Q&A
About Resin Properties
Structures in which a PVC sheet comes into contact with ABS resin seem prone to decline (via stress cracking) in the ABS. Why? Moreover, oil adhering to the product is considered sub-optimal. Why?
*Please also see our page on chemical resistance .
The problem of deterioration (stress cracks) occurring when ABS resin comes into contact with any substance can be explained by the resin's chemical resistance.
Even if the solvent is not strong enough to dissolve ABS resin, if an ABS molded product has internal stress (residual stress) that occurred during the molding process, cracks (stress cracks) can occur at the stressed parts of the molded product when it comes into contact with chemicals that do not dissolve ABS but have swelling or penetrating (attacking) properties, such as glacial acetic acid, alcohol, or gasoline.
Stress cracks occur in ABS when it comes into contact with a PVC sheet because the plasticizer contained in the PVC sheet (soft PVC) migrates partially from the PVC sheet to the ABS resin, acting as an aggressive chemical on the ABS and causing stress cracks.
In the past, it was common for ABS to deteriorate due to PVC sheets, as mentioned in the question, but recently the plasticizers in PVC sheets have been changed to non-migratory plasticizers, and this type of ABS deterioration has become less common.
There are various chemicals that can cause stress cracks in ABS (are aggressive), as shown in the table below. Even with animal-based and vegetable-based oils, there is a difference in aggressiveness, with vegetable-based oils tending to be stronger.
This stress cracking can occur in resins other than ABS as well, but the chemical resistance of the resin to the chemical is strongly influenced by the composition of the resin and the chemical composition of the chemical, as well as the amount of distortion in the molded product.
The chemical resistance of ABS resin for general substances is evaluated based on the distortion using the 1/4 ellipse method and the amount of distortion (critical distortion value) at which stress cracks occur when chemicals are applied.
The chemical resistance data for common ABS resins is shown in the table below.
Chemical resistance of ABS
| Drug name | Critical strain (%) | Drug name | Critical strain (%) | Drug name | Critical strain (%) |
|---|---|---|---|---|---|
| 10% hydrochloric acid 10% caustic soda, ethyl alcohol, gasoline, kerosene, silicone oil, silicone grease, salad oil, sesame oil, butter, vinegar |
0.7 or higher 0.7 or higher 0.25 Less than 0.2 0.5 0.7 or higher 0.7 or higher 0.56 0.63 0.62 0.7 or higher |
Hair spray Hair tonic Cleansing cream Hair liquid Fragrance Bouquet Forest bathing Flon R-11 Rust inhibitor cutting oil Earth aerosol ink |
0.22 0.31 0.45 0.56 0.25 0.24 0.68 0.6 0.3 0.48 0.5 |
Family Mama Lemon Strong Look My Pet Mama Royal Charmy Green Toilet Magiclean Toilet Look Quickle DOP (PVC plasticizer) |
0.45 0.7 or higher Less than 0.2 0.31 0.5 0.42 0.29 0.7 or higher 0.7 Less than 0.2 |
| Test method: Techno (formerly Mitsubishi Chemical) bending form (1/4 ellipse) method 23℃, 17 hours, test piece 2mm pressed sheet |
|||||
| Drug name | Critical strain (%) | ||||
|---|---|---|---|---|---|
| 10% hydrochloric acid 10% caustic soda, ethyl alcohol, gasoline, kerosene, silicone oil, silicone grease, salad oil, sesame oil, butter, vinegar |
0.7 or higher 0.7 or higher 0.25 Less than 0.2 0.5 0.7 or higher 0.7 or higher 0.56 0.63 0.62 0.7 or higher |
||||
| Drug name | Critical strain (%) | ||||
| Hair spray Hair tonic Cleansing cream Hair liquid Fragrance Bouquet Forest bathing Flon R-11 Rust inhibitor cutting oil Earth aerosol ink |
0.22 0.31 0.45 0.56 0.25 0.24 0.68 0.6 0.3 0.48 0.5 |
||||
| Drug name | Critical strain (%) | ||||
| Family Mama Lemon Strong Look My Pet Mama Royal Charmy Green Toilet Magiclean Toilet Look Quickle DOP (PVC plasticizer) |
0.45 0.7 or higher Less than 0.2 0.31 0.5 0.42 0.29 0.7 or higher 0.7 Less than 0.2 |
||||
| Test method: Techno (formerly Mitsubishi Chemical) bending form (1/4 ellipse) method 23℃, 17 hours, test piece 2mm pressed sheet |
|||||
[How to interpret the results]
Based on the critical strain values from this test, the guidelines for actual use are shown below.
Please note that this guideline is merely an estimate of the occurrence of whitening, cracks, etc. during actual use based on the results of test pieces. Please confirm this through practical testing at your company.
| Critical strain value | 0.3% or less : | Unusable level. There is a high possibility that cracks will occur due to slight stress during product assembly, transportation, etc. |
| Contact with chemicals may cause whitening and cracks. Particular care is required when subjected to strong stress. | ||
| 0.7% or more: | Suitable for practical use. There is little possibility of cracks occurring due to contact with chemicals. |
| Critical strain value |
|---|
| 0.3% or less: Unusable level. There is a high possibility that cracks will occur due to slight stress during product assembly, transportation, etc. |
| 0.3% to 0.7%: Contact with chemicals may cause whitening and cracks. Particular care is required when subjected to strong stress. |
| 0.7% or more: Suitable for practical use. There is little possibility of cracks occurring due to contact with chemicals. |
In order to prevent stress cracks, it is necessary and effective to take measures against the two causative factors.
- Aim to reduce residual stress in molded products.
Stress cracks are prevented by keeping the residual stress of the molded product below the critical strain value of the aggressive chemical. Specifically, this mainly involves measures on the molding side, such as measures for the shape of the molded product and optimization of moldability conditions. - Change the type of chemicals that come into contact with the PVC sheet, such as by changing the type of additives used, or prevent contact altogether.
The main measures are to deal with the chemicals used, such as changing to less aggressive chemicals or avoiding contact with the substance.
