JP4172878B2 - Method for forming biaxially stretched polyethylene terephthalate sheet - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a biaxially stretched polyethylene terephthalate sheet.
[0002]
[Prior art]
Conventionally, it has been considered extremely difficult for industrial production to form a physically very tough biaxially stretched polyethylene terephthalate (hereinafter abbreviated as PET) sheet by hot platen molding or press molding. Japanese Patent Laid-Open No. 62-18339 discloses a solution for pressure forming at the time of molding under the conditions of molding temperature (T) = 220 to 245 ° C. and molding pressure (P) ≧ [30+ (220−T) / 2] kg / cm ^2. It is shown. However, this condition makes it possible to form by applying a very high pressure forming pressure of about 20 to 40 kg / cm ² when actually forming pressure.
[0003]
[Problems to be solved by the invention]
The above-described biaxially stretched PET sheet molding method requires a very high pressure forming pressure of about 20 to 40 kg / cm ² , and therefore requires special manufacturing equipment, which is practical in the field of low-cost one-way containers and the like. It hasn't arrived. The subject of this invention is the method of shape | molding biaxially-stretched PET sheet | seat by the low forming pressure equivalent to the normal hot-plate pressure forming of 3.0-4.5 kg / cm < ² >, without requiring such a high pressure forming pressure Is to provide.
[0004]
[Means for solving problems]
In order to solve the above problems, in this invention, the stretch ratio obtained by stretching and crystallizing a polyethylene terephthalate-based resin is 2.5 times or more in the longitudinal direction and 2 or more times in the transverse direction, A sheet having a crystallinity of 38% or more and 50% or less,
(A) The relationship between the sheet heating time X (seconds) and the sheet heating temperature Y (° C.)
Y ≧ 220-1.5X
X ≧ 1
(B) Molding was performed under a pressure forming pressure of 3.0 kg / cm ² or more and 6.0 kg / cm ² or less.
[0005]
Moreover, it is particularly preferable that Y ≧ 238−1.5X.
[0006]
Embodiment
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 sheet heating type pressure forming apparatus by contact with a hot plate which is usually used. As shown in FIG. 1 (a), the mold 10 and the hot platen 20 are arranged facing each other across the sheet S, and the sheet S is intermittently fed in the direction of the arrow. The mold 10 is provided with a plurality of cavities 11, and a plurality of air 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 number of air supply / exhaust holes 22 that open to the surface 21 thereof.
[0007]
When forming the sheet S, as shown in FIG. 1 (b), the sheet S is brought into close contact with the heating plate 20 by being evacuated from the air supply / exhaust hole 22 of the heating plate 20 and heated by the heater 23. At this time, pressure gas may be supplied from the air supply / exhaust hole 12 of the molding cavity 11 to assist the close contact action. Next, as shown in FIG. 1 (c), pressurized gas is supplied from the air 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 be formed. At this time, the moldability can be improved by evacuating from the air supply / exhaust hole 12 of the cavity 11. Finally, as shown in FIG. 1 (d), the pressure gas is discharged from the air supply / exhaust hole 12 of the cavity 11 and released.
[0008]
As described above, since the heating method of the sheet S requires uniform heating of the entire sheet, the direct heating method using a hot platen is most suitable. In the indirect heating method, uneven heating of the sheet is likely to occur, and in an extreme case, the insufficiently heated portion is broken during molding.
[0009]
And it is important to perform molding under 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 pressure forming pressure can be sufficiently molded at a very low pressure of at least 3.0 kg / cm ² . Molded products obtained by this molding method have heat resistance (deformation begins at 100 ° C or higher, but does not significantly deform even at higher temperatures, and does not melt or puncture at 230 ° C). It has excellent properties such as properties, tensile strength, impact strength, gas barrier properties, and fragrance retention. If the conditions of the sheet heating temperature and the sheet heating time are below the above range, molding cannot be performed sufficiently, and the reproducibility of the detailed shape becomes insufficient.
[0010]
In particular, an excellent molded product can be obtained by molding under 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 ≧ 238−1.5X.
X ≧ 1
As long as molding is performed within the range of this condition, the pressure forming pressure can be sufficiently molded at a very low pressure of at least 3.0 kg / cm ² . Further, when molded in this condition range, as shown in the examples described later, the heat resistance is very excellent in that the volume change rate when the molded product is immersed in a silicone oil bath heated to 160 ° C. for 20 minutes is less than 10%. A molded product 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 below the above ranges, the heat resistance of the molded product is greatly reduced even if molding is possible.
[0011]
In the above molding method, the pressure forming time can be formed in about several seconds as in the case of forming a general-purpose resin sheet. Even if the pressure forming time is extremely long, the cost is increased and a great effect cannot be obtained. Further, when the pressure forming pressure is less than 3 kg / cm ² , the forming cannot be sufficiently performed. There is no problem with increasing the pressure forming pressure, but if it is higher than 6 kg / cm ² , air leakage during molding is likely to occur. Not good at all.
[0012]
The PET resin used in the present invention is a copolymer (for example, a resin containing a PET unit of 85 mol% or more) that does not impair the characteristics of homopolymerization and PET, and this is a known biaxially stretched crystallized polyester film. The film was formed into a sheet shape by biaxial orientation and crystallization by the production method described above. It should be noted that if the crystallinity of the stretched and crystallized PET sheet (including film) is less than 38%, the heat resistance is poor, and if it exceeds 50%, the material is poorly stretched and cannot be molded. The crystallinity is derived based on the following formula.
[0013]
Crystallinity Xc = dc (d-da) / d (dc-da)
Where da (density when completely non-crystalline) = 1.335
dc (density at complete crystal) = 1.501
d = Sample density Biaxially stretched PET sheet made of these materials can be used for organic and inorganic substances such as antistatic agents, antifogging agents, surfactants, ceramic coats, fillers such as aluminum vapor deposition and glass fibers, etc. It is optional to add. Furthermore, at least one barrier layer can be provided on the resin layer. Examples of the resin for the barrier layer include polyvinylidene chloride, ethylene-vinyl alcohol copolymer, various nylons, and the like. The thickness of the biaxially stretched PET sheet is usually 70 to 500 μm, and particularly suitable for the molding method of the present invention is 150 to 350 μm.
[0014]
In this invention, the sheet heating temperature at the time of biaxial stretching PET sheet shaping | molding adjusted to arbitrary draw ratios and crystallinity in the said range is 200-245 degreeC. If this temperature is less than 200 ° C., the resin does not extend sufficiently and it is difficult to mold by pressure forming. Further, at a temperature higher than 245 ° C., the sheet becomes molten and adheres to the hot platen and cannot be molded.
[0015]
[Example 1]
The containers shown in FIGS. 2 and 3 were hot-plate pressure-molded under the following molding conditions using two types of molding dies.
[0016]
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.
[0017]
The material used was a biaxially stretched PET sheet (Embret made by Unitika) having a crystallinity of 40%, and the thickness of the sheet was 250 μm. The result of visually observing the state of the molded container is shown in FIG.
[0018]
[Example 2]
Using the mold for molding the container of FIG. 3 used in Example 1, hot platen was formed under the following molding conditions.
[0019]
The molding conditions were a mold temperature of 60 ° C., a molding temperature of 230 ° C., a sheet heating time of 8 seconds, and a pressure forming time of 8 seconds.
[0020]
The material used was a biaxially stretched PET sheet (Embret made by Unitika) having a crystallinity of 40%, and the thickness of the sheet was 250 μm. The state of the molded container is shown in FIG.
[0021]
[Example 3]
A heat resistance test was carried out on three types of molded products formed by hot platen pressure molding under the following molding conditions using the container mold of FIG. 3 used in Example 1. The test method measured the volume change rate (%) when each molded article was immersed in the silicone oil bath heated to various temperatures for 20 minutes.
[0022]
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.
[0023]
The material used was a biaxially stretched PET sheet (Embret made by Unitika) having a crystallinity of 40%, and the thickness of the sheet was 250 μm. In addition, 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. The results are shown in FIG. The molded products of Samples 2 and 3 showed excellent heat resistance with a volume change rate of 10% or less even at 160 ° C. When the volume change rate was 10% or less, the change of the container was not so noticeable.
[0024]
[Example 4]
By using a mold having a truncated cone cavity having an inner diameter of 230 mm and a depth of 10 mm, the molding temperature and the heating time are changed as shown in FIG. 7 under the same conditions as in Example 1. A test was conducted. That is, one end of the molded sample piece (5 mm × 20 mm × 0.024 mm) was fixed by a thermal analyzer, and the ambient temperature was changed from 30 to 230 ° C. with a load of 417 g / cm ² applied to the other end. The sample was raised at a rate of 5 ° C./min, and the expansion / contraction rate (dL / L) of the sample was measured. The horizontal direction is omitted because the heat shrinkage is smaller than that in the vertical direction.
[0025]
FIG. 8 shows a comparison of the shrinkage rate when the sheet heating temperature is changed at a constant sheet heating time (8 seconds). In addition, FIG. 9 shows a comparison of the shrinkage rate when both the heating temperature and the heating time are changed. As can be seen, the molded product under the molding conditions of 235 ° C. and heating time of 8 seconds showed excellent dimensional accuracy under a high temperature environment with a shrinkage rate of 1% or less at 220 ° C.
[0026]
【The invention's effect】
According to the molding method of the present invention, as described above, by controlling the sheet heating temperature and time, it becomes possible to mold a biaxially stretched PET sheet even with molding pressure by ordinary hot platen pressure molding, and molding equipment Since the conventional hot platen pressure forming equipment and molds used for molding general-purpose resin sheets can be used, the existing molds can be used as they are, It is also possible to produce without investment.
[Brief description of the drawings]
FIG. 1 is a cross-sectional diagram showing an example of the molding method of the present invention. FIG. 2 is a plan view and (b) a cross-sectional view showing a product shape of Example 1. FIG. Shown (a) Plan view and (b) Cross-sectional view FIG. 4 is a table showing the sheet heating temperature, time and forming state of Example 1. FIG. 5 is a table showing forming pressure and forming state of Example 2. FIG. [Fig. 7] A graph showing the test results of Example 3. [Fig. 7] A table showing the sheet heating temperature and time of Example 4. [Fig. 8] A graph showing the test results of Example 4. [Fig. Graph to show 【Explanation 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

Claims (2)

A sheet having a draw ratio of 2.5 times or more in the longitudinal direction and 2 times or more in the transverse direction obtained by stretching and crystallizing a polyethylene terephthalate resin and having a crystallinity of 38% or more and 50% or less. The
(A) The relationship between the sheet heating time X (seconds) and the sheet heating temperature Y (° C.)
Y ≧ 220-1.5X
X ≧ 1
(B) A method for forming a biaxially stretched polyethylene terephthalate sheet, wherein the air pressure is formed under conditions of a pressure of 3.0 kg / cm ² or more and 6.0 kg / cm ² or less. A sheet having a draw ratio of 2.5 times or more in the longitudinal direction and 2 times or more in the transverse direction obtained by stretching and crystallizing a polyethylene terephthalate resin and having a crystallinity of 38% or more and 50% or less. The
(A) The relationship between the sheet heating time X (seconds) and the sheet heating temperature Y (° C.)
Y ≧ 238-1.5X
X ≧ 1
(B) A method for forming a biaxially stretched polyethylene terephthalate sheet, wherein the air pressure is formed under conditions of a pressure of 3.0 kg / cm ² or more and 6.0 kg / cm ² or less.

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