Gel coat ‖ is divided into several types and common problems and causes of analysis-Application of Functional Material Technology-Dongguan DENSON Functional Materials Co., Ltd-蒂森公司功能材料

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Gel coat ‖ is divided into several types and common problems and causes of analysis

2024-11-15 08:50:23 Application of Functional Material Technology

Gel coat (English name: gel coat) is a coloring thixotropic product developed by adding pigments and thixotropic agents to unsaturated polyester (UP) and dispersion of glass fiber reinforced plastic (FRP) and countertop paint.

Commonly used gel coat brands:

Phthalate type: high finish, excellent process performance, color stability in buildings, vehicles, cooling towers, feed barrels, etc

Isobenzene-neopentyl glycol type: excellent comprehensive performance, can be used for a long time in a strong ultraviolet ray, highly corrosive environment, through the inspection of boats, sanitary ware, vehicles, wind power, sports equipment, construction and other products

Flame retardant type: excellent flame retardant and construction technology, halogen-free and low smoke density buildings, vehicles and other flame retardant products

Grinding type: easy to polish, less pinholes, good adhesion to paint and need to be painted

Mold gelcoat type

Polyester type: high finish, high hardness ordinary FRP mold, commonly used colors are red, black, green

How to use colored gelcoats?

1. Choose the appropriate gelcoat model before use.

2. Prepare the mold completely and thoroughly, and the surface of the mold determines the surface of the product.

3. Stir each bucket of gelcoat fully before use, but the speed should be slow to avoid mixing bubbles.

4. Before starting the operation, keep the temperature of the gel coat and the mold at 16°C -30°C, and the ideal mold temperature should be 2°C - 3°C higher than the gel coat temperature. In this way, a glossier gelcoat surface is obtained after curing.

5. The relative humidity in the workshop should be less than 80%, and the high humidity will lead to an increase in the required curing temperature. In addition, it is necessary to prevent water from accumulating on the surface of the mold.

6. The surface of the mold needs to be fully waxed, and do not use silicone-containing release wax. Water-soluble release waxes must wait for their moisture to evaporate before applying gelcoats.

7. Do not dilute with solvents, such as acetone. If a lower viscosity is required for use, a small amount of styrene (<2%) can be added.

8. The dosage of curing agent (MEKP) is generally 1-2%. If the amount of curing agent is too high or too low, the water resistance and weather resistance of the product will be reduced.

9. If colorant is added, the uniformity and stability of the color should be ensured. Weigh as recommended and stir using low-shear equipment. Coloured gelcoats can also be used.

Precautions before using gelcoats

1. The gelcoat should be stored away from direct sunlight at a temperature of ≤ 25 °C, and stored separately from MEKP.

2. The pretreatment mold and gelcoat construction area should avoid the generation of dust. The gelcoat should be poured into a clean bucket.

3. When stirring the curing agent or color paste, do not mix too much air.

4. Do not use high-shear mixing equipment. Failure to do so will result in a decrease in the thixotropy index, separation/aggregation of the colorant, gel flow and bubbles.

5. It is forbidden to pour the color gelcoat directly on the mold and paint it directly.

6. Do not adjust the gel time too fast, which is not conducive to the escape of bubbles.

7. The amount of curing agent should be appropriate, and the amount of curing agent can be checked by measuring the gelling time.

8 Do not use silicone-containing release waxes, they will produce fisheyes.

9. Use MEKP with good quality, low water content, medium reactive oxygen content, and inferior curing agent will seriously affect the performance of gelcoat. (Nouryon M50, Shuojin KP-9, plus Ying M90, etc.)

10. Do not add accelerators to the color gelcoat to avoid affecting the color.

11. The performance of the gelcoat can only be fully reflected after it is fully cured, and customers with conditions should post-cure the product.

Analysis of common problems and causes of gelcoats in application

Fisheye	(1) There is static electricity on the surface of the mold, the release agent is not dry, and the release agent is not properly selected. (2) The gelcoat is too thin and the temperature is too low. (3) The gelcoat is contaminated with water, oil or oil stains. (4) The mold is dirty or has wax aggregates. (5) Low viscosity and thixotropy index.
Sag	(1) The thixotropy index of the gel coating is low, and the gel time is too long. (2) The gel coat is sprayed excessively, the surface is too thick, the nozzle direction is wrong or the caliber is small, and the pressure is too large. (3) The release agent coated on the surface of the mold is incorrect.
The gloss of the gel coat of the product is not good	(1) The finish of the mold is poor, and there is dust on the surface. (2) The curing agent content is small, the curing is incomplete, the curing degree is low, and the curing is not post-cured. (3) The ambient temperature is low and the ambient humidity is high. (4) The gelcoat layer is demolded before it is completely cured. (5) The gel coat has high filler and less matrix resin content.
The surface of the product is wrinkled	It is a common disease of gelcoat. The reason is that the gelcoat is coated with resin prematurely before it is fully cured, and styrene dissolves part of the gelcoat, causing swelling and wrinkling. There are the following ways to deal with it: (1) Check whether the thickness of the gel coat meets the specified value (0.3-0.5mm, 400-500g/㎡), and if necessary, it can be appropriately thickened. (2) Check the resin properties. (3) Check the amount of initiator added and the mixing effect. (4) Check whether the pigment will affect the curing of the resin after it is added. (5) Increase the workshop temperature to 18-20°C.
Surface pinholes	When small bubbles are latent in the gelcoat, pinholes appear on the surface after curing. Dust on the surface of the mold can also cause pinholes. The handling method is as follows: (1) Clean the surface of the mold and remove the dust. (2) Check the viscosity of the resin, and if necessary, dilute it with styrene, or reduce the amount of thixotropic agent. (3) If the release agent is not selected properly, it will cause poor wetting and pinholes, so the release agent needs to be checked. This phenomenon does not occur with polyvinyl alcohol. (4) When adding initiator and pigment paste, do not mix with air. (5) Check the spray gun spray speed. If the injection speed is too high, a pinhole will occur. (6) Check the atomization pressure and do not make it too high. (7) Check the resin formula. Excessive initiator can cause pre-gelling and latent bubbles. (8) Check whether the grade and model of methyl ethyl ketone peroxide or cyclohexanone peroxide are appropriate.
Changes in surface roughness	The change in surface roughness is manifested as spots and spots, and the gloss is uneven. This can be due to premature movement of the part on the mold or insufficient wax release agent. Here's how to overcome it: (1) Don't wax too much, but the amount of waxing should be able to achieve surface polishing. (2) Check whether the release agent of the product has been fully cured.
The gelcoat is shattered	The fragmentation of the gelcoat may be caused by poor adhesion between the gelcoat and the base resin, or the sticking of the mold during demoulding, etc., and the specific reasons should be found to be overcome. (1) The surface of the mold is not polished enough, and the gel coat sticks to the mold. (2) The wax quality is not good, the performance is not good, so it penetrates the gelcoat and destroys the wax polishing layer. (3) The surface of the gel coat is polluted, which affects the bonding between the gel coat and the base resin. (4) The curing time of the gel coat is too long, which reduces the adhesion to the base resin. (5) The composite material structure is not compact.
Interior white spots	The white spots on the inside of the product are caused by the glass fibers not being adequately saturated with resin. (1) During the layup operation, the laminated products are not fixed enough. (2) Lay dry felt and dry cloth first, and then pour resin, which is impervious to impregnation. (3) Laying two layers of felt at one time, especially the two layers of cloth stacking, resulting in poor resin penetration. (4) The viscosity of the resin is too large to soak the felt. A small amount of styrene can be added, or a low-viscosity resin can be used instead. (5) The resin gel time is too short, and it is not compacted before gelling. The amount of accelerator can be reduced, and the initiator or polymerization inhibitor can be changed to prolong the gel time.
delamination	Delamination occurs between two layers of composites, especially between two layers of coarse tartan cloth. The reasons for this and how to overcome it are as follows: (1) The amount of resin is insufficient. To increase the amount of resin and impregnate evenly. (2) The glass fiber is not impregnated. The viscosity of the resin can be appropriately reduced. (3) Surface contamination of the inner layer of glass fiber (or cloth/felt). In particular, when the layer is cured first and then the second layer is laid, it is easy to cause stains on the surface of the layer. (4) The layer is over-cured by the coated resin. It can reduce the curing time, and if it has been over-cured, it can be ground and roughened before applying a second layer. (5) There must be a layer of chopped fiber felt in the middle of the two layers of coarse lattice cloth, and the two layers of coarse lattice cloth must not be continuously laid.
Small spots	The surface layer of the gelcoat is covered with small spots. This can be due to poor dispersion of pigments, fillers or thixotropic additives, or by dusting on the surface of the mold. (1) Clean the surface of the mold, polish it, and then apply gel coat. (2) Check the mixing efficiency. (3) Use a three-roller grinder and a high-speed shear mixer to disperse the pigments.
discoloration	The color density is uneven, or color streaks appear. (1) The pigment is poorly dispersed and floats. Mix thoroughly, or change the pigment paste. (2) Excessive atomization pressure during spraying. Appropriate adjustments should be made. (3) The spray gun is too close to the surface of the mold. (4) The gel-coat layer is too thick in the vertical plane, resulting in glue flow, sagging, uneven thickness and other phenomena. The dosage of thixotropic agent should be increased. (5) The thickness of the gelcoat is uneven. The operation should be improved so that it is evenly covered.
Fibrous morphology is exposed	The form of glass cloth or felt is exposed to the outside of the product. (1) The gelcoat is too thin. The thickness of the gelcoat should be increased, or the surface felt should be used as the knot layer. (2) The gel coat is not gelled, and it is prematurely coated with resin and glass fiber base. (3) The product is demolded too early, and the resin has not been fully cured. (4) The peak temperature of resin exothermic is too high. The amount of initiator and accelerator should be reduced; or change the initiator system; Or change the operation, each time the layer is thinned.
Surface pussy opening	The surface of the mold is not covered with gelcoat, or the gelcoat is not soaked on the surface of the mold. If polyvinyl alcohol is used as a release agent, this phenomenon generally rarely occurs. should Check the release agent and switch to silane-free paraffin or polyvinyl alcohol.
bubble	Bubbles appear on the surface, or there are bubbles on the entire surface. After demolding, bubbles can be found in a short period of time or after a few months when they are post-cured. This can be caused by air or solvents lurking between the gelcoat and the substrate, or by improper selection of resin systems or fiber materials. (1) When covered, the felt or cloth is not soaked with resin. It should be better rolled and soaked. (2) Water or cleaning agent contaminates the gelcoat layer. Be careful that the brushes and rollers used must be dry. (3) Improper selection of initiator and misuse of high-temperature initiator. (4) The use temperature is too high, and it is eroded by moisture or chemicals. A different resin system should be used instead.
cracks or cracks	Cracks on the surface of the product are found immediately after curing or after a few months, and the tarnier is lost. (1) The gelcoat is too thick. It should be controlled at 0.3-0.5mm. (2) Improper selection of resin, or mismatch of initiator. (3) Excessive styrene in gelcoat. (4) The resin is undercured. (5) Excessive filler in resin. (6) Poor product configuration or mold design, resulting in abnormal internal stress in the use of products.
Star cracks	Star cracks in the gelcoat are caused by impact on the back of the laminate. Switch to a gelcoat with better elasticity, or reduce the thickness of the gelcoat, generally Less than 0.5mm.
Traces of subsidence	Dents occur on the back of the ribs or inserts due to resin curing and shrinking. It can be partially cured of the laminate first, and then the ribs, inlays Wait for it to be put on and continue to form.
whiting	There is a tendency to whiten during the normal service life of the product. (1) The curing of gelcoat is incomplete. The curing process and the amount of initiator and accelerator should be checked. (2) Improper selection of fillers or pigments, or excessive use. (3) The resin formula is not suitable for the requirements of the use conditions.
The gel coat comes out of the mold	Before the substrate resin is coated, sometimes the gel coat has come out of the mold, especially in the corners. Often due to styrene volatiles condensation in Caused by the bottom of the mold. (1) Position the mold so that the styrene vapor can escape, or use a suitable suction system to remove the styrene vapor. (2) Avoid excessive thickness of gelcoat. (3) Reduce the amount of initiator.
Yellowing	It is a phenomenon of yellowing of gelcoat when exposed to sunlight. (1) The air humidity is too high or the material is not dry during the layup operation. (2) Improper selection of resin. Resins that are UV stable should be used. (3) A benzoyl-amine peroxide initiation system was used. A different triggering system should be used instead. (4) The laminate material is under-cured.
The surface is sticky	Caused by under-curing of the surface. (1) Avoid laying in cold and wet environments. (2) Make a layer of coating with air-dried resin. (3) If necessary, the amount of initiator and accelerator can be increased. (4) Add paraffin wax to the surface layer resin.
Deformed or combined with discoloration	Deformation or discoloration is often caused by excessive exothermic during curing. The initiator and accelerator dosage should be adjusted, or a different initiator system should be used.
The product is deformed after being removed from the mold	(1) The demoulding is too early, and the product is not fully cured. (2) The strong ribs in the product design are insufficient, which should be improved. (3) Before demoulding, it is coated with a rich resin layer or a top layer of resin to achieve a balance with gel coat resin. (4) Improve the structural design of the product to compensate for the possible deformation.
The hardness of the product is insufficient and the rigidity is poor	It may be due to insufficient curing. (1) Check whether the dosage of initiator and accelerator is appropriate. (2) Avoid laying in cold and wet conditions. (3) Store fiberglass felt or fiberglass cloth in a dry environment. (4) Check whether the glass fiber content is sufficient. (5) Post-curing the product.
Repair of damaged products	Surface damage and depth of damage are only in the gelcoat or reinforcement layer. The repair steps are as follows: (1) Remove loose objects and protrusions, clean and dry the damaged area, and remove grease. (2) Brush in a small area around the damaged area. (3) Cover the damaged area and the grinding place with thixotropic resin, and the thickness should be larger than the original thickness for shrinkage, grinding and polishing. (4) The surface is covered with cellophane or film to prevent air from blocking polymerization. (5) After curing, remove the cellophane or peel off the film, and polish it with waterproof emery paper. Use No. 400 first, then No. 600 sandpaper, and grind carefully so as not to hurt Gelcoat. It is then polished with a fine friction compound or metal. Wax and polish.

Fisheye	(1) There is static electricity on the surface of the mold, the release agent is not dry, and the release agent is not properly selected. (2) The gelcoat is too thin and the temperature is too low. (3) The gelcoat is contaminated with water, oil or oil stains. (4) The mold is dirty or has wax aggregates. (5) Low viscosity and thixotropy index.
Sag	(1) The thixotropy index of the gel coating is low, and the gel time is too long. (2) The gel coat is sprayed excessively, the surface is too thick, the nozzle direction is wrong or the caliber is small, and the pressure is too large. (3) The release agent coated on the surface of the mold is incorrect.
The gloss of the gel coat of the product is not good	(1) The finish of the mold is poor, and there is dust on the surface. (2) The curing agent content is small, the curing is incomplete, the curing degree is low, and the curing is not post-cured. (3) The ambient temperature is low and the ambient humidity is high. (4) The gelcoat layer is demolded before it is completely cured. (5) The gel coat has high filler and less matrix resin content.
The surface of the product is wrinkled	It is a common disease of gelcoat. The reason is that the gelcoat is coated with resin prematurely before it is fully cured, and styrene dissolves part of the gelcoat, causing swelling and wrinkling. There are the following ways to deal with it: (1) Check whether the thickness of the gel coat meets the specified value (0.3-0.5mm, 400-500g/㎡), and if necessary, it can be appropriately thickened. (2) Check the resin properties. (3) Check the amount of initiator added and the mixing effect. (4) Check whether the pigment will affect the curing of the resin after it is added. (5) Increase the workshop temperature to 18-20°C.
Surface pinholes	When small bubbles are latent in the gelcoat, pinholes appear on the surface after curing. Dust on the surface of the mold can also cause pinholes. The handling method is as follows: (1) Clean the surface of the mold and remove the dust. (2) Check the viscosity of the resin, and if necessary, dilute it with styrene, or reduce the amount of thixotropic agent. (3) If the release agent is not selected properly, it will cause poor wetting and pinholes, so the release agent needs to be checked. This phenomenon does not occur with polyvinyl alcohol. (4) When adding initiator and pigment paste, do not mix with air. (5) Check the spray gun spray speed. If the injection speed is too high, a pinhole will occur. (6) Check the atomization pressure and do not make it too high. (7) Check the resin formula. Excessive initiator can cause pre-gelling and latent bubbles. (8) Check whether the grade and model of methyl ethyl ketone peroxide or cyclohexanone peroxide are appropriate.
Changes in surface roughness	The change in surface roughness is manifested as spots and spots, and the gloss is uneven. This can be due to premature movement of the part on the mold or insufficient wax release agent. Here's how to overcome it: (1) Don't wax too much, but the amount of waxing should be able to achieve surface polishing. (2) Check whether the release agent of the product has been fully cured.
The gelcoat is shattered	The fragmentation of the gelcoat may be caused by poor adhesion between the gelcoat and the base resin, or the sticking of the mold during demoulding, etc., and the specific reasons should be found to be overcome. (1) The surface of the mold is not polished enough, and the gel coat sticks to the mold. (2) The wax quality is not good, the performance is not good, so it penetrates the gelcoat and destroys the wax polishing layer. (3) The surface of the gel coat is polluted, which affects the bonding between the gel coat and the base resin. (4) The curing time of the gel coat is too long, which reduces the adhesion to the base resin. (5) The composite material structure is not compact.
Interior white spots	The white spots on the inside of the product are caused by the glass fibers not being adequately saturated with resin. (1) During the layup operation, the laminated products are not fixed enough. (2) Lay dry felt and dry cloth first, and then pour resin, which is impervious to impregnation. (3) Laying two layers of felt at one time, especially the two layers of cloth stacking, resulting in poor resin penetration. (4) The viscosity of the resin is too large to soak the felt. A small amount of styrene can be added, or a low-viscosity resin can be used instead. (5) The resin gel time is too short, and it is not compacted before gelling. The amount of accelerator can be reduced, and the initiator or polymerization inhibitor can be changed to prolong the gel time.
delamination	Delamination occurs between two layers of composites, especially between two layers of coarse tartan cloth. The reasons for this and how to overcome it are as follows: (1) The amount of resin is insufficient. To increase the amount of resin and impregnate evenly. (2) The glass fiber is not impregnated. The viscosity of the resin can be appropriately reduced. (3) Surface contamination of the inner layer of glass fiber (or cloth/felt). In particular, when the layer is cured first and then the second layer is laid, it is easy to cause stains on the surface of the layer. (4) The layer is over-cured by the coated resin. It can reduce the curing time, and if it has been over-cured, it can be ground and roughened before applying a second layer. (5) There must be a layer of chopped fiber felt in the middle of the two layers of coarse lattice cloth, and the two layers of coarse lattice cloth must not be continuously laid.
Small spots	The surface layer of the gelcoat is covered with small spots. This can be due to poor dispersion of pigments, fillers or thixotropic additives, or by dusting on the surface of the mold. (1) Clean the surface of the mold, polish it, and then apply gel coat. (2) Check the mixing efficiency. (3) Use a three-roller grinder and a high-speed shear mixer to disperse the pigments.
discoloration	The color density is uneven, or color streaks appear. (1) The pigment is poorly dispersed and floats. Mix thoroughly, or change the pigment paste. (2) Excessive atomization pressure during spraying. Appropriate adjustments should be made. (3) The spray gun is too close to the surface of the mold. (4) The gel-coat layer is too thick in the vertical plane, resulting in glue flow, sagging, uneven thickness and other phenomena. The dosage of thixotropic agent should be increased. (5) The thickness of the gelcoat is uneven. The operation should be improved so that it is evenly covered.
Fibrous morphology is exposed	The form of glass cloth or felt is exposed to the outside of the product. (1) The gelcoat is too thin. The thickness of the gelcoat should be increased, or the surface felt should be used as the knot layer. (2) The gel coat is not gelled, and it is prematurely coated with resin and glass fiber base. (3) The product is demolded too early, and the resin has not been fully cured. (4) The peak temperature of resin exothermic is too high. The amount of initiator and accelerator should be reduced; or change the initiator system; Or change the operation, each time the layer is thinned.
Surface pussy opening	The surface of the mold is not covered with gelcoat, or the gelcoat is not soaked on the surface of the mold. If polyvinyl alcohol is used as a release agent, this phenomenon generally rarely occurs. should Check the release agent and switch to silane-free paraffin or polyvinyl alcohol.
bubble	Bubbles appear on the surface, or there are bubbles on the entire surface. After demolding, bubbles can be found in a short period of time or after a few months when they are post-cured. This can be caused by air or solvents lurking between the gelcoat and the substrate, or by improper selection of resin systems or fiber materials. (1) When covered, the felt or cloth is not soaked with resin. It should be better rolled and soaked. (2) Water or cleaning agent contaminates the gelcoat layer. Be careful that the brushes and rollers used must be dry. (3) Improper selection of initiator and misuse of high-temperature initiator. (4) The use temperature is too high, and it is eroded by moisture or chemicals. A different resin system should be used instead.
cracks or cracks	Cracks on the surface of the product are found immediately after curing or after a few months, and the tarnier is lost. (1) The gelcoat is too thick. It should be controlled at 0.3-0.5mm. (2) Improper selection of resin, or mismatch of initiator. (3) Excessive styrene in gelcoat. (4) The resin is undercured. (5) Excessive filler in resin. (6) Poor product configuration or mold design, resulting in abnormal internal stress in the use of products.
Star cracks	Star cracks in the gelcoat are caused by impact on the back of the laminate. Switch to a gelcoat with better elasticity, or reduce the thickness of the gelcoat, generally Less than 0.5mm.
Traces of subsidence	Dents occur on the back of the ribs or inserts due to resin curing and shrinking. It can be partially cured of the laminate first, and then the ribs, inlays Wait for it to be put on and continue to form.
whiting	There is a tendency to whiten during the normal service life of the product. (1) The curing of gelcoat is incomplete. The curing process and the amount of initiator and accelerator should be checked. (2) Improper selection of fillers or pigments, or excessive use. (3) The resin formula is not suitable for the requirements of the use conditions.
The gel coat comes out of the mold	Before the substrate resin is coated, sometimes the gel coat has come out of the mold, especially in the corners. Often due to styrene volatiles condensation in Caused by the bottom of the mold. (1) Position the mold so that the styrene vapor can escape, or use a suitable suction system to remove the styrene vapor. (2) Avoid excessive thickness of gelcoat. (3) Reduce the amount of initiator.
Yellowing	It is a phenomenon of yellowing of gelcoat when exposed to sunlight. (1) The air humidity is too high or the material is not dry during the layup operation. (2) Improper selection of resin. Resins that are UV stable should be used. (3) A benzoyl-amine peroxide initiation system was used. A different triggering system should be used instead. (4) The laminate material is under-cured.
The surface is sticky	Caused by under-curing of the surface. (1) Avoid laying in cold and wet environments. (2) Make a layer of coating with air-dried resin. (3) If necessary, the amount of initiator and accelerator can be increased. (4) Add paraffin wax to the surface layer resin.
Deformed or combined with discoloration	Deformation or discoloration is often caused by excessive exothermic during curing. The initiator and accelerator dosage should be adjusted, or a different initiator system should be used.
The product is deformed after being removed from the mold	(1) The demoulding is too early, and the product is not fully cured. (2) The strong ribs in the product design are insufficient, which should be improved. (3) Before demoulding, it is coated with a rich resin layer or a top layer of resin to achieve a balance with gel coat resin. (4) Improve the structural design of the product to compensate for the possible deformation.
The hardness of the product is insufficient and the rigidity is poor	It may be due to insufficient curing. (1) Check whether the dosage of initiator and accelerator is appropriate. (2) Avoid laying in cold and wet conditions. (3) Store fiberglass felt or fiberglass cloth in a dry environment. (4) Check whether the glass fiber content is sufficient. (5) Post-curing the product.
Repair of damaged products	Surface damage and depth of damage are only in the gelcoat or reinforcement layer. The repair steps are as follows: (1) Remove loose objects and protrusions, clean and dry the damaged area, and remove grease. (2) Brush in a small area around the damaged area. (3) Cover the damaged area and the grinding place with thixotropic resin, and the thickness should be larger than the original thickness for shrinkage, grinding and polishing. (4) The surface is covered with cellophane or film to prevent air from blocking polymerization. (5) After curing, remove the cellophane or peel off the film, and polish it with waterproof emery paper. Use No. 400 first, then No. 600 sandpaper, and grind carefully so as not to hurt Gelcoat. It is then polished with a fine friction compound or metal. Wax and polish.