MASTER'S THESIS
Non-Drilling Solutions
The Investigation of user Friendly and Non-Destructive Adhesive Solutions for Wall Attachment
Emma Svensson 2015
Master of Science in Engineering Technology Industrial Design Engineering
Master Thesis in Industrial Design Engineering
Department of Business Administration, Technology and Social Sciences
Non – drilling solutions
“The investigation of user friendly and non- destructive adhesive solutions for wall attachment”
Emma Svensson
2014 Supervisor: Åsa Wikberg-Nilsson Examiner: Peter Törlind
Master of Science Thesis Non-drilling solutions
The investigation of user friendly and non-destructive adhesive solutions for wall attachment Master of Science Thesis in Industrial Design Engineering- Product design and development
© Emma Svensson Published and distributed by Luleå University of Technology SE-971 87 Luleå, Sweden
Telephone: + 46 (0) 920 49 00 00
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Luleå University of Technology Reproservice Luleå, 2015
Acknowledgement
The acknowledgement is the chance for the writer to say a couple of words about the project thank the persons involved or share reflections. I have dedicated this section to thank all the people who for any reason been involved in the project, here after follow a lot of thank you.
Thank you to Nathalie Ruter at IKEA of Sweden who initiated the project and have contributed to keeping the project on the right path.
Thank you to my tutor at LTU, Åsa Wikberg-Nilsson, for supporting me through the project and contributing with your insights in the product development process, methods and the academic aspect of the project.
Thank you to my tutors Michael Lindholm at IKEA of Sweden and Martin Nilsson-Lind at IKEA Components for guiding me in the right direction at IKEA and for sharing your ideas and knowledge.
Thank you to all the personnel at IKEA who have taken the time to give me advice and sharing their wisdom and contacts. Especially thank you to Sven-Ingvar Johansson at IKEA Test Lab for the support through all the tests carried out.
Thank you to Max Mallmin on the opposite side of the desk for always being available for discussions.
Thanks to all the people sitting in BA OSOF at IKEA of Sweden for making me feel welcome and a part of the group. You have contributed to a lot of laughter at the “fika” and lunches. Being surrounded by people who make you feel comfortable and happy contributes with energy and makes the work more easy and fun.
At last thank you to my family who have put up with me, supported me and just believed in me.
Luleå 23th of January 2015 Emma Svensson
Abstract
A master thesis project in Industrial Design Engineering at Lulea University of Technology in collaboration with IKEA of Sweden has been conducted during the fall 2014. IKEA wishes to investigate the possibility to extend their FIXA range with a product that enables attachment of hooks to the walls in the homes of the customers without using drills and screws. By offering sustainable, functional and qualitative products that enables non-drilling attachment and can be removed, IKEA wants to make everyday easier for the people whom for some reason not are able to use a drill in their homes.
The project has utilised the generic development process presented by Ulrich &
Eppinger. The phases, Planning, Pre-study and research, concept generation and evaluation has been elaborated to reach a pleasing outcome. By studying the fields of adhesives, PSA-tape, glue, usability and wall construction a knowledge base for the project has been created. Market analyses with the aim to investigate and identify potential non-drilling solutions and gain an understanding about wall construction in countries representative for IKEA’s market has been carried out.
Tests have been carried out to evaluate the performance of the non-drilling solutions identified. Adhesion to the most common wall substrates and product materials within IKEA has been evaluated as well as the removal from the walls.
In the end four adhesives was evaluated. The solutions chosen for evaluation are denoted A, B, C and D in this report.
The test data has been analysed and evaluated and the result has been used to present the solutions potential and to give recommendation to IKEA regarding if and how to proceed with the non-drilling solutions.
KEYWORDS: Non-drilling, adhesion, cohesion, tack, adhesives, glue, PSA-tape, wall substrates.
Sammanfattning
Ett examensarbete vid Luleå Tekniska Universitet i samarbete med IKEA of Sweden har utförts under hösten 2014. IKEA vill undersöka möjligheten att utöka deras sortiment med en eller flera produkter som kompletterar upphängning med borr och skruvar inuti hemmen hos kunder. Genom att erbjuda en hållbar, kvalitativ och funktionell produkt som tillåter upphängning utan borrning och penetrering av väggen, som kan avlägsnas vill IKEA underlätta vardagen för de många människorna som av olika anledningar inte har möjlighet att använda en borr i sitt hem. Projektet har avgränsats till att utvärdera upphängningen av krokar och material som ingår i IKEAs sortiment.
Projektet har utgått från en generisk utvecklingsprocess presenterad av Ulrich och Eppinger. De olika faserna: planering, förstudie, konceptgenerering och utvärdering har genomarbetats för att få fram önskat resultat. För att skapa förståelse för projektet och resultatet har en teoretisk grund bestående av ämnen som vidhäftning, PSA-tejp, lim, väggkonstruktion och användbarhet skapats.
Under projektet har en marknadsanalys utförts med syftet att identifiera vidhäftningsmaterial som kan användas av IKEA, även de vanligaste väggsubstraten i hemmen hos kunder i länder representativa för IKEAs marknad har analyserats.
För att utvärdera de olika lösningarna som identifierats har tester utförts.
Testerna har syftat till att utvärdera vidhäftningsförmågan vid de vanligaste väggmaterialen och produktmaterialen samt möjligheten till borttagning. I slutändan utvärderades fyra olika bindemedel som benämns A, B, C och D i rapporten.
All testdata har sammanställts och analyserats, resultatet har använts för att presentera ett antal olika lösningar och deras potential att användas till väggupphängning utan att penetrera väggen. Rekommendationer har gjort för hur IKEA kan arbeta vidare med lösningarna.
NYCKELORD: Ingen borrning, vidhäftning, sammanhållning, vidhäftningsämnen, klibbigt, lim, tejp, väggmaterial.
Content
1
Introduction 1
1.1
Project Incentives 1
1.1.1
The IKEA spirit 2
1.1.2
Democratic Design 5’s 2
1.1.3
Walls 2
1.2
Project Stakeholders 3
1.3
Project Objectives and Aims 3
1.4
Project Scope 4
1.5
Thesis Outline 4
2
Theoretical framework 6
2.1
Industrial design engineering 6
2.2
User centered design 6
2.2.1
Usability 6
2.2.2
Usability principles 6
2.2.3
Affordance 7
2.2.4
User 7
2.3
Theories of Adhesion 8
2.3.1
Mechanical theory of adhesion 8
2.3.2
Adsorption theory 8
2.3.3
Electronic theory 8
2.3.4
Diffusion theory 9
2.3.5
Weak boundary layer 9
2.4
Surface properties 9
2.4.1
Surface energy 9
2.4.2
Wetting 10
2.4.3
Surface roughness 11
2.4.4
Work of Adhesion 12
2.5
Walls 12
2.5.1
Wall structure 12
2.5.2
Covering materials 13
2.6
Paint 13
2.7
Adhesive 16
2.7.1
Adhesion 16
2.7.2
Cohesion 17
2.7.3
Tack 17
2.8
Adhesive failure 18
2.9
Glue 18
2.9.1
Curing 19
2.9.2
Area of use 20
2.10
Pressure Sensitive Adhesive (PSA)
Tape 21
2.10.1
Tape Structure 21
2.10.2
Adhesive mass 22
2.10.3
Backing 22
2.10.4
Liner 23
3
Method and Implementation 24
3.1
Process 24
3.2
Project planning 25
3.2.1
Gantt chart 25
3.2.2
List of requirements 25
3.3
Literature review 26
3.4
Pre-study 27
3.4.1
Interview 27
3.4.2
Questionnaire 28
3.5
Concept generation 29
3.5.1
Benchmarking 30
3.5.2
Workshop 31
3.5.3
Persona 33
3.5.4
Creative toolkit 34
3.5.5
Sketching 35
3.5.6
Concept combination table 36
3.5.7
Deductive qualitative analyse
(DQA) 36
3.5.8
Pros and cons 36
3.6
Redefinition of project 37
3.7
Test Planning 37
3.7.1
Design of Experiments 37
3.7.2
Solutions 38
3.7.3
Parameters 39
3.7.4
Wall material - Substrate 39
3.7.5
Product material 40
3.7.6
Size of adhesive layer 41
3.7.7
Preparation 41
3.7.8
Test Phases 41
3.7.9
Test Schedule 42
3.8
Evaluation 44
3.8.1
Patent search 44
3.8.2
Emission and VOC 44
3.8.3
XRF 45
3.8.4
Price 45
3.9
Reliability and validity 45
4
Results – Market analysis 46
4.1
Wall materials 46
4.1.1
Paint 46
4.2
Benchmarking 47
5
Results - Concept generation 48
5.1
Weight groups 48
5.2
Solutions 50
6
Result - Tests and Analysis 51
6.1
Load 51
6.1.1
Overall performance 51
6.1.2
Solution A 52
6.1.3
Solution B 53
6.1.4
Solution C 54
6.1.5
Solution D 54
6.2
Size of adhesive layer 55
6.2.1
Overall performance 55
6.2.2
Solution A 56
6.2.3
Solution B 57
6.2.4
Solution C 58
6.2.5
Solution D 59
6.3
Removal performance – wall
materials 59
6.4
Removal performance of adhesive
solutions 62
6.4.1
Solution A 62
6.4.2
Solution B 62
6.4.3
Solution C 62
6.4.4
Solution D 63
6.5
Failure scenarios of products 63
6.5.1
Gnugga 64
6.5.2
Stainless steel plate 65
6.6
Failure scenarios of adhesive
solutions 66
6.6.1
Solution A 67
6.6.2
Solution B 68
6.6.3
Solution C 69
6.6.4
Solution D 70
7
Result – Evaluation 71
7.1
Patent search 71
7.2
VOC 71
7.3
XRF 71
7.4
Price 71
8
Final Result 72
8.1
Removal 72
8.2
Adhesive layer and load 73
8.2.1
Small sized adhesive layer 73
8.2.2
Medium sized adhesive layer 74
8.2.3
Large sized adhesive layer 75
9
Discussion 76
9.1
Positioning the Result 76
9.1.1
Solution A 76
9.1.2
Solution B 76
9.1.3
Solution C 76
9.1.4
Solution D 76
9.2
Relevance 77
9.3
Reflection 78
9.3.1
Process 78
9.3.2
Pre-study 79
9.3.3
Concept generation 79
9.3.4
Test 80
9.4
Recommendations 81
10
Conclusions 82
10.1
What adhesives can be used to attach IKEA’s hooks to the wall without
drilling? 82
10.2
How well do the non drilling solutions perform in regard to different
parameters? 82
10.3
Can any other non-drilling solution rather than the existent be recommended?
83
10.4
Project objectives and aims 83
References 84
Email Communication 88
Appendices 89
Appendix I - Gantt chart 90
Appendix II – Interview questions 91
Appendix III – Questionnaire 92
Appendix IV Mindmap 93
Appendix V – Workshop agenda 94
Appendix VI – Persona 1 95
Appendix VII – Persona 2 96
Appendix VIII – IOS-MAT-0010 97
Appendix IX– VOC emission & XRF 98
Appendix X – IOS-MAT-0074 99
List of figures
Figure 1 Chart over different wall types. 3 Figure 2 Forces working in a material explaining
surface energy. 9
Figure 3 Surface energy for some materials, (Afcona, 2010 & Accu dyne test, 2009). 10 Figure 4 A liquid wetting a surface. 11 Figure 5 Surface energy for some diluents (Afcona,
2010). 15
Figure 6 Surface energy for some resins (Afcona,
2010). 15
Figure 7 The three main properties of adhesives.16 Figure 8 Classification of adhesives. 20 Figure 9 The product development process. 24 Figure 10 Countries included in the pre-study. 29 Figure 11 Participants in action during the
workshop. 30
Figure 12 Expectations of non-drilling solution. 32 Figure 13 Brainstorming, by using the 6-3-5
method. 32
Figure 14 Concept combination table. 36 Figure 15 Example of combining fragments. 36
Figure 16 Test walls 40
Figure 17 Small, medium and large size of the
adhesive layer. 40
Figure 18 Non-drilling solutions generated. 50 Figure 19 The total load performance of the
solutions. 51
Figure 20 The overall load performance for A. 52 Figure 21 The overall load performance for B. 53 Figure 22 The overall load performance for C. 54 Figure 23 The overall load performance of D. 55 Figure 24 The size of the adhesive layers impact
on the load case. 56
Figure 25 The performance of A in relation to the size of the adhesive layer. 57 Figure 26 The performance of B in relation to the size of the adhesive layer. 57
Figure 27 The performance of C in relation to the size of the adhesive layer. 58 Figure 28 The performance of D in regard to the size of the adhesive layer. 59 Figure 29 Scale used to evaluate the removal
performance. 60
Figure 30 Removal result on different wall
substrates. 61
Figure 31 Result from removal test for surface
finishes. 61
Figure 32 Result from removal test – solution A.
62 Figure 33 Result from removal test – solution B.
62 Figure 34 Result from removal test – solution C.
63 Figure 35 Result from removal test – solution D.
63 Figure 36 The hook Gnugga. 64 Figure 37 Failure scenarios for Gnugga. 64 Figure 38 Failure scenarios for large metal plate.
65 Figure 39 Total failure scenarios for all adhesives.
66 Figure 40 Failure scenarios for solution A. 67 Figure 41 Failure scenarios for solution B. 68 Figure 42 Failure scenarios for solution C. 69 Figure 43 Failure scenarios for solution D. 70 Figure 44 Visualisation of non-drilling solutions
and users. 72
Figure 45 Visualisation of the non-drilling solutions load performance in regard to the small size of the adhesive layer. 73 Figure 46 The load performance in regard to the medium size of the adhesive layer. 74 Figure 47 The load performance in regard to the large size of the adhesive layer. 75 Figure 48 The performance of the solutions
summarised. 77
1 Introduction
In this section an introduction of the project is made. Incentives, stakeholders, objectives and scope of the project are presented to provide the reader with an understanding of the project.
1.1 Project Incentives
IKEA’s vision is to create a better everyday life for the many people. By offering a wide range of well designed, functional home furnishing products at low prices IKEA wants to make everyday easier.
To accomplish IKEA’s vision every product complies with the Democratic Design 5’s; Function, Form, Quality, Price and Sustainability. In addition IKEA drive the whole process from suppliers to retailers. And never stop looking for innovative solutions to excite the customers and exceed their expectations.
IKEA’s is organized in Business Areas (BA), further divided into Home Furnishing Businesses (HFB).
Every BA focuses on one part of the home area. Within every BA there are functions responsible for one aspect of the product, together they form a complex group making sure the products fulfil IKEA’s vision.
This project will be performed within the BA called OSOF in HFB 18, Home organisation and HFB 19, Secondary storage.
IKEA is looking to provide the many people with functional, sustainable and high quality products. Laws and standards require that some of the furniture in their range must be safely attached to the wall or hold for a specified minimum amount of load. The attachment solutions
offered on the market today are limited. The most common solutions are screws and dowels, which require drilling before use.
Many people don’t have the ability or possibility to drill and therefore do not wall fasten their furniture for reasons such as:
- They don’t have the option to drill due to rented apartments or houses where they are not allowed to alter the walls.
- Lack of equipment or they don’t feel comfortable handling power tools.
- People like to redecorate and change the interior in their home frequently and do not want visible marks in their walls.
Not attaching furniture properly to the wall is a safety risk and decreases the functionality of the products. For the reasons mentioned non-drilling solutions are needed on the market.
IKEA offer non-drilling solutions for bathroom, suction cups and double sided tape, which work on mirror and glass surfaces. Now IKEA want to increase the range by investigate the possibility to develop non- drilling solutions functioning on other surfaces e.g. papered, painted, brick, plastered or concrete walls.
1.1.1 The IKEA spirit
Remember where it started and respect the roots makes it easy to understand IKEA. Småland and more specific Älmhult is the foundation and heart of IKEA. The conditions in Småland made the people find alternative yet simple solutions, to pay attention to details and thereby solving the problems of everyday life.
IKEA consist of a diverse group of people all sharing the same values but dare to be individuals and think differently. By working together as a team and sharing knowledge, problems are solved. IKEA gets things done by respecting co- workers, suppliers and customers and sees the potential in each individual and encourages them to grow by providing them responsibility. At low cost and small means IKEA manage to create and offer practical and realistic solutions to the customers. By always being on the way looking for new solutions and daring to be different IKEA continues to grow.
1.1.2 Democratic Design 5’s
IKEA is a global company driven by the belief that by offer products at low cost with high quality, the right functions, attractive form and expression and with sustainability in mind they can make everyday life easier for the many people. Every product IKEA distribute should fulfil
the criteria for democratic design 5’s:
Price, Quality, Function, Form and Sustainability. By finding the balance between the five criteria IKEA is able to deliver unique products and reach a broad target group all over the world.
1.1.3 Walls
In the construction industry many types of walls and denominations are used. In this project walls have been separated into two groups see Figure 1, light walls and massive walls. The light walls can be either interior walls with the purpose to separate spaces or non-bearing external walls called curtain walls. Light walls can be constructed on studs made of either steel or wood, or plasterboard or gypsum lath. A simplified light wall consists of the components stud, wall covering material, plaster and surface finish.
Massive walls are load-bearing walls that can be either external walls or interior walls. In the case of a bearing interior wall it is called main partition wall. Massive walls carry the vertical load and are the foundation of a building. They can be constructed of different kinds of concrete, drywall boards or bricks and mortar, which are complemented with plaster or joint compound to get the required surface smoothness (Interviews with construction engineers at Skanska, September 26, 2014).
Figure 1 Chart over different wall types.
1.2 Project Stakeholders
The end users of the solution are everyday people all around the world, with the need to attach furniture, more specific hooks to the wall without having to drill. In this project the focus is on home environment, all rooms in the home area are of interest.
The result is of interest for IKEA’s FIXA range where it can complement the existing products. IKEA Components (ICOMP) is supplying the customers and the department stores with components and is developing new non-drilling solutions, mainly for the bathroom;
hence they are also interested in the result of this project.
The initiator for the project is Nathalie Ruter, Business Leader in HFB 18, Home organisation and HFB 19, Secondary storage at IKEA of Sweden.
1.3 Project Objectives and Aims The purpose of the project is to investigate and analyse existing non- drilling solutions and present potential non-drilling solutions for IKEA. Investigate what kind of wall material the solutions are compatible with and see if it is possible to implement them on IKEA’s hooks.
This would enable the customers to complement their furniture with non-drilling wall attachments.
The aim is to investigate and identify non-drilling solutions, evaluate them and analyse if they can be interesting for IKEA to add in their FIXA range.
The project has strived to answer the following research questions:
- What adhesives can be used to attach IKEA’s hooks to the wall without drilling?
- How well do the non-drilling solutions perform in regard to different parameters?
- Can any other non-drilling solution rather than the existent be recommended?
The questions have kept the project on the right path and worked as a guiding frame throughout the project.
1.4 Project Scope
The project is a master thesis carried out during 20 weeks at IKEA of Sweden (IoS) in Älmhult. The project comprises the investigation of non- drilling solutions and if there are any solutions on the market, which could be of interest for IKEA.
Since the project is executed in collaboration with IKEA the solutions has to follow IKEA’s values, guidelines and requirements. For example PVC is not to be used in any of IKEA’s products. The bathroom area will not be investigated further since IKEA Components already look into the specific area. Wall construction and materials will be examined in selected countries representative for continents were IKEA acts. The non-drilling solutions will be assessed on IKEA products from HFB 18, main focus on hooks.
The project is of investigating character, the solutions presented will not be ready for implementation and launch in IKEA’s range.
Recommendations for further procedure will be made.
The project does not aim to create new materials but rather to identify existing materials and investigate their potential to become a non- drilling solution. With that said, there will be no negotiation with the
suppliers about rights or future cooperation.
1.5 Thesis Outline
The thesis outline provides the reader with a short description of each chapter.
In the first chapter an introduction of the project is made. Why it is carried out, the aim, stakeholders and the scope of the project is presented.
Chapter two provides the reader with the theory relevant for the project. It includes an introduction to adhesives, tape and glue as well as the properties of walls and paint.
Chapter three presents the process and methods utilised throughout the project.
Chapter four presents the results from the market analysis, presenting most common used wall materials and paint, and the solutions identified on the market.
In chapter five the result from the concept generation is presented.
Chapter six presents the result and analysis from the tests carried out providing the reader with an understanding of the adhesive’s performance.
In chapter seven the result from VOC emission, XRF and Patent search is presented as well as the price.
In chapter eight the results is compiled in tables providing the readers with an understanding of how the solutions can be used.
In chapter nine the process and result is discussed and recommendations for future work is provided.
In the tenth and last chapter the research questions are answered and the project is concluded.
2 Theoretical framework
This chapter describes and summarise theory relevant for the project. The theory aims to give a better understanding for and support the results and arguments presented through the project. The master program in Industrial Design Engineering at LTU is described, followed by the theoretical framework processing adhesion, usability, wall materials, paint and adhesives.
2.1 Industrial design engineering
The master programme Industrial Design Engineering at Lulea University of Technology provides the students with a broad knowledge base, combining industrial design with engineering. The education provides the students with tools and knowledge useful in the product development process and gives the students the ability to approach problems from different angles and adapt the products to the user, the production and the existent technology. The interaction between humans and product is the main focus for the programme.
2.2 User centered design
Since the end user of the non-drilling solution is everyday people around the world usability is a highly relevant area to look into. It is important to have in mind how design can make difficult things easy.
To prevent frustration among users a product should provide the clues needed for proper actions. As important it is to understand how to make a working product it is also important to have an understanding of the user and how they perceive and process stimulus.
2.2.1 Usability
Usability is a phrase often used in the context of product development,
but what does it really mean? R. B.
Miller (1971) defines it as a system that is easy to use. According to Nielsen (1993) usability is more complex and can be described by the five attributes; learnability, efficiency, memorability, errors and satisfaction. The product should be easy to learn, efficient to use, easy to remember, low frequency of errors, and when errors occur they should be easy to fix, and the product should be pleasant to use. Usability is defined by the international organisation for standardisation (ISO) in (ISO 9241-11. 1998)
“Extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.”
There are many different descriptions and definitions of usability, but they have similar framework. Usability means that the user should be able to be productive and feel satisfied when using the product.
2.2.2 Usability principles
Usability is a result of the product as well as the user. There are different ideas about principles for usability.
According to Norman (1988) a product should provide the users with the clues needed to operate it.
Keeping the structure simple, make sure the clues needed to operate the
product are visible and that the product provides feedback, is the key. By doing so and keep in mind during the development of the product what could go wrong and only provide the clues needed to find the main functions the product will be perceived well and be helpful for the user.
Wharton & Lewis (1994) emphasize the importance of designing with the user in mind and be aware of the different levels in knowledge base of the users. A novice may act in a different way than an expert. Both an expert and a novice should be able to operate a product why it is important that the product provide the right information to be able to reach the wanted outcome.
Both Norman (1988) and Wharton &
Lewis (1994) emphasize the importance of knowing the user you designing for. By knowing the user the designer can decide which clues are needed and where to place them to make it easy for the user to navigate the product.
2.2.3 Affordance
How can we manage a world where we every day come across new tasks and products, some which we only encounter once? The answer is that the clues are out in the world, in objects, animals and people as affordances that have to be perceived (Norman, 1999, Maier & Fadel, 2009).
The expression affordance was founded by J.J. Gibson (1979). He explains affordance as the information the environment offers and provides the animal. Any
substance, object, surface or layout has affordances, which are possible to understand without the need of any learning.
According to Maier & Fadel (2009) affordance is the relationship between two subsystems dependant of each other. Both subsystems are required for a potential behaviour or outcome to occur. Affordance can be used to describe the relationship between the subsystems: human and artefact (AUA) or between artefact and artefact (AAA).
Norman (1999) defines affordance as the assets of the world explaining the possible relationships between humans and objects. He distinguish between affordance and perceived performance which are different elements but both of great importance. When dealing with physical objects there can be both affordance and perceived affordance while dealing with screen-based interfaces only the perceived affordance can be controlled.
All authors agree that affordance have a significant impact on the relationship between two entities or subsystems. And that affordance is a main factor in communication between the two entities.
2.2.4 User
When designing user-friendly products one should design with the user in focus. It is hard to design a user-friendly product without involving the user in the development process (Norman, 1988). There are different degrees of user involvement, from fictitious users, such as personas, to the extent
were the users helps construct a system or product, participatory design (Nielsen, 1993).
For users an action is a way to reach the goal. To understand a user’s reaction in a specific situation it is important to understand the structure of an action. An action consists of three stages; first a goal is identified, second is to take action and third checking if the goal was achieved. The action can be either to do something (execution) or checking the outcome (evaluation) (Norman, 1988).
2.3 Theories of Adhesion
Adhesion refers to the bonding of one material to another. There are different theories explaining adhesion. Since many different phenomena are involved in adhesion and a great variety of materials can be bonded the different theories all contribute to the understanding of adhesion. It is important to understand that more than one adhesion mechanism can be involved in the process at the same time (Schultz & Nardin, 2002). The project will evaluate different adhesives why the reader is provided with insight in adhesion to be able to understand the project. To give an insight in the theories relevant today and provide a basic understanding regarding adhesion the theories are in short presented in this section.
2.3.1 Mechanical theory of adhesion The mechanical theory proposes that the strength of adhesion depends on how well the adhesive penetrates the pores of the surface, called mechanical interlocking. The mechanical theory emphasises that
penetration of the pores is the main parameter in bonding. Since good adhesion is possible between smooth surfaces good wetting, see 2.4.2 Wetting, is also required for good adhesion. (Schultz & Nardin, 2002) Mechanical interlocking is an important factor for adhesion.
Surface roughness examined on a macro scale level shows that the penetration of the adhesive into the pores of the substrate but also the fibres embedding in the adhesive is important for adhesion. Examining surface roughness on a macro scale level is enough for fibrous materials.
Mechanical interlocking on micro scale level has been proven to be important for bonding strength on metal (Allen, 1993).
2.3.2 Adsorption theory
Adsorption theory or
thermodynamic theory considers that adhesion is created when adhesive and substrate come in close contact and forces are formed between the adhesive and substrate.
Primary bonds such as covalent forces or secondary bonds such as van deer Waals forces will act between adhesive and substrate when they are in close contact.
Wetting and close contact between substrate and adhesive are necessary for adhesion according to the Adsorption theory (Schultz &
Nardin, 2002).
2.3.3 Electronic theory
The electronic theory suggests that an electrical double layer can be created when electrons transfer between the adhesive and substrate due to the Fermi level. The Fermi level is the electron energy level at 0 K, which states the work required to
add one electron to a body. It is the electrostatic forces working across the interfaces defining the adhesion strength according to the Electronic theory (Schultz & Nardin, 2002).
2.3.4 Diffusion theory
The diffusion theory is based on the beliefs that adhesion depends on the diffusion of macromolecules of polymers over the interface between adhesive and adhered. Molecular chains create a new interface, for this to happen the chain segments must be mobile and soluble. When diffusion is involved, adhesion strength depends on the number of crossing chains. Factors such as contact time, temperature and molecular weight of polymers have impact on adhesion strength according to the Diffusion theory (Schultz & Nardin, 2002).
2.3.5 Weak boundary layer
The weak boundary layer theory calls the area close to the interface the
“interfacial zone”. The theory considers variations in the adhesive occurring in the interfacial zone due to properties different from the rest of the material. It is the cohesive strength in a weak boundary layer in the interfacial zone of the adhesive that defines the adhesion strength.
Meaning that adhesion energy (G) equals cohesive energy (G!) (Shultz &
Nardin, 2002).
2.4 Surface properties
When examining the possibility of attachment without drilling or penetration the surface of the substrate is of importance. The substrate properties have impact on the adhesion and should be examined so the combination of
adhesive and substrate is compatible.
2.4.1 Surface energy
Surface energy can be defined as the energy connected to the presence of a surface. Unit per area is used to express surface energy (mN/m).
Within materials cohesive forces are acting between the molecules. These forces are responsible for the phenomenon called surface tension or surface energy (Afcona, 2010).
Surface energy is a main factor when adhesive bonds are formed but also when adhesive failure occurs.
Surface energy can be referred to as Gibbs free energy (G) or as surface tension (γ), they both refer to surface energy (Packham, 2003).
The cohesive forces within a material are in balance and equally distributed between the molecules.
At the surface the forces are unbalanced, as shown in Figure 2.
The uneven distributed forces at the surface create the surface tension.
The intermolecular forces acting in a material determine the value of the surface tension for a material.
Surface energy for some materials is presented in Figure 3. The magnitude of the surface tension depends on temperature, molecular size and shape (Afcona, 2010).
Figure 2 Forces working in a material explaining surface energy.
Figure 3 Surface energy for some materials, (Afcona, 2010 & Accu dyne test, 2009).
The phenomenon of wetting is closely related to surface energy. The contact angle created when a drop of liquid is in contact with a solid surface depends on the surface tension of the liquid and the solid.
Generally a material can wet any other material with higher surface energy than itself. The variable spreading energy or spreading coefficient (S) connects wetting and surface energy. The spreading energy is the change in energy when a liquid spreads over a surface. More specific it is the difference between the work of adhesion and cohesion. If S > 0 the liquid is wetting the solid, if S < 0 it is referred to as partial wetting (Packham, 2003).
The surface energy of a solid can be estimated by measuring the contact angle between the drop and surface
of solid, and relate it to surface energy via Young’s equation (1).
𝛾!" = 𝛾!"+ 𝛾!"𝑐𝑜𝑠𝜃 (1)
Or the surface forces apparatus can be used examining the load necessary to separate two surfaces in contact (Packham 2003).
2.4.2 Wetting
Wetting can be explained as the ability of a liquid to spread on a surface. When applying an adhesive its state can be seen as liquid. When the liquid spreads the close contact needed for bonds to form between adhesive and surface is achieved.
Close contact is a must for chemical and physical bonds to be formed why wetting is of interest (Shanahan, 2011).
For wetting to occur the surface energy of the adhesive should be
0 200 400 600 800 1000 1200
Copper Stainless steel Aluminium PC Epoxy paint Acrylic Polane paint ABS PP PE PTFE Te?lon
mN/m
Surface energy
lower than the surface energy of the surface. If so the adhesive will spread in varying extent and come within the distance (<0, 5 nm) needed for bonds to form. A solid can be said to be hydrophobic, a liquid drop have a hard time stick on to such a surface and is easy to remove, or hydrophilic were the liquid spreads over the surface or in extreme cases inside the solid and coexist (Bico, Thiele &
Quéré, 2002).
A contact angle (θ) between the liquid drop and the solid surface can be measured. As seen in Figure 4, a small contact angle is observed when the liquid spreads while a large contact angle is observed when the liquid forms a bead on the surface and partial wetting occur. The contact angle depends on the interfaces’ surface tension and defines how much a liquid will wet a surface. For a hydrophilic solid the liquid follows the surface, decreasing the contact angle (Bico et. al. 2002).
Wetting can occur in different extent, a liquid wet the surface when the contact angle is less than 90 degrees (θ > 90˚) and classifies as poor or partial wetting if the contact angle exceeds 90 degrees (θ > 90˚).
Usually when the contact angle is smaller the ability to wet is better and the better conditions for adhesives to form bonds (Shanahan, 2011).
Figure 4 A liquid wetting a surface.
2.4.3 Surface roughness
According to Gadelmawla et. al (2002) surface roughness have an impact on primary adhesion problems such as friction, joint strength and positional accuracy.
Parameters of surface roughness can be categorised in three groups;
amplitude parameters, spacing parameters and hybrid parameters.
The most used amplitude parameter is arithmetic average height (Ra). Ra
is defined as the average difference of a surface profile. The value of Ra
varies depending on factors such as material and manufacturing methods.Peak spacing is defined as vertical distance from the highest peak to the lowest valley. It is a spacing parameter, which is of importance when friction is examined. The bonding of paint can be increased by controlling the spacing parameter (Gadelmalwa et.
al. 2002).
All surfaces are more or less rough, the degree of roughness can be expressed by a Wenzel roughness factor (2)
𝑟 = 𝐴/𝐴! (2) A represents the interfacial area and A0 is the theoretical area. Wenzel’s
roughness factor is valid when a surface is examined on a general level. When roughness is examined on a more detailed level, factors such as the chemical nature of surface molecules must be taken into consideration. When referring to surface area and relating it to surface energy and work of adhesion it is the macroscopic area of an interface that is referred to (Packham, 2003).
Surface roughness is of importance when adhesive bonds are formed.
The strength of adhesion depends on the bonding area, generally the larger the bonding area is the stronger bonding. Therefore the rougher surface the lower probability of close contact and thereby a decrease in bonding area and adhesion (Hongbo, 2013). An adhesive’s ability to wet a surface is influenced by the surface roughness due to the effect on surface energy the roughness factor can result in (Packham, 2003).
2.4.4 Work of Adhesion
The work of adhesion as well as adhesive failure is closely connected to surface energy; they are factors important to understand to understand adhesion. Work of adhesion is defined as the energy required to separate two surfaces. If the surfaces are identical it is referred to as work of cohesion (Hongbo, 2013).
“Work of adhesion is defined as the free energy difference (per unit area) between two phases concerned, in contact at equilibrium and entirely separate, formally in vacuum” (Packham, 1995, pp.
123)
Surface energy is strongly connected
with the formation and breaking of adhesive bonds (Packham, 2003).
Two types of failures can take place;
adhesive failure and cohesive failure.
Adhesive failure refers to the phenomenon when failure occurs between substrate and adhesive while cohesive failure occurs when the forces between the molecules in the adhesive break. Adhesive failure (WA) and cohesive failure (WC) are defined by equation (3) and (4).
𝑊! = 𝛾!+ 𝛾!− 𝛾!" (3) 𝑊! = 2𝛾! (4) In equation (3) γ1 equals the surface energy of phase 1 and γ2 the surface energy associated with phase 2 which are phases present during adhesive failure. During cohesive failure, equation (4) only one phase is involved, so 2γ1 is the surface energy associated with phase 1 (Packham, 2003).
2.5 Walls
Non-drilling solutions can be attached directly on the walls without penetration. The surface properties affect the adhesion, surface energy and roughness are highly relevant factors to consider when evaluating adhesives. Different covering materials have different surface roughness and surface energy. Surface finishes such as paint can change the surface energy of the covering material, therefore it is important to know how walls are constructed in different parts of the world.
2.5.1 Wall structure
Interior wall studs are constructed to be either bearing, to carry a vertical
load or non-bearing, to separate spaces. Wall covering materials are fastened to wall studs using screws, nails or adhesives designed for the specific purpose. Joint compound or plaster is used to fill defects such as nail indentions and to make the surface smooth (Don Vandervort, n.d).
2.5.2 Covering materials
There are different covering materials and surface finishing materials on the market. Covering materials used can be different kinds of drywalls such as: gypsum board, plasterboard, plywood, hardboard, fibreboard, particleboard and wood paneling. Plastering is an alternative to drywalls; both gypsum plaster and cement plaster are on the market.
They can be applied on wooden latch or steel mesh lath, or they can be used to decorate the inside of cement or masonry walls. When applied on another substrate a bonding agent should be used. (Technical Services Information Bureau, n.d)
Gypsum board; gypsum is durable, a feature that makes it appropriate as covering material. Gypsum boards have a centre of gypsum, surrounded on both sides with paper. The sheets are nailed or screwed to the studs or to a masonry surface with furring strips. Adjoining sheets are covered with panel tape and joint compound in multiple layers to create a coherent and smooth surface.
Plywood used as wall covering have a factory applied finish which makes it tough and durable. Some panels can be fabricated with edges that almost conceal the joints but there are also battens which can cover joints.
Plywood must be adjusted to the room’s condition before being attached. The sheets can be attached directly to the wall studs using nails or adhesives. Plywood can be used to reinforce gypsum constructions and allows installations in the whole wall, whereas in a gypsum board without plywood it is important to mount in the studs to ensure stability (Ned Pelger, n.d).
The covering materials all have different surface roughness, which affects the strength of adhesion. The structure and roughness of the wall will affect the choice of adhesive for the non-drilling solution. It is important to take into consideration and evaluate the adhesive in relation to the different wall materials since the adhesion strength may differ.
2.6 Paint
Paint as surface finish on walls can change the surface energy of the substrate and thereby change the surface energy and roughness of the wall. Changing the parameters affect the adhesion why it is interesting to know paint and its properties.
Paint can be composed in a variety of ways depending on the surface material of application. Roughly paint can be said to consist of:
- Resins (alkyd, PVA, acrylic, epoxy)
- Pigment (ferric oxide, titanium oxide)
- Bulking agent/extender (lime, chalk)
- Diluents (water or thinner) - Additives (thickener, biocide) When explaining paint and its
qualities the bonding agent is most often referred to. So when referring to alkyd paint it means that the bonding agent is alkyd but it doesn’t say anything about the other parameters that affect the paints qualities (Hedqvist, 2014).
On materials such as gypsum, concrete and plaster an acrylic paint is often used while on wood panels alkyd paint is the more common choice. The alkyd and acrylic paint can be either solvent or water based and may have different degrees of shine. The shine of paint depends of how much of a medium, making the paint lacklustre is added, the bulk agent can affect the shine of paint.
Otherwise it is the structure of the paint that makes it more or less shiny. A smooth surface reflects the light so almost all the rays are gathered when reaching the eye, as for a lacklustre paint the surface is uneven which makes the rays spread and only a few rays reach the eye (Hedqvist, 2014).
For paint to attach well to a substrate and to create the wanted finish the properties of the substrate for
example surface tension is highly relevant to consider. Interfacial surface tension, working between and separating two non-miscible materials, is closely connected to paint defects. For polymer-solvent systems the surface tension measurement range from 0.0001-0.1 mN/m and for polymer-polymer systems the interval is 1-20 mN/m, surface tension for more materials are presented in Figure 5 and Figure 6 (Afcona, 2010).
For wetting to occur the paint should have lower surface tension than the substrate applied on. Spreading is the desired outcome when painting (Afcona, 2010). Some surfaces may be difficult to apply paint on: Such surfaces can be:
- Surfaces treated with bee wax - Industrial sprayed surfaces
(may contain silicone)
- Surfaces coated with plastic (low surface energy may reduce adhesion)
- Vinyl wallpaper with high amount of plasticiser.
(Hedqvist, 2014).
Figure 5 Surface energy for some diluents (Afcona, 2010).
Figure 6 Surface energy for some resins (Afcona, 2010).
0 10 20 30 40 50 60 70 80
Water Ethylene Glycol Cyclohexanon Xylene Toulene Acetate Aromatic White Spirit n-‐Butanol Acetone Iso-‐Propanol
mN/m
0 10 20 30 40 50 60 70
Melamine Resin Epoxy Polyester Polyacrylate Oil Alkyd
mN/m
2.7 Adhesive
Adhesives are the main focus as non- drilling solutions in this project. To understand the result it is good to have a basic understanding about adhesives and what makes them work.
Adhesives can roughly be grouped in two categories; synthetic and natural depending on how the adhesive is produced (Khan & Poh, 2011). There is a wide range of application and curing techniques for adhesives;
pressure sensitive tape, hot melt and epoxies are some examples.
Adhesion, cohesion and tack are three main properties explaining how and why adhesives works, see Figure 7. The properties can be changed to adjust the performance of the adhesive to different circumstances. No Adhesive will have a top performance in regard to all three properties. If the properties of Tack increase it will be at the
expense of one of the others or both (Khan & Poh, 2011).
2.7.1 Adhesion
Adhesion or peel strength refers to the force needed to unite or separate adhesive and substrate. It is the forces acting between substrate and adhesive. The magnitude is determined by how well the adhesive wet the substrate and thereby the surface energy of adhesive and substrate as well as surface roughness. Peel strength is expressed in N/m (Khan & Poh, 2011).
Peel strength is not a natural property of an adhesive but can be created through use of for example tackifiers and fillers (Khan & Poh, 2011). A peel test can be used to indicate how well the adhesive bonds to the substrate. The peel strength measured depends on adhesive but also on the type of peel test used to evaluate the performance (IHS Globalspec, 2014).
Figure 7 The three main properties of adhesives
Different factors such as tackifiers and fillers, molecular weight, temperature and peeling rate can modify the peel strength of an adhesive. Coating thickness or the amount of adhesive mass has impact on the peel strength. The peel strength increases with increased coating thickness due to the increased wettability of the substrate and the increased area of contact (Takahashi et. al., 2013).
2.7.2 Cohesion
Cohesion or shear strength refers to the forces working internally in a material, which can be explained as the inner strength of a material.
Cohesive strength of a solid depends on the chemical or physical forces attracting the molecules composing the solid. The forces of cohesion are the same forces involved in adhesion but instead of working between the surfaces of two materials (adhesion) the cohesion forces work internally in a material (Allen, 1993). With high cohesion come high temperature resistance, high holding power and low tack for the adhesive (Tesa, 2014). Forces working parallel to the bonding area is called shear forces, cohesion plays a crucial part in the withstanding of shear forces (Khan &
Poh, 2011).
As for peel strength, factors such as tackifiers and fillers, molecular weight and rate affect the shear strength. Opposite to peel strength the shear strength decreases with increased coating thickness and increased amount of filler due to a decrease in cohesive strength and amount of polymer content (Khan &
Poh, 2011).
2.7.3 Tack
Tack is described as the ability of an adhesive to wet a substrate. It is the ability of an adhesive to attach to a substrate with minimum pressure at first contact. Tack depends on the mass of the adhesive and coating weight (Tesa, 2014). Khan & Poh (2011) describes tack as the force per area expressed in N/m2, which creates bonds between adhesive and substrate. Tack can also be explained as the property of a material allowing measurable bonds to form instantly upon contact with a surface.
Tack can be measured by a variety of methods, the results depends on the test method used. The Rolling ball tack test and Pressure-Sensitive Tape Council are the most common used methods today. Tack increases with increased tackifier and filler and with increased coating thickness, since the ability to wet the surface is enhanced (Khan & Poh, 2011). Tack is connected to the initial formation of bonds, which is described in section 3.4.4 Adhesion work and is related to the surface energy explained in section 3.4.2 Surface energy.
According to Khan & Poh (2011, pp.
800) many different factors affect the properties of tack, both the formation and separation of bonds.
Some of the factors affecting the formation of bonding are:
-‐ Adhered surface properties – material, wettability or surface energy, roughness and porosity.
-‐ Preparation – cleanliness, pre-treatments, coating weight and uniformity,
