Method for producing a foamed granulate and use thereof

Abstract

The invention relates to a method in which a polyester melt containing one or more polyesters is produced, the polyester melt being foamed by a blowing agent and a foamed granulate is produced from the foamed polyester melt. The intrinsic viscosity (IV) of the polyester melt is reduced by the blowing agent about at least 0.05 dl/g, measured according to ASTM D4603, and the IV of the foamed granulate is then increased by means of a solid phase polycondensation (SSP).

Claims

1. A method, comprising; producing a polyester melt containing one or more polyesters; foaming the polyester melt with a blowing agent, the foaming of the polyester melt taking place in an extruder of a recycling plant; and producing a foamed granulate from the foamed polyester melt, wherein an intrinsic viscosity (IV) of the polyester melt is reduced by the blowing agent by at least 0.05 dl/g, measured according to ASTM D4603; and increasing the IV of the foamed granulate by subjecting the foamed granulate to solid phase polycondensation (SSP).

2. The method according to claim 1, wherein the blowing agent splits off water or another molecule with a mass less than 200 Daltons in the polyester melt.

3. The method according to claim 1, wherein an injection molding machine is used to process a polymer mass comprising at least 1 percent by weight of the foamed granulate to produce a preform or a container from the polymer mass and the foamed granulate with the injection molding machine.

4. The method according to claim 3, wherein the polymer mass comprises between 1 percent and 10 percent of the foamed granulate and as a result produces a white coloration in the container.

5. The method according to claim 3, wherein the polymer mass comprises between 1 percent and 10 percent of the foamed granulate and as a result produces a white container.

6. The method according to claim 3, wherein the blowing agent comprises between 1 percent and 5 percent by weight of the foamed polyester melt.

7. The method according to claim 1, wherein the polyester melt has an IV of at least 0.6 dl/g, measured according to ASTM D4603, prior to foaming.

8. The method according to claim 1, wherein the IV of the foamed granulate is increased by more than 0.05 dl/g, measured according to ASTM D4603, by means of the SSP.

9. The method according to claim 1, wherein the one or more polyesters in the polyester melt comprise recycled polymer of least 80 percent by weight, 90 percent by weight or substantially 100 percent by weight.

10. The method according to claim 1, wherein the polyester melt comprises at least 85 percent by weight of the one or more polyesters from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), polylactic acid (PLA), glycol-modified polyethylene terephthalate (PET-G), polypropylene furanoate (PPF), or copolymers of said one or more polyesters.

11. The method according to claim 1, wherein the one or more polyesters in the polyester melt comprise PET, wherein the material density of the foamed granulate, measured according to ASTM D1505-10, is less than 1.33 g/cm.sup.3 after the SSP.

12. The method according to claim 1, wherein a material density of the foamed granulate, measured according to ASTM D1505-10, is higher than 0.8 g/cm.sup.3 after the SSP.

13. The method according to claim 1, wherein the blowing agent is a chemical blowing agent splitting off a reactive molecular structure having a molecular weight of less than 200 Daltons.

14. The method according to any one of claim 1, wherein the chemical blowing agent has nucleating agents for cell formation.

15. The method according to claim 1, wherein the blowing agent contains one or more of sodium bicarbonate, potassium bicarbonate, disodium dihydrogen diphosphate, monocalcium orthophosphate, citric acid, or citric acid derivatives.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a flow chart illustrating a method of the invention.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

(2) FIG. 1 shows a flow chart. In a first step, only PET industrial waste from bottle production and PET flakes from post-consumer products as for example used PET bottles is fed to an extruder 1. At the same time, a masterbatch is fed to this polyester material, to which a blowing agent is added such as sodium bicarbonate and/or potassium hydrogen carbonate and/or disodium dihydrogen diphosphate and/or monocalcium orthophosphate and/or citric acid and/or citric acid derivatives. The weight proportion of the chemical blowing agent at the masterbatch is 40% in the present embodiment. The weight proportion of the masterbatch to the polyester melt is about 3% in the present example. By the extrusion process in the extruder 1, the fed material is melted to a polyester melt, wherein the weight proportion of one or more polyesters is at least 85%. The polyester or the polyesters consist of the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), polylactic acid (PLA), glycol-modified polyethylene terephthalate (PET-G), polypropylene furanoate (PPF) and copolymers of said polyesters. The chemical blowing agent acts as a nucleating agent for forming cells. Thus, when the polyester is molten, the chemical blowing agent reacts with the polyester melt and foams it. Prior to foaming, the polyester melt has an intrinsic viscosity of at least 0.6 dl/g, measured according to ASTM D4603. The intrinsic viscosity of the polyester melt is reduced by the blowing agent by at least 0.05 dl/g, measured according to ASTM D4603. The foamed polyester melt is formed into strands via nozzles and cooled in air or water. Subsequently, a rotating knife 2 cuts the strands into sections having a length of a few millimeters, the so-called granulate, which is foamed in the present embodiment and is present as spherical granulate. The foamed spherical granulate is fed, for condensation, to a solid phase condenser 3, which is also called Solid State Reactor (SSP) and which is located in a recycling plant. This increases the intrinsic viscosity. The intrinsic viscosity can be increased to about 1.6 dl/g, measured according to ASTM D4603, depending on the desired field of use. For the production of preforms, from which containers are blown or stretch blown in a second step, the intrinsic viscosity is increased to about 0.9 dl/g, measured according to ASTM D4603. The material density of the foamed spherical granulate is lower than 1.33 g/cm.sup.3 and higher than 0.8 g/cm.sup.3, measured according to ASTM D1505-19. It is understood that the foamed granulate can be food safe. The foamed granulate is transported to plants 6A, 6B, 6C processing polyester granulate. This is illustrated by the stylized truck 4, of which three arrows 5A, 5B, 5C point to these plants 6A, 6B, 6C. If necessary, unfoamed granulate can be added to the foamed granulate in the plants or also at the producer of the foamed granulate. Films can be produced in the plants, from which stretched end products can also be produced, as for example deep-drawn trays. The production of window profiles, pipes or deep-drawn sheets is possible. For example, containers are produced in the plant 6B. By means of an extruder 7A and a tool, not shown, preforms are produced, which are stretch blow molded in tools 8A, 8B, 8C of three stretch blow molding machines to containers, respectively bottles 9, which are subsequently supplied to a filling plant, not shown, for filling. By means of the extruder 7B, a hose is blown from granulate, which contains at least 1 percent by weight of foamed granulate, from which a container, such as a bottle, is extrusion-blown. By means of the extruder 7C, two different manufacturing methods for containers are to be symbolized. On the one hand, the containers are produced in an injection molding. On the other hand, injection molded parts are produced by injection molding, of which a predetermined range is blown. The containers manufactured with the different methods have an opaque white color and a wall bounding the container is permeable to a radiation incident on the container having a wavelength of 400 to 720 nm for a maximum of 30% or 40% or 50% of the incident radiation. Thus, by means of the containers, which are manufactured of foamed polyester granulate, the filling material can be protected from radiation. Certain ingredients of a product such as vitamin B2 (riboflavin), which is e.g. contained in the milk or in beer, can affect the taste of the product negatively when exposed to light. Protection against radiation in the wavelength range of 250 to 500 or 550 nm is particularly useful in this context. Thus, from foamed granulate, which may be obtained from PET recycling material, opaque white containers can be produced which prolong the shelf life of light-sensitive beverages without supplying such bottles with the previously used titanium oxide as a pigment. Due to the absence of this pigment, the bottles can easily be recycled after their use and thus be re-supplied to the described process.