Protection of the skin

• Prevent skin from directly contact with the photo-cured resin to mitigate the risk of skin inflammation. Wear thick nitrile gloves to segregate the skin from irritating chemical products. The likelihood of resin erosion and the permeability of glove materials should be taken into account when choosing a suitable glove.

• Porous PE glove and commonly worn PVC emulsion glove offers no long-term protected. Studies found that Nitrile Rubber and Butyl Rubber, the material of rubber gloves, offer the optimal protection against main compositions of the photo-cured resin. The sweat of human body is inclined to cause skin inflammation too. The rubber glove of the cotton intermediate layer can be worn to reduce the sweat, therefore protecting the skin.

• There are multiple skin care products protect the skin from chemical-induced irritation. They are especially effective when used during high-humidity seasons. Operate our product in a clean long-sleeves trousers, avoid photo-cured resin from touching the skin.

• Work should be carried out when wearing clean work clothes. Some cases show the soiled cloth causes skin inflammation too. The clothes should be thoroughly clensed and changed immediately when contacted with raw chemicals. When processing a large quantity of photo-cured resins, a steel-headed safety shoes or nitrile shoes should be worn. Canvas shoes or soft leather shoes may be permeated, which are unsuitable for processing chemicals. When the shoes are permeated by products pollution, they must be disposed of as chemical waste to avoid contact with bare skin.

Protection of eyes

• Eyes are extremely vulnerable organ. Therefore, safety glasses should be worn when processing liquid chemicals, especially photo-cured resins.

• Resins often come into contact with the edge part of the goggle, resulting in skin sensitization.

• The chemical smog is likely to adsorb to contact lenses, stimulating eyes. Hence, it is unsuitable to wear contact lenses during work. While working under strong, short wavelength light, a brown (or dark color) safety glasses should be worn. The dark colored lens reduces the intensity of light. As for the brown lens, it can filter out glaring ultraviolet or blue lights. Therefore, it is suggested to wear a brown safety glasses when curing the photo-cured resins.

Protection of the respiratory system

• Liquid material (including photo-cured resins) are volatile to some extent. Inhaling the volatile fume may cause headaches and sore throat. Although some low-volatility photo-cured resins are odorless, as they are cured, they exotherm, generating odor.

• Some photo-cured resins are handled under high temperature or in fume state, which highlights the importance of volatile control. The only solution to mitigate odor is the installation of ventilation system. From the unpackaging, handling, until the cure. Ventilation system is a rather affordable equipment to install.

• Personal protective equipements (PPEs) should be certified and approved by relevant authorities. The PPE, such as gas masks, are more suitably used in occasions with short handling time and a low level of odor. The activated carbon canisters should be replaced on a regular basis. Masks made of cotton or chemical fiber do not segregate harmful gases. Overall, there is no alternative of a properly installed ventilation system despite the good performance of PPEs.

Protection of the personal hygiene

• When each job finishes, it is important to thoroughly rinse skin that have had contact with chemicals. There is no other way to eliminate pollutants than a thorough clense.

Clean protection of the house

• To avoiding the skin inflammation, household cleanliness is a vital aspect. Otherwise the probability of infecting skin inflammation increases. In many examples, allergic does not appear immediately, making it not easily noticed. Sensitization only occurs when contact with chemicals repetatively occur.

By enhancing household tidyness, the chance to make a repeat contact with pollutants is minimized.

Measures of skin contacts of chemicals

• Remove the chemically polluted clothes. Rinse the surface of skin thoroughly by soap. In case the skin was in contact with high-visocsity photo-cured resin, a high-concentration detergent removes it more efficiently.

• In addition, soaking skin in warm water for 15 minutes can ensure the chemicals being completely rinsed. Do not remove the resin by organic solvents. Despite the organic solvents remove the resin in a faster rate, the solvents permeate into skin. A recent study discovered the use of adrenaline hormone cream effectively prevent blisters.

• Should skin irritation or sensitization remain after the removal of resin, this type of cream eases skin inflammation. To prevent further infection, once blisters, hospitalization should me made at the earliest possibility.

Treatment of eyes contact of chemicals

• Continuously rinse the eyes with clean warm water for 20-30 minutes. Hospitalize at the earliest possibility.

Inhale of ozone

• During the cure of photo-cured resin, ozone is released from the ultraviolet machine. Should ozone inhale, the operator must locate to circulating fresh air. Artificial respiration or oxygen should be offered. Hospitalize at the earliest possibility.

Ingestion of resin

• If the patient were conscious, they may consume 0.57 liter (1 pint) of warm water to dilute the ingested chemicals. They should be hospitalized at the earliest possibility.

• The induced vomiting must only be conducted by licensed medical practitioners. Further harm may be caused if the induced vomiting was carried out improperly.

Accident: Uncontrolled rapid polymerization

Photo-cured resin is a polymer made of multiple chain-reacted monomer. During the polymerization process, large exotherm is occurred. Exposing the entire bottle (barrel) of photo-cured resin to light, or heat, is extremely hazardous. The accident-induced polymerization is hardly controlled. Substantial exotherm may deform, combust, or degrade the container, during which the resin is degraded. In the worst case scenario, the resin may spontaneously combust.

Fire hazard

Photo-cured resin is combustible. Gas released during the combustion of photo-cured resin causes skin sensitization, accompanying severe harm if inhaled. The heat of flame degrades polymer, damaging the container, and thereby propagates the flame

Emergency procedures

Should the photo-cured resin exotherm, emerging it into cold bath of water is an effective preventative measure of hazard. If possible, open the container for better ventilation. Locate the container at a distance for further cool.

In case the photo-cured resin causes fire, utilize the personal protective equipments, such as masks, hood, safety shoes, and gloves. Evacuate all personnels, and maintain air circulation in the meanwhile. Fire should be extinguished by carbon dioxide fire extinguishers.

Disposal of containers

Containers with residual resin should be handed with care when disposed. Gloves must be worn whilst transporting emptied containers. Avoid exposure to light and heat. Usually, according to the RCRA classification, photo-cured resin is not a hazardos waste. It may be disposed of in accordance to regulations outlined by your local autority.

Storage

Photo-cured resin must be stored in places that does not cause its polymerization. Hence, the below points list a guideline for photo-cured resin storage.

1. Avoid sunlight

2. Store the photo-cured resin in cool, well-ventilated area

3. Do not modify the packaging of the resin

4. Make suitable selection when dispensing the resin (PE, PP, stainless steel, surface-treated steel drum, or glasswares)

5. Avoid contact with metals such as copper or iron, as they cause the polymerization

6. Do not vacuum photo-cured resin

7. Do not inject nitrogen, or gases that contains no oxygen

8. Do not fill the resin in your container completely. There must be certain space for oxygen to inhibit the polymerization

Should you follow the above-listed guidelines, photo-cured resin can be stored with great stability for over a year. In case a change of quality occurs, please review the above points and notify Everwide for analysis.

E01. Constituents

The constituents of one-component epoxy is almost identical to the two-component counterpart, including resin, curing agent, diluent, catalyst, toughener, filler, pigment, thixotropic modifier, and defoamers etc.

E02. Reasons of adopting a one-component formulation

Epoxy resin must be mixed with its curing agent and catalyst to have it cured. Two-component packaging is of the most common system. It locates the resin in part A; the curing agent and catalyst in part B. Therefore, curing agent can be designed in powder form: Insoluble under room temperature, soluble at an elevated temperature. With a finely dispersed and distributed powder curing agent, a one-component epoxy formulation is obtained. Certain catalysts or initiators are temperature-sensitive, meaning the reaction can only take place at temperature significantly above the room temperature.

E03. Advantages of a one-component epoxy formulation

1. Simplified process by waiving the mixing of resin and curing agent parts

2. Eliminating the chance of error, need not to weigh part A and B

3. The cost of resin dispenser for one-component epoxy is lower than the two-component one

4. Less production of waste

5. No limitation of operation time (pot life)

E04. Shortcomings of the one-component epoxy formulation

1. One-component formulation cannot be cured at room temperature, heat is needed

2. Shorter period for storage

3. May need refrigeration (or freezing) equipment

E05. Reasons behind the increased viscosity in one component epoxy resin over a period of time

The curing agent of one-component epoxy resin slowly leach out, eventually react with the resin. This partially reacted one-component epoxy explains why the viscosity of the resin gradually increase over time.

E06. Reasons behind the decreased viscosity in one component epoxy resin over a period of time

Some one component epoxy formulation incorporates an anti-sagging agents (thixotropic modifyers) to increase the thixotropic behavior.

The particle surfaces of these additives are interacted by hydrogen bonds. This tiny intermolecular force cause the particles to agglomerate, increasing the overall viscosity.

However, the amine curing agent (powder) in certain one-component epoxy resin form hydrogen bonds with the surface of the anti-sagging agent particles. This hydrogen bond between amine and anti-sagging agent particles replaces the hydrogen bonds between the anti-sagging agent particles themselves. This phenomenon causes the anti-sagging properties to decline, thereby decreasing the viscosity.

E07. Factors affecting the stability of one component epoxy resin

1. Moisture absorption of the curing agent shortens the shelf life of the final products. Attention should be paid to the humidity of the storage environment and the container. It should be tightly sealed at all time.

2. Generally, the lower storage temperature of final products, the more stable they are. However, some high-purity resins are prone to crystallization.

3. In formulations with a low viscosity, precipitate or floating of certain ingredients may occur, resulting in poor properties of the cured products.

4. Some formulations contain hydroxyl groups that cause gelation under low temperature. Others are alkali, rising the instability in cationic polymerization. Still others contains an excessive amount of chlorine, which affects the efficiency of alkaline catalysts.

5. The use of diluents often reduce the curing reactivity, causing a unstable viscosity during storage.

E08. Precautions for epoxy resin cured at different temperatures

Depending on the precise applications, one-component epoxy resin will be cured at multiple temperatures. This is to avoid an overly violent reaction while maintaining a reasonable reactivity. For resins and hardeners, two-component epoxy resins are homogeneous systems, little restrictions apply.

One-component epoxy formulation, on the other hand, uses powder curing agent (solute), which is dissolved into the resin (solvent) at a certain temperature. Therefore, the cure scheme cannot be arbitrarily designed. Otherwise, an incomplete cure may result.

E09. The two main constituents of composite materials

Composite materials are made of the matrix and the reinforcement. In most cases, matrix refers to the resin, and reinforcement is represented by fiber. Composite material is an anisotropic material that combines the properties of the matrix and reinforcement.

E10. Functions of resin (matrix) in composite materials:

1. Binds the fiber (reinforcement) tightly in a fixed position

2. Offers protection to the fiber against abrasion damage

3. The transfer of mechanical force to the reinforcement

4. Control electrical, chemical, and other relevant properties of composite materials

5. Provides shear strength between layers of composite materials

6. Determines the molding methods and processing parameters of composite materials

E11. Functions of fibers (reinforcement) in composite materials:

1. Endures the stress on composite materials

2. Inhibit the growth of small cracks

3. Control of mechanical properties of composite materials

4. Optimize the anti-creep and fatigue-resistance properties

5. Prolonging the life cycle and promoting the reliability of composite materials

F01. What's the key point of adhesion between epoxy resin and inorganic materials?

To maximize the adhesion strength, the understanding of the adhesion principle is important. Lists below are some common theories regarding adhesion of surfaces.

1. Balance theory: The simplest application is the consideration of surface tension. Only with a reduced surface tension of the resin can it effectively wet the substrate of adhesion.

2. Molecular theory: By selecting appropriate functional groups, a strong intermolecular force between the adhesives and the substrate is achieved.

3. The theory of adhesive speed. The resin must imparts a suitable viscosity and thixotropy to expand and soak into the substrate, achieving an optimal strength of adhesion.

F02. How evaluate the adhesive performance by observing the fractured surfaces of its tensile test samples?

1. The morphology of the fractured tensile test samples can be classified as follows: The delamination of adhesives: One side of the substrate adheres a residue of adhesives, leaving a smooth surface on the other. At this stage, effort should be made to ensure the adhesive adhere to both sides of the substrates.

2. The fractured surfaces of the substrates had adhesive remained. The surface was smooth, with micro cracks observed at the front edge. At this stage, the adhesive itself is brittle, lacked toughness, and its impact energy is low.

3. Both the fractured surface of the substrates observe a residual adhesives with extremely substantial surface roughness, standing in a form like fish scales. This stage represents the toughness of adhesives is high, and the fracture energy was maximized to obtain an optmal adhesive strength.

F03. Is there a correlation between the viscosity of adhesive and its strength?

In the Chinese language, viscosity is sometimes regarded as the ability to stick a material. Many Mandarin speaking customers hence interpret the adhesive strength as viscosity. In fact, the viscosity and adhesive strength is not necessarily correlated; high viscosity does not guarantee high adhesive strength.

On the basis of two identical chemical structures, the adhesive with lower viscosity penetrates the substrate better than the one with a high viscosity. Therefore, the adhesive with a lower viscosity may impart a more superior adhesive strength. As for the maximal viscosity allowed for adhesives before its strength decreases, different applications conclude a wide range of results. Overall, the correlation between viscosity and adhesion strength should be validated by experiments. In general, highly viscous liquid often behave in a thixotropic manner. With a high thixotropy, the penetrating ability is relatively poor. However, there are a few exceptions. When the viscosity of the adhesive is below a certain threshold, the thickness of adhesives becomes thin, resulting in poor adhesive strength.

F05. What’s the definition of Tg?

Tg (Glass transition temperature) is strictly defined in an academic context. Glass transition occurs at a temperature allowing a small molecular chain consisting of 4 to 5 atoms on the macromolecular main chain to migrate into the adjacent free volume. Temperature at which the glass transition takes place is defined as glass transition temperature (Tg). Besides, properties such as specific heat, thermal expansion coefficient, modulus, dielectric constant, and hardness, undergo a change as temperature increases to beyond the Tg of a material.

F06. Do materials with a high Tg offer better heat resistance?

Tg is not necessarily correlated to multiple physical characteristics. For instance, though the Tg of silicone is at sub-room temperature level, the heat resistance of silicone is better than many other materials with a high Tg.

For a formulation composed of a non-reactive diluent and an external plasticizer, even if its Tg exceeds a formulation containing reactive diluent and an internal plasticizer, its heat resistance is inevitably worse than the latter.

Therefore, the correlation between Tg and heat resistance is only worth-discussing in the formulations based on two identical materials (e.g., epoxy resin), manufactured by the same methodology. Once an essential constituent is changed, which may affect the high-temperature degradation behavior, the correlation between Tg and heat resistance complicates significantly.

F07. Why can’t the Tg presented in different technical data sheets across multiple manufactures be cross-compared?

There are many instruments that can be used to measure Tg, each with different principles. Even if the test was conducted using the same instrument, factors such as different configuration, different sample shapes, or different manufacturers of the instrument can all provide different results.

Taking DSC (differential scanning calorimeter) and DMA (dynamic mechanical analyzer) as an example, it is common that Tg of a certain material measured by the two instruments exhibits more than 50°C of discrepancies. In addition, the technical data sheet published by many manufacturers only lists the Tg value without outlining the methodology of measurement. Therefore, it is virtually impossible to make a cross-comparison.

To measure the Tg of multiple materials, the best method is to standardize the test criteria using the same instrument and conduct the test at the same time. Such comparison yields a higher level of confidence.

F08 What is the thermal expansion coefficient of epoxy resin?

The thermal expansion coefficient of filler-free epoxy formulation below its Tg is typically 80 ppm. For thermal expansion coefficients above the Tg, the value approximates between 160 to 200 ppm. The thermal expansion coefficient of a formulation containing inorganic filler is dependent on the volume ratio occupied by the inorganic filler. A low thermal expansion coefficient is expected with a high percentage of inorganic fillers.

F09. What is the shrinkage rate as epoxy resin cures?

Generally, the volume shrinkage rate of epoxy formulations without inorganic filler is roughly 3%. As for the linear shrinkage rate, the value is about 1%. Photo-cured resin without inorganic fillers has a volume and a linear shrinkage rate of about 8-10% and 3%, respectively. Mentioned above, the thermal shrinkage is dependent on the content of inorganic fillers.

F10. Why do some one-component epoxy resins generate bubbles after the cure?

1. Violent exothermic reaction, causing degradation to occur. A large expansion of the volume appears similar to foaming. This issue can be addressed by lowering the temperature and prolonging the time of cure.

2. Some small molecular weight components in the resin formulation imparts greater volatility, which is the source of bubbles.

3. Air bubbles embedded in the adhesive itself. Placing the adhesive on top of a glass to cure can determine whether the bubbles contain in the adhesive itself, or the bubbles generated by the influence of the substrate.

4. The hygroscope or damp of the substrate. The moist substrate releases water vapor, causing bubbles to form at high temperature. The most common examples are PC and Nylon. A solution to this is to pre-heat the substrate at 100°C to primarily evaporate the surface moist.

F11. Why do some epoxy resin formulations burst as they emerge into a wave soldering?

Some epoxy resin formulations use non-reactive diluents, plasticizers, and additives that do not take part in the reaction. These additives remain in the cured resin, volatilize as it encounters a high temperature wave soldering, causing the cured material to burst. Besides, some epoxy compositions decompose at high temperatures, resulting in odor, and even foaming.

F12. What is the maximum temperature an epoxy resin can withstand for an extended period?

The temperature that an amine cured aerospace grade epoxy resin can withstand is at a level of about 220 to 230°C.

For the acid anhydride cured counterpart, it is between 230 to 250°C. As a post-cure reaction needs to be carried out at 220°C for 5 hours in acid anhydride cured formulations, it is rarely seen in most epoxy resin applications.

F13. How to evaluate thermal degradation?

There are multiple methods. An appropriate choice can only be made from practical perspectives. For example, both adhesives in thin-film geometry or bulk structural materials can be evaluated based on the changes in their strengths before and after heating. Coatings can be evaluated based on the color changes before and after heating. In addition to the actual product evaluation, TGA (thermogravimetric analysis) is used to measure the weight loss due to pyrolysis. Sometimes, the FTIR (Fourier transform infrared spectroscopy) is used to observe the changes of functional groups to reflect the status of degradation.

F14. What are the possible sources of outgassing?

1. When organic materials are subject to heat, vacuum, or both, gas often escapes, resulting in weight reduction. This phenomenon is called outgassing. Its causes may originate from the following ways:

2. The released by-products during the condensation polymerization of the resin.

3. Small molecules, such as monomers, catalysts, diluents, and additives, etc. remain after the resin is cured.

4. Products of degradation at high temperature.

F15. What influences may outgassing cause?

1. Outgassing indicates the change of characteristics of the resin itself.

2. Volatiles may contaminate the surface of the parts.

3. Volatiles may corrode the electronic circuits.

4. Volatiles may cause cracks in plastic materials.

5. Volatiles may pollute the environment.

F16. What are the mechanisms of thermally conductive adhesives and grease?

As the thermal conductivity of air is 0.03W/mK, the gaps between the heating elements (e.g., processing chips) and the cooling elements (e.g., heat sinks) deteriorates the heat dissipation efficiency. Therefore, thermal adhesive and thermal grease are used to fill these gaps. Generally, the thermal conductivity of organic resin is about 0.3W/mK. Adding alumina in the resin increases the thermal conductivity to 1W/mK. Adding aluminum nitride into the resin further increases the thermal conductivity to 2～3W/mK. For silver, the thermal conductivity can reach up to 7W/mK. Some advertisements mistakenly describe the thermally conductive materials as thermally diffusing materials, which is an inaccurate concept. These materials ‘conduct’ the heat from a source to a heat-dissipation device, where the heat diffusion actually takes place.

C01. Epoxy resin is the second most commonly used thermosetting plastics. Its characteristics list as follows:

1. It has excellent mechanical properties, strong cohesive strength, and a superior strength compared to commodity plastics.

2. It has a high adhesive strength, suitable for the adhesion of metal, ceramic, and glass based materials.

3. It has a low curing shrinkage of approximately 1 to 3%, which is one of the lowest among the thermosetting plastics.

4. It has a good workability, no volatile is generated during the cure. It suits a variety of processing conditions.

5. It has a good electrical property; its volumetric resistivity is typically above 1014W·cm.

6. It is chemically stable, withstanding chemical corrosion from acids, alkalis and salts.

7. It is heat-resistant. Generally, it is capable of withstanding temperatures around 100°C. Some specialty grades can even endure heat of above 200°C.

C02. The constituents of two-component epoxy resin:

Part A consists of resin, part B consists mostly of hardener. In addition to these two primary components, additives such as diluents, catalysts, tougheners, fillers, pigments, anti-sagging agents, defoamers, etc are added into the formulation of two-component epoxy resins.

C03. The classifications of epoxy resin can be made upon its raw materials, listed as follow:

1. Glycidyl ethers (e.g., DGEBA, DGEBF)

2. Glycidyl esters

3. Glycidyl amines (e.g., TGDDM)

4. Aliphatic epoxy compounds

5. Cycloaliphatic epoxy compounds

6. Hybrid (e.g., acrylic epoxy) epoxy resins

C04. Chlorine content of epoxy resin:

During the synthesis of epoxy resin from its raw material, epichlorohydrin, some side reactions occur. For example, the residue of chlorine element present in the resin results in hydrolyzable chlorine and non-hydrolyzable chlorine. This chlorine residue is unavoidable, as epichlorohydrin contains chlorine. Ordinary-grade epoxy resin contains approximately 1800 ppm of the residual chlorine.

For cycloaliphatic epoxy produced by peroxide, as it does not introduce chlorine into the epoxy resin, the content of chlorine residue is extremely low.

C05. Commonly used curing agents for epoxy resins:

1. Amines (aliphatic amines, cycloaliphatic amines, aromatic amines, and polyamides, etc.)

2. Acid anhydrides

3. Polymercaptans

4. Catalyst-type curing agents (e.g., tertiary amine, imidazole)

C06. The use of diluents in epoxy resin.

The most commonly used epoxy resin (DGEBA) has a viscosity of about 15,000 cps. As some epoxy resins are highly viscous, diluents are added into the formulation to lower the overall viscosity, facilitating the application of the epoxy formulation. Diluents are categorized into reactive and non-reactive types. Reactive diluent consists of functional groups that react with the resin to become part of the polymer network, having less impact on the overall properties. As non-reactive diluent does not react with the resin, its long-term effects, such as its temperature of operation, environment, and system compatibility etc., on the polymerized network must be carefully evaluated.

C07. Function of catalysts in epoxy resin.

Catalysts promote the reactivity between epoxy resin and its curing agent, thereby shortening the time of cure.

C08. Functions of tougheners in epoxy resin.

Epoxy resin is a highly crosslinked thermoset; the cured material is hard and brittle. Tougheners improve the impact strength, fracture energy, and tolerance of crack defects to avoid rapid crack propagation during the weathering test. An iconic example is liquid rubber, which is evenly dispersed into the cured material, improving its toughness.

C09. Purposes of introducing fillers into epoxy formulation:

1. Improvement of specific physical and mechanical properties. For instance, the use of fillers reduces the shrinkage of cure and thermal expansion coefficient. It also resists cracking, promotes hardness and specific gravity. Some fillers improve the thermal conductivity.

2. Improved workability. Fillers sometimes purposefully increase the viscosity, providing anti-sagging properties.

3. Cost reduction. Fillers increase the proportion of part A, leveraging out the cost per unit weight.

4. Properties of some commonly used functional fillers list as follows:

• Alumina improves the thermal conductivity

• Aluminum hydroxide imparts the flame retardancy

• Calcium carbonate reduces cost per unit weight

• Barium sulfate increases specific gravity

• Talc is used for processing abrasive material.

C10. Function of anti-sagging agents in epoxy resin.

Anti-sagging agents form a continuous three-dimensional network in the resin by intermolecular hydrogen bonds, trapping the resin in the midst of this three-dimensional network. This impedes random flowing. The network is damaged as external force applies, reducing the overall viscosity, hence facilitating the operation. When external force disappears, the network restores. Therefore, functions of anti-sagging agents in epoxy resin are:

Prevention of the uncured resin from flowing freely.

Prevent fillers precipitate and migration.

Provision of a thixotropic behavior for resin.

C11. Function of defoamers in epoxy resin.

Epoxy resins incorporate bubbles during its manufacturing, especially mixing. The introduction of defoamer agents induces bubble burst, resulting in a nicer looking appearance of products.

D01. The causes of epoxy resin crystallization.

The most commonly used epoxy resins are crystalline solids under room temperature. Their melting points are typically around 45°C. Usually, these epoxy resins appear like clear liquid, as they situate in a supercooled state. Under the supercooled state, the crystallization rate is extremely low. In some circumstances, several months is required before crystallization occurs. As the storage temperature rises, the driving force of crystallization decreases from a thermodynamic perspective. In this occasion, crystallization is less likely to occur. Contrarily, if the resin is placed in a refrigerated environment, the crystallization rate becomes slow, due to the increase of resin viscosity. Crystallization is also not likely to occur. When the resin is placed in a surrounding area of about 10°C, the crystallization rate peaks. Crystallization is most likely to occur if the resins have a low chlorine content, a narrow distribution of molecular weight, and a high purity.

D02. How are crystallized epoxy resins treated?

Theoretically, the crystal epoxy resin is melted by applying a 60°C heat. For two-component epoxy without filler, part A can be treated this way. Uniformity of the products is ensured if stirring is followed by the heating process. For two-component epoxy that contains filler in its part A, stirring becomes necessary after the heating to avoid the precipitation of certain ingredients. Overall, for crystallized two-component epoxy resins, stirring followed by heating is recommended to ensure a homogeneous consistency.

D03. Reasons for amine agglomeration.

Some aliphatic amine curing agents are hydrophilic. Moisture and carbon dioxide are easily absorbed and reacted with amine to form ammonium carbonate. If the ammonium carbonate is not dissolved in the original aliphatic amine, agglomeration occurs. On the other hand, if these ammonium carbonates dissolve in the aliphatic amines, no agglomeration will occur. Nevertheless, amines with ammonium carbonate dissolved cause yellowing, compromised reactivity, reduced mechanical strength, and foaming when heated. Thus, it is important to keep the curing agent containers tightly closed.

D04. Reasons for acid anhydride agglomeration.

As acid anhydride is synthesized through the dehydration of dibasic acid, it is prone to re-absorbing moisture in ambient air, generating dibasic acid. As the produced dibasic acid cannot be dissolved into the original acid anhydride, the water absorbed acid anhydride appears turbid. There is a chance of precipitation, appearing like an agglomeration in some extreme cases. Besides, as agglomeration is particularly obvious around the lid of the containers, the container of acid anhydride curing agent must be tightly closed.

D05. Why do some cured epoxy resins become oily and foggy on their surfaces?

There are three possible reasons:

1. Improper use of defoaming agent and leveling agent.

2. Poor compatibility between the epoxy resin and hardener, causing hardener to float onto the surface during the cure.

3. Moisture and carbon dioxide absorption of the hardeners. This phenomenon is particularly noticeable under conditions of high humidity, low temperature, and slow reaction speed.

D06. How is gel time defined?

Gelation is a behavior describing a partially cured viscous resin. The reactivity of the resin to gel is about 30% to 40%, depending on the composition. When recording the gel time, it must record both the ambient temperature and the resin weight. Gel time is not a precision measurement. Rather, it should be taken as a reference only. Some resins have a slow cure kinetics, yielding their pot life (operation time) to several hours. Overall, gel time is not a suitable indication of an exact value, but a rough estimate of the pot life of an epoxy resin.

D07. How is pot life defined?

Pot life is a general time range in which the resin can be normally operated. Depending on the precise resin application methods, the definition of pot life varies from case to case. Sometimes, pot life refers to the time taken for the viscosity of resin to climb to 10,000 cPs. Others refer to the time taken for the viscosity of resin to double. Therefore, confusion about the pot life and gel time frequently occurs due to their vague definitions. Similar to gel time, pot life is not a precise value either. When noting down the pot life, both the ambient temperature and resin weight should be recorded. Generally speaking, high ambient temperature and heavy resin results in a short pot life.

D08. What is the cure exotherm of epoxy resins?

As an epoxy resin cures, heat is released (exotherm). This released reaction heat increases the temperature of resin itself, simultaneously catalyzing the reaction. When the temperature of resin rises dramatically, it may damage the surrounding components. The simplest way to evaluate the extent of the cure exotherm of the resin is a thermometer. Under a fixed amount of resin weight and a fixed ambient temperature (usually °C), the relationship between temperature and time is recorded. Plotting the temperature on a vertical axis, time on the horizontal one, the cure exotherm curve is obtained.

D09. The correlation of cure reactivity and reaction temperature of an epoxy resin.

According to the Arrhenius equation, the reactivity (R) and the activation energy (Ea) are proportionally related. From the equation R = Exp(-Ea/RT), it is derived that with a 10°C rise of reaction temperature (T), the reactivity is twice as fast as the original reactivity. In contrast, with a 10°C of temperature reduction, the reaction rate is halved from the original reactivity.

D10. In an arbitrary formulation, the ratio of epoxy resin to its curing agent is 100:50. Is the reactivity increased by increasing the amount of curing agent?

No. The ratio between epoxy resin and hardener is calculated based on their equivalent weights, with a minor tolerance (< 5%). Any significant change to the ratio will result in an undermined property of the cured product. Hence, the reactivity is irrelevant to the increased curing agent dosage.

D11. Can an epoxy resin achieve a complete reaction?

In the context of thermosets, complete reaction is not strictly defined. Instead, the extent of reaction is defined by reactivity. Epoxy resin is a typical example of this. For the reaction between difunctional resin and a curing agent to occur, the activation energy of the reaction must be overcome.

Especially after the resin’s gelation, during which the functional groups are connected by diffusion. With the increase of the reactivity, the concentration of functional groups gradually decreases, increasing the energy level for diffusion to occur. Overall, the activation energy required of some later-stage reactions may outweigh its structural degradation, hindering the resin to achieve a full reactivity.

D12. Is a high reactivity desirable?

The properties of many polymers are relevant to their reactivity. For instance, a high reactivity offers a better glass transition temperature, hardness, heat resistance, and mechanical strength etc. Some polymer properties are not necessarily dependent on their reactivity, such as adhesive strength and rupture energy. In practice, a reasonably fast reactivity is desirable. The pursuit of an ultra-high reactivity can sometimes lead to lengthy manufacturing processes, increased costs, and low feasibility. Taking epoxy flooring paints an example. The reactivity after 7 days of room temperature cure is between 70% and 75%, which is high enough to meet the requirements of hardness and scratch resistance outlined for dust-free floorings. It is not necessary to maximize the reactivity of flooring paints.

A great number of other applications conclude that pursuing a high reactivity is not necessary. At what reactivity is it considered appropriate is more of an issue to consider.

D13. Why does the cure condition of most room temperature cured epoxy resins outline a 7-day cure time?

25°C is considered the most common room temperature value. However, the room temperature itself is not held constant. Instead, it is a possible range between 10°C and 30°C. The cure time of the epoxy resin is cited with a wide range to factor in the changes of room temperatures. Some epoxy resins are poorly cured at temperature below 10° C. It is therefore not possible to properly cure this type of epoxy resin at this temperature for a long period. Therefore, attention should be paid to the low-temperature cure condition.

D14. What is the biggest difference between soft epoxy resin and soft PU (polyurethane)?

PU molecules are strongly bonded by hydrogen bonds, forming a special physical link, exhibiting an excellent flexibility as a result. The structure of epoxy resins is fundamentally different to PU, even toughening agents and softeners are introduced.

The performance of a soft epoxy in repetitive bending tests is not as good as PU. Besides, the reactivity of soft epoxy resin is slow, making its hardness tend to increase gradually after its cure.

D15. Can a cured epoxy resin be removed by solvent?

Once a thermoset is cured, it can no longer be dissolved by a solvent. However, by soaking the cured thermoset in an appropriate ratio of solvent, solvent is absorbed by the cured thermoset. Afterwards, the thermoset swells, softens, loses strength, eventually breaks into tiny particles. The commercially available paint removers adopt this principle of solvent-thermoset interaction. A combination of high boiling point and high polarity solvent can achieve the purpose of removing cured thermosetting resin.

D16. How is flame retardancy introduced into plastics?

In some plastic structures, the proportions of aromatic compounds are large, driving up the LOI (limiting oxygen index) value. The char yield of combustion is also high, offering them inherent flame retardancy. Phenol-formaldehyde resin and furan resin belong to this type of inherently flame retardant materials. For other plastics such as epoxy resin and photocured resin, flame retardant becomes essential to achieve flame retardancy. In addition, flame retardants are divided into halogen-based, phosphorus-based, nitrogen-based and inorganic systems etc. The majority of the aforementioned flame retardants are additive type. There are only a small number of flame retardants that fall into the reactive type. Nonetheless, both the reactive and additive flame retardant will affect some physical characteristics of the resin network.

D17. What attention should be paid during the application of two-component epoxy resins?

1. The four parameters, including viscosity, thixotropy, specific gravity, and compatibility between the two components should be noted. The discrepancy of such parameters must not be too large to avoid the inconsistent mixing.

2. Before using a two-component syringe, a small amount of adhesive should be pushed out to avoid inconsistent adhesive dispense.

3. Determine whether the length and type of the selected mixing rod meet the needs of uniform stirring.

A01. The reaction mechanisms of photo-cured resins are divided into:

1. Acrylic resin that undergoes free radical polymerization.

2. Epoxy resin that undergoes cationic polymerization.

A02. The constituents of photo-cured acrylic resin include:

Oligomers, monomers, initiators, and other additives.

A03. The oligomers commonly used in acrylic resins include:

Epoxy acrylates, urethane acrylates, polyether acrylates, etc. These oligomers all introduce acrylic functional groups at the chain ends of the original resin structure, enabling them to carry out free radical polymerization.

A04. Monomers commonly used in acrylic resins include:

Monofunctional groups, difunctional groups and polyfunctional groups. Most acrylic monomers are the esters produced by the reaction between acrylic acid and alcohol, accompanied with dehydration. Different structures exhibit different characteristics.

A05. The role of photoinitiator in UV-cured acrylic resin:

Photoinitiators absorb the energy of a specific light wavelength, generating free radicals. Both oligomers and monomers contain acrylic functional groups for the generated free radicals to react. The purpose of photocure is therefore achieved.

A06. Reaction principle of photo-cured epoxy resin:

The composition of photo-cured epoxy resin includes initiators, oligomers, monomers, and modifiers. As the initiators are irradiated by light, cations are generated to initiate the polymerization reaction.

A07. The advantages of photo-cured epoxy resin:

Compared to acrylic resin, epoxy resin has a lower shrinkage rate, a better heat, chemical, and moisture resistance. Besides, epoxy resin is insensitive to oxygen, has a lower volatility, and a lower irritation of the skin.

A08. The disadvantages of photo-cured epoxy resin:

Compared to acrylic resin, the reactivity of epoxy resin is slower.

The reaction depth is shallower, and the absorption wavelength for initiators is shorter. The absorption range is also narrower. Furthermore, there are fewer types of monomers and oligomers available for photo-cured epoxy resin systems, which undermines the variability of formulation.

A09. Effect of the photo-initiator absorption wavelength on the photo-cure reactivity:

The light absorption by photo-initiators is a continuous spectrum. Initiators with a low absorption wavelength are suitable to increase the cure reactivity on the surface of photo-cured epoxy resin. Initiators with an absorption wavelength near blue light are suitable for transparent materials that cannot be transmitted by ultraviolet light. The absorption wavelength of some initiators are above 550 nm, which are strongly light-sensitive. Products containing such long-wavelength photo-initiators must be handled under a yellow light illuminated area or a dark room.

A10. Effect of the initiator's absorptive sensitivity on the photo-cure reactivity:

Highly sensitive initiator imparts a high initial efficiency, achieving a similar reactivity in weak light intensity or a low light energy. It is suitable for dark colored photo-cured systems.

A11. Effects of the light source emission wavelength on the photo-cure reactivity:

The light source provides energy to be absorbed by photo-initiators for a photo-cure reaction to commence. The light source extensively used in photo-cure systems is a high-pressure mercury lamp, with a maximum emission wavelength of 365 nm. Also, a halogen lamp can be made by doping metal halides into a high-pressure mercury lamp, resulting in a maximum emission wavelength of between 400 and 450 nm, near the blue light region. Different applications use different photo-initiators and different light sources to achieve their suitable cure reactivity.

A12. Irradiance energy required for photocuring reaction:

A typical photo-cured acrylic resin requires about 800 - 2000 mJ/cm2 of irradiance energy at 365 nm wavelength. Photo-cured epoxy resin requires about 3000 - 6000 mJ/cm2. The value of irradiance energy depends primarily on the desired reactivity of cure.

A13. Common wavelengths of ultraviolet and visible light:

1. Long wave UV light is 365 nm

2. Short wave UV light is 254 nm

3. Visible light (blue light) is 436 nm

B01. What is the irradiance of a general UV lamp?

Take a 400W ultraviolet light source as an example. Its wavelengths of irradiance are a 365 nm UV-A wavelength and a 400-440 nm visible light. The irradiance energy measured at 10 cm below the bulb were 120 mW/cm2 (365 nm) and 80 mW/cm2 (436 nm). The irradiance energy is inversely proportional to the square of the distance from light source to the object. Hence, the irradiance energy decreases exponentially as the distance in between increases.

B02. What is the irradiance of a common point source?

The irradiance energy of commonly used ultraviolet lamp point source is at least 800-1000 mW/cm2 (365nm). Models with a higher irradiance energy can achieve 2000 mW/cm2 (365nm). Some point light sources belong to the visible light range, applied as indirectly projecting light, with a mere 20 mW/cm2 (365nm) or below of irradiance energy.

B03. What effects are caused to UV-cured adhesive exposed to an excessively strong irradiation?

An exceedingly strong irradiance energy will negatively impact the properties of the UV-cured adhesives. For instance, by increasing the irradiation by a nth order of magnitudes, the reactivity increases by the same order of magnitudes. This generates n times the amount of free radicals, promoting the free radical growth rate by n times. However, the speed of reaction termination is increased by n2 times in the meantime. In other words, too strong an irradiation reduces the molecular weight of an acrylic adhesive, creating more chain ends. With an excessive number of chain ends, the optimal strength of an acrylic adhesive is not obtained.

B04. What impacts the UV-cured adhesive when the irradiance energy becomes excessively large?

In general, the acrylic UV adhesive would rather be irradiated with an excessive level of energy than an insufficient irradiance energy. From either a theoretical or a practical point of view, even if the irradiance energy of this type of UV-cured adhesive were exceeded by 10 times the original recommended value, there are no obvious negative effects. Only if the irradiance energy exceeds the recommended value by up to hundreds of times does photodegradation become a concern.

B05. What are the concerns of insufficient irradiance energy on acrylic UV-cured adhesives?

If an acrylic UV-cured adhesive were irradiated with insufficient energy, some unreacted acrylic monomers remain in the network. These residual monomers function as a plasticizer in the UV-cured adhesives in the initial stage, resulting in low hardness, insufficient strength, high water absorption, and poor environmental performance. With the increase of time, these monomers gradually volatilize, causing the adhesive to harden gradually, causing the instability of physical properties. Some practical cases point out that these monomers may diffuse into the plastic substrates, causing cracks in these plastics (such as PC, Acrylates, etc.). Hence, UV-cured adhesives must be irradiated with a reasonably high level of energy to avoid insufficient cure.

B06. What are the causes of poor surface dryness in some UV-cured adhesives?

Photo-cured acrylic resin is cured by the chain reaction between free radical and acrylic monomers. Each time the free radicals and acrylic monomers react, new free radicals generate. However, free radicals also react with oxygen in the air to produce peroxide free radicals. The reactivity of free radicals with oxygen is hundreds of times faster than that of free radicals with monomers. Whereas, the reactivity of the generated peroxide radicals with acrylic monomers is very slow, lowering the reactivity as a result. Besides, this effect is most obviously observed near the surface of the resin. In a mild situation, the reactivity of the resin surface is simply lower, with a poor scratch resistance. In a more serious scenario, the surface becomes tacky, indicating a poor reactivity. If the film were thin, a complete cure may not obtain.

B07. What is the reaction mechanism of UV & anaerobic hybrid cured adhesive?

Acrylic resins undergo chain polymerization in the presence of free radicals. Free radicals are generated by a photoinitiator which absorbs a specific light wavelength. Alternatively,free radicals are obtained by elevating temperature to a level that decomposes the thermal initiator (peroxide).

The mechanism of UV & anaerobic hybrid cured adhesive is introducing a thermal initiator to the UV-cured adhesives. As both the presence of metal catalyst and the isolation of oxygen (air) satisfies, the free radicals obtained from a decomposing thermal initiator allows the UV-cured adhesives to cure without the exposure to light. Furthermore, metal catalyst lowers the decomposition temperature of peroxides. Metal catalyst is sourced from the surface of metal substrate or a pre-coated primer. The reason why oxygen (air) requires isolation is because oxygen reacts with the inhibitor, consuming the free radicals generated by peroxide. This hinders the curing reaction. Therefore, oxygen is segregated to perform the anaerobic curing reaction.

B08. What should be noted when packaging UV-cured adhesives?

1. Store it in a cool dry place. Avoid contact with sunlights.

2. Store in a well-ventilated place.

3. Do not modify the packaging of resins.

4. Select an appropriate container material for packaging (e.g., PE, PP plastic buckets, stainless steel buckets, black steel pail, or opaque glassware).

5. Avoid contacting metals such as copper and iron, as such metals cause polymerization.

6. Do not apply vacuum to the resin.

7. Do not fill resin packaging with nitrogen or oxygen-free gas.

8. Do not fully fill the container with resin. There must be a space in the container to maintain a level of oxygen to suppress the reaction.

B11. Is photo-cured resin completely and thoroughly reacted?

Similar to common thermosetting resins, photo-cured resins do not fully react.

From the number of acrylic functional groups, the reactivity of the photo-cured resin peaks at about 80% to 90%, with some residue of functional groups. Moreover, the reactivity of a polyfunctional monomer is lower than that of a monofunctional monomer, as there is a larger number of free radical residues in polyfunctional monomers. From the perspective of the photo-initiator, the photo-cure reaction consumes only 20% to 30% of the photo-initiator. The remaining photo-initiator is left in the cured material.

B12. How is water absorption rate measured?

The simplest way is to soak a number of samples in water at a specific temperature for a specific duration of time. The average weight changes of the water-soaked samples are represented as the water absorption rate.

B13. Is the water absorption rate of cured resin inevitably greater than 0?

Most cured resins will gain weight after soaking them in water. In other words, the water absorption rate of most cured resins outnumbers 0. Some constituents of resins might dissolve in water, causing weight loss. In such cases, the water absorption rate is lower than 0.

B14. How to evaluate the applicability of adhesives for plastic substrates?

For an adhesive to achieve a good adhesion between plastic-based substrates, there are some requirements to be satisfied:

The ability to swell the substrate.

The ability to form an interpenetrating polymer network (IPN) with substrate. Regarding the first point, there is a simple evaluation method: Apply the liquid adhesive on the plastic substrate and wipe it off after a few minutes to observe whether the surface of plastic trunks white or hazy.

Regarding the second point, a review on relevant literature and a sophisticated experimental experience are required to methodically prove the formation of an IPN between plastic substrates.

B15. What plastic materials can be adhered by a UV-cured adhesive?

• Materials such as PC, ABS, PVC, PS, acrylate, MS, and SAN are proven effective in UV-cured adhesives.

• Attempts have been made to adhere the following materials by UV-cured acrylic adhesives: Nylon, PET, and PBT, etc.

• Without surface treatment, the acrylic UV-cured adhesive is proven failed to bond the following materials: PE, PP, and silicone.

B16. When dyeing transparent plastics, which colors affect the UV-cured adhesive the least?

In principle, plastics dyed red are most difficult to cure. Orange might stand a chance, and blue should be the easiest. Dyed plastics should use a highly sensitive photo-initiator to improve their reactivity. As for whether the UV-cured adhesives can be properly cured, several parameters apply, including the saturation of the color and the thickness of plastics. There is no general rule to follow.

B17. How to evaluate whether UV light is transmitted through transparent plastics?

The simplest way is to take two pieces of plastic substrates, dispense UV-cured adhesive between them, and expose the substrates under UV light. Judgment is made by whether the adhesive is cured.

A digitized method is to place the plastic substrate on top of a lux meter, exposing it under a UV lamp afterwards. The reading of the lux meter can be taken as a reference of the transmittance of the material by a specific UV wavelength.

B18. Why does the viscosity of different photo-cured resins vary?

Many organic polymers are not pure substances. Substances such as homologs and by-products coexist in raw materials. Manufacturers aim to control the content and proportion of these substances within a range. However, it is not guaranteed that every batch of production generates identical compositions. Therefore, the viscosity of produced resin formulation changes in a certain range.

B19. Why can’t the viscosity outlined in different technical data sheets across multiple manufacturers be cross-compared?

Viscosity varies depending on several parameters, such as the configuration of viscometers, geometry of the rotor, data reading, instrumental set-up, calibration, and the accuracy of temperature control. In the measurement of low-viscosity and Newtonian fluids, the above-mentioned parameters are negligible. However, when measuring high viscosity, non-Newtonian fluids, the discrepancies in data between different manufacturers vary significantly. Therefore, to precisely measure the viscosity of certain liquid materials, testing the products by using identical instruments is the only key to obtaining accurate and reliable results.

B20. What are the correlations between viscosity and temperature?

According to the Arrhenius equation, viscosity (η) and temperature (T) are expressed as follows: η Exp(-Ea/RT). From this relation, it is derived that as temperature rises by 10°C, the viscosity halves from the original value. In contrast, when the temperature drops by 10°C, the viscosity is twice as large as the original. The relationship is generally applicable to Newtonian fluids, which is homogeneous (without inorganic fillers). However, in heterogeneous, non-Newtonian fluid, the relationships become unreliable.

B21. Can surface treatment significantly improve adhesion?

Not necessarily true, as the cause of adhesion failure plays a vital role. If the delamination between adhesive and the substrate were the cause of adhesion failure, surface treatment on the substrate can improve the adhesive strength. If it was due to an insufficient mechanical strength of the adhesive itself, adhesion strength cannot be improved by the surface treatment of substrates.

B22. How is surface treatment conducted?

1. Grinding: Introduce a rough surface of the substrate through wiping or sandblasting. Oxides and dust on the surface of the object can be removed this way. As the surface of the object is roughened, the surface area for bonding is increased, thereby improving the anchoring effect.

2. Solvent cleaning: The surface of substrates can be cleansed by soaking it in solvent, or emerging in an ultrasonic vibration tank. Solvent vapor is effective in removing the oil stains, organic impurities, and pollutants from the surface of substrates.

3. Degreasing with hot lye: Though soap or lye are effective to remove the oil from the substrate surface, these cleaners must be washed afterwards.

4. Chemical etching: Chemical etching is a technique that introduces chemical agents or flame treatment to remove oxides. With chemical etching, the reactivity of the surface of materials is improved. Surface functional groups are created, and the anchoring effect becomes pronounced

5. Physicochemical etching: Corona treatment, plasma treatment or UV irradiation are introduced to the substrate surface to alter its structure. Similar to chemical etching, the reactivity of the surface of materials is improved. Surface functional groups are created, and the anchoring effect becomes pronounced

6. Creation of a new surface: The surface of the metal is galvanized with a metal that differs from the substrate to improve the adhesive effect.

B23. What are the expected outcomes of surface treatment?

1. Removal of the contaminated surface from the substrate.

2. Improved anchoring effect of adhesive or primer.

3. Improved wettability of the substrate surface.

4. Established chemical bonds between the substrate surface and adhesive or primer.

B24. The common types of primer and their functions?

There is a diverse type and function of primers. A few examples list as below:

1. Organic silane establishes chemical bonds between inorganic surfaces and organic adhesives.

2. Organometal is commonly used in anaerobic adhesive to increase the cure reactivity of anaerobic adhesives.

3. Alkaline catalyst is commonly used in superglues to enhance the cure reactivity.

4. Long-chain aliphatic amine is often used in superglue systems to increase the cure reactivity of superglue and improve its adhesion to PE, PP, and silicone.

5. Chlorinated rubber is applied on the surface of PE and PP to improve the adhesive strength.

6. Solvent-based adhesive is applied on the surface of the substrate. Utilizing the solvent-based penetrating ability to create a higher anchoring effect, thereby improving the adhesive effect.

7. Other chemicals are sometimes used as interface compatibilizer, electrostatic absorber, and anti-corrosion agent of the surface to improve the adhesion effect.

B25. What makes rubber materials difficult to adhere to?

There are a variety of rubbers that cause confusion. Some non-rubber elastomers are often mistaken as rubber. Also, the softness, flexibility, and compressibility of rubber are exceptional. Therefore, it is difficult for relatively stiff adhesives to endure such a large extent of deformation from multiple directions. Furthermore, the molecular structure of rubber has almost no polarity, resulting in low surface tension. A low surface tension rubber is inherently disadvantageous for the adhesive to develop a strong force with rubber.

Additives such as processing oil are sometimes introduced during the production of rubber. The use of such additives on the rubber surface is another factor affecting rubber’s ability to be adhered to.

B26. What makes nylon and PET difficult to adhere to?

Nylon and PET are both crystalline polymers. They are resistant to chemical corrosion on their own. Therefore, swelling by epoxy resin or photo-cured resin into such material is hindered. Chemicals such as phenols or some high boiling point solvents, which are compatible with nylon and PET, are rarely introduced into the adhesives formulation, making nylon and PET troublesome to be adhered.

However, thermosetting epoxy resin offers nylon and PET a better adhesive effect than other adhesives. Also, by roughening the surface of the substrate, adhesive strength can be improved. Some commercially available PET surfaces have undergone corona treatment. Some PET surfaces are amorphous, rather than crystalline. Both types of surface-treated PET can effectively address the adhesive obstacles faced by ordinary PET.

On the other hand, some PET surfaces are hard-oated. The results of this type of modification increase the difficulty of adhesion. Resin formulations with better affinity to inorganic systems must be tested prior to their application.

B27. What makes PE and PE difficult to adhere to?

PE and PP are non-polar and high crystallinity materials. Similar to the case of nylon and PET, PP and PE make the adhesives to wet them difficult. Strong chemical bonds are hardly established. Plus, due to their high crystallinity, the surfaces of plastic are hardly swelled. Therefore, there is no suitable adhesive for plastics such as PE and PP.

However, using chlorinated PP as a primer, superglues can partially improve the adhesion to PE and PP. Conducting flame or corona treatment to the surface can achieve similar effects. Due to equipment or process limitations, these methods are not the optimal solutions.

The assembly of one-component glue gun and syringe follows the below steps:

1. Insert the push rod located at the rear of the glue gun upward to install the push plate.

2. The telescopic push plate is inserted through the gun head (the tooth pattern faces downward).

3. Push the push plate backward or pull it to the bottom.

4. Pull the push rod to the bottom and secure it (front).

5. Pull up the safety buckle.

6. Buckle the end of the one-component resin syringe into the fixture.

7. Fasten the safety buckle.

8. Securely press the buckle all the way to its end.

9. The combination of one-component resin syringe and glue gun is completed.

10. Press the wrench handle to drive the push plate forward. The piston behind the tube is pressed, releasing the adhesives.

11. After use, open the safety buckle.

12. Push the rear push rod upward and pull the push plate back to the end.

13. Remove the syringe to complete the work.

This section lists the necessary personal protective equipments when handling photo-cured resins.

• Goggles

• Two layers of gloves

Inner layer (general PE gloves)

Outer layer (nitrile gloves)

• Face mask

General notice:

• Photo-cured resin should be operated in a well-ventilated area.

• Should bare skins be exposed to the photo-cured resin, it should be removed by either IPA (Isopropyl alcohol) or acetone.

• After wiping hands with solvent, the hands should be washed with a soap and subsequently dried with a dry cloth before re-starting work.

• UV-cured resin contains N-Vinyl-2-Pyrrolidone (CAS No: 88-12-0). Though this material is not toxic, it causes skin irritation. Therefore, the use of personal protective equipments is recommended when handling photo-cured resin products.

Introduction to pneumatic packaging

• Special adapter assembly for converting syringes with different sizes.

• Adapter.

• FS series products 300 ml syringe.

• Combine the small syringe with the rear piston.

• Insert the inner piston all the way with the help of a tool.

• It is important to insert the rear piston thoroughly to the bottom.

Pneumatic equipment and dispensing sleeve tools

• Install the 300 ml syringe into the aluminum air pressure sleeve

• Lock the rear cover with a gasket inside to prevent air leakage from affecting the glue discharging pressure.

Pneumatic dispensing machine: Connect the air inlet pipeline and power supply to start

• The aluminum sleeve is installed on the air outlet of the pneumatic dispensing machine.

• Tighten the fixing groove according to the structure.

• Adjust the output air pressure

• Set the dispensing quantity and the time needed for each syringe.

• After the installation is completed, the dispensing operation may start.

• Carry out subassembly work and install the adapter kit.

• Install the pneumatic sleeve and expose the adapter.

• When installing a small size empty syringe, please tighten it.

• Prepare for packaging.

• The dispensing speed is controlled by air pressure, according to the viscosity of the adhesive.

• Continue dispensing until the required amount of adhesive is obtained.

• Remove the syringe and cover the front lid, replace with a new empty syringe and repackage again.

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• After dispensing, remove the syringe to complete disassembly.

• Complete the packaging operation and perform cleaning operations.

• After dispensing glue, remove the adapter and remove most of the remaining glue material in the tube.

• Then put in solvent to soak and clean. (MEK or acetone)

• Please clean the front of the large syringe, tighten the head plug, and store it dry.