Engineering for Success: The Aqueous Film Coating Process

Transcription

1 Engineering for Success: The Aqueous Film Coating Process A Special Presentation for: The International Society of Pharmaceutical Engineers, Los Angeles Chapter May 12, 2005 Fred A. Rowley Director, Corporate Manufacturing Technical Support Watson Labs., Inc. 1

2 Where Aqueous Coating Fits Into The Big Picture The Aqueous Film Coating Unit Operation Weigh and Screen Materials Wet or Dry Granulate as Required Add Lubricant Blend Materials Compress Tablets Aqueous Film Coating Tablet Printing (Optional) 2

3 Popular Myths About Tablet Coating It is more art than science. Coating pan operators are prima donnas. Water based coating is tricky. Coating solutions are just dyes in water and you can mix them anywhere. 3

4 Aqueous Coating Is Not Like Granulating and Tablet Compressing Aqueous film coating demands: Consistent tablet hardness Controlled spray rates Controlled operating temperature Controlled air flow rates for drying Bad things can happen in seconds. (Or you could end up with this) Popcorn ball 4

5 Our Topics For Today Introduction to Aqueous Film Coating The Coating Room Systems A Review of Coating Installations Around The World Types of Common Pumping Systems Typical Coating Suspension: Component Parts Suspension Preparation How The Coating Process Works Spray Guns: Anatomy and Function The Eight Critical Operating Parameters Common Coating Defects Seen on the Production Floor 5

6 Introduction To The Coating Room Basics of The Coating Area 6

7 View of a Typical Coating Operation: What The Operator Sees Coating Pan Suspension vessel Pumping System Spraying System 7

8 What the Operator Doesn t See Inlet side of the pan: Inlet air turbine Inlet air filtration with paper and HEPA filters Air treatment packages: Air heating system Steam, high pressure hot water, electricity (not recommended) Humidification and dehumidification systems Outlet side of the pan: Solvent recovery system (refrigeration, torch) Bag house (or scrubber) Outlet air turbine 8

9 The Entire Operation Then Looks Like This 9

10 The Entire Process Also Showing The Suspension Spraying System 10

11 A Side Vented Pan Showing Most of the System Parts Assembled at the Factory 11

12 Two Basic Types of Perforated Coating Pans Side vented (100% perforated): O Hara Accela Cota others Front vented (Partially perforated): Vector Freund others 12

13 A Comparison of Front and Side Vented Pans Side Vented Pan Front Vented Pan 13

14 Examples of Coating Installations Around The World 14

15 Examples of Front Vented Coating Installations in the Pharmaceutical and Nutritional Supplement Industries Pan Pumping system Control panel Ducts 15

16 An Example of a Side Vented 48 Pan in The Manufacturer s Testing Room 16

17 Fully Automated Aqueous Film Coater Pliva Pharmaceuticals (Poland) 17

18 Types of Common Pumping Systems 18

19 Common Pumping Systems, Coupled with a Magnetic Flow Meter, Used to Deliver Coating Suspensions Gear Pumps Peristaltic Pumps Rotary Lobe Pumps Used with a: Magnetic flow meter 19

20 Gear Pumps Advantages *Inexpensive *Solvent Friendly *High Pressure Disadvantages *Not used for Suspensions *Difficult to Clean *Difficult to Service 20

21 Peristaltic Pumps Advantages *Good for suspensions *Easy to clean *Easy to service Disadvantages *Pulses *Not for sugar coating *May or may not work for solvent coating 21

22 Rotary Lobe Pumps Advantages *Good for suspensions *High pressure *Low suction Disadvantages *Require high flow rates *Expensive *Seals may fail 22

23 Magnetic Flow Meters Advantages *Inexpensive *Cleanable Disadvantages *Solutions must be conductive *Not a direct mass reading 23

24 A Typical Coating Suspension Formulation: Component Parts 24

25 Aqueous Film Coating Formulation Typical Film Coating Composition Film-forming polymer % Plasticizer % Pigment/Colorant % 25

26 Aqueous Film Coating Formulation Water Soluble Polymers Hydroxypropyl methylcellulose (HPMC) Methylcellulose (MC) Hydroxypropyl cellulose (HPC) Polyvinylpyrrolidone (PVP) Food starch (modified) 26

27 Aqueous Film Coating Formulation Common Film Forming Materials in Sustained Release Products Sustained Release Ethylcellulose (EC) Methacrylic acid copolymers ( Eudragit types) Enteric Release Cellulose acetate phthalate (CAP) Hydroxypropyl methylcellulose phthalate (HPMCP) Polyvinyl acetate phthalate (PVAP) 27

28 Aqueous Film Coating Formulation Common Plasticizers Water soluble Polyethylene glycol (PEG) Propylene glycol (PG) Water insoluble Tributyl citrate (TBC) Acetylated monoglyceride (AMG) Dibutyl sebacate (DBS) Castor oil 28

29 Suspension Preparation Critical for Success. Frequently taken for granted! Check for: Even distribution of powders. Lumps and fish eyes should not be allowed. Screen suspension through an 80 mesh s/s screen. Mix during preparation but Stir during actual use. Be very careful of your terminology used on the batch record. Note: FDA is sensitive to the improper use of the two terms. Suspensions vs Solutions: Note that terms are commonly used interchangeably. 29

30 Example of An Optimized Suspension Preparation Process High shear material addition. Guarantees the best possible suspension. Little chance for lumps, fish eyes, paste. 30

31 Optimized Suspension Preparation Vessel: Engineered for Success Used to prepare the suspension. May also be used for transportation and as a holding tank. Turn off homogenizer. Low shear/speed stirring. Coating suspension 31

32 Suspension Holding Tank: Suboptimized Suspension Preparation Should be used for holding after manufacturing. Stir vs Mix. Portable. Unfortunately, commonly used with a mixer to prepare and hold the suspension. 32

33 Moving forward: How The Coating Process Works 33

34 How the Coating Process Works 34

35 An Internal View of the Coating Pan When Viewed Head On 35

36 Spray Guns Nomenclature and Process 36

37 Spray Pattern From an Aqueous Coating System Outside of the pattern is slower than the inside. This may require some degree of overlapping of spray patterns. 37

38 Air Cap Solution nozzle Gun Nomenclature Needle Air cap supplies atomizing and pattern air. Solution nozzle supplies coating suspension. Needle closes the suspension port. Manual setting adjusts both needle thrust and percent solution port opening. Note: Air cap/suspension nozzle and needle come in matched sets. 38

39 Critical Operating Parameters for Optimized Aqueous Coating How We Achieve Success on The Coating Floor 39

40 Time Out! Fred s Little Check List When I am asked to teach solid dosage or film coating, I perform my on line two minute audit to determine how professional the coating organization is: Does the operator have a flashlight, ruler and small brushes? Is there a range for gun to bed distance on the worksheet? Got a set of spare needles handy? Is there dried coating material stuck anywhere in the pan? Do the guns have drip cups? (Are there newspapers/magazines in the room?) 40

41 A Late Addition Side of A Vector HC-130: And Why Do You Think They Installed This Old Light On a New Coating Pan? Patheon, Monza, Italy 41

42 The Eight Critical Parameters For Aqueous Coating Gun Geometry Atomizing/Pattern Air Pan Pressure Pan Speed Spray Rate Inlet/Outlet Air temperature Total Air Volume Adhesion of particles to the gun surface 42

43 (1) Gun Geometry & Calibration: Our First Optimization Opportunity Gun to bed Boom placement Gun to Gun Gun to side of pan Cocked guns Position of the guns in relation to the tablet bed. 43

44 Boom Placement and Boom Type Varies between manufacturers and pan models. May be fixed or variable. Taken for granted and often overlooked as a variable during scale up or product transfer. Notice the photograph to the right. At the end of a 2.5 hour coating run we see beautiful yellow tablets with absolutely no adhesion of coating material anywhere in the pan. This should be our goal; we should not allow any other conditions. 44

45 Cocked Guns Guns become cocked from movement in/out of the pan, mechanical adjustment or operator abuse. Cocked side to side: over wet condition. Cocked up or down: solution sticks to the pan. Check guns by looking straight down the boom. Guns can also become cocked by loose fittings due to heat/cold expansion and contraction. 45

46 Gun To Bed Distance Well understood and reported in the literature. Usually stated as a specification on the worksheet. Most common settings for aqueous coating are 8 or 10 from the bed, depending on the spray rate used. Always fixed, never use a range. 46

47 Gun To Gun Distance Widely accepted or assumed to be fixed..but this is false. Not recognized as a variable in the literature. Usually not stated as a specification or set point on a worksheet. Setting is 5.5 or 6.0 gun tip to gun tip between guns. 47

48 Gun to Side of the Pan Measure tip of last gun on either side of the boom to either the front side of the pan or the back of the drum. Three possible problems may result: solution on the window (right) or solution on the side or back of the pan or both. Setting is widely understood but not recognized as a possible variable to be checked. Check the setting with placebos, then fix the gun. 48

49 Periodically, Check Your Operation! Use a flashlight. Look for problems. Pause, if necessary. Optimize! 49

50 Examples of Two Bad Pan Set Ups Pan speed is too fast, tablets are too active Back gun is too close to the rear of the pan (just barely). 50

51 Guns in Relation to Bed Height Tablet beds differ due to pan charge, size and shape of the tablet. Guns should be set at the bottom of the waterfall in the upper 1/3 of the bed. Recheck at the beginning of each campaign or when pan charge changes. 51

52 Three Pans Good, One Pan Bad 52

53 Gun Calibration Standardized Suspension Delivery 53

54 Gun Calibration is Important Variation in solution rates between guns is common. A variance of not more than +/- 10 ml. between guns is acceptable. What do you do if the variation exceeds recommended spread? Adjust the needle stroke from the back of the gun. 54

55 (2) Atomizing and Pattern Air 55

56 Atomizing and Pattern Air One of the 8 critical parameters for success. Converts a stream of suspension into a mist. Too much/too little atomizing air is bad. Fixed vs variable pattern air. Too much/too little pattern air is also bad. 56

57 A Visual Comparison of The Roles of Atomizing and Pattern Air Atomizing air joins suspension here Pattern air: flattens spray cone 57

58 Fixed Vs Variable Pattern Air Pattern air shapes the solution cone. The more air the flatter the cone. In some systems the pattern air is fixed. In some systems the pattern air is variable and is set by the operator. 58

59 Too Much or Too Little Pattern Air Too much pattern air flattens the cone and may create an over spray condition. Result: Over wetting that causes picking. Too little pattern air concentrates the cone in an insufficient area of the tablet bed. Result: Tablet erosion and or picking. 59

60 (3) Pan Pressure 60

61 Pan Pressure One of the 8 critical parameters for success. Never positive Usually between -0.1 H20 and H20. Never more than -1.0 H2O. (Excessive pressure causes unusual defects incorrectly attributed to other causes.) 61

62 Pan Pressure and Pan Seals Pan pressure is seriously reduced when the seals used to maintain pressure in the pan weaken and then break. In this picture we see an Accela Cota 48 pan with a broken seal. This should be replaced immediately. 62

63 (4) Pan Speed 63

64 Pan Speed: A Frequently Overlooked Optimization Opportunity One of the 8 critical parameters for success. There is no single specific setting. This is a relative setting based on tablet size, shape and load. Experience and observation are the initial basis of good science. Two basic pan speeds for each product: 1) Initial speed to achieve a basic covering and then 2) steady state speed. 64

65 Anti-Slide Bars and Pan Baffles 65

66 Anti-Slide Bars and Baffles Anti-Slide Bars (Blue): Used to center the tablet bed in front of the outlet air plenum. Not a mixing device. Almost mandatory. Baffles (Red): Mixing device. More than one kind. 66

67 (5) Spray Rate 67

68 Spray Rate One of the 8 critical parameters for success. Usually between ml/min./gun. Recommend 80 ml/min/gun with gun to bed distance of 8. Recommend 120 ml/min/gun with gun to bed distance of

69 (6) Inlet and Outlet Temperatures 69

70 Inlet/Outlet Air Temperature One of the 8 critical parameters for success. An alert organization keys on an outlet air temperature target and let the inlet vary within a range. Outlet air target is usually between 45 and 55 Deg. C. 70

71 Important Distinction! Inlet air temperature is a set point, whereas outlet air temperature is a function Inlet air CFM + Inlet air Temp + Spray Rate+ Atomizing air = Outlet Temp. Inlet temp is a set point, outlet temp is a function Monitoring outlet air temperature helps us determine if any of the other factors have changed or shifted. 71

72 (7) Air Volume ( CFM ) Drying Capacity 72

73 Total Air Volume ( CFM or cubic feet per minute) Means Total Drying Capacity The Coating process is usually somewhat tolerant to variations in total air volume. However it becomes a critical parameter for products sensitive to heat or moisture Total CFM Is a factor in coating efficiency. 73

74 (8) Adhesion of Particles To The Spray Guns 74

75 Adhesion of Coating Material to the Gun Assembly One of 8 critical parameters for success. Serious problem when left unattended. Solution: Leave atomizing air on, then: Stop spraying Leave atomizing air on Brush residue off Resume coating. 75

76 Use a Brush To Remove The Dry Particles Stop spraying. Keep atomizing air on. Brush the guns & assembly. Resume spraying 76

77 Putting It All Together and Summary Aqueous film coating is a controllable process with eight critical operating parameters. It cannot be fully controlled by a computer. Fully trained and knowledgeable operators are required for success in this unit operation. 77

78 You know you re in trouble in the coating room if you hear: So what if the gun drips a bit Let me check with the mechanic The nozzles are fixed at the factory What do I need a ruler for? Flashlights aren t allowed in the coating room A little coating material at the back of the pan is normal Needles bend a little, doesn t matter Pan pressure is the pressure of the tablets pressing up against the drum, the more the better 78

79 Common Coating Defects & Causes 79

80 Rough/Orange Peel Appearance Problem: Spray drying of membrane Causes: Not enough vehicle High CFM/inlet temp. High atomization air. 80

81 Picking Problem: Tablets are too wet. Possible Causes: Spray rate too high Guns too close together Insufficient atomizing air Pan speed too low 81

82 Film Cracking Problem: Small cracks appear in the coating. Causes: Wrong plasticizer. Insufficient plasticizer. Solution too concentrated (Thick). Insufficient atomizing air. 82

83 Film Chipping Problem: Coating gone from the tablet edge. Causes: High pan rpm Low spray rate Both together Sharp tablet edges 83

84 Bridging of the Logo Problem: The letters and numbers fill in with dried suspension. Causes: High spray rate coupled with high CFM (drying capacity). Inadequate atomizing air Poor tooling design. 84

85 Film Peeling Problem: Tablets are baking and the coating ruptures. Causes: Very high spray rate Low CFM Tacky coating material Lack of adhesion (nothing to stick to, the tablet is too hard) 85

86 Twins or Twinning Twinning Problem: Tablets stick together: Causes: High spray rate Inadequate drying capacity Tablet shape/design Belly band too thick Tablet too long One or more factors 86

87 Logo Erosion Problem: Tablet erodes before coating can adhere to the surface. Causes: Spray rate too slow Pan speed too fast Both Soft tablets/combined with items shown above. 87

88 Film Cracking Rather rare defect. Not seen often Happens when solution evaporates or is mixed too thick. 88

89 Stability Issues: Physical Changes in Tablet Appearance Problem: Off color with (maybe) off odor tablets Causes: Microbial contamination Moisture sensitivity. Heat sensitivity. Incompatibility: Film to tablet Excipients to API. Both factors combined. 89

90 Grand Summary: Film coating is unforgiving. Coating is easily optimized. You may avoid errors If You understand the critical operating parameters 90

91 Thank You For Listening! Comments are always welcomed: Fred Rowley 91