the following equation.

Crystallinity Xc = dc (d-da) / d (d
c-da) where da (density in completely non-crystal) = 1.335 dc (density in completely crystal) = 1.501 d = density of sample Further, the biaxially stretched PET sheet made of these materials is:
It is optional to add an organic substance and an inorganic substance such as an antistatic agent, an antifogging agent, a surfactant, a ceramic coat, aluminum vapor deposition, and a filler such as glass fiber, if necessary. Further, at least one barrier layer may be provided on the resin layer. Examples of the resin for the barrier layer include polyvinylidene chloride, ethylene-vinyl alcohol copolymer, and various nylons. The thickness of the biaxially stretched PET sheet is usually from 70 to 500 μ, and the thickness particularly suitable for the molding method of the present invention is from 150 to 350 μ.

In the present invention, the sheet heating temperature at the time of forming a biaxially stretched PET sheet adjusted to an arbitrary stretching ratio and crystallinity within the above ranges is 200 to 245 ° C. If the temperature is lower than 200 ° C., the resin does not sufficiently elongate, and it is difficult to form the resin by pressure molding. If the temperature is higher than 245 ° C., the sheet is in a molten state and adheres to the hot plate, so that the sheet cannot be formed.

[0015]

Example 1 A container shown in FIGS. 2 and 3 was subjected to hot platen pressure molding using two types of molds under the following molding conditions.

The molding conditions were a mold temperature of 60 ° C., a molding pressure of 3.5 kg / cm ² , and a compressed air molding time of 8 seconds.

The material used was a biaxially stretched PET sheet having a crystallinity of 40% (emblem manufactured by Unitika) and the thickness of the sheet was 250 μm. FIG. 4 shows the result of visual observation of the state of the molded container.

[0018]

Example 2 A hot platen pressure molding was carried out under the following molding conditions using a mold for molding the container shown in FIG. 3 used in Example 1.

The molding conditions are: mold temperature 60 ° C., molding temperature 2
At 30 ° C., the sheet heating time was 8 seconds, and the pressure forming time was 8 seconds.

The material used was a biaxially stretched PET sheet having a crystallinity of 40% (emblem manufactured by Unitika) and the thickness of the sheet was 250 μm. Figure 5 shows the state of the molded container.
Shown in

[0021]

EXAMPLE 3 A heat resistance test was carried out on three types of molded products obtained by pressurized hot platen molding under the following molding conditions using the container mold of FIG. 3 used in Example 1. In the test method, the volume change rate (%) when each molded product was immersed in a silicone oil bath heated to various temperatures for 20 minutes was measured.

The molding conditions were a mold temperature of 60 ° C., a molding pressure of 3.5 kg / cm ² , and a pressure forming time of 8 seconds.

The material used was a biaxially stretched PET sheet (emblem manufactured by Unitika) having a crystallinity of 40%, and the thickness of the sheet was 250 μm. The sheet heating time of each sample was 8 seconds, and the heating temperature was 220 ° C. for sample 1, 230 ° C. for sample 2, and 235 ° C. for sample 3. FIG. 6 shows the results. The molded product of Samples 2 and 3 is 160 ° C
However, it exhibited excellent heat resistance with a volume change rate of 10% or less.
When the volume change rate was 10% or less, the change in the container was not so conspicuous.

[0024]

Embodiment 4 Using a mold having an inner diameter of 230 mm and a depth of 10 mm and having a truncated conical cavity, the molding temperature and heating time were changed as shown in FIG. The following heat-shrinkage test was performed. That is, the sample piece (5
(mm x 20 mm x 0.024 mm), and with a load of 417 g / cm ² applied to the other end, the ambient temperature is increased from 30 to 230 ° C at a rate of 5 ° C / min to expand the sample. -The shrinkage rate (dL / L) was measured.
Note that the heat shrinkage in the horizontal direction is smaller than that in the vertical direction, so that the description is omitted.

FIG. 8 shows a comparison of shrinkage rates when the sheet heating temperature is changed while the sheet heating time is constant (8 seconds). FIG. 9 shows a comparison of shrinkage rates when both the heating temperature and the heating time were changed. As can be seen from the figure, the molded article under the molding conditions of 235 ° C. and a heating time of 8 seconds exhibited excellent dimensional accuracy in a high temperature environment, with a shrinkage rate of 1% or less at 220 ° C.

[0026]

According to the forming method of the present invention, as described above, by controlling the sheet heating temperature and time, the biaxially stretched PET sheet can be formed even at the forming pressure of the ordinary hot platen pressure forming. It becomes possible to use molding equipment and molding dies, which can be the same as the conventional hot platen pressure molding equipment and dies used for molding general-purpose resin sheets. It is possible and can be produced without new investment.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a molding method of the present invention.

FIGS. 2A and 2B show a product shape of Example 1; FIGS.
Sectional view

FIGS. 3A and 3B show the product shape of Example 1 (A) Plan view and (B)
Sectional view

FIG. 4 is a table showing sheet heating temperature, time, and molding state in Example 1.

FIG. 5 is a table showing a molding pressure and a molding state in Example 2.

FIG. 6 is a graph showing test results of Example 3.

FIG. 7 is a table showing sheet heating temperature and time in Example 4.

FIG. 8 is a graph showing test results of Example 4.

FIG. 9 is a graph showing test results of Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Mold 11 Cavity 12 Supply / exhaust hole 20 Heating plate 21 Heating plate surface 22 Supply / exhaust hole 23 Heater S sheet

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 4F208 AA24C AC03 AH58 AR02 AR06 AR11 MA02 MC01 MG12 MK08 MK15 4F210 AA24C AC03 AH58 AR02 AR06 AR11 QC05 QG01

Claims (2)

[Claims] A stretch ratio obtained by stretching and crystallizing a polyethylene terephthalate-based resin is 2.5 times or more in a longitudinal direction, 2 times or more in a transverse direction, and a crystallinity is 38% or more. For a sheet of 50% or less, (a) the relation between the sheet heating time X (second) and the sheet heating temperature Y (° C.) is as follows: Y ≧ 220−1.5X X ≧ 1 (b) The compressed air forming pressure is 3.0 kg. / Cm ² or more, 6.0
A method for forming a biaxially stretched polyethylene terephthalate sheet, which is formed under a condition of not more than kg / cm ² . 2. The stretch ratio obtained by stretching and crystallizing a polyethylene terephthalate resin is 2.5 times or more in the machine direction and 2 or more times in the transverse direction, and the degree of crystallinity is 38% or more. For a sheet of 50% or less, (a) the relation between the sheet heating time X (second) and the sheet heating temperature Y (° C.) is as follows: Y ≧ 238−1.5X X ≧ 1 (b) The compressed air forming pressure is 3.0 kg. / Cm ² or more, 6.0
A method for forming a biaxially stretched polyethylene terephthalate sheet, which is formed under a condition of not more than kg / cm ² .