KR20230078138A - Foam sheet having improved contraction percentage - Google Patents

Abstract

The present invention relates to a foam sheet with improved shrinkage, and provides a foam sheet with a crystallinity of 4 to 10% and machine direction (MD) shrinkage of 8% or less after heat treatment at 200℃ for 60 seconds. According to the present invention, the shrinkage of the foam sheet can be improved by controlling crystallinity, density, thickness, cooling conditions, etc.

Description

Foam sheet having improved contraction percentage}

The present invention relates to a foam sheet, and more particularly to a foam sheet having improved shrinkage.

Polyester, as an eco-friendly material, has excellent mechanical properties and excellent heat resistance and chemical resistance, so it can be used in various fields requiring light weight and high physical properties. Polyester resin has excellent mechanical and chemical properties, so it can be used for many purposes, such as drinking water containers, medical supplies, food packaging, food containers, sheets, films, automobile molded products, etc. this is being done

As a representative polyester resin, a polyethylene terephthalate resin polymerized using terephthalic acid as a dicarboxylic acid component and ethylene glycol as a glycol component may be cited as an example, and is widely used due to its excellent physical and chemical properties and dimensional stability.

However, polyethylene terephthalate resin has a problem of poor processability due to its crystallinity, and there is a limit to improving light weight due to high process temperature when manufactured into a foam. Accordingly, efforts to expand the utilization by improving the physical properties of polyester resins are being made in various ways, but the polyester resins developed to date have a problem in that the control of thermal properties is not easy.

Therefore, it is necessary to develop a foam sheet having excellent physical properties while using a polyester resin.

An object of the present invention is to provide a foam sheet with improved shrinkage and a manufacturing method thereof.

In order to achieve the above object, the present invention provides a foam sheet having a crystallinity of 4 to 10% and MD (Machine Direction) shrinkage after heat treatment at 200° C. for 60 seconds of 8% or less.

The foam sheet according to the present invention may have a density of 10 to 800 kg/m 3 .

The foam sheet according to the present invention may have a thickness of 0.5 to 5 mm.

The difference between MD shrinkage and TD (Transverse Direction) shrinkage of the foam sheet according to the present invention may be 2 times or less or 3% or less.

In addition, the present invention comprises the steps of foaming the foaming composition in the form of a sheet; and cooling the foamed sheet using a mandrel and an air ring.

In the present invention, the air velocity of the air ring may be 2 to 16 m/sec.

In the present invention, the cooling temperature of the mandrel may be 5 to 15 ° C.

In the present invention, the air temperature of the air ring may be 2 to 20 ° C.

In the present invention, the cooling time may be 10 minutes or less.

According to the present invention, the shrinkage rate of the foam sheet can be improved by controlling the crystallinity, density, thickness, cooling conditions, and the like.

1 is a graph showing the shrinkage rate according to the density and thickness of the foam sheet.
Figure 2 is a graph showing the difference in shrinkage rate according to the air ring wind speed.

Hereinafter, the present invention will be described in detail.

The present invention relates to a foam sheet having improved surface roughness. Foam sheet according to the present invention is characterized in that the crystallinity is 4 to 10%, and the MD (Machine Direction) shrinkage rate after heat treatment at 200 ° C. for 60 seconds is 8% or less. The shrinkage rate may refer to the export rate at the time of post-foaming.

MD shrinkage may vary depending on the degree of crystallinity, density and thickness of the foam sheet. A foam sheet with a high degree of crystallinity has a low shrinkage rate. This is because one of the main causes of shrinkage is crystallization upon heating. For example, the range of MD shrinkage of the high-crystallization degree foam sheet may be 0 to 2%. In this case, the high-crystallization degree foam sheet may mean a foam sheet having a crystallinity of more than 10%. The crystallinity of the high-crystallization degree foam sheet may be specifically 10.1 to 35%, 10.5 to 34.5%, 11 to 34%, 11.5 to 33.5%, 12 to 33%, 13 to 22% or 15 to 30%.

However, the high-crystallinity foam sheet has a low foaming rate, and especially has a post-foaming rate of 1 to 1.2 times, making it difficult to realize the properties of the foam sheet. This is because when the crystallinity is high, post-foaming also decreases due to the decrease in molecular structure movement. Therefore, a high-crystallization degree foam sheet is unsuitable as a foam sheet.

On the other hand, a foam seat|seet with a low degree of crystallinity has a high shrinkage rate. Instead, it has a high expansion rate, so it is suitable as a foam sheet.

Accordingly, the present invention is characterized by providing a foam sheet having a high foaming rate and a low shrinkage rate by applying a low-crystallization degree foam sheet having a low crystallinity.

The crystallinity of the low-crystallization degree foam sheet used in the present invention may be 10% or less, specifically 4 to 10%, 5 to 9%, 6 to 8%, 4 to 6% or 7 to 10%. If the crystallinity is too low, physical properties such as heat resistance may be deteriorated. MD shrinkage of the low-crystallization degree foam sheet having a crystallinity within this range may be 8% or less, specifically 0.1 to 8%, 0.2 to 7%, 0.3 to 6%, 0.4 to 5%, or 0.5 to 4.7%. . As described above, physical properties suitable for the foam sheet are 10% or less in crystallinity and 8% or less in MD shrinkage. A foam sheet having crystallinity and shrinkage within these ranges may have good formability and good processability.

During post-foaming of the sheet, the sheet may shrink in MD and TD (Transverse Direction) directions. The shrinkage rate at this time is lower as the density and crystallinity of the sheet are higher. In particular, if the density is low, more shrinkage may occur. For example, at 200° C. or lower, the high-density foam sheet may have little difference in shrinkage rate, and the low-density foam sheet may increase the shrinkage rate. Therefore, by setting an appropriate density, the effect of reducing the shrinkage rate of the low-density foam sheet can be obtained.

The density of the foam sheet is 10 to 800 kg/m3, 30 to 750 kg/m3, 50 to 700 kg/m3, 70 to 650 kg/m3, 100 to 600 kg/m3, 120 to 550 kg/m3, 150 to 500 kg/m3, or 170 to 450 kg/m3. If the density is too low, the shrinkage rate may increase and the foam sheet may break. If the density is too high, it may be difficult to implement the characteristics of the foam sheet due to the low foaming rate.

The foam sheet may have a thickness of 0.5 to 5 mm, 0.6 to 4 mm, 0.8 to 3 mm, or 1 to 2 mm. If the thickness is too thin, the shrinkage rate may increase and the foam sheet may break. If the thickness is too thick, the price may increase and molding may be difficult. Generally, the thicker the sheet, the less stretched it is, the higher the density, and the lower the shrinkage tends to be.

The difference between MD shrinkage and TD shrinkage of the foam sheet may be 2 times or less, preferably 3% or less, 0 to 2.7%, 0 to 1.8%, or 0 to 0.9%. The difference between the MD shrinkage rate and the TD shrinkage rate can be controlled by the cooling conditions of the cooling step during the manufacturing process of the foam sheet, specifically, the air velocity of the air ring, the cooling temperature of the mandrel, the air temperature of the air ring, and the cooling time.

In addition, the present invention comprises the steps of foaming the foaming composition in the form of a sheet; and cooling the foamed sheet using a mandrel and an air ring.

First, in the foaming step, the foaming composition is foamed into a sheet form. The foam sheet may have a single-layer structure or a multi-layer structure, and may include a non-foam layer. The foam sheet may be formed from a foam composition containing a resin, a thickener, a nucleating agent, a foaming agent, and the like.

As resin, a polyester resin etc. can be used, for example. Examples of the polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polylactic acid (PLA), polyglycolic acid (PGA), polyethylene adipate (PEA), and polyhydroxyalkanoate. (PHA), polytrimethylene terephthalate (PTT), and polyethylene naphthalene (PEN) may be used, and preferably polyethylene terephthalate (PET) may be used. By using PET resin, it is environmentally friendly and can be easily reused.

The thickener is added to control the melt viscosity of the foam composition, and for example, pyromellitic dianhydride (PMDA) and the like can be used.

A nucleating agent is used to control the cell density, for example, talc, mica, silica, diatomaceous earth, alumina, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, Inorganic compounds such as magnesium carbonate, potassium sulfate, barium sulfate, sodium hydrogen carbonate and glass beads can be used.

A foaming agent is added to foam the composition and control the density of the foam sheet, for example, gases such as N ₂ , CO ₂ , Freon; physical blowing agents such as butane, pentane, neopentane, hexane, isohexane, heptane, isoheptane, and methyl chloride; Chemical blowing agents such as azodicarbonamide-based compounds, P,P'-oxybis(benzenesulfonylhydrazide)-based compounds, and N,N'-dinitrosopentamethylenetetraamine-based compounds may be used.

The foamed resin composition may use 0.1 to 3 parts by weight of a foaming agent, a thickener, and a nucleating agent, each independently, based on 100 parts by weight of the resin.

In addition, the foam composition is a surfactant, a sunscreen, a hydrophilizing agent, a flame retardant, a heat stabilizer, a waterproofing agent, a cell size expander, an infrared attenuator, Plasticizers, fire retardant chemicals, pigments, elastomers, extrusion aids, antioxidants, fillers, antistatic agents, UV absorbers and the like may be further included.

The foam sheet may be formed through bead foaming or extrusion foaming. Bead foaming is a method of making a product by first foaming by heating beads, aging them for an appropriate time, filling them into plate-shaped or cylindrical molds, and heating them again to fuse and mold them by secondary foaming. Extrusion foaming continuously extrudes and foams a resin melt, thereby simplifying process steps, enabling mass production, and realizing better compressive strength by preventing cracks between beads and granular breakage during bead foaming. can

Next, in the cooling step, the foamed sheet is cooled using a mandrel and an air ring. The mandrel and the air ring correspond to a cooling device, and cool the sheet foamed from the foaming device. In particular, the air ring is introduced to reduce the temperature difference between the upper and lower parts of the sheet as the thickness of the sheet increases when the foam sheet is manufactured.

The air velocity of the air ring may be 2 to 16 m/sec, 2 to 15 m/sec, 2 to 12 m/sec, 2 to 9 m/sec, 2 to 6 m/sec, or 2 to 3 m/sec. The difference between the MD shrinkage rate and the TD shrinkage rate may be reduced as the air velocity of the air ring decreases.

The cooling temperature of the mandrel may be 5 to 15 °C, 7 to 13 °C, 9 to 11 °C, 5 to 10 °C or 10 to 15 °C. The air temperature of the air ring may be 2 to 20 °C, 4 to 17 °C, 6 to 15 °C, 8 to 12 °C, 5 to 10 °C or 10 to 15 °C. The cooling time may be 10 minutes or less, 1 to 10 minutes, 2 to 8 minutes, 4 to 6 minutes, 1 to 5 minutes, or 6 to 10 minutes.

Hereinafter, the present invention will be described in more detail by way of examples.

[Example]

100 parts by weight of PET resin, 1 ± 0.5 parts by weight of a thickener (PMDA), 1 ± 0.5 parts by weight of a nucleating agent (talc), 1 ± 0.5 parts by weight of a foaming agent (carbon dioxide or butane), etc. Then, by cooling the foamed sheet using a mandrel and an air ring, a foam sheet having a crystallinity of 4 to 10% was prepared.

[Test Example]

Shrinkage, crystallinity, density, etc. of the foam sheet prepared in Examples were measured.

(1) Shrinkage rate

A foam sheet specimen was cut into a size of 10 cm in width and 10 cm in length, and the shrinkage rate (%) was calculated by Equation 1 below using the difference between the lengths in the MD and TD directions measured under the condition of applying heat at 200 ° C. for 60 seconds. .

[Equation 1]

Shrinkage rate (%) = (length after 60 seconds at 1 - 200℃ / length before applying heat) × 100

(2) Crystallinity

Melting enthalpy at melting temperature and crystallization enthalpy at cooling crystallization temperature were measured using differential scanning calorimetry (DSC), and crystallinity was calculated according to Equation 2 below.

[Equation 2]

Crystallinity = ΔHm - ΔHc / ΔHm

ΔHm means melting enthalpy, ΔHc means crystallization enthalpy, and ΔHm means standard melting enthalpy (140 J/g).

(3) Density

Density was measured under KS M ISO 845 conditions using Alfa Mirage's EW-300SG.

Table 1 and FIG. 1 show post-foaming and shrinkage data, and specifically show the shrinkage rate according to the density and thickness of the foam sheet.

density shrinkage rate 1.0T 2.0T kg/㎥ % % 170 4.7 2.4 200 3.5 2.8 300 2.8 1.7 350 2.5 1.5 450 1.0 0.5

As can be seen from Table 1 and Figure 1, the shrinkage rate decreased as the density increased, and the shrinkage rate decreased as the thickness increased. represents the cooling condition.

wind speed Shrinkage rate difference (MD-TD) Ieast maximum m/s % % 3 0 0.9 6 0 0.9 9 0 1.8 12 0 2.7 15 0 2.7

Mandrel cooling temperature range 5~15℃ air temperature range 2~20℃ cooling time ~10 minutes

As can be seen from Table 2 and FIG. 2, the lower the air ring wind speed, the lower the difference in shrinkage.

Claims (9)

A foam sheet having a crystallinity of 4 to 10% and an MD (Machine Direction) shrinkage rate of 8% or less after heat treatment at 200 ° C. for 60 seconds. According to claim 1,
A foam sheet having a density of 10 to 800 kg/m 3 . According to claim 1,
A foam sheet having a thickness of 0.5 to 5 mm. According to claim 1,
A foam sheet with a difference between MD shrinkage rate and TD (Transverse Direction) shrinkage rate less than 2 times. As a method for producing a foam sheet according to claim 1,
foaming the foaming composition into a sheet form; and
A method for producing a foam sheet comprising the step of cooling the foamed sheet using a mandrel and an air ring. According to claim 5,
The air velocity of the air ring is 2 to 16 m / sec manufacturing method of the foam sheet. According to claim 5,
The cooling temperature of the mandrel is 5 to 15 ℃ manufacturing method of the foam sheet. According to claim 5,
The air temperature of the air ring is a method for producing a foam sheet of 2 to 20 ℃. According to claim 5,
A method for producing a foam sheet having a cooling time of 10 minutes or less.

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