JPH0547570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention relates to a foamed sheet of thermoplastic polyester resin.

(Conventional technology) Thermoplastic polyester resin (hereinafter referred to as
PAT) is a high molecular weight chain polyester obtained by reacting an aromatic dicarboxylic acid with a dihydric alcohol. Terephthalic acid is the most commonly used dicarboxylic acid, and ethylene glycol is commonly used as the alcohol.
Therefore, polyethylene terephthalate is considered to be a typical PAT.

PAT has high mechanical strength, good shape stability, and excellent heat resistance that can withstand temperatures of 200℃. Furthermore, PAT is a crystalline resin, and molded products with different degrees of crystallinity are produced depending on the molding method. In this case, as the crystallinity of the molded article increases, its heat resistance and rigidity improve, but on the other hand, the ease of printing, adhesion, ease of secondary processing, etc. decreases.

It is also known to make PAT into a foam. However, PAT is said to be a resin that is difficult to foam. This is because PAT is a crystalline resin, and when it is heated, it rapidly melts and its viscosity decreases, and the temperature range in which it exhibits a viscosity suitable for foaming is narrow.

It was suggested that the crystallization rate of PAT should be taken into account when making PAT foams. For example, Japanese Patent Publication No. 61-48410 states that when a string with a cross-sectional area of 1 to 200 mm ² is made by extrusion foam, extrusion at an extrusion speed that has a special relationship with the crystallization speed of PAT results in poor stretchability. It is stated that it is possible to obtain a cord that is easy to heat-process. Further, Japanese Patent Publication No. 61-48411 states that when PAT is extruded and foamed under conditions such that the degree of crystallinity is 30% or more, a string that is easy to bend and easily woven can be obtained. However, consideration of the crystallization rate of PAT is limited to the production of strings.

Generally, the crystallinity of a resin can be measured by the density of the resin, an X-ray diffraction image, a nuclear magnetic resonance absorption spectrum, and the like. However, resin foam
The degree of crystallinity cannot be measured by these methods due to the large number of small air bubbles contained therein. Therefore, for PAT foam,
It was not clear how the degree of crystallinity could be measured.

It is also known that after PAT is made into a foam, the surface of the foam is heated to promote crystallization of the PAT and increase the degree of crystallinity, resulting in a strong foam. However, no attempt has been made to partially vary the degree of crystallinity in a single PAT foam to make it suitable for special uses.

(Problems to be Solved by the Invention) This invention is based on the fact that the degree of crystallinity of PAT foam can be accurately measured by a thermal method.
It is an object of the present invention to provide a PAT foam sheet, thereby providing various conveniences in the post-processing of the PAT foam sheet.

(Means for Solving the Problems) The inventor noticed that extrusion foaming is convenient when foaming PAT to make a foam sheet. Immediately after extrusion, the extruded PAT foams to become a foam sheet, but since it is still at high temperature and contains many small air bubbles, the cooling conditions can be changed between the front and back sides of the sheet, and cooling It was confirmed that it is easy to change the degree of crystallinity between the front and back sides of the same foam sheet by changing the operation.

The inventor also confirmed that the degree of crystallinity of a PAT foam sheet can be accurately measured using the thermal properties of PAT. The principle of using thermal properties is to measure the heat of fusion and cold crystallization of PAT. The principle behind this is that when PAT foam is heated, the crystals first grow and then melt; when the crystals grow, they generate heat, and when they melt, they absorb the heat of fusion, so this property is utilized. Specifically, the degree of crystallinity is determined by measuring the cold crystallization heat emitted during crystallization and the fusion heat absorbed during melting, and comparing these with the fusion heat derived from the theory of perfect crystals. It is calculated. The inventor has confirmed that the degree of crystallinity can be calculated to one decimal place by this method.

The inventor also found that when the degree of crystallinity is calculated as described above, if there is a numerical difference of 1% in the degree of crystallinity, the two surfaces exhibit different behavior. In other words, the general crystallinity of PAT foam sheets is 5-30%, but there are obvious differences in the heat resistance, adhesion, and wettability index of PAT foam when the crystallinity changes by 1%. but,
At 1% or less, the difference does not appear so clearly. For example, it was confirmed that printing ink easily adheres to a surface with a low degree of crystallinity, indicating that the surface is suitable for printing, while on the other hand, a surface with a high degree of crystallinity has greater heat resistance. Therefore, if a container is formed with the side with a high degree of crystallinity facing the inside, the inside will have high heat resistance and can be used as a heat-resistant container, while the outside will have printability or adhesion, so it can be used for printing and other purposes. It has been found that adhesion is facilitated, which provides a great advantage. This invention was completed based on such knowledge.

(Summary of the Invention) This invention provides a PAT foam sheet with a thickness of 0.5 mm or more, which has different degrees of crystallinity between the front and back sides of the sheet, and the average crystallinity on both sides differs by at least 1%. The gist is a foamed sheet of thermoplastic polyester resin, which is characterized by:

The resin used in this invention is PAT.
As mentioned above, PAT uses aromatic dicarboxylic acids,
It is a high-molecular chain polyester obtained by esterification with a dihydric alcohol. In addition to terephthalic acid, dicarboxylic acids include isophthalic acid,
There are also those using 2,6-naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, and diphenoxy dicarboxylic acid. In addition to ethylene glycol, dihydric alcohols include diethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexane dimethylol, and 2,2-bis(4-β-hydroxyethoxyphenyl)propane. be. Such PATs are commercially available. In this invention,
Such commercially available PAT can be used.

Various foaming agents can be used. Broadly divided into solid compounds that decompose at temperatures above the softening point of PAT and generate gas, and solid compounds that generate gas when heated,
Either a liquid that vaporizes within the PAT or an inert gas that can be dissolved in the PAT under pressure can be used. The solid compounds mentioned above are, for example, azodicarbonamide, dinitrosopentamethylenetetramine, hydrazocarbonamide and the like. The vaporized liquids mentioned above are, for example, saturated aliphatic hydrocarbons such as hexane, pentane, butane, propane, saturated alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as benzene, xylene, and methylene chloride. , Freon (registered trademark)
halogenated hydrocarbons such as The inert gases mentioned above are, for example, carbon dioxide, nitrogen, etc. In addition, as a foaming agent, JP-A-59-
As taught in JP 135237, high molecular weight linear aromatic polycarbonates can also be used.

Extrusion foaming of PAT is carried out, for example, as follows. First, put PAT into an extruder and melt it.
The blowing agent was forced into the extruder midway and melted.
Add a foaming agent to PAT. A mouthpiece is attached to the tip of the extruder, and an extrusion hole extending linearly or annularly is provided in the mouthpiece, and PAT containing a foaming agent is passed through the extrusion hole.
extrude to make a foam sheet.

The extruded PAT sheet foams in the atmosphere and becomes a foam sheet. While the extruded sheet has foamed and is still at a high temperature, at least one side of the sheet is brought into contact with a cooling liquid or solid to cool that side and create a temperature difference or cooling rate difference between it and the other side. Continue cooling. Then, on the surface that has been cooled rapidly, there is less metal to crystallize and the degree of crystallinity is small, but when the other surface is allowed to cool naturally or is heated, crystallization is promoted and crystallization is reduced. Causes a large degree of severity. The greater the temperature difference, the greater the difference in crystallinity.

In this invention, the thickness of the PAT foam sheet was limited to 0.5 mm or more because, on the one hand, it was thought that this thickness was necessary in order to cool the sheet to different degrees of crystallinity. On the other hand, it was thought that this level of thickness was necessary in order to actually measure crystallization. To explain the latter reason in more detail, in order to measure the degree of crystallinity between the front and back sides of a PAT foam sheet, the front and back sides must be able to be separated from the center of the rest of the sheet. . Since the minimum thickness at which the front surface or back surface can be separated is considered to be 150μ, the thickness is set to 0.5mm for convenience based on this.
That's what I did.

For convenience, the degree of crystallinity on the front and back surfaces of the PAT foam sheet is measured as follows. First, peel off the 150μ thick surface or back surface, leave the rest as the center, and divide the entire foam sheet into three parts. The crystallinity of the thus obtained front surface portion or back surface portion is measured separately by the above-mentioned thermal method, and the crystallinity degree of each portion is calculated.

In fact, differential scanning calorimetry is preferably used to measure the heat of cold crystallization and heat of fusion of the PAT foam. In differential scanning calorimetry, the heaters for the measurement sample and the standard sample operate independently, and when a temperature difference occurs between them during the constant-rate heating process, the heat flow increase or suppression mechanism for one of them automatically operates. This cancels out this difference, so this difference in heat flow velocity is directly recorded. The degree of crystallinity is theoretically calculated according to the following formula.

(Heat of fusion per mole - Heat of cold crystallization per mole) ÷ Heat of fusion per mole of perfectly crystalline PAT x 100
= Crystallinity (%) Here, since the heat of fusion per mole of fully crystalline PAT is 26.9 KJ according to the Polymer Data Handbook (published by Baifukan), this value will be used.

If the degree of crystallinity is measured by a thermal method, the degree of crystallinity can be accurately measured to one decimal place when expressed in %. More specifically, the degree of crystallinity can be measured with an accuracy of ±0.2%. Therefore, a difference of 1% in crystallinity can be reliably measured, and thereby the difference in properties between the front and back surfaces can be confirmed.

The difference in properties between the front and back surfaces can be more clearly observed when there is a difference in crystallinity of 5% or more between the two surfaces. Further, the difference in crystallinity is also related to the absolute value of the crystallinity of both surfaces. Specifically, it is desirable that the degree of crystallinity in the larger portions between the front surface portion and the back portion is 1.1 times or more as compared to the crystallinity degree in the smaller portions.

When there is a difference in crystallinity between the front and back sides as described above, this PAT foam sheet brings various advantages. In other words, a surface with a high degree of crystallinity has the advantage of being rich in heat resistance and rigidity, but has the disadvantage of being inferior in adhesiveness and printability.
A surface with a low degree of crystallinity has opposite advantages and disadvantages, so for example, by molding a container with the surface with a high degree of crystallinity facing inward, the heat resistance of the inner surface can be increased. By improving the printability of the outer surface,
You can make heat-resistant containers with printing.
Also, by applying adhesive to the side with low crystallinity,
By bonding it with other materials, it is possible to create a bonded product with high heat resistance and rigidity on the surface.

The PAT used in this invention can contain various additives. For example, a small amount of talc powder can be included as a foam control agent, and in addition, antistatic agents, pigments, and flame retardants can be included. In order to improve the melting properties of PAT, acid dianhydrides such as pyromellitic anhydride, epoxy compounds such as diglycidyl terephthalate, oxides of metals belonging to groups a and a of the periodic table, and carbonic acid Sodium etc. can be contained alone or in combination. The amount of these additives is 0.5-5% by weight
within the range of

(Effect of the invention) In this invention, the thickness of the PAT foam sheet is 0.5 mm.
Based on the above, the PAT foam sheet according to the present invention can be easily manufactured by the extrusion foaming method, and by changing the degree of cooling between the front and back surfaces during the manufacturing process. . Furthermore, since the thickness is set to 0.5 mm or more, the crystallinity degree of both parts can be easily measured by peeling off the front part and the back part. Additionally, P.A.T.
When the degree of crystallinity is high, it has the advantage of being excellent in heat resistance and rigidity, but it has the disadvantage of being inferior in anti-surface adhesion and printability. However, in this invention, since the degree of crystallinity is made to differ by 1% or more between the front and back surfaces, it has the above-mentioned advantages and disadvantages on the one hand. ,
On the other hand, PAT has opposite advantages and disadvantages.
A foam sheet is obtained. Therefore, by taking advantage of these strengths and weaknesses, it is possible to create products with unprecedented characteristics. For example, as mentioned above, by making a container with a heat-resistant and rigid surface on the inside, you can create a distinctive container with a heat-resistant and rigid inner surface and an outer surface that is highly printable. be able to. In this respect, the PAT foam sheet according to the invention offers significant benefits.

(Example) The advantages of the present invention will be specifically explained with reference to Examples. In the following, the term "part" simply means part by weight.

Example (Manufacture of foamed PET sheet) Polyethylene terephthalate (hereinafter referred to as PET) pellets (manufactured by Teijin Ltd., TR8580) with an intrinsic viscosity of 0.81 were used as PAT, and the pellets were heated at -
It was dried for 5 hours with hot air at 30°C and 160°C. Then, 0.3 parts of pyromellitic anhydride was added to 100 parts of PET.
0.1 part of sodium carbonate and 0.6 part of talc powder were mixed, the mixture was thoroughly mixed in a tumbler, and then the mixture was put into an extruder.

In the extruder, the cylinder temperature was maintained at 274-287°C, 1.0 part of butane as a blowing agent was injected into the extruder, and the blowing agent-containing PET was extruded from the die with the die temperature set at 277°C.

The die has an annular extrusion hole, and the extrusion hole has a slit width of 0.4 mm and an inner diameter of 60 mm. The PET extruded from the extrusion hole was foamed and passed on a cooling mandrel, and the inner surface was brought into contact with the mandrel and rapidly cooled, but the outer surface was allowed to cool naturally in the atmosphere at 25°C. Cooling water was circulated inside the mandrel to maintain the surface at 20°C.

After passing through a mandrel, the foamed PET sheet was cut into a cylindrical shape and rolled up into a flat sheet. The obtained foam sheet is
The density was 0.262 g/m ³ , the thickness was 1.45 mm, and the width was 640 mm. From the surface of the foam sheet that was in contact with the mandrel (hereinafter referred to as the back surface), approximately
A 150μ thick skin was peeled off and its crystallinity was measured. Its crystallinity was 9.7%. On the other hand, a layer approximately 150 μ thick was removed from the opposite surface of the foam sheet (hereinafter referred to as the surface) and its crystallinity was measured, and the crystallinity was 14.0%.

(Adhesiveness of foamed PET sheet) A PET film was laminated to the PET foamed sheet obtained above, and surface adhesion was examined. As the PET film, a 50μ thick film (FFL) manufactured by Teijin was used.

First, the above film was layered on the back side of a PET foam sheet, and the film was sandwiched between a pair of rolls and bonded together.
At that time, the roll temperature was set to room temperature on the foam sheet side and 135°C on the film side, and the roll was passed between the rolls at a speed of 3.6 m/min. Next, the above film was layered on the surface of the PET foam sheet and bonded in the same manner.

The peel strength of the bonded film was measured in this way. Measurement is specified in JIS K 6301
The test was conducted in accordance with the 90 degree peel test. The width of the test piece at that time was 25 mm. Peeling load on the back side is 3.73
Kgf, and it did not come off even if I rubbed it with my finger or a sharp blade. On the other hand, the peeling load on the surface was 0.4 kgf, and it was easily peeled off when rubbed from above with a finger. This results in a crystallinity of 9.7%.
It was confirmed that when there was a difference of 14.0%, there was a large difference in adhesion.

Claims (1)

[Claims] 1 A foamed sheet of thermoplastic polyester resin with a thickness of 0.5 mm or more, the front and back sides of the sheet have different degrees of crystallinity, and the average crystallinity of both sides is 1.
A foamed sheet of thermoplastic polyester resin, characterized by a difference of at least %.