Field of the invention

The invention relates to the field of chemistry and polymer in relation to the development of purging compound for cleaning said plastic processing machine, e.g. plastic molding machine and mixing machine.

Background of the invention

In the production of plastic parts in many industries, e.g. flexible packaging, container, cap, medical, automotive or custom molders. There is a large amount of waste products or defects occurred during machine cleaning when changing plastic materials and coloring agents or routine maintenance. This problem leads plastic manufacturer to a loss of material, a decrease in manufacturing efficiency, and also affect to the manufacturer’s profitability. In the past, cleaning of the plastic processing machine; extruder screw, barrel, breaker plate, and die between production runs was done by clearing the extruder to empty the hopper, screw and barrel, then fudging with the plastic resin which required plenty of materials before all parts can be clean. Mostly, the trapped color or black speck occurred from carbon buildup cannot be clean from the barrel and screw. Thus, it generates lots of scrap and off-spec products cause wasted materials and non-productive time, especially in case that require the operators to breakdown the machine for manual cleaning. Therefore, many options including development of purging compounds and methods of cleaning the barrel have attracted much attention in the present.

Recent developed purging compounds were categorized to three primary types. The first type, mechanical purging compound which is effective across a wide variety of applications, rely on shear force from the machine’s power and differences in material viscosities. The mechanical type sometime consists of an abrasive material e.g. glass fiber, clay, calcium or talcum. The second type, chemical purging compound is a liquid or solid compound which can be effective in areas of low pressure where mechanical purges are sometime less effective, there is a chemical reaction occurs in the barrel or die to shorten the molecular chain of the residual resin, thus normally require soaking in the barrel for a specific period of time. The last type, hybrid purging compound which is the combination between mechanical and chemical purging compounds.

Many purging compounds are commercially available. This help the manufacturer to reduce the defects, e.g. black specks, minimize the time for cleaning screw and barrel, and no need the machine disassembly. However, some purging compounds, especially mechanical type purging compound, cause an aggressive scouring to the screw and barrel by abrasive fillers in the formulation. Some purging compounds take long soaking time and may generate some smoke and/or odor from low molecular weight or thermally unstable components while using with high processing temperature which may be unsafe to an operator. The manufacturer should select the appropriate purging compound to use with their process materials and types of machine; e.g. blow molding machine; injection molding; pipe, sheet, or profile extrusion machine. The research and development of purging compound with higher efficiency, low smoke, odor free, and economical applications have been mentioned in several patent documents. Some examples are as follows:

The first example, U.S. patent application no. US20160101553A1, wherein the title of invention is “process for cleaning melt processing equipment”, discloses a process for cleaning melt processing equipment comprising at least 75 wt% of polyethylene having a viscosity number from 300 to 3,500 ml/g and an average particle size, d50, from 50 to 1000 micron, heating the melt processing equipment to a temperature sufficient to allow the purge material to be extruded through the equipment, and running the equipment to extrude the purge material while cleaning the melt processing equipment.

The second example, U.S. patent application no. US6022420A, wherein the title of invention is “purge compound for removal of residual plastic resin from extruder consists of fluoropolymer particles”, describes the process of purging an extruder of thermoplastic resin after an extrusion run by passing a purging compound through the extruder, said extruder containing a residual thermoplastic resin to be purged, the improvement comprising carrying out said passing with the extruder being at a passing temperature and wherein said purging compound is fluoropolymer particles, the fluoropolymer of said particles being non-melt flowing at said passing temperature.

According to the patent document disclosed above, the research and development exist for a purging compound composition with no reaction that require time for soaking, low smoke and odor, and economical application in melt processing of plastic resin, while improve efficiency for cleaning impurities or any residuals in the screw and barrel.

Summary of the invention

The present invention relates to the development of purging compound for cleaning plastic processing machine wherein the purging compound comprising of virgin thermoplastic polymer and fluoropolymer component 0.1 -5.0% by weight of purging compound. According to one aspect of the invention, the virgin thermoplastic polymer is selected from low-density polyethylene, high-density polyethylene, ultrahigh molecular weight polymer, or combination thereof. The ultrahigh molecular weight polymer in the present invention having a molecular weight from 1-10 Million g/mol.

In one embodiment, the most preferred virgin thermoplastic polymer comprises of low- density polyethylene 55-76% by weight, high-density polyethylene 19-25% by weight, and ultrahigh molecular weight polymer 5-20% by weight of purging compound.

The objective of the invention is to develop purging compound that works well with low smoke and odor at the temperature range of 160-350 degree Celsius and can be used with the cleaning of various types of plastic resin, e.g. low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene resin (LLDPE), polypropylene (PP), polyacrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA) or polybutylene succinate (PBS) to clean industrial plastic processing machine that are chosen from extrusion machine, injection machine, or blow molding machine.

Detailed description of the invention

The invention relates to the development of purging compound that works well with low smoke and odor at the temperature range of 160-350 degree Celsius to clean the plastic processing machine that are chosen from extrusion machine, injection machine, or blow molding machine. The purging compound from the present invention can be used with the cleaning of various type of plastic resin, e.g. low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene resin (LLDPE), polypropylene (PP), polyacrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA) or polybutylene succinate (PBS).

According to the present invention, the purging compound is comprising of virgin thermoplastic polymer and fluoropolymer component 0.1-5.0% by weight of purging compound, wherein said virgin thermoplastic polymer comprising of low-density polyethylene 55-76% by weight, high-density polyethylene 19-25% by weight, and ultrahigh molecular weight polymer 5- 20% by weight of purging compound.

According to one preferred embodiment of the present invention, the ultrahigh molecular weight polymer can be an ultrahigh molecular weight polyethylene (UHMWPE) in powder form which has high abrasion resistance and low coefficient of friction properties. An average molecular weight of UHMWPE can be chosen from 1-10 Million g/mol, for example from 3.2-6.0 Million g/mol.

According to another preferred embodiment of the present invention, the fluoropolymer can be a fluoro elastomer which is small molecule that can penetrate between impurity and screw or barrel resulting in better cleaning efficiency. The suitable composition of the fluoropolymer used herein is 1.5-3.0% by weight of purging compound.

According to another preferred embodiment of the present invention, the mixture of LDP E and HDPE, and the mixture between powder of UHMWPE and fluoropolymer component are mixed using tumbler mixer before compounding for better mixing performance. The purging compound is prepared by twin screw extruder wherein the plastic mixture of LDPE and HDPE is separatel fed via the main feeder, while the mixture between powder of UHMWPE and fluoropol mer component is fed via side feeder to allow more accurate quantit control of the elements.

According to another embodiment of the present invention, inorganic filler can be comprised in the purging compound formulation for cost reduction purpose. The inorganic filler is preferably chosen from magnesium carbonate (MgCCb), calcium carbonate (CaCC>3), talcum, calcium sulphate (CaSCfr), barium sulfate (BaSCL), silica, alumina, or nanoclay; and wherein the inorganic filler provides good efficienc for cleaning of plastic processing machine. The suitable ratio of said inorganic filler is 0.1-10% by weight of purging compound. The preferred size of inorganic filler is 2 micrometers, and the most preferred inorganic filler according to the present invention is calcium carbonate.

According to another preferred embodiment of the present invention, tais&v extruder used for preparation of the purging compound is specially set up to its best condition, i.e. extruder temperature of 80-230 degree Celsius, by increasing temperature of extruder from hopper to nozzle, and screw speed of 120 round per minutes (rpm) for good results.

According to another preferred em odiment of the present invention, the process for preparation of purging compound according to the present invention is done by following steps:

1. Weighing the specified chemical compounds into twin screw extruder wherein:

1.1. The mixture of LDPE and HDPE is mixed using tumbler mixer, and separately fed via main feeder. 1.2. The mixture between powder of UHMWPE and fluoropolymer component are mixed using tumbler mixer, and separately fed via side feeder.

2. Specifically setting up twin screw extruder, i.e. extruder temperature of 80-230 degree Celsius, by increasing temperature of extruder from hopper to nozzle, and screw speed of 120 round per minutes (rpm).

3. Cooling down said purging compound derived from twin screw extruder by rinse with water and cut them into 2-4 millimeters.

It is intended that other embodiments of purging compound for cleaning plastic processing machine are not limited by the present invention. The following examples are just one embodiment of the present invention wherein the chemicals or other ratios known by those skilled in the art as the same kind of chemicals or providing the same results are not limited by the present invention, and wherein the improvement or modification may be carried out as long as it is under the claims of the present invention.

Example 1 The preparation of different formula of purging compound with various mixing ratio. The purging compounds with various mixing ratio are prepared by saidpreparationprocess according to one of preferred embodiment of the present invention to investigate the effect on cleaning efficiency of the plastic processing machine, i.e. injection molding machine. The formula of purging compound with various mixing ratio are shown in table 1.

Table 1. Shows the formula of purging compound with various mixing ratio. Example 2. The melt flow rate (MFR) of purging compound for cleaning plastic processing machine according to the present invention for various temperature.

In an initial set of tests, melt flow rate (MFR, g/10 min of the purging compound with various mixing ratio derived from Example 1 was determined by condition ASTM D-1238 for various temperature from 200-320 degree Celsius. The results are shown in figure 1.

According to the results in figure 1. the MFR of the purging compound is decrease with increasing composition of HOPE and UHMWPE. On the other hand, an increasing amount of fluoropolymer component increases the MFR of the purging compound. While molecular weight of UHMWPE shows minor effect to the viscosity (or MFR) of the purging compound.

Efficiency evaluation of the purging compound with various mixing ratio derived from Example 1 is performed by cleaning of contaminate in an injection molding machine. The injection molding machine of the size 65 tons, namely “Battenfeld HM65”, was used wherein the purging compound is injected into the mold to control test environment at a similar stage. The mold is rectangular shape with 101.6 millimeters width x 152.4 millimeters length x 3.175 millimeters thickness. The efficiency evaluation procedure by injection molding machine is as following steps:

1. Set temperature of barrel all zone at evaluation’s temperature

2. Prepare contaminate by dry blend simulant with black masterbatch

3. Then feed 500 g of contaminate into injection molding machine and purge all of residual contaminate to empty the barrel

4. Feed purging compound into hopper

5. Inject purging compound into mold until the sample is continued perfect clean (without any black spots) 3 shots, then record a number of shot (including 3 perfect clean shots) and weight it all which is called “1 ^st PURGE”.

6. Purge all of residual purging compound to empty the barrel again

7. Feed simulant into hopper

8. Start inject simulant into mold until a sample is continued perfect clean (without any purging compound) 5 shots, then record number of shot (including 5 perfect clean shots) and weight it all which is called “2 ^nd PURGE”.

Example 3 The efficiency evaluation of purging compound for cleaning plastic processing machine according to the present invention by using polypropylene (PP) as a simulant. Efficiency evaluation of the purging compound with various mixing ratio derived from Example 1 for cleaning of PP simulant is performed by cleaning of mimicked contaminate PP, prepared by dry blend PP simulant 99% by weight with black masterbatch 1% by weight, by injection molding machine. The injection temperature is set to 230 degree Celsius and injection speed is 50 rpm.

The efficiency evaluation is compared the total weight of purging material, which is sum of weight of purging compound (1 ^st PURGE) and weight of PP simulant (2 ^nd PURGE) used until a sample is perfect clean. The efficiency of purging compound is compared to commercial pelletized purging compound. Test results are shown in table 2. Table 2. Shows the MFR and weight of purging compound used to clean the mold of injection molding machine by using polypropylene (PP) as a simulant at 230 degree Celsius.

According to the test result shown in table 2, it is obvious that it requires less purging compound of formula 1-7 from Example 1 according to the present invention, thus, it also requires less time for cleaning the plastic processing machine than using the commercial purging compound. It signifies that purging compound for cleaning plastic processing machine according to the present invention is more efficient than the compared commercial purging compound. Moreover, the advantage of using purging compound according to the present invention is no smoke generate at the recommended temperature along the process for cleaning plastic processing machine.

Compare between difference mixing ratio, formula 8 that has inorganic filler content shows quite low efficiency for 2 ^nd purge due to the particles of inorganic filler were distributed in the simulant and difficult to clean from the mold of injection machine than other formula. For other formula without inorganic filler, it clearly shows that the formula which blend with HOPE can clean the mold of injection molding machine with higher efficiency than the formula with LDPE alone, and the efficiency of cleaning is strongly depend on viscosity of the purging compound wherein the purging compound with higher viscosity (lower MFR) show higher cleaning efficiency (lower total weight of purging material) to clean the mold o f inj ection molding machine by using PP as a simulant.

Example 4 The efficiency evaluation of purging compound for cleaning plastic processing machine according to the present invention by using polyacrylonitrile-butadiene-styrene (ABS) as a simulant. Efficiency evaluation of the purging compound with various mixing ratio derived from

Example 1 for cleaning of ABS simulant is performed by cleaning of mimicked contaminate ABS, prepared by dry blend ABS simulant 99% by weight with black masterbatch 1% by weight, by injection molding machine. The injection temperature is set to 320 degree Celsius and injection speed is 50 rpm. Similar to Example 3 , the efficiency evaluation is compared the total weight of purging material, which is sum of weight of purging compound (1 ^st PURGE) and weight of ABS simulant (2 ^nd PURGE) used until a sample is perfect clean. The efficiency of purging compound is compared to commercial pelletized purging compound. Test results are shown in table 3.

Table 3. Shows the MFR and weight of purging compound used to clean the mold of injection molding machine by using polyacrylonitrile-butadiene-styrene (ABS) as a simulant at 320 degree Celsius.

According to the test result shown in table 3 , similar results with Example 3 , formula 8 that has too high inorganic filler content shows quite low efficiency to clean from the mold of injection machine than other formula. For other formula without inorganic filler, it is obvious that commercial pu ging compound used as compared reference in the experiments cannot clean the mimic ed contaminate ABS at the recommended temperature which normally use for injection of ABS, while suitable mixing ratio as Formula 3 shows best cleaning efficiency compared to all formula. On the other hand, the total weight of purging material which referred to efficiency of cleaning is not depend on viscosity of the purging compound but strongly depend on an amount of fluoropolymer. In this case, the higher amount of fluoropolymer, the higher efficiency for cleaning of ABS from the mold of injection molding machine at the recommended temperature. Moreover, there is low/no smoke generate at quite high temperature along the process for cleaning ABS from the mold of injection molding mac ine.

Example 5 The efficiency evaluation of purging compound for cleaning plastic processin machine according to the present invention by using polylactic acid (PLA) and polybutylene succinate (PBS) as a simulant.

In order to observe efficiency of the purging compound for cleaning of biopolymer, PLA and PBS are use as representative simulants. The purging compound formula 5, which has high efficiency regarding to the test results from Example 2 to 4, is applied for cleaning of mimicked contaminate PLA and PBS. The mimicked contaminate prepares by dry blend simulant 99% by weight with black masterbatch 1% by weight. The efficiency evaluation is performed by injection machine which injection temperature is set to 230 degree Celsius and injection speed is 50 rpm. Test results confirmed that the purging compound according to the present inven ion has high efficiency for cleaning various kind of simulant as shown in table 4. Table 4. Shows the MFR and weight of purging compound used to clean the mold of injection molding machine by using various simulants.

It is intended that the scope o f the present invention herein disclosed should not b e limited by the particular disclosed embodiments of purging compound for cleaning processing machine and preparation of purging compound for cleaning plastic processing machine described above. Any other modifications or changes can be made and considered being within the scope of the present invention.

Best mode of the invention

In accordance with the detailed description of the invention.